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Influence of sulfates on chloride binding in cements
Abstract
Cement pastes with water to cement ratio of 0.60 were prepared using three cements with C3A contents of 2.43, 7.59 and 14 percent. The chloride treatment levels of 0.6 and 1.2 percent by weight of cement, derived from sodium chloride, were used in conjunction with sulfates. Sulfates derived from sodium sulfate, were added in such quantities that for each of the two 0.6 and 1.2 percent chloride-bearing cement pastes the total SO3 content of the cements were raised to 4 and 8 percent on a weight basis. The pastes were allowed to hydrate in sealed containers for 180 days and then subjected to pore solution expression. The expressed pore solutions were analyzed for chloride and hydroxyl ion concentrations. It was found that the alkalinity of the pore solution is significantly increased by the addition of sodium sulfate in the chloride-bearing hydrated cement pastes. This is attributable to the formation of sodium hydroxide as a result of reaction between sodium sulfate and calcium hydroxide liberated during cement hydration. The addition of sulfates also caused a significant increase in the chloride ion concentration in the pore solution, for both chloride levels in all the three cements tested. DTA results show that the sulfate addition reduces the formation of Friedel's salt, which possibly results in an increase in the chloride ion concentration the pore solution. The interactive effect of increase in alkalinity and chloride ion concentration with sulfate addition is not a consistent increase or decrease in the Cl−/OH− ratio of the pore solution. For a given chloride level, whether sulfate addition increases or decreases the Cl−/OH− ratio of the pore solution, and hence the corrosion risk, depends upon the interactive effect of equivalent alkali content and C3A content of the cement.
... This reduces the amount of residual C 3 A to bind the chlorides. This has been reported by several researchers [68,[71][72][73][74][75][76]; for example, Figure 4 shows the bound chloride content vs. free chloride content for slag blends, with or without anhydrite ($). For the slag blends with anhydrite (i.e., C2S1$ and C2S2$), additional anhydrite ($) was blended with the original slag blends (i.e., C2S1 and C2S2) so as to bring the sulphate contents of the slag blends to that of the plain cement. ...
... This reduces the amount of residual C3A to bind the chlorides. This has been reported by several researchers [68,[71][72][73][74][75][76]; for example, Figure 4 shows the bound chloride content vs. free chloride content for slag blends, with or without anhydrite ($). For the slag blends with anhydrite (i.e., C2S1$ and C2S2$), additional anhydrite ($) was blended with the original slag blends (i.e., C2S1 and C2S2) so as to bring the sulphate contents of the slag blends to that of the plain cement. ...
... Both chlorides and sulphates react with hydrated aluminate phases to form Friedel's salt and ettringite, respectively. However, in combination, sulphates are preferentially bound to aluminates, leading to reduced chloride binding [71,126,127]. Yet, many factors, including ion concentrations [128,129], cation type [5,73,130], supplementary cementitious materials (SCMs) or type of cement [17,127,131], temperature [132,133], exposure conditions (wetting and drying versus static submersion) [134,135], etc., can affect the dynamics of chloride and sulphate interactions. These factors are discussed further below. ...
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.
... For the first category, in early studies, some researchers mixed different sulfates and chlorides into cement pastes, extracted the pore solution, and then analyzed it to explore the influence of sulfates on chloride binding and pore solution chemistry [34][35][36]. Ehtesham Hussain et al. [37] added sodium sulfate into chloridebearing hydrated cement pastes and found that chloride concentration in the pore solution was significantly increased by the addition of sulfates. They attributed it to the reduction in the formation of Friedel's salt (FS) respectively. ...
... This interesting finding shows that the binding mechanism of chloride ions in concrete under binary attack of chlorides and sulfates is different from that in concrete under single chloride environment. In combined chloride-sulfate environment, for one thing, the amount of chemical bound of chloride ions would decrease [23,37,38]. For another, the quantity of chloride ions adsorbed in gypsum and/or ettringite increase, although there is a slight decline in the amount of chloride ions in calcium silicate hydrate (C-S-H) [39]. ...
Reinforced concrete (RC) structures may suffer from serious durability problems during long-term service. To investigate the deterioration of RC structures subjected to the dual attacks of chlorides and sulfates, this study proposes a coupled model for external sulfate attack (ESA) and its effect on chloride binding and diffusion. To account for the influence of sulfate attack on chloride binding, a reduction function is proposed. The effect of sulfate-induced damage on the chloride diffusion and chloride binding is considered through a damage function. The coupled model is validated against third-party experimental data from multiple perspectives. Some important factors such as solution concentration, immersion time, curing time and water-cement ratio, as well as how these factors affect the impact of sulfate attack on chloride transport, were elaborated. The findings may bring insights to the durability design of RC structures serving in harsh environments.
... Frias et al. (2013) attributed improved early-age performance to the partial inhibition of Friedel's salt as sulfate reacts with calcium aluminate hydrates preferentially to precipitate non-expansive ettringite inside the pores. Sulfates are also known to reduce chloride binding by cement hydrates, leading to increased free chloride in the exposed mortar or concrete matrix (De Weerdt et al., 2014;Ehtesham Hussain and Rasheeduzzafar, 1994). ...
... In slag blended cements, slag reactivity is activated by the presence of high concentration of chloride in the pore solution as sulfate is preferentially bound to the aluminates, causing the formation of hydrated aluminates of layered structure, which then transform to Friedel's salt through ionic exchange between hydroxide and chloride (Frias et al., 2013). This causes a reduction in porosity, resulting in a more compact microstructure, which supports the increased flexural strengths observed (Caijun et al., 2017;Divsholi et al., 2014;Ehtesham Hussain and Rasheeduzzafar, 1994;Frias et al., 2013;Goni et al., 1994;Maes and De Belie, 2014). ...
The durability of reinforced concrete structures exposed to aggressive environments remains a challenge to both researchers and the construction industry. This study investigates the hydration, mechanical properties and durability characteristics of ground granulated blast-furnace slag (GGBS) - blended cements and mortars exposed to a combined sodium chloride - sulphate environment, at temperatures of 20°C and 38°C. The conditions were chosen so as to assess the performance of slag blends under typical temperate and warm tropical marine climatic conditions. Slags, having CaO/SiO2 ratios of 1.05 and 0.94, were blended with CEM I 52.5R at 30% replacement level to study the influence of slag composition and temperature. Parallel control tests were carried out with CEM I 42.5R. Pastes and mortar samples were cast using 0.5 water to binder ratio, pre-cured for 7 days in water before exposure. Flexural strengths were determined once the samples were 7, 28 or 90 days old. Hydration was followed using x-ray diffraction (XRD), thermal analysis, and calorimetry. Also, sorptivity, gas permeability and chloride diffusion tests were carried out on mortar samples to measure transport and durability characteristics. The results show improved mechanical and transport properties for slag blended cements exposed to environments rich in sodium chloride and sulphate.
... La presencia de otras especies aniónicas en el sistema pasta de cemento-ambiente afecta a la capacidad de fijación química de los iones cloruros a las fases alumínicas (17)(18)(19). ...
... Muchos autores han estudiado como influye la capacidad de fijación de los iones Cl" con los aluminatos de un cemento en presencia de SO^^" y de iones alcalinos (2,9,17,(25)(26)(27)(28). Observaron que a medida que aumenta la cantidad de sulfatos y álcalis en un cemento se produce un efecto inhibidor en la capacidad de fijación de los cloruros. ...
