Prediction of compressive strength of recycled aggregate concrete using machine learning and Bayesian optimization methods

Evaluating compressive strength of concrete made with recycled concrete aggregates using machine learning approach

Objective: The objective is to determine the effect of treated RCA on the mechanical strength of hardened concrete, and determine the influence of treated RCA on water transport within the matrix of hardened concrete. Aim: The study aims to use pozzolanic concentration of cement and RHA slurry to pretreat coarse RCA for full replacement of NCA for sustainable concrete production. Background: One of the common modes of disposal of construction waste is strained landfills. This study proposes a constructive way of recovering the coarse aggregates of recycled aggregates from laboratory concrete waste taken through a focused treatment process with pozzolan. The study aims to replace the proportions of the cement slurry to treat and replace with rice husk ash (RHA) for the modification of recycled concrete aggregate (RCA) and replace fully natural coarse aggregate (NCA) for sustainable concrete production. One of the main challenges of recycled concrete aggregate (RCA) is the fractured surface, which often results in reduced strength and loss of concrete durability. The strength of concrete with RCA is principally influenced by the fractured hardened paste attached to the surface, predominantly characterized by voids and gaps resulting from its production using a mechanical method. High water penetration within and around the aggregate matrix due to the presence of micro- and macro-cracks results in strength and durability deterioration of concrete. Methods: This study addresses these problems by specifying aggregate treatment with a pozzolanic slurry of cement and RHA. This was conducted in two (2) phases; first, to determine the optimum proportion of cement slurry concentration (0, 20, 40, 60, 80, and 100%), and second, to increase the silicate formation in cement slurry by substituting the proportions of cement with RHA (0, 5, 10, and 15%). The performance of concrete was evaluated by mechanical strength (compressive and split tensile strength) at 7, 28, and 56 days and water transport within the concrete (surface suction and submergence) at 28 and 56 days of curing age. Results: The use of cement slurry treatment at various concentrations generally increased compressive strength at 28 days compared to untreated RCA. The findings show that at a 20% concentration of cement slurry, the increase in compressive strength is 38.4%. Upon replacement of cement in treatment slurry of RCA with 5% RHA, the increase in compressive strength was 61%, while the split tensile strength increased by 10.2%. The amount of water absorbed was observed after 30 minutes of full submergence in water, indicating that samples with 20% cement concentration at 28 days resulted in the lowest water absorption of 2.01%. However, with the replacement of 5% RHA, the water absorption slightly increased to 2.3%, but still less than the requirement of 3.5%. The corresponding test results for water suction by capillarity, initial and secondary sorptivity coefficients (Si and Ss) were found to be 0.0330mm/√sec. (1.98mm/√hr.) and 7.95×10−4mm/√sec. (0.04mm/√hr.) respectively, all less than 6mm/√hr requirement. This improved performance was attributed to the increased strength and structure of the interfacial transition zone (ITZ) around the RCA. Conclusion: Based on the results of mechanical strength and water transport, characteristics of the new concrete were improved when coarse RCAs were pretreated with 20% pozzolanic concentration containing cement and RHA. The use of a pozzolanic treatment slurry containing 15% cement and 5% RHA to treat coarse RCA can produce concrete with characteristics similar to those of natural concrete aggregates. This study presents a methodological utilization and improvement of RCA wastes for field application.

Green recycled aggregate concrete (RAC) with high strength and low shrinkage is prepared based on recycled coarse aggregate produced by the particle-shaping and aggregate-strengthening method and green low-carbon new cement. This not only effectively alleviates the shortage of natural resources, but also improves the performance of recycled aggregate concrete, which is of great significance for multi-channel resource utilization of construction waste. In this study, three kinds of recycled coarse aggregates (RCA), including simple crushing recycled coarse aggregate (JD-RCA), one-time particle-shaping recycled coarse aggregate (KL-RCA) and two-time particle-shaping recycled coarse aggregate (EKL-RCA), were prepared from the preparation technology of recycled aggregate, and high belite sulphoaluminate cement with excellent performance was used. The effects of aggregate quality, aggregate replacement ratio, and cementitious material content on mechanical properties and shrinkage properties of green recycled aggregate concrete were studied in comparison with ordinary Portland cement-based recycled aggregate concrete. The testing results show that the particle-shaping method can effectively improve the aggregate quality. The compressive strength and dry shrinkage performance of recycled aggregate concrete made of particle-shaped aggregate are only a little different from those of natural aggregate concrete, and even the performance of recycled aggregate is better than that of natural aggregate concrete under the condition of a low replacement ratio of recycled aggregate. In addition, high belite sulphoaluminate cement-based recycled aggregate concrete (HBRAC) not only has early strength and rapid hardening, but also has excellent drying shrinkage resistance, and its shrinkage rate can be reduced to more than 75% compared with ordinary Portland cement-based recycled aggregate concrete (OPRAC).

