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Effect of tricalcium aluminate content of cement on chloride binding and corrosion of reinforcing steel in concrete
Abstract
Cement pastes with water-cement ratio of 0.60 were prepared using four cements with C,A contents of 2.04, 7.59, 8.52, and 14 percent. Four levels of chlorides corresponding to 0.3, 0.6, 1.2, and 2.4 percent by weight of cement were added to the mix water. The pastes were allowed to hydrate in sealed containers for 180 days and then subjected to pore solution expression. The expressed pore fluids were analyzed for chloride and hydroxyl ion concentrations. It was found that the free chloride concentration in the pore solution decreases significantly with an increase in the C,A content of the cement. Typically for a 0.6 percent chloride addition, the unbound chlorides decreased from 41 to 12 percent when the C,A content of the cement was increased from 2 to 14 percent. The high C,A content was found to be especially beneficial for binding chlorides in the range of 0.3 to 0.6 percent. With increasing level of chloride addition, although the absolute amount of bound chloride increases, the ratio of bound to total chlorides decreases. For example, in the 14 percent C,A cement, the ratio of bound to unbound chloride is about 14 times higher for the 0.3 percent chloride addition compared to 2.4 percent chloride addition. For a threshold Cl-/OH- ratio of 0.30, the threshold chloride values for the 2.04, 7.59, 8.52, and 14 percent C,A cements were found to be 0.42, 0.62, 0.68, and 1.0 percent by weight of cement. The effect of the C,A content in significantly influencing corrosion is also confirmed by the corrosion initiation times, which were found to be 1.75, 1.93, and 2.45-fold more for the 9, 11, and 14 percent C,A cements compared to 2 percent C,A cement. The pore fluid analysis indicates some chloride binding even in the low 2.04 percent C,A cement when chlorides are added at the time of mixing.
... This mass transport takes place when the concrete surface or overlapping layers have contact with seawater or, in most cases, contact with marine aerosol (Meira, Andrade, Alonso & Borba, 2007a; Meira, Andrade, Padaratz, Alonso & Borba, 2007b; Lindvall, 2007). Studies on the influence of the material characteristics in the chloride transport into concrete show the role of aspects such as the porous structure of materials (Tuutti, 1982; Jaegermann, 1990; Mangat and Molloy, 1994), the presence of cracks (Mangat and Gurusamy, 1987; Bakker, 1988) and chloride binding ability of the cementitious matrix (Byfors, 1990; Rasheeduzzafar, Al-Saadoun, Al-Gahtani, and Dakhil, 1990) on accelerating or delaying chloride transport into concrete. Papers on the influence of environmental characteristics represent another group of studies, covering aspects such as temperature (Page, Short, & El Tarras, 1981; Al-Khaja, 1997), concrete carbonation (Byfors, 1990; Jones, McCarthy, and Dhir, 1994; Malheiro, 2015), location of structures (Vera et al., 2009) and saturation degree of concrete porous network (Climent, de Vera, López, Viqueira, & Andrade, 2002; Nielsen and Geiker, 2003; Guimarães and Helene, 2005; de Vera, Climent, Viqueira, Antón, & Andrade, 2007; Guimarães et al., 2011). ...
... Lower chloride contents can be observed in the mortar region when the mortar is less porous and richer in cement (Table 2). This relationship is closely linked to the porosity reduction of higher cement content mortars and their consequent higher C3A content (Byfors, 1990; Rasheeduzzafar et al., 1990). ...
... This aspect reflects on chloride profiles shown in Figures 5 and 6, as higher open porosity makes the chloride transport easier (Tuutti, 1982; Jaegermann, 1990). Considering the C3A content, higher cement content means higher C3A content available to fix chlorides in the cementitious matrix (Byfors, 1990; Rasheeduzzafar et al., 1990). This stronger binding ability reduces the amount of free chlorides, which are the ones able to effectively be transported. ...
This work studied the influence of rendering mortar layer on chloride transport into concrete structures. Concrete specimens rendered with three different mortar mixtures and two rendering thickness were used. Five of the six faces of the specimens were coated with epoxy resin to simulate unidirectional flux. The specimens were subjected to weekly wetting and drying cycles in a sodium chloride solution for 49 days. At the end, total chloride profiles were obtained. Results show that rendering mortars influence chloride transport into concrete and this is more accentuated for less porous mortars and with higher cement content. There is also a chloride accumulation close to the interface mortar-concrete region, which is explained by the differences on chloride transport ability between mortar and concrete. Although mortars are more porous than concrete, they can represent an additional protection against chloride penetration into concrete.
... Sulphate-resisting Portland cements (Type V cements according to ASTM or CEM 1-SR in EN 197-1) have lower C 3 A contents so as to inhibit expansive ettringite formation. Thus, these cements have lower chloride binding capacities and, thus, allow for greater free chloride penetration for a given permeability than ASTM Type I cements [45,46]. Hussain [47] observed that an increase in the C 3 A content from 2.43 to 14% resulted in approximate 2.65-and 2.85-fold increases in the chloride binding capacity and chloride threshold, respectively. ...
... Sulphate-resisting Portland cements (Type V cements according to ASTM or CEM 1-SR in EN 197-1) have lower C3A contents so as to inhibit expansive ettringite formation. Thus, these cements have lower chloride binding capacities and, thus, allow for greater free chloride penetration for a given permeability than ASTM Type I cements [45,46]. Hussain [47] observed that an increase in the C3A content from 2.43 to 14% resulted in approximate 2.65-and 2.85-fold increases in the chloride binding capacity and chloride threshold, respectively. ...
Corrosion of steel reinforcement due to chloride attack remains a major reinforced concrete durability concern. The problem is prevalent for concrete structures located within marine environments or frost-prone locations where chlorides containing de-icing salts are used. This paper is a state-of-the-art review into chloride binding in Portland cement concrete, with consideration of the differences induced by the presence of sulphates, such as found in seawater. The review also considers the use of supplementary cementitious materials (SCMs), the use of which has increased because of their potential to enhance durability and reduce the carbon footprint of concrete production. Such materials impact on phase assemblage and microstructure, affecting chloride binding and transport properties. Therefore, field and laboratory studies are critically reviewed to understand how these could help in the design of more durable concretes. The contributions of chloride binding, hydrate compositions and microstructures of the binding materials affecting chloride transport in concretes are also evaluated to suggest a more robust approach for controlling the problem of chloride attack.
... The higher chloride concentration in the pore solution creates more chances to get bound to the adsorption sites [78]. The amounts of bound chloride increase with an increase in the chloride concentration and this trend is same for external chloride as well as internal chloride [77,[79][80][81] . Dhir et al. [3] found the chloride binding capacity to be directly proportional to the exposure chloride concentration. ...
... Midgley and Illson observed that only unhydrated C 3 A reacts with intruding chlorides; however, Nagataki et al. [82] reported that a certain proportion of hydrated C 3 A also reacts with chlorides to form Friedel's salt. Rasheeduzzafar et al. [80] found that the unbound chlorides were significantly higher in the case of external chlorides for OPC pastes having same composition and total chloride content in both cases of chloride source. It should be mentioned that water extraction technique was used in the case of external chloride while high pressure squeezing method was applied in the case of admixed chlorides. ...
... Chlorides may enter into through various routes [175]: ...
... The C 3 A phase plays an important role in chloride binding. Type V cements, which have lower C 3 A contents than Type I cements, generally shows less resistance to chloride penetration than Type I cements [175,[203][204][205]. Hussain [204] observed that an increase in the C 3 A content from 2.43 to 14% resulted in an increase of about 2.65 and 2.85-fold in the chloride binding capacity and chloride threshold respectively. ...
The use of GGBS as supplement for cements has been shown to improve the long-term strength and durability properties of concrete. In practice, while the chemical composition of GGBS from a single plant may be constant, due to the varying sources from which GGBS is obtained the chemical composition from plant to plant may vary. The wide variability in the use of GGBS as a SCM in different climates, coupled with differences in chemical composition, is bound to have impact on the performance of slag blends.
