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Keywords = waste concrete (WC)

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21 pages, 4770 KiB  
Article
Prediction of Compressive Strength of Sustainable Concrete Incorporating Waste Glass Powder Using Machine Learning Algorithms
by Sushant Poudel, Bibek Gautam, Utkarsha Bhetuwal, Prabin Kharel, Sudip Khatiwada, Subash Dhital, Suba Sah, Diwakar KC and Yong Je Kim
Sustainability 2025, 17(10), 4624; https://doi.org/10.3390/su17104624 - 18 May 2025
Viewed by 936
Abstract
The incorporation of waste ground glass powder (GGP) in concrete as a partial replacement of cement offers significant environmental benefits, such as reduction in CO2 emission from cement manufacturing and decrease in the use of colossal landfill space. However, concrete is a [...] Read more.
The incorporation of waste ground glass powder (GGP) in concrete as a partial replacement of cement offers significant environmental benefits, such as reduction in CO2 emission from cement manufacturing and decrease in the use of colossal landfill space. However, concrete is a heterogeneous material, and the prediction of its accurate compressive strength is challenging due to the inclusion of several non-linear parameters. This study explores the utilization of different machine learning (ML) algorithms: linear regression (LR), ElasticNet regression (ENR), a K-Nearest Neighbor regressor (KNN), a decision tree regressor (DT), a random forest regressor (RF), and a support vector regressor (SVR). A total of 187 sets of pertinent mix design experimental data were collected to train and test the ML algorithms. Concrete mix components such as cement content, coarse and fine aggregates, the water–cement ratio (W/C), various GGP chemical properties, and the curing time were set as input data (X), while the compressive strength was set as the output data (Y). Hyperparameter tuning was carried out to optimize the ML models, and the results were compared with the help of the coefficient of determination (R2) and root mean square error (RMSE). Among the algorithms considered, SVR demonstrates the highest accuracy and predictive capability with an R2 value of 0.95 and RMSE of 3.40 MPa. Additionally, all the models exhibit R2 values greater than 0.8, suggesting that ML models provide highly accurate and cost-effective means for evaluating and optimizing the compressive strength of GGP-incorporated sustainable concrete. Full article
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20 pages, 5021 KiB  
Article
Eco-Friendly Lightweight Aggregate Concrete of Structural Grade Made with Recycled Brick Aggregate Containing Expanded Polystyrene Beads
by Bogdan Rosca
Sustainability 2025, 17(7), 3050; https://doi.org/10.3390/su17073050 - 29 Mar 2025
Viewed by 780
Abstract
The quantity of construction demolition waste (CDW) has been increasing due to the demolition of many old buildings throughout the world. So far, all the statistics indicate that there is a very large generation of CDW, which increases annually. The increasing amount CDW [...] Read more.
The quantity of construction demolition waste (CDW) has been increasing due to the demolition of many old buildings throughout the world. So far, all the statistics indicate that there is a very large generation of CDW, which increases annually. The increasing amount CDW in landfills will cause a scarcity of landfill space and will also increase pollution and cost due to transportation. Recycled brick aggregate concrete (RBAC) incorporating polystyrene (EPS) aggregate beads has emerged as an alternative lightweight material with numerous obvious sustainable benefits, suitable for a future circular economy. The goal of this paper is to assess the feasibility of obtaining lightweight aggregate concrete of structural grade with recycled brick aggregate (RBA) as a coarse aggregate and the incorporation of polystyrene beads in a certain percentage by conducting an experimental study on the dry and apparent density, compressive strength, split-tensile strength and elasticity modulus. In addition, the effects of the w/c ratio and cement content on these properties were studied to provide useful information for the performance optimization of this concrete with RBA and polystyrene (EPS) beads. The properties were investigated for two cement contents, 400 and 360 kg/m3, and two ratios between water and cement, 0.43 and 0.39, respectively. The RBAC mixtures containing EPS beads in 15%, 25% and 35% replacement percentages were evaluated through a comprehensive test program based on the European standards. The results showed that, in general, the use of polystyrene (EPS) beads decreased the mechanical properties of the recycled brick aggregate concrete; however, the outcome indicates the potential for producing lightweight concrete of different grades, including structural classes. It was found that the developed lightweight concrete presents a uniform distribution of the polystyrene granules in the hardened volume of concrete. Also, it was found that the recycled brick aggregate with a 16 mm maximum size did not negatively influence the uniform distribution of the EPS beads, avoiding concentrations of beads. With the increase in the percentage of EPS beads, the properties of the recycled brick aggregate concrete were found to be less sensitive to the water-to-cement ratio. Full article
(This article belongs to the Section Sustainable Materials)
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15 pages, 6204 KiB  
Article
Effect of Early Curing Experiences on Mechanical Properties and Microstructure of ECO-UHPC Prepared by Gold Tailings Sand
by Qi Ouyang, Xianxiang Zhou, Xian Liang and Biao Luo
Materials 2025, 18(4), 842; https://doi.org/10.3390/ma18040842 - 14 Feb 2025
Viewed by 551
Abstract
Fine gold tailings particles generated from gold mining and refining have the potential to replace high-cost quartz sand in the preparation of economical ultra-high-performance concrete (ECO-UHPC) due to their large stockpiles, low cost, and elimination of grinding. In this study, ECO-UHPC was prepared [...] Read more.
