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Recycled Aggregate Concrete and Alternative Binders for Sustainable Building Engineering (Second Volume)

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A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Construction and Building Materials".

Deadline for manuscript submissions: closed (10 August 2023) | Viewed by 19218

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Special Issue Editors

Prof. Dr. Miguel Bravo

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CERIS, IST-ID, Department of Civil Engineering, Architecture and Georresources, Instituto Superior Técnico (IST), Universidade de Lisboa, 1049-001 Lisbon, Portugal
Interests: materials science; sustainability in construction; recycled aggregate concrete; cementitious materials from industrial byproducts; supplementary cementitious materials; alkali-activated materials
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Prof. Dr. Rui Vasco Silva

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CERIS, IST-ID, Department of Civil Engineering, Architecture and Georesources, Instituto Superior Técnico (IST), Universidade de Lisboa, Lisbon, Portugal
Interests: materials science; civil engineering; sustainability in construction; recycled aggregate concrete; alkali-activated materials; supplementary cementitious materials
Special Issues, Collections and Topics in MDPI journals

Prof. Dr. António P.C. Duarte

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CERIS, IST-ID, Department of Civil Engineering, Architecture and Georresources, Instituto Superior Técnico (IST), Universidade de Lisboa, Lisbon, Portugal
Interests: materials science and technology; recycled aggregate concrete; sustainability of construction; structural and computational mechanics; steel–concrete composite structures; composite materials
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The construction industry is considered one of the most important sectors of socioeconomic development. However, its dynamism gives rise to two major environmental issues: (i) a significant increase in construction and demolition waste (CDW), which represents more than 30% of the solid waste generated by all economic sectors, and (ii) an increase in the production of Portland cement concrete, which is the most widely used construction material in the world and, through the production of cement alone, constitutes about 7% of all greenhouse gas emissions. Hence, it is essential to find, on the one hand, solutions for discarded CDW in addition to their use as recycled aggregates and, on the other hand, alternative sustainable binders that can replace Portland cement.

This Special Issue focuses on the development of sustainable cementitious composites, either by the replacement of natural aggregates with recycled aggregates or by the use of sustainable binding technologies that constitute a viable alternative to Portland cement.

The main topics covered in this Special Issue are (but not limited to) the following:

Experimental characterization (rheological, physical, mechanical, durability-related, thermal, etc.) of cementitious composites containing recycled aggregates (of all origins);
Experimental characterization of new sustainable alternative binders and cementitious composites containing them;
Development and implementation of analytical methods, numerical models, and optimization algorithms applied to the characterization of sustainable materials and structures produced from them;
Development of inspection and diagnostic methodologies and techniques for evaluating the performance of sustainable materials and structures containing them;
Life cycle assessment (LCA) and life cycle cost analysis (LCC) of sustainable materials and structures produced from them.

Work on subjects other than the aforementioned that contribute to advancing knowledge of sustainable materials and their applications are also welcome in this Special Issue.

We kindly invite you to submit a manuscript(s) for this Special Issue. Full papers, communications, and reviews presenting and discussing the most recent trends in the field are all welcome.

Prof. Dr. Miguel Bravo
Prof. Dr. Rui Vasco Silva
Prof. Dr. António P.C. Duarte
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Materials is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

sustainable construction
recycled aggregate concrete
sustainable alternative binders
supplementary cementitious materials
construction and demolition waste
carbon dioxide
alkali-activated materials
low environmental impact

Published Papers (13 papers)

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22 pages, 14873 KiB

Open AccessArticle

Eco-Innovative UHPC—Enhancing Sustainability, Workability, and Ductility with Recycled Glass Cullet Powder and Plastic Bottle Hybrid Fibers

