•New models are developed by GEP technique to predict mechanical properties of recycled aggregate concrete (RAC).•A comprehensive database covering a wide range of parameters is assembled through an ...extensive review of the literature.•weff/c and RCA% are the most influential parameters on mechanical properties of RAC.•Simple and accurate formulations with a wide range of applicability have been proposed.•Predictions of the proposed models are consistent with those of the currently used code expressions for natural aggregate concrete.
This paper presents new empirical models for prediction of the mechanical properties of recycled aggregate concrete (RAC) using gene expression programming (GEP) technique. A large and reliable test database containing the results of 650 compressive strength, 421 elastic modulus, 346 splitting tensile strength, and 152 flexural strength, tests of RACs containing no pozzolanic admixtures is collated through an extensive review of the literature. The performance of existing mechanical property models of RACs is then assessed using the database, and the results of this assessment are presented using selected statistical indicators. New expressions for the predictions of 28-day compressive strength, elastic modulus, flexural strength, and splitting tensile strength of RACs are developed based on the database. The assessment results indicate that the predictions of the proposed models are in close agreement with the test results, and the new models provide improved estimates of the mechanical properties of RACs compared to the existing models.
In this study, the effect of waste glass on the mechanical properties of concrete was examined by conducting a series of compressive strength, splitting tensile strength and flexural strength tests. ...According to this aim, waste glass powder (WGP) was first used as a partial replacement for cement and six different ratios of WGP were utilized in concrete production: 0%, 10%, 20%, 30%, 40%, and 50%. To examine the combined effect of different ratios of WGP on concrete performance, mixed samples (10%, 20%, 30%) were then prepared by replacing cement, and fine and coarse aggregates with both WGP and crashed glass particles. Workability and slump values of concrete produced with different amounts of waste glass were determined on the fresh state of concrete, and these properties were compared with those of plain concrete. For the hardened concrete, 150 mm × 150 mm × 150 mm cubic specimens and cylindrical specimens with a diameter of 100 mm and a height of 200 mm were tested to identify the compressive strength and splitting tensile strength of the concrete produced with waste glass. Next, a three-point bending test was carried out on samples with dimensions of 100 × 100 × 400 mm, and a span length of 300 mm to obtain the flexure behavior of different mixtures. According to the results obtained, a 20% substitution of WGP as cement can be considered the optimum dose. On the other hand, for concrete produced with combined WGP and crashed glass particles, mechanical properties increased up to a certain limit and then decreased owing to poor workability. Thus, 10% can be considered the optimum replacement level, as combined waste glass shows considerably higher strength and better workability properties. Furthermore, scanning electron microscope (SEM) analysis was performed to investigate the microstructure of the composition. Good adhesion was observed between the waste glass and cementitious concrete. Lastly, practical empirical equations have been developed to determine the compressive strength, splitting tensile strength, and flexure strength of concrete with different amounts of waste glass. Instead of conducting an experiment, these strength values of the concrete produced with glass powder can be easily estimated at the design stage with the help of proposed expressions.
•Coal gangue is used instead of fine and coarse aggregates to improve utilization rate.•A coal gangue concrete model is proposed for predicting splitting tensile strength.•Volcanic-activated SiO2 and ...Al2O3 participate in secondary hydration reaction.•Hydration product gismondine is observed in the reaction of coal gangue concrete.
Coal gangue is waste rock generated from coal mining, which results in vast land occupation in mines and severe environmental pollution. Owing to the similarity between coal gangue and natural aggregates, concrete preparation from coal gangue has been considered effective for solving gangue problems. In this study, to further improve the on-site utilisation rate of coal gangue, coal gangue was used to replace fine and coarse aggregates for preparing mortar and concrete. The macro and microscopic characteristics of coal gangue mortar (CGM) and coal gangue concrete (CGC) were investigated while considering the effects of coal gangue fine aggregate (CGFA) replacement ratio, curing time, and water-to-cement ratio. To investigate the macro properties, flexural, compressive, and splitting tensile tests were performed. The results show that CGM and CGC with an appropriate CGFA replacement ratio of 25% exhibited optimal performance. Additionally, by replacing all aggregates with CGFAs and coal gangue coarse aggregates, the 28 d compressive strengths of samples W0.5R100 and W0.4R100 were 44.8 and 52.24 MPa, respectively, which satisfied the C30–C50 concrete strength requirements. Moreover, a model is proposed for predicting the splitting tensile strength of the CGC to address the overestimation of existing national standards. For microscopic analysis, X-ray diffraction, thermogravimetric analysis, and scanning electron microscopy were conducted to illustrate the hydrated products and micromorphology of CGC under different conditions, as well as to discuss the effect of the mechanism on strength. Based on the micro analysis, the mechanism of CGFAs is summarised as a coal gangue–Ca(OH)2–H2O reaction system: volcanic-activated SiO2 and Al2O3 in CGFAs react with calcium hydroxide (CH) crystals, and more CH is consumed; subsequently, more calcium silicate hydrate gels and ettringite crystals are produced in the secondary hydration reaction, contributing to a denser microstructure and improvement in concrete strength at the late stage. In particular, gismondine is observed as a new hydration product in the reaction of CGC, which differs from that of normal concrete. This study provides a basis for the large-scale utilisation of coal gangue in situ.
