Replacement Of Natural Coarse Aggregate Research Articles

Performance of fly ash/GGBFS based geopolymer concrete with recycled fine and coarse aggregates at hot and ambient curing

The incorporation of recycled aggregates in geopolymer concrete (GPC) exhibits higher environmental sustainability due to its ability to utilize industrial by-products and construction and demolition (C&D) waste. This study investigates the combined effect of fine and coarse recycled aggregates on the behavior of GPC. In this research, fly ash (FA) and ground granulated blast furnace slag (GGBFS) were used as binder, whereas sodium silicate (Na2SiO3) and sodium hydroxide (NaOH) were used as alkaline activators. Recycled fine aggregates (RFA) were used at 30%, 60% and 100% replacement of natural fine aggregates (NFA) and recycled coarse aggregates (RCA) were used at 0%, 50% and 100% replacement of natural coarse aggregates (NCA). To study the effect of curing temperature, two types of curing regimes, i.e. hot and ambient curing, were employed. Performance of developed GPC was evaluated in terms of workability, mechanical properties (compressive strength, splitting tensile strength, and flexural strength) and durability properties such as water absorption, sorptivity, resistance against acid attack, resistance against marine environment and electrical resistivity. It was found that the behavior of GPC is improved when the samples were cured at high temperature for 24 h, as compared to the samples cured under ambient curing conditions. Furthermore, NFA can be replaced up to 100% with NCA, and up to 60% in the presence of 50% RCA and up to 30% in the presence of 100% RCA. It was also found that with an increase in the percentage of recycled aggregates, durability performance gradually declined. The results showed that GPC can be developed with inclusion of both recycled fine and coarse aggregates, which can help to preserve valuable natural resources, reduce CO2 emission, and dispose C&D waste.

Performance of Fly ash/GGBFS based geopolymer concrete with recycled fine and coarse aggregates at hot and ambient curing

The incorporation of recycled aggregates in geopolymer concrete (GPC) exhibits higher environmental sustainability due to its ability to utilize industrial by-products and construction and demolition (C&D) waste. This study investigates the combined effect of fine and coarse recycled aggregates on the behavior of GPC. In this research, fly ash (FA) and ground granulated blast furnace slag (GGBFS) were used as binder, whereas sodium silicate (Na2SiO3)and sodium hydroxide (NaOH) were used as alkaline activators. Recycled fine aggregates (RFA) were used at 30%, 60% and 100% replacement of natural fine aggregates (NFA) and recycled coarse aggregates (RCA) were used at0%,50% and 100% replacement of natural coarse aggregates (NCA). To study the effect of curing temperature, two types of curing regimes, i.e. hot and ambient curing, were employed. Performance of developed GPC was evaluated in terms of workability, mechanical properties (compressive strength, splitting tensile strength, and flexural strength) and durability properties such as water absorption, sorptivity, resistance against acid attack, resistance against marine environment and electrical resistivity. It was found that the behavior of GPC is improved when the samples were cured at high temperature for 24 hours, as compared to the samples cured under ambient curing conditions. Furthermore, NFA can be replaced up to 100% with NCA, and up to60%in the presence of 50% RCA and up to 30% in the presence of 100% RCA. It was also found that with an increase in the percentage of recycled aggregates, durability performance gradually declined. The results showed that GPC can be developed with inclusion of both recycled fine and coarse aggregates, which can help to preserve valuable natural resources, reduce CO2emission, and dispose C&D waste.