Numerous studies have suggested using recycled concrete aggregates (RCA) as a possible alternative to natural aggregates in the manufacture of concrete because of the financial and environmental advantages that come with it. However, RCA's engineering qualities are inferior to those of natural aggregates (NA) because of its high water absorption. In order to improve the mechanical and durability qualities of RCA, researchers have proposed a number of pretreatment techniques, such as thermal, mechanical, and chemical treatment. This experimental study examined the effects of carbonation treating RCA on the compressive strength and indirect tensile strength of concrete that substituted varying amounts of RCA (0, 20, 30, 40, 50, and 100 % by weight) for 10-20 mm natural coarse aggregate. The study's findings indicate that, adding recycled concrete aggregates to concrete mixtures can have a detrimental influence on the mixes' compressive and tensile strengths; however, this effect can be lessened by carbonation treating the recycled aggregates. Replacing 100% of carbonated aggregate leads to approximately 14 and 23% enhancements in the compressive and tensile strengths of concrete, respectively, when compared to concrete made with 100% untreated recycled aggregate. Keywords: Recycled aggregates, Replacement level, Carbonation, Compressive Strength, Splitting Tensile Strength.

The surface zone of the recycled aggregate plays a significant role in the strength and durability of concrete. In this research, various concrete series incorporating natural coarse aggregate [NCA], untreated recycled coarse aggregate RCA(UN), mechanical scrubbing treated coarse aggregate RCA(MS), sulfuric acid treated coarse aggregate RCA(H2SO4) and hydrochloric acid treated aggregate RCA(HCl) were investigated. Manufactured sand was used as an alternative to natural river sand in five series of concrete with 100% replacement ratio. The mechanical properties: compressive, split tensile, and flexural strength, respectively, were determined at the age of 28 and 56 days. Durability properties: water absorption, drying, sulfuric acid, sodium sulphate and sorptivity test were determined at the age of 28, 56 and 90 days and the results were compared to reference concrete. According to the results, RCA(UN) was found to marginally decreased the concrete performance, and the above mentioned treated aggregate shows a significant improvement in overall performance compared to RCA(UN), especially RCA(MS), which enhances the concrete more significantly than other methods. Moreover, the scanning electron microscope results also emphasize the enhanced microstructure of treated recycled aggregate in concrete. The photographic view of the cross sections of the samples shows a superior interfacial transition zone in all kinds of treated aggregate concrete than in untreated recycled aggregate concrete.

The usage of recycled aggregate (RA) for concrete works is spreading for gaining wide acceptance around the world, and total amount of RA utilized in concrete industry increases day-by-day. RA is used in many concrete products, such as concrete interlocking blocks, pavements, etc. One of the physical causes of concrete deterioration is surface wear or loss of mass for concrete products which are especially exposed to vehicular traffic (i.e., industrial floors and pavements). Besides, the loss of mass by concrete surface wear becomes the primary factor of one or more processes of chemical deterioration as a result of an increase in permeability due to mass loss of the concrete surface wear. The main goal of this research is to investigate the abrasion behavior of recycled aggregate concrete (RAC) with/without silica fume (SF) related with the mechanical and the physical properties of RAC. In this research, lower quality RA (<15 MPa) is utilized as recycled coarse aggregate (RCA1 and RCA2) and recycled fine aggregate (RFA) with 25, 25, and 50% replacement ratios, respectively, in concrete mixes. As a result, RCA2 with/without SF gives better performance than RCA1 and RFA if abrasion resistance is considered only. Besides, RFA utilization in concrete decreases the abrasion performance of RAC. Also the relations of compressive strength-abrasion loss and elasticity modulus-abrasion loss are examined, and high regression coefficient (R) for the relations is found. Keywords: abrasion resistance, mechanical properties, physical properties, recycled aggregate, silica fume

