Development of sustainable alkali-activated slag grout for preplaced aggregate concrete

Abstract

Cement production is currently the third largest source of CO2 anthropogenic emissions. To mitigate the associated climate change threats, alkali-activated systems have emerged as a promising cleaner alternative binder. The present study deploys orthogonal experimental design and ANOVA analysis to develop alkali-activated slag (AAS) grouts with adequate fresh and hardened properties for preplaced aggregate concrete (PAC). Alkali-activated slag grouts with different alkaline activator concentration (silicate modulus and Na2O%), water-to-slag (w/s) ratio and superplasticizer dosage were produced to determine the efflux time, which is the most important fresh state property of PAC. The compressive strength of grout mixtures with appropriate fresh state properties was determined at 7, 28 and 56 days. Moreover, scanning electron microscopy and X-ray diffraction analyses were carried out to assess microstructural features of the AAS grout. The experimental results revealed that most mixtures with w/s ratio of 0.55 had appropriate efflux time. For those mixtures with appropriate efflux time, the highest mechanical strength (56 MPa) was achieved by the mixture made with 6% Na2O (by weight of slag) and silicate modulus (Ms: Na2O/SiO2) of 0.8. Results of microstructural analyses corroborated mechanical strength results. SEM suggests that mixtures with low Na2O ratio should be used to mitigate microcracks observed at high Na2O dosage. Results indicate potential to develop sustainable AAS-PAC with much less paste volume, high recycled binder content, lower energy of production, and no rheological problems associated with aggregates.