Comprehensive assessment of engineering and environmental attributes of geopolymer pervious concrete with natural and recycled aggregate

This study aims to conduct comprehensive assessment of engineering and environmental attributes of geopolymer pervious concrete with natural and recycled aggregate. Pervious concrete mixtures were fabricated with different paste and aggregate types for laboratory characterization at different scales. As compared to traditional cement pervious concrete, mechanical strengths of geopolymer pervious concrete increase significantly when either natural coarse aggregate (NCA) or recycled concrete aggregate (RCA) is used. The replacement of NCA with RCA reduces concrete strength but the advantage of geopolymer pervious concrete is maintained. Micro-scale observations indicate that geopolymer pastes have better bonding to RCA. Life-cycle assessment (LCA) results show that the lower global warming potential (GWP) and eutrophication potential (EP), but the greater energy consumption (EC) and acidification potential (AP) are achieved by geopolymer-based pervious concrete. Photochemical ozone creation potential (POCP) is found greater for fly ash-based but smaller for metakaolin-based geopolymer pervious concrete. The use of RCA brings environmental benefit at raw materials and transportation stages, in addition to avoiding landfilling and preserving natural aggregate. The pervious concrete with metakaolin-based geopolymer achieves the best overall performance considering multi-criteria of strength and environmental indicators regardless of aggregate type.

Bond Stress Behavior of a Steel Reinforcing Bar Embedded in Geopolymer Concrete Incorporating Natural and Recycled Aggregates

Abstract: The rise in greenhouse gases, particularly carbon dioxide (CO2) emissions, in the atmosphere is one of the major causes of global warming and climate change. The production of ordinary Portland cement (OPC) emits harmful CO2 gases, which contribute to sporadic heatwaves, rapid melting of glaciers, flash flooding, and food shortages. To address global warming and climate change challenges, this research study explores the use of a cement-less recycled aggregate concrete, a sustainable approach for future constructions. This study uses fly ash, an industrial waste of coal power plants, as a 100% substitute for OPC. Moreover, this research study also uses recycled coarse aggregates (RCAs) as a partial to complete replacement for natural coarse aggregates (NCAs) to preserve natural resources for future generations. In this research investigation, a total of 60 pull-out specimens were prepared to investigate the influence of steel bar diameter (9.5 mm, 12.7 mm, and 19.1 mm), bar embedment length, (4 and 6), and percentage replacements of NCA with RCA (25%, 50%, 75%, and 100%) on the bond stress behavior of cement-less RA concrete. The test results exhibited that the bond stress of cement-less RCA concrete decreased by 6% with increasing steel bar diameter. Moreover, the bond stress decreased by 5.5% with increasing bar embedment length. Furthermore, the bond stress decreased by 7.6%, 7%, 8.8%, and 20.4%, respectively, with increasing percentage replacements (25%, 50%, 75%, and 100%) of NCA with RCA. An empirical model was developed correlating the bond strength to the mean compressive strength of cement-less RCA concrete, which matched well with the experimental test results and predictions of the CEB-FIP model for OPC. The CRAC mixes exhibited higher costs but significantly lower embodied CO2 emissions than OPC concrete.

USE OF WASTE PLASTIC WITH BACTERIAL COATING AS A SUSTAINABLE BUILDING MATERIAL IN CONCRETE

The use of plastic is increasing day by day, although steps were taken to reduce its consumption. The suitability of recycled plastics shredded as coarse aggregate in concrete and its advantages are discussed here. Tests were conducted to determine the properties of plastic aggregate density, specific gravity and aggregate crushing value. As 100% replacement of natural coarse aggregate (NCA) with shredded plastic is not feasible, partial replacement at various percentage were examined. Higher compressive strength was found with 5% NCA replaced concrete.

Optimal utilization of low-quality construction waste and industrial byproducts in sustainable recycled concrete