This study investigated the combined influence of difference in slag composition and temperature on the performance of slag blends. Performance was evaluated in terms of strength and transport properties. Paste samples were characterised by calorimetry, TGA, XRD and SEM to follow hydration and microstructural development. Mortar samples were used to follow strength development and transport properties. All tests were carried out at temperatures of 20 and 38°C. Curing at 38°C accelerated the early hydration, but not the later hydration. This led to higher early strengths and lower later strengths, and was attributed to the coarsening of the pore structure caused by the high temperature curing. Except at the early ages at 20°C, both slag blends showed better strength performance than the reference cement. The slag blends also showed better transport properties than the reference cement, especially at 38°C, and this was attributed to their finer pore structure and higher chloride binding capacity.
Of the two slags studied, the more reactive slag (slag 1) had better performance, especially at 38°C. Performance of the slag blends at 20°C was influenced mainly by the length of curing, and by the difference in chemical composition at 38°C.
... These interactions include the chemical reactions of Clions with the components of cementitious matrix and the formation of stable Cl based components (for instance: calcium chloroaluminate hydrate). They include also electrostatic adsorption of the Clions on the solid components (Rasheeduzzafar, 1991;Francy and François, 1998). In both cases, Clions are bound and cannot participate in the corrosion of the embedded reinforcement. ...
... The cementitious matrix volume being equal for CEM-I H and CEM-III H or for CEM-I L and CEM-III L mortars, only the nature of the hydrates can explain this difference. The affinity of the Clions for the Portland cement's hydrates (probably for calcium aluminate hydrates) is significantly higher than that for the slag cement's hydrates (Nilsson et al, 1996;Rasheeduzzafar et al, 1991). However, this difference between the two cements concerning the Cl binding capacity does not prevent CEM-III cement to present lower diffusion coefficient then CEM-I cement (Grandubé, 2007). ...
The durability of reinforced concrete structures in chloride environment depends on the resistance to penetration of chloride (Cl-) ions through the concrete porosity up to the steel. The physico-chemical interactions of the Cl- ions with the cement matrix interfere significantly with the penetration process. The objective of this work is to assess the influence of the cement type and content and the proportion of three mineral admixtures on the Cl binding capacity of mortars. Binding isotherms are obtained on crushed mortars by analysis of the residual Cl quantity in the solution at the equilibrium. The cement type and its content are the main parameters controlling the Cl binding. Portland cement has a higher binding capacity than blast furnace slag cement. The contribution of the mineral admixtures depends on their nature and proportion as well as on the cement type.
... ·10H 2 O), as well as intermediates and solid solutions made from these end products, are all grouped together under the term "AFm"[52]. Friedel salt (C 3 A•CaCl 2 ·10H 2 O) may eventually be produced by chloride ions linked to the AFm phase[53]. If the concentration of Cl − in the surrounding environment stays generally constant, Friedel salt does not break down and stays stable[51]. ...
The durability of reinforced concrete structures constructed in Iraq is affected by different environmental factors, where the two most common and harmful factors on the durability of concrete are the presence of chloride and sulfate salts in the surrounding environment. Therefore, the main objective of the research is to study the combined effect of these salts on the properties of green concrete, knowing that the individual impact of these salts has been widely studied. Still, there is a lack of understanding regarding how they interact and how their combined presence affects the durability and service life of concrete. In addition, its durability can be improved by replacing cement with supplementary cementitious materials thus reducing carbon dioxide emissions. To achieve this goal, seven mixtures were prepared, one of which was a reference without any substitute and six mixtures that included silica fume (SF) and ground granulated blast furnace slag (GGBS) independently and in varying amounts (3, 5, 7% SF) and (30, 40, 50% GGBS). After adequate curing, they were exposed to aggressive chemicals: (5% sodium chloride + 2% calcium chloride), (5% sodium sulfate), and combined (5% sodium chloride + 2% calcium chloride + 5% sodium sulfate), in addition to tap water (i.e. reference). Strength and durability were evaluated using tests including compressive strength, electrical resistivity, porosity, total absorption and length change, along with repeated visual inspections. In addition, the intensity of chlorine and sulfur components in the concrete was evaluated using X-ray diffraction. The results indicated less deterioration in concrete samples with silica fume and GGBS compared to the reference mixture (without replacing) exposed to the above solutions. Chloride ions do not cause deteriorated effects on concrete and enhance its physical and mechanical properties, which is essential for their role in mitigating sulfate attacks on concrete. In the combined solutions, the deterioration is less severe than in the sulfate solutions. The inhibitory mechanism of chloride ions on concrete sulfate attack indicates that while they cannot completely prevent sulfate attack, they can somewhat mitigate the associated risk. Mixtures with the highest replacement ratio (7% SF and 50% GGBS) showed the highest resistance to aggressive environments and the highest durability.
... Chloride-induced corrosion by chlorine ions is having a major impact on reinforced concrete structures constructed in coastal areas. Corrosion damage to such structures is often visible through expansion of reinforcement bars, surface cracking, and detachment of the concrete cover due to the corrosion, etc [13], [14]. ...
This research addresses the dual imperatives of durability and sustainability in modern construction by exploring the use of Supplementary Cementitious Materials (SCMs) to partially replace Ordinary Portland Cement (OPC) in concrete mixes. The study aimed to achieve three key objectives: improving economic feasibility, enhancing sustainability, and optimizing concrete performance. Various SCMs such as fly ash, ground granulated blast furnace slag (GGBS), and micro silica were blended to create quaternary concrete mixes (TM2, TM3, TM4, and TM5), which underwent comprehensive laboratory testing. Tests included assessments of compressive strength, water permeability, Rapid Chloride Penetration Test (RCPT), Rapid Chloride Migration Test (RCMT), and electrical resistivity. Results demonstrated that SCM-based concretes exhibit superior strength, enhanced durability, and improved microstructure compared to traditional OPC concrete. TM4, notably with 25% GGBS replacement, showed optimal performance, meeting stringent standards for water permeability at 28 and 56 days. RCPT and RCMT results confirmed reduced chloride ion penetration across all mixes, with TM4 exhibiting the lowest rates. Electrical resistivity tests highlighted TM3 and TM5 as top performers, surpassing industry durability benchmarks. The study advocates for widespread adoption of SCM-blended concretes in construction, citing their economic benefits and positive environmental impact
... Chloride in concrete exists as free a chloride dissolved in the pore water, or as a bound chloride. The bound chlorides are either chemically bound to the tricalcium aluminate (C3A) and the calcium aluminoferrite (C4AF) or physically bound to the surface of the hydration products C-S-H gel [54][55][56][57][58]. ...
This paper describes a method to use solely recycled and by-product materials as constituents to form concrete that can be used in buildings structural applications. As concrete is one of the most important materials in human civilization, where it is used widely in construction, cement and aggregate the main components of concrete cause an emission of large amounts of carbon dioxide, which is the main cause of global warming. The production of one tonne of cement, for example, causes the emission of about 800 kg of this CO2. The growing demand for concrete constitutes a threat to the environment and its resources into the future. According to a market study by The Freedonia Group, in 2019 the world demand for cement was 5.1 billion tonnes which means that more than 2.5 billion tonnes of water and more than 11 billion tonnes of aggregates, both of which are scarce resources, will also be consumed. The goal of this Paper is to describe a 100% substitution of concretes normal constituents to form a sustainable concrete with zero carbon footprint and without compromising concrete mechanical properties. This will demand a pre-treatment of the recycled and by-products components to compensate for the natural strength loss due to their inclusion. Therefore, an innovative novel treatment method is selected for recycled concrete aggregates and chipped rubber to be separately treated and tested to mitigate the loss of strength in proposing a novel recycled activator for GGBS and silica fume. Then these waste recyclable materials are combined in a concrete mix that is 100% recycled and, therefore, significantly more sustainable.
... In this context, Byfors [82] and Arya et al. [83] indicated that the C3A content has very little influence on the binding capacity of the hydrated cement paste. Rasheeduzzafar et al. [84] suggested that this is certainly due to the reaction of C3A with all the sulphates available during hydration. In this case, the major part of the C3A will have already reacted with the sulphates and there will hardly be any C3A left to react with the chlorides. ...
