Properties of Cement Paste Containing High Volume γ-C₂S and MgO Subjected to CO₂Curing

Abstract

Carbonation of concrete causes reduction of pH and subsequently causes steel corrosion for reinforced concrete structure. However, for plain concrete structure or PC product, it can lead to a decrease in porosity, high density, improvement of concrete, shrinkage-compensation. Recently, based on this theory, research of CO2 curing effect has been performed, but it was mainly focused on its effects on compressive strength using only ordinary portland cement. Researches on CO 2 curing effect for concrete containing CO 2 reactive materials such as γ-C 2 S, MgO haven't been investigated. Therefore, this study has performed experiments under water-binder ratio 40%, and the replacement ratios of γ -C2S and MgO were 90%. Micro-chemical analysis, measurement of compressive strength according to admixtures and CO 2 curing were investigated. Results from this study revealed that higher strength was measured in case of CO2 curing compared with none CO2 curing for plain specimen indicating difference between 1.08 and 1.26 times, in case of γ -C2S 90, MgO 90 specimen, incorporating high volume replaced as much as 90%, it was proven that when applying CO 2 curing, higher strength which has difference between 14.56 and 45.7 times, and between 6.5 and 10.37 times was measured for each specimen compared to none CO2 curing. Through micro-chemical analysis, massive amount of CaCO3, MgCO3 and decrease of porosity were appeared.

Enhancement of the Strength of MgO-Based Binder by Accelerated Carbonation

“…2 조건과 비교하여 약 3배정도 낮았다. 이는 CO 2 와의 반응으로 생성된 Ca 2+ 와 Mg 2+ 를 함유한 다량의 탄산염화 물에 의한 것으로 판단된다(Mo et al, 2010;Sung et al, 2015). 20% CO 2 조건에서 양생된 공시체들은 전반적으로 양 생기간이 길수록 강도가 증가하는 경향을 보였으며, 28일 에서 60일 사이에 가파른 증가율을 나타내었다.…”

“…이는 MgO의 느린 수화 반응에 의한 팽창현상이 긴 양생 기간에 따른 PC의 수축 현상을 상쇄시켜 P100보다 GGBS와 FA 내 SiO 2 , Al 2 O 3 와 같은 물질들과 수화반응 및 CO 2 와 탄산염화 반응을 한 것으로 보인다. 따라서 이 과정에서 생성되는 Mg 2+ 를 함유한 다량의 수화 및 탄산 염화물이 공시체의 팽창을 일으켜 공시체의 건전성을 유 지시키지 못한 것으로 판단된다(Mo et al, 2010;Hwang et al, 2013;Kim et al, 2014;Sung et al, 2015). 그 러므로 마그네슘계 고화제 내 MgO가 적정량 혼합되었을 때 산업부산물의 알칼리 활성화제로 작용하여 강도 증진 효과를 촉진시키지만(Maria and Suurenda, 2003; Kwon et al, 2013), 필요 이상으로 혼합될 경우 과도한 탄산염 화 물질을 생성하여 오히려 강도 저하를 일으킬 수도 있 다는 것을 확인 할 수 있었다(Jang et al, 2011; Kim and Jun, 2015).…”