Utilization of Gold Ore Tailings as a Partial Replacement to the Fine Aggregates in the Production of Geopolymer Concrete with Recycled Coarse Aggregates

Abstract

The mining industry generates a large amount of waste, particularly in the form of tailing dumps, which creates major environmental difficulties, such as air pollution, water pollution, soil erosion, acid mine drainage, and so on. Earlier studies confirmed that the mine waste could be used in making building materials, such as bricks, tiles, concrete blocks, pavement blocks, precast concrete elements etc. The Gold Ore Tailings (GOTs) are one of the waste materials in the mining industry. The disposal of these tailings could be the problem to human health and major environmental concern from several years. Hence, the attempt should be made for effective utilization of these mine waste in different forms. In this study, the GOTs were utilized as an alternative material to the River Sand (RS) in the production of Geopolymer Concrete (GPC). In total, 11 mix proportions of GPC cubes, beams and cylinders were prepared by partially replacing the class F Fly Ash (FA) with Ground Granulated Blast Furnace Slag (GGBFS) as binder in steps of 10% up to 100%, along with GOTs (as a partial substitute to the river sand in steps of 5% up to 30%) and Recycled Coarse Aggregates (RCAs). These mix proportions were named as Mix Proportion-I, Mix Proportion-II, Mix Proportion-III, Mix Proportion-IV, Mix Proportion-V, Mix Proportion-VI, Mix Proportion-VII, Mix Proportion-VIII, Mix Proportion-IX, Mix Proportion-X and Mix Proportion-XI respectively. In addition to the above said 11 mix proportions, one more set of GPC cubes, cylinders and beams were prepared using FA, GOTs and Natural Coarse Aggregates (NCAs), which is designated as Mix Proportion-XII. Furthermore, Conventional Concrete (CC) of M25 (CC1) and M40 (CC2) grades were created using a mixture of Ordinary Portland Cement (OPC) of 43 grade, RS, and NCAs with a water/cement (W/C) ratio of 0.45 and 0.4, respectively. Among 12 types of mix proportions, GPC sample GOT-12-0 of Mix Proportion-XII (i.e. FA-100%, GOT-0%, NCAs-100%) showed a maximum slump value of 89.3 mm, whereas GPC sample GOT-1-0 of Mix Proportion-I (i.e., FA-100%, GOT-0%, RCA 100%) exhibited the maximum slump of 65.3 mm. Further, Conventional Concrete (CC) of M25 (CC1) and M40 (CC2) grades were showed the slump values of 110 mm and 58.3 mm, respectively. vii The GPC samples were cast and cured at room temperature until the curing ages and after that the compressive strength, split tensile strength and flexural strength of samples were determined. The laboratory tests demonstrated a maximum compressive strength of 52.25 MPa, split tensile strength of 5.99 MPa and flexural strength of 7.98 MPa for sample GOT-11-15 (11 indicates Mix Proportion-XI and 15 indicates 15% of GOTs) of Mix Proportion-XI. For Mix Proportion-XII, the highest compressive strength of 43.71 MPa, split tensile strength of 4.17 MPa and flexural strength of 6.13 MPa was achieved for sample GOT-12-15 (12 indicates Mix Proportion-XII and 15 indicates 15% of GOTs). Further, the CC2 samples exhibited the maximum compressive strength of 47.4 MPa, split tensile strength of 4.4 MPa, and flexural strength of 4.89 MPa for 28 days of curing. Based on the test results, the sample GOT-8-15 (i.e., FA-30%, GGBFS-70%, GOTs 15%, and RCAs-100%) of Mix Proportion-VIII was considered as the best mixture among all the mix proportions, with a slump value of 35.1 mm, compressive strength of 47.8 MPa, split tensile strength of 5.01 MPa, and flexural strength of 6.98 MPa when compared to CC2 sample (i.e., standard mix of same composition). The developed GPC samples were tested to know their durability properties, such as resistance to sulphates and chlorides. The sulphate attack test was conducted by immersing the CC and GPC samples in 5% magnesium sulphate (MgSO4) solution for a period of 28 days, 56 days, 90 days, 180 days, 270 days, and 365 days. In this test, the GPC samples showed the reduction in compressive strength, which is slightly more when compared to CC samples, for 270 and 365 days of exposure condition. The Rapid Chloride Penetration Test (RCPT) was also conducted to know the chloride ion penetration in which GPC sample (GOT-8-15) exhibited less chloride penetration when compared to CC1 and CC2 samples. Further, the Toxic Characteristic Leaching Procedure (TCLP) analysis showed that the GOTs has very high concentration of hazardous metals, such as arsenic (As), zinc (Zn), iron (Fe), and mercury (Hg). But the concentration of cyanide (CN-) was minimum in GOTs. In this regard, geopolymerization would be a better method for immobilizing the hazardous metals present in GOTs. viii The mineralogical and chemical composition of raw materials (i.e., GOTs and FA) was analyzed using X-Ray Diffraction (XRD) and X-Ray Fluorescence (XRF), respectively. The XRD analysis revealed that the quartz has highest peak intensity of 55% in GOTs and 50% of corundum in FA. The XRF analysis exhibited that GOTs and FA have high silicon oxides up to 39% and 38% respectively, and hence these materials can be effectively utilized in the manufacture of GPC. The crushed GPC samples were analyzed using Field Emission Scanning Electron Microscopy (FESEM) to observe the morphological changes. The FESEM analysis indicated that Si and Al are the two main constituents in GOTs and FA. This analysis also revealed the existence of uneven forms of quartz particles in GOTs, as well as the spherical shapes of FA particles adhering in the RCAs. The GPC sample comprised 15% GOTs exhibited denser and compacted microstructures. The multiple regression analysis illustrated R2 value of 69.9%, 70.9%, and 68.0%, respectively for compressive strength for 3, 7, and 28 days curing period. Similarly, the R2 value for split tensile strength and flexural strength was 89.0% and 85.5%, respectively, for 28 days curing period. The P-value for the developed model was less than 0.05 and hence the developed model was considered as significant and best-fit model. Finally, the cost analysis was done to know the economic feasibility of raw materials. It was found that the cost of GPC was more than that of CC2 about 38.20%.