GEO-POLYMER CONCRETE SOLIDIFICATION OF FOUNDRY SAND AND FLY ASH: CHARACTERIZATION OF HEAVY METAL LEACHING AND OPTIMIZATION OF COMPRESSIVE STRENGTH

Abstract

This research work evaluated the structural and environmental performance of partial fine aggregate replacement in low calcium fly ash in geo-polymer concrete (GPC), which consequently reduces its carbon footprint. The novelty of this research work is primarily in the utilization of waste foundry sand for partial replacement of fine aggregate in GPC. The brand name for a binder is Geo-Polymer (alkaline solution), which is emerging as an innovative environment-friendly construction material. In this study, we examined the effect of mixture ratios of ground granulated blast furnace slag (GGBFS), waste foundry sand, and fly ash on GPC characteristics. The cylindrical GPC sample mould size 100×200mm was made based on the statistical experimental design with varying fine aggregate (30–55 wt%), foundry sand (15–40 wt%) and fly ash (20–30 wt%). The total heavy metal concentrations in the material ash are determined by the method defined by Baker and Amacher, while heavy metal leaching by the MBA method and Korean standard leaching method. Field emission-scanning electron microscopy and energy dispersive X-ray diffraction (XRD) were used for the morphological characterization and mineral phase analysis. The optimum compressive strength of GPC was 19.0N/mm2 (7th day) and 22.2N/mm2 (28th day) from the mixture percentage of51.9wt% fine aggregate, 24.8wt% foundry sand and 23.3wt% fly ash. Under the same experimental condition, this was higher than that of the conventional concrete which was 16.5N/mm2 (7th day) and 18.5N/mm2 (28th day), respectively. The compressive strength of GPC increased with the increase in curing time from 7 to 28 days, respectively, which is due to the improved bonding of silicon dioxide and calcium oxide on GPC. Furthermore, cured GPC specimen achieved heavy metal immobilization in the range of 44-78% which is promising for environmental applications. The alkaline solution used for GPC converted the heavy metals compounds in the materials into highly insoluble metal hydroxide and simultaneously encapsulates the fly ash thermal residue. The leaching heavy metal concentration of cured GPC is Pb (0.18mg/l), Cr (0.015mg/l), Cu (0.15mg/l), Fe (0.87mg/l), Ni (0.0065mg/l) and Zn (0.02mg/l). These results ascertained that foundry sand can be used efficiently as an eco-friendly construction material in GPC by substituting raw materials which result in a cost carbon emission reduction. Though, this research shows the potential of substituting fine aggregate by foundry sand, further research are required to practically apply in the real field, considering the field condition and result of this fundamental experimental study.