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Abstract

Expansive soils are a common problem to overlying geotechnical structures risking for distress and damage caused by moisture induced ground movements. Calcium-based stabilization is readily adopted to improve and enhance the problematic expansive subgrade increasing strength and the volume change behaviour. For ground improvement, the use of lime and Ordinary Portland Cement (OPC) to treat expansive soil has been in common practice; however, Calcium Sulfoaluminate (CSA) cement can be an effective alternative due to the reduced environmental impact. To date, limited literature surrounds the understanding of CSA cement in expansive soil, but largely focussed its applications on concrete infrastructure. This paper investigates the stabilization mechanism of CSA treated expansive soils by identifying the major hydration products and microstructural characteristics with respect to CSA cement dosage and curing rate. The study reveals CSA cement stabilization directly affects mechanical properties and microstructural characteristics due to three key phases of cationic exchange, flocculation and agglomeration between the clay sheets and cementitious hydration. The addition of CSA cement in the ground stabilization serves to shift towards a sustainable approach in reducing the carbon impact of traditional stabilization techniques.

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... Subramanian et al. [73] and Subramanian et al. [74] studied the use of CSA cement in the treatment of sand revealing the ability of CSA cement to treat soil for greater initial strength in applications above and below the water table. Pooni et al. [59] have studied the use of CSA cement in stabilization of expansive soils revealing the same key phases as GP cement during the stabilization process; cationic exchange, flocculation and agglomeration between the clay sheets and cementitious hydration. The reaction products of the cementitious hydration phase of CSA cement differs from OPC cement due to the differing constituents. ...
... However, traditional calcium-based stabilizers consume large amounts of energy and resources during its production resulting in the release of significant carbon dioxide (CO 2 ) emissions, which cause serious environmental problems. On the other hand, CSA cement for subgrade soil stabilization offers a solution with a lower carbon footprint, such as shown by the authors recent work which highlights reduced spacing between the clay sheets, decreased specific surface and formation of space filling ettringite needles that serve to enhance the strength of problematic soils [59]. To date, however, the potential performance of CSA cement in expansive subgrade soil applications is scarce. ...
... This indicates a broader optimum moisture content rather a single distinct peak; hence there is no significant effect on the maximum dry density. This occurs as the additive particles occupy the regions in the bulk sample that would have been otherwise occupied by soil particles [59,83]. Furthermore, at lower moisture contents, density increase is due to the specific gravity of CSA cement in soil, but at high moisture contents, cement hydrates harden soil particles, thus resisting its movement into a densely packed position [83]. ...
Article
Problematic soils cause significant damage and distress in pavements from moisture induced volume and strength changes. Calcium based stabilization are well known to permanently stabilize expansive soils. Traditional calcium-based stabilizers typically include lime and cement for ground improvement of plastic clays to enhance strength. Calcium Sulfoaluminate (CSA) cement can be an effective and sustainable alternative with improved environmental considerations. The application of CSA cement to treat expansive/weak subgrade soils are limited. This research paper examines the efficiency of CSA cement compared to traditional calcium-based stabilizers in road pavements. The comprehensive laboratory study evaluates the durability of stabilized soils by assessing the mechanical performance under the effect of moisture impacts by means of investigating the bearing capacity, unconfined compressive strength (UCS) during wet-dry cycles, the resilient modulus (Mr) and UCS across practical moisture ranges and mechanical strength from vacuum saturation and moisture susceptibility testing. Results from the study reveals that the calcium-based stabilizers are effective in treating expansive soils by increasing strength across the moisture ranges tested. All stabilized soil specimens showed an increase in UCS after the completion of one wet-dry cycle and resistance to both vacuum saturation and moisture susceptibility testing. While the addition of CSA cement treatment showed considerable improvements over untreated expansive soils, it is not as effective in improving the durability performance of expansive soils compared to traditional cement and lime stabilizers under tested conditions. However, the use of CSA cement has high potential for improving weak subgrade conditions through sustainable ground stabilization.
... The dry density, optimum water content, and bearing capacity were determined by comparing stabilized soils and untreated samples. Based on literature, secondary additives were used in following quantities; lime 3% [36], enzyme DMR = (1:500) and AMR = (1%) [56,50,58], CSA cement 3% [52], and polymer 3% [35]. The tests are described in detail in the following section. ...
... In soil-fly ash-polymer mixture, contents were added together and homogeneously mixed in dry conditions. Water was then added up to the Table 6 Chemical composition and physical properties of CSA cement [52,51]. ...
Article
Expansive soils are widespread in many parts of the world. Due to its low strength, high compressibility, and massive volumetric changes, these soils are a potential origin of damage to roads, buildings, foundations and other geo-infrastructure. Extensive research has been conducted on the utilisation of fly ash to stabilize expansive soils. This paper describes how the efficiency of fly ash based soil stabilization can be improved using secondary additives. Class F fly ash, an industrial by-product, was used as the base additive. Lime, CSA cement, enzyme and polymers were utilized as secondary additives. A series of mechanical and microscopic tests (CBR, compaction test, SEM, XRD, FTIR and TGA) was carried out on different combinations of additives. The results indicate that secondary additives can be effectively used to improve the efficiency of fly ash based soil stabilization. Soil-fly ash-lime-enzyme was identified as an optimum combination to enhance bearing capacity while soil-fly ash-lime and soil-fly ash-enzyme also showed substantial improvements in subgrade performance. Findings from laboratory investigations were verified applying into 3-D numerical modelling to evaluate the pavement performance which revealed substantial benefits of pavement thickness reduction when treated using secondary additives.
... The benefits of using CSA cement are not limited to low carbon emissions and energy savings, CSA cement also has promising engineering properties for different applications. For example, the fast setting and hardening of CSA cement makes it suitable for urgent repairing, ceiling, and soil stabilization [20,21]. In some other cases, the retardation of CSA cement is needed for achieving a longer setting time, while the hydration mechanism in the presence of retarders remains unknown to some extent [22]. ...
Article
Calcium sulfoaluminate (CSA) cement can be used as a replacement for Portland cement to reduce CO2 emissions. However, the performance of CSA cement remains unknown with regard to its hydration mechanism, mechanical and long-term performance. Therefore, it would be beneficial to consolidate the literature on CSA cement to facilitate its use in the construction industry. To this end, recent progress and technical challenges of using CSA cement are discussed in this paper. We begin with the introduction of the different types of CSA cement and the manufacturing process. This is followed by a detailed discussion on the hydration mechanisms and phase assemblage, mechanical performance, and long-term durability of CSA cement. Finally, the applications of CSA cement are discussed.
... Compared with OPC solidified soil, D2 is increased by 30.4%. Compared with traditional cement-based soil stabilizers [27,28], such as OPC and calcium sulfoaluminate cement (CSA), 7 days UCS value of MOC stabilized soil is the highest. erefore, in order to make the strength of the MOC solidified soil higher, MgO should not be less than 5% and the ratio of MgCl 2 to H 2 O is about 1 to 10∼15. ...
Article
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Due to the poor performance of ordinary Portland cement (OPC) as a solidified soil road and the large pollution in the production process, environment-friendly magnesium oxychloride cement (MOC) was used as the soil curing agent to prepare the solidified soil, exploring the optimal ratio of various raw materials when MOC is used as a curing agent. Analyzing the properties of MOC solidified soil in the application of road subgrade. This paper tests compaction, mechanical properties, and durability of the MOC solidified soil, simulates the development trend of 7 days unconfined compressive strength of MOC solidified soil, and then analyzes the hydration process and strengthens the formation mechanism of MOC in solidified soil. The study found that the addition of MOC as a curing agent to the soil can effectively improve the compaction and mechanical properties of the soil. Matlab simulation found that when the MgO content is 5.5% to 6% and the ratio of raw materials MgO, MgCl2, and H2O is 2.45 : 1 : 14 to 6.3 : 1 : 14, the performance of MOC solidified soil is excellent. Fitting UCS data, it is found that MOC solidified soil has early strength characteristics. The excellent compaction and mechanical properties of MOC solidified soil are due to the formation of a small amount of phase 5 and layered Mg(OH)2 by the hydration of MOC, and the formation of amorphous gel with SiO2 in the soil. This reaction improves soil compaction and reduces internal porosity from a microscopic perspective. The strength loss rate of MOC solidified soil is higher after immersion in water at the initial stage of curing, but it is still better than that of traditional cement-based solidified soil. Poor performance after immersion in water is associated with disruption of the network-like structure. As an environment-friendly soil curing agent, MOC can be used in engineering practice with low environmental humidity.
... Therefore, it needs to be stabilised before being used for infrastructure construction [2]. To date, various stabilisation such as chemical stabilisation [3][4][5][6], reinforcement [7][8][9], deep mixing [10,11], and prefabricated vertical drain [12,13] have been utilised to improve the engineering properties of unsuitable soils, and this issue leads to stable constructions. ...