... Salt damage to concrete structures arises from external factors such as the penetration of chlorine ions from the outside or the intermixture of sea water. Particularly, it directly results in the corrosion of embedded reinforced bars, and it has been known that the degree or frequency of the damage is very serious [1,2]. The chloride ion, which affects concrete performance degradation, has the form of free chloride or exists in the phase equilibrium state of binding ion within concrete [3,4]. ...
Reinforced concrete structures located on coastal landfill frequently adjoin sea-water environment, and are exposed to sea water and humid environment during construction. Particularly, in the case of large-scale structures like dams, their drying shrinkage is accompanied by fatal cracking, and thus chlorine ion penetration becomes easier. The present study develops a salt damage-resistant agent (SRA) to which aluminum salts, oligomer condensate, and amino alcohol derivatives with the alkyl group are applied as binding inducers. SRA performs the roles of reducing the drying shrinkage of cement composites, binding chlorine ions, and preventing erosion by sulfate ions. This study tests and evaluates its resistance to degradation factors that may occur to structures constructed on coastal landfill and so on. As a result of evaluating shrinkage cracking properties by performing the restrained shrinkage cracking test, SRC showed the shrinkage reduction compared with BSC. As for the performance of resistance to chlorine ion and the chemical sulfate erosion rate, SRC showed the highest resistance performance, followed by BSC and OPC, regardless of the concentration of aqueous solutions for immersion. In addition, as for the rate of mortar weight change by sulfate erosion, the SRA-intermixed SRC mixture showed a weight reduction rate at the level of 1/3 of BSC and 1/6 of OPC, respectively.
... Plusieurs études de la littérature (Rasheeduzzafar, 1993;Balázs et al., 1997;Csizmadia et al., 2001;Sumranwanich et al., 2004) ont montré qu'entre toutes les phases anhydres constituant le ciment Portland : C3A, C4AF, C3S et C2S, seuls les aluminates tricalciques C3A et les alumino-ferrite tetracalciques C4AF réagissent avec les ions chlorure présents dans la solution porale. Ces phases anhydres réagissent avec les ions chlorure pour former les chloro-aluminates dont le monochloroaluminate ou sel de Friedel de formule C3A.CaCl2.10H2O ...
La corrosion des armatures en acier est la plus grande cause de défaillance des ouvrages en béton armé. Ce phénomène électrochimique est déclenché par la présence d’ions chlorure en quantité suffisante au niveau de l’armature ou la carbonatation du béton d’enrobage (action du CO2). L’objectif de cette thèse est de développer des modèles utilisables par l’ingénieur dans une démarche d’approche performantielle pour la prédiction de la durée d’utilisation des ouvrages en béton armé soumis à l’attaque par les ions chlorure ou la carbonatation, suite à l’amorçage et au développement de la corrosion en leur sein. Il s’agit du développement de trois modèles : un modèle de transfert des ions chlorure, un modèle de carbonatation et un modèle de corrosion qui permettent d’estimer la durée d’initiation et la durée de propagation de corrosion. Ces modèles prennent en considération les facteurs liés au matériau (i.e. indicateurs de durabilité), à la mise en œuvre, à l’environnement et à la géométrie. La démarche adoptée pour le développement de ces modèles repose sur l’exploitation de plusieurs bases de données, sur des ouvrages vieillissants et des corps d’épreuve de bétons, issues de la littérature (BHP-2000, Perfdub, etc.). Ces exploitations ont permis d’améliorer la capacité prédictive de modèles existants (transfert des ions chlorure) et de développer de nouveaux modèles (carbonatation et corrosion).
... Chloride-induced corrosion of steel reinforcement has been identified as the primary cause of untimely deterioration of marine concrete structures [1,2]. These chlorides usually permeate into the hardened concrete through diffusion or they may be introduced into the fresh concrete when chloride-contaminated water is used in preparing the concrete mix [3,4]. The presence of chloride in the concrete decreases the pH of the concrete's pore solution [5] and this in turn weakens the protective passive layer surrounding the steel reinforcement, thereby making it easy for corrosive elements to gain access to the steel reinforcement to induce corrosion. ...
Globally, extreme environmental conditions lead to premature degradation of maritime concrete structures, causing them to fail before their projected service life. The key mechanism responsible for premature degradation of reinforced concrete (RC) structures has been established as reinforcement corrosion. This is primarily controlled by chloride ingress, resistivity, and porosity of RC structures. This has been a major concern for RC structures exposed to Escravos river with seawater predominantly known to be saline in nature and houses many RC structures built to facilitate ease of oil and gas operations. Advances in engineering methods are required for reliable structural assessment of existing structures. This work aims to evaluate the extent of deterioration of two existing RC structures, built in this river and determine the constituent compounds present therein with a view of identifying their influence on deterioration of existing structures and to meet future design needs in an economic way and avoid unnecessary reconstructions.
This work adopted two methods in approaching the deterioration challenges in these structures. First, a general condition assessment methodology consisting of in-situ, non-destructive measurement techniques and detailed testing of samples from the existing structures was studied. The structure's current compressive strength was determined using the Schmidt rebound hammer, and corrosion rates measured based on weight loss of corroded steel reinforcement samples. Secondly, an idealized experimental study was set up under controlled site conditions and electrically accelerated corrosion process to measure chloride concentration at different concrete depths. The analysis also used the chloride threshold value of 0.07% by weight-of-concrete per BSEN 206-1 to determine corrosion initiation point. All specimens were submerged in the Escravos seawater’s sample for maximum of 35days. In compliance with standard practice, water samples were analyzed to determine the presence of corrosion-causing agents in this seawater and their effect on the existing structures.
The results revealed that the quay structure suffered a major chloride attack from surrounding seawater due to its long exposure whereas the jetty structure is still in a safe state since it was recently constructed. In-situ corrosion tests on quay reinforcement samples revealed a high corrosion rate of 0.65uA/cm3 over 45years, as shown by a weight reduction of approximately 47% per meter of steel. The rebound hammer test revealed an average concrete strength of 29N/mm2, a decrease of 27% from the as-built value of 40N/mm2. Chloride diffusion was determined using Fick's second law of diffusion, while weight loss due to steel corrosion was calculated using Faraday's law. Predicted chloride ingress trends showed that the critical chloride level occurred at the reinforcement depth after 16years. With this 45years old structure, the level was exceeded in the quay structure 29years ago with a remaining service life of 15years. This conforms with the recommended 50years intended working life of RC structures in seawater environment per BSEN 206-1. The results showed that the rate of corrosion and strength deterioration depended on the environmental nature and exposure time. The experimental test results will also serve as guidance information for future engineering design of new structures in this region.
... When the chloride ions in the environment migrate to the lining concrete, the chloride ions react with the unhydrated cement clinker C 3 A in the lining concrete to form Friedel's salt, as shown in Fig. 15a [43][44][45][46][47]. Further, the chloride ions in the lining concrete pore solution also form Friedel's salt by replacing OH − , SO 4 2− , and CO 3 2− in the cement hydration product AFm structure [48][49][50]. ...
In this study, the chloride ion transport behavior of lining concrete under the coupling action of flowing groundwater and loading is investigated. The results indicate that the damage layer thickness and chloride ion concentration of the lining concrete increases with the increase of erosion age. The flowing groundwater accelerates the dissolution of the lining concrete, alkaline substances such as CH and NaOH in the lining concrete dissolve out. Under the action of the loading, the micro-cracks in the tension zone of the lining concrete continue to expand and the pores are connected to each other. Therefore, for same erosion age and distance from the lining concrete surface, the chloride ion concentration in the tensile zone is the highest under the coupling action of flowing groundwater and loading; that is followed by the action of flowing groundwater alone, and then, by the action of static groundwater. The chloride ion concentration in the pressure zone is the lowest, and the addition of fly ash and silica fume is found to help in decreasing the total chloride ion concentration and increasing the bound chloride ion concentration. In this study, a chloride ion transport model is established considering the accelerated dissolution of flowing groundwater, damage caused by loading in terms of micro-cracks and pore structure, and the effect of bound chloride ion on the total chloride ion transport, further, the rationality of the model is verified.
... The transport of CO 2 is influenced by the relative humidity in the micro pores and the way CO 2 reacts with the mineral phases in the hydrated cement paste [9]. During the ingress of chlorides, they can chemically react with the AFm phase in hydrated Portland cement to form Friedel's salt (FS) or be physically absorbed by the C-S-H gel [10,11]. It is considered that only the free chloride ions, which can move into the vicinity of the steel bars, can contribute to their corrosion [12]. ...
