Flocculated foamed aggregate and macroporous concrete for use in ecological ditch: Phosphorus removal effect, basic physical property and mechanism

Abstract

Concrete ecological ditch is an effective management practice for agricultural non-point source pollution control. However, it is still a huge challenge to utilize the compositional and structural characteristics of concrete to achieve maximum interception of phosphorus nutrient. In this paper, foamed aggregates with flocculation function are designed as an alternative of traditional stones to prepare no-fine macroporous concrete and improve phosphorus-removal (P-removal) capacity. The results show that the P-removal rate increases with the increase of flocculant polyaluminum sulfate (PAS) content. Chemical adsorption is the main P-removal mechanism according to adsorption kinetics. The addition of PAS is beneficial to increase the average pore size and total porosity of FFA, especially for the volume proportions of >1.6 mm pores, which is attributed to the high hydrolysis heat of PAS promoting H₂O₂ foaming. According to the analysis of hydration heat, XRD, XRF and SEM-EDS, PAS accelerates the hydration of sulphoaluminate cement (SAC) to generate more ettringites to provide more ions exchange opportunities for PO₄^3- to replace SO₄^2-. PAS promotes the P-removal rate of macroporous concrete increase, and the compressive strength and dry density decrease, and the performance correlation coefficients reach above 0.9. This study proposes a novel and effective phosphorus removal method that is superior to traditional fillers such as ceramsites and zeolites, providing a theoretical basis for the preparation and application of fillers for concrete ditches and offering scientific support for the water purification science related to agricultural non - point source pollution.