Mechanical Strengths of High-Strength Concrete Containing Waste Sludge from Thu Duc Water Supply Plant

An enormous amount of waste sludge (WS) is released from Thu Duc water supply plant every year, resulting in occupying a land area in the plant and causing air pollution. Accordingly, the aim of the present study was to explore mechanical strengths of high-strength concrete (HSC) using such WS as a partial replacement of Portland cement to reduce CO2 emission from cement production as well as to utilize such WS towards environmental protection. Four substitution ratios of Portland cement by WS were 0, 10, 20, and 30% by mass of cementitious materials. Mechanical strengths of HSC with a low water-to-cementitious materials ratio of 0.38 included compressive strength and flexural strength of hardened concrete up to an age of 56 days in addition to slump of fresh concrete. The experimental results showed that as the WS replacement increased from 0 to 30%, the slump of fresh concrete decreased by 14.3–57.1%, and the compressive strength and flexural strength of hardened concrete decreased by 12.9–40.1% and 11.9–46.2%, respectively. The compressive strength corresponding to an age of 28 days of hardened concrete with 10% WS replacement reached 64.9 MPa, satisfying the strength requirement prescribed in TCVN 10306:2014. In conclusion, the WS from Thu Duc water supply plant could be used as a partial replacement of Portland cement in the HSC production towards sustainable development in the construction industry.