Deterioration of reinforced concrete is often studied in idealised scenarios where only one exposure environment is dominant. For example, to study concrete structures exposed to de-icing salt environments, the effect of a cyclic wetting and drying regime is considered, but deterioration by carbonation is not given any emphasis. However, some studies have shown that carbonation could result in the release of bound chlorides and this could lead to an increase in chloride content near steel in reinforced concrete. Through an investigation on the influence of carbonation on the bound chlorides in different cementitious pastes, this paper highlights the positive initial effects that carbonation has on the chloride binding behaviour and later the changes that occur in both the pH of concrete and the bound chloride content for both low and high w/b mixes. Two mathematical expressions are put forward for mapping: (i) the changes in apparent pH as a function of the duration of carbonation and mix ingredients; and (ii) the reduction in the bound chlorides with a proportional reduction in apparent pH. The latter is valuable in quantifying the changes to binding capacity in service life models due to carbonation, with the help of a simple pH measurement.
... Many studies pointed out that the chloride ion shows the strong binding affinity with cementitious materials (Rasheeduzzafar, 1992;Larsen, 1998;Tang and Nilsson, 1993). The relationship between and is non-linearly described by chloride binding isotherm or partition coefficient (m 3 /kg) (i.e. the derivatice is = ). ...
... On addition to cement, CaCO 3 nanoparticles react with the aluminium oxides present in cement and form carboaluminate hydrates, besides accelerating C 3 S and C 3 A hydration [89]. The increased C 3 A content reduces the free chloride concentration in the concrete pore solution and forms a dense structure where the ionic transport is minimal as the diffusion of chloride ions depends on the permeability [90]. Thus, in CFN and CFNI concretes the chlorides are present in the bound form of Friedel's salt. ...
The urge to reduce the carbon footprints from cement production warrants the development of more sustainable approaches in the construction industry. Towards this, the long term corrosion resistance of the embedded steel rebar in a novel ternary-blended reinforced concrete system with 56 wt% Ordinary Portland cement (OPC), 40 wt% fly ash, 2 wt% nanomodifiers, and 2 wt% corrosion inhibitor (referred to as CFNI) was studied by chemical and electrochemical tests in a simulated chloride environment for 180 days. The performance was compared with three other concrete systems (CC (100% OPC), CF (60 wt% OPC and 40 wt% fly ash) and CFN (58 wt% OPC, 40 wt% fly ash and 2 wt% nanomodifiers). The electrochemical results indicated a significant enhancement in the corrosion resistance of steel in the CFNI concrete as compared to other systems. A five times higher value of polarization resistance (Rp) is obtained in CFNI, as compared to the control concrete, indicate the better resistance of CFNI. Further, in CFNI specimen, the chloride ingress rate was significantly lower and the Field Emission Scanning Electron Microscopy (FESEM) images showed no microcracks or pores at the corroded concrete-steel interface of CFNI specimens. The apparent diffusion coefficient (Dcl) of the concrete system was determined using the bulk diffusion test and chloride profiling. The value of Dcl for CFNI concrete was found to be one order less in magnitude than other concrete specimens, indicating the enhanced resistance against chloride attack. These results show that CFNI concrete is a promising ternary-blended concrete mix to achieve long corrosion-free service life for the structures in aggressive chloride environments.
... One of the major causes of corrosion of steel in concrete is the exposure of the concrete to chloride ions [3]. Chlorides may become present in the freshly mix concrete when chloride-contaminated materials are used in preparing the mix or they may permeate into the hardened material at a later stage when the concrete is exposed to seawater, groundwater or de-icing salt (typically sodium or calcium chloride) [4,5]. Chloride ingress results in the breaking down of the passivity of the steel reinforcement and thereby presents a risk of corrosion, which can lead to loss of reinforcement cross section and spalling of the concrete cover [6]. ...
Chloride induced reinforcement corrosion is the major cause of premature deterioration of reinforced concrete structures in the chloride-laden Niger Delta region of Nigeria. This study evaluated the extent of deterioration of an existing 45 years old concrete quay structure. The methodology adopted for the study includes conducting a visual inspection on the structure to determine the current condition of the structure and the nature of testing required. Next, several non-destructive tests were carried out to determine the compressive strength, nature of corrosion and the impact on the structure. Water samples were also collected for chemical analysis, to ascertain the corrosion inducing compounds present in the surrounding seawater. The results indicated that the quay structure suffered from chloride-induced corrosion, imposed by the surrounding seawater. Measurement of the level of corrosion carried out on steel reinforcement samples obtained from the quay showed a high-level of corrosion, with rates of 0.65 uA/cm 3 , evident by an average weight loss of 47% per meter length of steel. Compressive strength obtained via rebound hammer test showed average concrete strength loss of 28% from the original as-built strength of 40 N/mm 2. The results showed that the rate of corrosion and strength deterioration depended on the nature and length of exposure. Elements of the structure that were exposed to tidal exposure conditions experienced greater levels of deterioration compared to elements that were continuously submerged.
... With the increase of immersion time, the chloride ion erosion is greater than the cement hydration reaction, the inner part of rubber concrete is eroded, the cracks increase, and the wave velocity shows a temporary decline phenomenon. en, the chloride ion gradually invades the inner part of the test block along the pores in the concrete and reacts with the hydration product of cement, calcium chloride hydrate (C 3 A·CaCl 2 ·10H 2 O), namely, Friedel's salt, and Ca(OH) 2 , to form soluble CaCl 2 and C 3 A, and CaCl 2 reacts with C 3 A to produce calcium chloroaluminate hydrate [23][24][25][26]. e micromorphology is shown in Figure 3(b), and the chemical equation is ...
Chloride corrosion test was carried out in 4% NaCl solution to study the chloride corrosion resistance of rubber concrete. Rubber concrete was prepared by using 20 mesh, 1∼3 mm, and 3∼6 mm rubber particles instead of sand by 5%, 10%, 15%, and 20% of the cementitious material mass. The P-wave velocity and compressive strength of rubber concrete were measured. The microstructure of rubber concrete corroded by chloride was analyzed by SEM. The micromorphology was compared with the macrofailure characteristics under uniaxial compression. The results show that the rubber concrete was still in the early stage of erosion. With the increase of immersion time at the age of 110 days, the P-wave velocity and compressive strength of concrete were generally on the rise. Furthermore, during the period of erosion, the mechanical properties of rubber concrete increased with the increase of rubber particle size and decreased with the increase of the content. Therefore, when the rubber particle size was 3∼6 mm and the content was 5%, the antierosion performance was the best. This study has a certain guiding significance for the chloride corrosion resistance of rubber concrete.
... A similar interpretation could be made on the interaction between the Al 2 O 3 and Cl t . It has been reported that, for a fixed amount of Cl t , the amount of chlorides bound chemically to the calcium monosulfate hydrate (AFm) phases increase with increasing amount of Al 2 O 3 in the unhydrated paste mixture (Rasheeduzzafar et al. 1991). The same study reported that an increase in the amount of Cl t could increase the amount of chlorides chemically bound to the Afm phases at a fixed w/a models-Equation (9) shows the simplified or non-chemistry model for predicting w/a for all binder systems evaluated here. ...
... It was pointed out by many researchers (Rasheed et al. 1992;Larsen 1998;Tang and Nilsson 1993;Ishida et al. 2008) that the chloride ion shows strong binding affinity with cementitious materials. The aluminate (C 3 A) and aluminoferrite (C 4 AF) phases in cement have been found to bind with chloride ion chemically, which form Friedel's salt and calcium chloroferrite. ...
