Search results
1 – 10 of over 3000Hamed Hemmati Pourghashti, Malek Mohammad Ranjbar and Rahmat Madandoust
The purpose of this paper is to conduct a laboratory investigation on measuring the tensile strength of recycled concrete using a double punch test. Furthermore, one of the main…
Abstract
Purpose
The purpose of this paper is to conduct a laboratory investigation on measuring the tensile strength of recycled concrete using a double punch test. Furthermore, one of the main goals of this study is to compare the tensile and compressive strengths of recycled concrete samples.
Design/methodology/approach
Recycled concrete samples were made with variables such as aggregate type (natural stone and aggregate recycled concrete), different water-to-cement ratios and different treatment conditions in the first stage. In the next stage, the double punch test was performed on them, and finally the results obtained from experiments were analyzed and investigated.
Findings
According to the above tests, it was concluded that: first, according to the laboratory results, the strength of concrete containing recycled aggregates becomes closer to the strength of concrete containing natural aggregates whenever the water-to-cement ratio is higher. Second, upon investigating the treatment conditions, it was observed that the treatment had a greater effect on the strength of the recycled concrete. However, this effect was less tangible in tensile strength. Third, upon investigating the results of tensile strength, it can be said that the Barcelona test results were closer to the direct tensile test results compared to the Brazilian test results. This indicates the higher viability of Barcelona’s test results. Fourth, the results obtained from the Barcelona tensile test for recycled concrete were closer to the results of the direct tensile test compared to the concrete containing natural aggregates, which suggests that the Barcelona test is more suitable as a tensile test for recycled concrete. Fifth, the effects of various factors on tensile strength were somewhat less compared to the compressive strength, although very close. Sixth, the relationships provided by the regulation for concrete tensile strength on compressive strength were highly inconsistent with the results obtained from the direct tensile test, for which the consistency was higher for concrete containing natural aggregates compared to recycled concrete. Seventh, the dispersion of results obtained from tensile tests was higher for recycled concrete compared to concrete containing natural aggregates, but lesser of this dispersion was observed in the compressive strength.
Originality/value
According to the laboratory results, the strength of concrete containing recycled aggregates becomes closer to the strength of concrete containing natural aggregates whenever the water-to-cement ratio is higher. Upon investigating the treatment conditions, it was observed that the treatment had a greater effect on the strength of the recycled concrete. However, this effect was less tangible in tensile strength. On the basis on the results of the tensile strength, it can be said that the Barcelona test results were closer to the results of the direct tensile test compared to those of the Brazilian test. This indicates the higher viability of Barcelona’s test results. The results obtained from the Barcelona tensile test for recycled concrete were closer to the results of direct tensile test compared to the concrete containing natural aggregates, which suggests that the Barcelona test is more suitable as a tensile test for recycled concrete. The effects of various factors on tensile strength were somewhat less compared to the compressive strength, although very close. The relationships provided by the regulation for concrete tensile strength on compressive strength were highly inconsistent with the results obtained from the direct tensile test, for which the consistency was higher for concrete containing natural aggregate compared to recycled concrete. The dispersion of results obtained from tensile tests was higher for recycled concrete compared to concrete containing natural aggregate, but lesser of this dispersion was observed in the compressive strength.
Details
Keywords
Alan Richardson, Pierre Allain and Maxime Veuille
A current trend is to use waste and by‐products in concrete to replace binders and aggregates. This trend reduces the impact on the environment and the use of finite natural…
Abstract
Purpose
A current trend is to use waste and by‐products in concrete to replace binders and aggregates. This trend reduces the impact on the environment and the use of finite natural resources. This paper aims to investigate whether concrete which includes crushed, graded and washed recycled construction demolition waste, used as a coarse aggregate, can be manufactured to a comparable strength as concrete manufactured from virgin aggregates.
Design/methodology/approach
Laboratory testing investigated the strength development of concrete manufactured with varying degrees of coarse aggregate replacement. All of the concrete samples were tested at five, seven, 14 and 21 days and the concrete with the recycled aggregate was compared to a plain control sample manufactured with virgin aggregates. The mixes tested against the control sample were: 100 per cent gravel replacement with recycled aggregate, and the same mix with a viscosity modifying agent. A 50 per cent partial coarse aggregate replacement was used in one batch to compare against the control and the 100 per cent recycled aggregate concrete. Compressive strength was used to compare the different concrete batch performance. Density was used to indicate the degree of particle packing and void content which was measured across the range of samples to evaluate the relationship between the different concrete mixes.
