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19 pages, 8155 KiB

Open AccessArticle

Asphalt Mixes Processed with Recycled Concrete Aggregate (RCA) as Partial Replacement of the Natural Aggregate

by Carlos U. Espino-Gonzalez, Wilfrido Martinez-Molina, Elia M. Alonso-Guzman, Hugo L. Chavez-Garcia, Mauricio Arreola-Sanchez, Adria Sanchez-Calvillo, Marco A. Navarrete-Seras, Jorge A. Borrego-Perez and Juan F. Mendoza-Sanchez

Materials 2021, 14(15), 4196; https://doi.org/10.3390/ma14154196 - 27 Jul 2021

Cited by 7 | Viewed by 1718

Abstract

Materials play a fundamental role in any branch of civil engineering. From ancient times to the present day, society has required enormous amounts of construction materials, which implies an excessive exploitation of the natural environment. The present research work consisted in the design [...] Read more.

Materials play a fundamental role in any branch of civil engineering. From ancient times to the present day, society has required enormous amounts of construction materials, which implies an excessive exploitation of the natural environment. The present research work consisted in the design and development of asphalt mixes with a partial substitution of the natural aggregate (NA) by means of recycled concrete aggregate (RCA). The mix was designed with the Marshall methodology, considering the next percentages of substitution and addition by mass: 90% NA and 10% RCA; 80% NA and 20% RCA; 70% NA and 30% RCA. The mixtures were elaborated and analysed under the international standards and the Mexican regulation of the Communications and Transport Ministry, to determine the best option regarding their performance. The materials were characterized according to the current regulations and later employed in the mixes design. A total of 38 specimens were elaborated for each mixture, determining the optimum asphalt content; after that, mechanical tests were performed to analyse and determine the best results. In the aftermath of the examination of all mixtures, we concluded that the 70%AN/30%RCA is the best alternative option according to its performance and numeric results, complying with the cited regulations, and allowing a lower content of asphalt during the process. Full article

(This article belongs to the Special Issue Recycled Aggregate Concretes: From Raw Materials Selection to Field Applications)

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19 pages, 47066 KiB

Open AccessArticle

The Simple Mix Design Method and Confined Behavior Analysis for Recycled Aggregate Concrete

by Chong Rong, Jing Ma, Qingxuan Shi and Qiuwei Wang

Materials 2021, 14(13), 3533; https://doi.org/10.3390/ma14133533 - 24 Jun 2021

Cited by 3 | Viewed by 1405

Abstract

For the environment protection and sustainable development in building construction, waste concrete can be processed into recycled aggregate to mix the recycled aggregate concrete (RAC). However, the existing mix design methods of RAC were complex, and the mechanical properties of RAC were more [...] Read more.

For the environment protection and sustainable development in building construction, waste concrete can be processed into recycled aggregate to mix the recycled aggregate concrete (RAC). However, the existing mix design methods of RAC were complex, and the mechanical properties of RAC were more weakened than ordinary concrete. This paper presents a simple mix design method for RAC, including orthogonal test and single-factor test. Then, in order to study the behavior of confined RAC, this paper presents a comprehensive experimental study on the RAC filled in steel tube (RCFST) specimens and the RAC filled in GFRP tube (RCFST) specimens. The results show that the proposed mix design method can mix different stable strength grades of RAC promptly and efficiently. In addition, the steel tube and GFRP tube can provide a well confining effect on core RAC to improve the mechanical behavior of column. Moreover, the properties of core RAC in steel tube are the same as the common passive confined concrete, and the properties of core RAC in the GFRP tube are the same as the common active confined concrete. The study results can provide reference for other kinds of RAC mixtures as well as be a foundation for theoretical studies on confined RAC. Full article

(This article belongs to the Special Issue Recycled Aggregate Concretes: From Raw Materials Selection to Field Applications)