Cement paste possesses complex microstructural features including defects/pores over a range of length-scales, from nanometres to millimetres in size. As a consequence, it exhibits different ...behaviour under loading depending on the size. In this work, cubic specimens in a size range of 1: 400 were produced and tested by a one-sided splitting concept using different testing instruments. The smallest specimen with size of 100 μm showed a high nominal splitting strength (18.81 MPa), an order of magnitude higher than the measured strength of 40 mm specimen (1.8 MPa). The test results were used to fit existing analytical size effect models. Although a good fit can be found for the existing size effect models, special attention should be given to the physical meaning behind these empirical parameters. In addition, a multi-scale modelling strategy that considers microstructural features at different length scales was adopted to model the trend of decreasing strength with specimen size observed in experiments. A good agreement between experimental observations and modelling results indicates that the featured material structure dominates the observed size effect on measured strength in the size range considered.
•Tire-derived aggregates (TDA) contribute to sustainability of concrete applications.•Mechanical properties of light-weight aggregate concrete with TDA are investigated.•Experimental studies include ...six mix designs containing 0–100% of TDA substituion.•The effect of TDA on compressive, tensile, flexural, and impact tests are reported.•Results provide insights on the toughness and ductility of TDLWAC.
A detailed investigation of rubberized lightweight aggregate concrete was conducted using 38 cylindrical and 36 beam specimens. Six mix designs, incorporated in the study, contained rubber replacement ratios from 0% to 100% by volume replacement of a lightweight expanded-shale coarse aggregate. The objective of this study is to investigate mechanical properties of lightweight tire-derived aggregate concrete, including compressive strength, modulus of elasticity, splitting-tensile strength, flexural strength, and flexural toughness. Further, an impact test was conducted using a falling weight to investigate dynamic properties of specimens subjected to flexure. Results suggest tire-derived aggregates reduces the mechanical strength of specimens, but, enhances ductility and toughness of materials. These enhancements are valuable for dynamic applications of lightweight concrete.
•Influence of the aggregates’ crushing process on the concrete’s (RAC) performance.•Influence on concrete mechanical properties of coarse aggregates from concrete waste.•Influence of two types of ...superplasticizer (average and high water-reducing capacity).•Relative efficiency of superplasticizers in RAC compared with conventional concrete.
Waste management has become vitally important since the demand for natural resources and the amount of construction and demolition waste have greatly increased, putting huge pressure on the environment. The main goal of this study is to evaluate the effects of the introduction of superplasticizers on some mechanical properties of concrete with recycled concrete aggregates and compare them with the corresponding properties of conventional concrete made with natural aggregates. The experimental program is described and the results of workability, specific density, compressive strength, splitting tensile strength and abrasion resistance tests carried out on concrete are presented. Two different crushing processes and their effects on aggregate properties were tested. By varying the replacement percentage of natural by recycled aggregates, with or without the addition of superplasticizers, it was possible to identify some weaknesses and strengths of the recycled aggregates concrete which can contribute to developing the more widespread use of this material.
•Concrete incorporated with silicomanganese (SiMn) slag, marine sand and seawater was studied.•SiMn slag reduced concrete compressive and tensile strengths by 9.2% and 17.5% respectively.•SiMn slag ...concrete exhibited comparable durability in the long term.•Marine sand had advantageous effect on durability of concrete.
This experimental investigation has validated the feasibility of utilizing silicomanganese (SiMn) slag, marine sand and seawater in concrete production. Compressive and splitting tensile strengths of concrete were evaluated. Assessment was also performed on concrete durability which included water absorption, sorptivity, chloride penetration and sulphate resistance. SiMn slag was found to reduce concrete compressive and tensile strengths by 9.2% and 17.5% respectively. Nevertheless, the concrete exhibited comparable durability to conventional concrete at 90-day age, though it showed reduced value at 28-day age. The research also illustrated that marine sand improved concrete durability by at least 42.3% and 11.5% in aspect of sorptivity and chloride penetration respectively, while seawater showed little effect. More durable concrete can be produced by utilizing SiMn slag, marine sand and seawater for potential industrial application.
