Impact of hemp shives aggregate mineralization on physical–mechanical properties and structure of composite with cementitious binding material

Abstract

This article analyses the possibility of fibre hemp shives (FHS) to be used as lightweight aggregate in composite with cement binding material. Cement and plant origin aggregates are hardly compatible, because water-soluble or alkaline environment soluble compounds inhibit cement hydration. To avoid harmful effect on cement hydration, it is necessary to mineralize FHS aggregates with complex mineralizer (which consists of Al2(SO4)3 and Ca(OH)2) in order to minimize the impact of hydration retarders on cement hydration. Rational amount of super plasticizer for forming mixture is selected in accordance with viscosity of cement paste. Amount and ratio of mineralizer was selected according to kinetics of hydration temperature of forming mixture, compressive strength, ultrasonic pulse velocity (UPV). It was determined that the increase in the amount of mineralizer from 27% to 54 % (estimated based on FHS mass) promotes the cement hydration, shortens the time needed to reach EXO maximum and increases its temperature, because the higher content of the Ca(OH)2 participates in the process of dissolution and makes the EXO reaction faster. The highest acceleration of cement hydration in a composite sample is caused by optimum amount of component mineralizer which is 54%. The lower content of component mineralizer did not completely bind sugar released from FHS, therefore, causing inhibition of cement hydration. Optimal amount and ratio of mineralizer allow obtaining the compressive strength after 28 days of curing of 8.03 MPa as well as thermal conductivity of 0.179 W/(m K). Microstructure analyses show that cement matrix with optimal amount of complex mineralizer is dense enough and well bonded with new monolithic hydration products.