Fine gold tailings particles generated from gold mining and refining have the potential to replace high-cost quartz sand in the preparation of economical ultra-high-performance concrete (ECO-UHPC) due to their large stockpiles, low cost, and elimination of grinding. In this study, ECO-UHPC was prepared by substituting quartz sand with gold tailing sand (GTS) at substitution rates of 0%, 25%, 50%, 75%, and 100%. The mechanical properties of ECO-UHPC, including its cubic compressive strength, elastic modulus, and prismatic compressive strength, as well as its leaching toxicity, were experimentally analyzed under various early curing experiences such as ambient-water curing (WC), hot-water curing (HWC), hot-air curing (HAC), and combined curing (CC). Additionally, scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) were employed to interpret the macroscopic behavior of ECO-UHPC. The results indicate that the incorporation of waste GTS slightly reduces the fluidity of fresh ECO-UHPC, decreasing it by approximately 6.1% at a full 100% replacement. As a result of waste GTS substitution, the cubic strength of ECO-UHPC experiencing the WC environment during early curing is reduced by 0.7–12.2%. However, the strength of thermally cured ECO-UHPC is comparable to or even higher than that of pure quartz-based G0, with the maximum value occurring in G-50. Specifically, the strength of G-50 cured with HWC, HAC, and CC varies by +20.0%, +40.2%, and +57.7%, respectively, as compared to that of G-50 cured with WC. The evolution of the elastic modulus and the prismatic strength of ECO-UHPC under different early curing conditions and GTS replacement rates aligns closely with that of its cubic strength. In addition, the implementation of thermal curing conditions also limits the leaching of heavy metals from ECO-UHPC, with the best effect observed under CC. This is because appropriate thermal curing promotes the densification of a cementitious substance and the bonding of GTS-cementitious material. Overall, this study demonstrates the feasibility of utilizing waste GTS as a partial or full replacement for quartz sand in ECO-UHPC while maintaining desirable mechanical performance and environmental safety. The findings provide valuable insights into the influence of GTS substitution and early curing regimes on ECO-UHPC properties, highlighting the potential of thermal curing to enhance strength and mitigate leaching risks. Future research should further explore the long-term durability of GTS-based ECO-UHPC and its broader applicability in sustainable construction practices. Full article
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15 pages, 6778 KiB  
Article
Maximizing Nano-Silica Efficiency in Laboratory-Simulated Recycled Concrete Aggregate via Prior Accelerated Carbonation: An Effective Strategy to Up-Cycle Construction Wastes
by Cheng-Gong Lu, Xiu-Cheng Zhang and Xue-Fei Chen
Molecules 2024, 29(24), 5995; https://doi.org/10.3390/molecules29245995 - 19 Dec 2024
Cited by 3 | Viewed by 885
Abstract
Herein, the study explores a composite modification approach to enhance the use of recycled concrete aggregate (RCA) in sustainable construction by combining accelerated carbonation (AC) and nano-silica immersion (NS). RCA, a major source of construction waste, faces challenges in achieving comparable properties to [...] Read more.
