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This paper aims to investigate some properties of recycled aggregates concrete (RAC) containing various amount of recycled concrete aggregates (RCA) supplied from different parent concrete strength. Three concretes with different strengths were made. After hardening, they were crushed and the obtained RCA were used to substitute 20%, 40% and 60% of coarse ordinary aggregates (COA) in concrete mix. The properties of these RCA according to their parent concrete strength were analyzed and their effects on the workability, compressive strength and shrinkage were quantified. Concrete workability and final shrinkage seem to be related to the equivalent water absorption of coarse recycled aggregates. An equivalent granular expression can be used in classical model to predict compressive strength according to the RCA content and its parent concrete strength.

The construction industry produces an enormous quantity of waste that may be recovered and expended as recycled aggregates to replace or supplement natural aggregates. A more sustainable construction sector is a result of recycling since it decreases waste and energy usage. Because of natural aggregates are in short supply and have a related carbon footprint, recycled materials are being evaluated more and more for use in concrete. Using recycled aggregates in concrete has environmental advantages, however the physical characteristics of the aggregates causes it to perform poorly. Lightweight aggregate concrete encompasses of water, lightweight aggregates (LA), and cement. Full lightweight concrete uses just light aggregates (coarse and fine) and sand lightweight concrete uses either all or part of common sand for the fine aggregate. A combination of low strength, large water absorption, low apparent density, and great porosity characterizes the lightweight aggregate used in this kind of concrete. There are three distinct kinds of LA based on where they come from, for example, expanded slag ball, fly ash ceramisite, cinder, light sand, and other industrial waste products that undergo processing to become lightweight aggregate. Artificial LA is manufactured using local resources such as expanded perlite, and clay ceramisite, whereas natural porous stone is produced using natural processes. Examples of natural aggregate include pumice, light sand, and volcanic cinder. Lightweight aggregates may be categorized into two types according to the size of the particles namely lightweight coarse aggregate and lightweight fine aggregate, often known as sand lightweight. In this research, we have used a scientometric approach to assess the most recent research advancements (1975-2023) to assess their contribution. There is a substantial number of publications (651), as well as a significant number of research papers (421). Furthermore, there are a lot of authors (1791) who are engaged in this field of work. The output of the study is largely influenced by international collaboration nearly 17.18%. Each work obtains, on average 19.2 citations, demonstrating its significant influence in this expanding field. For aspiring researchers who are interested in conducting research in this area, this paper is an invaluable resource.

No-Fines Concrete is a type of concrete produced without fine aggregate or sand. Because of its high porosity, it allows rainwater to seep into the ground, directly replenishing the groundwater aquifer. With a design load of three tons, no-fine concrete can be utilized as pavement for rural roads. Additionally, this type of concrete can be utilized as a sub-base material in both flexible and rigid pavements. Aside from No-Fines Concrete's permeability properties, asphalt overlays are another option. This research studied the impact of silica fume and polypropylene fiber on the properties of no-fine concrete with recycled aggregate. The ratios of cement to aggregate and water to cement were 1:4 and 0.3, respectively. The recycled aggregate was demolished reactive powder concrete used in percentages of 10, 20, and 30% as a substitution for coarse aggregate by volume. The recycled aggregate percentage of 10% was the optimal percentage as it showed the least adverse effect on the no-fine concrete mixes. The polypropylene fiber was then added to the no-fine concrete mixes with 10% recycled aggregate in the percentages of 0.5, 1, and 1.5% by volume. The optimum percentage of polypropylene fiber was 0.5%, which improved the mechanical properties of no-fine concrete. Silica fume was used as a partial substitution for cement at a percentage of 10% and added to no-fine concrete mix with 10% recycled aggregate. The results show that using 10% silica fume and 0.5% polypropylene fiber with 10% recycled aggregate increased the splitting tensile strength, flexural strength, compressive strength, and modulus of elasticity by (22.54 and 40.32%), (22.22 and 35%), (21 and 35.37%), and (22 and 38.19%) compared to reference mix (NC) and the no-fine concrete mix with 10% recycled aggregate (RNC10), respectively. In comparison, the dry density was higher by (1.34%) than RNC10 and lower by (0.68%) than NC.

This investigation investigates the structural behavior of slender reinforced concrete RC containing different RCA replacement portions in addition to the slenderness effect. To perform this, eight (8) slender RC columns with two main types of transverse reinforcement (ties and spiral reinforcement) and three recycled coarse aggregate RCA replacement percentages (25, 50, and 100%) were modeled and subjected to axial concentric loading. The gathered experimental results are monitored and analyzed to better estimate the structural characteristics of the RC slender column (The ultimate carrying load, first cracking load, load-displacement curve, and load-strain response). The results showed that replacing NCA with (25, 50, and 100%) of RCA reduced the ultimate capacity of tied RC columns by (13.41, 14.07, and 23.33%), respectively, and reduced their first cracking load values by (19.64, 15.96, 22.50%), respectively. The reduction in ultimate load capacity and the first cracking load were (4.10, 17.33, 22.63%) and (12.26, 23.15, 25.00%) for spirally RC columns, respectively. Spiral transverse reinforcement slightly increases the carrying load capacity compared to tie reinforcement. It delays the fast propagation of the first cracking load, furthers the effect of spiral reinforcement in improving the deformation capacity, reducing the longitudinal and lateral mid-height strains, and developing the flexural stiffness of the load-displacement curve.

The present work presents the results of the experimental investigation of using crushed concrete as recycled coarse aggregates (RCA) and new models of hybrid deep beams. Six specimens of deep beams have been tested under static loads: two specimens as controls and three hybrid specimens with different types of hybridization models for concrete sections (horizontal, curved, and arched). This study aims to search for the optimum distribution of the concrete types for the hybrid deep beams such that the lowest cost is obtained and the RCA obtained from building demolition waste is introduced into the concrete mixes at 100%. The behavior has been tracked by the cracking and failure loads, loading history, crack width, and toughness. It was found that the capacities increased by 7.7, 18.7, 17.2, and 28.2%, respectively, in the horizontal, curved, arched, and arched with inclined stirrups hybrid models compared to the control specimen with RCA. Moreover, toughness was enhanced for the same specimens by 50.9, 71.1, 100.5, and 144.6%, respectively, compared to the control specimen with RCA.

In order to better use the old cement concrete pavement materials in the cement stabilized base of the reconstruction or new road. In this paper, metakaolin was used to replace recycled fine aggregate with different proportions to prepare cement stabilized recycled aggregate base mixture, and the physical and mechanical properties and dry shrinkage properties of cement stabilized recycled aggregate base mixture were studied. The results of the study show that adding a proper amount of metakaolin can reduce the optimal water content of the mixture, increases the maximum dry density and 7d unconfined compressive strength of the mixture, and also reduces the total water loss and dry shrinkage of the mixture. The research results can provide new ideas for the recycling of road waste materials.