• KSCE Journal of Civil and Environmental Engineering Research
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• v.44 no.3
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• pp.283-290
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• 2024

Currently, the quality standards for recycled aggregates in Korea are very high, at almost the same level as natural aggregates, so recycled aggregates cannot be widely used for concrete. In particular, it is necessary to evaluate how the moisture conditions and curing conditions of recycled aggregates with high absorption rates and wearing rates affect the compressive strength of concrete. Therefore, in this study, we wanted to investigate the effects on compressive strength through experiments using the moisture conditions and curing conditions of recycled coarse aggregate as variables, and compare the compressive strength characteristics of natural coarse aggregate concrete. As a result of this experimental study, the effect of compressive strength on concrete using recycled coarse aggregates according to curing conditions was similar to that of natural aggregate concrete, and the compressive strength showed a low strength of about 13 to 17 %. The effect of the moisture conditions of recycled coarse aggregates was that in the case of wet curing, concrete using wet aggregate showed slightly higher compressive strength than concrete using dry aggregate, but in the case of air curing, on the contrary, dry recycled aggregate concrete was relatively higher than wet aggregate concrete.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.525-528
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• 2006

Recently, Korea government prepared Act on facilitation of construction waste recycling in December 2003 for effective recycling of rapidly increasing construction wastes, and has enforced the Act on Jan. 2005. This Act limits the definition of recycled aggregates to the aggregates which obtained quality certificate and for this purpose, government has operated quality standard and certificate system of recycling aggregate. The objective of this experimental study is to evaluate the mechanical properties of recycled coarse aggregate concrete according to curing method by ready-mixed concrete. Compressive strength ratio of recycled aggregate concrete under air-dry curing/wet curing was $74{\sim}91%$. KCI code for conventional concrete overestimated elastic modulus for recycled coarse aggregate concrete.

• Advances in concrete construction
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• v.8 no.4
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• pp.321-333
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• 2019

The present study targets to access the consequence of utilization of coarse aggregates retrieved from waste concrete as a substitution of coarse fraction of natural aggregates and silica nano-particles as partial substitution of cement using principles of factorial design. Furthermore, procedures of design of experiments are employed to examine the effect of use of recycled aggregates and nano-silica. In this investigation, compressive strength found after at 7, 28, 90 and 365 days, split and flexural tensile strength, ultrasonic pulse velocity and rebound number and are chosen as responses, whereas the percentages of recycled coarse aggregates (RCA%) and nano-silica (NS(%)) are selected as factors. Analysis of Variance has been conducted on the experimental results for the selected responses with consideration the both factors, which indicates that RCA (%) and NS (%) have substantial impact on the various responses. However, the present analysis depicts that interaction between factors has considerable effect on the chosen parameters of concrete. Furthermore, validation experiments are carried to validate these models for compressive and tensile strength for 100% RCA and 1% NS. The results of comparative study indicates that that the error of the estimation determined using the relevant models are found to be small (±5%) in comparison with the analogous experimental results, which authenticates the calculated models.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2021.05a
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• pp.23-24
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• 2021

The use of recycled concrete aggregates (RCA) as a substitute for natural aggregates in new concrete produces both economic and environmental advantages. Most of the RCA applications for pavements have been primarily applied to support layers for roads and airfields. This paper summarizes a work completed at the University of Illinois in partnership with the O'Hare Modernization Program to examine the effect of coarse and fine RCA on the concrete's fresh and hardened properties for airfield rigid pavement applications. Ten different RCA concrete mixtures were prepared with the incorporation of different percentages of RCA fines as well as replacement of cement with high volume percentages of supplementary cementitious materials such as Class C fly ash and ground granulated blast furnace slag to improve the workability and long-term properties of RCA concrete. All the mixes on this stage included 100% recycled coarse aggregates and the Two-Stage Mixing Approach was used as a mixing procedure. Based on the results obtained in the research, mixes with high percentages of recycled fine and coarse aggregates could be used for construction of airfield concrete pavements in conjunction with supplementary cementitious materials

• Advances in concrete construction
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• v.5 no.2
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• pp.145-154
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• 2017

In the present day scenario, concrete construction is rapidly becoming uneconomical and non sustainable practice, due to the scarcity of raw materials and environmental pollution caused by the manufacturing of cement. In this study an attempt has been made to propose recycled aggregates from demolition wastes as coarse aggregate in geopolymer concrete (GPC). Experimental investigations have been conducted to find optimum percentage of recycled aggregates (RA) in GPC by replacing 20%, 30%, 40%, 50% and 60% of coarse aggregates by RA to produce recycled aggregate geopolymer concrete (RGPC). From the study it has been found that the optimum replacement percentage of recycled aggregates was 40% based on mechanical properties and workability. In order to study and compare the flexural behaviour of RGPC and GPC four beams of size $175mm{\times}150mm{\times}1200mm$ were prepared and tested under two point loading. Test results were evaluated with respect to first crack load, ultimate load, load-deflection characteristics, ductility and energy absorption characteristics. Form the experimental study it can be concluded that the addition of recycled aggregate in GPC causes slight reduction in its strength and ductility. Since the percentage reduction in strength and behaviour of RGPC is meager compared to GPC it can be recommended as a sustainable and environment friendly construction material.