Variation in mechanical properties of concrete having recycled brick aggregates, recycled concrete aggregates and recycled plastic aggregates: A review

The application of recycled concrete aggregates (RCAs) has become increasingly popular for different types of structures, as presented in several studies. However, depending on the type of structure and the region, RCAs might have different properties. This study aims to investigate the application of RCAs of different origins for substructure layers of the cycle paths located in Central Europe, which was not analysed previously. Recycled aggregates from an airport, road overpass, and building demolition were tested according to European standards and used to produce concretes, in which compressive strength, density, water absorption, and frost resistance were tested. After 28 days, RCA concrete had compressive strengths from 5.9 to 17.3 MPa and frost resistance ratios close to 1.0. The concrete parameters indicate that RCAs might be used for the construction of cycle path substructural layers with the appropriate class of cement and W/C ratio. To meet the requirements of EN 12390-3 to achieve class C8/10, RCA concrete with CEM II B/V 32.5 should be used with a W/C ratio of 1. To meet the requirements of D-04.05.01v02, RCA concrete with CEM II B/V 32.5 and a W/C ratio smaller than 1.50 should be used. Applying recycled RCAs in various structures helps protect natural resources by reusing materials. However, the variability in RCA properties requires testing to guarantee quality.

Properties of recycled aggregate concrete prepared with scattering-filling coarse aggregate process

Recycled aggregate concrete (RAC) contributes to mitigating the depletion of natural aggregates, alleviating the carbon footprint of concrete construction, and averting the landfilling of colossal amounts of construction and demolition waste. However, complexities in the mixture optimization of RAC due to the variability of recycled aggregates and lack of accuracy in estimating its compressive strength require novel and sophisticated techniques. This paper aims at developing state-of-the-art machine learning models to predict the RAC compressive strength and optimize its mixture design. Results show that the developed models including Gaussian processes, deep learning, and gradient boosting regression achieved robust predictive performance, with the gradient boosting regression trees yielding highest prediction accuracy. Furthermore, a particle swarm optimization coupled with gradient boosting regression trees model was developed to optimize the mixture design of RAC for various compressive strength classes. The hybrid model achieved cost-saving RAC mixture designs with lower environmental footprint for different target compressive strength classes. The model could be further harvested to achieve sustainable concrete with optimal recycled aggregate content, least cost, and least environmental footprint.

This study investigated the sulfate resistance of modified recycled aggregate concrete (RAC) by applying carbonation and nano-silica soaking methodologies. Recycled concrete aggregates (RCA) derived from concretes of C30 and C60 strength grades were subjected to these modification techniques and subsequently utilized in the fabrication of RAC specimens. The results show notable porosity and crack density within the interfacial transition zone (ITZ) interfacing recycled aggregate and cement paste in recycled aggregate concrete (RAC). Specifically, the porosity within the ITZ of RAC is observed to be up to 30% higher than that of virgin aggregate concrete. These pathways facilitate the penetration of sulfate ions, subsequently inducing deterioration and resulting in a compression strength reduction of up to 40%. While carbonation treatment exhibits a moderate enhancement in sulfate resistance, decreasing the sulfate penetration depth by 15%, the incorporation of 2% nano-silica by weight of cement proves significantly more effective. This addition reduces the sulfate penetration depth by over 30% and lowers the sulfate concentration by 25%. Furthermore, the compressive strength of RAC modified with nano-silica increases by 15% following 28 days of sulfate exposure. Additionally, a 30% reduction in the sulfate ion mass equilibrium depth is observed in nano-silica-modified RAC, accompanied by a markedly lower sulfate concentration in the pore solution. After 56 days of sulfate attack, the compressive strength of nano-silica-modified RAC retains 85% of its initial value, whereas unmodified RAC decreases to 70%. Notably, the quality of recycled aggregate significantly impacts sulfate resistance, with high-strength RCA (exceeding 40 MPa) demonstrating superior resistance compared to low-strength RCA (below 20 MPa). Consequently, RAC produced with high-strength RCA experiences only a 20% loss in compressive strength under sulfate attack, whereas RAC containing low-strength RCA suffers a 40% loss. The novelty of this study is the effective use of nano-silica soaking and carbonation to enhance the sulfate resistance and compressive strength of recycled aggregate concrete originated from both normal and high-strength reference concrete.

