Abdullah Hamid Radhi

This research aims to experimentally assess the influence of steel fibres (SF) on the shear performance of sustainable selfcompacting concrete (SCC) beams made using 100% recycled aggregates (RA). For this aim, a simple treatment procedure was first utilised to improve the characteristics of the recycled aggregate by saturating particles in a cement-silica fume slurry (CSFS). After that, seven concrete beams of dimensions 1700 mm × 250 mm × 150mm. Five of which were made from SCC mixes containing hooked-end, micro, and hybrid steel fibres with 0.5% and 1% volume fractions, and 100% recycled aggregate. The remaining two were made with either normal aggregate or recycled aggregate and without any steel fibres to serve as references. All beams were made without shear reinforcement and were designed to assess the concrete's contribution to the shear capacity. The beams were tested under a four-point bending configuration, based on which the load–deflection diagram, failure load, and crack pattern were documented and discussed. Additionally, a comparative analysis was performed to evaluate the validity of the typical codes and mathematical models proposed by researchers for predicting the shear capacity of the tested beams. The results showed that using recycled aggregate lowered the maximum shear capacity of reinforced SCC beams by about 15% compared to the reference beam made of normal aggregate. However, the incorporation of steel fibres resulted in a significant enhancement of the shear capacity. The shear enhancement was about 47% and 37% for micro and hooked SF with 0.5% Vf and 75%, 54%, and 70% for 1% micro, hooked, and hybrid SF, respectively. Additionally, the comparative analysis has shown that the equations proposed by IS: 456 (2000) and Li et al. (1992) were able to yield the best shear strength prediction for non-fibrous and fibrous beams, respect

Recycled concrete aggregates have been developed as a replacement for decreasing natural sources of normal aggregates. Despite the use of numerous treatment strategies to improve the performance of recycled concrete aggregate (RCA), its properties remain inferior to those of natural coarse aggregate (NA), necessitating future treatment in this area. This study aims at investigating the following influencing parameters: (a) three types of coarse aggregate (natural coarse aggregate (NA), recycled concrete aggregate RCA, and treated recycled concrete aggregate TRA); (b) three types of steel fibers (Micro, Hooked, and Hybrid), (c) three volume fractions of steel fibers: 0%, 0.5%, and 1%; and (d) two treatment methods: (i) enhanced microstructure of RCA by cement silica fume slurry (CSFS) and (ii) enhanced structure of sustainable SCC mixes by steel fibers. Eight SCC mixes were utilized in the experimental work with reference to NA, RCA, TRA, and TRA + SF, reinforced with varying types of steel fiber amounts (0%, 0.5%, and 1%). Slump flow, T500, V-funnel, compressive strength (fcu), Splitting tensile strength (fst), and flexural strength (fr) tests were performed in accordance with the appropriate standards. The test results indicated that the fresh characteristics of SCC mixes were adversely affected by the use of untreated RA, particularly at higher replacement amounts. While a drop in concrete strength for untreated RCA mixes was observed compared to the reference mix. The treated RA enhanced the concrete mechanical properties by about 12%, 11%, and 10% for fcu, fst, and fr, respectively, compared to the untreated RCA. On the other hand, for mixes with steel fibers, it was noted that incorporating steel fibers led to a considerable increase in fcu, fst, and fr values, particularly when 1% hybrid steel fibers (HYSF) was added.

This paper presents the findings of an experimental investigation into the performance of reinforced self-compacting concrete beams made of 100% recycled aggregates (RA). Three distinct types of steel fibers (SF) were utilized in the study: micro, hook-ended, and a hybrid of both, at varying percentages of 0.5% and 1%. A straightforward and economical treatment has been put forth, entailing the impregnation of recycled aggregates (RAs) with a cement-silica fume slurry (CSFS), with the objective of enhancing their characteristics. The experimental program comprised seven RA-SCC beams, which were divided into two distinct groups. The first group consists of two non-fibrous beams made with natural and recycled aggregate, while the second group includes five fibrous beams reinforced with steel fibers by two percentages, 0.5 and 1%, respectively. Furthermore, this study employed the DIC method to capture the deflection response, crack width, and crack pattern and morphology of the fibrous and non-fibrous beams with treated recycled aggregate, micro-SF, hooked SF, hybrid SF, and volume fraction of SF. The experimental findings indicated that the utilization of RA reduced the flexural strength of reinforcement SCC beams by approximately 12% in comparison to the reference beam. Notwithstanding the type and amount of fibers utilized, the incorporation of steel fibers yielded flexural performance that was commensurate with or exceeded that of the control beams. Furthermore, a comparison of the DIC data with the experimental results demonstrated the superior accuracy of the DIC method in comparison with visual inspection, particularly in the assessment of cracking loads

