Figure 3 - uploaded by Carlos Hidalgo Signes
Content may be subject to copyright.
Source publication
Cement concrete is the most widely used construction material worldwide due to its favourable mechanical characteristics. However, it is responsible for 8% of the total carbon emissions in the world, which are generated mainly during the production of clinker. Due to that fact, finding alternatives to cement for some applications in which it is not...
Context in source publication
Context 1
... representing the different processes involving the production of the two kinds of concrete and their contribution to the total carbon emissions are depicted in Figure 3 and Figure 4. In the case of the cement slab, it can be observed that almost 90% of the emissions occur during the production of clinker. ...
Citations
... Poured earth construction offers a promising alternative to cementbased concrete [7][8][9]. As with cement-based concrete, poured earth initially requires a fluid material to enable pouring into a formwork, followed by solidification and formwork removal. ...
Building sustainable earth construction to replace cement concrete is a major challenge in fast-developing tropical regions. Poured earth, shaped like concrete, offers a cost-effective and eco-friendly alternative. Poured earth usually relies on industrial dispersants and hydraulic binders to fluidify and solidify the soil paste. However, these additives strongly increase environmental costs. Recent studies have highlighted the potential of tannins, which are organic extracts from wood, as an eco-friendly alternative. In particular, tannins combined with iron oxides can fluidify soils at an elevated pH, and chemical reactions between tannins and iron oxides lead to rapid solidification, enabling rapid unmolding and improving water resistance. Tropical soils naturally have a high iron oxide content. This study investigated whether tannins could react with the iron oxides naturally present in tropical soil and be used as a single additive for poured earth. Optimal reactions between soils, tannins and iron oxides require an elevated soil pH, and tannins were combined with sodium carbonate (Na2CO3), a low-cost, eco-friendly alkali. Mortars prepared with different dosages of tannin+Na2CO3 were tested and compared to the industrial dispersant sodium hexametaphosphate (NaHMP), using three tropical soils from French Guiana. Results showed that both tannin+Na2CO3 and NaHMP could fluidify the three soils, improved mechanical strength and water resistance, and reduced initial water content and shrinkage. However, tannin+Na2CO3 induced faster solidification, which was attributed to the formation of ferric tannate observed by infrared spectroscopy (ATR-FTIR). This study paves the way for designing poured earth with tropical soil using a single, largely bio-sourced additive: tannin+Na2CO3.
... One of the most urgent problems that the society has to address is lowering global carbon emissions. Since the first declaration of a climate emergency, the effects of climate change have become obvious, making their mitigation essential to safeguarding ecosystems [5]. Numerous studies have been concluded, and new mitigation strategies, laws, and technologies have been introduced to cut greenhouse gas emissions (GHG) while operations are still in progress [6]. ...
Utilization potential of industrial by-products/wastes as construction material requires adequate workability, strength and other required properties as specified by standard codes of practice and certain sustainability criteria. Coal combustion byproduct (fly ash) and mine waste are a few of the abundantly available wastes that create a challenging task in their disposal with the current practice of dumping on-sites and landfilling. This study enumerates the suitability of utilizing magnesite mine wastes in self-compacting concrete (SCC) as binder and aggregate replacements by considering the evaluation factors such as fresh, hardened properties, life cycle assessment (LCA) and eco-efficiency. The results from the experimental investigation revealed that aggregate blended SCC performed well in terms of both fresh and mechanical properties, while cement blended mixtures exhibited satisfactory results. Additionally, fly ash and magnesite mine waste substantially reduced CO2 emissions and costs with added strength benefits. Eco-efficiency evaluation of mine waste blended SCC reported up to 75% higher efficiency than conventional SCC.
... Several studies proposed alternative strategies to deflocculate clay and fluidify earthen materials [14,15,[24][25][26][27]. One method consists in modifying the soil pH to changes the surface charge of the clay fraction and induces electrostatic repulsion between the clay particles [26]. ...
... Acacia tannins+Na 2 CO 3 improved workability from DP= 6.5 ± 0.2 mm to around 20.9 ± 2 mm but the mortar did not reach a fluid consistency. This showed that tannins+NaOH mixes act as suitable dispersants on lateritic soils, confirming and extending previous studies performed on other soil types [24,25,27]. In addition, these results indicated that certain tannins+Na 2 CO 3 mixtures also acted as efficient dispersants, suggesting that Na 2 CO 3 could represent an alternative to NaOH and NaHMP. ...
