Effect Of Recycled Concrete Aggregate Research Articles

Effect of recycled concrete aggregates on the punching strength of slab-column connections without shear reinforcement

This paper presents the results of tests on six reinforced concrete slab-column connections. The slabs were octagonal, centrally supported on square columns, and concentrically loaded at their borders. The tests investigated the effects of replacing natural coarse aggregates with recycled concrete aggregates. The experimental results were also compared to resistance estimates from ACI 318 (2019) and Eurocode 2 (2004) and results from a database with tests on slabs without recycled concrete aggregates. The results show that using RCA reduces the concrete's modulus of elasticity and tensile strength but has little effect on its compressive strength. Furthermore, using RCA has little impact on the flexural response and punching resistance of the slabs. The findings suggest that RCA has potential for use in concrete applications, but further tests are required to draw definitive conclusions.

Self-compacting concrete produced with recycled concrete aggregate coated by a polymer-based agent: A case study

Understanding the effects of recycled concrete aggregate (RCA) and polymer impregnation on the properties of self-compacting concrete (SCC) is crucial for the construction industry's efforts to reduce environmental impact and utilise recycled materials. This study aims to examine the impact of RCA inclusion and polymer impregnation on the properties of SCC, in response to the urgent demand for sustainable construction practices. Two different methods of polymer impregnation were evaluated to assess their impact on the workability and hardened characteristics of SCC. The SCC mixtures were prepared using river sand (natural fine aggregate (NFA)), natural crushed limestone (natural coarse aggregate (NCA)) and a polymer impregnation level of 0.05 wt% of the water content, with a water-to-cement ratio of 0.34. RCA was used as a complete replacement for NFA and NCA, adhering to the American Society for Testing and Materials (ASTM) C33 standards for recycled fine concrete aggregate (RFCA) and recycled coarse concrete aggregate (RCCA)The workability of the SCC mixtures was evaluated based on the criteria set by the European Federation of National Associations Representing for Concrete (EFNARC). Among the hardened properties, the compressive strength of the hardened properties was tested at four different time intervals (1, 3, 7 and 28 days), and the integrity of the SCC specimens was assessed using ultrasonic pulse velocity. The polymer impregnation process resulted in a slower compressive strength development rate compared to that observed in the control concrete. However, combining polymer impregnation type 1 with either RFCA and NCA or RCCA and NFA significantly increased the 28-day compressive strength by 5.02% and 1.80%, respectively. These findings provide valuable insights into the behaviour of SCC incorporating RCA and polymer impregnation. Optimising the selection and combination of materials can enhance the performance and sustainability of SCC in construction applications.

Performance evaluation of loadbearing compressed fully recycled aggregate concrete bricks

Due to rapid expansion of infrastructure around the world, many countries are facing severe shortage of natural resources. Further, environmental issues originating from Construction and Demolition (C&D) waste are becoming a concern for society. Recycling of C&D waste is one of the most viable options that can help to reduce the burden on natural resources as well as provide an eco-friendly and sustainable solution. Recycled Concrete Aggregates (RCAs) obtained by recycling of C&D waste have been used in the production of Recycled Aggregate Concrete (RAC). In this study, the effect of RCAs on compressive strength and durability performance of loadbearing concrete bricks manufactured by Compression Casting Technique (CCT) is investigated. The concrete bricks were prepared using different mixes containing 100% RCAs using ratios of coarse-to-fine aggregates i.e., 60:40 and 70:30. For comparison, Natural Aggregates Concrete (NAC) and burnt-clay bricks were also tested. They were tested in compression and durability tests such as water absorption (WA), cycling ponding test in acidic and brine solution, efflorescence and drying shrinkage were conducted. The results showed that RAC bricks satisfied the density, WA and compressive strength requirements specified in ASTM standards. Compared to burnt-clay bricks, density and compressive strength of RAC bricks were higher (20.7–30.5% & 11.2–25.2%, respectively) while WA was less (34.4–68.5%). The RAC bricks performed better than NAC under 5% sulfuric acid and supersaturated brine solutions. The drop in compressive strength for RAC bricks after 4 cycles of immersion in acidic solution for 28 days was negligible. An increase of 21% in compressive strength of RAC bricks with 60:40 ratio of RCAs, and 10% cement was achieved after 4 cycles of immersion in the supersaturated brine solution for 56 days. The RAC bricks were more susceptible to drying shrinkage due to their porous nature. No efflorescence problem was observed in both RAC and NAC bricks. This study concluded that masonry units made using 100% RCAs fulfill performance criteria specified in international standards are structurally viable and are an eco-friendly solution. The commercial use of RAC bricks will have a significant positive impact on the environment and ensure sustainable development in construction industry.