Construction and demolition waste (CDW) contains abundant low-quality recycled brick aggregates (RBA) that can potentially substitute natural aggregates (NA) in concrete production. However, recycled brick aggregate concrete (RBAC) shows inferior mechanical and durability performance compared to natural aggregate concrete (NAC), posing barriers to RBAC widespread adoption. This study investigates the combined influence of supplementary cementitious materials (SCMs) derived from industrial byproducts and hooked-end steel fibers (HSF) on properties of concrete with 0%, 50% and 100% RBAs from CDW as replacement for natural coarse aggregates (NCA). Addition of 0.5% HSF and 20%, 10%, and 30% fly ash (FA), silica fume (SF), and ground granulated blast furnace slag (GGBS) as cement replacement, respectively, were considered. Effect of different SCMs and HSF on compressive strength, splitting tensile strength, flexural strength, ultrasonic pulse velocity (UPV), water absorption (WA), freeze-thaw (FT) and acid attack resistance of concrete were studied. Results indicated that individual incorporation of HSF showed more contribution towards mechanical performance while combined incorporation of SCMs and HSF enhanced both mechanical and durability properties, along with reduction of up to 15.6% in embodied carbon of RBAC. Microstructural examination showed pore refinement and interfacial transition zone densification in RBAC with SCMs and HSF. This study demonstrates that sustainable RBAC with excellent mechanical and durability requirements could be produced using demolished brick waste and industrial byproducts.

Effects of Over-burnt Bricks on Gradation, Water Absorption and Specific Gravity of Aggregates, Workability and Compressive Strength of Concrete

Demand of bricks is increasing day by day by the requirement of new structures. Due to manufacturing of bricks, over-burnt bricks are also made. Generally over-burnt bricks are the waste materials which is generally used for dumping purpose and sometime it is thrown in useful land that create social and environmental problems. Therefore, this material should be properly treated, recycled and used in concrete as coarse aggregate. In this research work, six (06) batches were made with 1:2:4 mix and 0.5 water cement ratio. Each batch consists of five (05) samples. Six (06) batches were made with 0%, 20%, 40%, 60%, 80% and 100% replacement of natural coarse aggregates with over-burnt bricks aggregates. The outcome of study reveals that the gradation of both the aggregates shows same pattern and the trend of curve was almost similar, with minor difference in range values over a sieve. The water absorption of over-burnt bricks aggregates was more than the water absorption of natural coarse aggregates and the specific gravity of over-burnt bricks aggregates was less than the specific gravity of natural coarse aggregates. The result of slump test shows that there was continuous decrease in workability of concrete mix, as replacement of over-burnt bricks aggregates increased. 30 concrete cubes of (6” x 6” x 6”) size were prepared and cured for 28 days followed by compressive strength. The result shows that the concrete derived from over-burnt bricks aggregates attained lower compressive strength than the regular concrete. However, the values obtained from over-burnt bricks aggregates are still acceptable, especially for reasonable levels of the replacement ratio up-to 60%. This concrete can be used in new constructions, but it is proposed to be initially utilized in low load areas.

Influence of recycled coarse aggregate on properties of fly ash and slag-based geopolymer concrete cured under oven and ambient temperature