A vast bibliography revision is done about the Friedel's salt. The structure, more possible mechanisms of formation and stability intervals in presence of other salts and temperature effect and by pH are pointed out.
... Algunas de las fases presentes en el clínker resultan ser alteradas: tanto el aluminato tricálcico (C 3 A) como el ferritoaluminato tetracálcico (C 4 AF) pueden interactuar con el ión sulfato para producir ettringita secundaria expansiva (AFt), responsable esta última de la fisuración del cemento mientras facilita la difusión del ión cloruro a través del cemento API clase H, favoreciéndose así el ataque de este ión sobre las piezas metálicas embebidas en el cemento (10). Por otro lado, los silicatos anhidros bicálcico (C 2 S) y tricálcico (C 3 S) se hidratan originando tobermoritas y portlandita (CH) que, a su vez, reacciona con el anhídrido carbónico y el ácido sulfhídrico solubilizados en las aguas salinas para originar carbonato cálcico y sulfuro de calcio, entre otras fases, inhibiendo parcialmente la formación de silicatos de calcio y posibilitando episodios de corrosión (11). ...
... Some of the phases in the clinker are altered: both the tricalcium aluminate (C 3 A) and the tetracalcic ferritoaluminate (C 4 AF) can interact with the sulfate ion to produce expansive secondary ettringite (AFt), which is responsible for cement fissuring at the same time as it favours chloride ion diffusion throughout the API class H cement, thereby promoting the attack of this ion on the metallic elements embedded in the cement (10). Furthermore, the anhydrous tri-and di-calcium silicates (C 2 S) and (C 3 S) hydrate to produce tobermorites and portlandite (CH). ...
This paper discusses the attack of the major ions (sulfate, chloride, and magnesium) and sour gases, present in natural gas (CO2 y SH2), on API class H cement, the type used in gas wells under high pressure and temperature. The effects of these chemical agents on this cement was simulated to study the physicochemical changes due to the action of sour gases and formation water. Cement specimens were immersed in neutral solutions containing fixed concentrations of the major ions inside Parr reactors. These solutions were analysed and XRD analyses were conducted for over two months to identify mineralogical variations from 14 to 60 days. The objective of this research was to determine the effects of the joint attack of major ions and sour gases on cement pastes. The main effects of both gases, jointly or separately, on cement durability were, respectively, the carbonation process and the leaching of some components.
... La diminution de la capacité de fixation des ions chlorure pour les pâtes PCV et L75 est attribuée à la dilution des anhydres C3A et C4AF (composants du Clinker) dans ces pâtes contenant une teneur élevée de substitution du ciment par des additions (Hussain et al., 1994). Nguyen (2014) a remarqué aussi cette même tendance. ...
La prédiction de la durée de vie des ouvrages en zones maritimes nécessite la compréhension des principaux phénomènes liés au transfert des chlorures. Ces derniers peuvent être fixés physiquement dans les feuillets de C-S-H constituant une double couche électrique (DCE). Plusieurs études de quantification de la DCE ont été réalisées par des mesures du potentiel zêta sur des phases hydratées ainsi que sur des ciments en suspension. En revanche, les travaux concernant les matériaux cimentaires sont peu nombreux et généralement basés sur des techniques de mesure qui nécessitent un broyage fin du matériau. L’objectif de cette thèse est de quantifier les phénomènes de la DCE et d’étudier leur influence sur le transfert des chlorures au sein de la microstructure de matériaux cimentaires. En parallèle, il est question d'étudier l’évolution de cette microstructure suite au transfert des chlorures. Dans un premier temps, une caractérisation expérimentale a été réalisée afin d’obtenir les propriétés de transfert de matériaux cimentaires contenant diverses additions minérales (laitier de haut fourneau, cendre volante, fumée de silice et métakaolin), ainsi que deux ciments de Type CEMI et CEMV. Ensuite, et afin de quantifier la DCE, des mesures de potentiel zêta selon la technique du potentiel d’écoulement ont été réalisées sur ces mêmes matériaux cimentaires. Les résultats ont montré une dépendance de potentiel zêta à la teneur en C-S-H et particulièrement à la surface spécifique des pores des pâtes de ciment. Ainsi les pâtes à base de laitier ont présenté les valeurs les plus électronégatives du potentiel zêta. De plus, nous avons mis en évidence les modifications de la DCE et de la microstructure de pâtes de ciment suite à un essai de migration des ions chlorure. Nous avons constaté une baisse des valeurs absolues du potentiel zêta et des diminutions plus ou moins importantes du volume et de la taille des pores de nos pâtes de ciment suite à un essai de migration des chlorures. Enfin, un modèle de transfert multi-espèces intégrant les phénomènes de la DCE a été proposé à la lumière des modèles développés auparavant. Nous avons confronté les profils issus des simulations numériques à ceux de pénétration des chlorures obtenus expérimentalement par des essais d’immersion au laboratoire. L'effet de la DCE était plus remarquable dans les pâtes à base de laitier, cela est principalement dû aux diamètres de pores qui sont très petits. Pour les autres types de pâtes, l’influence de la DCE sur les profils des ions chlorures est négligeable voire inexistante.
... Zhang & Shao, 2016) as chloride-induced corrosion and carbonation of concrete are strongly influenced by each other (Geng et al., 2016;Kuosa et al., 2014;Rumman et al., 2022;Wang et al., 2017). It has been found that weathering carbonation reduces the critical threshold level (CTL) in corrosion initiation (Ehtesham Hussain et al., 1994). Carbonation of concrete leads to accelerated movement of free chloride ions, thus, increasing the total chloride content available for attack on the rebar surface (Wan et al., 2013). ...
This paper presents the performance of a multifunctional generic compound, 4-Aminobenzoic acid (4ABA) as migratory inhibitor applied on hardened concrete surface to curb corrosion due to combined chloride and carbonated environment. Electrochemical techniques (LPR and EIS), gravimetric analysis were applied to evaluate the corrosion performance and the inhibition mechanism of 4ABA. Chloride and carbonation profiles were developed to investigate the dominant cause of corrosion during the exposure. Visual and microscopic analysis of concrete surface and rebar surface was also done. Compressive strength test was performed to study the effect of corrosion inhibitor on strength property of hardened concrete. Results confirm that 4ABA prolonged the passive state of rebar when used as preventive measure and restrained the on-going corrosion process when employed as repair strategy. Combined exposure by chlorides and CO2 leads to redistribution of chloride ions in concrete matrix. The results also conclude that during the combined exposure, chloride ions initiate the corrosion process and carbonation aggravates this process. Application of 4ABA does not influence the strength properties of concrete. ABA has performed the inhibition by protective layer development and shield formation against the negatively charged corrosive ions. Blended cement concrete system which was observed to be more vulnerable to corrosion was seen to attain similar corrosion resistance as OPC concrete after inhibitor application.
... Carbonation of concrete can strongly influence the rate of corrosion due to chloride attack [9]. Along with the reduction in critical threshold level for corrosion initiation of steel [10], carbonation of concrete also accelerates the movement of free chloride ions and increases the total chloride ions available for attack on rebar surface [11,12]. It was also reported that the free to bound chloride ratio increases when carbonation is involved [13]. ...
