Fundamental Properties of Fly ash Concrete Containing Lightly Burnt MgO Powder

Abstract

Although the lightly burnt MgO at 850~1000℃ has expansibility, it does not lead to unsound concrete. The expansion of MgO could compensate for shrinkage of concrete for a long-term, because the hydration of MgO occurs at a slow pace. Recently, the study and application of mineral admixture such as fly ash and blast furnace slag have increased for the hydration heat reduction, durability improvement, and reducing CO2 emission in the construction industry. Thus, it is necessary to research on the concrete that contains both a mineral admixture and MgO as an expansion agent. This study investigates fundamental properties of fly ash concrete with lightly burnt MgO through various experiments. The adiabatic temperature test results showed that the fly ash concrete with MgO of the 5% replacement ratio had the slower pace of the temperature rise and the lower final temperature than the fly ash concrete. The influences of MgO on long-term compressive strength varied depending on water-binder ratio, and the long-term length change test results indicated the expansion effects of the FA concrete containing MgO. 초 록 850~ 1000℃ 정도의 저온에서 소성된 MgO 분말을 적정량 치환한 콘크리트는 장기팽창성을 갖는다. 이러한 팽창성은 저온소성한 MgO 분말 의 느린 수화반응을 통해 이루어지기 때문에 장기재령까지 수축을 보상하는 특성을 가진다. 최근 수화열 저감, 내구성 향상 등의 이유와 함께 건 설 산업의 탄소저감을 위한 방안으로 플라이애시 및 고로슬래그 등과 같은 혼화재의 사용이 증가하고 있다. 따라서 저온소성한 MgO 분말을 팽 창재로 사용하기 위해서는 이러한 혼화재와 MgO 분말을 함께 사용한 콘크리트의 특성 규명이 필요하다. 이 연구에서는 플라이애시 콘크리트 에 저온소성한 MgO 분말을 치환한 콘크리트의 슬럼프, 공기량, 수화열뿐만 아니라 장기재령 압축강도 및 길이변화 등의 기본 물성을 실험을 통 해 조사하였다. 단열온도 상승시험 결과, 5% 수준으로 MgO 분말을 치환한 콘크리트의 단열온도상승속도 및 최종온도가 플라이애시 콘크리트 보다 다소 작게 나타났다. 또한 압축 강도 실험결과 물-결합재비에 따라 저온소성한 MgO 분말이 장기재령 압축강도에 미치는 영향이 다르게 나 타났으며, 장기적인 길이변화 실험 결과 저온소성한 MgO 분말을 치환한 콘크리트에서 큰 팽창효과를 확인할 수 있었다.

Self-healing cementitious composites incorporating innovative materials

“…Therefore, for validation of this concept, it was expected that more hydration products of MgO to be found within the crack walls of proposed self-healing ECC-MgO system. (Choi et al, 2013). Although the TGA/DSC analysis was conducted on ECC-MgO samples at later age (450 days), the degradation peaks of Mg(OH)2 shown in Figure 7-15 (C and D) were relatively small either in sample located in crack walls or within MgO cement paste and thereby these peaks might not be considered (marked by red stars in Figure 7-15).…”

Mitigating shrinkage in ultra-high performance concrete using MgO expansion agents with different activity levels

“…It can make concrete produce specific precompression stress characteristics during hardening, reduce volume shrinkage and improve crack resistance. At the same time, it can replace part of the cement and, more importantly, less water is consumed in the hydration reaction (Choi et al, 2013;Choi et al, 2014;Yang et al, 2021). Recently, researchers have found that MEA can compensate for the early shrinkage of UHPC (Li, 2012;Wang et al, 2022), and it has been applied in practical engineering (Li S. et al, 2020).…”

Influence of Lightly Burned MgO on the Mechanical Properties and Anticarbonization of Cement-Based Materials

“…In recent years, magnesia-based expansion agents have been used in water conservancy projects, showing good anticracking performance [15,16]. Compared with the expansion agents of calcium oxide and ettringite, the expansion agent of lightly burned magnesium oxide (LBMO) has the advantages of less water demand for hydration, a moderate expansion rate, a long expansion period, delayed microexpansion and a stable hydration product, which makes it more applicable for modern concrete [17][18][19].…”