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17 pages, 5556 KiB

Open AccessArticle

Statistical and Reliability Study on Shear Strength of Recycled Coarse Aggregate Reinforced Concrete Beams

by Hyunjin Ju, Meirzhan Yerzhanov, Alina Serik, Deuckhang Lee and Jong R. Kim

Materials 2021, 14(12), 3321; https://doi.org/10.3390/ma14123321 - 16 Jun 2021

Cited by 13 | Viewed by 1959

Abstract

The consumption of structural concrete in the construction industry is rapidly growing, and concrete will remain the main construction material for increasing urbanization all over the world in the near future. Meanwhile, construction and demolition waste from concrete structures is also leading to [...] Read more.

The consumption of structural concrete in the construction industry is rapidly growing, and concrete will remain the main construction material for increasing urbanization all over the world in the near future. Meanwhile, construction and demolition waste from concrete structures is also leading to a significant environmental problem. Therefore, a proper sustainable solution is needed to address this environmental concern. One of the solutions can be using recycled coarse aggregates (RCA) in reinforced concrete (RC) structures. Extensive research has been conducted in this area in recent years. However, the usage of RCA concrete in the industry is still limited due to the absence of structural regulations appropriate to the RCA concrete. This study addresses a safety margin of RCA concrete beams in terms of shear capacity which is comparable to natural coarse aggregates (NCA) concrete beams. To this end, a database for reinforced concrete beams made of recycled coarse aggregates with and without shear reinforcement was established, collecting the shear specimens available from various works in the existing literature. The database was used to statistically identify the strength margin between RCA and NCA concrete beams and to calculate its safety margin based on reliability analysis. Moreover, a comparability study of RCA beams was conducted with its control specimens and with a database for conventional RC beams. Full article

(This article belongs to the Special Issue Recycled Aggregate Concretes: From Raw Materials Selection to Field Applications)

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18 pages, 5702 KiB

Open AccessArticle

Strength Properties of Sustainable Mortar Containing Waste Steel Slag and Waste Clay Brick: Effect of Temperature

by Md Jihad Miah, Suvash Chandra Paul, Adewumi John Babafemi and Biranchi Panda

Materials 2021, 14(9), 2113; https://doi.org/10.3390/ma14092113 - 22 Apr 2021

Cited by 13 | Viewed by 2198

Abstract

The use of waste streams for the production of sustainable cement-based materials cannot be overemphasized. This study investigates the feasibility of reusing waste steel slag (WSS) and waste clay brick (WCB) as a replacement for natural sand (NS) in mortar. Numerous studies have [...] Read more.

The use of waste streams for the production of sustainable cement-based materials cannot be overemphasized. This study investigates the feasibility of reusing waste steel slag (WSS) and waste clay brick (WCB) as a replacement for natural sand (NS) in mortar. Numerous studies have reported mainly the compressive strength of concrete/mortar, while limited research is available that focuses on the tensile and flexural strength of mortar, and especially the performance at elevated temperature. Hence, this study investigates the tensile and flexural strength of mortar with three different replacement percentages (0, 50 and 100% by volume of NS) of NS by WSS and WCB at normal temperature (without thermal treatment) and after exposure to elevated temperatures (250, 400 and 600 °C). At ambient condition, both tensile and flexural strength were enhanced as the WSS content increased (76 and 68%, respectively, at 100% WSS). In comparison, the strength increased at 50% WCB (25 and 37%, accordingly) and decreased at 100% WCB (23 and 20%, respectively) compared to 100% NS. At elevated temperatures, both the tensile and flexural strength of mortar mixes decreased significantly at 600 °C. Full article

(This article belongs to the Special Issue Recycled Aggregate Concretes: From Raw Materials Selection to Field Applications)

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17 pages, 3200 KiB

Open AccessEditor’s ChoiceArticle

Cement-Matrix Composites Using CFRP Waste: A Circular Economy Perspective Using Industrial Symbiosis

by Pierluca Vitale, Rosanna Napolitano, Francesco Colella, Costantino Menna and Domenico Asprone

Materials 2021, 14(6), 1484; https://doi.org/10.3390/ma14061484 - 18 Mar 2021

Cited by 13 | Viewed by 2481

Abstract

This study aims to provide a mitigation strategy for reducing the economic and environmental impacts of carbon fiber wastes deriving from automotive industry. Recycling and reuse in the construction industry is proposed, according to an industrial symbiosis within a circular economy perspective. Specifically, [...] Read more.