Article
Full-text available
The subgrade layer’s stability considerably influences the long-term performance of pavement systems. This study investigates the influence of lime as a traditional stabiliser and activated carbon with coir fibre (ACF) as waste materials and an environmentally friendly binder to stabilise lateritic subgrade soil. Experiments, including the one-dimensional consolidation and unconfined compressive strength (UCS) tests, have been conducted to investigate the geotechnical properties of stabilised soil in various percentages of additives 3%, 6%, 9%, and 12% lime and 1%, 2%, and 3% ACF. The results demonstrate that 3% ACF and 12% lime can significantly improve the strength parameters and decrease the void ratio and permeability in the stabilised soil. Furthermore, microstructural analysis was performed before and after stabilisation for optimum content. The microstructural analysis proves that AC and lime particles fill soil voids, and gel formation binds the soil particles in the stabilised soil matrix. The results show that 3% ACF stabilised soil is comparable with 12% lime in UCS value and decreasing void ratio. Furthermore, both are suitable for subgrade of low-volume road stability according to Malaysian standards.
... Although a decline was observed in UCS of cement stabilised soil with the addition of tyre rubber powder, the ductility of cement soil mixtures increased, which is effective in transportation layers. The curing time in which the targeted strength was achieved has been longer for ash-based geopolymer than for cement stabilised soil, indicating the higher effectiveness of cement in projects where a short construction time is essential [242]. ...
Article
Railway transportation is one of the most advantageous modes of transportation because of its high capacity, which obviates the increasing demand for conveying passengers and cargo. However, high initial costs and ongoing maintenance costs (partially resulting from the degradation of the subgrade and embankments) are drawbacks. Besides, railway subgrade soil experiences a high impact load and alternate drying-wetting and freeze-thawing cycles. In order to counter these problems, various kinds of soil improvement have been employed to improve the engineering properties of soils and minimise embankment and subgrade degradation. Chemical, mechanical, and geosynthetic techniques are currently being used to improve railway embankments. Some methods, such as columnar systems and deep mixing, fortify embankment foundations or subsoil, while others (e.g. chemical binders) can be used as mixed material to stabilise embankments and subgrade soil to a shallow depth. Hence, this review paper first discusses the correlation between railway track elements, failures, and the degradation of embankments in railway networks, and then compares the soil stabilisation techniques from multiple aspects.
... To fill this gap, ordinary Portland cement (OPC) of concrete is partially or totally replaced with calcium sulfoaluminate (CSA) cement and the long-term durability of GFRP rebars embedded inside such concrete mixes is investigated in detail. CSA has been widely applied in concrete constructions [31]. In comparison to the OPC concrete, the pH of CSA concrete is much lower (only 10.5 to 11), which is mainly ascribed to the lime forming a tighter covalent bond in hydration products (namely anhydrous calcium sulfoaluminate (4CaO·3Al 2 O 3 ·CaSO 4 ), dicalcium silicate (2CaO·SiO 2 ) and gypsum (CaSO 4 ·2H 2 O)) of CSA cement. ...
Article
Full-text available
Glass fiber-reinforced-polymer (GFRP) composites have been considered a good alternative to conventional steel rebars in structures. However, the high-pH value (∼13) of normal concrete would lead to severe degradation of GFRP rebars. Yet limited research seems to have investigated the durability of GFRP rebars embodied in low-pH concrete. In this study, the physical and mechanical properties of GFRP rebar embedded in low-pH concrete (∼11) are evaluated by replacing ordinary Portland cement (OPC) with calcium sulfoaluminate (CSA) cement. The tensile strength retention of GFRP rebars inside the CSA concrete (pH = 11) is observed to be around 17% higher than that inside the OPC concrete (pH = 13) at 40°C after 12 months. Additionally, the tensile strength retention of GFRP rebars in CSA concrete at 23°C after 100 years is greatly increased from 52.7% to 79.1% in comparison to GFRP rebars in OPC concrete based on the prediction equation. Even though the glass transition temperature of vinyl ester and its hydrolysis reaction are insensitive to the concrete alkalinity, the improved durability can be explained by fewer glass fiber fractures, vinyl ester matrix cracking and interfacial debonding for GFRP rebars embedded in the CSA concrete. The results of this study provide engineers with a new approach to improving the durability performance of GFRP rebars.
... As a special cement, calcium sulfoaluminate cement (CSA) has attracted a lot of attention due to its good hydration properties, such as fast hardening and early strength [7][8][9][10][11]. Studies by Péra et al. [9] have shown that CSA can be used to produce concrete with ultra-early strength while still maintaining workability of 1 h. ...
Article
To meet the urgent demand of ultra-early strength cementitious materials for modern infrastructure, this work explored the preparation of ultra-early strength cementitious materials based on calcium sulfoaluminate cement (CSA) from solid waste with 3% graphene oxide (GO) (named G3 sample) and 3% triethanolamine (TEOA) modified GO (TGO) (named TG3 sample). The results show that CSA doped with TGO has more potential to prepare ultra-early strength cementitious materials, which originated from the better dispersion of TGO in CSA paste, caused by the fewer –COOH group and more –OH group branched chains in TGO with an enhanced steric hindrance effect. Compared with the blank group, the initial setting times of G3 and TG3 were decreased by 11.90% and 26.19%, respectively, while for the compressive strength at 3 h and 28d, the G3 sample was increased by 253.4% and 6%, respectively, while for TG3 it was 294.9% and 23.38%. This is due to the better dispersion of TGO in the CSA paste and better storage capacity of water molecules, which results in a significant catalytic effect on the early hydration as well as the later continuous hydration of CSA. Meanwhile, the ability of TGO to effectively refine the pores and micro-cracks in the cement matrix also contributes to its strength. In addition, the hydration kinetics of TG3 at different reaction stages demonstrated that the activation energy needed for each order reaction section of hydration was obviously reduced, resultantly, the hydration reaction occurred easily.
... Moon et al. (2020) studied the impact of a small proportion of fines on CSA cemented sands, revealing an increase in strength and stiffness with increasing fine contents. Pooni et al. (2020) studied the stabilisation mechanism of CSA cement in expansive soil revealing involves three key phases; cationic exchange, flocculation and agglomeration between the clay sheets, and cementitious hydration occur during the stabilisation process. Soil stabilised with CSA cement exhibited a reduced spacing between the clay sheets, decreased specific surface and formation of hydration products, including space filling ettringite needles which improve the soil strength. ...
Article
Unsealed roads are still the backbone for many countries’ growth and development with many kilometres of road unpaved globally. Given low traffic volumes, economic considerations cannot justify higher class paved roads and, as a result, are prone to distress in the form of surface and structural defects. Research studies have shown that the targeted application of additives and specific techniques to unsealed pavements can improve the engineering and geotechnical properties of the pavement structure. This paper covers a comprehensive up to date literature review of various techniques for improving unsealed roads durability. The literature is categorized based on non-chemical and chemical additive techniques, covering mechanical stabilisation, chemical additives, alternative cementitious additives and bituminous additives used in unsealed road construction. These techniques are reviewed and discussed to provide a critical overview of the stabilisation mechanisms, properties, performance and durability. Performance aspects of each technique are discussed to describe the benefits, limitations and suitability of soil stabilisers in unsealed roads. This review highlights the shift towards sustainable stabilisation of unsealed roads without considerable impact to current pavement practices, but at the effect of a sound understanding of stabilisation approaches and long-term performance data. The review will benefit researchers and scientists to capture the current state-of-knowledge in the field of unsealed road pavements.
... Calcium sulphoaluminate (CSA) and Ca-sulphoaluminate-belite (CSA-C2S) cements are increasingly coming into focus as sustainable, less CO 2 intensive alternatives to OPC [3][4][5][6][7][8]. CSA cements exhibit mechanical-chemical properties similar or even exceeding that of the OPC-e.g., in terms of rapid strength development, low shrinkage and chemical durability-that has allowed their use in different construction applications replacing or along with OPC [5,[9][10][11], but also in geotechnics for weak soil stabilisation [12,13]. ...
Article
Full-text available
Growing concerns on global industrial greenhouse gas emissions have boosted research for developing alternative, less CO2 intensive binders for partial to complete replacement of ordinary Portland cement (OPC) clinker. Unlike slag and pozzolanic siliceous low-Ca class F fly ashes, the Ca- and S-rich class C ashes, particularly these formed in circulating fluidised bed combustion (CFBC) boilers, are typically not considered as viable cementitious materials for blending with or substituting the OPC. We studied the physical, chemical-mineralogical characteristics of the mechanically activated Ca-rich CFBC fly ash pastes and mortars with high volume OPC substitution rates to find potential alternatives for OPC in building materials and composites. Our findings indicate that compressive strength of pastes and mortars made with partial to complete replacement of the mechanically activated CFBC ash to OPC is comparable to OPC concrete, showing compared to OPC pastes reduction in compressive strength only by <10% at 50% and <20% at 75% replacement rates. Our results show that mechanically activated Ca-rich CFBC fly ash can be successfully used as an alternative CSA-cement type binder.