This work aims to improve the mechanical characteristics of recycled aggregate self-compacting concrete (SCC) mixtures by immersing recycled aggregate (RA) in a cement silica fume slurry (CSFS). An experimental study was conducted on several mixtures made up of a variety of aggregate type (normal aggregate, untreated recycled aggregate, treated recycled aggregate) utilizing different replacement ratios of 0%, 30%, 60%, and 100% of recycled aggregate. All mixes were tested for their fresh characteristics using slump flow, T500, and V-funnel tests, and their hardened characteristics were measured by compressive, splitting, and flexural concrete strength. The results indicated that the suggested treatment approach was effective for the physical characteristics of treated recycled aggregate, which exhibited greater specific gravity and reduced water absorption compared to untreated recycled aggregate. Regarding the fresh properties, research results indicated that most of the untreated RA-SCC mixtures met the Self-Compacting Concrete criteria (EFNARC guidelines), influencing the stated slump flow diameter of 600–685 mm, T500 ranging from 2.2–3.8 seconds, and V-funnel flow time between 5.1–13.7 seconds. For hardened characteristics, it was observed that replacing natural aggregate (NA) with recycled aggregate (RA) resulted in a significant reduction in compressive and tensile concrete strength values. In contrast, SCC mixtures, including treated RA, exhibited enhanced compressive, splitting tensile, and flexural strengths proportional to the replacement percentage. Thus, the results indicated that it is possible to produce SCC mixtures using treated recycled aggregates that offer reliable structural performance when utilized in reinforced elements. Finally, the effects of untreated RA, treated RA, and replacement ratio on the mechanical properties of the SCC mixes were individually quantified by the power equations, and a model for predicting the splitting and flexural strength of sustainable concrete mixes was proposed and verified.

Using recycled aggregate (RA) instead of natural aggregate (NA) is one of the most sustainable choices in concrete construction in terms of decreasing the consumption of natural aggregates, reducing the landfill area, and improving the environment. However, being possesses relatively more defects compared to natural aggregates (NA), RA concrete is found to be generally associated with poor performance in terms of its mechanical performance as well as cracking behaviour. Accordingly, it is essential to implement strategies that can enhance the RA performance. For this to be tackled, a number of strategies and procedures have been proposed in numerous research works. In this regard, steel fibers, up to a certain limit, have been found to have a positive impact on RA-based concrete. The aim of the present paper is to conduct a critical review regarding the fresh and hardened properties of fiber reinforced RA-based concrete (SFRAC). The study has shown a light on the microstructure of RA and material characteristics of SFRAC. It also emphasizes the influences of steel fibers on the fresh properties, compressive strength, splitting tensile strength, and flexural strength of RA concrete mixes. The investigated properties will be discussed in terms of maximum replacement ratio, SF type and aspect ratio, and SF volume fractions (Vf).

In this study, the flexural behaviour of steel fibre reinforced self-compacting concrete (SCC) beams made of 100% recycled aggregates (RA) was experimentally and analytically investigated. Two types of steel fibres, namely micro and hook-ended, were utilised at different volume fractions ( Vf) of 0.5 and 1%. Hybrid steel fibre (a combination of micro and hooked-end) was also utilised in this investigation. A simple treatment method was implemented to enhance the properties of RAs by impregnating them in a cement-silica fume slurry (CSFS). After the treatment process was completed, a series of rectangular simply supported reinforced SCC beams were prepared and tested until failure. The performance of the tested beams was assessed considering cracking and ultimate failure loads, crack pattern, and load–deflection response. A comparative analysis was conducted to examine the validity of standard codes and analytical models proposed by researchers to predict the flexural capacity of the tested beams. The obtained results indicated that using RA lowered the ultimate flexural load of reinforced SCC beams by about 12% compared with the control beam. On the other hand, the inclusion of steel fibres resulted in comparable or even superior flexural performance when compared with the control beams, irrespective of the fibre types and volume fractions. The specimen containing 1% hybrid steel fibre had the maximum flexural capacity with a 20% improvement over the control specimen (beam without any recycled aggregates). Additionally, the use of 0.5% microsteel fibre might be recommended as it sufficiently compensates for the inferior performance of RA concrete, hence enables the full replacement of natural aggregate (NA) with recycled aggregate in SCC beams. Furthermore, the standard codes and analytical models proposed in the literature were found to provide conservative predictions for the flexural capacity of all the tested beams. Nevertheless, these codes and models could be reasonably used to design reinforced fibrous and nonfibrous RA beams.

Although many treatment techniques has been implemented to enhance the performance of recycled aggregate (RA), its characteristics is still lower than that of natural aggregate (NA), and therefore, further treatment is needed in this regard. An experimental investigation to improve the mechanical performance of RA self-compacting concrete (SCC) was presented in this study. To achieve this purpose, RA was first subjected to a simple treatment method by submerging it in a cement-silica fume slurry in order to enhance its physical performance. After completing the treatment process, several SCC mixes, incorporating NA, RA, and treated recycled aggregate (TRA), as well as micro steel fibers (MSF) with a volume fraction (Vf) of 0.5 and 1%, were prepared. The prepared mixes were tested in fresh state by slump flow, T500, and V-funnel tests, and in hardened state by compressive strength (fcu), splitting tensile strength (fst), water absorption, and unit weight. The results pointed out that the proposed treatment method is effective, such that the physical properties of TRA showed higher specific gravity and lower water absorption than that RA. With regard to the fresh properties, all the tested mixes, after the required superplasticiser dosage was added, met the self-compactibility criteria. For mixes without steel fibers, it was found that replacing NA by RA led to a considerable drop in fcu and fst values. However, a slight reduction in these values were noticed when TRA was used instead of NA. On the other hand, when TRA mixes comprised MSF, a significant improvement in fcu and fst were observed, particularly when 1% MSF was added.