CHARACTERIZATION OF WATER TREATMENT SLUDGE AND ITS IMPLICATIONS ON CONCRETE AS A PARTIAL REPLACEMENT OF CEMENT

Abstract

Application of supplementary cementitious materials (SCMs) in concrete is advantageous as it reduces the need for cement production, thereby lessening the environmental carbon footprint. However, this practice is restricted the release of contaminants from concrete into the environment. This study aims to investigate the physical, chemical, morphological, and mineralogical properties of WTS and evaluate its feasibility as a partial cement replacement in cement mortar and concrete. Moreover, this study evaluates the environmental impacts of cement production with optimal clinker replacement by WTS through heavy metal leaching and Life Cycle Analysis (LCA). Cement mortar and concrete specimens were prepared with various WTS addition levels, and tested for different properties of concrete and mortar. The leaching behavior of heavy metals was also investigated, while the LCA was performed using the cradle to-grave method. The study found that WTS particles are irregular with an average size of 9.20 µm. WTS has high SiO2, Al2O3, and Fe2O3 content which meet the pozzolanic standards. The cement mortar with the mix ratio of 1:2 and WTS of 7.5% shows the highest compressive strength compared to other mix ratios. In addition, flexural strength peaks at 5% WTS but continues to drop beyond this limit. However, compressive strength of the concrete is increased up to 5% WTS addition while, the unit weight decreases with higher WTS, ranging from 2160-2567 kg/m³. The leaching concentration trend of partially replaced concrete at 63 days was as follows: Cu > Mn > Ni > Cr > Fe > Cd. The differences in leaching concentration between the control and partially replaced concrete were determined to be 1.2-2.8 times higher for the 1:2:4 ratio and 1.3-3.6 times higher for the 1:1.5:3 ratio. However, concentrations stabilize after 40 days and stay within regulatory limits. The study also found that replacing 5% clinker with WTS in cement production reduces the carbon footprint by 1.91% and shows a reduction in various other environmental impact categories by 0.09% to 3.31%. This study demonstrates that WTS can effectively be used as a partial cement replacement, offering environmental benefits and improved mechanical performances at optimal levels.