Purpose The purpose of this paper is to investigate the effect of the replacement of natural coarse aggregate (NCA) with different percentages of recycled coarse aggregate (RCA) on properties of low calcium fly ash (FA)-based geopolymer concrete (GPC) cured at oven temperature. Further, this paper aims to study the effect of partial replacement of FA by ground granulated blast slag (GGBS) in GPC made with both NCA and RCA cured under ambient temperature curing. Design/methodology/approach M25 grade of ordinary Portland cement (OPC) concrete was designed according to IS: 10262-2019 with 100% NCA as control concrete. Since no standard guidelines are available in the literature for GPC, the same mix proportion was adopted for the GPC by replacing the OPC with 100% FA and W/C ratio by alkalinity/binder ratio. All FA-based GPC mixes were prepared with 12 M of sodium hydroxide (NaOH) and an alkalinity ratio, i.e. sodium hydroxide to sodium silicate (NaOH:Na2SiO3) of 1:1.5, subjected to 90°C temperature for 48 h of curing. The NCA were replaced with 50% and 100% RCA in both OPC and GPC mixes. Further, FA was partially replaced with 15% GGBS in GPC made with the above percentages of NCA and RCA, and they were given ambient temperature curing with the same molarity of NaOH and alkalinity ratio. Findings The workability, compressive strength, split tensile strength, flexural strength, water absorption, density, volume of voids and rebound hammer value of all the mixes were studied. Further, the relationship between compressive strength and other mechanical properties of GPC mixes were established and compared with the well-established relationships available for conventional concrete. From the experimental results, it is found that the compressive strength of GPC under ambient curing condition at 28 days with 100% NCA, 50% RCA and 100% RCA were, respectively, 14.8%, 12.85% and 17.76% higher than those of OPC concrete. Further, it is found that 85% FA and 15% GGBS-based GPC with RCA under ambient curing shown superior performance than OPC concrete and FA-based GPC cured under oven curing. Research limitations/implications The scope of the present paper is limited to replace the FA by 15% GGBS. Further, only 50% and 100% RCA are used in place of natural aggregate. However, in future study, the replacement of FA by different amounts of GGBS (20%, 25%, 30% and 35%) may be tried to decide the optimum utilisation of GGBS so that the applications of GPC can be widely used in cast in situ applications, i.e. under ambient curing condition. Further, in the present study, the natural aggregate is replaced with only 50% and 100% RCA in GPC. However, further investigations may be carried out by considering different percentages between 50 and 100 with the optimum compositions of FA and GGBS to enhance the use of RCA in GPC applications. The present study is further limited to only the mechanical properties and a few other properties of GPC. For wider use of GPC under ambient curing conditions, the structural performance of GPC needs to be understood. Therefore, the structural performance of GPC subjected to different loadings under ambient curing with RCA to be investigated in future study. Originality/value The replacement percentage of natural aggregate by RCA may be further enhanced to 50% in GPC under ambient curing condition without compromising on the mechanical properties of concrete. This may be a good alternative for OPC and natural aggregate to reduce pollution and leads sustainability in the construction.

Investigation of tensile strength performance of green concrete incorporating steel slag

This study examined the compressive and tensile strength performance of steel slag-containing concrete composites in a sulphate environment. Steel slag sourced locally was mechanically crushed and sieved into aggregates ranging in size from 20 to 1 mm. The control concrete of grade 20 and other five (5) batches of concrete with 10 to 50% steel slag at a step of 10% as replacement for natural coarse aggregate were produced. The physical properties of the aggregate specimens (steel slag and granite) were evaluated in the laboratory, as well as the concrete workability and the 7- and 28-day compressive and tensile strengths after exposure to 50 g/l of magnesium and sodium for 7 and 28 days. According to the results, the concrete workability decreased as the steel slag content increases. The 20 N/mm2 desire strength with rise in compressive and split tensile strengths as the steel slag contents increased from 0 to 50% after curing in water for 28 days. The concrete compressive and tensile strengths improved with steel slag content ranging from 0 to 40% but decreased with increase in steel slag content from 30 to 50% after exposure to Na2SO4 for 28 days. For the concrete exposed to MgSO4, the compressive and split tensile strengths increased when the steel slag content increased from 0 to 40% before it decreased with further increase in steel slag from 40 to 50% after 28 days. The experimental findings revealed that up to 40% steel slag is sufficient as replacement for natural coarse aggregate in concrete work exposed to aggressive sulphate climate. Thus, for improved compressive and tensile performance, the optimum of 40% steel slag is suggested as replacement for natural coarse aggregate substitution for healthier sulphate attack resistance.

