جستجوی مقالات مرتبط با کلیدواژه "recycled aggregate" در نشریات گروه "عمران"

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 a 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.

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.

Recycling of concrete has been the focus of researchers owing to the large volume of concrete waste and the limited resources of valuable materials. Recycled aggregate concrete (RAC) contains aggregates of various types of concrete and building materials that have been destroyed due to their shelf life or as a result of war and natural disasters. In order to use different types of recycled aggregates (RA), it is necessary to conduct more detailed and sensitive research on the behavior of RAC in order to reach the highest possible level of quality and cost in the construction process. On the other hand, RA are made of concrete with different properties and its aggregates have been subjected to different form of loading, hence it is important to carefully examine their behavior and properties. Therefore, in this study, the strength and the durability of RAC after freeze and thaw cycles were compared with natural concrete while different water/cement ratios are used.
In this study, RA were extracted from demolished waste concrete specimens and used to produce three mixtures named RC, RN and NC while 100, 50 and 0 percent of RA were replaced respectively. Water to cement ratio were kept as 45 and 55 percent of cement. A total number of 57 samples for flexural, compressive, tensile strength and ultrasonic tests were made. 24 samples were placed in the refrigerator and freeze and thaw cycles were applied on. 18 and 15 specimens were prepared for testing at 28 and 120 days of age, respectively. According to ASTM C666, the relative dynamic modulus of the specimens was tested using ultrasonic test after each 40 cycle’s period. After the test was finished, compressive strength, single point bending, indirect tensile tests and elastic modulus were determined for each specimens. Finally, the behavior of recycled and natural concrete was compared.
The results showed that the freeze and thaw cycles reduced the resistance of both RAC and NAC. Recycled aggregates have 2.5 times more water absorption than Natural aggregates. RAC has lost 41%, 18%, 10% and 28% of its compressive, flexural, tensile strength and modulus of elasticity, after the freeze and thaw cycle, respectively. The 100% replacement of RA reduced even more the mechanical behavior of samples. The relative dynamic modulus at the end of the cycles for RAC was 2% higher than that of NAC, indicating its better durability properties against freeze and thaw cycles. Concrete with 50% replacement of recycled aggregate has almost the same durability and strength as NAC, hence is recommended to be use in similar condition

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.

Given that one of the most concrete and concrete construction materials with suitable compressive strength, ductility, tensile and flexural strength is low. For this purpose, in the past few years by adding fiber to fiber reinforced concrete and concrete construction, greatly improve the weaknesses. The purpose of this study is to investigate the effect of different fibers on the flexural behavior of reinforced concrete beams made with natural and recycled aggregates. In this research, 12 samples of reinforced concrete beams in two groups (6 beams made of natural aggregate and 6 beams made of recycled aggregate) were made in real scale with dimensions of 150×50×20 centimeters, which The reinforcement details of all the beams were the same and three types of steel fibers, polypropylene and Kortta were used separately and hybrid in the construction of the beams. Four-point flexural strength test was performed on the samples. Fracture mode, fracture behavior as well as absorbed energy parameters, ductility and final load capacity of beams made with natural and recycled aggregates were investigated. The results showed that the addition of hybrid fibers had a greater effect on improving the above parameters than separate fibers and also the flexural behavior of recycled samples with hybrid fibers could be closer to natural samples with separate fibers.

This experimental research has investigated in particular the durability of fully recycled concrete containing natural zeolite (NZ), microsilica (SF) and fly ash (FA) pozzolans. Recycled concretes consist of recycled concrete aggregates and contain different percentages of replacement of SF, FA and NZ. A total of 11 mixing designs were constructed, including plain reference concrete (RC), 100% recycled concrete without pozzolans, and 9 mixing designs of fully recycled concretes containing the mentioned pozzolanic materials as separate applications. To evaluate and compare some mechanical properties and especially properties related to the durability of this type of concrete, in the age range of 28- to 91-day, compressive strength (CS), in the age range of 28-day the ultr-pulse velocity, and in the age range of 180-day immersion water absorption, capillary water absorption, electrical resistivity and electrical conductivity of specimens made of this type of concretes, were measured. The results showed that although the complete replacement of recycled aggregates in this type of concrete leads to a decrease in their CS compared to the RC, but the replacement of pozzolanic materials such as SF in fully recycled concrete can lead to gain more CS than RC. Also, the rate of loss of durability properties in fully recycled concretes without pozzolans is much higher than the loss of mechanical properties compared to the RC. However, due to changes in the chemical structure of recycled concretes from pozzolanic materials such as NZ, some of the durability properties of these concretes did not change significantly compared to RC.

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.