The penetration of chloride ion leads to the corrosion initiation in reinforced concrete, which results in decreasing the durability of concrete. A theoretical diffusion-convection model describing the process of chloride ion penetration into concrete under external water pressure is described by considering multiple affecting factors such as unsaturated flow, fluid-solid coupling, and chloride binding. A numerical model of unsaturated concrete is built to simulate the coupled process. Based on this model, the classic expression of effective diffusion coefficient is modified by considering constrictivity factor, and the sensitivity analysis is carried out on five sets of parameters (i.e., effective diffusion coefficient, saturated permeability, van Genuchten parameters, initial saturation, and binding capacity parameters) aiming at evaluating the robustness of the model. The simulation results show that the multi-mechanism penetration model is computationally feasible, and the multiphysics coupling model can well reproduce the chloride ion transfer process in a microscopic perspective. Furthermore, the sensitivity analysis results indicate that the parameters governing moisture transport process are more sensitive to the prediction of the chloride ion penetration into undersea tunnel concrete.
... Also, it reacts with aluminum phase of the cement paste to form calcium carboaluminate hydrates [57][58][59] and accelerates the hydration of C 3 S and C 3 A phases [60]. It was also reported that increased C 3 A content in concrete significantly reduces the free chloride concentration in the pore solution, which greatly influences the corrosion of concrete [61]. The hydration of overwhelmingly increased C 3 A content forms denser pore structure leading to a reduction in the ionic transport. ...
This paper presents a method for enhancing the corrosion resistance of reinforcements through nanophase modification of fly ash concrete. A combination of natural and accelerated corrosion tests were performed to evaluate the corrosion resistance of reinforcements. The tests were conducted on four types of fly ash concrete specimens with and without nanoparticles designated as fly ash concrete with 40 wt% fly ash (FA), fly ash concrete with 2 wt% nano-CaCO3 (FAC), fly ash concrete with 2 wt% nano-TiO2 (FAT) and fly ash concrete with 1 wt% nano-CaCO3 and 1 wt% nano-TiO2 (FATC). Electrochemical measurements showed that reinforcements in nano-CaCO3 modified fly ash concrete (FAC) exhibited noble potential value, high polarization resistance and lower corrosion rate. Impressed voltage test also corroborate the enhanced corrosion resistance of FAC specimens, which was evident from the longer crack initiation time with minimum anodic current as compared to fly ash concrete without nano additives. Corrosion products of cover concrete showed a comparatively lesser amount of detrimental phases like lepidocrocite and goethite which was in agreement with the corrosion results. The least depth of chloride ion penetration indicated the effective plugging of pores by nano-CaCO3 particles that prevent diffusion and movement of chloride ions to surface of the rebar and thereby maintaining the passivity of the thin iron oxide layer around the steel rebar.
... Also, it reacts with aluminum phase of the cement paste to form calcium carboaluminate hydrates [57][58][59] and accelerates the hydration of C 3 S and C 3 A phases [60]. It was also reported that increased C 3 A content in concrete significantly reduces the free chloride concentration in the pore solution, which greatly influences the corrosion of concrete [61]. The hydration of overwhelmingly increased C 3 A content forms denser pore structure leading to a reduction in the ionic transport. ...
This paper presents a method for enhancing the corrosion resistance of reinforcements through nanophase
modification of fly ash concrete. A combination of natural and accelerated corrosion tests were performed
to evaluate the corrosion resistance of reinforcements. The tests were conducted on four types of
fly ash concrete specimens with and without nanoparticles designated as fly ash concrete with 40 wt% fly
ash (FA), fly ash concrete with 2 wt% nano-CaCO3 (FAC), fly ash concrete with 2 wt% nano-TiO2 (FAT) and
fly ash concrete with 1 wt% nano-CaCO3 and 1 wt% nano-TiO2 (FATC). Electrochemical measurements
showed that reinforcements in nano-CaCO3 modified fly ash concrete (FAC) exhibited noble potential
value, high polarization resistance and lower corrosion rate. Impressed voltage test also corroborate
the enhanced corrosion resistance of FAC specimens, which was evident from the longer crack initiation
time with minimum anodic current as compared to fly ash concrete without nano additives. Corrosion
products of cover concrete showed a comparatively lesser amount of detrimental phases like lepidocrocite
and goethite which was in agreement with the corrosion results. The least depth of chloride
ion penetration indicated the effective plugging of pores by nano-CaCO3 particles that prevent diffusion
and movement of chloride ions to surface of the rebar and thereby maintaining the passivity of the thin
iron oxide layer around the steel rebar.
... In order to develop a prediction model for time-to-cracking of concrete, experimental data will be used from the studies of Maaddawy et al. [4], Alonzo et al. [8], Andrade et al. [13], Vu et al. [14], Rasheeduzzafar et al. [20], Cabrera et al. [21], Mangat et al. [22], Torres et al. [23], and Al-Harthy et al. [24]. In their studies, the following main variables were considered and found to be affecting the timeto-cover cracking of concrete: (1) compressive strength of concrete (f'c); (2) rebar diameter; (3) Elastic modulus of concrete; (4) concrete cover; (5) tensile strength of concrete; (6) current density; (7) thickness of the porous zone and (8) molar mass of corrosion products. ...
To monitor the initiation of concrete cracking beyond the service life of the structure, a novel prediction model of time to cracking of concrete cover using artificial neural network (ANN) was developed in this study. Crack mitigation prevents corrosion and crack development to occur in a more rapid phase that is an essential component in performance-based durability design of reinforced concrete structures. Data available in various literatures were used in the development of the ANN model which is a function of compressive strength, tensile strength, concrete cover, rebar diameter, and current density. The neural network model was able to provide reasonable results in time predictions of cracking of concrete protective cover due to formations of corrosion products. The performance of ANN model was also compared to various analytical and empirical models and was found to provide better prediction results. Even with limitations in the available training data, the ANN model performed well in simulating cracking of concrete due to reinforcement corrosion.
... This expansion would induce tensile stresses in the surrounding concrete and can cause cracking of concrete. It is evident that the penetration of chloride ions into reinforced concrete can lead to loss of serviceability as well as reduction in strength and safety of structures (Rasheeduzzafar et al. [3]). ...
Long-term durability and sustainability of crucial infrastructure systems such as bridges and pavements are of utmost importance for the economic health of any society. Understanding factors that affect long-term deterioration of reinforced concrete structures can help enhance durability and sustainability of these systems. This paper investigates the effect of the type of coarse aggregate used in concrete on chloride ions penetrability. Twelve coarse aggregate types of different geologic formations (sedimentary, igneous, and metamorphic) were used to prepare fresh concrete in which silica fume and class C fly ash were used. All mix parameters including gradation and quantities of different aggregates were held constant in different mixes with the only variable being the aggregate type. The Rapid Chloride Penetration Tests were conducted on concrete specimens made with various aggregate types at ages of 28, 56, 91 and 365 days. Analysis of test results showed that the aggregate type as well as aggregate absorption rates have significant influence on the electrical charges passed through concrete, especially in early ages of concrete specimens containing aggregates with sedimentary rock origin and relatively high absorption. These specimens exhibited the highest RCPT results indicating higher capacity to allow chloride ion penetration when compared to specimens with igneous and metamorphic rock aggregate of lower absorption values. This influence (discrepancy) diminishes with time for both aggregate type and absorption rates in terms of the magnitude of measured total charge passed.
... Cement with higher C 3A are considered to have a higher binding capacity for chlorides that ingress from external sources (1,2). Figure 2 plots the ratio of measured water-soluble to acid-soluble results for mixtures that used Type II (higher C3A) compared to mixtures with Type V (lower C3A) cement. ...
... It is the free chlorides present in the pore water that are responsible for steel depassivation, so when more chlorides are bound, less free chlorides will be available for depassivation. Several factors have been reported to affect the formation of bound chlorides, such as the quantity of C 3 A in the cement, the incorporation of supplementary cementitious materials (SCMs) in the mix, the alkalinity of the pore solution, the cation type of the salt, and the presence of other anions, like sulphates and carbonates [2][3][4][5][6][7][8][9]. ...
This study has investigated the impact of a change in GGBS chemical composition on the chloride ingress resistance of slag blended cements under different temperature regimes. Two slags, having alumina contents of 12.23 and 7.77% respectively, were combined with a CEM I 52.5 R at 30 wt% replacement. Chloride binding and diffusion tests were conducted on paste and mortar samples respectively. All tests were carried out at temperatures of 20 °C and 38 °C. The higher temperature resulted in an increase in chloride binding; attributed to greater degrees of slag hydration. Despite this, chloride ingress was greater at 38 °C; attributed to changes in the pore structure and the chloride binding capacities of the slag blends. The more reactive, aluminium-rich slag performed better in terms of chloride binding and resistance to chloride penetration, especially at the high temperature and this was attributed to its higher alumina content and greater degree of reaction at 38 °C.