• Journal of the Korea Institute of Building Construction
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• v.17 no.1
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• pp.55-61
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• 2017

This paper is to investigate experimentally the effect of substitution of recycled coarse aggregate(RCA) under 13mm on the engineering properties of the concrete using gap graded coarse aggregates. Concretes with 0.4 of water to cement ratio(W/C) were fabricated to achieve 30MPa of design strength with coarse aggregate over 13mm in size with the maximum size of 25mm. RCA was substituted for coarse aggregate over 13mm from 10% to 50% and crushed coarse aggregate under 13mm was also substituted for coarse aggregate over 13mm from 20% to 40%, respectively. Test results indicated that the replacement of RCA up to 20% resulted in an increase of fluidity and strength. It also caused a decrease in the drying shrinkage due to dense packing effect by achieving continuous grading of mixed aggregates. For practical application of RCA, when properly substituted, the use of RCA enabled the concrete to reduce water contents and sand to aggregate ratio in mixing design stage of the concrete. And, it can also enhance the compressive strength of the concrete.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2013.05a
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• pp.337-338
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• 2013

Recent research is needed for the reduction of the pH of the recycled aggregates, recycled aggregates for alkali social problems have emerged. This was confirmed through preliminary experiments using a self-made reactor with dry ice, the possibility of reducing the pH of the recycled aggregates. The pH reduction of coarse recycled aggregates plant was made to apply the field to the middle of construction waste treatment process to reduce the pH of the plant room, and measured the pH change with time. The measurement results showed that dry ice after the reaction, the pH of the aggregate 5% reduction than untreated recycled aggregates.

• International Journal of Highway Engineering
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• v.7 no.1 s.23
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• pp.1-9
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• 2005

This is a basic research for producing hot-mix recycled asphalt mixtures and suggesting methods for solving quality problems, if any. Various mixing methods are introduced to mate aging evenly between old and virgin aggregates and to improve aging conditions. Gel-permeation chromatography(GPC) analysis was performed to evaluate aging of binders coated on coarse aggregates and a matrix separately. Round-shaped aggregates(13m gravel) were used in manufacturing mixtures for analysis of aging levels in recycled mixtures. It was found out that there was significant difference in aging levels between the binder coated on RAP's coarse aggregates and on virgin aggregates in a recycled mixture. The difference in the aging level was reduced by modifying mixing method(RAP and virgin binders were mixed first and then virgin aggregates were introduced). Among A to E mixing methods studied, the D was turned out to be the best.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.1
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• pp.11-17
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• 2013

The use of wasted concrete can settle the environmental pollution and shortage of natural aggregate. However, recycled aggregate includes substantial amount of cement paste, so that these aggregates are more porous, and less resistant to mechanical actions than natural aggregates. Recently, the new manufacturing processes of high quality recycled aggregates were suggested such as heating. In this paper, for the purpose of manufacture of high quality recycled aggregates, the heating processes was considered to the existing process of recycled aggregates. To find the optimum process, the experiment was performed through the statistical design of experiment. The heating temperatures of 4 levels (300, 450, 600 and $750^{\circ}C$) and heating duration time (5, 20, 40, 60minute) were main experimental variables. Through the test results, it was found that the optimum manufacturing condition of coarse recycled aggregate was evaluated to be $600^{\circ}C$ and 40minute.

• Advances in concrete construction
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• v.4 no.4
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• pp.263-281
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• 2016

Concrete continues to be the most consumed construction material in the world, only next to water. Due to rapid increase in construction activities, Construction and Demolition (C&D) waste constitutes a major portion of total solid waste production in the world. It is important to assess the amount of C&D waste being generated and analyse the practices needed to handle this waste from the point of waste utilization, management and disposal addressing the sustainability aspects. The depleting natural resources in the current scenario warrants research to examine viable alternative means, modes and methods for sustainable construction. This study reports processing Recycled Coarse Aggregates (RCA) using a rod mill, for the first time. Parameters such as amount of C&D waste for processing, nature of charge and duration of processing time have been optimized for obtaining good quality RCA. Performance of RCA based concrete and performance enhancement techniques of 50% RCA based concrete are discussed in this paper.