Search

Calcium sulfoaluminate (CSA) cements exhibit useful properties such as shrinkage compensation and rapid strength development. Acid resistance of CSA cement is majorly governed by its phase composition that varies significantly depending on the desired properties. In this study, acid resistance of CSA cement (i.e., non-expansive) and gypsum blended CSA cement (i.e., expansive) is explored. The current work emphasizes that a small change in phase assemblage can cause large difference in the performance under acidic environment. Conventional acid immersion tests with hydrochloric acid (HCl) of 1 % and 2 % conc., and sulfuric acid (H 2 SO 4) of 2.95 % conc. were considered in the study. Furthermore, a recently developed acid consumption method was used to rank the binders with regard to their acid resistance in HCl and H 2 SO 4 environments. It was found that the gypsum-blended CSA cement showed poorer performance than CSA cement in acidic environment despite having marginally higher compressive strength before the acid exposure. [ABSTRACT FROM AUTHOR]

Biogenic acid attack of concrete is prevalent in sewers, posing a serious durability concern and financial burden. There are very limited number of field studies on durability of concrete under biogenic acid attack. Field study poses challenges with respect to the variation in climatic conditions and limited accessibility in sewers. Such a biogenic acid attack study in Indian conditions has not been performed. In this study, the biogenic acid resistance of Portland cement (PC) and calcium sulfoaluminate (CSA) cement-based binders under an in-situ sewer exposure is reported. The results show that the CSA-based binder used in this study outperformed PC in the biogenic acid resistance. The superior performance of CSA-based binder could be attributed to its acid neutralisation capacity offered by the aluminum hydroxide phase and bactericidal properties. For the first time, the bacteriostatic effect of CSA cement was demonstrated by analyzing the field exposed specimens. [Display omitted] [ABSTRACT FROM AUTHOR]

Calcium sulfoaluminate (CSA) cements were developed for shrinkage compensation of concrete. The expansive nature of CSA-based cements can be used to enhance the resistance against shrinkage cracking by inducing compressive stress in concrete. Because of the higher water demand of CSA cement for achieving full hydration, as compared with ordinary portland cement (OPC), elevated water-cement ratios (w/c) for OPC-CSA cement blends are required for a successful mitigation of shrinkage. This study examines the effects of presoaked lightweight aggregate (LWA) addition on deformation properties of OPC-CSA mortar and concrete as an alternative to increasing the w/c. The motivation behind this work is to promote CSA hydration and increase the early-age expansion of OPC-CSA blends by curing concrete internally while avoiding the undesirable impacts of increased w/c on the microstructure of the mixture. The influence of LWA addition on autogenous and drying shrinkage of OPC-CSA blend was studied. It is shown that the early-age expansion of OPC-CSA blends can be dramatically increased when internal curing is implemented using LWA. Based on thermogravimetric (TG) results, it is indicated that the increase in expansion is partially due to the enhanced hydration of CSA cement in the mixture, which results in an increased rate of ettringite formation. Furthermore, the effects of LWA on total capillary porosity and compressive strength of OPC-CSA blends was also examined to verify the benefits of using LWA to promote CSA hydration as compared to increased w/c. [ABSTRACT FROM AUTHOR]

Cementitious materials are alkaline in nature. As a result, they are prone to neutralisation reaction by acids and possible deterioration. Among the existing binders, the acid resistance of calcium sulfoaluminate (CSA) cement is not well explored. Moreover, the phase composition of CSA cement varies significantly to reflect its expansive and non-expansive characteristics. In this article, the effect of chemical composition on acid resistance is evaluated in terms of acid neutralisation capacity (ANC) or acid consumption, providing a novel approach to evaluate the durability of CSA cements in low pH environment. This research focuses on evaluating citric acid and sulfuric acid resistance of Portland cement (PC), high ye'elimite CSA cement (CSA (HY)), and calcium aluminate cement (CAC). The tests were performed on monolithic specimens as well as powdered hydrated samples using an autotitrator. The acid resistance of three binders could be evaluated from total acid consumption and predicted based on early period of test depending on a binder's acid - pH interaction curve. Furthermore, a procedure was developed to correlate powder and monolithic tests. [ABSTRACT FROM AUTHOR]

Calcium sulfoaluminate (CSA) cements were developed for shrinkage compensation of concrete. This study investigates the expansion characteristics of CSA-portland cement (CSA-OPC) systems in the presence of mineral admixtures (MA). Unrestrained expansion of CSA-based cement pastes incorporating Class C fly ash (FA), Class F FA, and silica fume (SF) were monitored at water-cementitious material ratios (w/cm) of 0.34 and 0.44. Despite the same amount of expansive component, CSA-OPC-MA mixtures exhibited noticeable difference in expansion. The Class F FA increased the unrestrained expansion at early age for both w/cm, which was attributed to lower material resistance (that is, stiffness) due to the presence of Class F FA. Furthermore, the expansion of the Class C FA-based mixture ceased at 2 days at both w/cm due to faster consumption of ye'elimite. A calorimetric study of Class C FA-based mixture revealed early depletion of sulfates, which correlated well with the completion time of expansion. Additionally, the presence of SF lowered the expansion, which was attributed to the lower alkalinity of pore solution, incomplete hydration of ye'elimite, and increased material stiffness. [ABSTRACT FROM AUTHOR]

Calcium sulfoaluminate (CSA) cement-based binders are low CO 2 binders which exhibit rapid hardening or shrinkage compensating characteristics. Due to their unique properties, they have potential to be used in concrete elements exposed to acidic environment such as sewage system. In this paper, the performance of CSA-based binders in acidic environment is examined and compared against Portland cement (PC). Attack of sulfuric acid and citric acid on PC and CSA-based binders was evaluated with respect to mass loss, dimensional change, cumulative H+ ion neutralisation, strength loss, and changes in mineralogical and microstructural characteristics. CSA-based binder exhibited higher resistance than PC-dominated binder in citric acid attack (pH ∼ 2–3), whereas PC-dominated binder outperformed CSA-based binder in case of sulfuric acid attack (pH ∼ 1.5–2). The mechanism of acid attack was found to be dependent on acid type. A calcium citrate salt was identified as the major product in case of citric acid attack of PC-dominated binders. [ABSTRACT FROM AUTHOR]