Herein, the study explores a composite modification approach to enhance the use of recycled concrete aggregate (RCA) in sustainable construction by combining accelerated carbonation (AC) and nano-silica immersion (NS). RCA, a major source of construction waste, faces challenges in achieving comparable properties to virgin aggregates. Nano-silica, a potent pozzolan, is added to fill micro-cracks and voids in RCA, improving its bonding and strength. AC pretreatment accelerates RCA’s natural carbonation, forming calcium carbonate that strengthens the aggregate and reduces porosity. Due to the complexity of the original RCA, a laboratory-simulated RCA (LS-RCA) is used in this study for the mechanism analysis. Experimental trials employing the composite methodology have exhibited noteworthy enhancements, with the crushing index diminishing by approximately 23% and water absorption rates decreasing by up to 30%. Notably, the modification efficacy is more pronounced when applied to RCA derived from common-strength concrete (w/c of 0.5) as compared to high-strength concrete (w/c of 0.35). This disparity stems from the inherently looser structural framework and greater abundance of detrimental crystal structures in the former, which impede strength. Through a synergistic interaction, the calcium carbonate content undergoes a substantial increase, nearly doubling, while the proportion of calcium hydrate undergoes a concurrent reduction of approximately 30%. Furthermore, the combined modification effect leads to a 15% reduction in total porosity and a constriction of the average pore diameter by roughly 20%, ultimately resulting in pore refinement that equates the performance of samples with a water-to-cement ratio of 0.5 to those with a ratio of 0.35. This remarkable transformation underscores the profound modification potential of the combination approach. This study underscores the efficacy of harnessing accelerated carbonation in conjunction with nano-silica as a strategic approach to optimizing the utilization of RCA in concrete mixes, thereby bolstering their performance metrics and enhancing sustainability. Full article
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24 pages, 6241 KiB  
Article
Soft-Computing Analysis and Prediction of the Mechanical Properties of High-Volume Fly-Ash Concrete Containing Plastic Waste and Graphene Nanoplatelets
by Musa Adamu, Yasser E. Ibrahim and Mahmud M. Jibril
Infrastructures 2024, 9(12), 214; https://doi.org/10.3390/infrastructures9120214 - 22 Nov 2024
Viewed by 1182
Abstract
The rising population and demand for plastic materials lead to increasing plastic waste (PW) annually, much of which is sent to landfills without adequate recycling, posing serious environmental risks globally. PWs are grinded to smaller sizes and used as aggregates in concrete, where [...] Read more.
The rising population and demand for plastic materials lead to increasing plastic waste (PW) annually, much of which is sent to landfills without adequate recycling, posing serious environmental risks globally. PWs are grinded to smaller sizes and used as aggregates in concrete, where they improve environmental and materials sustainability. On the other hand, PW causes a significant reduction in the mechanical properties and durability of concrete. To mitigate the negative effects of PW, highly reactive pozzolanic materials are normally added as additives to the concrete. In this study, PW was used as a partial substitute for coarse aggregate, and graphene nanoplatelets (GNPs) were used as additives to high-volume fly-ash concrete (HVFAC). Utilizing PW as aggregates and GNPs as additives has been found to enhance the mechanical properties of HVFAC. Hence, this study employed two machine-learning (ML) models, namely Gaussian Process Regression (GPR) and Elman Neural Network (ELNN), to forecast the mechanical properties of HVFAC. The study input variables were PW, FA, GNP, W/C, CP, density, and slump, where the target variables are compressive strength (CS), modulus of elasticity (ME), splitting tensile strength (STS), and flexural strength (FS). A total of 240 datasets were employed in this study and divided into calibration (70%) and validation (30%) sets. During the prediction of the CS, it was found that GPR-M3 outperforms all other models with an R-value equal to 0.9930 and PCC value of 0.9929 in the calibration phase, and R-value = 0.9505 and PCC = 0.9339 in the verification phase. Additionally, during the modeling of FS, it was also noticed that GPR-M3 surpasses all other combinations with R = 0.9973 and PCC = 0.9973 in calibration and R = 0.9684 and PCC = 0.9428 in the verification phase. Moreover, in ME modeling, GPR-M3 is the best modeling combination and shows high accuracy with R = 0.9945 and PCC = 0.9945 in calibration and R = 0.9665 and PCC = 0.9584 in the verification phase. On the other hand, GPR-M3 outperforms all other models during the modeling of STS with R = 0.9856 and PCC = 0.9855 in calibration, and R = 0.9482 and PCC = 0.9353 in the verification phase. Further quantitative analysis shows that, in the prediction of CS, the GPR improves the prediction accuracy of ELNN by 0.49%, while during the prediction of the splitting tensile strength, it was also found that the GPR improved the accuracy of ELNN by 1.54%. In FS prediction, it was also improved by 7.66%, while in ME, it was improved by 4.9%. In conclusion, this AI-based model proves how accurate and effective it was to employ an ML-based model in forecasting the mechanical properties of HVFAC. Full article
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63 pages, 13096 KiB  
Review
A Review of the Utilization of Recycled Powder from Concrete Waste as a Cement Partial Replacement in Cement-Based Materials: Fundamental Properties and Activation Methods
by Kubilay Kaptan, Sandra Cunha and José Aguiar
Appl. Sci. 2024, 14(21), 9775; https://doi.org/10.3390/app14219775 - 25 Oct 2024
Cited by 10 | Viewed by 3427
Abstract
Recycled powder (RP) is the primary by-product generated during the reclamation process of construction and demolition waste (CDW). There is existing literature on the use of RP as supplemental cementitious materials (SCMs) in cement-based materials, but a comprehensive evaluation on the characteristics of [...] Read more.
