Mitigating the risk of early age cracking in fly ash blended cement-based concrete using ferronickel slag sand

Abstract

A concrete mix (FNS25) including 50% natural sand replacement by ferronickel slag (FNS) sand and 25% ordinary portland cement (OPC) substitution by fly ash (FA) was considered to mitigate the risk of early-age cracking in fly ash blended cement-based concrete. Experiments were carried out to accurately quantify early-age shrinkage and tensile creep and assess their influence on early-age cracking in reinforced concrete members. The results show the free shrinkage strain is not influenced by either fly ash or FNS significantly, whereas the tensile creep of FNS25 is significantly larger than that of both OPC100 and FA20. Both restrained ring test and simulations on reinforced concrete members confirm that partly replacing conventional sand by FNS sand reduces the risk of early-age cracking. Microstructural analysis of the Interface Transition Zone (ITZ) of FNS sand shows that excess in Portlandite is absent in FNS sand ITZ leading to a higher early-age tensile strength of FNS25 concrete.