Influence of admixing natural pozzolan as partial replacement of cement and microsilica in UHPC mixtures

Abstract

Ultra-high performance concrete (UHPC), comprising of high amounts of cement and microsilica as binder and micro filler, is a new generation of concrete possessing highly dense microstructure with excellent mechanical properties, durability characteristics and ductility (fracture toughness). However, the use of high amounts of cement and microsilica makes UHPC costly and environment-unfriendly. In the present study, an effort is made to study the effects on properties of UHPC mixtures due to incorporation of natural pozzolan (NP) as a partial replacement of cement and microsilica. Targeting a significant reduction in consumption of cement and microsilica without compromising the required workability, six UHPC mixtures were considered. The first mixture was taken as control mixture without replacement of cement and microsilica by NP. In the second and third mixtures, 25 and 50% microsilica was replaced by NP, respectively. In fourth, fifth and sixth mixtures, 10, 20 and 30% of cement was replaced by NP, respectively. Specimens were moist-cured for 14 days before exposing them to air in the laboratory conditions. All the six UHPC mixtures were tested to determine the mechanical properties (compressive and tensile strengths, modulus of elasticity, and fracture toughness), drying shrinkage, and chloride permeability. Test results indicate that the replacement of cement (up to 30%) and microsilica (up to 50%) by NP did not significantly affect the fresh and hardened properties of UHPC mixtures confirming the potential of using NP for producing cost-effective and environment-friendly UHPC mixtures.