Dynamic compressive behaviors of polyethylene terephthalate fiber reinforced recycled aggregate concrete

AbstractPolyethylene terephthalate (PET) fibers are green, environmentally friendly materials. They mainly come from recycled plastic bottles and other products. The addition of PET fibers to recycled aggregate concrete (RAC) has the potential to reduce concrete damage and increase specimen toughness. In this study, the influences of recycled coarse aggregate (RCA) replacement ratio and fiber volume ratio on the impact response of PET fiber reinforced RAC at various strain rates were experimentally investigated. It was found that the compressive strength, critical strain, and toughness grew with the increasing strain rate, followed by the aggravation of the concrete damage. Owing to the strain rate effect, the failure mode of concrete specimen at a high strain rate was different from that under a quasi‐static loading. This led to the reduction of differences in the dynamic compressive strength between the natural and recycled aggregate concrete at a high strain rate. Although the replacement of natural coarse aggregates with RCAs resulted in the decrease in the dynamic compressive strength, it increased the critical strain of the specimen. To reduce the brittleness of concrete materials, flexible fibers, PET fibers were added into the concrete matrix. It was found that the addition of PET fibers increased the critical strain and significantly reduced concrete damage. The empirical equations were proposed to describe the rate‐dependent dynamic compressive strength, critical strain, and toughness based on experimental data.

Experimental investigation of eco-friendly fiber-reinforced concrete using recycled and natural fibers, integrated with recycled aggregates

This study investigates the integration of recycled and natural fibers with recycled concrete aggregates to develop environmentally friendly fiber-reinforced concrete (FRC), with a primary aim of maintaining or enhancing its properties. Four concrete mixtures, namely plain concrete (C-Plain), recycled steel fiber-reinforced concrete (C-RSF), recycled plastic fiber-reinforced concrete (C-RPF), and kenaf fiber-reinforced concrete (C-KF), were formulated and analyzed for their fresh, hardened, and durability characteristics. A 50% replacement of natural coarse aggregates’ weight with recycled concrete aggregates (RCA) was implemented. By standardizing fiber volume fractions at 1.0% for all FRC mixtures, the study evaluated properties such as workability, dry density, ultrasonic pulse velocity (UPV), compressive strength, modulus of elasticity, post-cracking flexural performance, modulus of rupture, flexural toughness, splitting tensile strength, and freeze-thaw resistance after 100 and 300 cycles. Testing involved three specimens for each parameter at 7 and 28 days. The results indicated positive effects on post-cracking flexural performance, modulus of rupture, flexural toughness, splitting tensile strength, and durability with the incorporation of recycled and natural fibers. Notably, C-RSF demonstrated the highest compressive strength (46.63 MPa), flexural toughness (64.35 kN-mm), and modulus of rupture (7.46 MPa) compared to other FRC composites. Additionally, it exhibited minimal weight loss (2.18% and 3.07%) after freeze-thaw cycles, indicating exceptional durability. C-RSF exhibited superior performance, while C-KF showed enhancement slightly below that of C-RSF. Although not reaching the level of C-RSF, C-RPF positively influenced concrete performance. Compressive response either maintained performance or exhibited marginal reduction. The findings carry significant implications for developing environmentally conscious construction materials with enhanced mechanical and durability properties, thereby advancing sustainable construction practices.

USE OF RECYCLED AGGREGATE TO REPLACE AGGREGATE NATURAL REINFORCED WITH STEEL FIBER

This paper aims to use and manufacture recycled aggregate from the use of RCD (construction and demolition waste) for partial replacement of natural coarse aggregate in the manufacture of concrete for structural purposes. Partial replacements were made with between 10% and 20% recycled aggregate. Six experimental groups were created, two for reference and four for comparison. Each group comprised eight (8) cylindrical specimens (dimensions of 100 mm x 200 mm) and a beam (dimensions of 150 mm x 150 mm x 600 mm). The results indicated the feasibility of replacing up to 20% of natural aggregate with recycled aggregate, according to the processing procedures outlined in this study, particularly in relation to compression properties. Furthermore, the validity of substitution of up to 10% for evaluations of tensile strength in compression was verified, showing an analogous behavior between the corresponding samples.