by Mohammad Iqbal Khan, Galal Fares, Yassir M. Abbas and Fahad K. Alqahtani

Materials 2024, 17(2), 393; https://doi.org/10.3390/ma17020393 - 12 Jan 2024

Viewed by 576

Abstract

Utilizing waste materials in producing ultra-high-performance concrete (UHPC) represents a highly effective approach to creating environmentally sustainable concrete using renewable resources. This study focused on incorporating ground glass cullet (GP) at various replacement levels in UHPC production. Additionally, plastic bottle fibers (PBFs) were derived from discarded plastic bottles and employed in the mix. The replacement levels for GP spanned from 0% to 40%. Single-use plastic bottles were transformed into strip fibers, both with and without the inclusion of microsteel fibers, at varying contents of 1.1% and 2.2% (volume-based). A single-fiber test was conducted on PBFs under different strain rates. The introduction of optimal GP content had a profound positive iMPact on compressive strength. Incorporating 2.2% plastic strips induced strain hardening behavior, while further inclusion of microsteel fibers resulted in substantial enhancements in mechanical properties. Two types of microsteel fibers were employed, characterized by different aspect ratios of 65 and 100. The optimum GP content was identified as 10%. Moreover, the UHPC mix achieved superior compressive strength, exceeding 140 MPa when composed of 1.3% (volume-based) microsteel fibers with an aspect ratio of 65 and 2.2% PBF (volume-based). Notably, mixtures featuring microsteel fibers with a higher aspect ratio demonstrated the highest flexural strength, exceeding 8000 N in the presence of 2.2% PBF. Longer microsteel fibers exhibited adequate slip properties, facilitating strain transfer and achieving a strain-hardening response in conjunction with plastic bottle fibers. These findings illuminate the potential for harnessing hazardous waste materials to improve the performance and sustainability of UHPC formulations. Full article

(This article belongs to the Special Issue Recycled Aggregate Concrete and Alternative Binders for Sustainable Building Engineering (Second Volume))

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16 pages, 5951 KiB

Open AccessArticle

Damage Generated and Propagated by the AAR Reactive Aggregate from Kingston, Ontario, Canada

by Cassandra Trottier and Leandro F. M. Sanchez

Materials 2024, 17(1), 166; https://doi.org/10.3390/ma17010166 - 28 Dec 2023

Viewed by 433

Abstract

It remains unclear in the literature what the cause of the so-called alkali–carbonate reaction (ACR) damage to concrete is. However, expansion and cracks as distress features are often attributed to the alkali–silica reaction (ASR). Therefore, this work aims to assess the damage to concrete generated and propagated by the so-called ACR-susceptible reactive aggregate through mechanical testing (i.e., the direct shear test), microscopy (the damage rating index—DRI), and other techniques. Distinct induced expansion levels (i.e., 0%, 0.05%, 0.12%, and 0.20%) were selected to compare the distress caused by ACR to concrete affected by ASR. The results show that the behavior of ACR, namely, as captured through the DRI, is inconsistent with that of ASR, thus attesting to ACR being a distinct distress mechanism. The damage captured through mechanical testing does not distinguish ACR from ASR; however, microscopy reveals that cracks in the cement paste are the main damage mechanism. The proportions of cracks in the cement paste are 40–50% of the total number of cracks, whereas open cracks in the aggregates normally characterizing ASR represent only up to 20% of the total cracks. Full article

(This article belongs to the Special Issue Recycled Aggregate Concrete and Alternative Binders for Sustainable Building Engineering (Second Volume))

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18 pages, 3229 KiB

Open AccessArticle

Pervious Concrete Made with Recycled Coarse Aggregate and Reinforced with Date Palm Leaves Fibers

