Hydration and material properties of blended cement with ground desert sand

Abstract

The potential of existing supplementary cementitious materials (SCMs), such as fly ash and slag, has been dramatically decreased after decades of use. For future development, finding new SCMs to address the sustainability issue of cement and concrete is essential. Due to its global distribution and reserves, and the fact that it has not been officially used for construction, desert sand may become a new option for SCM for cement. Since desert sand has a very fine and uniform particle size, regular milling in the field can conveniently transform it into a powder comparable to cement fineness. This study investigated the technical possibility of desert sand powder as an SCM through physical experiments, thermodynamic modeling, and life cycle analysis. The mechanical strength of blended cement with desert sand powder was generally lower than that of pure cement due to the cement reduction and increased effective water-cement ratio. When the dosage of desert sand powder was within 15%, the 28-day strength of blended cement exceeded 75% of that of pure cement, and the strength development of blended cement was better than that of pure cement after 28 days till long curing ages (112 days). Both the initial and renewed stages of early cement hydration were promoted by desert sand powder. The desert sand powder's leading minerals, quartz and calcite, participated in the cement hydration reactions, generating corresponding hydration products, calcium silicate hydrate (C-S-H) and carbonate-based aluminate ferrite mono-sulfate (AFm). The microstructure showed the interactions between the desert sand powder particles and the hydrated cement matrix, including physical and chemical aspects. In the case of high dosage, the hardened matrix's pore structure was apparent with a less dense matrix due to excess water and reduced hydration products. The thermodynamic modeling theoretically quantified the phase assemblage of hydrated cement with desert sand powder, connecting to the observed reactivity of desert sand powder in cement hydration. The life cycle analysis showed that the carbon emission of desert sand powder was comparable to the conventional SCMs (fly ash and limestone powder). However, if it was proposed to be used outside the desert and surrounding regions, the carbon emission may increase due to the extended transportation distance.