Properties and activation modification of eco-friendly cementitious materials incorporating high-volume hydrated cement powder from construction waste

Abstract

Utilizing hydrated cement powder (HCP) as alternative binder in new cementitious materials provides a new way of recycling construction waste, while the relatively low activity of HCP limits its application to some extent. This work investigated the properties and heat activation modification of mortar including high-volume HCP. The HCP with irregular micro-structure mainly contains C-S-H gel, calcium hydroxide, calcite and quartz, and the incorporated HCP in cementitious materials reduces the number of new hydration products. The HCP after heat activation appears new active components (such as calcium silicate and calcium oxide), and the addition of such heat-activated HCP improves the micro-structure and helps the hydration reaction of new paste. The nanoindentation test highlights that the elasticity modulus and indentation hardness of paste including heat-activated HCP are higher relative to paste including untreated HCP. The activity index of HCP ranges from 73.63% to 91.81% as the modification temperature increases from 20 °C to 600 °C. Incorporating high-volume HCP is detrimental to the mechanical strength and transport properties of newly-prepared mortar, and the compression strength and capillary absorption coefficient of mortar with 50% HCP is approximately 50% lower and 193.7% higher relative to plain mortar. The activation modification of HPC reduces its adverse impact on performance of newly-prepared mortar, and the performance of mortar including HCP after 400–1000 °C activation is obviously better relative to mortar with untreated HCP. Based on the micro-characteristics, mechanical performance and transport properties, 600–800 °C activation temperature is recommended in modify the performance of cementitious materials incorporating high-volume HCP.