This paper presents the performance of three generic compounds, 4-Aminobenzoic acid (ABA), 2-Aminopyridine (AP) and Salicyaldehyde (SA) as migratory inhibitor on hardened concrete surface to curb corrosion due to combined chloride and carbonated environment. Two types of cement viz. portland cement and fly ash blended cement were used to prepare concrete mixes. Electrochemical techniques (LPR and EIS), gravimetric analysis were applied to evaluate the corrosion performance. Percolation ability of the inhibitors was assessed by UV–visible spectroscopy. Also, chloride profile and carbonation depth was analyzed after definite durations of exposure to identify the dominant cause of corrosion and effect of inhibitor application on these two parameters. Electrochemical and gravimetric results conclude that steel in blended cement is more vulnerable to corrosion as compared to portland cement. Obtained carbonation depth and chloride profile revealed carbonation had significant impact on the corrosion during combined exposure. Degradation of reinforced concrete due to corrosion occurs in two phases in combined environment. In the first phase, chloride ions initiate the corrosion process causing pitting corrosion and carbonation dominates this process during the second phase by aggravating the corrosion mechanism. Application of CoI reduces the corrosion rate effectively, where ABA displayed highest inhibition efficiency of 79.64% in portland cement and 88.31% in blended cement concrete, followed by AP and SA. The inhibition order followed the order of its concentration at rebar level showing direct relation between the two parameters. Optical examination of exposed concrete surface and extracted rebar’s surface validated the inhibition effect of the inhibitors. Reduction in the crack width was noticed on the concrete surface with inhibitor application. Blended cement concrete system which was observed to be more vulnerable to corrosion before the application of inhibitors was seen to attain similar corrosion resistance as portland cement concrete after inhibitor application.
... It was found that when the cation type was Mg 2+ , the pH of the sample pore solution decreased slightly, the free Clconcentration decreased with the increase of Mg 2+ concentration, and the corrosion of Na 2 SO 4 was opposite. Hussain [74] tested the effect of Na 2 SO 4 on Clbinding ability and found a similar law. Xu [75] studied the effects of Na2SO4、K2SO4、MgSO4 sulfate on the stability of bound Cland the results showed that more bound Clwas released under K 2 SO 4 attack and less bound Clwas released under MgSO4 attack. ...
... The total sulfate oxide content is totally 3.3 wt% (1 wt % from cement clinker and 2.3 wt% from added gypsum seen in Table 1). Since the sulfate has been well identified to negatively affect the Fs formation, the chemical binding of chloride is suppressed to some extent, which results in less chloride bound in Fs [10,54,55]. With the addition of alumina compound and MK, more Fs is formed as aforementioned and more chloride is bound. ...
In order to prolong the service life of reinforced concrete structures either serving in chloride-rich environment or prepared with chloride contaminated ingredients, the chloride binding behaviors of cementitious materials with alumina compound addition are investigated in this work. The chloride binding capacity, phase conversion and solution chemistry of mixtures during chloride exposure were discussed. The applied alumina compounds are γ-Al 2 O 3 , γ-Al(OH) 3 and colloidal nano-alumina, and metakaolin is used as a reference additive. The results show that alumina compounds exhibit obviously higher potential of forming AFm-type phases than metakaolin and therefore significantly improve the chloride binding capacity. During chloride exposure, the charge-balancing anions like hydroxyls, carbonates and sulfates can be replaced by chlorides to form Friedel'salt and increases the pH of exposure solution. The released sulfates reacting with SO 4-AFm lead to delayed ettringite formation, binding large amount of mixing water and reducing calcium hydroxide content. Besides, the transformation of carboaluminate to Friedel'salt also accounts for partial reduction of calcium hydroxide in hydrated blended after chloride exposure, due to the released carbonates precipitating with calcium ions in the system.
... Compared with J4, J0 experienced an 86% reduction and an 89% reduction in bound chlorides before and after ECR treatment, respectively. This finding is consistent with previous studies [12,35]. The reason behind these observations is that under chloride and sulfate coexistence, C 3 A preferentially reacts with sulfates to first form ettringite. ...
... This suggests that depassivation is partly manage by the relative concentrations of free corrosion-inducement chloride ions and corrosion inhibiting hydroxyl ions in the pore water of hardened mortar paste. Hence, factors which influence the concentrations of the free chloride and hydroxyl ions in the pore solution are undeviatingly associated in determining corrosion risk (Hansson et al., 1985;Hussain et al., 1994;Andrade and Alonso, 2001;Lee et al., 2002;Fang et al., 2006). Passivation layer of reinforcing steel bar will be assaulted by chloride ions, and disturbance of passive film will start corrosion of reinforcing steel bar, initiating corrosion damage. ...
This study provides an insight for investigating the short-term effects of sodium sulfate and sodium chloride concentrations on the strength and durability characteristics of hardened mortars. For this aim, a comprehensive experimental campaign was conducted on 16 groups of mortar specimens, which were produced with and without reinforcing bars and cured in different environments such as air, water, sodium sulfate and sodium chloride solution. The 12 groups of the specimens, which were produced without reinforcing bars, were then subjected to flexural strength, compressive strength, unit weight, volumetric water absorption, capillary water absorption, ultrasound velocity and length change tests weekly between 7th and 77th days. The remain 4 groups of the specimens, which were produced with reinforcing bars, were then subjected to corrosion activity tests. The destructive and nondestructive test results showed that the specimens were produced with high water/cement ratio and then exposed to NaCl and Na2SO4 concentration has lower strength and durability characteristics than that of the specimens produced with normal water/cement ratio were exposed or not exposed to NaCl and Na2SO4 concentration.
... In cases when both carbonation and chloride ingress are at hand, general corrosion would co-exist with chloride-induced, localized corrosion on the steel surface. Here again, the initially chemically-bound chlorides could be released, increasing the chloride threshold level for corrosion initiation [47,48], and/or contributing to an already ongoing corrosion process. ...
The corrosion of reinforced steel, and subsequent reinforced concrete degradation, is a major concern for infrastructure durability. New materials with specific, tailor-made properties or the establishment of optimum construction regimes are among the many approaches to improving civil structure performance. Ideally, novel materials would carry self-repairing or self-healing capacities, triggered in the event of detrimental influence and/or damage. Controlling or altering a material’s behavior at the nano-level would result in traditional materials with radically enhanced properties. Nevertheless, nanotechnology applications are still rare in construction, and would break new ground in engineering practice. An approach to controlling the corrosion-related degradation of reinforced concrete was designed as a synergetic action of electrochemistry, cement chemistry and nanotechnology. This contribution presents the concept of the approach, namely to simultaneously achieve steel corrosion resistance and improved bulk matrix properties. The technical background and challenges for the application of polymeric nanomaterials in the field are briefly outlined in view of this concept, which has the added value of self-healing. The credibility of the approach is discussed with reference to previously reported outcomes, and is illustrated via the results of the steel electrochemical responses and microscopic evaluations of the discussed materials.
... Increasing the sulfate content in the chloride-containing environment has been observed to increase the penetration of free chloride ions in concrete (Maes and De Belie, 2014) and to retard chloride binding (Chen et al., 2016). The latter could be related to the preferential reaction of sulfates with C 3 A (Ehtesham et al., 1994;Luo et al., 2003). ...
