Abstract: In order to overcome the disadvantage of poor mechanical properties of composite cementitious material system with large dosage, the response surface method was adopted to optimize the hybrid fiber composite cementitious material system, and the prediction model was established by taking the dosage of steel fiber, polypropylene fiber and desulphurization gypsum as the variable factors, and 28 d flexural strength and compressive strength of cement mortar as the evaluation indexes. Besides, the test of cement mortar and concrete was carried out to verify the predictive model. The results show that when the volume dosage of steel fiber is 0.4%, the volume dosage of polypropylene fiber is 0.116% and the mass dosage of desulphurization gypsum is 8%, the working and mechanical properties of composite materials reach the optimum, the predicted values of the 28 d flexural and compressive strength can be up to 7.0 and 37.4 MPa. The relative errors of flexural and compressive strength between the predicted values and the experimental values are only 2.86% and 1.32% and the standard deviation of the test values of flexural strength and compressive strength is 0.148 8 and 1.345 9, proving that the response surface method has high prediction precision, accuracy and scientificity. The optimisation effect of the composite cementitious material system is proved through this study, which provides a new solution idea and test basis for the multi-objective optimisation problem of composite materials.

Key words: composite cementitious material, steel fiber, polypropylene fiber, hybrid fiber, response surface methodology, multi-objective optimization