Search

Calcium sulfoaluminate (CSA) cements are widely being promoted as alternative low CO2 binders. CSA cements can also be expansive and designed to be shrinkage-compensating. The main phase of CSA cement is ye’elimite, which hydrates in the presence of calcium sulfate to form ettringite as the main hydration product. The availability of calcium sulfate can be used to control the hydration kinetics of ye’elimite, which affects the expansion characteristics of CSA cement. Sulfates in the form of gypsum or anhydrite are usually blended with CSA cement in the manufacturing stage. The presence of sulfates in the external environment also affects the expansion characteristics of CSA cement. This study aims to understand the effect of different exposure conditions on the expansion characteristics of CSA-based blended cement. The expansion of the specimens exposed to calcium sulfate solution was found to increase with the amount of calcium sulfate. The addition of CSA cement to Portland cement was found to have a significant influence on the early age expansion characteristics of the system, without affecting the mechanical properties such as compressive strength and dynamic modulus.

© The Minerals, Metals & Materials Society 2019. Slags with varied amorphous and crystalline content, typical of iron and steel production, are generally underutilized. One promising reuse pathway for these wastes is chemical activation, producing alternatives to conventional building materials with lower embodied energy. The formation of a hardened binder is dependent on the slag mineralogy and, specifically, the reactivity of relevant phases. Reactivity can be understood by monitoring elemental dissolution rates through inductively coupled plasma (ICP-OES) analysis. Post-dissolution ICP analysis of activating solution and spectroscopic analysis of remaining solids was performed on several highly crystalline slags and on relevant synthetic minerals to track changes in chemical and phase composition. Amorphous and ionic phases have been observed as more reactive than other crystalline phases. This work aims to inform future studies on waste blending in alkali-activated systems, a promising avenue for valorization of industrial wastes with varied physicochemical properties. To this end, dissolution tests with varied initial Si, Al, and Ca concentrations in activating solution were also performed.

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. Keywords: Biomass ash; Clay; Characterization; Pozzolanicity; Alkali-activation; Amorphous content, National Science Foundation (Grant DMR-1419807)

R27-139 (Phase 2), The application of pre-soaked lightweight aggregates (LWA) as an internal curing agent in concrete to reduce the cracking due to drying shrinkage is thoroughly studied in this report. It is determined that although LWA can significantly reduce autogenous shrinkage, its effect on drying shrinkage is minimal and in some cases it can even increase the drying shrinkage. Moreover, the combined effects of LWA and expansive cement (Type K) and LWA and shrinkage-reducing admixtures (SRAs) on drying shrinkage is also studied. It is shown that addition of Type K cement or SRA to mixtures containing LWA can significantly reduce drying shrinkage and make the mixture more volumetrically stable.