Optimization of mix proportions for hybrid fiber engineered cementitious composites based on Box-Behnken design response surface model

In this paper, basalt fiber (BF) and polyethylene fiber (PE) were mixed into cement matrix to prepare a new hybrid fiber Engineered Cementitious Composite. The Box-Behnken experimental design method within the Response Surface Methodology (RSM) was employed, the effects of water-binder ratio, sand-binder ratio and fiber content on compressive strength, flexural strength and equivalent bending toughness of hybrid fiber ECC were studied. Analysis of variance (ANOVA) was used to verify and optimize the model equation, and the ratio of water-binder ratio 0.2, sand-binder ratio 0.35, BF content 1.25%, PE content 1% was obtained. The results show that the synergistic effect of PE and BF has a favorable effect on the mechanical properties of hybrid fiber ECC. PE can achieve high energy absorption and maintain high strain capacity of matrix. BF increases the strength of the specimen. When the BF content increases from 0.9% to 1.2%, the compressive strength increases by 9.6%. The fiber content is highly sensitive to flexural strength and equivalent bending toughness, and the significance level of each factor is more than 95%. The significance level of each factor is BF content > sand-binder ratio > waterbinder ratio. The experiment verified that the established prediction model has high accuracy, and the relative error between the optimized RSM value and the experimental value is less than 5%. To provide a certain reference for the design of ECC mix proportions for preparing multi strength and multi toughness series.