Sodium Aluminate Activation of Non-ferrous Waste Foundry Sand: A Feasibility Study

Abstract

The study was conducted to investigate the feasibility of sodium aluminate activation of nonferrous waste foundry sand. The aim was to solidify nonferrous foundry sand via geopolymerisation into useful civil engineering materials. Green foundry sand was mixed with sodium aluminate to make a paste which was filled into 50 × 50 × 50 mm3 mold. The mixture was cured in an oven for 5 days. The concentration of sodium aluminate, granulated blast furnace slag (GBFS) : waste foundry sand (WFS) ratio, liquid to solid ratio (L/S) and temperature were varied respectively to establish the optimum curing conditions. The results indicated that sodium aluminate has a high potential to be used as an alkaline activator in the synthesis of WFS geopolymers. The geopolymer prepared with 6 M sodium aluminate yielded the highest UCS of 3.59 MPa after curing for 5 days which did not meet the minimum requirements for ASTM C34-13, C129-14a and South African standard (SANS227: 2007). The addition of GBFS in the WFS geopolymer mix design enhanced the mechanical strength of WFS geopolymers. The GBFS modified WFS geopolymer prepared with 50% GBFS, 4M sodium aluminate, L/S ratio of 0.15 and cured at 80°C yielded the highest UCS of 10.57 MPa. The GBFS modified WFS geopolymer met the minimum requirements for ASTM C34-13, C129-14a and South African standard (SANS227: 2007). The results also show a, high potential ability to valorise WFS and GBFS reduce building material problems, while also providing the building and construction industry with a useful and inexpensive new raw material with less CO2 emissions.