재생골재를 사용한 철근콘크리트 보의 구조적 특성에 관한 연구

Abstract

This study identified materials and structural characteristics of the reclaimed aggregates affecting reinforced concrete through material tests and supplementary tests such as compressive strength test, splitting tensile strength test, fire resistance test, bending test and shear test according to types of materials and mixing rates(0%, 30%, and 60%) to use broken red bricks and waste concrete as substitute concrete and obtained the following results: 1) When compressive strengths were compared according to mixing rates, RCA and RBA specimens with 30% mixing rate showed similar strength to no-mixing specimen. When no-mixing specimen was compared with the specimen with 60% of mixing rate, RBA 60% specimen showed the strength within the range of 8.5% -14.4% according to different days of age and RCA 60% specimen showed the strength within the range of 15.5%-17.6%. It indicates that when more than 60% of the reclaimed aggregate was mixed, granularity of aggregate was not good, which caused more gaps between aggregates. 2) For the manifestation ratio of the compressive strength, RBA specimen showed 87%-93% of the design standard strength at the 14th day of age while RCA specimen showed the strength within the range of 84%-92% at the 7th day of age. 3) As a result of the splitting tensile strength test, this study found that like the compressive strength, 30% mixing specimen showed almost same tensile strength as no-mixing specimen. For manifestation rates of splitting tensile strength according to different days of age, RBA specimen showed 87%-89% of the strength manifested at the 28th day of age at the 14th day of age, and RCA specimen showed the highest strength at the 7th day of age, 70%-89% of the strength manifested at the 28th day of age. For the ratio of compressive strength to tensile strength. concrete with reclaimed aggregates showed tensile strength within the range of 1/7-1.13 of compressive strength of normal concrete. 4) As a result of measuring compressive strength and neutralization after heating, it was found that as more reclaimed aggregates are mixed and heated in higher temperature, compressive strength decreased. It indicates that the reclaimed aggregates were burned by heat and their adhesion and combination force were lost. 5) As a result of the bending test of reinforced concrete beams, it was found that ductile coefficient of the RBA 30 specimen was 7.5% lower and the ductile coefficient of RBA 60% specimen was 10.9% lower compared to that of the no-mixing specimen. 6) As a result of the shear test of reinforced concrete beam, it was found that the initial crack strength, yield strength, and maximum strength of the specimen with reclaimed aggregates showed similar behaviors compared with those of normal concrete. For ductile coefficient of the shear test of the concrete with reclaimed aggregates, that of RBA 30% specimen was 37.1% lower, that of RBA 60% specimen was 43.4% lower, and those of RCA 30% and 60% specimens were 46.75 lower than that of no-mixing specimen. 7) To sum up the results of the material tests and supplementary tests, when 60% of broken red bricks and waste concrete were mixed and used, the mixed concrete had almost the same compressive strength, tensile strength, bending behaviors, and shear behaviors as normal rubble concrete. So it was concluded that concrete mixed with broken red bricks and waster concrete can be applicable for actual structures of reinforced concrete beams. And this study suggests that further studies on mixing and application of mixed materials which can improve ductile coefficients are needed.