Combining different fiber types may improve the mechanical properties of fiber reinforced concrete. The present study is focused on investigating hybrid fiber reinforced concrete (HFRC) with steel and basalt fiber. Mechanical properties of fiber reinforced fine-grained concrete are investigated. The results demonstrate that using optimal steel and basalt fiber reinforcement ratios avoids concrete mixtures’ segregation and improves their homogeneity. Concrete with hybrid steel and basalt fiber reinforcement has higher strength. Effective methodology for proper design of HFRC compositions was proposed. It is based on the mathematical experiments planning method. The proposed method enables optimal mix proportioning of high-strength fine-grained concrete with hybrid steel and basalt fiber reinforcement.

The paper deals with the effectiveness of various types of polymers (naphthalene formaldehyde, polycarboxylate, and lignosulfonate) as superplasticizers of concrete mixtures based on low-clinker slag Portland cement. Using the mathematical planning experimental method and statistical models of water demand of concrete mixtures with polymer superplasticizers, as well as concrete strength at different ages and under different curing conditions (normal curing and after steaming) were obtained. According to the models, the superplasticizer’s water-reducing effect and relative change in concrete strength were obtained. The proposed criterion for evaluating the effectiveness and compatibility of superplasticizers with cement takes into account the water-reducing effect of the superplasticizer and the corresponding relative change in concrete strength. The results demonstrate that the use of the investigated superplasticizer types and low-clinker slag Portland cement allows for achieving a significant increase in concrete strength. The effective contents of various polymer types, which allow the achieving of concrete strengths from 50 MPa to 80 Mpa, has been found.