Effect of recycled concrete aggregates on the mechanical and durability properties of self-cured concrete for sustainable construction

Effect of recycled concrete aggregates on the mechanical and durability properties of self-cured concrete for sustainable construction

Changing the soaking method of microbially induced calcium carbonate precipitation technology to improve the reinforcement effect of recycled concrete aggregates

In this study, the effects of the soaking method employed during the concrete reinforcement process on the properties of recycled concrete aggregates (RCAs) with different particle sizes were investigated based on biodeposited calcium carbonate technology. The microstructure and properties of RCAs and the macroscopic properties of recycled aggregate concrete (RAC) before and after the enhancement treatment were studied. The results showed that the presoaked bacterial solution can improve the reinforcement of RCAs, and the best performance of RCAs was obtained after reinforcement by soaking twice (first time, soaking RCAs into nutrient solution after presoaking with the bacterial solution (Method B), the next time soaking RCAs directly into mixed culture solution (Method A)). After immersing twice, the biodeposited calcium carbonate reinforced the defects of RCAs and coated the surface of RCAs. The mechanical properties of RAC were significantly improved owing to the use of the enhanced RCAs, and the RCAs with secondary soaking treatment endowed the concrete with superior mechanical performance.

Compressive and flexural behavior of alkali-activated slag-based concrete: Effect of recycled aggregate content

Alkali-activated concrete (AAC) is a more eco-friendly alternative than conventional concrete since its production does not need cement. As a majority of the concrete volume is consumed by aggregates, there is a need to reduce the utilization of natural aggregates thereby reducing the exploitation of natural resources. This paper deals with the effect of recycled concrete aggregate (RA) content on the compressive and flexural behavior of slag-based AAC. The compressive stress-strain behavior (i.e., failure pattern, compressive strength, peak strain, elastic modulus and toughness) and flexural properties were studied. Finally, the carbon emissions and cost effectiveness of AAC with various RA contents were assessed. The results show that all the concrete specimens under both compression and flexure exhibit brittle failure modes due to the poor aggregate-matrix interfacial transition zones. The addition of RA weakens the flexural properties of concrete. However, as the RA content changing from 0% to 100%, the compressive properties of peak strength, elastic modulus and toughness exhibit a first slight increase and then decrease trend. The RA content in AAC can reach 75% to achieve the same compressive strength compared to plain concrete due to the excellent dense structures. Based on the test results in current study and literature, an empirical analytical model is developed to generate the compressive stress-strain curve of AAC with various RA contents.

Effect of recycled concrete aggregate with different degrees of initial alkali–aggregate reaction damage on the mechanical behavior and porosity of self-compacting recycled aggregate concrete

