• Journal of the Korea Institute of Building Construction
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• v.8 no.4
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• pp.105-114
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• 2008

This study investigates the saturation level of surface dryness, quantity of adhesive mortar, and the alien substance content of recycled aggregates for concrete to develop an adequate quality testing method for understanding the properties of recycled aggregates, which differ greatly from preexisting aggregates. For tests that measure the saturation level of surface dryness, where detail methods are applied differently according to the tester, various testing methods from across world were compared and analyzed. This study revealed that when measuring the saturation level of surface dryness of a certain sample, aggregates must be supplemented immediately whenever the height of the sample becomes lower than the measuring mold, and allowing the tamper to free fall on the sample will provide the most accurate results. When measuring the quantity of adhesive mortar of recycled aggregates for concrete, an acid solution was used, and since the quantity of adhesive mortar increases as the particle sizes gets smaller, the sample for testing should represent the entire granularity. Sulfuric acid solution is adequate for immersion, and the concentration should be 20% for best results. According to the alien substance content measurement, which was examined by the naked eye, the error range caused by the difference in particle size was neglectable, and therefore the sample should be $2.5{\sim}5.0mm$ in size concerning the accuracy and measuring time. Also, for coarse recycled aggregates, the sample should amount to 1kg for measuring alien substance content by the naked eye, which proves that assortment by the naked eye is the most adequate method for measuring the alien substance content of a recycled aggregate.

• Journal of the Korean Recycled Construction Resources Institute
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• v.12 no.2
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• pp.178-187
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• 2024

In this study, it was determined that it was necessary to consider the replacement rate when applying recycled coarse aggregate to concrete, so data on existing research trends and results were collected and the mechanical properties of concrete according to the replacement rate of recycled coarse aggregate were analyzed. In collecting data on recycled coarse aggregate, data without processes such as compressive strength and removal of residual mortar attached to recycled coarse aggregate were collected among the concrete measurement items. In the case of concrete with 50 % and 100 % replacement of recycled coarse aggregate, it was confirmed that the mechanical properties were lower or higher than ordinary concrete by -36.0 ~ 9.9 % and -40.0 ~ 10.4 %, respectively, on average. Accordingly, it is judged that additional water should be mixed in consideration of the absorption rate when mixing, and the replacement rate of recycled coarse aggregate, which has mechanical properties of 80 % or more compared to ordinary concrete, should be less than 50 %.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2015.11a
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• pp.160-161
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• 2015

This research reviewed the characteristics of waste concrete sludge occurred from recycled aggregate producing process and the physical and mechanical properties of the mortar incorporated the pulverized the waste concrete sludge. From the results of the experiment, as the replacement ratio of waste concrete sludge powder was increased, the dosage of superplasticizer to satisfy the target flow of 200 ± 10 was increased, and the compressive and flexural strengths were decreased. On the other hand, when the sludge powder replacement ratio was 25 %, outstanding performance of general characteristics of mortar was obtained while it was lower than Plain mixture, thus, further detail study on various replacement ratios of waste concrete sludge powder is needed.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2011.11a
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• pp.251-252
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• 2011

This study is to investigate experimentally the strength properties of mortar using recycled fine aggregates(RA) and blast furnace slag powder(BS) without cement according to type of fine aggregate. In the results of the study, compressive strength of RA was the highest. It can be considered that the results are due to the reaction of the non-hydration cement in RA to the latent hydraulicity reaction of the BS.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2013.11a
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• pp.126-127
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• 2013

For the decades, various of materials were used to instead of cement as the high volume CO₂ occurred during the process of cement manufacture. In this paper, incineration plant ash was used in the mortar which incorporating high volume of blast furnace slag. Water to binder ratio(W/B) is fixed as 50%,BS+RP's replacement ratio is fixed as 80%,and the replacement ratio of WA1 is range as 0,0.5,1,2,3,4,5%.For the fresh mortar, flow and chloride contents has been tested. For the hardened mortar, compressive strength at 3,7,28 days has been tested. the result shows that when the replacement ratio of WA1 is 0.5%,the chloride contents is less than 0,3 kg/m3,the flowability and strength also performed better than other replacement types of mortar.

• International Journal of Concrete Structures and Materials
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• v.7 no.1
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• pp.61-69
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• 2013

This paper discusses the properties of RCA, the effects of RCA use on concrete material properties, and the large scale impact of RCA on structural members. The review study yielded the following findings in regards to concrete material properties: (1) replacing NA in concrete with RCA decreases the compressive strength, but yields comparable splitting tensile strength; (2) the modulus of rupture for RCA concrete was slightly less than that of conventional concrete, likely due to the weakened the interfacial transition zone from residual mortar; and (3) the modulus of elasticity is also lower than expected, caused by the more ductile aggregate. As far as the structural performance is concerned, beams with RCA did experience greater midspan deflections under a service load and smaller cracking moments. However, structural beams did not seem to be as affected by RCA content as materials tests. Most of all, the ultimate moment was moderately affected by RCA content. All in all, it is confirmed that the use of RCA is likely a viable option for structural use.

