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The utilization of recycled materials in the concrete industry has become one of the most essential environmental needs today, and more technical and economic studies are being performed every day in this subject. The effect of recycled materials on the shear behavior of geopolymer concretes was investigated in this work, along with a comparison to conventional recycled concretes and the effect of recycled aggregates on both concrete groups. For this purpose, ten mixing designs with recycled aggregate replacement percentages of 0, 25, 50, 75 and 100 were made in two groups of ordinary concrete and geopolymer concrete, as well as mechanical tests such as compressive strength, modulus of elasticity, and pull-off test. A reinforced beam without shear element was also created for each mixing design to study the effect of this type of aggregate on the shear behavior of the beam. The findings revealed that increasing the percentage of recycled aggregates causes a loss in mechanical characteristics in the designs and a reduction in beam bearing capacity, indicating that geopolymer concrete has a higher replacement capacity than regular concrete. [ABSTRACT FROM AUTHOR]

In recent years, a new type of fiber-reinforced concrete, consisting of several different types of fibers, known as hybrid fibers reinforced concrete, has attracted the attention of researchers. The aim of this paper for experimental evaluation of the effect of replacement ratio of recycled aggregates with natural aggregates on the mechanical properties of reinforced concrete with hybrid fibers (steel and polypropylene fibers). To this end, reinforced concrete with hybrid fibers with volume fractions of "0.0%" , "0.5%" , and "1%" of steel fibers and "0.0%" and "0.4%" of polypropylene fibers and replacement ratios of "0.0%" , "25%" , and "50%" recycled coarse aggregate of natural coarse aggregates were tested for compressive strength, Brazilian tensile strength, and flexural strength by four-point bending tests. The results show that increasing the replacement ratio of recycled aggregate leads to a decrease in compressive, tensile, and flexural strength. If polypropylene and steel fibers are added to concrete containing recycled aggregates, the compressive, tensile, and flexural strengths of concrete increase, whose steel fibers are more efficient in improving the tensile and flexural strength of concrete than polypropylene fibers. The combination of polypropylene fibers with steel fibers increases energy absorption and increases the flexural toughness of concrete containing recycled aggregates. Moreover, reinforced concrete with hybrid fibers does not disintegrate after breaking, and hybrid fibers play an important role in maintaining the cohesion of concrete.

Recycled concrete aggregates are one of the types of recycled aggregates that have the most abundance compared to other recycled aggregates. In this research, by using the replacement of recycled concrete aggregates instead of natural aggregates, the mechanical properties of this type of concrete have been investigated. The replacement of natural aggregates with recycled aggregates was done in four percentages of 0, 15, 30 and 45, and this replacement was done both independently (i.e. sand or gravel separately) and simultaneously (both sand and gravel together). According to the use of 50% sand and 50% sand in the reference mixing plan and by replacing the percentages with coarse and fine recycled concrete aggregates, 21 mixing plans were used. The ratio of water to cement was kept constant in all mixing plans and was considered equal to 0.42. To compensate for the decrease in strength due to the replacement of recycled aggregates, micro silica in different percentages of 7.5 and 15 and super plasticizers were used in the mixing designs. By performing various tests, the mechanical properties of concrete samples were investigated. The results showed that the best mixing design in terms of compressive strength is the design containing 7.5% micro silica and 15% recycled sand, in terms of tensile strength, the design containing 7.5% micro silica and 45% recycled sand, in terms of flexural strength, the design containing 7.5% micro silica and 30% recycled sand, the plan containing 15% micro silica and 15% recycled sand was determined. By examining the mechanical properties of concrete samples, it was determined that the recycled mixing plans contain 15%, 30% recycled gravel and 45% recycled sand with 7.5% microsilica, as well as the mixing plan of 15% recycled sand with 15% microsilica., among the recycled mixing plans, they had the highest amount of overall utility. [ABSTRACT FROM AUTHOR]

Due to the fact that concrete is one of the most widely used construction materials and concrete has low ductility, tensile strength and flexural strength along with good compressive strength. To this end, in recent years, by adding fibers to concrete and making reinforced fiber concrete, these weaknesses have been greatly improved. In this study, four samples of reinforced concrete beams were made with recycled aggregate and one sample of beams was made with natural aggregate and in real scale with dimensions of 150×50×20 centimeters. Separate and hybrid types of steel and Kortta fibers were used in the manufacture of beams. In three beam specimens, steel and Kortta fibers were used separately and hybrids and no fibers were used in the beam specimen. In fiber beams and one of the beams without fibers, recycled aggregate was used in their concrete and in one of the fabricated beams, neither fiber nor recycled aggregate was used and it was used as a reference sample in the performed studies. Four-point flexural strength test was performed on the samples. Fracture mode, flexural behavior parameters of beams made with recycled aggregates were investigated. The results showed that the addition of hybrid fibers has a very positive effect on improving the flexural behavior of reinforced concrete beams and eliminates the weakness of recycled aggregates in flexural behavior compared to beams made with natural aggregates.