by Adil Tamimi, Sami W. Tabsh and Magdi El-Emam

Materials 2023, 16(23), 7496; https://doi.org/10.3390/ma16237496 - 04 Dec 2023

Cited by 1 | Viewed by 956

Abstract

This study considers 12 pervious concrete mixes incorporating 100% recycled coarse aggregate from old concrete demolition waste and containing various amounts of natural fine aggregate and date palm leaves fibers. First, the properties of the recycled aggregate in terms of their particle size distribution, abrasion resistance, crushing values, specific gravity and water absorption are obtained. Next, the pervious concrete density, compressive strength, tensile strength, permeability and porosity are determined by experimental testing following the relevant standards. The results are analyzed and compared to determine the influence of using recycled coarse aggregate in the mixtures and the impact of the amount of natural sand and volume fraction of the fibers on the mechanical properties, permeability and porosity of the concrete. Findings of the study showed that the use of recycled coarse aggregate in pervious concrete without fine aggregate reduced the compressive strength by 36% and tensile strength by 57%. Replacing 11.7% of the recycled coarse aggregate with natural sand and adding date palm leaves fibers in an amount equivalent to 0.64% volumetric content to such concrete helped increase the compressive strength by 16.2% and tensile strength by 3.2% above the corresponding strengths of the control mix. There is a clear relationship between permeability and porosity due to their correlation with the density of pervious concrete, and the effect of porosity on tensile strength is more influential than it is on the compressive strength. An equation that can predict the tensile strength of pervious concrete from the compressive strength is proposed, as a function of the natural fine aggregate fraction of the coarse aggregate and volumetric content of natural fibers. Results of the research confirm the feasibility of using recycled aggregate in pervious concrete mixes and the positive impact of natural fibers on the mechanical properties. Full article

(This article belongs to the Special Issue Recycled Aggregate Concrete and Alternative Binders for Sustainable Building Engineering (Second Volume))

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23 pages, 6143 KiB

Open AccessArticle

Multi-Criteria Optimization of Cost-Effective and Environmentally Friendly Reactive Powder Concrete Incorporating Waste Glass and Micro Calcium Carbonate

by Joaquín Abellán-García, Nemesio Daza, Marielena Molinares, Yassir M. Abbas and Mohammad Iqbal Khan

Materials 2023, 16(19), 6434; https://doi.org/10.3390/ma16196434 - 27 Sep 2023

Cited by 1 | Viewed by 749

Abstract

In pursuit of developing an eco-friendly and cost-effective reactive powder concrete (RPC), we utilized a multi-objective optimization technique. This approach pivoted on the incorporation of byproducts, with a spotlight on ground glass powder (GP) as a pivotal supplementary cementitious material (SCM). Our goal was twofold: engineering cost-efficient concrete while maintaining environmental integrity. The derived RPC showcased robust mechanical strength and impressive workability. Rigorous evaluations, containing attributes like compressive strength, resistance to chloride ion penetration, ultrasonic pulse speed, and drying shrinkage, highlighted its merits. Notably, the optimized RPC, despite an insignificant decrease in compressive strength at 90 days compared to its traditional counterpart, maintained steady strength augmentation over time. The refinement process culminated in a notable 29% reduction in ordinary Portland cement (OPC) usage and a significant 64% decrease in silica fume (SF), with the optimized mix composition being 590 for cement, 100 for SF, 335 for GP, and 257 kg/m³ for calcium carbonate. Additionally, the optimized RPC stood out due to the enhanced rheological behavior, influenced by the lubricative properties of calcium carbonate and the water conservation features of the glass powder. The reactive properties of SF, combined with GP, brought distinct performance variations, most evident at 28 days. Yet, both mixtures exhibited superior resistance to chloride, deeming them ideal for rigorous settings like coastal regions. Significantly, the RPC iteration, enriched with selective mineral admixtures, displayed a reduced tendency for drying-induced shrinkage, mitigating potential crack emergence. Full article

(This article belongs to the Special Issue Recycled Aggregate Concrete and Alternative Binders for Sustainable Building Engineering (Second Volume))

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18 pages, 3496 KiB

Open AccessArticle

Medical Waste Incineration Fly Ash as a Mineral Filler in Dense Bituminous Course in Flexible Pavements

by Rumpa Chowdhury, Mir Tanvir Al Biruni, Antara Afia, Mehedi Hasan, Mohammed Russedul Islam and Tanvir Ahmed