The improper management and disposal of carbon fiber reinforced plastic (CFRP) waste to landfill or incineration can cause serious environmental implications. In recent years, efforts have been made ...to utilize recycled carbon fibers (rCFs) into the cement composites. However, no information is available on the environmental impacts of utilizing rCFs into the cement composites. In this study, efforts were made to assess the resourceful recycling of this waste to cement-based materials and to investigate the effects of recycled carbon fibers (rCFs) as reinforcement on the mechanical performance and environmental impacts of cement composites. Moreover, in-use stocks of carbon fiber reinforced plastic (CFRP) in commercial aeronautical and wind power sectors of China were calculated to estimate the prospective CFRP waste available in China for recycling. The experimental results resolved that the addition of rCFs to cement composites can provide significant improvement in mechanical performance. Among other notable results, cement composite reinforced with 1% by volume of rCFs showed optimum performance with an increase in elastic modulus, splitting tensile strength, and fracture toughness of up to 57%, 188%, and 325%, respectively. Environmental impact assessment revealed that the addition of 1% of rCFs while replacing 10% of cement with silica fume, the overall global warming potential (GWP) in terms of CO2 emissions, comes out to be 13.69% less than plain cement paste GWP impact. On the other hand, 222% of energy consumption and 70% of the cost can be saved by replacing the virgin carbon fibers (vCFs) with rCFs into the cement composites. Estimation of in-use stocks of CFRP highlighted that about 97000 Tons of CFRP waste would be cumulated into the landfills of China by the year 2044 that can be recycled to recover carbon fibers to effectively utilize them in the production of eco-friendly cement composites.
The present research work investigates the utilization of metakaolin as a mineral admixture in improving the properties of concrete mixes, containing varying percentages of recycled coarse aggregates ...(RCA). For this, fifteen concrete mixes have been designed by substituting natural coarse aggregates (NCA) with 0%, 50% and 100% RCA and cement with 0%, 5%, 10%, 15% and 20% metakaolin. Nine different properties of concrete including workability, compressive strength at three different curing ages (3, 7 and 28 days), splitting tensile strength, flexural strength, ultrasonic pulse velocity, rebound number, water absorption, density and volume of voids have been experimented to examine the effect of metakaolin and RCA on the properties of concrete. The outcomes of the study reveal that the workability becomes higher with higher percentage of RCA; however it slightly reduces when metakaolin is used. The mechanical properties like compressive strength, splitting tensile strength, flexural strength and dry density get reduced when quantities of RCA increases. The non-destructive parameters like ultrasonic pulse velocity and rebound number of concrete follows similar pattern as that of compressive strength. The water absorption and volume of voids shows higher values for recycled aggregate concrete (RAC) mixes. However, the use of metakaolin in RAC significantly reduces the water absorption and volume of voids. The optimum replacement percentage of metakaolin is found to be 15% as the RAC mixes shows best performance at this replacement level. Furthermore, the properties of concrete mix containing 100% RCA and 15% metakaolin are similar to that of normal concrete. Therefore, it is feasible to produce sustainable concrete by using maximum waste concrete i.e. 100% RCA and 15% metakaolin without much affecting the strength criteria.
•Concrete containing recycled coarse aggregates has lower mechanical properties as compared to natural aggregate concrete.•Incorporation of metakaolin enhances the characteristics of both natural and recycled aggregate concrete.•Non-destructive characteristics of recycled aggregate concrete mixes also increase with the inclusion of metakaolin.•Recycled aggregate concrete mixes containing 15% metakaolin shows similar properties as that of natural aggregate concrete.
This paper presented 180 specimens to investigate mechanical properties of steel fiber reinforced Nano-concrete (SFRNC) after elevated temperature through the method of compression test, splitting ...tension test and flexure test. The test parameters effects of different elevated temperature and different content of steel fiber on mechanical properties including compressive strength, splitting tensile strength and flexural strength of SFRNC were analyzed in this paper. The integrity of Nano-concrete after elevated temperature could be improved because of the mixing of steel fiber, which could be observed from the failure process of SFRNC. Furthermore, mixing of steel fiber can change failure mode of Nano-concrete and improve the ductility of concrete greatly. It could be summarized that the elevated temperature had negative effects on compressive strength, splitting tensile strength and flexural strength of SFRNC. And it also could be found that Nano-concrete mixed with steel fiber can improve residual compressive strength, splitting tensile strength and flexural strength of these specimens after high temperature.
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