Portland–limestone cement concretes were stored in two chloride–sulfate solutions, corresponding to exposure classes XS2, XA2 and XA3 specified by the standard BS EN 206:2013, at 5 ± 1°C. Their performance was evaluated in terms of the limestone content (15% or 35% w/w) of the cements used and the partial replacement of limestone cement with natural pozzolana, fly ash, blast-furnace slag or metakaolin. Sulfate attack was monitored through visual inspection of the specimens, mass measurements, compressive strength tests and X-ray diffraction analysis. The penetration of chloride ions was evaluated by determining total (acid-soluble) and free (water-soluble) chloride contents, as well as apparent chloride diffusion coefficients. Limestone cements favoured thaumasite sulfate attack and chloride accumulation in concrete compared to ordinary Portland cement. Mineral admixtures improved the concrete's durability against sulfate attack, inhibited chloride penetration and enhanced chloride binding. Fly ash, metakaolin and blast-furnace slag were more effective than natural pozzolana. Higher sulfate content of storage solutions promoted deterioration, and decreased chloride diffusion coefficients. The results obtained for concretes with mineral admixtures were competitive with those achieved when ordinary Portland cement was used.
... 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.
... In general, chloride ions diffuse more rapidly than sulfate ions in the hardened cement paste (Rahman and Bassuoni 2014). However, the presence of sulfates has been reported to decrease chloride binding by the hardened cement paste (Frias et al. 2013;Xu 1997), retard chloride diffusion (Chen et al. 2016), and increase the concentration of chloride ions in pore solution (Ehtesham Hussain and Al-Gahtani 1994). These phenomena are attributed to several factors, including the preferential reaction of sulfates with C 3 A (Ehtesham Hussain and Al-Gahtani 1994; Luo et al. 2003), the release of chemically bound chlorides because of the decomposition of Friedel's salt and its conversion into the more stable ettringite during sulfate attack (Brown and Badger 2000;Geng et al. 2015;De Weerdt et al. 2014;Xu et al. 2013), the release of physically bound chlorides previously absorbed on C-S-H phase (De Weerdt et al. 2014;Xu et al. 2013), and the increase of the pore solution alkalinity in the presence of sulfates (Dehwah et al. 2003;Maes and De Belie 2014;De Weerdt et al. 2014;Xu et al. 2013). ...
An ordinary portland cement and two portland limestone cements [15 and 35% weight-to-weight ratio (w/w) limestone content] were used for concrete and reinforced mortar specimens preparation. The specimens were exposed to two corrosive solutions (chloride sulfate and chloride) at 5°C. Total (acid-soluble) and free (water-soluble) chloride contents, and apparent chloride diffusion coefficients, were determined in concrete specimens. Reinforcement corrosion half-potential and current density, mass loss of steel rebars, and carbonation depth were measured in mortar specimens. Limestone cements showed very good behavior, although the environments were very corrosive. Total and free chloride ions concentration increased with exposure time and limestone content. Limestone cements showed less capability of binding chlorides than pure portland cement. The cement with low limestone content was the most effective in preventing reinforcement corrosion during mortar exposure to the combined chloride-sulfate solution, although it allowed the most intensive corrosion in the case of the chloride-bearing solution. The presence of sulfates led to higher chloride ion concentrations, less chloride binding and, generally, higher values of chloride diffusion coefficient, and also promoted reinforcement corrosion to a greater extent. Low temperature conditions retained a relatively low corrosion rate.
... A Na 2 SO 4 adagolás hatására aztán megnő a pórusvíz kloridion koncentrációja, mivel a SO 4 2--ionok jelenlétében az ettringit (C 3 A·3CaSO 4 ·32H 2 O) és a monoszulfát (C 3 A·CaSO 4 ·12H 2 O) képződés következtében a Friedel-só képződése háttérbe szorul. Adott kloridion tartalom esetén a Na 2 SO 4 a cement ekvivalens alkáli-tartalmától és C 3 A tartalmától függően növelheti, vagy csökkentheti a Cl -/OHarányt és ez által a korróziós veszélyt (Ehtesham Hussain et al, 1994). ...
... There are some literatures concerning the influence of C 3 A in cement on chloride binding capacity, depending on the source of chlorides. For example, chlorides in cast were significantly removed or/and bound by C 3 A in cement clinker [5,6]. However, chlorides penetrated from an external source had no benefit of C 3 A in being bound in the cement matrix [7]. ...
The present study concerns the influence of C 3 A in cement on chloride transport in reinforced concrete. Three modified cement was manufactured in the variation of the C 3 A content, ranging from 6.0 and 10.5 up to 16.9%. The setting time of fresh concrete was measured immediately after mixing, together with the temperature at the time of initial set. For properties of hardened concrete in the variation in the C 3 A, a development of the compressive strength and chloride permeation were measured using mortar specimens. Simultaneously, chloride binding capacity was measured by the water extraction method. To ensure the influence of pore structure on chloride transport, the pore structure was examined by the mercury intrusion porosimetry. As a result, it was found that an increase in the C 3 A content resulted in an increase in chloride binding capacity. However, it seemed that increased binding of chlorides is related to the higher ingress of chlorides, despite denser pore structure. It may be attributed to the higher surface chloride, which could increase the gradient of chloride concentration from the surface, thereby leading to the higher level of chloride profiles. Substantially, the benefit of high C 3 A in resisting corrosion, arising from removal of free chlorides in the pore solution, would be offset by increased chloride ingress at a given duration, when it comes to the corrosion-free service life.
... Thus sulphate ions contribute to reduce the chloride binding capacity of concrete. Holden et al. [94] reported that sulphate ions preferentially react with C 3 A. Hussain et al. [95] investigated the chloride uptake by cement pastes with different C 3 A contents and Na 2 SO 4 concentrations. They observed that chloride binding capacity decreased with the increase of sulphate concentration in the pastes. ...
... When sulphates are included in the concrete matrix the sulphate and the chloride ions have been observed to compete to react with the aluminoferrite phases of the concrete. As the sulphate ion typically binds more successfully than the chloride ions the result is often an increased level of free chlorides in the concrete pore solution 32 . The composition of the sulphate itself influences the degree with which they may compete with chloride ions in concrete. ...
... There are several ways by which chloride ions in concrete bind with the cement hydration products (Chatterjee, 1978;Jones, 1962). The C 3 A and tetra-calcium aluminoferrite C 4 AF phases of the cement are responsible for the binding of chloride ions to form Friedel's salt (FS), 3CaO.Al 2 O 3 :CaCl 2 :10H 2 O, and its ferrite analogue, 3CaO.Fe 2 O 3 :CaCl 2 :10H 2 O, respectively (Ethesham Hussai et al., 1994;Page et al., 1981;Rasheeduzzafar, 1992;Suryanashi et al., 1995;Taylor Woodrow, 1980). Friedel's salt is the common name of the chloride lamellar double hydroxide (LDH). ...