• Journal of the Korea Concrete Institute
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• v.28 no.3
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• pp.329-340
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• 2016

Increase in demotion and repair works on buildings in the construction market generates a large amount of construction waste. Recycling of construction waste is important for saving of resources, preservation of environment and constant advance of the construction industry. Accordingly, the environmental and economic value of recycled aggregate, which is produced after waste concrete is crushed, is increasingly highlighted. It is generally known that compared to concrete made of ordinary aggregate, concrete made of recycled aggregate has low quality, and the low quality is dependent on the amount of the bonding heterogeneous (cement paste and mortar) as well as the amount of the pores within the bonding heterogeneous. Reports on carbonation mechanism shows that the pores of cement-based materials are filled up by the progress of carbonation. Therefore, this study aims at an estimation of the period for optimum carbonation reforming appropriate for the thickness of the bonding heterogeneous of recycled aggregate, based on carbonation mechanism, with a view to improving the product quality by means of filling up the pores of the bonding heterogeneous of recycled aggregate. This study drew the carbonation depth according to the passage of age by calculating the bonding ratio and bonding thickness of the bonding heterogeneous as against the particle size distribution of recycled aggregate as well as by chemical quantitative analysis according to the age of accelerated carbonation of mock-up samples imitating bonding heterogeneous. Based on the correlation between the age of accelerated carbonation and carbonation depth, this study also proposed the estimated period of carbonation reforming of recycled aggregate appropriate for the thickness of the bonding heterogeneous.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.05b
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• pp.101-104
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• 2005

It analyzed the supply status of fine aggregate and find the point of issue related alternative fine aggregate through researches and interviews. The conclusions of the study are as follows. 1. Ready mixed concrete manufacture used crushed fine aggregate (15.5$\%$) and recycled fine aggregate (1.5$\%$) for alternatives aggregate than 1.3$\%$ in 1991. It is not allowed to use a recycled fine aggregate in ready mixed concrete, but they used it. 2. All alternative aggregate are satisfied the Korean Standard, But they showed low properties of mortar compared to when it replaced with natural fine aggregate. So, it is needed to make another special Korean Standard to use alternative aggregate in normal concrete by mixing method to recover the workability and compressive strength.

• International Journal of Highway Engineering
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• v.17 no.1
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• pp.7-16
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• 2015

PURPOSES : This study was performed to determine a systematic approach for measuring the coefficient of thermal expansion (COTE) of concrete specimens. This approach includes the initial calibration of measurement equipment. Test variables include coarse aggregate types such as natural aggregate, job-site produced recycled concrete aggregate, and recycled aggregate processed from an intermediate waste treatment company. METHODS : First, two cylindrical SUS-304 specimens with a known COTE value of $17.3{\times}10^{-6}m/m/^{\circ}C$. were used as reference specimens for the calibration of each measurement system. The well-known AASHTO TP-60 COTE apparatus for concrete measurement was utilized in this study. Four different measurement apparatuses were used with each LVDT installed and a calibration value was determined using each measurement apparatus. RESULTS : In the initial experimental stage, calibration values for each measurement apparatus were assumed to be almost identical. However, using the SUS-304 samples as a reference, the calibration values for the four different measurement apparatuses were found to range from 3.49 to $8.86{\times}10^{-6}m/m/^{\circ}C$. Using different adjusted values for each measurement apparatuses, COTE values for the three different concrete specimens were obtained. The COTE value of concrete made with natural coarse aggregate was $9.91{\times}10^{-6}m/m/^{\circ}C$, that of job-site produced recycled coarse aggregate was $10.45{\times}10^{-6}m/m/^{\circ}C$, and that of recycled aggregate processed from the intermediate waste treatment company was $10.82{\times}10^{-6}m/m/^{\circ}C$. CONCLUSIONS : We observed that the COTE value of concrete made from recycled concrete aggregates (RCA) was higher than that of concrete made from natural coarse aggregate. This difference is due to the fact that the total volumetric mortar proportion in the RCA mix is higher than that in the concrete mix made with natural coarse aggregate.

• Journal of the Korea Concrete Institute
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• v.20 no.5
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• pp.557-563
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• 2008

Recently, the amount of disposed construction materials like demolished concrete is growing fast and the shortage of natural concrete aggregate is becoming serious. Therefore, recycling of aggregate extracted from the demolished concrete is getting important and use of the recycled aggregate for concrete has been seriously considered. However, the use of the recycled aggregate even for low performance concrete is very limited because recycled aggregate which contains large amount of old mortar has very low quality. Therefore, removing the paste sticked to the recycled aggregate is very important in the manufacturing of high quality recycled aggregate. We have studied a series of research according to complex crushing method, which is removed the ingredient of cement paste from recycled fine aggregate using both the low speed wet abrasion crusher as mechanical process and the acid treatment as chemical processes. This paper is to analyze the quality of the recycled fine aggregate produced by those complex method and investigate optimum manufacturing condition for recycled fine aggregate by the design of experiments. The experimental parameters considered are water ratio, coase aggregate ratio, and abrasion time. As a result, data concerning the properties of recycled sand were obtained. It was found that high quality recycled fine aggregate could be to obtain at the condition of the fifteen minute of abrasion-crusher time and the over 1.0 of recycled coarse aggregate ratio.