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Calcium sulfoaluminate belite (CSAB)-based cement exhibits useful properties such as low CO2 footprint, high early-age strength and shrinkage compensating behavior. Our previous study examined the mechanism of carbonation in CSAB-based binder and reported a higher degree of carbonation in CSAB-based binder compared to Portland cement (PC) binder. This study examines the admixing strategies to improve the carbonation resistance of CSAB-based binders. The addition of gypsum or calcium hydroxide reduced the carbonation depth (in natural and accelerated environments) in the CSAB binder. Gypsum addition reduced the pH and resulted in pore refinement. Whereas calcium hydroxide addition increased the pH and promoted the formation of monosulfate (AFm). Although the carbonation depth was reduced in the presence of gypsum or calcium hydroxide, the addition of calcium hydroxide offered a better admixing strategy due to its higher pH which is crucial for the passivation of reinforcement. [ABSTRACT FROM AUTHOR]

Calcium sulfoaluminate belite (CSAB) cement has gained prominence as a viable environmentally friendly substitute for conventional portland cement (PC). The current study investigates the relative performance of expansive and nonexpansive CSAB cement-based concretes, and PC-based concretes when subjected to chloride-rich conditions. Multiple testing methodologies, including surface resistivity measurements, chloride migration, rapid chloride penetration, long-term bulk diffusion, and water sorptivity, were employed to assess the durability of these concrete systems. Surface resistivity measurements indicated that CSAB systems exhibited significantly higher resistivity when compared with PC-based counterparts. Increased resistivity in CSAB systems was influenced by the conductivity of the pore solution, emphasizing that the formation factor provides a more accurate representation of the pore structure within the system. The expansive and nonexpansive CSAB cement–based concrete outperformed PC-based concrete in migration-based tests and rapid chloride penetration test (RCPT). In contrast, the CSAB and PC systems demonstrated similar performance in the long-term bulk diffusion-based test. Although CSAB systems exhibit finer pore structures than PC-based counterparts, their performance in chloride-rich environments is affected by their reduced binding capacity. The study emphasizes that the conclusions drawn from accelerated tests and resistivity measurements of CSAB cement–based concrete must be cautiously interpreted because these results may not indicate real-world performance. [ABSTRACT FROM AUTHOR]

Calcium sulfoaluminate belite (CSAB) binder is an alternative low CO2 binder. CSAB cement has ye'elimite as the primary clinker phase which hydrates to form monosulfate or ettringite as the main hydration product. The hydration and mechanical characteristics of CSAB cement and PC-CSAB blended cement have been reported in several studies; however, studies on the durability characteristics such as carbonation are limited. This study focuses on evaluating the microstructural and mechanical alterations due to carbonation in a CSAB binder system and understanding the underlying mechanism of development of the carbonation front. CSAB binder was found to carbonate rapidly compared to PC binder, accompanied by a reduction in compressive strength. This was attributed to the increase in the pore volume due to the carbonation of the ettringite-rich microstructure, facilitating further ingress of CO2 into the microstructure. The rate of carbonation in CSAB binders diverged significantly from the square root of time model used for PC binders. [ABSTRACT FROM AUTHOR]

Calcium sulfoaluminate (CSA) cement is a low-CO2 binder exhibiting useful properties, such as shrinkage compensation and rapid hardening, which can be achieved by altering its phase composition. In this paper, a hypothetical scenario of CSA cement manufacturing at an existing Indian cement plant is investigated for the environmental consequences (that is, CO2 emissions and energy consumed) using the life cycle assessment methodology. Thirteen laboratory-scale studies from the literature were selected for potential upscaling to industrial level production. The analysis showed that the manufacturing of CSA clinker could result in a 15 to 55% reduction in the CO2 emissions without a significant change in energy consumption when compared to ordinary portland cement. The impacts of CSA cement manufacturing were comparable to those of blended cements, such as those with slag and fly ash. [ABSTRACT FROM AUTHOR]

An untapped source of amorphous SiO2, industrially generated Indian biomass ash (SA)—90% amorphous, with composition of ~60% SiO2 and ~20% unburnt carbon—can be used to produce cementitious and alkali‐activated binders. This study reports dissolution of amorphous Si from SA in 0.5 mol/L and 1 mol/L aqueous NaOH, with and without added Ca(OH)2, at SA:Ca(OH)2 wt% ratios of 100:0, 87.5:12.5, and 82.5:17.5. Monitoring of elemental dissolution and subsequent/simultaneous product uptake by ICP‐OES offers an effective process for evaluating utility of industrial wastes in binder‐based systems. After 28 days in solution, up to 68% of total Si is dissolved from SA in 1 mol/L NaOH, with values as much as 38% lower in the presence of Ca(OH)2, due to the formation of tobermorite‐like C‐S‐H. FTIR, 29Si MAS‐NMR, and XRD are used to characterize solid reaction products and observe reaction progress. Product chemistries calculated from ICP‐OES results and verified by selective dissolution in EDTA/NaOH—namely, Ca/Si of 0.6‐1 and Na adsorption of 1‐2 mmol/g—are found to be consistent with those indicated by aforementioned techniques. This indicates the efficacy of ICP‐OES in estimating product chemistry via such a methodology. [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]

Calcium sulfoaluminate ( CSA) cements have lower carbon footprint than that of portland cement, which makes them a suitable alternative as a sustainable cementitious binder. Early-age expansion of CSA cements can be exploited to induce compressive stress in restrained concrete which can later counteract tensile stress developed during drying shrinkage, thus enhancing the resistance against shrinkage cracking. However, a proper understanding of the expansion behavior is critical to eliminate any risk related to expansion-induced cracking. This study examines the expansion and hydration characteristics of various ordinary portland cement ( OPC)- CSA blends. Early-age expansion of paste samples was monitored. The increase in CSA cement content increased the extent of expansion. Samples having the highest CSA content (30% by mass) exhibited excessive expansion which led to their cracking. Quantitative X-ray diffraction, pore solution extraction, porosity, tensile strength, and dynamic modulus tests were performed to monitor the physico-chemical changes in OPC- CSA blends. It was shown that the ettringite supersaturation in the investigated systems gave rise to the crystallization stress, responsible for the expansion. Thermodynamic models enabled a reasonable prediction of tensile failure, particularly in the blends with the higher CSA content. [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]

Fresh and hardened properties of a suite of cementitious binders with cement kiln dust (CKD) as the main binding component (70% by weight) are evaluated in this study. Two CKDs with different chemical and physical properties were used in formulating CKD-fly ash (FA) and CKD-slag mixtures without portland cement. The setting time, workability, and strength development of these pastes were evaluated first and the best-performing binders were then used as a component in making concrete. The strength and durability of such concrete is also evaluated. The CKD (I)-slag combination outperformed all other mixtures with respect to the strength and durability performance under various curing conditions. The elevated temperature curing was found to be essential for the property development of the CKD-FA binder. The performance of CKD containing mortar mixtures with respect to the delayed ettringite formation (DEF) and the alkali-silica reaction (ASR) was also good. The CKD that exhibited better performance contained 5% free lime, 3% Na2Oeq alkali, and 10.6% SO3 with an average particle size of 4 mm (0.00016 in.). [ABSTRACT FROM AUTHOR]