The hydration reactions of the systems C3A, C3A +gypsum (1 : 1.5 mole ratio) and C3A + gypsum + lime (1 : 1.5 : 1 mole ratio) in 0.1 and 1 molar solutions of sodium chloride at room temperature were studied. The hydration products formed after 2 min and up to 7 days were investigated using X-ray diffraction analysis. The filtered solutions were also analysed for sulfate, chloride, aluminium and calcium contents and the pH values of these solutions were determined. X-ray diffraction analysis indicated the formation of the chloro-compound known as Friedel's salt in all the studied systems. The ettringite phase and Friedel's salt appeared in systems containing gypsum and lime. Increasing the concentration of NaCl solution increased the rate of formation of both compounds. Thomas Telford Ltd
... Ehtesham Hussain et al (1994) investigated the chloride binding in three portland cements with C 3 A content 2.43, 7.59 and 14.00 %. The chloride source was NaCl dissolved in the mixing water (w/c = 0.6) to 0.6 and 1.2 % Clof the cement weight. ...
A literature review has been made on chloride binding based on a computer assisted literature search. In addition a few simple experiments have been made to clarify matter. The following conclusions are drawn: Chloride binding in cementitious systems is dominated by the content of C 3 A and C 4 AF no matter the chloride source. Both C 3 A and C 4 AF form Friedels salt, even with NaCl. The sulphates in the cement form stronger bonds than the chlorides, so only a fraction of the original content of C 3 A and C 4 AF is accessible for chloride binding. Chloride sorption is dominated by the amount of CSH gel. Calcium chloride can in addition be bound through the formation of compounds with calcium hydroxide. Such compounds are not formed to any significant extent by sodium chloride.
... In China, the output of slag is very large and the slag has to be reused efficiently, so it is necessary to have a detailed research about it. In China, the output of gypsum is also large and it is also necessary to reuse the gypsum efficiently, so some researches intended to reuse the GGBS blended with some gypsum because sulfates may improve the pore structure and decrease the chloride diffusion coefficient for the expanding reaction between sulfates and C 3 A, though sulfates may influence the chloride-binding capability for GGBS [9,10]. Thus, details about the effects of sulfates on the performance of GGBS to resist chloride-induced corrosion should also be known clearly. ...
Ordinary Portland cement (OPC) and OPC/ground granulated blastfurnace slag (GGBS) 70%, with or without 5% sulfates, were widely investigated in respect to their pore structures, chloride diffusion coefficients, internal and external chloride-binding capabilities by expression method and leaching method and the microstructure analysis on Friedel's salt such as differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). It can be concluded that GGBS can improve the pore structure of OPC and decrease the chloride diffusion coefficient greatly, and that sulfates do not do good for the pore structure and chloride diffusion for GGBS. GGBS increases the chloride-binding capability greatly without reference to the internal or external chloride and sulfates decrease the chloride-binding capability of GGBS greatly. It can be also found that the maximum intensity peak corresponding to Friedel's salt appears at about 8.0 Å, its endothermic effect appears at about 360 °C, its morphology is hexagonal slice whose size is about 2–3 μm; that the output of Friedel's salt formed by GGBS is much more than OPC; and that sulfates influence the output of Friedel's salt greatly. The corresponding mechanism was also analyzed.
The effect of sulfates on chloride ingress and microstructure in Portland-limestone cement – metakaolin paste was studied. Crystalline and amorphous phases were investigated with X-ray powder diffraction and solid-state nuclear magnetic resonance spectroscopy. Free chlorides were determined with ion chromatography. The influence of metakaolin on the microstructure and chloride binding was highlighted by comparing the material with pure Portland-limestone cement paste. The results showed that the high Al content in metakaolin increased the chloride binding ability of the binder and Al incorporation in the C‒S‒H phase. Close to the surface, metakaolin admixture contributed in greater polymerization of the silicate chains of C‒S‒H, while larger amounts of unreacted clinker were observed, compared to deeper parts. At higher depths, chlorides bound in the form of Friedel’s salt and free chlorides, were considerably reduced, attributed to refinement of the matrix. The presence of sulfates in the exposure solution affected chloride binding by inhibiting the formation of Friedel’s salt and increasing free chlorides in the pore solution. Moreover, sulfates decreased the polymerization of the silicate chains in the C‒S‒H of the Portland-limestone cement – metakaolin paste and reduced the hydration of clinker in pure Portland-limestone cement paste.KeywordsPortland-limestone CementMetakaolinChloride IngressSulfate AttackNMR Spectroscopy
This work examined the effects of seawater (SW) on the hydration of tricalcium aluminate (C3A) in C3A–gypsum and C3A–gypsum–Ca(OH)2 systems through the characterization of hydration heat release, the evolution of aqueous phase composition and hydration products with the hydration time. It was found that SW increased the dissolution driving force of C3A and solubility of gypsum, which accelerated the early hydration of C3A and the formation of ettringite (AFt), leading to a higher hydration degree of C3A at an early age compared with the deionized (DI) water–mixed pastes. After gypsum depletion to form AFt, and in the absence of Ca(OH)2, the formation of chloroaluminate hydrates was slower due to the insufficient Ca resulted in an accumulation of Al in solution. This would delay the subsequent transformation of AFt to monosulfate (SO4–AFm) and the formation of hydrogarnet (C3AH6), which would further reduce the hydration degree of the C3A at the later ages. However, in the presence of Ca(OH)2, the hydration degree of C3A–gypsum–Ca(OH)2 at later ages was increased, which was similar to that of the corresponding DI pastes. This can be inferred that the amount of Ca available in SW‐mixed cement concrete can affect the hydration degree of C3A in cement.
Lacking effective and in particular direct methods, the study on Cl⁻ and Na⁺ ion binding during hydration has rarely been reported. In this study, a specially developed Nuclear Magnetic Resonance setup was employed to study the Cl⁻ and Na⁺ ion binding of cement pastes during hydration. Influence factors, such as slag and fly ash replacement, on the ¹H, ³⁵Cl and ²³Na relaxation of the cement paste made with 1 mol/L NaCl solutions were investigated. It was found that the increase of slag in the cement gives rise to bigger pores during hydration, and the fly ash resulted in less water being consumed. The Cl⁻ signals would first be stable then gradually decrease as a function of time. The slag in cement has minor impacts on the Cl⁻ ions binding, and the fly ash replacement in the cement would result in less Cl⁻ ions binding during the hydration. Results also suggest that the slag could result in later Na⁺ binding, and the fly ash in the cement will significantly reduce the Na⁺ binding. Besides, the Cl⁻ ions will bind earlier compared to the Na⁺ ions, which is probably related to the characteristics of the hydrates. The normalized ³⁵Cl and ²³Na signal intensity, in general, decrease with water consumption reflecting the hydration. Furthermore, the early formed hydrates would consume relatively less water but bind more Cl⁻ and Na⁻ ions.
In order to prolong the service life of reinforced concrete structures either serving in chloride-rich environment or prepared with chloride contaminated ingredients, the chloride binding behaviors of cementitious materials with alumina compound addition are investigated in this work. The chloride binding capacity, phase conversion and solution chemistry of mixtures during chloride exposure were discussed. The applied alumina compounds are γ-Al2O3, γ-Al(OH)3 and colloidal nano-alumina, and metakaolin is used as a reference additive. The results show that alumina compounds exhibit obviously higher potential of forming AFm-type phases than metakaolin and therefore significantly improve the chloride binding capacity. During chloride exposure, the charge-balancing anions like hydroxyls, carbonates and sulfates can be replaced by chlorides to form Friedel'salt and increases the pH of exposure solution. The released sulfates reacting with SO4-AFm lead to delayed ettringite formation, binding large amount of mixing water and reducing calcium hydroxide content. Besides, the transformation of carboaluminate to Friedel'salt also accounts for partial reduction of calcium hydroxide in hydrated blended after chloride exposure, due to the released carbonates precipitating with calcium ions in the system.