Materials 2023, 16(16), 5612; https://doi.org/10.3390/ma16165612 - 13 Aug 2023

Cited by 6 | Viewed by 1981

Abstract

Medical waste incineration fly ash (MWIFA) contains heavy metals that are toxic by nature and pose numerous health risks. The paper deals with the suitability of MWIFA as a mineral filler in the bituminous layer as an alternative to conventional stone dust (SD) through an appropriate combination of engineering and environmental assessments. Engineering parameters, such as Marshall stability, stability loss, flow, unit weight, air voids (V_a), voids filled with asphalt (VFA), and voids in the mineral aggregate (VMA) of the asphalt mixtures, were evaluated with varying filler ratios, from 2% to 10%. All parameters for both fillers at optimum bitumen content satisfied the Marshall Mix Design criteria. The optimum bitumen contents of all filler ratios were within the standard limit recommended by the Bangladesh Roads and Highways Department. It was found that mixes prepared with MWIFA can resist moisture effects, making them durable in the monsoon. The mixes with 5.5% MWIFA as mineral filler performed the best, whereas 9% SD filler was required to achieve similar performance. The environmental test results show no environmental restriction on stabilizing the MWIFA into paving mixtures. The mobility of heavy metals (As, Pb, Cu, Cr, Ni, Cd, Hg, and Zn) from the asphalt-MWIFA mix was insignificant. The cumulative concentrations of heavy metals (Cd, Ni, Zn, Cu, and Pb) from long-term leaching tests were far below the Dutch regulatory limit (U1). MWIFA can be considered an eco-friendly and sustainable mineral filler for the dense bituminous pavement layer. Full article

(This article belongs to the Special Issue Recycled Aggregate Concrete and Alternative Binders for Sustainable Building Engineering (Second Volume))

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23 pages, 1831 KiB

Open AccessArticle

The Influence of Recycled Cement, Fly Ash, and Magnesium Oxide on the Mechanical Performance of Sustainable Cementitious Materials

by Lucas Sequeira, Blas Cantero, Miguel Bravo, Jorge de Brito and César Medina

Materials 2023, 16(7), 2760; https://doi.org/10.3390/ma16072760 - 30 Mar 2023

Cited by 1 | Viewed by 1186

Abstract

In the construction industry, cement is the most widely used material. So, to achieve greater sustainability in this industry, it is imperative to improve the sustainability of this material. One way to reduce the ecological footprint of cement is to replace it, even if partially, with other more sustainable materials that can act as binders. This paper analyses the mechanical properties of more sustainable mortars containing recycled cement (RC), fly ash (FA), and magnesium oxide (MgO). Different types of binary, ternary, and quaternary mortars were used: containing recycled cement (5% and 10%), fly ash (10% and 20%), and MgO (7.5% and 15%). An experimental campaign was carried out analysing air content, density, compressive and flexural strengths, modulus of elasticity, and ultrasonic pulse velocity. The ternary mortars showed decreases between 0.4% (M-5RC10FA) and 35.3% (M-10RC15Mg) in terms of compressive strength at 365 days (compared to RM), when the theoretically expected decrease (the sum of the decreases obtained with the individual incorporation of these materials) would be between 16.6% and 41.5%, respectively. The results obtained allow for concluding that the joint use of these materials in ternary mortars improves the mechanical capacity, relative to the individual incorporation of each material in binary mortars. Full article

(This article belongs to the Special Issue Recycled Aggregate Concrete and Alternative Binders for Sustainable Building Engineering (Second Volume))

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19 pages, 8363 KiB

Open AccessArticle

Life Cycle Assessment of River Sand and Aggregates Alternatives in Concrete

by Le Hung Anh, Florin-Constantin Mihai, Anna Belousova, Radek Kucera, Klaus-Dieter Oswald, Wolfgang Riedel, Naveedh Ahmed Sekar and Petra Schneider