... This is consistent with the results of previous research (see for e.g. [62,[67][68][69][70]). Furthermore, the higher specific surface area of the Slag particles (Table 3) means that more chloride ions bind onto the surface of the Slag particles [43]. ...
This paper presents the results of an investigation that aimed to evaluate the influence of sodium chloride (NaCl or salt) on the yield stress and evolution of the strength of a cemented tailings material (called cemented paste backfill, CPB) that contains ground granulated blast furnace slag (Slag-CPB) in sub-zero environments. About 200 CPB specimens with different NaCl concentrations (0, 5, 35, and 100 g/L) and cured at −6 °C are tested at different curing times (0, 0.25, 1, 2, and 4 h for yield stress measurement; 7, 28, and 90 days for uniaxial compressive testing). Moreover, microstructural analyses are conducted on cement-slag paste and Slag-CPB samples with various concentrations of NaCl. The results show that the addition of NaCl provides better flowability of the fresh Slag-CPB and significantly affects the strength development of Slag-CPB. The results presented in this study have significant implications for backfill practices in permafrost and cold regions.
... Chloride in concrete may exist either as free chloride, that is, dissolved in the pore water, or as bound chloride. The bound chlorides are either chemically bound to the tricalcium aluminate (C 3 A) and the calcium aluminoferrite (C 4 AF) phases in the form of Friedel's salt (3CaO.Al 2 O 3 .CaCl 2 .10H 2 O) or physically bound to the surface of the hydration products (C-S-H gel) [2]. It is the free chlorides present in the pore water that are responsible for the depassivation of the steel reinforcement, so when more chlorides are bound, less free chlorides will be available for the depassivation of the steel reinforcement. ...
... It has been reported that degradation kinetics of various chlorinated organics was proportionally promoted by increase of the concentration of hydroxide ion in the system [31,32]. High pH environments caused by cement slurries, thus, would be favorable for degrading PCE via base-catalyzed hydrolysis/substitution [33][34][35]. Fig. 8 shows the effect of PCE concentration (0.25-2.0 mM) on the dechlorination kinetics of PCE by nFeS-Cbl(III) in cement slurries at pH 13.5. The PCE removal efficiency was continuously maintained although the PCE concentration increased. ...
... In addition, the total amount of bound chlorides and the formation of chloroaluminates are probably more related to the total aluminate content (C3A + C4AF) than to the C3A content. Although, an increase in C3A content results in a decrease in free chloride concentration (Rasheeduzzafar et al., 1992). In addition, physical binding is influenced by the CSH content. ...
Concrete is a well-known construction material with a lot of positive properties such as high compressive strength, low cost, wide applicability, etc. Therefore, it is commonly used for marine constructions. This type of constructions mostly have an important social function with a high economic impact (e.g. bridges, wharfs, piers, tunnels, etc.), which makes durability a key issue. Nevertheless, a lot of damage is reported for constructions in marine environments. In this aggressive environment, the durability of concrete is strongly influenced by the presence of chlorides and sulphates, the main components of sea water. On the one hand, the sulphate attack degrades the concrete directly by forming expansive reaction products as well as strength decreasing reaction products. On the other hand, chlorides attack the concrete indirectly, by initiating corrosion at the reinforcement steel. In addition, earlyage cracks are a common problem, specifically for the massive structural components. These cracks promote the penetration of the aggressive substances. Thus, fast repair of the cracks is desirable. Without appropriate treatment, the amount and size of the cracks will increase. However, repair costs are large and in some cases repair is impossible due to inaccessibility. So in order to investigate the durability of concrete in marine environments, two main focus points can be defined. Firstly, it is important to understand the attack mechanisms occurring in marine environments in detail in order to understand the cause of the deterioration. Secondly, as a possible solution the material characteristics with regard to crack formation should be improved.
... This expansion induces tensile stresses in the surrounding concrete and will cause the concrete to crack. It is evident that the penetration of chloride ions into the reinforced concrete leads to cracking and spalling of concrete thus causing loss of its serviceability and degradation in strength and safety of structures [1]. ...
... Other forms of expression such as chloride/hydroxyl ion ratios are also common (Pettersson, 1993, Rasheeduzzafar et al., 1992and Goni and Andrade, 1990. A review by Glass et al. (1997) revealed that the best way of expressing the chloride threshold is by total chloride content expressed relative to the weight of cement. ...
An extensive chloride profiling program was undertaken on concrete pier stems erected in the vicinity of the Dornoch Bridge located at the Dornoch Firth in Northeast Scotland. The pier stems were 2 m (6.562 ft) high and octagonal in plan with 0.66 m (2.165 ft) wide faces. The piers were constructed in sets of three with the lowest of each set in the tidal zone and the highest in the atmospheric zone. The pier stems were placed in such a way that they would represent the exposure conditions of the actual bridge piers of the Dornoch Bridge. In all, six of the pier stems were made using plain ordinary portland cement (OPC) concrete (with three of these having the surface treated with silane); the remaining three pier stems had a concrete containing caltite as an additive. Three exposure zones were studied: the tidal zone, the splash zone, and the atmospheric zone. The tidal zone was further subdivided into two levels defined as low-level and high-level. Chloride profiles were obtained from the different regimes over a period of 7 years for all nine pier stems. This paper describes the nature of chloride ingress and the usefulness of diffusion parameters in classifying each exposure regimes. Furthermore, the effectiveness of silane and caltite in protecting concrete from chloride ingress in different exposure zones was studied.
Criteria related studies have been conducted under SHRP Contract C-102D for the cathodic protection of reinforced concrete structures. Corrosion rate studies were conducted in a packed bed of sand wetted with simulated pore water solution to facilitate weight loss measurements. Corrosion rates were determined in such cells as a function of chloride concentration, pH and temperature at various levels of cathodic protection current. Corrosion rate was found to be especially sensitive to chloride concentration and pH. Cathodic protection current was found to be a highly effective means of stopping corrosion in this environment. The amount of polarization needed to reduce corrosion to an acceptable level was found to be a complex function of many variables. A maximum polarization of 150 mV was found to be sufficient protection in almost all cases studied.
An improved and simplified control criterion for cathodic protection is proposed. This new criterion, which uses a "Corrosion Null Probe", assures that the most anodic areas are made net cathodic, effectively stopping corrosion. This approach is technically accurate, simple to apply, and does not rely on the long-term stability of embedded reference electrodes. Laboratory and test yard data are presented, and additional field studies are recommended.
Severe deterioration due to corrosion of reinforcing steel in concrete structures is a source of major concern with respect to the maintenance of a safe and reliable infrastructure. A significant amount of work has been performed over the past 30 years, and the understanding of corrosion of reinforcing steel in concrete has progressed significantly. Although the effect of chloride (Cl−) has been studied extensively, the effect of other environmental variables in combination with the Cl− are not as well understood. In addition, the effect of concrete chemistry on the corrosion behavior of reinforcing steel has not been well characterized. In this paper, the effects of Cl− concentration, temperature, and humidity on the corrosion behavior of a typical reinforcing steel, in a typical concrete mix, were examined. The main effects of the above variables and their interaction were studied using a full factorial three level experimental design along with statistical methods to provide prediction of corrosion rates as a function of Cl− concentration, temperature, and humidity.
Severe deterioration of a reinforced concrete cooling tower, which comprised pre-cast columns, beams, wall panels, and slab panels was noticed during the last few years. A diagnostic survey was conducted to identify the cause and extent of deterioration. The concrete deterioration was very advanced in some areas, particularly on the external side of the end walls and posing a safety hazard to plant personal. Internally, the level of defects was very low with only minor patches of delamination and cracks. Both chloride and sulfate ions were present in the concrete cover at rebar depth well in excess of their threshold levels. About 12% of the half-cell potential results indicated high (90%) corrosion risk and 53% of the results exhibited medium (50%) corrosion risk in all tested areas of the structure.