Responding to the strategy of sustainable development, Cement manufacturing industry become an effective method to dispose municipal solid waste (MSW). Zinc is a heavy metal element that might be introduced by industrial wastes to the cement kilns, resulting in a performance degradation. High-Ferrite Cement (HFC), as a kind of sulphate-resistant Portland cement has attracted extensive interesting. Different from the mineral composition of Portland cement, HFC have a low C3S and high C4AF, which may be have a better solidification capacity due to the content increase of solid solution C4AF. This study attempt to explore the influence of doping ZnO on the performance of HFC. The results indicated that the compressive strength of 28 days increased from 57.1 to 70.3 MPa when the content of doping ZnO reached 1.5 wt% and hydration reactivity increased with the increase of ZnO content. The reason could be ascribed to the decrease of retardation effect on C3S and increase of promotion effect on C4AF with the change of miner composition of cement clinker. Beyond that, promotion plays a pivotal role between the two factors. The mechanism analysis indicated that ZnO doping promoted the transformation of Fe in the C4AF from [FeO4] to [FeO6] and increased the effective charge, resulting in a higher hydration reactivity. The result obtained varied from that reported in previous researches, and proved out that HFC can be a good material to Zn solidification/stabilization.
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.
Severe corrosion of post-tensioned (PT) tendons with pre-packaged thixotropic grout was documented in Florida bridges after less than 8 years of service. In those bridges, corrosion of steel tendon components was associated with deficient grout characterized by high moisture content, high sulfate levels, low chloride levels, and no indication of carbonation. Earlier research described in Parts 1 and 2 of this series of papers had emphasis on the role of sulfate ions in corrosion. However, at the time of observed corrosion of the bridge tendons in deficient grout, there were separate cases of bridges with similar pre-packaged grout materials but containing significant chloride ion contamination that exceeded typical acceptance limits. As a response to the potential risk to the bridge inventory, research was conducted to assess the risk associated with elevated chloride levels. Recommendations were made, but the proposed limits did not directly consider the effect of grout deficiencies such as that observed in the tendon failures in Florida. Therefore, there was interest to verify that the corrosion risk assessment of PT tendons by grout chloride concentration is adequate for adverse grout conditions such as due to segregation. In continuation of this series of papers on corrosion of post-tension strand in physically and chemically deficient grout, the work presented here sought to verify the role of elevated free sulfate ion concentrations in segregated grout containing low-level chlorides. Small and large scale laboratory specimens with geometries allowing for mix water volume displacement produced deficient grout. Physical and chemical deficiencies in segregated grout reduced the extent of chloride binding. Corrosion activity developed in grout with elevated sulfate concentrations. However, there were synergistic effects to reduce corrosion resistance for grouts with the combined presence of sulfate and chloride ions. It was shown that corrosion currents increased for steel in deficient grouts with elevated sulfate levels with the presence of low-level chloride ions (below conventional chloride threshold values). It was therefore evident that the assessment of corrosion susceptibility in deficient grout by chloride values alone is insufficient as sulfate ion presence and grout characteristics are also important.
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.
In this paper, the slump flow of the concrete, suspension, pH, corrosion effect, bleeding and the characteristics of coompressive strength were analyzed using antiwashout underwater admixture and antiwashout underwater agent+corrosion inhibitor mixed admixtures(1type). The results showed that there were no rare difference in physical properties but in the results of rapid corrosion tests there were lots of corrosion inhibitor ratio differences between concrete using only antiwashout underwater admixture and the corrosion inhibitor mixed(1type). In the case of only antiwashout underwater admixture 5.4%, the case corrosion inhibitor mixed(1type) 0.07%, the Antiseawater of the concrete which uses the Corrosion Inibitor Mixed(1type) appeared highly.
The diffusion of chloride ions in hardened cement paste (HCP) under steady-state conditions and accounting for the highly heterogeneous nature of the material is investigated. The three-dimensional HCP microstructures are obtained through segmentation of x-ray images of real samples as well as from simulations using the cement hydration model CEMHYD3D. Moreover, the physical and chemical interactions between chloride ions and HCP phases (binding), along with their effects on the diffusive process, are explicitly taken into account. The homogenized diffusivity of the HCP is then derived through a least square homogenization technique. Comparisons between numerical results and experimental data from the literature are presented.
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.
Corrosion behaviour of reinforcement steel embedded in cement pastes incorporating different amounts of mineral and chemical admixtures has been studied in 5% Na2SO4 solution using different electrochemical techniques. The results show that, the reinforced steel embedded in cement paste incorporating silica fume with different amounts of chemical concrete admixtures, manifests a high degree of passivation on soaking the samples in the investigated medium. The effect of each admixture changes depending on its type and concentration.
This paper describes a review on the major factors affecting reinforcement corrosion in concrete structures in the Arabian Gulf region and case studies on the performance of concrete structures in Madinat Al-Jubail Al Sinaiyah. The effect of high salinity and concomitant presence of chlorides and sulfates in ground water and soil and high ambient temperature on reinforcement corrosion are presented. Examples on the performance of concrete structures in Madinat Al-Jubail Al Sinaiyah, which has exposure conditions typical to those in the Gulf region, are presented. Emphasis is given on the structures that are generally susceptible to reinforcement corrosion. Available data on the performance of some of the concrete protection measures, such as use of mineral admixtures, increased cover over reinforcing steel, surface coatings and use of waterproofing membrane are also reported.
Cement mortar specimens made with three different C3A cements with a steel bar embedded centrally were partially immersed in a 5 percent NaCl solution, and half-cell potentials were monitored. When the potential value reached -270 mV versus saturated calomel electrode (SCE), taken as the threshold potential for the onset of corrosion of the embedded bar, the specimens were taken out and pore solution extracted from the mortar surrounding the bar. The pore solutions were analyzed for Cl- and OH- concentrations and threshold Cl-/OH- ratios computed. The threshold Cl-/OH- ratio seemed to depend on the pore solution pH and was found to vary from 1.28 to 2.0 for a pore solution pH of 13.26 to 13.36. The free (water-soluble) chloride concentration in the pore solution was converted into threshold free chloride and total (acid-soluble) chloride contents. It was found that the threshold free chloride content was 0.22 to 0.29 percent by weight of cement and was independent of the C3A content of the cement. However, the threshold total chloride content was found to depend on the C3A content of the cement and varied from 0.48 to 0.59, 0.73 to 0.85, and 1.01 to 1.20 percent for 2.43, 7.59, and 14 percent C3A cements, respectively.