Materials 2023, 16(5), 2064; https://doi.org/10.3390/ma16052064 - 02 Mar 2023

Cited by 7 | Viewed by 3290

Abstract

Urbanization processes in Asia are still ongoing; thus, aggregate demand is expected to increase in following years. Even though construction and demolition waste is a source for secondary building materials in industrialized countries, it is not yet an alternative construction material source in Vietnam as the urbanization process is still ongoing. Thus, there is a need for river sand and aggregates alternatives in concrete, namely manufactured sand (m-sand) from primary solid rock materials and secondary waste materials. The focus in the present study for Vietnam was on m-sand sand as alternative for river sand, and different ashes as alternatives for cement in concrete. The investigations comprised concrete lab tests according to the formulations of concrete strength class C 25/30 in accordance with DIN EN 206, followed by a lifecycle assessment study in order to identify the environmental impact of the alternatives. In total 84 samples were investigated, consisting of 3 reference samples, 18 samples with primary substitutes, 18 samples with secondary substitutes, and 45 samples with cement substitutes. This kind of holistic investigation approach comprising material alternatives and accompanying LCA was the first study for Vietnam, and even for Asia, and represents a substantial added value for future policy development in order to cope with resource scarcity. The results show that with the exception of metamorphic rocks, all m-sands meet the requirements for quality concrete. In terms of cement replacement, the mixes showed that a higher percentage of ash reduces the compressive strength. The compressive strength values of the mixes with up to 10% coal filter ash or rice husk ash were equivalent to the C25/30 standard concrete formulation. Higher ash contents up to 30% lead to the reduction of the concrete quality. The LCA study’s results highlighted the better environmental footprints across environmental impact categories in the 10% substitution material in comparison to the use of primary materials. The LCA analysis results showed that cement as a component in concrete holds the highest footprint. The use of secondary waste as alternative for cement provides significant environmental advantage. Full article

(This article belongs to the Special Issue Recycled Aggregate Concrete and Alternative Binders for Sustainable Building Engineering (Second Volume))

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22 pages, 4341 KiB

Open AccessArticle

Assessment of the Applicability of Selected Data Mining Techniques for the Classification of Mortars Containing Recycled Aggregate

by Bernardeta Dębska

Materials 2022, 15(22), 8111; https://doi.org/10.3390/ma15228111 - 16 Nov 2022

Cited by 2 | Viewed by 1014

Abstract

The article contains the results of selected tests of physical and mechanical properties of mortars differentiated in terms of the binder used: cement, epoxy, epoxy modified with PET waste glycolysate and polyester. Each type of mortar was modified by partial (0–20% vol.) substitution of sand with an agglomerate made from waste polyethylene. The obtained results were used to build a database of mortar properties, which was then analyzed with the use of three different techniques of knowledge extraction from databases, i.e., cluster analysis, decision trees and discriminant analysis. The average results of the properties tested were compared, taking into account the type of mortar, indicating those with the most favorable parameters. The possibilities and correctness of mortar classification with the use of the indicated “data mining” methods were compared. The results obtained confirmed that it is possible to successfully apply these methods to the classification of construction mortars and then to propose mortars with such a composition that will guarantee that the composite will have the expected properties. Both the presented method of plastic waste management and the proposed statistical approach are in line with the assumptions of the currently important concept of sustainable development in construction. Full article

(This article belongs to the Special Issue Recycled Aggregate Concrete and Alternative Binders for Sustainable Building Engineering (Second Volume))

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22 pages, 4379 KiB

Open AccessArticle

Prediction of Strength Properties of Concrete Containing Waste Marble Aggregate and Stone Dust—Modeling and Optimization Using RSM

by Syed Roshan Zamir Hashmi, Muhammad Imran Khan, Shabir Hussain Khahro, Osama Zaid, Muhammad Shahid Siddique and Nur Izzi Md Yusoff

