The Strength of Concrete with an Elastic Additive of Tires Rubber Waste under Cyclic Loading

Concrete strength under cyclic loads is much lower compared to short-term loading strength because cyclic loads stimulate the growth of microcracks in the cement matrix, reduce the adherence of cement stone and aggregates and cause higher creep deformations. The paper presents the deformations of samples with or without a rubber waste additive subjected to cyclic loads and determined by the methods developed during research. The obtained results show that relative plastic strains under cyclic load and relative residual strains after the removal of the load depend on the rubber additive. Relative strains in the rubberized concrete samples loaded at 70% prism compressive strength are 63% higher and residual strains after the removal of the load are 234% higher. When the samples are loaded at 80% of prism compressive strength, relative strains and residual strains after the removal of the load in concrete with the rubber additive are respectively 56% and even 360% higher if compared to the samples without the rubber additive. When the samples are loaded at 90% of prism compressive strength, the obtained respective relative strains are 63% and 219% higher compared to the samples without rubber additives. An increase in relative plastic and residual strains shows the influence of the rubber additive on the stress-strain behaviour of concrete subjected to cyclic loads. The conducted investigation has revealed that concrete with rubber waste additive under cyclic loads changes ultimate strains. We can see a significant difference in the yield deformations leading to the ultimate failure of concrete with or without the rubber additive. When the samples of rubberized concrete are loaded at 70% of prism compressive strength, the longitudinal ultimate strains are 36% higher; loading at 80% results in 47% higher strains and that at 90% results in 42% higher strains compared to the non-rubberized concrete samples. The analysis of changes in deformation conducted by the created method does not give a precise forecast as to the number of cycles that one or another type of concrete will resist under a certain load. Nevertheless, the obtained changes in deformations enable to make rather precise decisions with regard to the ability of concrete to absorb cyclic stresses with the higher strains of the concrete matrix. A detailed analysis of the test results has revealed the following tendencies: concrete with rubber additives has better deformation abilities under cyclic loads because of bigger plastic (residual) strains and bigger ultimate strains. This leads to the presumption that rubber additives present in the concrete matrix are able to absorb cyclic-load-stimulated internal stresses driving the concrete fragmentation process.