Experimental Investigation on Plastic Aggregate and Silica Fume In Concrete

Plastic consumption is increasing on a daily basis, despite efforts to minimize it. On the other hand, the management of waste plastic was a significant issue in several countries around the world. A healthy and sustainable reuse of plastics has numerous benefits. The acceptability and benefits of recycled plastics as Coarse aggregate in concrete are explored here. Plastic aggregate parameters such as density and specific gravity were determined through tests. Because complete replacement of natural Coarse aggregate with plastic Coarse aggregate is impractical, partial replacement at various percentages was investigated. In addition to that silica fume is added as a binding material at a constant of 10%. The substitution of 15 Percent Plastic aggregate resulted in high compressive, splitting tensile, and flexural strength.

Evaluation Of Mechanical Properties And Water Absorption Replacing Natural Coarse Aggregate With Recycled Aggregate In Concrete

The Indian construction sector is surge to be slated in resulting significant rise in gap with respect to construction materials such as aggregates (fine and coarse), cements and bricks etc. On the side, the huge number of unseasoned Construction and Demolition (C&D) waste posed consequent issue in one or the other place, especially in buildings like residential, institutional, industrial or commercial construction navel. Extensive research attempts to analyze and discuss the existing codification and challenges, and recommends an information structure for standardized collection, storage, treatment/processing, and disposal of C&D waste. The application of recycled aggregate (RA) , its limitations, and the best practices of utilizing these aggregate are important constituents of the proposed framework for processing mechanism, potential management in India. In the present paper it is discussed and focused on the prejudicial impact of recycled aggregate, ways to generate less wastes and its proper handling. Also the effects of recycled aggregate concrete on compressive strength and split tensile strength by using recycled aggregate as a replacement of natural coarse aggregate (NCA). Percentages replacement used were 20%, 40%, 60%, 80% and 100% with 0% replacement was used as control. Mix design of 1:1.5:2 was used in the study with water to cement ratio of 0.45. Influence of RCA on compressive strength was determined for all the mixes as per IS 516:1959 standard. Results of compressive strength indicated that concrete with 40% replacement of NCA can be effectively used in structural concrete without incorporating much on strength. Also the water absorption test was conducted to assess the one of durability property of the concrete replaced with RA.

Orthogonal experimental design for compressive strength of recycled coarse aggregate concrete with silica fume-slag-fly ash hybrid micro-powders

Recycled Coarse Aggregate Concrete (RAC) is a type of concrete that uses recycled coarse aggregate (RCA) instead of natural coarse aggregate (NCA), which helps to reduce the negative environmental impact of construction waste. In order to improve the low compressive strength of RAC and solve the problem of shortage of natural aggregates, this paper develops a high-performance concrete called recycled coarse aggregate concrete with silica fume-slag-fly ash hybrid micro-powders (HMRAC) by replacing part of the cement with a mixture of micronized silica fume (SF), slag (SG) and fly ash (FA) and using RCA of 50% mass instead of NCA. The optimum combination parameters and prediction model for the compressive strength of HMRAC were also proposed by orthogonal experimental design. A constant water-cement ratio of 0.45 and a 50% mass replacement of natural coarse aggregate (NCA) by recycled coarse aggregate (RCA) were adopted in the experiment, and the mass replacement ratios of silica fume (SF), slag (SG), and fly ash (FA) for ordinary Portland cement (OPC) were used as the test variables. In total, 16 combinations were tested, including a control group where 50% of the NCA mass was replaced by RCA. First, we investigated the degree and significance of the effect of the mass substitution ratio of SF, SG, and FA on the compressive strength of HMRAC using analysis of variance (ANOVA) and extreme difference analysis. Then, we determined the optimal combination ratio of SF, SG, and FA. Secondly, multiple regression analysis was used to propose a multiple regression model for predicting the compressive strength of HMRAC. Finally, we computed and analyzed the carbon emissions of HMRAC. The results indicated that the mass substitution rates of FA and SG had a greater effect on the compressive strength, and the mass substitution rate of SF had a lesser effect on the compressive strength. The interaction of SF, SG, and FA can significantly enhance the compressive strength of RAC. The optimal compressive strength performance of HMRAC was observed when the proportions were as follows: SF constituted 10%, SG made up 15%, and FA accounted for 5%. The regression model has reasonable accuracy and a small standard deviation of residuals. It can effectively predict the compressive strength value of HMRAC, aligning well with the experimental results. It exhibits a superior carbon reduction rate of 21.90%, compared to conventional concrete.