Numerous tests are used to determine the performance of concrete, but compressive strength (CS) is usually regarded as the most important. The recycled aggregate concrete (RAC) exhibits lower CS compared to natural aggregate concrete. Several variables, such as the water-cement ratio, the strength of the parent concrete, recycled aggregate replacement ratio, density, and water absorption of recycled aggregate, all impact the RAC’s CS. Many studies have been carried out to ascertain the influence of each of these elements separately. However, it is difficult to investigate their combined effect on the CS of RAC experimentally. Experimental investigations entail casting, curing, and testing samples, which require considerable work, expense, and time. It is vital to adopt novel methods to the stated aim in order to conduct research quickly and efficiently. The CS of RAC was predicted in this research utilizing machine learning techniques like decision tree, gradient boosting, and bagging regressor. The data set included eight input variables, and their effect on the CS of RAC was evaluated. Coefficient correlation (R2), the variance between predicted and experimental outcomes, statistical checks, and k-fold evaluations, were carried out to validate and compare the models. With an R2 of 0.92, the bagging regressor technique surpassed the decision tree and gradient boosting in predicting the strength of RAC. The statistical assessments also validated the superior accuracy of the bagging regressor model, yielding lower error values like mean absolute error (MAE) and root mean square error (RMSE). MAE and RMSE values for the bagging model were 4.258 and 5.693, respectively, which were lower than the other techniques employed, i.e., gradient boosting (MAE = 4.956 and RMSE = 7.046) and decision tree (MAE = 6.389 and RMSE = 8.952). Hence, the bagging regressor is the best suitable technique to predict the CS of RAC.

Increasing amount of construction waste and, concrete remnants, in particular pose a serious problem. Concrete waste exist in large amounts, do not decay and need long time for disintegration. Therefore, in this work old demolished concrete is crashed and recycled to produce recycled concrete aggregate which can be reused in new concrete production. The effect of using recycled aggregate on concrete compressive strength has been experimentally investigated; silica fume admixture also is used to improve recycled concrete aggregate compressive strength. The main parameters in this study are recycled aggregate and silica fume admixture. The percent of recycled aggregate ranged from (0-100) %. While the silica fume ranged from (0-10) %. The experimental results show that the average concrete compressive strength decreases from 30.85 MPa to 17.58 MPa when the recycled aggregate percentage increased from 0% to 100%. While, when silica fume is used the concrete compressive strength increase again to 29.2 MPa for samples with 100% of recycled aggregate.

Chloride transport and induced steel corrosion in recycled aggregate concrete: A review

This study presents a framework for designing low-carbon and cost-effective mixtures of recycled aggregate concrete (RAC) with supplementary cementitious materials by integrating machine learning and grey wolf optimizer algorithms. The concrete mix design process considers key performance parameters such as compressive strength, chloride ion penetration resistance, and carbonation resistance. A dataset comprising 5306 data samples from 154 scientific resources is collected from the literature to train the machine learning models. Four different techniques, namely random forest, extreme gradient boosting (XGBoost), light gradient boosting (LightBoost), and category boosting (CatBoost) are employed to model the compressive strength, chloride ion penetration, and carbonation resistances of RAC. The best-performing models are then utilized to optimize the RAC mix design by minimizing the cost and reducing the carbon footprint. The results indicate that the CatBoost model demonstrates better predictive performance for the compressive strength and carbonation resistance, while the XGBoost and LightBoost models perform better in estimating chloride ion penetration resistance. Furthermore, the adoption of low-carbon mix design principles leads to a reduction in carbon footprint by 5.0% to 31.5% compared to cost-effective mix design for different compressive strength targets, with varying permeability levels. The framework provides a promising approach for designing environmentally friendly RAC mixtures while considering economic and durability factors.