Engineering Properties of the Concrete Using Reject Ash as Pre-mixed Fine Aggregate

리젝트애시를 잔골재로 프리믹스하여 활용하는 콘크리트의 공학적 특성

Abstract

The purpose of this study is to analyze the fundamental characteristics of concrete with the change of reject ash(Reject ash=Rj) in the mixed aggregate where single grain aggregate of different grain size and aggregate of opposite grain size are mixed together, to analyze the possibility of a mixed aggregate system that premixes at an aggregate manufacturing plant and delivers it as one aggregate. As a result of the experimental study, it was found that the grain size regulation is satisfied if the mixed aggregate(CSb+SS) is substituted for about 5% of Rj. In the case of the fluidity slump, slump flow and air volume, it was found that they decrease as the substitution ratio of Rj increases, while the compressive strength increases as the substitution ratio of Rj increases. Therefore, it is analyzed that it would contribute greatly to an improvement of quality such as improvement of compressive strength if adequate fluidity and air quantity are secured by the water reducing agent and AE agent while premixing the Rj, which is disposed of by landfill, with about 5% of the mixed aggregate.

본 연구는 서로 다른 입도의 단일골재 및 반대 입도의 골재를 혼합한 혼합골재에 리젝트애시(Reject ash=Rj)의 치환율 변화에 따른 콘크리트의 기초적 특성을 분석함으로써 골재 제조공장에서 프리믹스하여 1개의 골재로 납품하는 혼합골재 시스템의 가능성을 분석하였다. 실험연구결과 입도규정의 경우는 혼합골재(CSb+SS)에 Rj를 5% 정도 치환할 경우 입도규정을 만족하는 것으로 나타났다. 유동성인 슬럼프 및 슬럼프 플로와 공기량의 경우에는 Rj의 치환율 증가에 따라 감소하는 것으로 나타났으나, 압축강도의 경우에는 Rj의 치환율이 증가함에 따라 증가하는 것이 확인되었다. 따라서 매립 처분되는 Rj를 5% 정도 혼합골재에 프리믹스하여 활용하면서 감수제 및 AE제 등으로 적정 유동성 및 공기량은 확보하여 준다면 압축강도 증진 등 품질향상에 크게 기여할 것으로 분석되었다.

Photo 1. SEM of Rj

Fig. 1. Grading curve of aggregates

Fig. 2. Mixing sequence of concrete

Fig. 3. Grading curve depending on different types of mixedaggregate(CSb+SS)

Fig. 4. Grading curve depending on different types of mixedaggregate(CSb+SS+Rj)

Fig. 5. Slump with fine aggregate type and Rj replacement

Fig. 6. Slump flow with fine aggregate type and Rj replacement

Fig. 7. Air contents with fine aggregate type and Rj replacement

Fig. 8. Compressive strength with fine aggregate type and Rj replacement(3 days)

Fig. 9. Compressive strength with fine aggregate type and Rj replacement(7 days)

Fig. 10. Compressive strength with fine aggregate type and Rj replacement(28 days)

Table 1. Experimental plan

Table 2. Mixture proportions of concretes

Table 3. Physical properties of cement

Table 4. Physical properties of Rj

Table 5. Physical properties of aggregate

Table 6. Comparison of performance of concrete depending on Rj contents