혼화재 섬유 혼입 콘크리트 구조체의 비파괴시험에 의한 장기재령 강도추정

Abstract

본 연구는 혼화재 및 섬유를 사용한 콘크리트에 대해 코어 채취용 구조체를 제작, 파괴시험과 비파괴시험을 통하여 장기 재령에 대한 강도 추정식을 제안한 것으로 그 결론은 다음과 같다. 1) 파괴시험 및 비파괴시험 결과, 재령 28일에 설계기준강도 이상의 강도 발현을 보였으며 재령이 경과할수록 강도는 증가하였다. 또한, 섬유 콘크리트는 기존의 연구와 본 연구를 통해 압축강도의 영향은 미세한 것으로 나타났다. 2) 혼화재를 사용한 콘크리트는 초기강도의 발현은 낮게 나타났으나 재령이 경과할수록 장기재령에서 보통 콘크리트보다 높은 것으로 나타났다. 섬유를 혼입한 콘크리트의 초기강도는 보통 콘크리트와 유사한 경향을 보였으나, 재령이 경과할수록 보통 콘크리트보다 낮게 나타났다. 혼화재 및 섬유 사용 콘크리트에 기존 제안식을 적용할 경우 파괴강도와 추정강도는 많은 차이를 보일 것으로 사료되며, 혼화재를 사용한 콘크리트에 적절한 추정식이 필요할 것으로 판단된다. 3) 시험체별 추정강도가 파괴강도와 가장 일치하는 재령은, 혼화재 혼입 콘크리트의 경우 단기재령에서 재령 60～90일의 추정강도가 -8.4%～7.5% 정도로 가장 일치하였으며 재령이 경과할수록 -3.9%～16.9% 정도 일치를 보였다. 섬유 혼입 콘크리트의 경우 재령 730일의 추정강도가 약 -0.2%～4.9% 정도로 파괴강도와 가장 유사하게 나타났으며, 재령별 변화는 크지 않는 것으로 나타났다. 4) 반발경도 및 초음파속도 측정 결과를 기존 제안식에 적용하여 강도를 추정한 결과, 반발경도법의 경우 1%～63% 정도, 초음파속도법의 경우 1%～44% 정도 추정강도가 파괴강도와 차이를 보였으며, 기존 제안식 중 반발경도법은 일본재료학회식과 대우건설기술연구소식, U.S Army 시험소식이, 초음파속도법은 일본건축학회식과 J.Pysziak의 제안식, 한전기술연구소식이 파괴압축강도와 유사한 경향을 보였다. 5) 시험체별 파괴시험과 비파괴시험 실시 결과를 복합법에 의한 기존 제안식에 적용하여 강도를 추정해 본 결과, 일본건축학회식은 46%～148%, 谷川식은 127%～189%, 김무한식은 58%～148% 정도 파괴압축강도와 일치를 보였다. 모든 제안식이 추정강도가 파괴강도보다 높게 나와 현장에서 기존 제안식을 사용했을 경우 추정강도가 파괴강도보다 높게 평가될 것으로 사료된다. 6) 단일법과 반발경도와 초음파속도로 중회귀분석한 복합법을 비교했을 경우, 초음파속도법, 반발경도법, 복합법의 결정계수가 높게 나타나 단일법보다 복합법이 적합하며, 코어공시체를 상부와 하부로 구분한 시험체의 결정계수가 무 구분한 시험체보다 높게 나타나 구조체의 위치별로 추정식을 적용하는 것이 바람직할 것으로 사료된다. 7) 기존 제안식과 본 연구 추정식의 오차율을 비교한 결과, 재령별로 다소 차이는 있지만 반발경도법은 2.8%～7.5% 정도, 초음파속도법은 2.8%～11.7% 정도, 복합법은 7.2%～20.2% 정도로 기존의 제안식보다 본 연구의 추정식 오차율이 감소하여 혼화재 및 섬유를 사용한 콘크리트에 바람직할 것으로 판단된다. 8) 혼화재 및 섬유를 사용한 콘크리트에 대해 기존의 보통 콘크리트 제안식을 적용하면 오차율이 발생하므로, 본 연구에서는 혼화재와 섬유를 사용한 콘크리트 종류 및 비파괴시험 위치에 추정식을 제안한다.|This study manufactured core sampling structure for concrete using additive and fiber and suggested strength equation of long-term aging through destructive and non-destructive tests. The conclusions of this study are as follows. 1) As a result of destructive and non-destructive test, strength more than design standard strength on the 28th day of aging was revealed and as the aging developed, the strength also increased. Also, from the previous and the present studies, the influence of compressive strength on fiber concrete was weak. 2) Concrete using additives showed low revelation in early strength, but as aging developed, its strength was higher than that of normal concrete. The early strength of concrete adding fiber showed a similar trend to normal concrete, but as the aging developed, it was lower than normal concrete. In case of applying existing equation to concrete using additives and fiber, it was thought that there would be a lot of differences in destructive and estimated strengths and an appropriate equation for concrete using additives will be needed. 3) In the aging that estimated strength by specimens was identical with destructive strength, concrete using additives was most identical in -8.4%～7.5% of estimated strength in 60～90 days of aging in short-term aging and as the aging developed, it was identical in -3.9%～16.9%. In case of fiber added concrete, estimated strength in the 730 days of aging was -0.2%～4.9% and it was most similar to destructive strength and there was no great change by aging. 4) As a result of applying the measurement results of rebound hardness and ultrasound velocity to existing equation and estimating the strength, rebound hardness showed difference of 1%～63% between estimated and destructive strengths and ultrasound velocity showed that of 1%～44% between them, and the rebound hardness showed similar trend to the equations of Materials Research Society of Japan, Daewoo Architectural Institute and U.S Army Laboratory Institute. Ultrasound Velocity method was similar to the equations of Construction Research Society of Japan, J.Pysziak and Technological Research Institute of KEPCO in destructive and compressive strength. 5) As a result of applying the results of destructive and non-destructive test by species to existing equations by combined method and estimating the strength, the equation of Architectural Institute of Japan showed coincidence with destructive and compressive strength as 46%～148%, that of 谷川 coincided with destructive and compressive strength as 127%˜189% and that of Kim Mu Han was identical with destructive and compressive strength as 58%～148%. It was considered that estimated strengths of all equations were higher than destructive strength and then when existing equations are used in the field, estimated strength will be higher than destructive strength. 6) When combined methods having multiple regression analysis with rebound hardness and ultrasound velocity were compared to single method, coefficient of determination of ultrasound velocity method, rebound hardness method and combined method was higher and combined method was better than single method, and the coefficient of determination of specimen which core specimen was divided into upper and lower parts was higher than the specimen without division and it was considered that applying the equation by the position of structure would be desirable. 7) As a result of comparing error rates between existing equations and the equation of this study, there were some differences by aging, but rebound hardness method showed decrease of error rate of 2.8%～7.5% compared to existing equations, ultrasound velocity method showed that of 2.8%～11.7%, combined method also showed that of 7.2%～20.2%, and it was judged that it would be desirable for the concrete using additive and fiber. 8) As the equation of existing normal concrete was applied to the concrete using additive and fiber, error rate was great and this study suggested the estimation of types of concretes using additive and fiber and the location of non-destructive test.