This paper presents the results of an experimental study on the properties of environmentally friendly concrete. In the making of specimens, 0%, 15%, and 30% of ordinary Portland cement (OPC) was replaced by recycled concrete powder (RCP) and silica fume (SF). In addition, 0%, 50%, and 100% of natural aggregates (NA) was replaced by recycled concrete aggregates (RCA). In the production of RCA, 3 types of concrete waste with initial strength of 20, 40, and 80 MPa were used. In this study, rheological, mechanical (compressive, splitting tensile and flexural strengths), economic and environmental (GWP) properties of 28 mix designs were investigated. The results showed that the use of RCA and RCP has a negative effect on rheological and mechanical properties. However, the results showed that the use of RCA and RCP has a positive effect on environmental and economic properties. Moreover, the results indicated that the negative effect of RCA can be prevented by increasing the initial strength of RCA, and the negative effect of RCP can be prevented by using SF. Finally, by optimization of mixing designs, it was concluded that it is justified to use 50% of RCA with initial strength of 40 and 80 MPa and 30% of RCP and SF, in terms of rheological, mechanical, economic and environmental properties.

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

The reusing of recycled aggregates produced from waste concrete is a sustainable solution to reduce the shortage of natural resources. This paper presents the effects of the addition of Nano silica and polyvinyl alcohol (PVA) fiber on the mechanical and microstructural properties of recycled aggregate concrete containing coarse and fine recycled aggregates. Recycled aggregate concrete was produced by 50% and 100% volume substitution of natural fine and coarse aggregate with recycled aggregate. In total, 21 series of concretes are evaluated. The Nano silica in weight ratios of 0%, 2%, 4%, and 6%, and the polyvinyl alcohol fibers in volume fraction of 0%, 0.5%, and 1% were used. The compressive strength, tensile strength, and flexural strength at the different ages of 7, 28, and 90 days are measured in this research. Also, the microstructure of the recycled aggregate concrete was studied via scanning electron microscopy on the selected mixtures.Test results show that the addition of Nano-silica and polyvinyl alcohol fiber can improve the mechanical and microstructural properties of the recycled aggregate concretes. Also, it was seen that polyvinyl alcohol fiber improves the post-peak behavior of specimens. Moreover, high ratios of Nano silica and PVA fiber in the concrete mixture caused negative effects on the compressive strength of recycled aggregate concrete.

In this research, the effect of recycled aggregates obtained from the demolition of the old building on the preparation of concrete mixtures has been studied. The purpose of this study was to determine flexural behavior, flexural strength in reinforced concrete beams made of recycled aggregate. In the production of samples, recycled aggregates are used with 0%, 50% and 100% natural aggregates, respectively. The samples were tested for static quadrilateral bending and tested after 28 days of experiment. Therefore, by examining the results of laboratory studies, the flexural behavior of RC beams with the expansion of the recycling has been investigated. In addition, the results are compared with the relationships provided by ACI318, CSA and EuroCode2. The results obtained from this review show that by adding the ratio to the recycled aggregate substitute, the amount of net bending size at the criterial level increases and, with the expansion of the crack extending to the place of loading, the load is released flexibly. In addition, the use of 100% recycled aggregate increases the shape and flexural strength of RC 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 study, the feasibility of the use of slag from blast furnaces as an alternative to a percentage of cement and recycled coarse aggregate and simultaneously as a substitute for natural coarse aggregate was investigated, both of which are secondary and waste products and are fine for the construction of self-consolidating concrete blends. For this purpose, mixtures with 0, 15%, and 25% of slag volume replaced cement, and mixtures with 25%, 50%, 75%, and 100% of recycled coarse aggregate replaced natural coarse aggregate in the 15 mix design with a water-cement ratio 48%. For characterizing the mechanical properties of recycled self-consolidating concrete containing slag flexural strength testing at ages 7, 28, and 91 days were measured. Furthermore, to determine the rheological properties of self-consolidating concrete slump flow and J ring tests were used. The water absorption tests were also used as an indicator of permeability and durability of concrete at ages 2, 3, 7, and 28 days and the tensile strength test was also conducted at 28 days. The results show that the compressive strength of slag samples containing 7-day aged was a little, but gradually after a while reasonable strength was achieved at age of 28 and 91 days. The best result of this study showed that cement replacement by 15 percent of slag and natural coarse aggregate replacement by 25 percent of recycled coarse aggregate, in terms of compressive strength, tensile strength, water absorption and rheological properties of self-consolidating concrete permissible and acceptable results were obtained.

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.

In recent years developments in technology have made it possible to make high strength concrete with higher workability and strength compared with conventional concrete. Now a day, in order to reduce current costs and reduce or eliminate the environmental problems the use of recycled materials and natural Pozzolan have become one of the topics of interest to many researchers. In this study, the use of zeolite as natural pozzolan and recycled aggregate concrete as recycled material in self-compacting concrete was investigated. For this purpose recycled self compacting concrete mix design was optimized and different percentages of cement was replaced with zeolite (0%, 10%, 15%, 20%, 25% and 30%). In this study, after studying the compressive strength, tensile strength and modulus of elasticity in self-compacting concrete containing recycled aggregates and zeolite, empirical relations between compressive strength, tensile strength and modulus of elasticity have been established.