Recycled powder (RP) is the primary by-product generated during the reclamation process of construction and demolition waste (CDW). There is existing literature on the use of RP as supplemental cementitious materials (SCMs) in cement-based materials, but a comprehensive evaluation on the characteristics of RP generated from concrete waste has been missing until now. This paper critically reviews the use of RP from concrete waste in cement-based materials, as concrete waste makes up a significant amount of CDW and other components have designated recycling methods. In this sense, this study conducted a critical analysis on the use of RP as an SCM, using detailed literature research. The technology used for producing RP is detailed along with its chemical, mineralogy, and microstructural characteristics. Fresh-state properties in cementitious matrices with RP are introduced with the view of mechanical grinding, thermal activation, carbonation, chemical treatment, biomineralization, mineral addition, nano activation, and carbonation. The review highlights the significant potential of utilizing RP in cement-based materials. Specifically, RP can be advantageously utilized in the production of value-added construction materials. Full article
(This article belongs to the Section Civil Engineering)
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15 pages, 2905 KiB  
Article
Alternative Fine Aggregates to Natural River Sand for Manufactured Concrete Ensuring Circular Economy
by Tarek Uddin Mohammed, Md. Aktaruzzaman Rony, Mohammad Zunaied Bin Harun, Naba Uddin, Debasish Saha, Md. Nafiur Rahman and Aziz Hasan Mahmood
Constr. Mater. 2024, 4(4), 640-654; https://doi.org/10.3390/constrmater4040035 - 1 Oct 2024
Cited by 4 | Viewed by 3060
Abstract
To address SDG12 (ensure sustainable consumption and production patterns), and to provide technical evidence for alternative concrete constituents to traditional natural river sand, stone fine aggregate (SFA), brick fine aggregate (BFA), ladle-refined furnace slag aggregate (LFS), recycled brick fine aggregate (RBFA), and washed [...] Read more.
To address SDG12 (ensure sustainable consumption and production patterns), and to provide technical evidence for alternative concrete constituents to traditional natural river sand, stone fine aggregate (SFA), brick fine aggregate (BFA), ladle-refined furnace slag aggregate (LFS), recycled brick fine aggregate (RBFA), and washed waste fine aggregate (WWF), ready-mix concrete plants were investigated. Concrete and mortar specimens were made with different variables, such as replacement volume of natural sand with different alternative fine aggregates, water-to-cement ratio (W/C), and sand-to-aggregate volume ratio (s/a). The concrete and mortar specimens were tested for workability, compressive strength, tensile strength, and Young’s modulus (for concrete) at 7, 28, and 90 days. The experimental results show that the compressive strength of concrete increases when natural sand is replaced with BFA, SFA, and LFS. The optimum replacement amounts are 30%, 30%, and 20% for BFA, SFA, and LFS, respectively. For RBFA, the compressive strength of concrete is increased even at 100% replacement of natural sand by RBFA. For WWF, the compressive strength of concrete increases up to a replacement of 20%. Utilizing these alternative fine aggregates can be utilized to ensure a circular economy in construction industries and reduce the consumption of around 30% of natural river sand. Full article
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12 pages, 1474 KiB  
Article
Optimizing Porous Concrete Using Granite Stone-Crushing Waste: Composition, Strength, and Density Analysis
by Leonid Dvorkin, Oleh Bordiuzhenko, Tomasz Tracz and Katarzyna Mróz
Appl. Sci. 2024, 14(16), 6934; https://doi.org/10.3390/app14166934 - 8 Aug 2024
Cited by 3 | Viewed by 1442
Abstract
This study examines the utilization of granite stone-crushing waste in the production of porous concrete, with a particular emphasis on the influence of aggregate composition and cement paste layer thickness on the material’s strength and density. Two types of aggregates were employed in [...] Read more.
