Influence of Intensive Vacuum Mixing on the Compressive Strength of RPC Containing Secondary Slag as Cementitious Material

Abstract

This research investigates the influence of intensive vacuum mixing on the compressive strength of reactive powder concrete (RPC) containing secondary slag as cementitious material. The quickly cooled granulated copper slag (QCS) was ground intensively using a planetary ball mill. A low water-to-binder ratio of 0.185 was chosen for the RPC in this study. Various concrete and cement paste samples were produced with increasing copper slag contents from 0 to 20 wt.% in steps of 5 wt.%. Particle size distribution (PSD) and specific surface area (SSA) of the secondary slag were assessed using laser diffraction and the Blaine permeability test, respectively. The RPC mixes were evaluated on workability, density, and compressive strength. In order to obtain a homogenous mixture and improve the performance of RPC, a high speed mixer with vacuum was applied. The performance of RPC was assessed under vacuum conditions (100 mbar) as a comparison to that of the atmospheric pressure (1013 mbar). The microstructure of RPC was investigated by a scanning electron microscopy (SEM). The pozzolanic activity of QCS was determined by the Frattini test. At 28 days, the strength of RPC with copper slag prepared under 100 mbar was better than the reference (containing no copper slag). In contrast, the strength of RPC containing copper slag mixed under 1013 mbar was lower than the reference. Results also showed that 10% copper slag replacement for OPC under vacuum conditions gave the highest compressive strength. There is a slight increase in the RPC density under 100 mbar compared to the RPC density under 1013 mbar. The workability of fresh RPC under atmospheric pressure was higher than that of the fresh RPC under vacuum conditions. Assessment of the pozzolanic activity by means of the Frattini test indicates pozzolanic reaction of the secondary slag after curing for 15 days.