... Other minor phases can be also found in CSA cement, such as C 2 S, CA, C 4 AF, and CŜ. CSA cement has been used to stabilize radioactive elements [1516], to mitigate the alkali silica reaction in mortars [17], to stabilize Zn [18], in 3D printing as an additive to OPC cement [192021], for soil treatment [22] and in special applications requiring a high strength development at early ages [23]. However, modifications in the cement composition could affect the technical properties, the environmental behavior and the durability of cement based materials. ...
Article
Calcium Sulfoaluminate Cements (CSA) are considered as an alternative to Ordinary Portland Cement (OPC) for some applications. There is still a lack of knowledge on their durability and degradation mechanisms. The goal of this study is to investigate the influence of CSA cement composition on CSA cement paste durability. In addition to a commercial cement, two CSA cements with different amounts of ye’elimite (50 and 75 w.t. %) were synthetized for this study Three cement pastes were prepared and leached for one year in pure water at a temperature of 20 °C. The leachates were analyzed by ICP/AES and the cement pastes were characterized by X-Ray Diffraction (XRD), thermogravimetric analysis (TGA/DTG), Mercury Intrusion Porosimetry (MIP), and Scanning Electron Microscope (SEM). The results show that the leaching mechanism is first dissolutive than diffusive independently of the composition of calcium sulfoaluminate cement. Before leaching, the paste generated by the cement containing 50 w.t. % of ye’elimite had the highest porosity and was the only one to contain Stratlingite. During leaching, this material exhibited the lowest decalcification rate and showed the smallest degraded zone after one year of degradation. This study reveals that the presence of stratlingite has an important role in improving the durability of calcium sulfoaluminate cement paste.
... o com efeito cimentante ao promover a floculação das argilas(Abbaslou, Hadifard & Ghanizadeh, 2020), conforme verifica-se na Tabela 1 que o nível desse elemento no solo antes da implantação do experimento já se encontrava em valores elevados, o que pode ter contribuído para que os resíduos adicionados ao solo não incrementassem a agregação do solo.Pooni et al. (2020) verificaram que a adição de material cimentante rico em cálcio e alumínio promove a estabilidade do solo, apontando três mecanismos principais: realização de trocas catiônicas, floculação e aglomeração de argilas e hidratação cimentícia.Em relação aos demais atributos não foi verificada nenhuma restrição quanto a utilização do pó de roc ...
Article
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O feijão-comum (Phaseolus vulgaris L.) constitui um alimento básico na dieta brasileira, atuando como fonte de proteína vegetal de baixo custo. Apesar da possibilidade de ser cultivado em diferentes condições edafoclimáticas e tecnológicas, o seu cultivo em regiões de baixa fertilidade ou a ocorrência de manejo incorreto da fertilidade pode limitar a sua produtividade. Objetivou-se verificar o efeito do pó de ardósia e rocha calcária na produtividade, componentes de produção e atributos físicos do solo em área cultivada com feijoeiro comum no norte de Minas Gerais. Para isso foi instalado um experimento no delineamento de blocos casualizados com quatro repetições, adicionalmente foram incluídos dois tratamentos testemunhas. Os tratamentos consistiram de cincos doses de pó de ardósia: 0; 1,25; 2,5; 3,75 e 5,0 t.ha-1. Os tratamentos testemunhas foram constituídos da aplicação de pó de rocha calcária na dose de 1,0 t.ha-1 combinados ou não com o uso do pó de ardósia na dose de 2,5 t ha-1. O aporte de potássio e magnésio ao solo com a utilização do resíduo de ardósia pode ter contribuído com incrementos de até 11,10 e 54%, respectivamente, na massa de mil grãos e na produtividade do feijoeiro. O pó de rocha calcária não interfere na produção, e nos componentes de produção do feijoeiro. Ambos os pós de rocha testados não interferem nos atributos físicos do solo.
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Radioactive cobalt release poses concerns since the attention to radiation safety. In this work, soil and groundwater sampled from the surroundings of the long-distance pipeline of a proposed nuclear power plant were used to assess radiation safety by studying Co(II) adsorption. The Freundlich and Langmuir models fitted the experimental data well. The results indicated that Co adsorption was an entropy-driven, spontaneous, endothermic and chemical process. The adsorption mechanism was mainly the inner-sphere complexation, and CoSO4(aq) contributed to the partially reversible occurrence. This study provided fundamental information about the environmental behaviours and adsorption mechanism of radioactive Co(II) surrounding the effluent pipeline.
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The effects of sodium aluminate (NA) and reverse-osmosis brine (RW) on alkali-activated slag cement (AASC) using sodium hydroxide and sodium silicate as activators were investigated. NA was mixed at 0%, 2.5%, and 5.0% by binder weight, and the mix waters tested were tap water (TW) and RW. In the experiment NA showed the effect of improving the compressive strength, with the highest strength value obtained at 2.5%. However, the strength improvement effect of NA was more clearly demonstrated in RW samples than in TW samples. Changes in the C4AH13 (Tetracalcium aluminate hydrate; Ca4Al2(OH)14·6H2O), C2ASH8 (stratlingite; Ca2Al2SiO7·8H2O), and C3AH6 (katoite; Ca3Al2(OH)12) phases were observed according to the increase in NA through hydration reaction analysis. Friedel’s salt (Ca4Al2O6Cl2·10H2O) was additionally observed in the RW sample. In the TW samples, more of the C3AH6 phase was formed than in the RW samples, which affected the strength reduction. In the RW samples, increases in the chloride ions and calcite phase in the pore solution due to carbonation of Friedel’s salt were confirmed. This phenomenon of the RW samples became more pronounced as the NA concentration increased. The technique of utilizing RW in AASC showed the possibility of being used as a novel stabilization/solidification method for reverse osmosis brine.
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In this study, systematic investigations were conducted to solidify dredged marine sediments using the low-carbon composite binder made by mixing Ordinary Portland and calcium sulfoaluminate cement (OPC-CSA). A series of tests to evaluate physical and mechanical properties of samples, which indicated that the OPC-CSA composite binder could effectively improve the engineering characteristics of solidified dredged marine sediments, such as the immediate California Bearing Ratio (I-CBR) index, unconfined compressive strength, splitting tensile strength, and elastic modulus. In addition, simple models were proposed to correlate the unconfined compressive and splitting tensile strength with the elastic modulus of treated sediments. Importantly, the elastic modulus of treated sediments was defined by the local small-strain sensor method. In addition, the correlation between the strength and the three kinds of failure mode of the specimens was revealed. Lastly, simplified carbon footprint analysis indicated that OPC-CSA composite binder offers potential CO2 emissions savings of 14%-41%. The laboratory tests have revealed that the mechanical and environmental behaviors of solidified dredged marine sediments meet the environmental and engineering requirements of the standards and regulations. Low-carbon and sustainable OPC-CSA composite binder-solidified dredged marine sediments could be reused as subbase or roadbed infill materials for low traffic.
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Red soil, composed of a clayey bed containing hematite, is used as pavement material in southern Iran. As an effective and economical technique, soil improvement with cement is common practice for improving the engineering properties of different soil and pavement layers. The formation of nanostructured calcium silicate hydrate (C-S-H) is the primary factor contributing to this improvement. On the other hand, the presence and dissolution of hematite in the soil structure can also influence C-S-H formation. The present study investigates the effects of cement on the engineering properties of the hematite-rich red soil from a microstructural point of view, with particular emphasis on changes in the C-S-H nanostructure. For this purpose, red soil specimens were stabilized with 2, 4, 6, 8 and 10 wt% cement for different curing times. The soil's engineering properties were evaluated by macrostructural testing, namely by soil particle size analysis and slake durability, water absorption, Unconfined Compressive Strength (UCS), and Ultrasonic Pulse Velocity (UPV) tests. Furthermore, the soil stabilization process and the effects of hematite on the C-S-H microstructure were evaluated by pH and Electrical Conductivity (EC) tests, X-Ray Diffraction (XRD), energy-dispersive X-ray analysis (EDX), and Scanning Electron Microscope (SEM) imaging. It was shown that adding cement to hematite-rich soil promotes Calcium Ferrite Hydrate (C-F-H) and ilavite (C-F-S-H) formation and, consequently, improves the red soil's stability and compressive strength. In fact, using 6 wt% cement, the presence of hematite, and the formation of Fe-containing nanostructures helped the red soil specimen develop a compressive strength of 2.04 MPa (17 times that of the natural soil) in seven days.