This study examines the utilization of granite stone-crushing waste in the production of porous concrete, with a particular emphasis on the influence of aggregate composition and cement paste layer thickness on the material’s strength and density. Two types of aggregates were employed in this study: granite crushing screenings and granite crushed stone. The impact of aggregate grain size on the properties of porous concrete properties was investigated, and it was found that the use of granite screenings (2.5–5 mm) resulted in superior concrete characteristics compared to granite crushed stone (5–10 mm). This study puts forward a method for optimizing the composition of porous concrete to achieve an optimal balance of compressive strength and density. A method for the design of porous concrete was proposed, incorporating experimental results and the dependencies of strength on the water/cement ratio (W/C). Equations were developed to predict concrete strength based on W/C and cement paste layer thicknesses (CPLTs). The method provides preliminary mix proportions, which should be validated and adjusted for the final design. The findings demonstrate the potential for utilizing stone-crushing waste to produce environmentally sustainable and high-quality porous concrete. Full article
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24 pages, 10999 KiB  
Article
Microstructural and Residual Properties of Self-Compacting Concrete Containing Waste Copper Slag as Fine Aggregate Exposed to Ambient and Elevated Temperatures
by Bypaneni Krishna Chaitanya, Ilango Sivakumar, Yellinedi Madhavi, Daniel Cruze, Chava Venkatesh, Yenigandla Naga Mahesh and Chereddy Sonali Sri Durga
Infrastructures 2024, 9(5), 85; https://doi.org/10.3390/infrastructures9050085 - 13 May 2024
Cited by 6 | Viewed by 1781
Abstract
In recent times, with rapid development in the construction sector, the use of enormous amounts of materials is required for the production of concrete. Fire penetrates concrete, leading to chemical contamination, small cracks, and lightening. These effects can significantly change the properties of [...] Read more.
In recent times, with rapid development in the construction sector, the use of enormous amounts of materials is required for the production of concrete. Fire penetrates concrete, leading to chemical contamination, small cracks, and lightening. These effects can significantly change the properties of concrete’s structure, reduce its strength and durability, and also change the behavior of the structure and lead to effects on the environment. An attempt was made to study the effects of elevated temperature on the mechanical characteristics of self-compacting concrete (SCC) with by-products including fly ash as a partial replacement for cement and waste copper slag as a partial replacement for fine aggregate at 0%, 10%, 20%, 30%, 40%, 50%, 60%, and 70%. The SCC specimens were subjected to elevated temperatures ranging from 200, 400, 600, and 800 °C, respectively, for a steady-state of two hours in a digital muffle furnace. The residual compressive strength, mass loss, ultrasonic pulse velocity, and residual density along with a visual inspection of cracks and color changes were observed. In this study, with over 400 °C temperatures, surface fractures appeared. The residual compressive strength (R-CMS) of all the individual temperatures of the SCC-WCS% mixes exhibited a gain in strength range from 31 to 34 MPa at 400 °C, 26 to 35 MPa at 600 °C, and 22.5 MPa to 33.5 MPa at 800 °C, respectively. Microstructural analysis of SCC-WCS% mixtures subjected to elevated ambient temperatures is carried out with a scanning electron microscope (SEM) and X-ray diffraction (XRD). Full article
(This article belongs to the Section Infrastructures Materials and Constructions)
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20 pages, 6840 KiB  
Article
Fresh, Mechanical, and Thermal Properties of Cement Composites Containing Recycled Foam Concrete as Partial Replacement of Cement and Fine Aggregate
by Jan Pizoń
Materials 2023, 16(22), 7169; https://doi.org/10.3390/ma16227169 - 15 Nov 2023
Cited by 3 | Viewed by 1736
Abstract
The research presented in this article was conducted to evaluate the suitability of recycled foam concrete (RFC) as an ingredient in newly created cement mortars. The basis for an analysis was the assumption that the waste is collected selectively after separation from other [...] Read more.