The majority of concrete structures, particularly those in coastal environments, often suffer from both chloride and atmospheric carbonation attacks. Application of polymer-based concrete surface coating is one of the solutions available for the long-term protection of the reinforcement steel from corrosion. This paper deals with the performance of concrete slabs coated with acrylic-based coating against chloride and atmospheric carbon dioxide attacks. For this purpose, fully and partially surface-coated slabs were exposed to repeated cyclic wetting by sodium chloride solution followed by drying. After completion of the cyclic exposure regime, the slabs were exposed to laboratory drying environment and then were subjected to experimental investigations. The experimental results showed practically no chloride penetration into the concrete beneath the acrylic-based surface coating even after long-term exposure. On the other hand, for the uncoated concrete, the amount of chlorides and their depth of penetration into the concrete were found to be dependent on the water-cement ratio of the concrete. The amount of chlorides penetrating laterally, and the distance they penetrate from the uncoated concrete into the adjoining concrete below the acrylic-based surface coating is also a function of the w/c of concrete. Further, both x-ray diffraction studies and phenolphthalein spray tests showed the acrylic-based coating to be very effective in controlling the carbonation of the concrete below it, especially when the coating was applied by spraying. The coating maintained good adhesion with the substrate concrete even after the long-term repetitive wetting and drying cycles.
The aim of this paper is to investigate the time-dependent chloride binding capacity of various
types of cement pastes. Three types of cement (type I, III and V) were used in this study. Cement paste
specimens with different water to cement ratio, cement types, curing times and chloride exposure periods
were tested. From the experimental results, the chloride binding capacity of cement paste exhibits time-dependent. It depends on the curing time prior to chloride attack and exposure period in chloride solution.
Cement pastes having longer age prior to chloride exposure bind less amount of chloride than those exposed
at the earlier age. Longer exposure period of paste results in larger content of bound chloride. Moreover, the
chloride binding capacity also depends upon other factors, such as water to cement ratios and cement types.
Higher water to cement ratio results in smaller amount of bound chloride than the lower one does. Type V
cement binds less, but type III cement binds more amount of chloride than type I cement does.
The effect of magnesium and sulphate present in sea water on chloride binding in Portland cement paste was investigated. Ground well hydrated cement paste was exposed to MgCl2, NaCl, NaCl + MgCl2, MgSO4 + MgCl2 and artificial sea water solutions with a range of concentrations at 20 °C. Chloride binding isotherms are determined and pH of the solutions were measured. A selection of samples was examined by SEM-EDS to identify phase changes upon exposure. The experimental data were compared with calculations of a thermodynamic model. Chloride binding from sea water was similar to chloride binding for NaCl solutions. The magnesium content in the sea water lead to a slight decrease in pH, but this did not result in a notable increase in chloride binding. The sulphate present in sea water reduces both chloride binding in C–S–H and AFm phases, as the C–S–H incorporates more sulphates instead of chlorides, and part of the AFm phases converts to ettringite.
In this studies, methly celluloes was used as antiwashout admixture and when considering the physical properties and economical efficiencies of Underwater Concrete as the results of making an experiencing slump flow, flow loss, setting time, suspension and pH also compressive strength and underwater/an air compressive strength ratio according to the adding amount changes 5, 7, 9, 11 kg/ to Underwater Concrete of melamine superplasticizer, the using amount of melamine superplasticizer in Underwater Concrete approximately represents 9 kg/.
Modified hydrotalcites (MTHs) represent a group of technologically promising materials for addition to concrete to improve its durability in aggressive environment, owing to their low cost, relative simplicity of preparation, and plenty of unique composition variables that may be adopted. Up to date, a lot of academic work and commercial interest on MHTs have been invested, but relatively few studies focus on cementitious materials, particularly in exploiting their potential applications in corrosion protection of reinforced concrete structures. In this article, the mechanism of corrosion in reinforced concrete and concrete properties that affect corrosion of reinforcement are briefly introduced. In addition, the existing knowledge with regard to synthesis and characterisation methods of MHTs, ion exchange within the MHT structure as well as the application of MHTs in the cementitious materials were reviewed accordingly. As a new emerging class of smart additive of reinforced concrete, MHTs are expected to contribute to the effort of searching for effective measures to improve the durability of reinforced concrete.
This paper reports results of a study conducted to evaluate the releases of bound chlorides from pastes made of ordinary Portland cement alone and a mixture of ordinary Portland cement and the partial replacements of cement with 10% silica fume (SF), 30% pulverised fly ash(PFA) and 50% ground granulated blastfurnace (GGBS) subjected to Na2SO4, K2SO4 and MgSO4 attacks. The pastes were prepared by mixing water, cementitious materials and sodium chloride considering three levels of water/cementitious material ratios and four levels of sodium chloride. Powder samples collected by triturating the cement paste specimens were immersed in 5.0% Na2SO4, K2SO4 and MgSO4 solutions, respectively for allowing releases of bound chlorides. The chloride concentrations and pH values of the leachates obtained by filtering the solutions were measured, and the chemical phases of insoluble powders in the solutions were analysed by X-ray diffractometer (XRD). It has been found that the bound chlorides are partially released by sulphate attacks to form free chlorides. The released chlorides are affected by the water–binder ratio, total chloride content, mineral admixtures and sulphates with different associated cation type. After the sulphate attacks, Friedel’s salt has transformed to ettringite, which contributes to the releases of bound chlorides. Besides, by means of the index of Cl−/OH−, the influences of various mineral admixtures and sulphate types on the corrosion risk of steel reinforcement have also been discussed.
This paper discusses a durability study conducted on API class B cement, the type used in shallow oil wells, when exposed to aggressive formation water. Its resistance to the major ions, namely –SO4 = , Mg +2 and Cl - –, is related both to its capacity to assimilate the aggressive action of each harmful agent and to the changes in the chemical reactivity of some of its components. The methodology used consisted in preparing and immersing cement specimens in neutral solutions containing variable concentrations of these ions to monitor the chemical reactions taking place. These solutions were analyzed and XRD studies were conducted for over a year to identify mineralogical variations. The purposes of the study were to determine the effects of joint ionic attack on this kind of cement and to monitor the variations in the calcium concentration in the aqueous solutions of Na 2 SO 4 , MgCl 2 and NaCl in contact with API class B cement pastes
A new inspection technique that uses near-infrared spectroscopy is focused on as a method for detecting the chlorideion content in concrete structures. The authors have been working to confirm the possibility of estimating comparatively easily the chloride content in concrete without chemical analysis and in a short time on site. In this study, mortar specimens deteriorated by the combination of chloride attack and carbonation were prepared for investigating the method of evaluating the chloride ion content in mortar with the near-infrared spectroscopic technique. As a result, it was found that the chloride ion content in a carbonated mortar specimen can be evaluated with a method similar to that used to detect deterioration due solely to chloride attack.
The capacity of cement to bind chloride is considered to be one of the controlling parameters in the process of chloride-induced corrosion of steel in concrete. In this work, a literature review has been undertaken to identify factors affecting chloride binding. Data from 21 previously published works have been collated and used to develop a neural network model to predict the free chloride concentration as a function of 18 input variables. These predictions are relatively free of the indiscriminate variations present in individual measurements. The influence of factors not yet fully evaluated is identified. in addition, the relative importance of a wide range of factors is quantified. The neural network model provides a powerful tool for generating binding isotherms for use in models of chloride ingress into concrete.