The use of recycled concrete aggregate (RCA) is an effective approach to achieve environmental sustainability. However, the presence of defects due to previous alkali–aggregate reactions (AARs) has caused reluctance toward its use in constructions. This study investigated the application and influence of RCAs with different degrees of initial AAR damage on the mechanical behavior and porosity of self-compacting recycled aggregate concrete (SCRAC). Concrete cubic specimens with different degrees of AAR were produced by soaking the raw materials in a high-alkaline solution. In order to obtain RCAs with different initial AAR durations of 7, 28, 60, and 210 days. The specimens were then crushed using a jaw crusher. The residual reactivity of the RCA produced from concrete affected by the AAR was detected using the accelerated mortar bar test. The rheological properties of the SCRAC with different RCAs were tested. Compressive strength, flexural strength, mercury intrusion porosimetry, and scanning electron microscopy tests were conducted to analyze the effects of RCAs with different degrees of initial AAR damage on the mechanical properties and porosity of the SCRAC. The results show that the RCA can maximally strengthen the compressive strength of the SCRAC after 60 days of alkali immersion at a replacement rate of 30 %. Furthermore, a prediction model considering the filling effect for calculating the influence of RCAs with initial AAR damage on the compressive strength of the SCRAC was proposed. For practical engineering applications, the AAR can strengthen RCAs and improve the utilization rate of RCA, which is beneficial for the sustainable development of the environment.

Autogenous and drying shrinkage of structural concretes incorporating recycled concrete aggregates from different sources

AbstractThe main relevant difference between recycled concrete aggregates (RCAs) in comparison with the companion natural ones, is the presence of the Attached Mortar content which confers to the RCAs higher porosity and, consequently, higher water absorption capacity. In the last decades, several studies have been performed worldwide for unveiling the role of the employed RCAs on the resulting concrete mixture performances at both fresh and hardened states. On the other hand, the effects of RCA on the early‐age and/or long‐term concrete deformations (e.g., shrinkage) are still very limited. In this context, this article summarizes the results of a wide experimental campaign aimed at evaluating the influence of RCAs on the autogenous and drying shrinkage of normal (35 MPa) and high (60 MPa) strength recycled aggregate concrete (RAC) mixtures. A total of 10 mixtures were realized by considering the variation of both the original source and size of employed RCAs. The results showed a clear correlation between the intrinsic properties (i.e., Attached Mortar content) of the employed RCAs and the resulting concrete deformation. Moreover, although the drying shrinkage is higher for RAC mixtures, the presence of a more porous aggregates mitigates the observed autogenous shrinkage. Consequently, the overall total shrinkage result to be almost unaffected by the presence of the recycled particles.

Stabilization of Recycled Concrete Aggregate Using High Calcium Fly Ash Geopolymer as Pavement Base Material

This research investigated high calcium fly ash geopolymer stabilized recycled concrete aggregate (RCA-FAG) as pavement base material. The effect of recycled concrete aggregate (RCA):high calcium fly ash (FA) ratios, sodium silicate (Na2SiO3):sodium hydroxide (NaOH) ratio, and curing time on the unconfined compressive strength (UCS) and scanning electron microscope (SEM) properties of RCA-FAG samples were evaluated. The maximum dry unit weight of the RCA-FAG sample was 20.73 kN/m3 at RCA:FA ratio of 80:20 and Na2SiO3:NaOH ratio of 60:40. The 7-d UCS of RCA-FAG samples increased as the FA content and Na2SiO3:NaOH ratio increased. The 7-d UCS of the RCA-FAG sample was better than that of the RCA with no FA because FA particles filled in RCA particles, resulting in a dense matrix. The 7-d UCS of RCA-FAG samples passed the 7-d UCS requirement for the low-traffic road. All ingredients met the 7-d UCS requirement for the high-traffic road except the sample with RCA:FA of 100:0 and Na2SiO3:NaOH of 50:50 and 60:40. The 7-d SEM images indicated that spherical FA and RCA particles are bonded together, resulting in the dense matrix for all Na2SiO3:NaOH ratios. The proposed equation for predicting the UCS of RCA-FAG offered a good coefficient of correlation, which is useful in designing pavement base material from RCA-FAG material.

