Mineral phase profiling on accelerated carbonation cured cement paste

Abstract

산업에서의가스배출문제는지난수십년간많은환경문제를야기하였다. 이에대한해결방법의하나로최근공장배출가스를산업에재활용하기위한 많은연구가진행되고있으며콘크리트의탄산화양생도그중하나이다. 본연 구에서는 CO2 가스를콘크리트양생용기체로활용하는연구를수행하였으며, 이는환경적기여는물론구조물의성능확보에도이익이될수있다. 실험을 통해가속탄산화양생이후기및조기시멘트페이스트의내부물질의변화에 미치는영향을알아보기위해광물계상(mineral phase)에대한프로파일링을수 행하였다. 이때정량적 X선회절(QXRD) 및열중량분석(TGA)을사용하였다. 가속탄산화처리된후기및조기시멘트페이스트의광물상프로파일링, 즉 깊이별물질분석은다음과같은방법으로진행되었다. 후기탄산화의경우수화 14일또는 28일후추가로 14일또는 28일간 10% 농도의 CO2 조건에노출하 였다. 조기탄산화의경우배합직후 6시간, 1일또는 3일의수화후 1일또는 3 일간탄산화하였으며, 이때 4 단계의 CO2 가스농도(5%, 10%, 15% 및 20%)를 사용하였다. 조기탄산화된페이스트의기계적특성, 즉압축강도및동탄성계수 뿐아니라, 추가재탄산화깊이를측정해이후가속탄산화양생된콘크리트의 자연탄산화저항성을평가하였다. 실험결과, 사전일반양생기간은깊이에따른탄산칼슘결정의종류와형 성량에큰영향을미치는것으로확인하였다. 먼저, 탄산화양생전의일반양생 기간은표면의탄산칼슘발생량을결정한다. 그러나일정깊이이상의탄산칼슘 발생량은탄산화지속시간의영향을덜받는다. 전반적으로가속탄산화에의한 탄산화깊이는, 페놀프탈레인수용액을이용해확인한바 12-20mm 수준이다. 이 결과는탄산칼슘의발생량과연동되었다. 탄산칼슘의생성량은탄산화표면에서 페이스트의총부피의 40-50%까지도달하였다. 표면의포틀란다이트양은두 조기및후기탄산화조건모두에서감소하였다. 한편, 조기탄산화시, 탄산화가 완료된후에도수화로인해포틀란다이트의양이추가로발생하였다. 시간에따른물리적강도발현은탄산화조건에따른단순한선형변화가 아니었다. 이것은탄산화와동시에발생한건조로인한것으로판단되는데, 극초 기탄산화시수화를위한물이부족했기때문으로예상된다. 따라서탄산화와 동시에수분공급이된다면물리적성능개선에더효과적일것으로판단된다.|Industry gas emission being an issue for many decades. Nowadays, much research has been conducted to utilize the factory’s gas, and concrete carbonation curing is one of them. This paper conducted research to utilize CO2 gas as a concrete curing agent, which will have mutual benefit for the structures as well as environmental contribution. The effect of the accelerated carbonation curing on the phase formation of the later age and early age cement paste was conducted via phase profiling. The study was conducted using quantitative x-ray diffraction (QXRD) and thermogravimetric analysis (TGA). Mineral phase profiling of the later age and early age cement paste, subjected to accelerated carbonation; was conducted through the depth. The later age carbonation was conducted at 14 or 28 days followed by 14 or 28 days of carbonation, with a concentration of 10% CO2. The early age carbonation was conducted at 6hr, 1day or 3 days of hydration followed by 1 day or 3 days of carbonation, four CO2 gas concentrations (5%, 10%, 15% and 20%) were used. In addition, the mechanical (compressive and dynamic modulus) and further carbonation resistance of the early age carbonated was investigated. The pre-curing period has a significant effect on the formation of type and amount of calcite on the front surface and through the depth. The pre-curing period determines the concentration of the calcite on the surface. However, the calcite formation on the front surface of specimens is less influenced by the duration of the carbonation. On the other hand, the duration of the carbonation influences the formed calcite through the depth. Overall, the depth of the carbonation in the accelerated carbonation is reached 20 mm in the later age, and 12 mm at the early age. Whereas 3 days and 28 days pre-cured resulted in an approximately similar amount of calcite and vaterite on the surface, which is the maximum total amount of CaCO3 reached up to 40% of the total volume of the paste. The amount of portlandite on the surface is diminished for both conditions. Whereas through the depth, early age carbonated has a relatively greater amount of portlandite which could be due to the hydration after the carbonation was completed. The mechanical strength does not have increasing consistency as usual throughout the time. This possibly from the dehydration ultimately resulted in a lack of water for anhydrous hydration, basically for lower water to cement ratio. If there is additional further water curing after the carbonation, there will be an improvement.