Effect of recycled crushed glass and recycled coarse aggregate on the properties of self-compacting concrete

This research was developed to use recycled coarse aggregate (RCA) and recycled crushed glass (RCG) to produce self-compacting concrete (SCC) mixtures. Natural coarse aggregate (NCA) was replaced by RCA from 0% to 100%, and natural fine aggregate (NFA) was replaced by RCG from 0% to 20%. Slump flow with T500 time, L-box, and V-funnel tests were done to ascertain the workability properties of SCC mixtures. The mechanical properties studied were compressive, flexural, and splitting tensile strength at 28 and 56 days. Ultrasonic pulse velocities (UPV) were also measured for the SCC mixtures at 28 and 56 days. Ten shear-critical beams with different shear span-to-depth (a/d) ratios were also cast and tested under 4-point bending. Cracking load, failure load, load-midspan deflection curves, and deflection corresponding to ultimate load were observed. The recommendations of the American Concrete Institute (ACI 318–14 and ACI 318–19), Eurocode (EC2), and Japanese Society of Civil Engineers (JSCE) for shear design were also evaluated on a database of 222 beams cast with SCC and recycled aggregate concrete (RAC) along with the beams tested in the presented study. Results indicate that the workability and mechanical properties were reduced when the replacement level of RCA was increased. The use of RCG as a replacement for NFA enhanced the workability properties and mechanical properties at the age of 56 days. The replacement of NCA with RCA slightly reduced the shear capacity and stiffness of the RC beams. However, the shear capacity and stiffness of RC beams improved when NFA was replaced with RCG. The design provisions of ACI 318–19 yielded accurate estimates of shear capacity compared to JCSE, EC 2, and ACI 318–14.

Punching Behaviour of Flat Slab Using Recycled Aggregate

Recently, researchers have shown an interest in researching recycling aggregates from old concrete and using them in new construction as a means of protecting the environment and natural resources. This thesis includes an experimental investigation into the punching shear behaviour of continuously supported slabs of concrete with natural and recycled coarse aggregate. In the Laboratory at the MS Ramaiah Institute of Technology the tests on punching shear behaviour of inner slab-column connections in flat plates. ''Natural and recycled'' aggregates were used in six two-way slab models. The slabs were made to only fail while being used as a punching shear. Three specimens of recycled aggregate concrete (RAC) slabs and three specimens of natural aggregate concrete (NAC) slabs were used in the experimental study. Simply supported on four edges, all of the slabs were tested using a central patch load. In order to attain a 25 MPa concrete strength after 28 days, the IS mix design technique was used. For each aggregate size of 12.5mm (Downsize), five concrete mix proportions were used with (0%, 25%, 50%, 75%, and 100%) replacement of natural coarse aggregate with recycled coarse aggregate. Then, casting with a size of 1000 × 1000 × 100 mm was tried with 0% and the highest of the other four (75%). The test findings were then compared with the experimental data and the Codal Provisions for the Accuracy of Ultimate load.

