Original Article

Econ. Environ. Geol. 2017; 50(4): 257-266

Published online August 31, 2017

https://doi.org/10.9719/EEG.2017.50.4.257

© THE KOREAN SOCIETY OF ECONOMIC AND ENVIRONMENTAL GEOLOGY

The pH Reduction of the Recycled Aggregate Originated from the Waste Concrete by the scCO2 Treatment

Chul-woo Chung1, Minhee Lee2*, Seon-ok Kim3 and Jihyun Kim1

1Department of Architectural Engineering, Pukyong National University, Busan, 48513, Republic of Korea
2Department of Earth Environmental Sciences, Pukyong National University, Busan, 48513, Republic of Korea
3Department of Energy Resources Engineering, Pukyong National University, Busan, 48513, Republic of Korea

Correspondence to : heelee@pknu.ac.kr

Received: August 9, 2017; Accepted: August 30, 2017

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided original work is properly cited.

Abstract

Batch experiments were performed to develop the method for the pH reduction of recycled aggregate by using scCO2 (supercritical CO2), maintaining the pH of extraction water below 9.8. Three different aggregate types from a domestic company were used for the scCO2-water-recycled aggregate reaction to investigate the low pH maintenance of aggregate during the reaction. Thirty five gram of recycled aggregate sample was mixed with 70 mL of distilled water in a Teflon beaker, which was fixed in a high pressurized stainless steel cell (150 mL of capacity). The inside of the cell was pressurized to 100 bar and each cell was located in an oven at 50 ℃ for 50 days and the pH and ion concentrations of water in the cell were measured at a different reaction time interval. The XRD and SEM-EDS analyses for the aggregate before and after the reaction were performed to identify the mineralogical change during the reaction. The extraction experiment for the aggregate was also conducted to investigate the pH change of extracted water by the scCO2 treatment. The pH of the recycled aggregate without the scCO2 treatment maintained over 12, but its pH dramatically decreased to below 7 after 1 hour reaction and maintained below 8 for 50 day reaction. Concentration of Ca2+, Si4+, Mg2+ and Na+ increased in water due to the scCO2-water-recycled aggregate reaction and lots of secondary precipitates such as calcite, amorphous silicate, and hydroxide minerals were found by XRD and SEM-EDS analyses. The pH of extracted water from the recycled aggregates without the scCO2 treatment maintained over 12, but the pH of extracted water with the scCO2 treatment kept below 9 of pH for both of 50 day and 1 day treatment, suggesting that the recycled aggregate with the scCO2 treatment can be reused in real construction sites.

Keywords recycled aggregate, scCO2, waste concrete, cement, waste recycling, CO2 reduction, pH neutralization

초임계이산화탄소를 이용한 폐콘크리트 순환골재의 중성화

정철우1 ·이민희2* ·김선옥3 ·김지현1

1부경대학교 건축공학과, 2부경대학교 지구환경과학과, 3부경대학교 에너지자원공학과

요 약

Article

Original Article

Econ. Environ. Geol. 2017; 50(4): 257-266

Published online August 31, 2017 https://doi.org/10.9719/EEG.2017.50.4.257

Copyright © THE KOREAN SOCIETY OF ECONOMIC AND ENVIRONMENTAL GEOLOGY.

The pH Reduction of the Recycled Aggregate Originated from the Waste Concrete by the scCO2 Treatment

Chul-woo Chung1, Minhee Lee2*, Seon-ok Kim3 and Jihyun Kim1

1Department of Architectural Engineering, Pukyong National University, Busan, 48513, Republic of Korea
2Department of Earth Environmental Sciences, Pukyong National University, Busan, 48513, Republic of Korea
3Department of Energy Resources Engineering, Pukyong National University, Busan, 48513, Republic of Korea

Correspondence to:heelee@pknu.ac.kr

Received: August 9, 2017; Accepted: August 30, 2017

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided original work is properly cited.

Abstract

Batch experiments were performed to develop the method for the pH reduction of recycled aggregate by using scCO2 (supercritical CO2), maintaining the pH of extraction water below 9.8. Three different aggregate types from a domestic company were used for the scCO2-water-recycled aggregate reaction to investigate the low pH maintenance of aggregate during the reaction. Thirty five gram of recycled aggregate sample was mixed with 70 mL of distilled water in a Teflon beaker, which was fixed in a high pressurized stainless steel cell (150 mL of capacity). The inside of the cell was pressurized to 100 bar and each cell was located in an oven at 50 ℃ for 50 days and the pH and ion concentrations of water in the cell were measured at a different reaction time interval. The XRD and SEM-EDS analyses for the aggregate before and after the reaction were performed to identify the mineralogical change during the reaction. The extraction experiment for the aggregate was also conducted to investigate the pH change of extracted water by the scCO2 treatment. The pH of the recycled aggregate without the scCO2 treatment maintained over 12, but its pH dramatically decreased to below 7 after 1 hour reaction and maintained below 8 for 50 day reaction. Concentration of Ca2+, Si4+, Mg2+ and Na+ increased in water due to the scCO2-water-recycled aggregate reaction and lots of secondary precipitates such as calcite, amorphous silicate, and hydroxide minerals were found by XRD and SEM-EDS analyses. The pH of extracted water from the recycled aggregates without the scCO2 treatment maintained over 12, but the pH of extracted water with the scCO2 treatment kept below 9 of pH for both of 50 day and 1 day treatment, suggesting that the recycled aggregate with the scCO2 treatment can be reused in real construction sites.

Keywords recycled aggregate, scCO2, waste concrete, cement, waste recycling, CO2 reduction, pH neutralization

초임계이산화탄소를 이용한 폐콘크리트 순환골재의 중성화

정철우1 ·이민희2* ·김선옥3 ·김지현1

1부경대학교 건축공학과, 2부경대학교 지구환경과학과, 3부경대학교 에너지자원공학과

Received: August 9, 2017; Accepted: August 30, 2017

요 약

    KSEEG
    Apr 30, 2024 Vol.57 No.2, pp. 107~280

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