Conference Paper
Stabilization of problematic soils for civil engineering applications to achieve the needed soil engineeringproperties while considering cost and environmental impacts is essential. Soil stabilization can be donephysically or chemically, and in many times, it imperatively become a basic advance for making construc-tion. Several chemical additives, with lime, cement, or fly ash are typically used for this objective. For aridand semi -arid regions in developing countries where acute shortage of such construction materials andheight cost of chemical additive like cement, instead cheaper alternative stabilizer could be used. Anexperimental based investigation was carried out to study and assess the effectiveness of a low-costalternative stabilizer, namely the use of lime for stabilizing cohesive soils and mechanical compactionfor cohesionless soils and their effects on the geotechnical properties of stabilized tropical soil. Five soilsamples from each type of soil were collected from Khartoum, which are representing wide range of trop-ical soils available in arid regions. Cohesive soils were mixed with different amounts of lime, varying from0, 5, 7, 9, and 11% by dry weight of soil whereas mechanical compaction was done for cohesionless soils.Laboratory tests such as consistency test, compaction, and California Bearing Ratio test (CBR) were per-formed to measure the engineering characteristics of the stabilized soils. The result showed that with thesupplement of various proportions of lime, both the liquid limit and plasticity index values reduce as theconcentration lime is increased, and the plastic limit of the cohesive soil exhibit an increasing trend andthe optimum moisture content, whereas the maximum dry density decreased. The stabilized soil strengthis observed to be increasing with the increase of lime content, the heigh values of CBR which is attributedto the lesser voids in the admixture soils with low plasticity and dry unit weight.
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Numerous laboratory-based solutions have been proposed in the recent literature for the stabilization of unsaturated expansive soil by recycling lignosulphonate (LS). However, the practical assessments of the proposals for the treatment of the rainfall-induced surficial failure in unsaturated expansive soil slopes are required, considering the frequency of this failure and associated economic loss. Moreover, in conventional geotechnical practice, the slope stability is generally evaluated only with consideration of the hydraulic response of the soil, ignoring the hydro-mechanical coupling effect associated with the swelling behavior of soil. Since LS-based stabilizers mainly impart the reduction of the swelling potential of expansive soils, therefore, the assessment of the stability of the LS-treated surficial layer of unsaturated expansive soil slopes requires consideration of the hydro-mechanical effect. For this purpose, the uncoupled and hydro-mechanical coupled analyses were conducted for dealing with the hydraulic and hydro-mechanical responses of the surficial layer of soil slopes, respectively. Specialized experimentations and pertinent literature review were performed to acquire the required input data for these analyses. It is observed that the LS-based surficial layer treatment affects the pore water pressure (PWP) profiles as well as wetting front depth (WFD), which are the critical aspects for influencing the stability of unsaturated expansive soil slopes. Among all LS-based stabilizers, only the stabilizer named composite cementing admixture (CCA) reasonably ameliorated the PWP profiles and WFD of the slope considering disastrous environmental impacts (i.e., wetting-drying cycles). Moreover, the heave problem of expansive soil slopes was observed to be mitigated by LS-based treatment among which the CCA performed the most efficiently. Furthermore, the critical factor of safety (FS) required for slope stability was also affected by the LS-based treatment, whereas the CCA was observed to provide the safest critical FS for slope stability.
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Naturally available sands are always found with finer particles of varying sizes and proportions which are generally not accounted for in the geotechnical design of a cemented soil system. This paper explores the behavior of cemented sand with fine particles in smaller proportions. Two types of cements: (i) Ordinary Portland Cement (OPC), (ⅱ) Calcium Sulfoaluminate cement (CSA); three cement contents: 3%, 5%, 7% and four fine (kaolin powder) contents: 0%, 1%, 3%, 5% are considered in this study. The ultrasonic pulse velocity (UPV), shear wave velocity (V_s) and unconfined compressive strength (UCS) are measured to investigate the effects of fine particles on the cemented sand. The results show that fine particles do affect quite significantly the mechanical properties of cement-treated sand, even at negligent proportions. The strength and stiffness increase with fine content in both types of cement. The increase in strength and stiffness with increasing fine contents is attributed to the increased density with kaolin acting as a filler material facilitating more contact points among the particles. The results also show that the effect of fine particles on cemented sand depends not only on their relative volume and mineralogy but also on the type of the binding material.
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Cement stabilization of soil is a useful method to improve the mechanical behaviors and engineering performance of soils in geotechnical design and construction projects involving weak or liquefiable soils. Among the factors affecting the strength of cement-stabilized soils, water content and water–cement ratio are important but less well understood because of controversial views. This paper presents a systematic laboratory study to investigate the effects of water content and water–cement ratio on the unconfined compressive strength, with good control of the packing density and void ratio of the tested specimens. The effects of void ratio and cement content are also investigated. The strength of the cement-stabilized sand continuously decreased with increasing water–cement ratio within the range of 0.5 to about 3. A general equation is suggested to evaluate the unconfined compressive strength of cement-stabilized soil. Finally, a new conceptual characterization chart is proposed with consideration of the effects of cement content, water content, and water–cement ratio.
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Lightweight alkali-activated ground granulated blast furnace slag (LAS) is an energy-efficient and environment-friendly cementitious material that can be used as a binder for the fill soil stabilization in subgrade construction. Although physical, hydraulic and mechanical properties of LAS stabilized clayey soils have been previously characterized, their long-term durability under deteriorating environments has not yet been well assessed. This paper reports an experimental study on the sulfate attack resistance of a LAS stabilized clayey soil, which is composed of GGBS, sodium silicate, calcium carbide residue (CCR), air foam, and clayey soil. Stabilized soil specimens are submerged in a sodium sulfate solution for varying periods (3, 7, 14, 28, 60, 90 and 120 days). The mass change percentage, unconfined compressive strength and thermogravimetric characteristics are evaluated at the end of each varying soaking periods. The same virgin soil stabilized by the lightweight Portland cement (LPC) is also tested as a benchmark. The results suggest that the LAS stabilized soil has superior sulfate attack resistance in terms of greater water absorption and higher strength, which is attributed to the presence of larger amount of cementitious hydration products in the LAS stabilized soil, as confirmed via thermogravimetric measurement.
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Calcium carbide residue (CCR) is a by-product of acetylene gas production. Stockpiles of CCR have continued to accumulate worldwide in many developed and developing countries. Sustainable reuse options for CCR in civil infrastructures, such as roadembankments, have been recently evaluated in the laboratory. However, to date there are limited studies on the actual field performance of CCR in stabilizing clayey soils in highway subgrades. In this study, a field trial was conducted to ascertain the viability of using CCR stabilized clayey soil as a highway subgrade course material. Quicklime was selected as a control binder in the field trial for comparison purposes. The construction procedures of theCCR and quicklime stabilizations in two field sections are presented. A series of field tests, including California Bearing Ratio (CBR) test, plate loading test, Benkelman beam deflection test, and dynamic cone penetrometer (DCP) test were undertaken after the embankment construction. The results indicated that in the top zone of the filled soil layers with 94% degree of compaction, the CCR stabilized subgrade soil exhibited higher values of CBR andresilient modulus, and lower values of resilient deflection and DCP Index relative to the quicklime stabilized soil. The field trial results indicated that CCR had negligibleenvironmental effects and furthermore resulted in low construction costs. Based on the field test results, CCR was found to be a viable alternative binder for stabilizing soft subgrade soils. The outcomes of this research are significant from engineering, economic and environmental perspectives.
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Calcium carbide residue (CCR) is an industrial by-product, stockpiles of which are rapidly accumulating worldwide. Highway embankment construction has been identified as an avenue to consume huge quantities of CCR as an economical, less energy intensive and environmental-friendly chemical additive for soil stabilization. Previous studies have investigated the mechanical behavior of soils stabilized by CCR or blends of CCR with other additives; however, interpretation of the macro-scale geomechanical behavior of CCR stabilized soft soils from a systematically microstructural observation and analysis is relatively unknown. This paper presents a multi-scale laboratory investigation on the physical, mechanical and microstructural properties of CCR stabilized clayey soils with comparison to quicklime stabilized soils. Several series of tests were conducted to examine the Atterberg limits, particle size distribution, compaction characteristics, unconfined compressive strength, California-Bearing-Ratio and resilient modulus of the CCR stabilized clayey soils. The influences of binder content, curing time, and initial compaction state on the physical and mechanical properties of treated soils are interpreted with the aids of physicochemical and microstructural observations including soil pH, soil mineralogy obtained from X-ray diffraction and thermogravimetric analysis, and pore size distribution obtained from mercury intrusion porosimetry. Soil particle flocculation and agglomeration at the early stage and pozzolanic reactions during the entire curing time, which originate from the finer particle size, greater specific surface area and higher pH value of calcium carbide residue, are the controlling mechanisms for the superior mechanical performance of CCR stabilized soils. The outcomes of this research will contribute to the usage of CCR as a sustainable and alternative stabilizer to quicklime in highway embankment applications.
