Recently, there has been an increasing trend toward the use of sustainable materials. Sustainability helps the environment by reducing the consumption of non-renewable natural resources. Concrete – the second most consumed material in the world after water – uses a significant amount of non-renewable resources. As a result, an experimental investigation was conducted to study the hardened properties of concrete constructed with 20% and 50% recycled concrete aggregate (RCA) (coarse) as well as 6% silica fume. This experimental program consisted of six mix designs. Experimental results showed that the compressive and tensile strength of concrete improve by using recycled concrete aggregate (RCA) (coarse) and silica fume in the mix design. For example, the compressive strength of concrete containing 6% silica fume and 20% recycled concrete aggregate at age of 56 days was 14% greater than reference concrete mix, while with increasing percentage of recovered concrete aggregate by 50%, this parameter increased by only 4% which shows the inverse effect of increasing the amount of recovered concrete aggregate on compressive strength. The hardened properties of concrete were compared with the provisions of the international design codes (U. S., Australia, Canada, Europe, and Japan) as well as a database of conventional concrete. Results showed that the RCA has superior hardened properties compared with the reference concrete mix.

In this study، some mechanical properties of roller compacted concrete (RCC) containing recycled concrete aggregate (RCA) have been investigated. Different mixtures of RCC، in which the fine، coarse or fine and coarse fractions have been replaced with RCA have been made and their mechanical properties including compressive strength، flexural strength، elastic modulus and energy absorption have been evaluated. The compressive and flexural strength of the mixtures have been measured at the different curing ages of 7، 28 and 91 days، while the elastic modulus and energy absorption have been evaluated on the specimens cured for 28 days. Results show that the mixtures containing RCA have a slightly less compressive strength than the control mixture made of natural aggregate. The highest compressive strength was obtained for the mixture containing recycled coarse fraction and natural fines. The flexural strength test results showed that the mixtures containing recycled aggregates have a higher flexural strength than the control mixture، with the highest flexural strength for the mixture containing coarse RCA and natural fines. Furthermore، the ratio of flexural to compressive strength، which is used as an indicative of energy absorption، is higher for the mixtures made of RCA، with the highest for the mixture containing both fine and coarse RCA. The elastic modulus test results show that the mixtures containing RCA have a higher energy absorption than the control mixture، while their elastic modulus is less than the that of the control mixture. The lowest elastic modulus was obtained for the mixture containing both coarse and fine fraction of RCA. This research results show that RCA obtained from structural concrete is feasible to be used in RCC.

This research aimed to investigate the mechanical and physical properties of Roller Compacted Concrete (RCC) used with Recycled Concrete Aggregate (RCA) as a replacement for natural coarse aggregate. The maximum dry density method was adopted to prepare RCC mixtures with 200 kg/m³,of cement content and coarse natural aggregates in the concrete mixture. Four RCC mixtures were produced from different RCA incorporation ratios (0%, 5%, 15%, and 30%). The compaction test, compressive strength, splitting tensile strength, flexural tensile strength, and modulus of elasticity, porosity, density, and water absorption tests were performed to analyze the mechanical and physical properties of the mixtures. One-way Analysis of Variance (ANOVA) was used to identify the influences of RCA on RCC’, s mechanical properties. As RCA increased in mixtures, some mechanical properties were observed to decrease, such as modulus of elasticity, but the same was not observed in the splitting tensile strength. All RCCs displayed compressive strength greater than 15. 0 MPa at 28 days, splitting tensile strength above 1. 9 MPa, flexural tensile strength above 2. 9 MPa, and modulus of elasticity above 19. 0 GPa. According to Brazilian standards, the RCA added to RCC could be used for base layers.

In recent decades, concurrent with expansion of cities, the demand for new buildings and structures has increased. On the other hand, aggregates constitute the biggest portion of concrete. As such, providing natural aggregates for producing concrete has become a challenge due to shortage of resources. Also, treatment of construction waste materials resulted from demolition of old structures has been another concern. One way to handle these problems is reusing concrete waste as a new material in new construction. Nowadays, recycled concrete aggregate (RCA) is used in concrete as a partial or complete replacement for natural aggregate (NA). Performance of recycled aggregate concrete (RAC) is influenced by the characteristics of the parent concrete from which RCA is obtained. In this research, the mechanical properties and the durability of three types of RCAs from different sources were evaluated. For this purpose, the aggregates' Los Angeles abrasion value and freeze/thaw soundness value were determined. Moreover, eight concrete mixes incorporating different amounts of the RCAs as coarse aggregate were cast and their water absorption coefficient, compressive strength and deicer-salt scaling resistance were assessed. The results showed that the mechanical properties of RCAs had a direct relationship with the mechanical properties and durability of RACs. Also, the type of RCAs had no significant impact on the performance of RACs. However, increasing the replacement amount of RCA decreased the strength and deicer-salt scaling resistance of RACs.