Findings
The optimum concrete mix design using recycled construction waste was obtained by using a 50‐50 per cent mix of virgin gravel and recycled aggregates. Using recycled construction waste as a 100 per cent coarse aggregate replacement produces concrete with a lower compressive strength when compared to concrete made with virgin aggregates.
Originality/value
The paper investigates ways of incorporating construction demolition waste as recycled aggregate to reduce the environmental impact of the production of concrete.
Details
Keywords
Olalekan Shamsideen Oshodi, Bankole Osita Awuzie, Julius Akotia, Adesola S. Ademiloye and Alfred Ngowi
The use of recycled concrete (RC) can reduce the greenhouse emissions associated with the production of cement, which is one of the primary materials used for the execution of…
Abstract
Purpose
The use of recycled concrete (RC) can reduce the greenhouse emissions associated with the production of cement, which is one of the primary materials used for the execution of construction projects. This research aims to review the state of knowledge in the field of RC research. An understanding of the state of the art in the RC domain justifies future research in this field.
Design/methodology/approach
A systematic and comprehensive search of RC-related literature was conducted using the Scopus database. In this research, the bibliometrix R-package was used for the analysis of bibliometric information of the selected papers. The software was used to create a map, which highlights the trends and gaps in the RC knowledge domain.
Findings
The results reveal the research themes, clusters, collaboration networks and advancement of knowledge in the field of RC research. The study integrates the literature focussed on RC research and provides a platform for progression of knowledge in this field.
Originality/value
The study contributes to the growing body of knowledge by providing an up-to-date RC knowledge map based on an analysis of bibliographic data. Information gleaned from previous studies suggests that bibliometric review can strengthen and complement the findings emerging from other forms of literature reviews. The study reported here is one of the first studies to provide insights into the evolution of RC research.
Details
Keywords
Angelo De Luca, Linda Chen and Koorosh Gharehbaghi
Due to the high demand of concrete, significant volume of natural resources is required, including virgin aggregates. Many studies have shown that the production of concrete has…
Abstract
Purpose
Due to the high demand of concrete, significant volume of natural resources is required, including virgin aggregates. Many studies have shown that the production of concrete has one of the highest CO2 levels. Although efforts are in place to recycle, enormous effects on landfill and the wider environment remain. Research has suggested the importance of reusing construction and demolition waste such as aggregate for use in recycled concrete. However, robust construction and demolition waste reduction strategies are required. There have been numerous researches on the use of recycled concrete and its management in the construction industry. This paper further consolidates this position.
Design/methodology/approach
This paper exhibits the barriers and benefits of using recycled aggregates for construction industry. This is achieved via reviewing the current construction and demolition waste reduction strategies used mainly in three countries: the UK, Australia and Japan. These countries were selected since they seemingly have similar construction industry and environment. Subsequently, evolving barriers and benefits of using recycled aggregates for construction industry are also reviewed and discussed. And to support such focus, robust construction and demolition waste reduction strategies will be advocated.
Findings
The findings are summarized as follows. The recycling construction and demolition waste could have a positive net benefit compared to the procurement and production of virgin aggregate materials with the same properties. This is not only financially beneficial but also environmentally viable, as fewer resources would be required to produce the same aggregate material. There are effective ways to achieve a high recycle rate target, as demonstrated by Japan. The implementation of a similar recycling process could be implemented globally to achieve a more effective recycle rate through the help of governments at all levels. By creating awareness about the financial and environmental benefits of using recycled aggregate products, large recycling companies can be also enticed to follow suit.
Practical implications
The findings from this paper can ultimately support the construction industry to further consolidate and advocate the use of recycled aggregates.
Originality/value
To achieve the research aim, this paper reviews some of the main sustainability factors of recycled aggregates (including coarse and fine aggregates) and provides comparison to virgin aggregates.
Details
Keywords
Mohammed Ahmed Abed and Eva Lubloy
Fire can severely affect concrete structures and with knowledge of the properties of materials, the damage can be assessed. Aggregate, cement matrix and their interaction are the…
Abstract
Purpose
Fire can severely affect concrete structures and with knowledge of the properties of materials, the damage can be assessed. Aggregate, cement matrix and their interaction are the most important components that affect concrete behaviour at high temperatures. The effect of incorporating recycled concrete aggregate or cementitious materials, namely, cement type and pulverized fly ash, are reviewed to provide a better understanding of their involvement in fire resistance.