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This paper presents details of a study that deals with determination of engineering properties, identification of phases of major hydration products, and microstructural characteristics of a zinc-contaminated (referred to as Zn-contaminated in this paper) kaolin clay when it is stabilized by a cement additive. Investigations were carried out with respect to the effect of the level of zinc (Zn) concentration on the overall soil properties including Atterberg limits, water content, pH, stress–strain characteristics, unconfined compressive strength, and secant modulus. In addition, X-ray diffraction, scanning electron microscopy, and mercury intrusion porosimetry studies were conducted to understand the mechanisms controlling the changes in engineering properties of the stabilized kaolin clay. The study reveals that the level of Zn concentration has a considerable influence on the engineering properties, phases of hydration products formed, and microstructural characteristics of the stabilized kaolin clay. These changes are attributed to the retardant effect of Zn on the hydration and pozzolanic reactions, which in turn alters the phases of hydration products and cementation structure – bonding of the soils. Theoretical simulation of the pore-size distribution curves demonstrates that the cement-stabilized kaolin exhibits bimodal type when the Zn concentration is less than 2%, whereas it displays unimodal type when the Zn concentration is 2%. With an increase in the Zn concentration, the characteristics of the interaggregate pores in terms of volume and mean diameter change considerably, whereas those of intra-aggregate pores remain nearly unchanged.
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Three testing methods for predicting the durability of cement-stabilized soils-the tube suction (TS), 7-day unconfined compression strength (UCS), and wetting-drying durability tests-were tested and compared for their correlations and influence factors using a problematic low plastic silt clay from subgrade commonly encountered in Louisiana. A series of samples was molded at six different cement dosages (2.5, 4.5, 6.5, 8.5, 10.5, and 12.5 % by dry weight of the soil) and four different molding moisture contents (15.5, 18.5, 21.5, and 24.5%). The test results indicate that the water-cement ratio of cement-stabilized soil had the dominant influence on the maximum dielectric value (DV), 7-day UCS, and durability of stabilized samples tested, although the dry unit weight of cement-stabilized soil could cause the variation of the results. This study confirms that TS, 7-day UCS, and wetting-drying durability tests are equivalent in predicting durability, and tentative charts to ensuring the durability of cement-stabilized low plasticity soils are developed using their 7-day UCS or the maximum DV values.
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This paper presents an evaluation of the long-term field performance of Farm-to-Market Road 2, the construction of which involved geosynthetic stabilization to address concerns related to the presence of expansive clays and associated environmental loads. A comprehensive study was conducted to quantify the benefits of geosynthetic stabilization in the performance of the roadway after having been subjected to 9 years of wet and dry season cycles. Control sections and seven design schemes (including various combinations of geosynthetic-stabilized base and lime-stabilized subbase courses) were incorporated in 32 test sections. Evaluation of the development of environmental longitudinal cracks over the 9-year period showed that the use of geosynthetics to stabilize the roadway base led to a significantly improved performance, as quantified based on the extent and length of environmental load–induced longitudinal cracks. The improvement, observed for all the geosynthetics considered in this study, was found to be more significant during dry seasons, which is when environmental longitudinal cracks develop. In addition, results from the field performance monitoring program revealed that lime stabilization of the subbase not only did not help but generally compromised the performance of road sections subjected to environmental loads.
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This paper presents an experimental study on the strength behaviour of the soils stabilized by the composite of steel slag, cement and metakaolin (SCM composite), at different clay fractions, water contents and curing periods. The SCM composite can effectively improve the soil strength and the SCM stabilized soil shows the similar property to cemented soils. The microstructures of SCM stabilized soils with different curing periods and water contents are also presented via scanning electron microscope tests. Comparing the microstructure and fissure between stabilized soils, mortar and concrete, it is clear that the non-free water absorbed at the surface of clay minerals does not involve the hydration/pozzolanic process. Moreover a new variable, the free water content, is proposed, which equates to total water content subtracts n times of plastic limits of the original soils. The free water content is effectively employed to characterize the unconfined compression strength of stabilized soils observed in this research and also in literatures. With this proposed concept, the binder stabilized soils can be accommodated by the framework for traditional cementitious material (concrete and mortar).
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A C 4 A 3 $-C 2 S (ye'elimite-belite) clinker system with different C 2 S and C 4 A 3 $ contents is synthesized from analytical reagents and a C 4 A 3 $-C 2 S hydration system with or without gypsum addition is established. The crystal/amorphous ratio in the C 4 A 3 $-C 2 S hydration system with or without gypsum addition was characterized using X-ray diffraction (XRD), Thermo-gravimetric (TG) analysis, Fourier transform infrared (FTIR) spectroscopy and Mercury intrusion porosimetry (MIP) tests. The Rietveld quantitative phase analysis (RQPA) method and the thermal calculation method were used to determine the compositions of the system hydration products. The compressive strength of the samples were also investigated. When the hydration degree is close to each other and the hydration sample is not affected by structural defects, the effect of the crystal/amorphous ratio of hydration products on the mechanical property of the sample is dominated. When the numerical range of the crystal/amorphous ratio is 0.8–1.4, the corresponding compressive strength at 90 d are all greater than 50 MPa. Appropriate amount of gypsum can change the crystal/amorphous ratio, increase the strength, and partially lead to the change of the porosity. The phases’ contribution rate to strength in the C 4 A 3 $-C 2 S hydration system with or without gypsum addition were ranked as follows: AH 3 gel ≥ C-S-H gel > AFt > C 2 ASH 8 ≥ AFm > C$H 2 .
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For ground improvement, the use of calcium sulfoaluminate (CSA) cement, which has lower carbon footprint is examined as an alternate to ordinary Portland cement (OPC). The use of additives like lime or fly ash results only in partial replacement of OPC, while complete replacement of OPC is possible using CSA binder. For CSA-treated sand, the optimized gypsum content is experimentally determined as 30% since it enables high initial strength and durable strength gain. In both wet and dry curing, CSA-treated sand has significantly high strength gain compared to OPC. Finally, a unified strength prediction model for cemented soil is proposed for wide ranges of cement and soil types.
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This paper studies the effectiveness of calcium sulfoaluminate (CSA), which has a much lower carbon footprint than conventional ordinary portland cement (OPC), in applications which use high water:cement ratios. Unconfined compressive strength is used to compare OPC and CSA treated sand. Apart from its ecofriendly characteristics, CSA-treated sand has significantly high initial strength development due to the fast hydration of ye’elimite. Two curing methods are used to simulate wet field and dry field conditions. For both OPC-treated and CSA-treated sand, the samples cured underwater have lower strength than the dry-cured samples. However, the strength reduction due to wet curing is less for CSA than for OPC. In addition, recoverable strength loss is observed in CSA-treated sand subjected to wet curing between 7 and 14 days, which is not observed in dry curing. The effect of water content on the strength of cemented sand is presented. The use of CSA would help move toward a sustainable approach to reduce the carbon footprint in geotechnical applications.
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The use of deep soil mixing (DSM) in ground-improvement projects, for structures subjected to low to medium loads, has increased over the past decade due to its convenient and practical implementation and its economic advantages. Traditionally, Portland cement and lime have been the most popular binders for DSM applications. However, the ground-improvement industry has been keen to explore environmentally friendly alternatives with low carbon dioxide emission. The aim of this research is to investigate the use of two stockpiled industrial waste by-products, namely, fly ash (FA) and slag (S), as alternative green binders in ground-improvement projects that would reduce the carbon footprint of these projects. In this research, combinations of FA and S, activated by a liquid alkaline activator (L), were evaluated for the ground improvement of a soft marine clay, namely, Coode Island Silt (CIS). The performance of the FA + S geopolymers was compared with that of traditional cement and lime control binders. The soil moisture content was set at 0.75, 1.0 and 1.25 of the liquid limit (LL) of the soil to replicate the field conditions. 10, 20 and 30% binders, by dry soil mass, were added to the soil, and the samples were cured for 7 and 28 days. Unconfined compression strength (UCS), flexural beam and scanning electron microscopy (SEM) imaging tests were conducted to evaluate the changes in the engineering behavior and the microstructure of the mixtures. The results indicated that the strength and stiffness of the soft clay were significantly increased by the use of these new FA + S binders, which substantiated them as alternatives to traditional cement or lime binders. The optimum binder content was found to be 20%, while CIS + 5%FA + 15%S was found to be the optimum mixture. Furthermore, correlations between the UCS and the modulus of elasticity (E50) and between the UCS and the modulus of rupture (R) for the geopolymer mixtures were proposed. They will be valuable to both designers and practitioners of ground-improvement works.