The research presented in this article was conducted to evaluate the suitability of recycled foam concrete (RFC) as an ingredient in newly created cement mortars. The basis for an analysis was the assumption that the waste is collected selectively after separation from other waste generated during demolition. The motivation for the research and its main problem is a comparison of the performance of RFC used in various forms. RFC was used in two forms: (1) recycled foam concrete dust (RFCD) as a 25 and 50% replacement of cement, and (2) recycled foam concrete fine aggregate (RFCA) as a 10, 20, and 30% replacement of sand. The basic properties of fresh and hardened mortars were determined: consistency, density, initial setting time, absorbability, compressive strength, thermal conductivity coefficient, and heat capacity. Research is complemented with SEM observations. The properties of fresh mortars and mechanical parameters were decreased with the usage of any dosage of RFC in any form, but the thermal properties were improved. The required superplasticizer amount for proper consistency was raised four times for replacing cement with 50% of RFCD than for 25% of such replacement. The mix density dropped by about 8% and 9% for mortars with the replacement of 50% cement by RFCD and 30% sand by RFCA in comparison to reference mortar. A 30% decrease in initial setting time was observed for cement replacement. In the case of sand replacement, it was the opposite—an increase of 100%. The dry density decreased by about 14% and 11% for mortars with the replacement of 50% cement by RFCD and 30% sand by RFCA in comparison to reference mortar. Absorbability was raised by about two times after replacement with both RFCD and RFCA. Compressive strength after 28 days dropped significantly by 75% and 60%, and the thermal conductivity coefficient decreased by 20% and 50% with 50% RFCD added instead of cement and 30% RFCA replacing sand. It indicates greater efficiency in thermomechanical means from RFCA in comparison to RFCD. This material can be used especially in the production of plaster and masonry mortar. Linear correlations of dry density and thermal conductivity coefficient and the latter and compressive strength were proven as reliable for RFCD replacement of cement and RFCA replacement of sand in mortars with greater w/c ratio. Full article
(This article belongs to the Special Issue Processing of End-of-Life Materials and Industrial Wastes–Volume 2)
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19 pages, 971 KiB  
Article
Influence on Physical and Mechanical Properties of Concrete Using Crushed Hazelnut Shell
by Nicole Gálvez Cartagena, Grissel Muñoz Araya, Sergio J. Yanez, Sandra González Sepúlveda and Juan Carlos Pina
Appl. Sci. 2023, 13(22), 12159; https://doi.org/10.3390/app132212159 - 9 Nov 2023
Viewed by 1702
Abstract
Concrete production requires a significant amount of natural resources, with aggregates comprising between 55% and 80% of the total volume. However, the over-exploitation of natural aggregates has led to the exploration of alternative materials for use in concrete production. In this study, crushed [...] Read more.
Concrete production requires a significant amount of natural resources, with aggregates comprising between 55% and 80% of the total volume. However, the over-exploitation of natural aggregates has led to the exploration of alternative materials for use in concrete production. In this study, crushed hazelnut shells were investigated as a partial replacement for fine aggregate, addressing the problem of natural resource depletion and offering a second use for this important agricultural waste product available in Chile. Hazelnut shells were incorporated in percentages of 2.5%, 5%, and 10% by weight of sand for water/cement ratios of 0.4 and 0.5. The compressive strength at 7 and 28 days and bending strength at 28 days were determined, alongside physical properties such as the workability, temperature, air content, fresh density, and hardened density of the concrete. Our findings showed that replacing 2.5% of the fine aggregate with hazelnut shells led to a higher compressive strength at 28 days, exceeding the strength of the standard specimens by 9.5%, whereas replacing 5% of the fine aggregate led to the highest bending strength, exceeding the strength of the standard specimens by 3.5%. Moreover, the 0.4 w/c ratio consistently led to better results for both compressive and bending strength, with fewer and lower reductions in mechanical strength compared to the standard mixture. Our results suggest that concrete mixes with hazelnut shells as a replacement for fine aggregate at a percentage of up to 2.5% can be used in construction systems with a compression strength lower than 17 MPa, and mixtures with up to 10% hazelnut shell replacement can be used in structures with tensile bending stress requirements lower than 6 MPa. Overall, the use of hazelnut shells as a partial replacement for fine aggregate in concrete production presents an environmentally friendly and cost-effective solution for the construction industry. Full article
(This article belongs to the Special Issue Advances in Cement-Based Materials)
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19 pages, 5000 KiB  
Article
Evaluation of the Solidification of Radioactive Wastes Using Blast Furnace Slag as a Solidifying Agent
by Ji-Hun Jeon, Jong-Hwan Lee, Woo-Chun Lee, Sang-Woo Lee and Soon-Oh Kim
Materials 2023, 16(19), 6462; https://doi.org/10.3390/ma16196462 - 28 Sep 2023
Cited by 1 | Viewed by 1627
Abstract
The decommissioning process of nuclear power facilities renders hundreds of thousands of tons of various types of waste. Of these different waste types, the amount of concrete waste (CW) varies greatly depending on the type of facility, operating history, and regulation standards. From [...] Read more.
