Pore structure characteristics, mechanical properties, and freeze–thaw resistance of vegetation-pervious concrete with unsintered sludge pellets

Abstract

To make full use of municipal solid waste, the sludge was used to make unsintered sludge pellets. Then unsintered sludge pellets was used to make vegetation-pervious concrete. The effects of the sludge pellet content and the water-to-cement ratio (W/C) on the pore structure characteristics, mechanical properties, ecological properties, and freeze–thaw resistance of the concrete were investigated. The results show that sludge is suitable for preparing pellets due to its good plasticity and high SiO2 and Al2O3 content. A 1:2:1 gypsum/fly ash/lime curing agent is selected to cure unsintered sludge pellets. The total porosity, hydraulic conductivity, ecological properties, and freeze–thaw resistance of the pervious concrete improve with an increase in the sludge pellet content and W/C, while its compressive and flexural strengths decrease. The plant roots penetrate the pervious concrete slab and maintain normal growth after 30 days of germination. In addition, a model considering the effective porosity and mean pore size is proposed for predicting the pore channel tortuosity of pervious concrete. The Kozeny–Carman model for calculating the hydraulic conductivity of pervious concrete is then modified based on the established calculation model of pore channel tortuosity. A model is also developed for predicting the compressive and flexural strength of pervious concrete based on its total porosity and mean pore size. In addition, the mechanism for the freeze–thaw resistance of pervious concrete is analyzed according to hydrostatic pressure. This research explains the full utilization of municipal solid waste materials and guides further research into the properties associated with pervious concrete.