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Portland cement is traditionally used as a binder in ground improvement projects on soft soil foundations. The use of cement in ground improvement projects, however, is fraught with both, financial and environmental concerns due to its relatively high cost, the use of natural resources and the high carbon footprint from cement production. Attempts are being made to find alternative environmentally friendly binders with a low carbon footprint using industrial by-products such as fly ash (FA) and slag (S). Using waste by-products such as FA and S to produce geopolymer binders, as novel green cementitious materials, may provide an environmentally friendly and effective ground improvement option. In this study, the effect of adding geopolymers to a soft soil was investigated for usage in deep soil mixing (DSM) applications. The soil was a soft marine clay known as Coode Island Silt (CIS). Different combinations of FA and S with six combinations of sodium and potassium based liquid alkaline activators (L) were added to the soil to study the effects on its engineering and chemical properties. These changes were evaluated via an unconfined compression strength (UCS) test, scanning electron microscopy (SEM) imaging and energy-dispersive X-ray spectroscopy (EDS) tests. The tests were conducted after 3, 7, 14 and 28 days of curing. Based on the results, the important role of L in strength development was studied, and the combination of 30% NaOH with 70% Na2SiO3 was found to achieve the highest strengths. Furthermore, increasing the S content was found to result in significant improvements in strength. The excellent correlation between strength and stiffness shown in the results are expected to help in the development of relationships for strength prediction of these green binders in geotechnical applications. This study shows that FA and S based geopolymers can be used as sustainable binders in DSM projects, with significant environmental benefits.
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The main objective of this study was to investigate the phase and strength development of calcium sulfoaluminate-belite (CSAB) cement pastes with different amounts of gypsum and water. Thermodynamic modeling and a series of experiments including X-ray diffraction (XRD), thermogravimetric analysis, isothermal calorimetry, and compressive strength tests were performed. Decreasing the mixing water increased the strength of CSAB pastes, but decreased the degree of hydration. Interpretation of the early age XRD results and thermodynamic modeling suggested the formation of a meta-stable phase from the hydration of belite, possibly C-(A)-S-H, which transformed into strätlingite at later ages only in the samples with high water content, likely due to easier diffusion of ions at higher w/c. Furthermore, the XRD results and thermodynamic modeling confirmed that the amount of gypsum controls the hydration of ye'elimite as well as belite in the CSAB cements.
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While moisture-induced distress is one of the major causes of premature pavement failure, geosynthetics are only seldom used to provide internal drainage within the structure of roadway systems. This is likely because conventional geosynthetic drains are only suitable to manage flow under saturated soil conditions, whereas unsaturated conditions prevail in pavement systems. Recent insight into the interaction between geosynthetics and unsaturated soils has led to new advances in geosynthetic manufacturing, including the development of geotextiles with enhanced lateral drainage (ELD), which allow drainage even under unsaturated conditions. This paper highlights the benefits of ELD in a number of roadway situations, including: (1) enhanced lateral drainage of moisture migrating upward from a high water table, (2) enhanced lateral drainage of moisture infiltrating downward from the surface, (3) control of frost heave-induced pavement damage, (4) control of pavement damage caused by expansive clay subgrades, and (5) enhanced lateral drainage in projects involving soil improvement. The mechanisms of moisture migration, as well as the impact of ELD are evaluated in each of these situations. Additionally, case histories involving recently constructed pavements involving the use of ELD geosynthetics are presented for each specific drainage application. The selected case histories involve post-construction evaluation of the ELD geosynthetic's performance either through assessment of lateral drainage, condition surveys of pavement sections with and without ELD geosynthetics, or in-situ monitoring of moisture content. Assessment of the data collected illustrates the beneficial impact of ELD used in the various pavement scenarios. Overall, this paper illustrates that incorporation of enhanced lateral drainage in roadway systems results in a range of improvements for pavement performance.
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The fast-track repair of deteriorated concrete pavement requires materials that can be placed, cured, and opened to the traffic in a short period. Type III cement and Calcium Sulfoaluminate (CSA) cement are the most commonly used fast-setting hydraulic cement (FSHC). In this study, the properties of Type III and CSA cement concrete, including compressive strength, coefficient of thermal expansion (CTE) and shrinkage were evaluated. The test results indicate that compressive strength of FSHC concrete increased rapidly at the early age. CSA cement concrete had higher early-age and long term strength. The shrinkage of CSA cement concrete was lower than that of Type III cement concrete. Both CSA and Type III cement concrete had similar CTE values. Based on the laboratory results, the CSA cement was selected as the partial-depth rapid repair material for a distressed continuously reinforced concrete pavement. The data collected during and after the repair show that the CSA cement concrete had good short-term and long-term performances and, therefore, was suitable for the rapid repair of concrete pavement.
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This paper, which forms part of the UNEP White Papers series on Eco-Efficient Cements, provides a brief discussion of the class of cementing materials known as ‘alkali-activated binders’, which are identified to have potential for utilization as a key component of a sustainable future global construction materials industry. These cements are not expected to offer a like-for-like replacement of Portland cement across its full range of applications, for reasons related to supply chain limitations, practical challenges in some modes of application, and the need for careful control of formulation and curing. However, when produced using locally-available raw materials, with well-formulated mix designs (including in particular consideration of the environmental footprint of the alkaline activator) and production under adequate levels of quality control, alkali-activated binders are potentially an important and cost-effective component of the future toolkit of sustainable construction materials.
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This study investigates the effects of carbonation, water content, and pozzolanic reaction under the drying condition on the strength development of cement-treated soils. Two soil specimen types (i.e., sand mixture and sand–loam mixture) were cured under sealed, drying, and changing water content conditions. The measured compressive strength of the specimens under the drying condition was higher than that under the sealed condition because of carbonation and suction. The relationship between the strength and the water content under the drying condition was established. The progress of the chemical reactions in the specimens was also evaluated. The contributions of cement hydration, carbonation, pozzolanic reaction, and suction to strength development under the drying condition were then quantitatively analyzed. The results indicated that not only cement hydration and pozzolanic reactions, but also carbonation and changes in the water content, substantially contributed to the strength development of cement-treated soils.
Article
The hydration of four sulfoaluminate cements have been studied: three sulfoaluminate systems, having different content of sulfate and silicate, and one blend Portland-CSA-calcium sulfate binder. Hydration was followed up to 90 days by means of a combination of X-ray diffraction and solid state MAS-NMR; Differential scanning calorimetry and Scanning electron microscopy were also performed in order to help the interpretation of experimental data. High amount of amorphous phases were found in all the four systems: in low-sulfate cements, amorphous part is mainly ascribed to monosulfate and aluminium hydroxide, while strätlingite is observed if belite is present in the cement; in the blend system, C-S-H contributes to the amorphous phase beyond monosulfate.
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Steel is an inherently never-ending product, in terms of recycling and reuse. The steelmaking process creates an industrial by-product termed as slag. Ladle furnace slag (LFS) is produced at the final stages of the steelmaking process in ladle refining furnaces. The potential use of LFS as a base/subbase material requires a thorough knowledge of its engineering properties. In this research, an extensive suite of engineering characterization tests were carried out to evaluate the engineering properties of LFS. The effect of curing on the strength of unbound LFS was investigated using unconfined compression strength (UCS) and resilient modulus tests. The results showed that the UCS of unbound LFS increased by almost four times with 7 days of curing in a temperature-controlled and moisture-controlled chamber. The resilient modulus value of unbound LFS increased when increasing either confining pressure or deviator stress. The specimens with 7 and 28 days of curing had higher resilient modulus values than uncured samples, which were substantiated by UCS test results. The curing period was found to play an important role in the UCS development of unbound LFS samples, which was attributed to the relatively high lime content of the material. The chemical composition and microstructure of LFS samples were evaluated using X-ray fluorescence (XRF) and scanning electron microscopy (SEM) analyses. In terms of usage in pavement-base/subbases, the engineering properties of LFS were found to be equivalent or even superior to typical quarry materials.
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Marble sludge waste was used as a major cement raw material in sintering sulfoaluminate cement clinker successfully in the laboratory. The influences of raw mix composition as well as different burning temperatures were investigated. Starting materials and prepared cement were characterized through different techniques including; Fourier transform infrared spectroscopy (FTIR); X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results reveal that calcium sulfoaluminate–belite cement can be produced by burning a raw mixture contains in weight percent (25% kaolin, 20% gypsum and 55% marble sludge waste) at firing temperature ranging between 1200 and 1250 °C.
Article
Strätlingite, a siliceous AFm-type phase associated with blended cement hydration, is often assigned a fixed composition, 2CaO·Al2O3·SiO2·8H2O, but our knowledge of its stability and compatibility with other phases is limited. The phase relations and thermal stability of strätlingite in the CASH system are reported. Strätlingite shows a relatively fixed composition and is compatible with C–S–H and hydrogarnet solid solution at appropriate temperatures but is not compatible with portlandite and decomposes in its presence. It is stable in cement hydrate systems high in aluminosilicate content. Its stability decreases with increasing temperature, with an upper limit of stability approximately 90 ± 5 °C: above which it progressively decomposes to other solids, mainly hydrogarnet solid solution.