This paper presents the results of a study conducted to assess the effect of sulphate contamination on the chloride-binding capacity of plain and blended cements. Cement paste specimens admixed with a fixed quantity of sodium chloride and varying dosages of sodium sulphate or magnesium sulphate were prepared. The pore solution was extracted from these specimens and analysed to determine OH- and Cl- concentrations. The chloride concentration increased with increasing quantity of sodium sulphate contamination. In the specimens admixed with magnesium sulphate, a marginal increase in the Cl- concentration was noted up to 1% SO42-. The increase in the Cl- concentration in the specimens admixed with more than 1% SO42- was minimal. In plain cements the chloride binding was influenced by the C(3)A content of cement. The Cl-/OH- values in plain cements admixed with sodium chloride and sodium sulphate increased marginally with increasing sodium sulphate concentration. However, the Cl-/OH- ratio in plain and blended cements admixed with sodium chloride and magnesium sulphate increased with increasing quantity of magnesium sulphate up to 1% SO42-. For SO42- concentrations of more than 1%, a decrease in the Cl-/OH- was noted.
This paper reviews the chloride binding of cement-based materials subjected to external chloride environments. Chloride ion exist either in the pore solution, chemically bound to the hydration products, or physically held to the surface of the hydration products. Chloride binding of cement-based material is very complicated and influenced by many factors, such as chloride concentration, cement composition, hydroxyl concentration, cation of chloride salt, temperature, supplementary cementing materials, carbonation, sulfate ions and electrical field etc. Four different types of binding isotherms, namely linear, Langmuir, Freundlich and BET binding isotherm have been proposed to describe the relationship between free and bound chloride, none of which can accurately express the relationships between free and bound chloride within the whole concentration range. Freundlich binding isotherm seems to be the most approximate one. However, some field data fit linear isotherm well. This may be ascribed to the leakage of hydroxyl ion. Many service life prediction models based on diffusion mechanism alone have been proposed during the past two decades. If chloride ion binding is not considered in the models, it underestimates the predicated service life.
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.
An investigation was made into the binding of chloride by hydrated cement in mortar or concrete and into the velocity of penetration of chloride into a cement sand mortar (1:3, wcr equals 0. 50). Of great influence appeared to be the degree of hydration of the cement, the maximum capacity of binding chloride of the relevant cement, the volume porosity of mortar or concrete, the pH and the circumstances of hydration (dry or wet conditions).
Description
The symposium on Chloride Corrosion of Steel in Concrete was presented at the Seventy-ninth Annual Meeting of the American Society for Testing and Materials held in Chicago, Ill., 27 June-2 July 1976. Committee G01 on Corrosion of Metals sponsored the symposium. D. E. Tonini, American Hot Dip galvanizers Association, Inc., and S. W. Dean, Jr., Air Products and Chemicals, Inc., presided as symposium cochairmen and also as editors of this publication.
Pore solution study has been carried out on 2.43 and 14% C3A hardened cement pastes. Data have been analyzed in conjunction with the data developed in two pore solution studies made by Page and Vennesland and Diamond using 7.37 and 9.1% C3A mature cement pastes. The results show that C3A and alkali contents of a cement have significant effect on its chloride-binding capacity. For similar alkali content, the levels of free chlorides in the pore solutions of 2.43 and 9.1% C3A cement pastes are respectively 4.7 and 2.8 times more than in a 14% C3A cement. The alkali content of a cement appears to have an inhibiting effect on its chloride-binding capacity. However, this effect is overshadowed by a conjoint strong elevation of the OH− ion concentration in the pore solution due to cement alkalies, causing a net lowering of the Cl−/OH− ratio which roughly ascertains corrosion risk. Threshold chloride values have been evaluated for different C3A cements. The threshold chloride content for a typical Type I portland cement with C3A upto 8% and Na2O equivalent upto 0.60%, may be taken as 0.4% chlorides by weight of cement. However, for a similar alkali cement with a high C3A content of about 14%, the chloride threshold value is 2.5 times higher and may be taken as 1.0% by weight of cement.
Chloride binding in concrete has been investigated by analysing pore solution expressed from cement paste specimens using a pore press. For chlorides introduced at the time of mixing, cement type, the type and proportion of cement replacement material, the chloride salt and total chloride content were found to be the most important factors governing binding. Binding also increased with increases in water/cement ratio, curing temperature and age. Similar, though less pronounced, trends were observed when chlorides were introduced externally by immersing thin discs of hardened, but relatively immature, cement paste, although SRPC gave similar results to OPC. Water/cement ratio and curing time prior to immersion had little effect, but the level of binding increased with exposure time and chloride concentration of the external solution. Solutions of calcium chloride, and particularly magnesium chloride, produced far higher levels of binding than sodium chloride.
The influence of various factors on the binding of chloride in cement and the chloride concentration of the pore solution was investigated. It was shown that the pore solutions of samples prepared under addition of chloride taken from the same cement and with identical content of total chloride exhibited different chloride concentrations only, if their hydroxide concentrations diverged. The fact that the residual chloride concentration depends on the composition of the pore solution in general, and on the hydroxide concentration in particular, was confirmed by tests with subsequent chloride addition. Chloride-free cement pastes, when stored in chloride solutions of the same concentration, had bound different quantities of chloride, if the hydroxide concentration of the storing solution (pH-value) was different.
The influence of an Australian flyash on Cl− and OH− ion concentration of cement mortar pore solutions was investigated by preparing NaCl and CaCl2-bearing mortars with 30% replacement of cement with flyash, and analyzing the pore solutions extracted from the mortars cured for prescribed times up to 12 weeks. The flyash had little effect on Cl− ion concentration in pore solutions of mortars below at least the dosage of 2% Cl− as CaCl2. However, the addition of the flyash considerably reduced Cl− ion concentration in mortars treated with NaCl at 1 and 2% Cl− level. It was also found that the flyash raised the Cl−/OH− ratio in pore solution at the dosages up to 2% Cl− in both calcium and sodium chloride-bearing mortars.
A device is described that has been used for several years for expression pf pore solution from hardened portland cement pastes and mortars. Particulars with respect to the design, fabrication, and operation of such equipment are given, and methods for the analysis of the resulting small volumes of pore solutions are briefly discussed. It is believed that the compositions of the pore solutions obtained are representative of that of the bulk of the pore solution within the paste or mortar from which the solutions have been obtained.
The relative tendency of different Portland cements to remove chloride ions from concrete mix water by forming insoluble complexes is an important determinant of the corrosion behaviourod steel in concrete. Whilst the C3A phase plays a dominant role in binding chloride ions, other cement minerals may be of secondary importance but their effects are not well established. The reported investigation is an attempt to elucidate the extent to which chloride binding occurs within the hydration products of the C3S (alite) phase of Portland cement when sodium chloride is present in the mix water.
Calcium chloride may be present in the free, adsorbed or interlayer state in hydrating tricalcium silicate. Attempts have been made to study these states to correlate some of the physical, chemical and mechanical properties. Le chlorure de calcium peut se présenter à l'état libre ou absorbé ou encore dans les couches intermédiaires au cours de l'hydratation du silicate de tricalcium. On a tenté d'étudier ces états et de faire le lien entre certaines propriétés physiques, chimiques et mécaniques. RES
Chloride Corrosion of Steel in Concrete
- Mehta