Study on mix ratio optimization of recycled aggregate pervious concrete based on RSM-BBD

To study the influence of recycled aggregates on performance permeable concrete, this paper selected ultra-fine fly ash (UFA), water-binder ratio (W/C) and hydroxypropyl methylcellulose (HPMC) as the influencing factors, and adopted Box-beheken design (RSM-BBD), with 28 d compressive strength, permeability coefficient and porosity as the response values. Results showed that the R² of the established regression models were >0.95, indicating a good fit in the established regression model. W/C had extremely significant effect on strength; UFA and HPMC also had extremely significant effects. The optimization result showed that the order of influence on strength was B>C>A>AC>AB>BC; on permeability coefficient: C>A>B>AC>BC>AB;on porosity:C>B>A>BC>AC>AB (A=UFA, B=W/C, C=HPMC). When the contents of UFA, W/C, and HPMC were 13%, 0.20, and 0.15% respectively, the permeable concrete exhibited a 28d compressive strength of 25 MPa, a permeability coefficient of 3.05 mm/s, and a porosity of 20.7%. These properties met the engineering requirements for C20 permeable concrete.