Freeze-thaw resistance and seawater corrosion resistance of optimized tannery sludge/metakaolin-based geopolymer

Abstract

In this study, tannery sludge was used to synthesize a geopolymer with optimum mixing proportions of raw material determined using Design-Expert. Compressive strength and total chromium leaching concentration were considered as markers for evaluating the performance of the geopolymer as a building material. The durability of the geopolymer in terms of freeze-thaw resistance under sulfate attack and seawater corrosion resistance was also studied. X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy tests were performed for the micro-analysis. The results demonstrate that the geopolymer exhibited optimal performance when metakaolin, tannery sludge, sodium silicate, and sodium hydroxide used for the synthesis were mixed in the ratios 50.34%, 13.48%, 28.95%, and 7.23% (weight%), respectively (deionized water was added in a liquid-solid ratio (L/S) of 1:10 (mL/g)). For these mix proportions, the compressive strength of the geopolymer reached 50.37 MPa, while the total chromium leaching concentration was 2.440 mg/L (the chromium retention rate was 97.93%) at 7 days. Meanwhile, the geopolymer exhibited good resistance to seawater corrosion and certain anti-sulfate attack-freeze-thaw coupling ability. After 21 days of seawater corrosion test and 14 cycles of sulfate attack-freeze-thaw test, the compressive strength of the geopolymer was 32.64 MPa and 19.48 MPa, respectively. Thus, the geopolymer has potential as a building material in cold coastal environments.