Performance of permeable concrete mixes based on cement and geopolymer in aggressive aqueous environments

Abstract

The permeable pavement efficiently manages stormwater, which is acidic and contains fine sediments and heavy metals exhausted by vehicles driving on this material. The heavy metal removal in permeable concrete samples based on geopolymer and Portland cement was examined in this study. Their performance when exposed to strong acids and turbid water were also investigated. They were able to infiltrate 28 L of water in 60 min and gained a compressive strength greater than 25 MPa in 2 weeks after casting. However, it was found that its porous structure was clogged with fine sediments when water containing bentonite clay passed through them for multiple cycles. To evaluate their metal removal capacity, a concentration of 10 mg/l of cadmium-containing solution was passed through such samples for a continuous period of 8 h. They were able to trap nearly 95% of the cadmium ions from the simulated wastewater during the column experiment. Their adsorption behaviour fits well with the pseudo-second-order kinetic and Langmuir isotherm models, implying that the main removal mechanism is chemisorption. To examine their acid resistance capacities, cement- and geopolymer-based mortar samples were exposed to acids for 2 weeks. The acid-exposed samples were severely degraded, as the mass loss in the geopolymer was determined to be 64% lower than that of the cement sample. Geopolymer-based permeable pavements are ecological, harden in moist air, gain higher strength at early ages, are acid resistant, and also remediate groundwater contamination.