The investigations concluded that deterioration of concrete has occurred mainly due to chloride- induced corrosion of the steel reinforcement. Patch repair and cathodic protection (CP) repair method was recommended to arrest the ongoing corrosion of the steel reinforcement. The CP system design, installation, and initial commissioning results are also described and discussed.
Investigations were conducted to assess condition and determine root cause of the ongoing concrete deterioration of the cooling tower. The beams, columns, wall panels of end walls, roof slab, bund wall, and louvers, were visually exhibiting severe concrete deterioration in many areas across the entire structure. In some areas, the concrete deterioration was very advanced and posing serious threat to integrity of the structure. Chloride had penetrated to full depth of the concrete cover in concentrations significantly higher than threshold level. Electrochemical measurements showed that the reinforcing steel was actively corroding under the sound concrete in >50% areas of the entire structure.
The visual condition of the exposed steel and the survey results concluded that the deterioration of concrete resulted due to chloride-induced corrosion of the reinforcing steel. There was no risk of carbonation-induced corrosion of steel and sulfate attack on concrete. Patch repair and cathodic protection (CP) repair method was recommended to arrest the ongoing corrosion of the steel reinforcement. The CP system design, installation, and initial commissioning and monitoring results are also described and discussed.
Recently, research results on PC-based or alkali-activated slag cement (AASC) using seawater as mixing water have been reported. Unlike seawater, reverse osmosis brine (brine) is waste discharged into the ocean from seawater desalination plants. There is a need to develop new and effective methods of disposing or utilizing brine to reduce marine pollution, protect marine ecosystems, and increase marine plant construction. However, research on cement or concrete using brine as a mixing water is very limited. Brine has almost the same composition as seawater, and the ion concentration is 2–4 times higher. Therefore, it is believed that new methods of using brine can be investigated and developed based on existing research and experimental results on seawater. The effects of brine and aluminum oxide (AO) on activated slag with calcium hydroxide (CH) were investigated for hydration and mechanical properties. 5% and 10% of CH were used, and samples using fresh water (FC) were prepared at the same time for comparison with brine. The slag sample without CH has a low initial (1 and 3d) strength of about 10 MPa for both FC and brine, but increases rapidly from 7d. Incorporation of CH was effective in improving the mechanical performance of FC and brine samples. In addition, the brine sample exhibited higher strength than the FC sample because it formed fewer C3AH6 phases that cause volume instability than the FC sample and affected the hydration promotion of slag particles. And more calcite phases were observed in the brine samples than in the FC samples. Through this study, the possibility of using brine as a building material was confirmed. In addition, the effect of chloride ion adsorption of slag mixed with AO and CH on the physical properties and mechanical performance of the hydration reaction was confirmed.
In this study, the ion corrosion behavior of tunnel lining concrete in complex underground salt corrosion environment was investigated using a self-designed corrosion simulation test device in a complex underground environment. The results indicated the following: the corrosion of flowing water leads to the dissolution of lining concrete, and the load promotes the development of cracks in the tensile area of lining concrete and inhibits the development of defects in the compression area, resulting in the transmission speed of chloride and sulfate ions in lining concrete under different corrosion conditions given as follows: concrete in tensile zone under flowing corrosive solution and load > flowing corrosion solution acting alone > static corrosion solution > concrete in compression zone under flowing corrosive solution and load. When the flowing corrosion solution alone and flowing corrosion solution and load act on the concrete in the tensile zone, the pore volume fraction of gel decreases and the macropore volume fraction increases. Under the combined action of static corrosion solution and flowing groundwater and load, the pore volume fraction of gel in the pressurized area increases and the harmless pore volume fraction decreases.
In this study, the erosion behavior of ions in lining concrete incorporating fly ash and silica fume under the combined action of load and flowing groundwater containing composite salt. The results show that the transmission speed of Cl⁻ and SO4²⁻ in lining concrete under different erosion conditions is: flowing groundwater–load action in the tension zone > flowing groundwater > static corrosion solution > flowing groundwater–load action in the compression zone. The addition of silica fume (SF) and fly ash (FA) can reduce the concentration of Cl⁻ and SO4²⁻ in lining concrete, increase the ratio of combined Cl⁻ to total Cl⁻, and reduce the ratio of combined SO4²⁻ to total SO4²⁻. The addition of FA and SF can increase the lining concrete's resistance to Cl⁻ corrosion by about 10% – 28%, and SO4²⁻ radical resistance by about 5% – 12%, and the more FA is added, the greater the increase.
When infrastructure is exposed to a complicated environment containing stray current, chloride and sulfate, it may be subjected to severe degradation. In order to analyze the interaction of different factors and the degradation mechanism of cement-based materials in a complicated environment, the blended solution with four molar concentration ratios of Cl⁻/SO4²⁻ (0, 0.5, 1, and 2) were prepared to simulate a range of aggressive medium. Meanwhile, 40V DC (direct current) electrical field was applied to cement-based materials to simulate stray current. After exposure, the transport properties, macro-properties, and microstructures of specimens were observed and measured. Additionally, the types and amounts of degradation products were tested to further analyze the degradation mechanism of cement-based materials. Experimental results show that chloride in the blended solution could inhibit SO4²⁻ transport into cement-based materials, causing the SO4²⁻ concentration in a specimen to decrease with the increase of Cl⁻/SO4²⁻ ratio. Therefore, the specimens appeared less degraded in terms of macro-properties. But the results of microstructural analysis showed that degradation products and cracks were generated in the interior of specimens. Friedel’s salt was detected in the specimens exposed to the solutions containing chloride. The formation of Friedel’s salt consumed calcium aluminate hydrate, which caused the amount of Al-phase involved in the formation of ettringite to reduce. Consequently, the amount of ettringite was reduced, and the degradation of compressive strength and appearance was also reduced. Additionally, an electrical field could induce the ion concentration in pore solution to change and even break the ion chemical equilibrium, which resulted in the decomposition of ettringite and Friedel’s salt. However, Friedel’s salt can also transform into ettringite at a specific condition. Therefore, the amounts of ettringite and Friedel’s salt in specimens were changed over the exposure time.
Concrete is one of the few construction materials, which has the ability to be produced directly on the building site. It is also based predominantly on locally available resources, for example, fine and coarse aggregates, and water. This often helps save on transportation time and costs, which, in the case of large structures, that is, water dams, can be tremendous. Despite all the positives, the production process and long-term use of concrete structures each come with their fair share of challenges. The situation becomes even more complicated when novel materials, that is, carbon nanotubes (CNTs) and carbon nanofibers (CNFs), are incorporated into the concrete. The addition of these materials can affect the properties of both fresh and hardened concretes. The ultimate effect depends on the type of binder matrix, its properties, the amount of CNTs and CNFs used, and the incorporation method. This chapter focuses on the effects of CNTs and CNFs on Portland cement-based concretes. Specifically, the effects on hydration processes, microstructure development, workability, shrinkage, mechanical properties, electrical properties, and durability will be discussed.
To explore the key inhibitory mechanism of external chloride ions on concrete sulfate attack, long-term partial- and full-immersion experiments of concrete in chloride solutions and chloride and sulfate composite solutions were performed. As corrosion time begins, visual inspection, compressive strength, and ultrasonic velocity were periodically observed or tested. Moreover, the micro-morphology, the contents of Cl and S elements in concrete, and the transport speeds of Cl⁻ and SO4²⁻ ions through concrete were investigated by using scanning electron microscope, X-ray fluorescence spectrum, and chemical analysis. Chloride ions neither have corrosive effects on concrete nor effects on concrete physical and mechanical properties, which is the prerequisite for chloride ions in inhibiting concrete sulfate attack. In the case of combined solutions, the transport speed of Cl⁻ ions into concrete is evidently higher than that of SO4²⁻ ions. Then, chloride ions enter concrete early and form Friedel's salt with AFm or with C3A and Ca(OH)2 in concrete, which inhibits the transport of SO4²⁻ ions into concrete and reduces the formation of expansive corrosion products of ettringite or gypsum. Thus, the sulfate attack on plain concrete is alleviated. Based on the inhibitory mechanism of Cl⁻ ions on concrete sulfate attack, the presence of Cl⁻ ions cannot completely avoid concrete sulfate attack but can partially reduce sulfate risk on concrete.