Article
This paper examines the microstructural behaviour of cement-treated soft Singapore marine clay. The microstructure was investigated using X-ray diffraction, (XRD) scanning electron microscopy, (SEM) mercury intrusion porosimetry, and laser diffractometric measurement of particle size distribution. The XRD analysis of cement-treated clay enables the identification of the formation of cementitious products, namely calcium silicate hydrate (CSH) and calcium aluminium silicate hydrate (CASH). The relative amount of cementitious products (CSH + CASH) is found to increase with increase of the cement content. The fabric of the treated clay changes to flocculated type, comprising clay-cement clusters separated by large intercluster voids with smaller intra-cluster pores, as can be seen from the SEM images of treated clay. This change is more pronounced with higher cement content and prolonged curing time. The flocculation of the clay particles also causes water to be trapped within the clay-cement cluster and increases both the effective size of the particles or cluster and the entrance pore diameter. This understanding clearly helps to explain the observed engineering behaviour of cement-treated clays commonly found in deep cement mixing or jet grouting techniques.
Article
A range of cements based on calcium sulphoaluminate, 4CaO·3Al2O3·SO3, 'C4A3S̄' are commercially available. The phase contents of some commercial clinkers have been determined. Their hydration behaviour, including calorimetric heat evolutions, are reported. The clinker mineralogies control reactivity and dimensional stability; typically, sulphoaluminate formulations with added lime, gypsum and calcium aluminates are expansive, but those consisting of C4A3S̄ and belite (Ca2SiO4,) hydrate rapidly but give rise to dimensionally stable products. The role of accelerating and retarding admixtures is explored. The presence of admixes has a secondary role in controlling the dimensional stability of belite-sulphoaluminate formulations.
Article
This paper summarizes the results from an experimental study on the behavior of concrete slabs-on-ground in a controlled environment. The test program characterizes the dimensional properties of selected concrete materials, evaluating their performance as real slabs-on-ground in that they are exposed to the controlled environment on the top surface and to the ground moisture on the bottom surface. The concrete mix designs examined included normal-strength portland cement concrete (PCC), high-strength concrete (HSC), concrete using shrinkage reducing admixtures (SRA), and concrete using calcium sulfoaluminate cement (CSA). The data include standard concrete material characterization test results, joint movements, internal relative humidity and temperature over the slab depth. It was found that the concrete using CSA was very stable with no long term shrinkage, cracking or warping, while typical PCC and HSC continued to show crack growth at over 600 days of age. The concrete using SRA had a minor impact at early age and limited impact on long term sectional stability.
Article
Lightweight Cellular Cemented (LCC) material has wide applications in the infrastructure rehabilitation and in the construction of new facilities. The roles of water content, cement content, air content, and fly ash (FA) replacement on the engineering properties including unit weight, flow and strength of LCC clay-FA material are investigated, analyzed and presented in this article. The engineering properties are strongly controlled by the generalized stress state, w/wL, where w is the water content and wL is the liquid limit. The FA replacement reduces wL, resulting in a change in w/wL. The workable state, recommended to produce the LCC clay-FA material, is w > 1.5wL. The flowability is independent of cement content and approximated in terms of w/wL and air content in logarithmic function. The void/cement ratio (V/C), defined as the ratio of the void volume to the cement volume in the mix, is found to be the dominant parameter governing the strength development in LCC clay-FA material. The fabric (arrangement of clay particles, clusters and pore spaces) reflected from both air foam content and water content is taken into consideration by the void volume while the inter-particle forces (levels of cementation bond) are governed by the input of cement (cement volume). A strength equation in terms of V/C at a particular curing time is introduced using Abrams’ law as a basis. From the critical analysis of test results, a mix design method to attain the target unit weight, flowability and strength is suggested. This method is beneficial from both engineering and economic viewpoints.
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A mixture of soil-cement and acrylic resin is used to improve the engineering properties of the soil for construction. This paper presents the results of an investigation into the mechanical behavior of soil-cement mixtures with different percentages of acrylic resin. A series of experiments was conducted on mixtures of soil-cement and soil-cement-resin with different percentages of two different resins. The results show that by increasing the cement content in the soil-cement mixture, the maximum dry density increases, and the optimum water content decreases in compaction tests. Compressive strength tests on soil-cement show that the increase in strength depends on the cement content and the curing time. The results also indicate that the strength of soil-cement is increased considerably by adding acrylic resin as an additive material. For a given cement content, the increase in shear strength is a function of curing time and the percentage of resin. DOI: 10.1061/(ASCE)MT.1943-5533.0000252. (C) 2011 American Society of Civil Engineers.
Article
Laboratory and field strength development of cement stabilized coarse-grained soils are studied in this paper. A phenomenological model to assess the laboratory strength development is developed. The model is divided into the dry and the wet sides of optimum water content. At the optimum and on the wet side of optimum, the strength development in cement stabilized soils at a particular curing time is dependent only upon the soil-water/cement ratio, w/C, which can reflect the combined effects of water content and cement content. It is moreover premised that the relationship between strength and water content is symmetrical around the optimum water content (OWC) in the range of 0.8 to 1.2 times the OWC. The proposed model is useful for assessing the strength development wherein water content, cement content and compaction energy vary over a wide range. Only the test result of a single laboratory trial is needed. From the field study, it is found that the field roller-compacted strength, qufr is lower than the laboratory strength, qul under the same dry unit weight, soil-water/cement ratio and curing time due to several field factors. The ratio qufr/qul varies from 50 to 100%. Non-uniformity in mixing soil with cement is realized by the ratio of field hand-compacted strength to laboratory strength, qufh/qul ranging from 0.75 to 1.2. For most data, the field roller-compacted strength is 55 to 100% the field hand-compacted strength. This might be caused by the difference in compaction method and curing condition between laboratory and field stabilization. From this field observation and the proposed model, a practical procedure for repairing damaged roads using the pavement recycling technique is introduced. The procedure consists of the determination of cement content, the execution of the field stabilization and the examination of the field strength. It can save on sampling and laboratory testing and hence cost.
Article
This paper presents a review of alkali-activation technology, moving from the atomic scale and chemical reaction path modelling, towards macroscopic observables such as strength and durability of alkali-activated concretes. These properties and length scales are intrinsically interlinked, and so the chemistry of both low-calcium (‘geopolymer’) and high-calcium (blast furnace slag-derived) alkali-activated binders can be used as a starting point from which certain engineering properties may be discussed and explained. These types of materials differ in chemistry, binder properties, chemical structure and microstructure, and this leads to the specific material properties of each type of binder. The secondary binder products formed during alkali-activation (zeolites in low-Ca systems, mostly layered double hydroxides in alkali-activated slags) are of significant importance in determining the final properties of the materials, particularly in the context of durability. The production of highly durable concretes must remain the fundamental aim of research and development in the area of alkali-activation. However, to enable the term ‘highly durable’ to be defined in a satisfactory way, the underlying mechanisms of degradation—which are not always the same for alkali-activated binders as for Portland cement-based binders, and cannot always be tested in precisely the same ways—need to be further analysed and understood. The process of reviewing a topic such as this will inevitably raise just as many questions as answers, and it is the intention of this paper to present both, in appropriate context.
Article
Organic soils are mostly composed of decayed plant matter and weathered rock material. Often, these soils are known for their inferior engineering behavior including very high compressibility and low shear strength. In order to improve these properties, organic soils are, by and large, modified with calcium based stabilizers such as lime, cement and fly ash. However, transportation agencies in the United States have mentioned that the anticipated improvements were never achieved or the improvement obtained disappeared quickly with time. Therefore, a research study was initiated to understand the behavioral mechanisms of lime and cement stabilized organic soils. Eight natural expansive soils bearing different organic contents (varying between 2 and 6%) were selected for the present investigation. First, optimum dosages of lime and cement were determined for the selected soils. Then treated and untreated (control) specimens were prepared to study their physical and engineering behaviors of the soil specimens at varied curing periods. There is a drastic increase in unconfined compressive strength (UCS) of lime and cement treated specimens until 28 days of curing. Beyond which, a negligible improvement in UCS property was recorded for lime treated specimens and a slight decrease in UCS for cement treated soils was noticed. This reduction in strength for cement treated specimens could be attributed to the reduction in pH concentration with curing as well as the formation of inorganic calcium humic acid at this stage.
Article
The main hydration reaction product in the ternary system fly ash, calcium sulphate and calcium aluminate cement (40/20/40) at 20 °C is a hydrated calcium sulfoaluminate compound, an AFt phase slightly different from “traditional ettringite”. The carbonation of ettringite develops gypsum but in this case rapidcreekite is formed. For the first time it has been observed that carbonation of the mentioned calcium sulfoaluminate compound (AFt), an hydrated calcium sulphate carbonated phase (Ca2(SO4)(CO3)·4H2O) is formed with the replacement of an SO4 row in a (0 4 0) layer of the gypsum by CO3 groups. The developed carbonated phase has been studied and analyzed through XRD, FTIR, Raman spectroscopy, and scanning electron microscopy.