This study aims to provide a mitigation strategy for reducing the economic and environmental impacts of carbon fiber wastes deriving from automotive industry. Recycling and reuse in the construction industry is proposed, according to an industrial symbiosis within a circular economy perspective. Specifically, the process consists of repurposing carbon fiber reinforced polymer (CFRP) scraps/waste into new cement-matrix composites, for which the resulting benefits, in terms of mechanical and environmental performance, are herein described. An experimental campaign, starting with a specific heat treatment of CFRP sheets and an accurate dimensional distribution analysis of the short carbon fibers, is presented. The influence of the fiber content and length on both the workability and the mechanical performance of cement-based carbon fiber reinforced mortars is also evaluated. A reduced amount of either sand or cement (up to 8% and 12.8% in volume, respectively) is also considered in the mix design of the fiber reinforced mortars and derives from the substitution of the sand or binder with an equivalent volume of CFRP fibers. The results show a satisfactory increase in compressive and flexural strength in the range 10–18% for the samples characterized by a volume fraction of fibers of approximately 4% and having a 2–5 mm length. Finally, a life cycle assessment (LCA, 14040/14044) was carried out to quantify the environmental burden reductions associated with the implementation of the proposed symbiotic scheme. Full article

(This article belongs to the Special Issue Recycled Aggregate Concretes: From Raw Materials Selection to Field Applications)

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20 pages, 3896 KiB

Open AccessArticle

Influence of Wetting and Drying Cycles on Physical and Mechanical Behavior of Recycled Aggregate Concrete

by Caroline S. Rangel, Mayara Amario, Marco Pepe, Enzo Martinelli and Romildo D. Toledo Filho

Materials 2020, 13(24), 5675; https://doi.org/10.3390/ma13245675 - 12 Dec 2020

Cited by 10 | Viewed by 1970

Abstract

Recently, concerns have been rising about the impact of increasing the depletion of natural resources and the relevant generation of construction and demolition waste, on the environment and economy. Therefore, several efforts have been made to promote sustainable efficiency in the construction industry [...] Read more.

Recently, concerns have been rising about the impact of increasing the depletion of natural resources and the relevant generation of construction and demolition waste, on the environment and economy. Therefore, several efforts have been made to promote sustainable efficiency in the construction industry and the use of recycled aggregates derived from concrete debris for new concrete mixtures (leading to so-called recycled aggregate concrete, RAC) is one of the most promising solutions. Unfortunately, there are still gaps in knowledge regarding the durability performances of RAC. In this study, we investigate durability of structural RAC subjected to wet-dry cycles. We analyze the results of an experimental campaign aimed at evaluating the degradation process induced by wetting and drying cycles on the key physical and mechanical properties of normal- and high-strength concrete, produced with coarse recycled concrete aggregates (RCAs) of different sizes and origins. On the basis of the results we propose a degradation law for wetting and drying cycles, which explicitly makes a possible correlation between the initial concrete porosity, directly related to the specific properties of the RCAs and the resulting level of damage obtained in RAC samples. Full article

(This article belongs to the Special Issue Recycled Aggregate Concretes: From Raw Materials Selection to Field Applications)

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32 pages, 3679 KiB

Open AccessEditor’s ChoiceArticle

Machine Learning-Based Evaluation of Shear Capacity of Recycled Aggregate Concrete Beams

by Yong Yu, Xinyu Zhao, Jinjun Xu, Cheng Chen, Simret Tesfaye Deresa and Jintuan Zhang

Materials 2020, 13(20), 4552; https://doi.org/10.3390/ma13204552 - 13 Oct 2020

Cited by 29 | Viewed by 2754

Abstract

Recycled aggregate concrete (RAC) is a promising solution to address the challenges raised by concrete production. However, the current lack of pertinent design rules has led to a hesitance to accept structural members made with RAC. It would entail even more difficulties when [...] Read more.