Materials 2022, 15(22), 8024; https://doi.org/10.3390/ma15228024 - 14 Nov 2022

Cited by 9 | Viewed by 1497

Abstract

Carbon footprint reduction, recompense depletion of natural resources, as well as waste recycling are nowadays focused research directions to achieve sustainability without compromising the concrete strength parameters. Therefore, the purpose of the present study is to utilize different dosages of marble waste aggregates (MWA) and stone dust (SD) as a replacement for coarse and fine aggregate, respectively. The MWA with 10 to 30% coarse aggregate replacement and SD with 40 to 50% fine aggregate replacement were used to evaluate the physical properties (workability and absorption), durability (acid attack resistance), and strength properties (compressive, flexural, and tensile strength) of concrete. Moreover, statistical modeling was also performed using response surface methodology (RSM) to design the experiment, optimize the MWA and SD dosages, and finally validate the experimental results. Increasing MWA substitutions resulted in higher workability, lower absorption, and lower resistance to acid attack as compared with controlled concrete. However, reduced compressive strength, flexural strength, and tensile strength at 7-day and 28-day cured specimens were observed as compared to the controlled specimen. On the other hand, increasing SD content causes a reduction in workability, higher absorption, and lower resistance to acid attack compared with controlled concrete. Similarly, 7-day and 28-day compressive strength, flexural strength, and tensile strength of SD-substituted concrete showed improvement up to 50% replacement and a slight reduction at 60% replacement. However, the strength of SD substituted concrete is higher than controlled concrete. Quadratic models were suggested based on a higher coefficient of determination (R²) for all responses. Quadratic RSM models yielded R² equaling 0.90 and 0.94 for compressive strength at 7 days and 28 days, respectively. Similarly, 0.94 and 0.96 for 7-day and 28-day flexural strength and 0.89 for tensile strength. The optimization performed through RSM indicates that 15% MWA and 50% SD yielded higher strength compared to all other mixtures. The predicted optimized data was validated experimentally with an error of less than 5%. Full article

(This article belongs to the Special Issue Recycled Aggregate Concrete and Alternative Binders for Sustainable Building Engineering (Second Volume))

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11 pages, 2923 KiB

Open AccessArticle

Influence of Sintering on Thermal, Mechanical and Technological Properties of Glass Foams Produced from Agro-Industrial Residues

by Fernando Antonio da Silva Fernandes, Dayriane do Socorro de Oliveira Costa and João Adriano Rossignolo

Materials 2022, 15(19), 6669; https://doi.org/10.3390/ma15196669 - 26 Sep 2022

Cited by 7 | Viewed by 1440

Abstract

This study investigates the technological, thermal, mechanical, and technological properties of glass foams produced with soda-lime glass residues and rice husk ash sintered at 850–950 °C. The results for apparent density (0.28–0.30 g/cm³), porosity (82–87 ± 4%), compressive strength (1.18 ± 0.03–1.25 ± 0.03 MPa), and thermal conductivity (0.283–0.326 W/mK) are within the limits for commercial foams. The volumetric expansion potential and low thermal conductivity of the glass foams produced favor their use as thermal insulating materials in coat walls, thus improving thermal comfort in the construction sector. The results of X-ray fluorescence show that the foam glass is of the soda-lime type (SiO₂, Na₂O, and CaO), the rice husk ash is rich in SiO₂, CaO, Na₂O, Al₂O₃, K₂O and Fe₂O₃, and the calcium carbonate is rich in CaO. The glass foams produced in this study are promising because they present more economical and efficient manufacturing, resulting in lightweight materials with thermal insulating properties that can be used in the construction sector. These glass foams also reduce the consumption of natural and synthetic raw materials, adding value to the waste used in this study by transforming them into co-products, thus favoring the economic circulation of the region. Full article

(This article belongs to the Special Issue Recycled Aggregate Concrete and Alternative Binders for Sustainable Building Engineering (Second Volume))

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17 pages, 5989 KiB

Open AccessArticle

Split Tensile Strength Prediction of Recycled Aggregate-Based Sustainable Concrete Using Artificial Intelligence Methods

by Muhammad Nasir Amin, Ayaz Ahmad, Kaffayatullah Khan, Waqas Ahmad, Sohaib Nazar, Muhammad Iftikhar Faraz and Anas Abdulalim Alabdullah

Materials 2022, 15(12), 4296; https://doi.org/10.3390/ma15124296 - 17 Jun 2022

Cited by 18 | Viewed by 1666

Abstract

Sustainable concrete is gaining in popularity as a result of research into waste materials, such as recycled aggregate (RA). This strategy not only protects the environment, but also meets the demand for concrete materials. Using advanced artificial intelligence (AI) approaches, this study anticipates the split tensile strength (STS) of concrete samples incorporating RA. Three machine-learning techniques, artificial neural network (ANN), decision tree (DT), and random forest (RF), were examined for the specified database. The results suggest that the RF model shows high precision compared with the DT and ANN models at predicting the STS of RA-based concrete. The high value of the coefficient of determination and the low error values of the mean absolute error (MAE), mean square error (MSE), and root mean square error (RMSE) provided significant evidence for the accuracy and precision of the RF model. Furthermore, statistical tests and the k-fold cross-validation technique were used to validate the models. The importance of the input parameters and their contribution levels was also investigated using sensitivity analysis and SHAP analysis. Full article

