•A research on the acquisition of macro-mechanical data of the ITZ in the meso-mechanical calculation of concrete.•The mechanical properties of the ITZ with different mix ratios were measured, the ...relationship between the bond strength and the microhardness of the ITZ in concrete is established.•A two-parameter linear relationship between the splitting tensile strength of the interface bond and the age and the W/B ratio was established.•The priority order of the calculated value of the interface strength in the numerical analysis of concrete meso-mechanics is proposed.
The problem of taking macro-mechanical data of the interface between aggregates and slurry in the calculation of meso-mechanics of concrete was studied in this paper. Through a systematic standard interface test study where the interfacial bond splitting tensile strength method and the interfacial transition zone (ITZ) microhardness method were used, mechanical properties were investigated at macro-scale (bond strength), and followed by ITZ microhardness at meso-scale, moreover the relationships between macro- and meso-mechanical properties were established. The results show that interfacial bond splitting strength of aggregates-slurry gradually increases with increasing hydration age and decreases with increasing water-binder ratio; the ITZ thickness decreases and the ITZ microhardness valley value increases with the extension of curing age. There is a certain correlation between macro-scale mechanical strength of interface and meso-scale mechanics of ITZ. There is a significant linear relationship between the splitting tensile strength of the interface bond and the splitting tensile strength of the cement slurry, so the interface strength can be calculated according to the splitting tensile strength of the slurry substrate. The interfacial bond splitting tensile strength and ITZ microhardness valley have different degrees of correlation. The interfacial bond splitting tensile strength has a particularly significant linear relationship with the microhardness value of the cement paste substrate. Therefore, the calculation value of the interface strength in the numerical analysis of concrete micromechanics should preferably adopt the linear relationship formula with the microhardness of the cement paste substrate.
•Sisal and coconut fibers were incorporated in the geopolymer mortar.•The properties of geopolymer mortar reinforced with fibers were tested.•The natural fibers test results were compared with ...synthetic fiber (glass fiber).•Natural fiber significant improves the indirect tensile strength similar to glass fiber.
This study investigated the properties of high calcium fly ash geopolymer mortars containing natural fibers. Two types of natural fibers, namely sisal fiber and coconut fiber were incorporated in the geopolymer mortar with varying proportions at 0%, 0.5%, 0.75%, and 1.0% volume fraction. The mechanical, thermal, and physical properties of geopolymer mortar reinforced with fibers were tested and compared with those of glass fiber (synthetic fiber) and control (0% fiber) geopolymer mortars. Results revealed that the addition of natural fiber (sisal and coconut fibers) as reinforcing materials resulted in significant improvement in tensile and flexural strength performances similar to the use of glass fiber. Meanwhile, the workability, dry density, ultrasonic pulse velocity, and compressive strength values tended to decrease.
In this study, the size effect on the strength of wastewater concrete under freeze-thaw cycles was evaluated. Cube specimens of wastewater concrete with side lengths of 40 mm, 100 mm, 150 mm, and ...200 mm were prepared, and the resulting compressive and splitting tensile strengths after exposure to 0, 10, 20, 30, 40, and 50 freeze-thaw cycles were determined. The results show that the size effect is increasingly affected by freeze-thaw cycles with the increase in the number of cycles, while the corresponding specimen brittleness is gradually reduced, and the plasticity is enhanced. The modified Bažant size effect model considering the effect of freeze-thaw cycles on size effect was established. The modified size effect curve considering the freeze-thaw damage can be used to predict the initial strength of specimens after freeze-thaw cycles. The predicted data points were mainly distributed on the size effect curve and could directly reflect the size effect phenomenon of wastewater concrete without freeze-thaw cycles.
•A modified Bažant size effect model considering freeze-thaw damage was established.•The strength size effect regularity of wastewater concrete under freeze-thaw cycle is revealed.•Based on the modified model, the initial strength of wastewater concrete could be predicted.
•Properties of high strength concrete (HSC) with PET waste fiber were investigated.•Behavior of reinforced concrete beam made of (HSC) with PET fiber was investigated.•Existence of PET waste fiber ...has some effect to enhance the crack control of HSC.•Compressive strength loss was observed and to a lesser degree the tensile strength of concrete due to the existence of PET fiber.•Cracking performance of the beam was enhanced, but PET fiber has no appreciable effect on the ultimate load capacity.
