International Concrete Abstracts Portal

This study investigates the behavior of recycled steel fibers recovered from waste tires (RSF) and industrial hooked-end steel fibers (ISF) in two single and hybrid reinforcing types with different volume content, incorporating microstructural and macrostructural analyses. Scanning electron microscopy (SEM) is used to study the microstructure and fractures, focusing on crack initiation in the fiber interface transition zone (FITZ). The macrostructural analysis involves using digital image correlation (DIC) software, Ncorr, to analyze the split tensile behavior of plain and FRC specimens, calculating strain distribution, and investigating crack initiation and propagation. The SEM study reveals that industrial fibers due to the presence of hooked ends promoted improved mechanical interlocking, anchors within the matrix, frictional resistance during crack propagation and significantly improved load transfer have better bonding, crack bridging, and crack deflection compared to recycled fibers. Recycled steel fibers significantly delay crack initiation and enhance strength in the pre-peak zone. The study suggests hybridizing recycled fibers from automobile tires with industrial fibers as an optimum strategy for improving tensile performance and utilizing environmentally friendly materials in FRC.

End hooks of steel fibers provide a stronger bridging force across the concrete matrix in steel fiber reinforced concrete (SFRC). In this work, SFRC beams were prepared with steel fibers of the same length and diameter but different types of end hooks (straight, 3D, 4D, and 5D) at increasing fiber volumes (0.0, 0.5, 1.0, 1.5, and 2.0%). Four-point bending tests conducted on each SFRC beam yielded load-deflection curves, from which the first cracking strength, flexural strength, and fracture toughness up to certain deflection-to-beam length ratios were obtained. The test results showed that the presence of end hooks remarkably enhanced the flexural strength and toughness of the SFRC beams, and this enhancement was amplified with an increasing number of hooks. Quantitative analysis revealed the hooking index, a factor introduced herein to delineate the efficiency of various types of hooks, was 1.00, 1.30, 1.60, and 2.10, respectively, for straight, 3D, 4D, and 5D steel fibers used in the present study. Lastly, empirical models for predicting flexural strength and toughness were established with high prediction accuracy.

This paper is aimed at investigating the effects of different fiber inclusion on the mechanical properties of ultra-high-performance concrete (UHPC) by adding mineral admixtures as cement replacement materials to reduce production costs and CO2 emissions of UHPC. Throughout this research, 21 mixture designs containing four cement substitution materials (silica fume, slag cement, limestone powder, and quartz powder) and three fibers (steel, synthetic macrofibers, and polypropylene) under wet and combined (autoclave, oven, and water) curing were developed. To investigate the mechanical properties in this research, a total of 336 specimens were cast to evaluate compressive strength, the modulus of rupture (MOR), and the toughness index. The findings revealed that at the combined curing, regarded as a new procedure, all levels of cement replacement recorded a compressive strength higher than 150 MPa (21.76 ksi). Furthermore, the mechanical properties of the mixture design containing microsilica and slag (up to 15%) were found to be higher than other cement substitutes. Also, it was shown that all levels of the fiber presented the MOR significantly close together, and samples made of synthetic macrofibers and steel fibers exhibited deflection-hardening behavior after cracking. The mixture design containing microsilica, slag, limestone powder, and quartzpowder, despite the significant replacement of cement (approximately 50%) by substitution materials, experienced a slight drop in strength. Therefore, the development of this mixture is optimal both economically and environmentally.

The purpose of this study is to investigate the effect of steel fiber content and type on the compressive and flexural ductility capacities of lightweight aggregate concrete (LWAC). Fiber-reinforced LWAC specimens were divided into four groups according to the type of fibers, such as conventional macrosteel fibers (SFs) with hooked ends, straight copper-coated microsteel fibers (CMSFs), crimping-shaped CMSFs, and hooked-end CMSFs. The fibervolume fractions (Vf) were 0.5, 1.0, and 1.5%. This study also modifies the ASTM C1018 method by using the initial crack point calculated from the elastic theorem to save a tedious and elaborated effort in determining the reference point at the load-deflection curve, particularly for beams with a strong hardening response. The test results revealed that the hooked-end CMSFs were better than SFs and crimping-shaped CMSFs with the same shape and length at decreasing the slope of the applied loads at descending branches of the compressive stress-strain and flexural load deflection curves for the LWAC. Compressive and flexural toughness indexes were derived as functions of the fiber reinforcing index based on the regression analysis of test data to assess the ductility improvement of LWAC with steel fibers.

Interlocking concrete block pavement (ICBP) is one of the pavement types adopted worldwide. The influential parameter of ICBP is comparatively more, which includes the geometric parameters of the interlocking paver blocks such as the size, shape, thickness, strength, and laying pattern of the blocks, and the gradations of the jointing and bedding sand. Other than the wearing surface, the thickness and properties of the bedding sand, base, and subgrade also play a vital role in the deflection properties of ICBP. The objective of the present study is to analyze the influence of block thickness, base thickness, and granular layer thickness on the deflection behavior and stress distribution of ICBP. The block thicknesses used for this study are 80, 100, and 120 mm; the bedding sand thicknesses are 30, 50, and 70 mm; and the base thicknesses are 150, 300, and 450 mm. The experimental work is carried out using the laboratory plate load test to determine the deflection and stress distribution of ICBP. Numerical analysis is also employed to simulate laboratory testing. The study attempts to find the most influential factor and the optimized parametric value for attaining lower deflection using Design-Expert software. The test results conclude that the thicknesses of the block and granular layer play an imperative role among the considered parameters.