Studies on the effect of recycled concrete aggregates on concrete with mixed fibre and pozzolans

The steel fibre and synthetic fibres can entirely replace traditional rebars in concrete under specific circumstances like industrial floorings, which are subjected to dynamic loading due to movement of heavy machinery. The large scale availability of Recycled Concrete Aggregates (RCA) can be utilized to make these concrete floors. These are generally substantiated by laboratory test to ensure that the performance criteria are satisfied. The usefulness of combining RCA in high strength quaternary blended mixed fibre reinforced concrete (h-MFR-QB) in resisting compression, flexure, split tensile strength, and repetitive low-velocity drop-weight impact was evaluated in an experimental programme. The experiments were carried out on three different groups of specimens. Fly ash, micro silica, Nano silica, hooked end steel fibres, and PP fibres were used in each group. The advantages of both fibres were accomplished for efficient concrete using a volume fraction of 0.2% and 1% of PP and steel fibres, respectively, to offset the detrimental effect of adding RCA. When compared to non-fibrous concrete, the h-MFR-QB concrete material specimens exhibit a strong resistance to compression, flexure, split tensile strength, and repetitive low-velocity drop-weight impact drop-weight impact.

Effect of recycled concrete aggregates and recycled filler on delayed ettringite formation: An experimental study compared to chemical modelling

This study investigates the development of delayed ettringite formation in concrete made of recycled concrete aggregates (RCA) and in mortars with a recycled concrete filler. Experimental results are compared to a chemical model of delayed ettringite formation by Sellier & Multon (2018). Three concretes were formulated, one with natural siliceous aggregates and two others with two different RCA. Concrete and mortar samples were screened for one year for DEF damage. Results show that RCA based concrete did not develop DEF damage, but concrete made of siliceous aggregate did. Recycled filler had a small negative effect on DEF but not as much as limestone filler. Comparison to chemical modelling, including six additional mortars from Yammine (2020), shows that the produced expansive volume cannot be directly linked to the measured expansion. The porosity of mortars and concrete plays an important role in controlling the expansion. All formulations that did exhibit large expansions had developed a maximum volume of expansive products higher than 30% of their porous volume. These results suggest a simple method to predict DEF related expansion in concrete with or without recycled concrete products.

EXPERIMENTAL INVESTIGATION OF SCC WITH RECYCLED RUBBER AND RECYCLED CONCRETE AGGREGATE

The replacement of natural aggregates (NA) with alternative aggregates in concrete can contribute to the sustainable development of the construction industry. This paper aims to present research investigating the effects of recycled concrete aggregate (RCA) and crumb rubber (CR) utilization on the performance of Self-Compacting Concrete (SCC) mixtures in both fresh and hardened states. For this purpose, SCC mixtures with three different replacement levels of CR - 0%, 20% and 30% by volume for fine aggregate and 100% coarse RCA were prepared along with the reference mixture containing NA only. To assess the effects of NA replacement, the physical and mechanical tests were conducted on prepared SCC mixtures and corresponding results were analysed and compared.

Effect of recycled concrete aggregate on mechanical, physical and durability properties of GGBS–fly ash-based geopolymer concrete

Effect of recycled concrete aggregate on mechanical, physical and durability properties of GGBS–fly ash-based geopolymer concrete

Behaviour of sustainable concretes modified with mineral admixtures and Nano-silica against aggressive media attacks

The goal of this study is to see how the effect of recycled concrete aggregate admixed with mineral admixtures and Nano-silica on concrete's durability after being exposed to aggressive media attacks. The coarse aggregates applied in the concrete were dolomite (control) and recycled concrete aggregate with the addition of various mineral admixtures such as ground granulated blast slag (GGBFS), granite, and Nano-silica. To lower the water/cement ratio, a superplasticizer (SP)-type (F) was used. The physical and mechanical properties of commonly used raw materials such as aggregates and other various concrete kinds were investigated. The effects of saltwater and 3% sodium chloride on concrete mechanical and microstructures properties were investigated. The slump values of dolomite concrete were found to be lower than those of recycled aggregate concrete. The concrete mix using recyclable aggregate has the highest compressive strength, according to the results. In terms of compressive strength, the addition of 1% NS (Nano-silica) and 15% slag increased both mechanical and durability properties of the recycled aggregate concrete in aggressive media.

