Experimental study on the effect of wastewater and waste slurry of mixing plant on mechanical properties and microstructure of concrete

With the increasing demand for concrete, there is an accompanying environmental pollution and resource shortage brought about by the concrete mixing and production process. To explore the methods of recycling concrete wastewater and waste slurry, this study attempts to use concrete mixing plant flushing wastewater and waste slurry for ready-mixed concrete production to study the effects of wastewater and waste slurry on the macroscopic mechanical properties and microscopic internal structure of concrete. The possibility of using wastewater and waste sludge for concrete preparation was investigated by using 0%, 10%, 30%, 50%, 75%, and 100% of wastewater to replace tap water for concrete mixing and 0%, 10%, 20% and 30% of waste slurry to replace cement. The results of the study showed that wastewater concrete has better compressive properties compared with ordinary concrete, in which the wastewater admixture of 75% can improve the compressive strength of concrete by about 20%, and the advantages are more obvious in its early age stage. The physical properties of the waste slurry dry powder prepared from waste slurry are close to those of fly ash and slag powder, which can theoretically be used to produce concrete and reduce production costs. The gelling substances contained in the wastewater can fill the pores of the concrete structure and improve its compressive strength. • The wastewater from the mixing plant can be used in concrete preparation. •Wastewater concrete has better compressive strength compared with normal concrete. •Wastewater can play a filling role in the pores of the concrete, increasing its denseness. •The cementitious materials contained in the wastewater were active, which promoted the hydration of cement and also produced more hydrated calcium silicate (C–S–H). •Wastewater improves its pore structure and interface characteristics and increases the compressive strength of concrete.