(This article belongs to the Special Issue Recycled Aggregate Concrete and Alternative Binders for Sustainable Building Engineering (Second Volume))

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18 pages, 6093 KiB

Open AccessArticle

Properties and Microstructures of Crushed Rock Based-Alkaline Activated Material for Roadway Applications

by Teewara Suwan, Peerapong Jitsangiam, Hemwadee Thongchua, Ubolluk Rattanasak, Thanon Bualuang and Phattharachai Maichin

Materials 2022, 15(9), 3181; https://doi.org/10.3390/ma15093181 - 28 Apr 2022

Cited by 3 | Viewed by 1189

Abstract

The worldwide demand for roads to serve global economic growth has led to the increasing popularity of road improvement using cement. This, in turn, has led to increased demand for cement and the associated problem of CO₂ emissions. Alkaline-activated materials (AAMs) could be an alternative binder for relatively low strength construction and rehabilitation as a cement replacement material. Compared to other applications, the lower strength requirements of road construction materials could ease any difficulties with AAM production. In this study, crushed rock (CR) was used as a prime raw material. The mechanisms and microstructures of the hardened AAM were investigated along with its mechanical properties. The results showed that CR-based AAM with an optimum mixture of 5 M of NaOH concentration, an SS/SH ratio of 1.00, and a liquid alkaline-to-binder (L/B) ratio of 0.5 could be used for roadway applications. At this ratio, the paste samples cured at room temperature (26 ± 3 °C) had an early compressive strength (3 days-age) of 3.82 MPa, while the paste samples cured at 60 °C had an early compressive strength of 6.45 MPa. The targeted strength results were able to be applied to a cement-treated base (CTB) for pavement and roadway applications (2.1 to 5.5 MPa). Full article

(This article belongs to the Special Issue Recycled Aggregate Concrete and Alternative Binders for Sustainable Building Engineering (Second Volume))

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Review

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18 pages, 345 KiB

Open AccessReview

Carbonation of Alkali-Activated Materials: A Review

by Ghandy Lamaa, António P. C. Duarte, Rui Vasco Silva and Jorge de Brito

Materials 2023, 16(8), 3086; https://doi.org/10.3390/ma16083086 - 13 Apr 2023

Cited by 4 | Viewed by 2224

Abstract

This paper presents a literature review on the effects of accelerated carbonation on alkali-activated materials. It attempts to provide a greater understanding of the influence of CO₂ curing on the chemical and physical properties of various types of alkali-activated binders used in pastes, mortars, and concrete. Several aspects related to changes in chemistry and mineralogy have been carefully identified and discussed, including depth of CO₂ interaction, sequestration, reactions with calcium-based phases (e.g., calcium hydroxide and calcium silicate hydrates and calcium aluminosilicate hydrates), as well as other aspects related to the chemical composition of alkali-activated materials. Emphasis has also been given to physical alterations such as volumetric changes, density, porosity, and other microstructural properties caused by induced carbonation. Moreover, this paper reviews the influence of the accelerated carbonation curing method on the strength development of alkali-activated materials, which has been awarded little attention considering its potential. This curing technique was found to contribute to the strength development mainly through decalcification of the Ca phases existing in the alkali-activated precursor, leading to the formation of CaCO₃, which leads to microstructural densification. Interestingly, this curing method seems to have much to offer in terms of mechanical performance, making it an attractive curing solution that can compensate for the loss in performance caused by less efficient alkali-activated binders replacing Portland cement. Optimising the application of such CO₂-based curing methods for each of the potential alkali-activated binders is recommended for future studies for maximum microstructural improvement, and thus mechanical enhancement, to make some of the “low-performing binders” adequate Portland cement substitutes. Full article

(This article belongs to the Special Issue Recycled Aggregate Concrete and Alternative Binders for Sustainable Building Engineering (Second Volume))

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