Effect of Wollastonite Microfibers and Waste Tire Rubber on Mechanical Properties of Concrete

The main objective of the present research is to investigate the effect of adding wollastonite microfibers and waste tire rubber on the mechanical properties of concrete. For this purpose, two different series of mixtures were considered. Different percentages (5, 10, 15, and 20 percent) of wollastonite microfibers were added to the ordinary concrete and tested in the first series. Then, in the second series, wollastonite microfibers were added to the specimens in the amount of 20% by the weight of cement, and waste tire rubber was replaced with fine aggregate in different percentages (3, 5, 7, and 10 percent by the weight of fine aggregate), and the specimens were tested again. All the specimens were cured at the two ages of 7 and 28 days, and they were tested for the slump, compressive strength, tensile strength, and flexural strength. The results showed that the addition of 20% wollastonite microfibers to the specimens increased the compressive, flexural, and tensile strengths of the concrete at 28 days of age by 16, 87, and 78%, respectively, compared to the control specimen. The outcomes also demonstrated that replacing fine aggregate with tire rubber in samples containing 20% wollastonite microfibers reduces the strength of the samples. The highest reduction is related to the sample containing 20% of waste tire rubber, which has a reduced compressive strength of about 20% compared to the control sample. Furthermore, the results of this research showed that adding wollastonite microfibers to concrete reduces the concrete slump, while the density of the samples increases with the addition of wollastonite. Moreover, the presence of wollastonite microfibers reduces the porosity of concrete, but there is an increase in the number of pores in concrete samples containing waste tire rubber.