Tropical regions like French Guiana need local building materials to cope with high population growth and the
high cost of imported cementitious materials. Poured earthen construction could represent a local, cost-effective,
and ecologically friendly alternative. To ensure good workability and facilitate pouring, the use of dispersants to
deflocculate clay particles is an effective strategy that reduces water demand and increases the material’s density
and strength. Natural organic dispersants can replace industrial ones while reducing costs and carbon footprint.
It is currently unknown how organic dispersants could improve the workability, physical and mechanical
properties of the iron-rich lateritic soils present in French Guiana. Here, different potential dispersants were
evaluated at constant water content on a lateritic soil-based mortar: citric acid, sodium carbonate, tannins,
tannins+sodium hydroxide (tannins+NaOH), tannins+sodium carbonate (tannins+Na2CO3). These dispersants
were compared to industrial sodium hexametaphosphate (NaHMP). Three types of tannins were tested: hydrolyzable tannins from oak and chestnut, and condensed tannins from acacia. This study shows that all formulations improved workability and mechanical strength but only tannins+NaOH or Na2CO3 had a strong dispersant
effect comparable to NaHMP. Furthermore, tannins+NaOH or Na2CO3 decreased the mortar’s density without
impacting strength, which may result from reactions between the soil’s iron oxides and tannins, as observed by
infrared spectroscopy (FTIR). Altogether, these results show that the addition of organic dispersant is an
appropriate strategy to improve the fresh and hardened properties of lateritic soils. Particularly, tannins combined with sodium carbonate may represent an eco-friendly dispersant for poured earth in regions with iron-rich
lateritic soils.
... The modulus of elasticity of RAC can be as low as 60% of NAC [42,43]. Many studies have shown that NA can be replaced by RCA for up to 30% without a significant decline in the mechanical performance of concrete [44][45][46]. Thomas et al. [47] reviewed the works of many researchers on RAC. They suggested that different factors like properties of RCA, workability preferred in the mix design, quantity of fines in RCA, etc., are involved in optimum replacement percentages of NA by RCA. ...
Needs for renovation and efficient use of available land space have led to the destruction of numerous deteriorated civil structures. Consequently, a huge amount of concrete demolished waste is generated annually worldwide. This demolished concrete waste has created an extra burden on the environment and landfills, making the development projects unsustainable. Demolished waste can be recycled and reused for sustainable development and to reduce the demand for fresh natural aggregates (NA). However, the poor performance of recycled aggregate concrete (RAC) compared to natural aggregate concrete (NAC) may be a significant drawback in the recycling and reusing of demolished concrete wastes. This limitation can be overcome by using a superplasticizer, which has the ability to improve different mechanical properties of concrete. The objective of this paper is to assess the effects of the superplasticizer on the mechanical characteristics of RAC. Concrete specimens were prepared to have replacement ratios (0%, 25%, 50%, and 100%) of fresh NA by recycled stone aggregates (RSA) and recycled brick aggregates (RBA). Half of the prepared concrete specimens were admixed with the superplasticizer, having 15% water reduction for concrete mixes. The obtained test results encourage the use of superplasticizers for improving the mechanical properties of RAC. It is observed that fresh, natural coarse aggregates in a concrete mix can be replaced with 50% RSA and 25% RBA with the addition of the superplasticizer without compromising the mechanical performance.
Resumo A terra como material de construção vem voltando ao foco da comunidade científica devido à sua baixa energia incorporada. Existem poucos estudos sobre matrizes de terra autoadensáveis como técnica construtiva. Dessa forma, o presente estudo tem como objetivo desenvolver um compósito de terra autoadensável estabilizado com ativação alcalina para construção de paredes monolíticas e avaliação do seu comportamento mecânico. Após um estudo de dosagem por planejamento fatorial, foi selecionada a melhor composição de terra, areia, metacaulim e solução ativadora para melhor avaliação do compósito e construção da parede. Com a mistura selecionada, foram realizados ensaios de caracterização física, difração de raios X (DRX), espectroscopia de infravermelho, funil V, resistência à compressão e à tração na flexão, além da construção de uma parede reduzida. A resistência à compressão do compósito foi de 8,12 MPa aos 3 dias e 9,75 MPa aos 28 dias. A parede apresentou fissuras de retração, que não influenciaram diretamente na sua ruptura, e atingiu uma tensão de 3,30 MPa. Por fim, o compósito apresentou um bom comportamento reológico tanto no estado fresco quanto no estado endurecido podendo ser utilizado na construção de paredes monolíticas.
Thermal characteristics of concrete is one of the main topics in concrete technology researches.
