The degree of hydration and mechanical properties of high volume fly ash cement

최근, 전세계적으로 온실 가스의 저감에 관심이 높아지면서 건설 산업에서도 FA를 대량 치환하는 HVFAC의 사용을 위한 연구가 수행되고 있다. 시멘트의 수화도와 FA 반응도의 정량적인 측정은 HVFAC의 강도발현 메커니즘을 명확히 이해할 수 있게 한다. FA가 포함된 시멘트 페이스트의 수화 및 포졸란 반응은 매우 복잡하고 수화 생성물의 조성을 정확하게 결정할 수 없으므로 간단한 방법으로 반응도를 설명하는 것은 매우 어렵다. 따라서, 이 연구는 재령에 따른 하이볼륨 FA 시멘트의 수화 특성을 조사하였다. 시멘트의 수화도와 FA의 반응도는 재령에 따른 선택용해법과 페이스트의 비증발 수량을 통해 평가하였다. 또한 HVFA 모르타르 시편을 이용하여 연령에 따른 압축강도를 측정하였다. 실험결과 FA의 치환율이 증가할수록 시멘트의 수화도는 증가하나 FA의 반응성은 감소하는 것으로 나타났다. Recently, there has been a growing interest in reducing greenhouse gases in all industrial fields. In the construction industry, studies have been conducted for the use of high-volume fly ash concrete to replace cement with fly ash. Quantitative measurements of cement hydration and fly ash reactivity enable a clear understanding of the strength development mechanism of high-volume fly ash concrete. It is very difficult to describe the reactivity in a simple way because the hydration and pozzolanic reactions of cement paste containing fly ash are very complex and the composition of the hydration product cannot be accurately determined. This study investigated the hydration and mechanical properties of high volume fly ash (HVFA) cement according to the substitution rate of fly ash (FA). The hydration degree of cement and the reactivity of FA were evaluated through the selective dissolution method and the non-evaporable water content of the paste according to age. In addition, compressive strength was measured using HVFA mortar specimens according to age. As a result of the experiment, as the substitution rate of fly ash increased, the hydration degree of cement increased, but the reactivity of FA decreased

Reductive removal of triclosan by Sn-bearing materials and cathode powder recovered from spent Liion batteries

Tin (Sn)-bearing materials, tin oxide (SnO) and elemental tin (Sn(0)), and cathode powder recovered from spent Liion batteries were examined as reductants to transform triclosan, a common antibiotic through batch experiments. The reductive removal of triclosan was rapidly observed within 1 h under the given conditions, however, the formation of a passivation layer, mainly composed of SnO2. Tin dioxide inhibited the reduction reactions on the surfaces of SnO and Sn(0). In contrast, dissolved Sn2+, formed by the addition of SnCl2, could rapidly reduce triclosan within 5 h, resulting in over 95% removal. The results supported the notion that the inhibition of Sn2+formation by SnO2 on the surface acted as a ratelimiting step in the reductive removal of triclosan by Sn(0) and SnO. Conversely, the removal of triclosan by cathode powder was due to sorption and reduction, and its efficacy was limited by increased pH. A synergistic combination of Snbearing materials and cathode powder significantly improved the reduction of triclosan. Our findings suggest that the application of cathode Sn(0)/SnO/cathode powder with SnCl2 holds promise as an effective approach for the reductive transformation of triclosan in engineered systems

Hydration and Mechanical Properties of High-volume Fly Ash Concrete with Nano-silica

최근 탄소중립에 관한 관심이 높아지면서 건설 산업에서 하이볼륨 플라이애시 콘크리트를 사용하는 연구가 다양하게 수행되고 있다. 하지만 HVFC는 초기 압축강도가 낮은 단점이 있어, 이를 개선하기 위해 나노 소재를 활용한 연구에 대한 관심이 높아지고 있다. 나노 실리카는 포졸란 재료로서 이러한 조기 강도 지연을 보완할 것으로 기대된다. 따라서 본 연구에서는 나노 실리카를 HVFC에 혼입하여 초기 수화반응에 미치는 영향과 이에 따른 미세구조의 개선에 대해 조사하였다. 초기 수화반응은 응결실험과 미소수화열을 통해 분석하였고, 재령에 따른압축강도와 열중량 분석을 진행하였다. 미세구조 개선의 효과는 수은압입법을 통해 평가하였다. 실험결과 나노실리카를 혼입하였을 때, 초기강도가 증가하였고 미세구조가 개선되는 것으로 나타났다. Recently, as carbon neutrality has been important factor in the construction industry, many studies have been conducted on the high-volumefly ash concrete. High volume fly ash concrete(HVFC) is usually made by replacing more than 50% of cement with fly ash. However, HVFC has adisadvantage of low compressive strength in early age. To overcome this shortcoming of HVFC, improve this, interest in techonolgy using nanomaterialsis increasing. Nano silica is expected to improve the early age strength of HVFC as a pozzolanic material. This study investigated the effect of nanosilica on the early hydration reaction and microstructure of HVFC. The early hydration reaction of HFVC was analyzed through setting time, isothermalcalorimeter, compressive strength and thermal weight analysis. In addition, the microstructure of HVFC was measured by mercury intrusionporosimetry. From the test results, it was confirmed that nano silica increased the early age strength and improve the microstructure of HVFC

Effect of Carbonation Curing on the Hydration Properties of Circulating Fluidized Bed Boiler Ash

본 연구에서는 유리석회 함량이 다른 순환유동층 보일러 애시의 수화특성 및 탄산화 특성에 대해 조사하였다. 또한, free-CaO 함량이 높은 CFBC ash를 탄산화 양생 전처리를 하여 시멘트계 재료로의 활용 가능성을 살펴보았다. Free-CaO 함량이높은 CFBC ash를 혼합한 경우 급결의 양상을 보였으며 낮은 초기 압축강도를 나타냈다. Free-CaO 함량이 높은 CFBC ash를 탄산화 양생하였을 때, 양생 기간에 따라 이산화탄소 포집량이 증가하였다. 또한, free-CaO 값이 함께 감소하였으며free-CaO가 이산화탄소와 반응한 것으로 보인다. Free-CaO 함량이 높은 CFBC ash를 탄산화 양생 전처리를 한 경우 급결이나타나지 않았으며, 초기 압축강도도 향상된 것을 확인할 수 있었다. 연구 결과 free-CaO 함량이 높은 CFBC ash의 경우적절한 탄산화 양생을 통해 시멘트계 재료로 활용 가능성이 높은 것으로 나타났다. In this study, the hydration and carbonation properties of circulating fluidized bed boiler (CFBC)ash with different free-CaO contents were i nvestiga ted. I n addition, the possibility of utilizing C FBC ash with a h igh free-Ca O content a s a c ementitious ma teria l was investigated by carbonation curing as a pretreatment. The CFBC ash with high free-CaO content exhibited rapid setting behavior and low early compressive strength when mixed with cement. For CFBC ash with high free-CaO content, carbon dioxide capture increased with the duration of carbonization curing. In addition, the free-CaO value decreased together, indicating that the free-CaO reacted with carbon dioxide. When the CFBC ash with high free-CaO content was pretreated by carbonation, no fresh set appeared, and the initial compressive strength was improved. From the results of this study, it is confirmed that CFBC ash with high free-CaO content has a high potential to be utilized as a cementitious material through proper carbonation curing