Recycled aggregate concrete (RAC) is a promising solution to address the challenges raised by concrete production. However, the current lack of pertinent design rules has led to a hesitance to accept structural members made with RAC. It would entail even more difficulties when facing application scenarios where brittle failure is possible (e.g., beam in shear). In this paper, existing major shear design formulae established primarily for conventional concrete beams were assessed for RAC beams. Results showed that when applied to the shear test database compiled for RAC beams, those formulae provided only inaccurate estimations with surprisingly large scatter. To cope with this bias, machine learning (ML) techniques deemed as potential alternative predictors were resorted to. First, a Grey Relational Analysis (GRA) was carried out to rank the importance of the parameters that would affect the shear capacity of RAC beams. Then, two contemporary ML approaches, namely, the artificial neural network (ANN) and the random forest (RF), were leveraged to simulate the beams’ shear strength. It was found that both models produced even better predictions than the evaluated formulae. With this superiority, a parametric study was undertaken to observe the trends of how the parameters played roles in influencing the shear resistance of RAC beams. The findings indicated that, though less influential than the structural parameters such as shear span ratio, the effect of the replacement ratio of recycled aggregate (RA) was still significant. Nevertheless, the value of v_c/(f_c)^1/2 (i.e., the shear contribution from RAC normalized with respect to the square root of its strength) predicted by the ML-based approaches appeared to be insignificantly affected by the replacement level. Given the existing inevitable large experimental scatter, more shear tests are certainly needed and, for safe application of RAC, using partial factors calibrated to consider the uncertainty is feasible when designing the shear strength of RAC beams. Some suggestions for future works are also given at the end of this paper. Full article

(This article belongs to the Special Issue Recycled Aggregate Concretes: From Raw Materials Selection to Field Applications)

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Review

Jump to: Research

20 pages, 2176 KiB

Open AccessReview

A Review on Alkali-Silica Reaction Evolution in Recycled Aggregate Concrete

by Miguel Barreto Santos, Jorge De Brito and António Santos Silva

Materials 2020, 13(11), 2625; https://doi.org/10.3390/ma13112625 - 9 Jun 2020

Cited by 34 | Viewed by 3905

Abstract

Alkali-silica reaction (ASR) is one of the major degradation causes of concrete. This highly deleterious reaction has aroused the attention of researchers, in order to develop methodologies for its prevention and mitigation, but despite the efforts made, there is still no efficient cure [...] Read more.

Alkali-silica reaction (ASR) is one of the major degradation causes of concrete. This highly deleterious reaction has aroused the attention of researchers, in order to develop methodologies for its prevention and mitigation, but despite the efforts made, there is still no efficient cure to control its expansive consequences. The incorporation of recycled aggregates in concrete raises several ASR issues, mainly due to the difficult control of the source concrete reactivity level and the lack of knowledge on ASR’s evolution in new recycled aggregate concrete. This paper reviews several research works on ASR in concrete with recycled aggregates, and the main findings are presented in order to contribute to the knowledge and discussion of ASR in recycled aggregate concrete. It has been observed that age, exposure conditions, crushing and the heterogeneity source can influence the alkalis and reactive silica contents in the recycled aggregates. The use of low contents of highly reactive recycled aggregates as a replacement for natural aggregates can be done without an increase in expansion of concrete. ASR expansion tests and ASR mitigation measures need to be further researched to incorporate a higher content of recycled aggregates. Full article

(This article belongs to the Special Issue Recycled Aggregate Concretes: From Raw Materials Selection to Field Applications)

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