This paper describes material properties of high strength concrete containing different PET waste fiber in terms of fiber volume and length. Structural behavior of reinforced concrete beams made of this newly developed concrete has been fairly investigated. Cracking performance of beams was found to improve as a result of using PET waste fiber, but there is no chance to increase the ultimate load capacity. There is some strength loss of the beam mainly attributed to the degradation take place in compressive strength of concrete, but mode of failure of tested concrete beams was almost identical to that of control beam without PET waste fiber. Ultimate moment capacity of concrete section with PET fiber can be calculated accurately following the recommendation of the ACI 318 code. The results are interested and can encourage researchers to work on this kind of recycled high strength concrete for structural applications in future.
•Using manufactured-sand and natural pozzolana in the production of concrete.•Proposing ML models to facilitate the production of manufactured-sand concrete (MSC)•Employing a database containing 9 ...features effective on the tensile strength of MSC.•Study the effect of stone nano powder, water/cement, and curing age on the MSC.•Comparison of the ML models’ behavior with the laboratory tests.
Many environmental issues have arisen as a result of the widespread usage of concrete, which has led to a reduction of river sand. The excessive extraction of river sand has led to various negative consequences, such as ecosystem disruption, groundwater depletion, coastal erosion, and biodiversity loss. Manufactured sand (MS) from waste deposits may be used in lieu of river sand to address this problem. In this study, to facilitate the production of manufactured sand concrete (MSC), the potential of twelve machine learning (ML)-based models was examined. These models were trained and tested on 248 and 62 laboratory datasets containing nine features effective on the mechanical properties of MSC. MSC's splitting tensile strength (STS) was considered the model's target. The influences that the water-to-cement (W/C) ratio, the stone nano-powder content (SNPC), and the curing age (CA) have on the STS of MSC were also analyzed. Detailed analysis of the results revealed that all the well-tuned ML models have acceptable potential for estimating the STS of MSC; however, the extra tree regressor (ETR) model was in the highest agreement with the laboratory results. Both the ML and laboratory findings showed that MSC with 10% SNPC benefits the long-term STS of MSC. A graphical user interface for the ML-based models was also developed to further aid in the estimation of STS for engineering challenges.The proposed models can be a suitable alternative to time-consuming, expensive, and complex laboratory methods to facilitate the MSC production.
•Influence of FRA on mechanical properties of RAC with different CRA contents.•Prediction model for elastic modulus of RAC using FRA and CRA.•Prediction model for splitting tensile strength of RAC ...with FRA and CRA.
This study aims to develop models for the elastic modulus (Ec) and splitting tensile strength (ftsp) of recycled aggregate concrete (RAC) incorporating coarse recycled aggregate (CRA) and fine recycled aggregate (FRA). An experiment was performed on 15 groups of RAC, using one type of CRA and two types of FRAs. Meanwhile, CRA replacement ratios (rCRA) of 0, 50, and 100% were used, while for each rCRA, three replacement ratios of each FRA (0, 50, and 100%) were investigated. Furthermore, the slump value, compressive strength, Ec, and ftsp were tested and analyzed. Based on the results, new models accounting for the influence of recycled aggregate were developed and validated using a database of test data. The results showed that: (1) the influence of FRA on the tested properties is independent of the CRA content, (2) the proposed models can effectively predict the Ec and ftsp of RAC.
An experimental investigation has been carried out to repair pre-existing cracks in mortar using the microbiologically induced calcium carbonate precipitation (MICP) technology. In the study, 20 ...cylinder mortar samples (50 mm in diameter and 40 mm in height) were split to have cracks with various sizes. Sixteen of the cracked samples, an average width ranging from 0.15 to 1.64 mm, were repaired using the MICP method, while four cracked samples, with an average width ranging from 0.17 to 1.72 mm, were soaked under distilled water. The water permeability and splitting tensile strength (TS) of these repaired mortars were tested. The amounts of calcium carbonate (CaCO3) precipitated on the cracked mortar surfaces were evaluated. The morphology of the CaCO3 was observed under a scanning electron microscope (SEM). The results indicated that the MICP repair technique clearly reduced water permeability of the cracked samples. While water-treated samples were too weak to test, the MICP-repaired samples had TS ranging from 32 to 386 kPa after 21 cycles of MICP solution treatment. A relationship between the TS and amount of CaCO3 precipitated was observed for samples with an average crack width between 0.52 and 1.1 mm, which indicated that TS increased with the amount of CaCO3 precipitated on the crack surfaces. The SEM revealed that the precipitated CaCO3 had possibly two forms: vaterite and calcite.
•Permeability of mortar is reduced after cracks are repaired using MICP technology.•Samples has regained up to 386 kPa of splitting tensile strength (TS) after the MICP repair.•TS regain from the repair is related to the amount of biogenic CaCO3 precipitated on crack surfaces.•The precipitated CaCO3 observed in the present study had possibly two forms: vaterite and calcite.
