With the continuous improvement of social productivity, the material resources in social life are becoming more and more abundant, but various difficult-to-degradable materials continue to emerge, especially the large number of waste rubber materials, which have become a worldwide treatment problem that pollutes the environment and easily triggers secondary disasters [1
]. In China, the number of waste rubber tires produced in 2012 exceeded 10 million tons, and the annual growth rate is increasing. The output of waste rubber tires was expected to exceed 20 million tons in 2020, equivalent to nearly 4 million tons of rubber resources [3
]. Only about 15% of such a large number of waste rubber tires can be effectively degraded and retreaded. Therefore, the recycling of waste rubber materials is an emerging problem. With the in-depth research on waste rubber materials, researchers discovered that waste rubber materials can be converted into rubber particles by physical grinding and then added to concrete. The incorporation of rubber improves the performance of concrete and at the same time reduces the environmental pollution of rubber. Rubber particles can fill part of the pores of concrete and improve the connection between cement and aggregate. The incorporation of rubber particles can play a role in mitigating energy consumption, thereby improving the crack resistance of the material [4
]. Moreover, based on the same principle, the incorporation of rubber also improves the impact resistance of concrete [5
]. Incorporating rubber particles into concrete can introduce a large number of bubbles, thereby improving the frost resistance of concrete [7
]. At the same time, due to the increase of internal voids, rubber concrete also has good heat insulation and sound insulation characteristics [10
]. However, while a large number of scholars’ studies have shown that the incorporation of rubber particles improves the toughness of concrete, it is negatively related to the mechanical properties of concrete [11
]. Therefore, in order to expand the scope of application of rubber concrete, it is necessary to further modify rubber concrete.
Basalt fiber is an environmentally friendly material made from basalt. Incorporating basalt fiber into concrete can form a stable spatial network structure and comprehensively improve various properties of concrete. In recent years, basalt fiber has been deeply studied because of its environmentally friendly manufacturing process and excellent mechanical properties [13
]. Algin et al. [16
] evaluated the influence of fiber length and fiber content on concrete mechanical properties and permeability. The test results showed that the incorporation of fibers is negatively related to the fluidity of concrete, but it can improve the mechanical properties of concrete. Wu et al. [17
] firstly used cement paste to wrap basalt fiber, and then mixed it into concrete. The results showed that the incorporation of an appropriate amount of basalt fiber is positively correlated with the mechanical properties of concrete. Katkhuda et al. [18
] studied the relationship between the basalt fiber content and the properties of modified concrete. The test results showed that adding an appropriate amount of basalt fiber has a positive effect on the flexural strength of concrete. Jalasutram et al. [19
] studied the failure mode of basalt fiber concrete during compression and found that the failure mode changed from brittleness to toughness during compression. Peng et al. [20
] modified concrete with different dosages of basalt fibers of 0, 1, 2, 3, 4 and 5 kg/m3
. The research results showed that the content of basalt fiber affects the compressive strength, splitting tensile strength and flexural strength of concrete to varying degrees.
The response surface method (RSM) is a method that can more effectively analyze and optimize an experimental response and it is being more and more widely used in concrete mix design [21
]. RSM is superior to traditional experimental design methods in many aspects. Compared with traditional methods, RSM can reduce the number of tests required, thereby minimizing test costs, and it can determine the optimal input variables based on the test results [22
]. The response surface method can establish a scientific mathematical model and provide information on the impact of individual factors and the interaction of factors on the test results within the set test numerical boundary. This method can better evaluate the nonlinear relationship between test variables and response values. At the same time, the three-dimensional response surface between the preparation parameters and the response index can be drawn in this article, so that the relationship between each factor and the response value can be understood more clearly. Algin et al. [16
] used RSM for multi-objective optimization analysis. Based on strength and permeability, the optimal volume and length of basalt fiber were obtained. Liu et al. [26
] studied the influence of four variables on the working performance and mechanical properties of basalt fiber reactive powder concrete using response surface methodology. In addition to the above literature, other scholars have used the RSM method to evaluate the effects of different influencing factors on concrete performance [28
In this study, in order to recycle waste rubber materials and give full play to the excellent properties of basalt fiber, an experimental RBFC mixture scheme was designed based on the RSM. Fine aggregates were replaced by an equal volume of rubber aggregates and basalt fibers were mixed with concrete for modification. The relationships between three preparation parameters (water-binder ratio (WBR), basalt fiber content (BFC), rubber content (RC)) and the working performance and mechanical properties of RBFC were analyzed. The mechanical properties and working performance of concrete were taken as response values to study the optimal mix ratio of RBFC. The optimization scheme of RBFC mix ratio was determined and verified by test results.