Design/methodology/approach
More investigation research is needed to understand the fire resistance of such sustainable concrete that was already constructed. The present study illustrates the effect of using recycled concrete aggregate and cementitious materials on the fire resistance of concrete. To do so, a literature review was conducted and relevant data were collected and presented in a simple form. The author's selected research findings, which are related to the presents study, are also presented and discussed.
Findings
Recycled concrete aggregate enhances the concrete behaviour at high temperatures when it substitutes the natural aggregate by reasonable substitution (more than 25–30%). It also almost eliminates the possibility of spalling. Moreover, utilizing both supplementary cementitious materials with recycled concrete aggregate can improve the fire resistance of concrete. The incorporation of pulverized fly ash and slag in Portland cement or blended cement can generally keep the mechanical properties of concrete at a higher level after heating to a high temperature.
Originality/value
Recycled concrete aggregate enhances the concrete behaviour at high temperatures when it substitutes the natural aggregate by reasonable substitution (more than 25–30%). It also almost eliminates the possibility of spalling. Moreover, utilizing both supplementary cementitious materials with recycled concrete aggregate can improve the fire resistance of concrete. The incorporation of pulverized fly ash and slag in Portland cement or blended cement can generally keep the mechanical properties of concrete at a higher level after heating to a high temperature.
Details
Keywords
Shahe Liang, Wenkun Liu and Zhongfan Chen
Recycled concrete is an economical and environmentally friendly green material. The shear performance of recycled concrete load-bearing masonry is studied, which is great of…
Abstract
Purpose
Recycled concrete is an economical and environmentally friendly green material. The shear performance of recycled concrete load-bearing masonry is studied, which is great of significance for its promotion and application and also has great significance for the sustainable development of energy materials.
Design/methodology/approach
In total, 30 new load-bearing block masonry samples of self-insulating recycled concrete are subjected to pure shear tests, and 42 samples are tested subjected to shear-compression composite shear tests. According to the axial design compression ratio, the test is separated into seven working conditions (0.1–0.8).
Findings
According to the test results, the recommended formula for the average shear strength along the joint section of recycled concrete block masonry is given, which can be used as a reference for engineering design. The measured shear-compression correlation curves of recycled concrete block masonry are drawn, and the proposed limits of three shear-compression failure characteristics are given. The recommended formula for the average shear strength of masonry under the theory of shear-friction with variable friction coefficient is given, providing a valuable reference for the formulation of relevant specifications and practical engineering design.
Originality/value
Simulated elastoplastic analysis and finite element modeling on the specimens are performed to verify the test results.
Details
Keywords
Yijiang Peng, Xiyun Chen, Liping Ying and Mahmoud M.A. Kamel
Based on the base force element method, a two-dimensional random circle aggregate model with Monte Carlo principle is proposed to carry out research on softening curve in…
Abstract
Purpose
Based on the base force element method, a two-dimensional random circle aggregate model with Monte Carlo principle is proposed to carry out research on softening curve in meso-level.
Design/methodology/approach
The meso-level structure of recycled concrete is considered as the five-phase materials composed of aggregate, old interfacial transition zone, old mortar, new interfacial transition zone and new mortar. A multi-polyline damage model is adopted to describe the nonlinear mechanical behavior of recycled concrete material. The destruction state of the element is determined by the first strength theory. The research studies on damage process of recycled concrete under the loading conditions of uniaxial tension were established using the base force element method.
Findings
The softening curves of recycled concrete are obtained, which are in good agreement with experiment results. Simulation results show that the macroscopic mechanical properties and failure mechanism can analyze more reasonably from mesoscopic structure. Besides that, it can be investigated from the numerical results of the size effect in recycled concrete through the mesoscopic heterogeneity. Furthermore, the form of aggregate distribution has influence on the crack path but little effect on the tensile strength of recycled concrete.
Originality/value
The results show that the base force element method has been successfully applied to the study of softening curve of recycled concrete under uniaxial tension.
Details
Keywords
Construction contractors and facility managers are being challenged to minimize the carbon footprint. Life cycle carbon‐equivalent (CO2‐e) accounting, whereby the potential…
Abstract
Purpose
Construction contractors and facility managers are being challenged to minimize the carbon footprint. Life cycle carbon‐equivalent (CO2‐e) accounting, whereby the potential emissions of greenhouse gases due to energy expenditure during construction and subsequent occupation of built infrastructure, generally ceases at the end of the service life. However, following demolition, recycling of demolition waste that becomes incorporated into 2nd generation construction is seldom considered within the management of the carbon footprint. This paper aims to focus on built concrete infrastructure, particularly the ability of recycled concrete to chemically react with airborne CO2, thereby significantly influencing CO2‐e estimates.