Article
Raman spectroscopy has been used to follow the hydration of the main calcium aluminate phases present in calcium aluminate cement (CAC) and calcium sulfoaluminate cement (CSA) clinkers, i.e. C3A, CA, C12A7, CA2, C4AF and C4A3S¯. We investigate the reaction products induced by hydration on these six compounds. Spectra of anhydrous pure samples and pastes hydrated for 48 h were recorded. In order to contrast the Raman analysis results, the samples were also characterized by XRD and FTIR techniques. Hydration of calcium aluminates led to the formation of C3AH6, C2AH8 and aluminum hydroxide, and hydration of ferrite phases led to hydrogarnet phases. Meanwhile the hydration of C4A3S¯ led to the formation of ettringite and AFm phases. The Raman spectra analysis developed gives the details of the vibration of the different functional groups present in the calcium aluminate hydrated samples and our results show the potential of Raman spectroscopy in the study of the aluminate hydration on the cement chemistry. The product identity was confirmed by XRD and infrared spectroscopy.
Article
This study explored the behaviour of laboratory-synthesised calcium sulphoaluminate (C4A3Š) in alkaline media. C4A3Š was hydrated in three liquid media: water, 8-M NaOH and 4 (wt.%) Na2CO3 added to the C4A3Š + water mix. Hydration kinetics were studied via isothermal conduction calorimetry and 2- and 28-day mechanical strength values were found. The reaction products were characterised with XRD and FTIR. The findings showed that whilst C4A3Š hydration kinetics were accelerated in the presence of alkalis, the resulting pastes had lower mechanical strength than the pastes hydrated with water and exhibited severe decay in some cases. An analysis of the hydration products revealed the presence of ettringite in the water-hydrated C4A3Š pastes, whereas under alkaline conditions the main calcium sulphoaluminate hydrate detected was U phase.
Article
Concentrated organic chemicals have been shown to cause large increases in the hydraulic conductivity of compacted clay. Mechanical and chemical methods of stabilizing four different types of compacted clay against chemical attack are investigated. Mechanical stabilization using a large compactive effort (modified Proctor compaction) or application of a compressive stress ≥ 10 psi (70 kPa) is found to render a compacted clay invulnerable to attack by concentrated organic chemicals under laboratory-test conditions. Attapulgite, a clay mineral having little electrical charge, was found to be relatively unaffected (compared to more common clay minerals such as kaolinite, illite, and semectite) by concentrated organic chemicals. Addition of approximately 7% (by weight) of lime, portland cement, or lime plus sodium silicate greatly improved the ability of compacted clay to resist attack by concentrated organic chemicals; in some cases the amended soils were less permeable to concentrated organic chemicals than the unamended soils were to water.
Article
This paper analyzes the strength development in cement-stabilized silty clay based on microstructural considerations. A qualitative and quantitative study on the microstructure is carried out using a scanning electron microscope, mercury intrusion pore size distribution measurements, and thermal gravity analysis. Three influential factors in this investigation are water content, curing time, and cement content. Cement stabilization improves the soil structure by increasing inter-cluster cementation bonding and reducing the pore space. As the cement content increases for a given water content, three zones of improvement are observed: active, inert and deterioration zones. The active zone is the most effective for stabilization where the cementitious products increase with cement content and fill the pore space. In the active zone, the effective mixing state is achieved when the water content is 1.2 times the optimum water content. In this state, the strength is the greatest because of the highest quantity of cementitious products. In the short stabilization period, the volume of large pores (larger than 0.1μm) increases because of the input of coarser particles (unhydrated cement particles) while the volume of small pores (smaller than 0.1μm) decreases because of the solidification of the cement gel (hydrated cement). With time, the large pores are filled with the cementitious products; thus, the small pore volume increases, and the total pore volume decreases. This causes the strength development over time.
Article
Pavement subgrades constructed with clay soils can cause significant pavement distress because of moisture-induced volume changes and low subgrade support values. Lime is well known for its ability to stabilize plastic clays; however, portland cement also provides highly effective clay stabilization, usually with the added benefit of higher strength gain. Stabilizing clays with cement or lime can improve subgrade properties at a lower cost than either removing and replacing material or increasing the base thickness to reduce subgrade stress. The clay soil stabilization mechanism for the calcium-based stabilizers portland cement and lime is reviewed. These materials modify soil properties through cation exchange, flocculation and agglomeration, and pozzolanic reaction. Additionally, cement provides hydration products, which increase the strength and support values of the subgrade materials as well as enhance the permanence of the treatment. Comparative laboratory and field performance studies by others, focusing on stabilization of clay soils with portland cement or lime, are critically reviewed. Several factors affecting stabilization are discussed, including stabilizer test procedures, dosage effects to soil properties, mixing, compaction, and gradation and pulverization. Additionally, durability of cement and lime as stabilizers is reviewed, including wetting and drying, freezing and thawing, leaching, and long-term field performance. The research reviewed indicates that, if proportioned and applied properly, both cement and lime can effectively improve the engineering properties of clay soils over the life of a pavement. The results presented provide a guide to the engineer about the property changes to expect when using portland cement and lime with regard to volume stability, strength, and durability.
Article
Analysis of published data on the compressibility behaviour of sensitive soils reveals that it is possible to predict the compressibility behaviour. If the in situ water content and vane strength are known, the e versus log sigma curve can be drawn. Conversely, it is possible to estimate the field bond strengths by superimposing the experimental paths on the contours developed for fixed bond strengths. However, a larger volume of data must be analysed in order to improve the numerical coefficients given in the equations. The authors suggest that the possiblity of extending this approach to stiff cemented clays merits examination.
Article
Expansive clay soils-those that change significantly in volume with changes in water content-are the cause of distortions to structures that cost taxpayers several billion dollars annually in the United States. Much has been learned about their behavior over the past 60 years, and relatively successful methods have been developed to modify and stabilize them. This paper reviews some of the key advances developed over the past 60 years in improving our understanding of the nature. and methods of modifying and stabilizing expansive clay soils. The state of the practice in stabilization is presented, and practical and research needs to help improve the state of the practice are discussed.
Article
The fundamental parameters such as after-curing void ratio (eot) and cement content (Aw) have been found sufficient to characterize the strength and compressibility of cement-admixed clay at high water contents. From analyses performed on the results of unconfined compression tests, the ratio eot/A w has been proven to combine together the influences of clay water content, cement content, and curing time on the strength of cement-admixed clay. Moreover, the results of oedometer consolidation tests revealed that while Aw governs the position of the postyield compression line, the magnitude of eot determines the magnitude of the one-dimensional vertical yield stress σ′ vy at particular Aw. The value of eot reflects, primarily, the clay water content and, secondarily, the cement content and the curing time. Normalizing the after-curing unit weight, after-curing water content, and after-curing specific gravity were incorporated in an empirical relationship of eot.
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This paper examines the structuration and destructuration characteristics of cement-treated Singapore marine clay and their relation to the observed microstructural behavior. The pozzolanic reaction is found to be very significant up to curing periods of 1 year, and thus the unconfined compressive strength increases notably leading to the formation of more structured treated clay. Due to the effect of structuration (existing of cementation bond), the yield stress increases resulting in an expansion of the yield surface and failure envelope under compression and shearing. The microstructural observation of treated clay structure at various stress levels from one-dimensional consolidation shows that destructuration (breaking of cementation bond) is progressive; the largest intercluster voids being the first affected. As the consolidation proceeds, both inter and intracluster voids are affected. Consolidated undrained triaxial results reveal that complete destructuration only takes place on the shear plane at which the clay-cement cluster crushes.
Article
An experimental investigation was undertaken to evaluate the mechanical behavior of soil–cement mixtures. The primary motivation for the study was to investigate the innovative use of colemanite ore waste (CW) modified active belite cement (BC) in soil stabilization engineering (applications). The specific objectives of the research were to evaluate and compare: (1) compaction characteristics, (2) unconfined compressive stress-axial strain behavior, (3) unconfined compressive strength, (4) Young's secant modulus of elasticity, and (5) undrained shear strength characteristics of belite cement (BC)–clay and ordinary portland cement (OPC)–clay mixtures. BC and OPC were mechanically mixed with clay in five different dosages, i.e. 1.0%, 2.5%, 5.0%, 7.5% and 10.0% by using dry weight of clay, separately. Compaction characteristics of untreated soil, BC–clay and OPC–clay mixtures were evaluated at standard Proctor compaction energy. For a meaningful comparison of unconfined compression and triaxial test results, all specimens (untreated soil, BC–clay and OPC–clay mixtures) were prepared at maximum dry unit weight and optimum water content. Cylindrical samples of 50.0 mm in diameter and 100.5 mm in length were compacted in three layers and their strength characteristics were investigated at 1-, 7-, 14-, and 28-days curing times. Results of unconfined compression tests showed that cement dosage less than 5% has little effect on unconfined compressive strength (UCS) and exhibits ductile type of failure for both OPC–Clay and BC–Clay mixtures. In contrast, for cement content equal or greater than 5%, cement treatment significantly improved UCS and displayed brittle stress–strain behavior especially for BC–Clay mixtures. Similar behavior is obtained from undrained triaxial tests. The variation of undrained cohesion intercepts with respect to cement type, cement content and curing time is more sensitive than that of undrained internal friction angle.