This study presents the results of laboratory experiments conducted to determine the mechanical parameters for cement mortar with various quantities of waste fibers, polypropylene microfibers, and steel microfibers. Waste fibers were used as samples and obtained using an end-of-life car tire recycling process. For comparison, samples with the addition of steel and polypropylene microfibers were tested. The same degrees of fiber reinforcement were used for all types of fibers. Ultimately, 22 mixtures of cement mortar were prepared. The aim of this study is therefore to present and compare basic mechanical parameter values. Compressive strength, flexural strength, fracture toughness, and flexural toughness were of particular interest. A three-point bending test was performed on three types of samples, without a notch and with a notch of 4 and 8 mm. The results show that the use of steel microfibers in the cement mortar produces a product with better properties compared to a mixture with steel cord or polypropylene fibers. However, the cement mortar with the steel cord provides better flexural strength and greater flexural toughness factors compared to the cement mortar with polypropylene fibers. This means that the steel cord is a full-value ecological replacement for different fibers.

Designing bending elements made of fiber composites requires knowledge of the residual strengths. Residual strengths determined according to PN-EN 14651, regardless of the type of matrix and the fibers used, are characterized by a very-high coefficient of variation, about 30%. The variability of this feature is so large that the normal distribution adopted in statistical analyses, which is consistent for compressive strength or tensile strength, may, in the case of residual strengths, result in a significant overdesign of the elements. Therefore, the article proposes a novel method of determining the residual strength with the use of centrally bent square plates simply supported at the perimeter. The coefficient of variation of this characteristic in the case of plate testing is about 8%.

This report presents the results of cracking tests on concrete beams. The test specimens were created in ten different series. Each series comprised two beams, six cylinders, and twelve cubic samples intended for the determination of strength properties. These samples varied in terms of the type of concrete mixture (fiber-reinforced fine aggregate concrete and plain concrete), the applied steel fibers (50/0.8 mm and 30/0.55 mm), the longitudinal reinforcement ratio in beams (0.6%, 0.9%, 1.3%, and 1.8%), and the inclusion (or exclusion) of compressed reinforcement and vertical stirrups. The fine aggregate concrete was made from waste sand, which is a byproduct of the hydroclassification process of gravel. The use of this sand in fiber concrete will help reduce the exploitation of natural resources and lower carbon dioxide emissions. Based on four-point beam bending tests, the study experimentally determined cracking moments, crack spacing, and crack width. Additionally, these results were compared with calculations proposed by L. Vandewalle and Domski, as well as with the methods outlined in Eurocode 2. The analyses conducted show that the best agreement between the research results and the calculations was obtained for Domski’s proposal. It follows that the average percentage error was 38.4%, indicating the safe use of this method.