Evaluating the effect of recycled concrete aggregate and sand in pervious concrete paving blocks

Pervious concrete paving blocks with individual and combined use of recycled concrete aggregate (RCA) and sand were investigated in terms of physical and hydrological properties (density, porosity and infiltration rate), compressive strength and abrasion capacity. First, the natural coarse aggregate was replaced by RCA at the levels of 15%, 30% and 50% by weight. Then, the incorporation of sand at the levels of 5% and 10% by total weight of aggregate was studied in the mixtures that presented the greater performance. As a result, the replacement of natural aggregate by 15% of RCA increased the compressive strength. Also RCA levels until 30% do not compromise the hydraulic and mechanical performance of previous concrete paving blocks. The incorporation of sand decreased the porosity and infiltration capacity of pervious concrete while preventing the mechanical performance to increase due to the lack of homogeneity of the mixture.

Understanding the effect of recycled concrete aggregate and cementitious materials on concrete's fire resistance

PurposeFire can severely affect concrete structures and with knowledge of the properties of materials, the damage can be assessed. Aggregate, cement matrix and their interaction are the most important components that affect concrete behaviour at high temperatures. The effect of incorporating recycled concrete aggregate or cementitious materials, namely, cement type and pulverized fly ash, are reviewed to provide a better understanding of their involvement in fire resistance.Design/methodology/approachMore investigation research is needed to understand the fire resistance of such sustainable concrete that was already constructed. The present study illustrates the effect of using recycled concrete aggregate and cementitious materials on the fire resistance of concrete. To do so, a literature review was conducted and relevant data were collected and presented in a simple form. The author's selected research findings, which are related to the presents study, are also presented and discussed.FindingsRecycled concrete aggregate enhances the concrete behaviour at high temperatures when it substitutes the natural aggregate by reasonable substitution (more than 25–30%). It also almost eliminates the possibility of spalling. Moreover, utilizing both supplementary cementitious materials with recycled concrete aggregate can improve the fire resistance of concrete. The incorporation of pulverized fly ash and slag in Portland cement or blended cement can generally keep the mechanical properties of concrete at a higher level after heating to a high temperature.Originality/valueRecycled concrete aggregate enhances the concrete behaviour at high temperatures when it substitutes the natural aggregate by reasonable substitution (more than 25–30%). It also almost eliminates the possibility of spalling. Moreover, utilizing both supplementary cementitious materials with recycled concrete aggregate can improve the fire resistance of concrete. The incorporation of pulverized fly ash and slag in Portland cement or blended cement can generally keep the mechanical properties of concrete at a higher level after heating to a high temperature.

Effect of recycled concrete aggregate (RCA) on mortar's thermal conductivity susceptibility to variations of moisture content and ambient temperature

Temperature and moisture are two factors that affect the thermal conductivity of building materials. Furthermore, the use of recycled concrete aggregate (RCA) in cementitious composites reduces their thermal conductivity due to increased porosity. However, this increase in porosity may affect the material's thermal conductivity susceptibility to changes in environmental conditions. No studies were found on the effect of RCA on thermal conductivity's susceptibility to moisture content and ambient temperature variations in cement mortars . To study these effects, a total of 135 thermal conductivity tests were performed on mortars with three levels replacement of natural aggregate by RCA, at different saturation degrees and temperatures within the range of expected service-life values. Compressive and flexural strength, permeable porosity, and bulk density were also evaluated. Remarkably, the use of RCA reduces the thermal conductivity's susceptibility to changes in ambient temperature. Besides, RCA increases the porosity, magnifying the susceptibility of thermal conductivity to moisture variations. These variations should be considered when thermal insulation is used as a factor for the environmental impact assessment of cement mortars. Finally, a combination of response surface method models was used to formulate a prediction equation that accurately estimates (error <5%) the thermal conductivity of cement mortars as a function of accessible porosity , saturation degree, and ambient temperature. This research contributes to a deeper understanding and more accurate prediction of RCA's effects on thermal conductivity of cementitious composites as a function of the environmental conditions, which is key to assessing RCA mortars' environmental impact during service life as part of a building component. • RCA reduced the thermal conductivity's susceptibility to ambient temperature changes. • Thermal conductivity's susceptibility to moisture content increases with RCA. • The increase on this susceptibility is related to the increase of porosity. • Thermal conductivity depends on porosity, moisture content and ambient temperature. • An equation that accurately estimates thermal conductivity of mortars is proposed.

