Effect of silica fume and PCE-HPMC on LC3 mortar: Microstructure, statistical optimization and life cycle Assessment

Abstract

With immense carbon emissions, the cement and concrete industries account for nearly eight percent of the world’s total. As the demand for urbanisation increases, the carbon footprint of the industry will also increase rapidly. A sustainable and greener low carbon cement called limestone calcined clay cement (LC3) is being developed as a promising alternative to ordinary Portland cement (OPC). The present study investigates the effects of silica fume (SF) on LC3 with variable dosages of polycarboxylate ether-based superplasticizer (SP) and hydroxypropyl methylcellulose (HPMC) admixtures. Using three level-three factorial (33) Box Behnken Design and response surface methodology (RSM), SF content, SP content, HPMC content, and flow value were set as input parameters to optimise and evaluate the eight output response parameters, namely, water binder (w/b) ratio, compressive strength (7 and 28 days), modulus of rupture, porosity, water absorption, ultrasonic pulse velocity, and water sorptivity. With a combined desirability of 90.8% for an optimised mix, the model showed that with 0% SF, 0.811% SP, 0.923% HPMC, and 124.12 mm of FV, a LC3-50-based cement system with higher physico-mechanical properties can be developed. The microstructural analysis was also conducted through a scanning electron microscope (SEM), Thermogravimetric Analyzer (TGA), and X-ray diffraction (XRD). The results showed Calcium silicate hydrate (C-S-H) development along with consumption of portlandite (CH) for LC3-50-based cement systems. Sustainability analysis of LC3-based mortar in terms of carbon emissions showed a 33.82% reduction in CO2 emissions as compared to OPC.