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•3D printing is an encouraging method to manufacture the lower tensile strength of CTB material.•Three shapes (cross, quarter, and 8 equal parts) of 3D printing polymers (3D-PPL) were ...employed.•Dynamic splitting characteristics of 3D-PPL reinforced CTB unveiled a robust strain rate dependence.•The best mechanical strength results were obtained for cross-shaped reinforced CTB (31.6% increase)•Addition of 3D-PPL effectively inhibits the overall damage process of ordinary CTB materials.
Originally developed for polymer materials, 3D printing is an encouraging technique to create versatile geometric shapes and high-precision construction elements from various materials. 3D-printed polymer structures are now employed effectively in various industries, including construction and mining since they significantly improve the ductility properties of cementitious materials like cemented tailings backfill (CTB). Considering the lower tensile strength of CTB (compared to its compressive strength), the study of fill's tensile properties is significant for improving the safety and ensuring the stability of the underground CTB structures. Indeed, this aspect is fairly crucial for the development of green mining which allows sustainable and affordable mining operations. To supremely enhance the tensile strength of CTB, three kinds (OR: ordinary resin) and forms (cross, quarter, and 8 equal parts) of 3D printing polymers (3D-PPL) were employed for this study. A number of experiments including Brazilian splitting tests, digital image correlation (DIC) measurements, and SEM failure/micro-structure analyses were fulfilled for exploring both dynamic splitting and crack propagation behavior of 3D-PPL reinforced CTBs. Results designated that dynamic splitting characteristics of 3D-PPL reinforced CTB samples unveiled a robust strain rate dependence. Besides, the tensile strengths of 3D-PPL reinforced CTB samples are increased under the same conditions and the best results are obtained for cross-shaped reinforced CTB increased by 31.6%. 3D-PPL reinforced CTB samples are characterized with higher strains, and the addition of 3D-PPL effectively inhibits the overall damage process of ordinary CTB and improves the backfill’s strength property. As a result, the results of this study are vital and prominent for realizing the tensile/crack behavior of the backfills placed in underground mined-out openings.
Amidst a world of never-ending waste production and waste disposal crises, scientists have been working their way to come up with solutions to serve the earth better. Two such commonly found trash ...deteriorating the environment are glass and tin can waste. This study aims to investigate the comparative suitability of response surface methodology (RSM) and artificial neural network (ANN) in predicting the mechanical strength of concrete prepared with fine glass aggregate (GFA) and condensed milk can (tin) fibers (CMCF). An experimental scheme has been designed in this study with two input variables as GFA and CMCF, and two output variables compressive and splitting tensile strength. The results show that both variables influenced the compressive and splitting tensile strength of concrete at 7, 28, and 56 days (p < 0.01). The maximum compressive and splitting tensile strength was found at 20% GFA with 1% CMCF and 10% GFA with 0.5% CMCF, respectively. The model predicted values in both techniques were in close agreement with corresponding experimental values in all cases. The results of different statistical parameters in terms of coefficient of correlation, coefficient of determination, chi-square, mean square error, root mean square error, mean absolute error, and standard error prediction indicate the functionality of both modeling approaches for concrete strength prediction. However, RSM models yield better accuracy in simulating the compressive and splitting tensile strength of concrete than ANN models.
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•Mechanical properties of concrete containing WFS are modeled using M5P model.•Elastic modulus, compressive, flexural, and splitting tensile strengths are studied.•Predictive models ...with reliable accuracy are developed for the mechanical properties.•More comprehensive dataset can improve the performance of the developed models.
Concrete is the most commonly used man-made material in buildings, pavements, and dams. The production of concrete requires large quantities of fine and coarse aggregates. To preserve the natural resources, the use of waste and by-product materials in concrete mixtures has been given lots of attentions. Fresh and hardened properties of the concrete mixtures containing waste foundry sand (WFS) as a partial or full replacement for fine aggregate have been the focus of several recent studies. The use of predictive models for the properties of the concretes can save in time and energy and provide information on scheduling the activities such as framework removal. In this study, M5P algorithm was used to model the compressive strength, modulus of elasticity, flexural strength, and splitting tensile strength of these concretes. For this purpose, a comprehensive dataset containing information on the mixture proportions and the values of the mechanical properties at different ages was collected from internationally published documents. The dataset was divided into two subsets of training data and testing data. Several performance metrics were used to evaluate the performance of the developed models. The results indicated that the proposed models can provide reliable predictions of the target mechanical properties. A more comprehensive dataset can further improve the performance of the models.
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