The decommissioning process of nuclear power facilities renders hundreds of thousands of tons of various types of waste. Of these different waste types, the amount of concrete waste (CW) varies greatly depending on the type of facility, operating history, and regulation standards. From the previous decommissioning projects, CW was estimated to comprise 60–80 wt.% of the total weight of radioactive wastes. This represents a significant technical challenge to any decommissioning project. Furthermore, the disposal costs for the generated concrete wastes are a substantial part of the total budget for any decommissioning project. Thus, the development of technologies effective for the reduction and recycling of CW has become an urgent agenda globally. Blast furnace slag (BFS) is an industrial byproduct containing a sufficient amount (higher than 30%) of CaO and it can be used as a substitute for ordinary Portland cement (OPC). However, there have been few studies on the application of BFS for the treatment of radioactive waste from decommissioning processes. This study was conducted to evaluate the performance of the solidification agent using ground granulated BFS (SABFS) to pack radioactive wastes, such as the coarse aggregates of CW (CACW), waste soil (WS), and metal waste (MW). The analytical results indicated that the CaO content of the ground granulated BFS was 36.8% and it was confirmed that calcium silicate hydrate (CSH) could be activated as the precursor of the hydration reactions. In addition, the optimum water-to-binder ratio was determined to be 0.25 and Ca(OH)2 and CaSO4 were found to be the most effective alkaline and sulfate activators for improving the compressive strength of the SABFS. The maximum packing capacities of the SABFS were determined to be 9 and 13 wt.% for WC and WM, respectively, when the content of CW was fixed at 50 wt.%. The results of the leaching tests using SABFS containing radioactive wastes contaminated with Co, Cs, and Sr indicated that their leachability indices met the acceptance level for disposal. Consequently, the SABFS can be used as a solidifying agent for the safe disposal of radioactive waste. Full article
(This article belongs to the Special Issue Advanced and Sustainable Low Carbon Cement and Concrete Materials)
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5 pages, 1110 KiB  
Proceeding Paper
Micro Structural Study of Concrete with Indigenous Volcanic Ash
by Muhammad Iqbal Bashir and Ayub Elahi
Eng. Proc. 2023, 44(1), 19; https://doi.org/10.3390/engproc2023044019 - 31 Aug 2023
Viewed by 1074
Abstract
Extraordinary efforts should be carried out in Pakistan to prepare green concrete from waste materials. The utilization of Volcanic Ash (VA) in concrete can make sustainable concrete that will produce less carbon dioxide (CO2) emissions and give positive outcomes. Hence, compressive [...] Read more.
Extraordinary efforts should be carried out in Pakistan to prepare green concrete from waste materials. The utilization of Volcanic Ash (VA) in concrete can make sustainable concrete that will produce less carbon dioxide (CO2) emissions and give positive outcomes. Hence, compressive strength was tested on VA concrete with changing concentrations ranging from 0, 10, and 20% with constant W/C, and the result was evaluated by scanning electron microscopy. The analysis of results reveals that the intrusion of VA with 10% replacement gives a significant response, and enhances the strength of the overall matrix. Full article
(This article belongs to the Proceedings of The 5th Conference on Sustainability in Civil Engineering)
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17 pages, 1871 KiB  
Article
Technical-Economic Opportunities of Mixture Optimization and Recycled Aptitude at a Pre-Casting Concrete Plant
by Jesús Montero and Jorge Cervera-Gascó
Appl. Sci. 2023, 13(13), 7782; https://doi.org/10.3390/app13137782 - 30 Jun 2023
Viewed by 1289
Abstract
Cost optimization is a key factor in the competitiveness of construction companies. Hence, in the case of a concrete manufacturing plant, the technical-economic optimization of the process involved in producing concrete is a determining factor in its activity being more competitive than that [...] Read more.
