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.

While the incineration of biomass residues is gaining traction as a globally available source of renewable energy, the resulting ash is often landfilled, resulting in the disposal of what could otherwise be used in value-added products. This research focuses on the beneficial use of predominantly rice husk and sugarcane bagasse-based mixed biomass ashes, obtained from two paper mills in northern India. A cementitious binder was formulated from biomass ash, clay, and hydrated lime (70:20:10 by mass, respectively) using 2M NaOH solution at a liquid-to-solid mass ratio of 0.40. Compressive strength of the biomass ash binder increased linearly with compaction pressure, indicating the role of packing density. Between the two mixed biomass ashes used in this study, the one with higher amorphous content resulted in a binder with higher strength and denser reaction product. Multi-faceted characterization of the biomass ash binder indicated the presence of aluminum-substituted calcium silicate hydrate, mainly derived from the pozzolanic reaction.

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The present study aims at examining the physico-chemical factors influencing the expansion characteristics of OPC-CSA blend in the presence of mineral admixtures. Three different admixtures: Class ‗F' fly ash (‗F'FA), Class ‗C' fly ash (‗C'FA) and silica fume (SF) were used as 15%, 15% and 5% replacement of total cementitious binder. Longitudinal expansion of cement pastes prepared at w/cm-0.44 showed that the Class ‗F'FA increased the expansion whereas the Class ‗C'FA and SF reduced the expansion. The pore solution of the OPC-CSA cement pastes was extracted at different ages to monitor the concentration of various ionic species. The saturation level of ettringite was determined using a geochemical modeling program (GEMS). Furthermore, an upper bound of crystallization stress was estimated. The expansion behavior in the presence of Class ‗F'FA and SF was found to be influenced by the changes in the stiffness, whereas the expansion of the Class ‗C'FA-based mixture was governed by faster hydration of ye'elimite.

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