Influence of intensive vacuum mixing and heat treatment on compressive strength and microstructure of reactive powder concrete incorporating secondary copper slag as supplementary cementitious material

Abstract

In this study the effect of vacuum mixing and heat treatment on the compressive strength and microstructure of reactive powder concrete (RPC), made with secondary copper slag as partial cement replacement is investigated. The quickly cooled granulated copper slag was ground using a planetary ball mill. A low water-to-binder ratio of 0.185 was chosen. The series of concrete mixtures and cement paste samples were produced with copper slag contents from 0 to 20wt%. The pozzolanic activity of slag was determined by the Frattini test. The performance of RPC mixed under vacuum conditions and heat-cured was compared to that of RPC mixed at atmospheric pressure without heat treatment. The porosity evolution of RPC was investigated by mercury intrusion porosimetry.A higher workability of the fresh RPC was obtained by mixing under atmospheric pressure. The presence of copper slag in the RPC had no adverse effect on compressive strength for all treatments. The heat treatment decreases the porosity and enhances the RPC strength. Assessment of the pozzolanic activity by means of the Frattini test indicates low pozzolanic reaction of the slag after 15days. The presence of slag in the paste tends to decrease the total heat production of the paste. The use of copper slag as cement replacement in the RPC production decreases the energy consumption and reduces the carbon footprint.