Thermodynamic equilibrium based modelling was carried out to quantify the influence of temperature on the mineralogy of hydrated ordinary Portland cement. In typical Portland cement system hydrated at 25 °C interlayer sites in the AFm phase are occupied by OH, SO4 or CO3 ions. Chloride which can be added as a set accelerating admixture or ingress from the outside environment, has the ability to displace hydroxide, sulfate and carbonate from the AFm structure leading to the formation of ‘Friedel's salt’ (Cl-AFm). However temperature variations may cause important compositional changes or even destabilization of Friedel's salt. A description of phase relations and changing balances between AFm and AFt (ettringite) phases is presented in a range of temperatures between 5 and 85 °C. With an increasing temperature Friedel's salt is predicted to decompose at the expense of monosulfoaluminate (SO4-AFm) formation. Due to the higher stability of hydroxy- AFm (OH-AFm) at lower temperature the OH substitution in the Friedel's salt is expected to be slightly higher as compared to room temperature.
La durabilité des ouvrages en béton armé est étroitement liée à la composition des matériaux dont ils sont formés, et plus particulièrement aux propriétés de ces derniers. Cette durabilité est caractérisée par des indicateurs parmi lesquels se trouve le coefficient de diffusion des chlorures. Ceux-ci pénètrent le béton et interagissent avec les ions composant la solution interstitielle (contenue dans les pores) ainsi que les composants de la matrice cimentaire. Il existe peu de travaux dans la littérature qui décrivent toutes ces interactions ioniques de façon simultanée et encore moins leur prise en compte dans l’étude et la modélisation des transferts. Ce travail de thèse présente une étude des interactions multi-espèces se produisant lors du transfert des ions chlorure. Pour ce faire, l’évolution de la composition de la solution interstitielle, de plusieurs pâtes de ciment contenant diverses additions minérales, est étudiée. La solution interstitielle des pâtes de ciment est extraite suite à un essai de migration par pressage et analysée par chromatographie ionique. Par ailleurs, l’évolution de la microstructure de ces matériaux suite au transfert des chlorures est caractérisée par porosimétrie à intrusion de mercure (PIM) et microscopie électronique à balayage (MEB). Ceci a permis de mettre en évidence les modifications provoquées par la diffusion des ions chlorures. Dans un second temps, et afin de simuler le transfert des chlorures dans la matrice cimentaire, un modèle de transfert multi-espèces est développé. Dans ce sens, plusieurs modèles de transfert mono et multi-espèces, sous l’effet d’un champ électrique ou non, en régime stationnaire et transitoire ont été développés auparavant. L’objectif de cette partie numérique est d’étendre ces modèles à la prise en compte de l’ensemble des ions composant la solution interstitielle ainsi que leurs interactions multi-espèces conduisant à la précipitation de composés à base de chlore et à la dissolution des hydrates. La formulation mathématique des phénomènes étudiés est établie à partir de la loi de conservation de masse et les équations de la thermodynamique. Les conditions initiales et aux limites sont adaptées pour tenir compte à la fois de la composition chimique réelle de l’eau de mer et de celle de la solution interstitielle. Les résultats obtenus permettent de mettre en exergue l’effet de ces phénomènes sur la composition chimique de la solution interstitielle ainsi que sur le transfert des chlorures.
Although blastfurnace slag has been in use in many countries for many years, its use in Hong Kong is only beginning. In addition to environmental and economical benefits, slag-blended concretes have also improved the properties of OPC concretes. With an increasing awareness of concrete durability problems, engineers in Hong Kong are now showing greater interest in knowing more about the use of slag in concrete. This paper describes the properties of slag-blended concrete, including low heat of hydration, strength development, reinforcement protection and resistances to alkali aggregate reaction, to chloride ingress, to sulfate and seawater attack, to in-situ temperature rise and to delayed ettringite formation.
In this paper the strength of concrete cubes and cylinders cast using M30 grade concrete and reinforced with steel and polypropylene fibres are presented. Also, hybrid fibres with crimped steel and polypropylene were used in concrete matrix to study its improvements in strength and durability properties. The steel, polypropylene and hybrid consisting of polypropylene and steel (crimped) fibres of various proportion i.e., 4 per cent of steel fibre, 4 per cent of polypropylene fibre and 4 per cent of hybrid (polypropylene and steel (crimped) fibres each of 2 per cent) by volume of cement were used in concrete mixes. Besides cubes, cylinders of 150 mm diameter × 300 mm high of M30 grade concrete were cast with 4 per cent of steel fibre, 4 per cent of polypropylene fibre, and 4 per cent of hybrid fibre, respectively, by volume of cement. The rapid chloride permeability test and water absorption test were conducted on 7, 28, 56 and 90 days and the test results show that the addition of steel and polypropylene fibres to concrete exhibit better performance. The test results show that use of steel fibre reinforced concrete improves compressive strength and split tensile strength. The durability of such concrete is also improved.
This chapter presents the key issues of the corrosion of metals in concrete, with emphasis on chloride-induced deterioration, quantitative approaches to forecast corrosion performance, and strategies to improve durability in new construction. Chloride-induced corrosion is widespread and causes severe structural damage throughout the world. Many of the findings, forecasting and control methods described also apply, with appropriate modification, to the problem of carbonation-induced corrosion. A two-stage description of the corrosion process can be used for carbonation-induced corrosion. In that case, during the initiation stage, the concrete carbonation front penetrates through the concrete until the pH of the pore solution at the reinforcement surface becomes low enough not to support passivity. The chapter discusses key factors affecting each of the deterioration stages and describes approaches to improve the durability of reinforced concrete subject to reinforcement corrosion. The scope is limited to those measures that can be taken at the design and construction stage and that do not involve external added systems. Improved resistance of galvanized reinforcement to that mode of attack has been documented in laboratory investigations, such as those by González and Andrade. Durability improvements for this mode could also be quantified in terms of a modified durability model. The overall galvanized reinforcement corrosion experience may be a promising starting point for future rational analyses based on the initiation-propagation model to glean effective values of the key durability parameters to supplement those to be derived from future research.
A novel non-destructive method of monitoring chloride penetration in reinforced concrete structures prior to corrosion is proposed. By measuring the change in the electrical characteristics induced by chloride in cement composites containing carbon nanotubes (CNTs), chloride penetration in the structures could be monitored in real time. To evaluate the feasibility of this method, cement composites containing various amounts of CNTs and sodium chloride were fabricated and their electrical characteristics were measured. Although the conductivity of the composite without CNTs fluctuated as a result of both reinforcement and moisture content, that of the composites with CNTs was seldom influenced by these factors, and the conductivity generally increased with increasing chloride content. The chloride content in the composites was estimated via regression analysis based on the electrical characteristics, implying that the CNT/cement composite could be used as a sensor for chloride penetration monitoring.
The principal objective of this paper is to investigate the modelling of chloride diffusion in fly ash and slag concretes laden in chloride environments. The capacity of the concrete cementitious system to bind chloride ions has an important effect on the rate of chloride ionic transport in concrete. Four mathematical models concerning chloride binding in concrete are stated and used. The analytical solution of Fick's second law of nonlinear (diffusivity ≠ constant) diffusion in conjunction with initial and boundary conditions is used as a predictive model. The experimental data obtained by Thomas and Bamforth [Modelling chloride diffusion in concrete: Effect of fly ash and slag. Cement and Concrete Research 1999;31:487-495] was cited as input parameters. The results at the present study show that after 30 years the predicted chloride profiles obtained by the nonlinear model may be one order of magnitude lower than that of linear (diffusivity = constant) model. The nonlinear model associated with four mathematical models related to chloride binding in concrete is not suitable to predict the transport mechanism of chloride diffusion in concrete containing fly ash and slag. However, the analytical solution of a nonlinear partial differential equation (PDE) in association with initial and boundary conditions for the concentration of Cl- in the aqueous phase [Cl(aq)-] (in kg/m3 pore solution) is proper to estimate the transport behavior of chloride diffusion in both fly ash and slag concretes. The Cl- bound in the solid phase [Cl(s)-] (kg/m3 concrete) can thus be computed algebraically. Further research in-depth is obviously needed and suggested. © 2015, Journal of Applied Science and Engineering. All rights reserved.
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