Optimization and economization of processes and structures have been considered from time immemorial and many things have been done to achieve this goal. Protecting the environment and reducing the amount of waste material in nature is very important. Today, the problem of using recycled materials resulting from the destruction of buildings and the reuse of these materials in the construction of concrete has been considered. In this research, the shear behaviour of concrete beams manufactured with recycled coarse aggregate was studied. 9 concrete beams with a cross-section 150 mm wide and 200 mm high and a length of 1500 mm manufactured and tested. Recycled aggregate from building demolition was used at 0%, 50% and 100% mass replacement of natural aggregate. Specimens underwent a four-point bending test. In this test, the shear capacity, maximum deflection at the mid-span of the specimens and tension strain were measured. The determination of the shear behaviour of recycled aggregates concrete beams according to transverse reinforcement spacing was the aim of this study. The results were also compared with ACI, CSA and Eurocode 2 requirements. According to the test results, it was found that there is a significant difference in the shear behaviour of recycled and natural aggregate concrete beams

Concrete, as one of the main components of the manufacturing industry since the beginning of the process of production, operation and destruction, plays a major role in the creation of environmental pollution. Since more than 70% of the main body of concrete is aggregate, the promotion of culture and considerations based on the principles of sustainable development in design, construction and demolition process of concrete is of great importance. One of the basic principles of sustainable development is the importance of recycling. Recycling of damaged concrete in the last century has become one of the most important interests of researchers. So, after studying and recognizing their durability and mechanical properties (MP’s), today in developed countries, the necessary relationships for the recognition of structural performance of these concretes is under construction. The purpose of this research is to investigate the results of research carried out in different countries in the field of recognition of the MP’s of recycled concretes (RC’s). More than 80 articles published in prestigious technical journals were examined and classified together in the six groups that the researchers considered in analyzing the MP’s of RC’s. The effect of each of these groups on compressive and tensile strengths and elasticity of concrete were studied. The results showed that the type, size and quality of recycled aggregates (RA’s) are very effective in determining the level of replacement of recycled materials (RM’s) in concrete. Curing conditions, water reducing and pozzolanic materials, although effective in improving the MP’s of RC’s, cannot reduce the adverse effects of increasing the replacement of RM’s on the mechanical properties of concrete. Concerning the effect of age on the mechanical properties of RC’s, it is common ground that some of these properties are similar to conventional ones.

In this research, recycled concrete aggregates are used instead of natural aggregates in concrete and then the recycled concrete is reinforced by fibers. The aim of this study is to investigate the effect of size and also the amount of the recycled concrete aggregates on the mechanical properties of concrete and then investigating the effect of addition of polypropylene and steel fibers on improving the mechanical properties of concrete. The results showed that compressive strength of concrete decreased by increasing replacement ratio of recycled aggregates. Also, the replacement of fine aggregate at the level of 30 percent has not significant effect on the compressive strength of concrete and so this mix can be selected as the optimum recycled mix design. In addition, the use of the fiber improves considerably the tensile and flexural strength of the recycled concrete so that the steel fiber has more positive effects on the tensile and flexural strength in comparison to the polypropylene fiber. In addition, when the concrete reinforced by the fiber is broken, the concrete is not disrupted and the fiber has an important role to reduce the growth of cracks after break. In this research, recycled concrete aggregates are used instead of natural aggregates in concrete and then the recycled concrete is reinforced by fibers. The aim of this study is to investigate the effect of size and also the amount of the recycled concrete aggregates on the mechanical properties of concrete and then investigating the effect of addition of polypropylene and steel fibers on improving the mechanical properties of concrete. The results showed that compressive strength of concrete decreased by increasing replacement ratio of recycled aggregates.Also, the replacement of fine aggregate at the level of 30 percent has not significant effect on the compressive strength of concrete and so this mix design can be selected as the optimum recycled mix design. In addition, the use of the fibers improve considerably the tensile and flexural strength of the recycled concrete so that the steel fiber has more positive effects on the tensile and flexural strength in comparison to the polypropylene fiber. Also, when the concrete reinforced by the fiber is broken, the concrete is not disrupted and the fiber has an important role to reduce the growth of cracks after break.