In this study, the toughness and durability of concrete with recycled aggregates and magnetic water against melting and freezing cycles and mechanical properties such as compressive and tensile strengths are investigated. Variables include the number of different cycles of water in the magnetic field, different amounts of super-plasticizer, steel fibers and micro-silica. A total of 242 samples were made in 11 different mix designs. It should be noted that half of the samples mentioned contains steel fibers. The results of most experiments have shown that magnetic water, although having a very high effect on the mechanical properties of concrete, should not be used alone as a compensating agent for defects caused by recycled aggregates. Using microsilica as a mineral admixture with magnetic water improves the concrete properties, significantly. The toughness indices were determined by ASTM C1018, JSCE and PCS method and concrete durability test by BS EN 140: 2003. Among the recycled aggregate concrete mixes, the best toughness results were for the samples containing microsilica and steel fibers. Also, ten round magnetic water resulted in an increase in the durability of recycled aggregate concrete by approximately 25% compared to one round of magnetization.

The main purpose of this study is to experimental investigation the properties of concrete containing recycled concrete aggregates and waste rubber with micro silica. For this purpose, recycled concrete aggregates in the amount of 0%, 25%, 50% and 100% by weight have replaced with coarse aggregate and micro-silica at the amount of 10% by weight have replaced with cement. Also, in two specimens with 50% recycled concrete aggregate, first without micro silica and second with micro silica, waste rubber with 30% by volume of fine aggregate has been replaced and used. In the next step, the amount of slump, compressive strength, tensile strength, flexural strength, stress-strain curve, density and permeability of the specimens are evaluated. The results of this study show that the presence of recycled aggregates reduces the compressive strength from 3.2% to 14.5% and also adding waste rubber powder to the specimen with 50% recycled aggregates reduces the compressive strength to the 71% compared to the reference specimen (specimen with natural aggregates and without micro-silica). All specimens with micro silica have higher compressive strength than similar specimens without micro silica. The highest compressive strength is related to the specimen with 25% recycled aggregate and micro silica, which is 9.6% higher than the reference specimen. Specimens containing 50% recycled aggregate in the presence and absence of waste rubber powder have 55 and 72% lower tensile strength and 30 and 67% lower flexural strength, respectively, than the reference specimen. The lowest water absorption is for the specimen without recycled aggregates with micro silica at the amount of 0.5%.

This study studied both the separate and combined effects of lightweight expanded clay aggregate (LECA) and recycled aggregate on the mechanical properties of concrete.For this purpose, three basic mixtures with target strengths of 40, 70 and 100 MPa were designed.At each base mixture, natural coarse aggregate was substituted with recycled coarse aggregate in proportions of 50% and 100% and LECA in proportions of 25% and 50% to develop three groups of mixtures, totaling 18 mixtures. The prepared samples were tested to determine compressive, splitting, shear strengths and elastic modulus after curing for 28 days. The results showed that replacing natural coarse aggregate with recycled coarse aggregate and LECA separately reduced the compressive strength by 26.2% and 34.1% compared to the base mix, respectively. Also, the decrease in compressive strength resulting from the simultaneous use of recycled coarse aggregate and LECA was significantly greater than the separate replacement of natural coarse aggregate with these materials, which was more observed in low-strength mixtures. the splitting strength, shear strength, and elastic modulus results in various mixtures showed a similar trend to compressive strength, meaning that these characteristics significantly decrease as natural coarse aggregate was replaced by recycled coarse aggregate and LECA, although the reducing effect of simultaneous use of recycled coarse aggregate and LECA was small. Furthermore, relationships were established between the square root of the compressive strength and the splitting strength, shear strength, and elastic modulus for different mixtures.

Today, it is quite clear that the speed of development of infrastructure in developing countries has led to much damage to the environment. Concrete is one of the products that plays an important role in the use of non-renewable resources. Today, the vision of sustainable development in the manufacturing industry is growing and increasing, and concrete is at the forefront of this as one of the most widely used construction products. The present study investigates the effect of the use of silica-fume (SF) pozzolan powder on the mechanical properties of recycled concrete made from fine recycled aggregates. Recycled concretes consists of different levels of replacement of fine recycled concrete with natural fines. In order to improve the quality of recycled concrete, Pozzolan was introduced at various levels with cement. To determine and compare the mechanical properties of concrete, 12 mixing designs were made and compressive strength tests at 7, 28 and 91 days, tensile strength, and ultrasound velocity at 28 days of age were performed. The results showed that, generally speaking, in the 28-day period, the use of SF can cause 25% recycled concretes to achieve a desirable 40 MPa strength. The use of 10% SF replacement rate, especially in concrete containing 25% recycled aggregates, made the mechanical properties of recyclable concretes significantly closer to conventional concrete.