Development of chemistry-informed interpretable model for predicting compressive strength of recycled aggregate concrete containing supplementary cementitious materials

Accurate prediction of compressive strength of recycled aggregate concrete (RAC) has great value for promoting the sustainable development of concrete field. The study aims to propose a chemistry-informed interpretable model for predicting compressive strength of RAC containing supplementary cementitious materials. First, this study collected the compressive strength records of RAC. Then, the unsupervised learning algorithm isolation forest was utilized to perform data cleaning, and 1600 samples were obtained to build the dataset. And the topological network constraint was introduced to represent the reactivity of cementitious systems. The five machine learning (ML) algorithms were employed to predict compressive strength of RAC, and the prediction accuracy of above models were compared. In addition, SHapley Additive exPlanations (SHAP) method was integrated with the ML model to shed more light on the outcome of ML model. Results showed that the Categorical Boosting (CatBoost) outperformed other ML models on the test set, and the coefficient of determination (R2), root mean square error (RMSE), and mean absolute error (MAE) were 0.961, 2.650 MPa, and 1.636 MPa. The introduction of chemical information enhanced the predictive accuracy of model, and the R2 increased from 0.935 to 0.961, the RMSE and MAE decreased by 22.7% and 15.1%, respectively. The SHAP values of curing age, natural coarse aggregate replacement ratio and water-binder ratio were higher than those other input variables, indicating that the three features were essential for predictive results of model. And the curing age played a positive role in the strength development of RAC, and the increase of natural coarse aggregate replacement ratio and water-binder ratio caused the loss of compressive strength. The influence trends of features on the outputs were in accord with the engineering experience, which proved the reliability of predictions. The contribution and importance of features on the predictions provide a theoretical guidance to aid the concrete mixture design for engineers to obtain the desired performance.

Structural and life cycle assessments of recycled aggregate concrete beams incorporating industrial hemp fibers

AbstractAs a sustainable concrete material, hemp and recycled aggregate concrete (HRAC) is produced by partial replacement of natural coarse aggregates (NCA) with recycled concrete coarse aggregates (RCA) and industrial hemp fibers. The objective of the reported research was to investigate the structural performance of reinforced concrete beams prepared with HRAC and designed to fail in flexure, shear, or bond splitting modes of failure, and to compare that performance with companion control beams cast with conventional concrete. The significance stems for the fact that no previous research is reported on mixtures using such a combination of hemp fibers and RCA. Test results indicated that HRAC beams with 0.75% volumetric percentage hemp fibers and 50% RCA replacement had comparable peak load capacities to the control beams with no RCA and no fibers, with ±4% difference for all tested modes of failure. Additionally, the fracture energy of the HRAC beam was higher than the control beam by 3.6%, 17.9%, and 14.4% for the flexure, shear, and bond modes of failure, respectively. Moreover, a life cycle analysis (LCA) was considered to compare HRAC mix with conventional concrete mix in terms of the environmental aspects. LCA results indicated that HRAC is a sustainable concrete, specifically with respect to structural performance and lower environmental impact.

Performance of slag based recycled coarse aggregate concrete with steel fibers

Designers may lessen the impact of concrete on the environment while yet ensuring enhanced performance and higher durability by using slag cement, which has proven long-term performance advantages. However, in actual practice, concrete constructions use slag to replace OPC up to 30 to 50 percent of the time, depending on the uses. By using M sand in place of river sand, this study shows differences in the strength and durability parameters of concrete manufactured using 100% with slag cement. Mechanical and durability study was made on replacement of natural coarse aggregates (NCA) with 30, 45 and 60% of recycled coarse aggregates (RCA); Based on the study optimum percentage of recycled aggregates for slag based concrete is 45%. Thus to study effect of fiber on concrete 45% of natural aggregates replaced by recycled aggregates with and without Nano silica.This reduces the consumption of natural resources and adds some additional benefits from a structural and financial standpoint. Steel fibers are added at a rate of between 0.5, 1 and 1.5 percent by volume of cement to give it strength. In order to obtain the optimum percentage of steel fibres using slag cement, concrete grades M20, M25, M30 and M35 were used. Testing techniques such as the compression test, flexural test, spill tensile test, Rapid Chloride penetration test used to assess properties recycled aggregate concrete and also performed the life cycle assessment. From the experimental study 1% Steel fibers was optimum for both with and without Nano silica.