Correlation of strength development of RCA in quaternary blended cementitious system

Recycled concrete aggregate (RCA) obtained from demolished structures can be used for concrete making, and is established as a promising material in the field of construction. In the present study, the effect of RCA on the mechanical properties of different strength concretes admixed with Micro silica, fly ash and nano-silica as a part replacement to cement was considered. The quantity of cement varied from 350-690 kg/m3 with the additions of Fly ash at 0, 20 and 30%, micro silica at 0, 5, 10 and 15%, and Nano silica at 0, 1, 2, 3 and 4%. The samples were cured for 7, 28, 56 and 90 days and tested for Compressive strength. Split tensile and flexural strength evaluation was carried out on samples which have been cured for 28 days. The workability of fresh concrete was determined. With the help of the tested database, equations for prediction of compressive strength using modified Bolomey's equation were generated. Equations for the flexural strength and split tensile strengths based on compressive strength were developed and compared with equations available in the literature.

DEM simulation of the thermo-geomechanical effect of recycled concrete aggregate assemblies in geothermal pavement bases

This paper studies the discrete element modeling (DEM) of the thermal-geomechanical effect of recycled concrete aggregate (RCA) assemblies when harnessing renewable geothermal energy from pavement bases. This research study aims to simulate the behavior of RCA under repeated load triaxial test (RLT) at temperatures varying from 20 °C to 80 °C, to simulate temperature effects when harnessing geothermal energy from pavements. The DEM approach was used to simulate unsaturated soil considering interparticle water meniscus and the variation in its force due to the temperature fluctuation. In this research study, RCA samples with different particle size distributions were simulated under RLT test condition for various temperature conditions. According to the macro-geomechanical results, the resilient modulus (MR), porosity, and accumulated strain of samples showed different trends under varying temperatures. Comparing the micro-geomechanical behavior of the samples indicated that matric suction decreased with increasing temperature. Furthermore, the particle scale matric suction was found to be affected by the size ratio of the contacted particles. It was observed that varying the size ratio between 1 and 4 led to a higher average matric suction. The evolution of coordination number (CN), contact normal and contact normal force indicated that samples with higher sand content experienced decrease in CN and magnitude of contact normal by increasing temperature. Meanwhile, samples with lower sand content tended to have an increased CN and magnitude of contact normal in the direction of anisotropy at increased temperatures. An equation was also proposed to predict MR based on matric suction and the ratio of fine over coarse content, based on the RCA particle sizes.

Enhancing the mechanical properties of pervious recycled aggregate concrete using silicafumes

The growth of construction industry in India is increasing enormously over the last few years. This demands a huge quantity of construction materials across the globe which indirectly has a serious impact on the environment that includes aggregate scarcity, inadequate ground water recharge due to impermeable paved surfaces, dust and noise pollution. The use of recycled concrete aggregate in construction industry will mitigate the impact to some extent and also the construction of permeable surface helps in ground water recharge. In this study, the effect of recycled concrete aggregate on mechanical properties of pervious concrete is studied. In addition, the strength of pervious concrete composed of recycled concrete aggregate is enhanced by the addition of silicafumes from 8% to 16% in increments of 2%. The effect of silica fume on permeability and flexural strength is also studied.