Design/methodology/approach
CO2‐e estimates were made in accordance with the methodology outlined in the Australian National Greenhouse Accounts (NGA) Factors and were based on the energy expended for each life cycle activity from audited records. Offsets to the CO2‐e estimates were based on the documented ability of concrete to chemically react with airborne carbon dioxide (“carbonation”) and predictions of CO2 uptake by concrete and recycled concrete was made using existing predictive diffusion models. The author's study focused on a built concrete bridge which was demolished and recycled at the end of the service life, and the recycled concrete was utilized towards 2nd generation construction. The sensitivity of CO2‐e and carbonation estimates were tested on several different types of source demolition waste as well as subsequent construction applications using recycled concrete (RCA). Whole‐of‐life CO2‐e estimates, including carbonation of RCA over the 1st and 2nd generations, were estimated and contrasted with conventional carbon footprints that end at the conclusion of the 1st generation.
Findings
Following demolition, CO2 capture by RCA is significant due to the more permeable nature of the crushed RCA compared with the original built infrastructure. RCA also has considerably greater exposed surface area, relative to volume, than a built concrete structure, and therefore more highly exposed surface to react with CO2: it therefore carbonates more comprehensively. CO2‐e estimates can be offset by as much as 55‐65 per cent when including the contribution of carbonation of RCA built within 2nd generation infrastructure. Further offsets are achievable using blended fly ash or slag cement binders; however, this study has focused on concrete composed of 100 per cent OPC binders and the effects of RCA.
Originality/value
Construction project estimates of life cycle CO2‐e emissions should include 2nd generation applications that follow the demolition of the 1st generation infrastructure. Life cycle estimates generally end at the time of demolition. However, by incorporating the recycled concrete demolition waste into the construction of 2nd generation infrastructure, the estimated CO2‐e is significantly offset during the 2nd generation life cycle by chemical uptake of CO2 (carbonation). This paper provides an approach towards inclusion of 2nd generation construction applications into whole‐of‐life estimates of CO2‐e.
Details
Keywords
Peter Lindsell and Mike Mulheron
Introduction In a recent paper in this journal, Campbell outlined some of the techniques and problems associated with the demolition of existing structures and touched upon the…
Abstract
Introduction In a recent paper in this journal, Campbell outlined some of the techniques and problems associated with the demolition of existing structures and touched upon the possibility of recycling the debris from this process. This reflects the growing awareness among the general public, local authorities and central Government that the recycling of waste materials, from all sources, is both necessary and desirable. Indeed, according to a recently published report from the Trade and Industry Committee of the House of Commons: ‘The benefits of recycling are obvious: rarely do environ‐mental and economic factors so unambiguously support the same goal’.
A.E. Richardson, K. Coventry and S. Graham
The purpose of this paper is to investigate whether concrete that includes un‐graded recycled aggregates can be manufactured to a comparable strength to concrete manufactured from…
Abstract
Purpose
The purpose of this paper is to investigate whether concrete that includes un‐graded recycled aggregates can be manufactured to a comparable strength to concrete manufactured from virgin aggregates.
Design/methodology/approach
A paired comparison test was used to evaluate the difference between concrete made with virgin aggregates (plain control) and concrete including recycled waste. Un‐graded construction demolition waste and un‐graded ground glass were used as aggregate replacements. With regard to concrete, compressive strength is widely used as a measure of suitability as being fit for purpose. Therefore compressive strength was mainly used to compare the different concrete batches; however density was measured across the range of samples.
Findings
The findings show that a lower average compressive strength is achieved when compared to the plain control sample manufactured with virgin aggregates. Correct particle packing may not be achieved and grading of aggregates is essential prior to mix design. The recycled aggregate was highly variable in terms of the fine particle content, which affected the water demand of the concrete.
Practical implications
This manufacturing practice is considered necessary because of the current trend in using waste products in concrete to replace binders and aggregates; thus reducing the impact on the environment and use of finite natural resources. The research shows the risk of mixing concrete using a simple aggregate replacement without careful aggregate grading and adjustments to the mix design.
Originality/value
The paper examines 100 per cent ungraded aggregate replacement with glass and demolition waste.
Details