Cost optimization is a key factor in the competitiveness of construction companies. Hence, in the case of a concrete manufacturing plant, the technical-economic optimization of the process involved in producing concrete is a determining factor in its activity being more competitive than that of other companies. Thus, the main objective of this experimentation is the optimization of the different concrete dosages used in a pre-casting plant. The cement volume, the water/cement (W/C) ratio, the influence of an accelerator additive and replacing coarse aggregate with recycled aggregate were analysed. As an application of the economic results, three different hypotheses were analysed for different mix combinations in a real concrete structure model. The results show that it is essential to monitor the actual initial moisture state of aggregates and the perfect definition of the effective water/cement ratio of the dosage (Wef/C) in manufacturing in order to obtain more homogeneous production. It is proposed to simplify the number of different mix proportions and reduce cement by 10–20% without decreasing resistance and functional capabilities. Regarding additive optimization, the results show that using low rates of accelerator additive significantly improves compressive strength. Replacing natural aggregates with recycled aggregates obtained from the concrete waste of non-conforming elements is suited to manufacturing recycled concrete using replacement rates of 50% and 100%. The cost analysis for a real industrial building applying the different dosing options studied shows that a cost reduction of up to 17.8% can be achieved. Full article
(This article belongs to the Special Issue Green Construction Materials and Structures in the Circular Economy)
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21 pages, 14341 KiB  
Article
Effect of Recycled Foundry Sand on the Workability and Mechanical Properties of Mortar
by Gilberto García Del Angel, Jose A. Sainz-Aja, Pablo Tamayo, Ana Cimentada, René Cabrera, Luis Ruiz Pestana and Carlos Thomas
Appl. Sci. 2023, 13(6), 3436; https://doi.org/10.3390/app13063436 - 8 Mar 2023
Cited by 6 | Viewed by 2475
Abstract
Modern society requires a large number of metal components manufactured by sand casting, which involves the generation of a waste product known as Used Foundry Sand (UFS), of which approximately 100 Mt are generated on an annual basis. Virtually all UFS is currently [...] Read more.
Modern society requires a large number of metal components manufactured by sand casting, which involves the generation of a waste product known as Used Foundry Sand (UFS), of which approximately 100 Mt are generated on an annual basis. Virtually all UFS is currently landfilled, despite the economic and environmental cost overruns that this entails. Here, the recovery of UFS as fine aggregates for the manufacture of concrete is proposed. Since the presence of UFS will mainly affect the mortar that binds the aggregates in the manufacture of concrete, it was decided to isolate this fraction and study only the effect of UFS in mortars. This study evaluated a total of 32 different mixes combining different W/C ratios varying between 0.5 and 0.7 with 5 replacement ratios of natural sand by UFS: 0, 25, 50, 75 and 100%, respectively. The combined effect was evaluated of the W/C ratio and the replacement ratio on the workability, physical properties, mechanical properties, mechanical durability, and microstructure of the mortars. The incorporation of UFS decreases the workability of the mortars due to the absorption of the residue. For the physical properties of the mortars, density decreased and porosity and absorption increased at all replacement percentages. Flexural and compressive strength decreased when the replacement percentage was higher than 25 wt.%. In terms of mechanical durability, the mortars with UFS showed abrasion marks within the limits of the EN-1338 standard. From the results obtained, it is possible to conclude that the mortars with UFS require a higher amount of water. Therefore, while small replacement levels lead to a slight improvement in the mechanical properties, this trend breaks down for high replacement levels due to the negative effect of the high W/C ratios required. The authors recommend that for replacements higher than 25 wt.% of UFS, the W/C ratio has to be taken into consideration to obtain the same workability as the control mortar, although this decreases the mechanical properties. Full article
(This article belongs to the Special Issue Eco-Efficient Construction and Building Materials)
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