They were extensively studied since the 80's to predict the behavior of the concrete in fire and the
performance of massive concrete. However, this topic was raised again after 2010 as a part of
sustainable, energy effective and ecofriendly buildings studies. The aim of this research is to
present a comparison between the thermal characteristics of self-compacted concrete (SCC) and
the geopolymer concrete (GPC) using collected previous researches. More than fifty references
were collected, sorted and analyzed in the last forty years. The results showed that (GPC) has better
thermal characteristics such as thermal conductivity, heat capacity, fire resistance, while (SCC)
has better mechanical properties such as compressive strength, early strength and elastic modulus.
Besides that, from ecological point of view, partially replacing of ordinary Portland cement (OPC)
with microencapsulated phase change materials (MPCM) such as fly ash, silica fume, slag, and
metakaolin remarkably decreases the CO2 footprint of construction industry.
This study focused on investigating the possibility of using different ratios (5, 10, 15 mass%) of recycled alum sludge (RAS) as partial replacement of ordinary Portland cement (OPC), to contribute to solving the problems encountered by cement production as well as stockpiling of large quantities of water-treated sludge waste. MnFe2O4 spinel nanoparticles (NMFs) were used to elaborate the mechanical characteristics and durability of different OPC-RAS blends. The outcomes of compressive strength, bulk density, water absorption, and stability against firing tests fastened the suitability of utilization of RAS waste for replacing OPC (maximum limit 10%). The inclusion of different doses of NMFs nanoparticles (0.5, 1 and 2 mass %) within OPC–RAS pastes, motivates the configuration of hardened nanocomposites with improved physico-mechanical characteristics and stability against firing. Composite made from 90% OPC–10% RAS–0.5% NMFs presented the best characteristics and consider the optimal choice for general construction applications. Thermogravimetric analysis (TGA/DTG), X-ray diffraction analysis (XRD), and scanning electron microscope (SEM) techniques. affirmed the positive impact of NMFs particles, as they demonstrated the formation of enormous phases as ilvaite (CFSH), calcium silicate hydrates (CSHs), MnCSH, Nchwaningite [Mn2 SiO3(OH)2 H2O], [(Mn, Ca) Mn4O9⋅3H2O], calcium aluminosilicate hydrates (CASH), Glaucochroite [(Ca, Mn)2SiO4, and calcium ferrite hydrate (CFH). These hydrates boosted the robustness and degradation resistance of the hardened nanocomposites upon firing.
Recently, recycling some industrial wastes becomes an essential way of the crucial challenges that mitigate their risks in the future. This work focused on utilization of recycled alum sludge (RAS) for partial replacing of Ordinary Portland cement (OPC), to contribute to solving the problems encountered by cement production as well as stockpiling of large quantities of water treated sludge waste, and to elaborate the particularities of different OPC-RAS blends by using MnFe 2 O 4 spinel nanoparticles (NMFs). The outcomes of compressive strength, bulk density, water absorption, and stability again firing tests fastened the suitability of utilization of RAS waste for replacing OPC (maximum limit 10%) to prepare building material having enhanced strength and toughness. Inclusion of NMFs nanoparticles (0.5 mass%) in OPC pastes superseded with different quantities of RAS waste, motivates the configuration of hardened nanocomposites with improved physico-mechanical characteristics and stability against firing. Composite having 90% OPC-10% RAS – 0.5% NMFs represented the optimal choice for general construction application. TG/DTG, XRD, and SEM techniques affirmed the activity of NMFs particles, as they demonstrated the formation of enormous phases (as MH, CAHs, MnCSH, CSHs, CASHs, and CFH), especially 0.5% addition. These products boosted the robustness and degradation resistance of the nanocomposites upon firing.
A new generation of self-compacting earth-based composites (SCEC) for vertical elements with fully exposed earth, in which the main feature is the elimination of compaction, is proposed in the current work. The first objective was to develop earth-based mixture compositions with locally available raw materials and achieve self-compactability. A Portuguese soil, typically employed in rammed earth construction, was stabilised using cementitious materials and a superplasticiser to ensure flowability. The mixture design studies allowed to achieve flowable fresh composites. Results on the hardened state showed that SCEC presents high compressive strengths (5–14 MPa). The electrical resistivity SCEC increased with time and achieved at least 5600 Ωm at 28 days, while mass loss stabilised after 14 days in a controlled environment room. Additional tests were performed on selected optimal SCEC mixtures: drying shrinkage and water capillary absorption, with promising results. Overall, this work provided initial boundaries for the mixture design and assessment of SCEC and opened the door for further studies on new and novel earth materials construction techniques.
