혼화재 및 섬유 사용 콘크리트의 비파괴 시험에 의한 강도 추정

Abstract

This study aims to estimate strength approximate to actual concrete strength by presenting appropriate non-destructive strength estimation expression with admixtures such as fly ash, blast furnace slag and silica fume which are used as cement substitute and polypropylene fiber and steel fiber and owing to their s of cement owing to their equal conditions to blending characteristics of concrete used for domestic structures and their recyclable properties. 1) As a result of destructive and non-destructive test, manifestation of strength over design standard strength was found at the 28 days of age and normal concrete strength was lowered after 60 days of age, but strength of concrete using admixtures and fiber showed increase after 90 days of age. In addition, it was found that PP fiber and S fiber had little influence on compressive strength and had influence on bending and tensile strength through existing studies and this study. 2) Concrete using admixtures showed lower trend in early compressive strength, ultrasound speed and repulsive hardness than normal concrete, but existing expressions were applied on the basis of result that as age is longer, it had higher result than normal concrete, it is considered that destructive and estimated strength showed much difference and it is judged that new estimation expression suitable to concrete using admixtures and fiber is needed. 3) In case of re-bound hammering, equation by Japanese Architecture Society was estimated 26～40% higher than destructive strength and remaining suggested equation was estimated 2%?18% lower. In case of ultrasound velocity, equation by Japanese Architecture Society was estimated 4%～11% higher than destructive strength till 60 days of age, but as age progresses, i is estimated to 15% lower than destructive strength and remaining suggested equation was estimated 3%～27% lower than destructive strength in almost age. In case of complex methods, all suggested equations were estimated to 24%～94% higher than destructive strength. 4) In case of comparing complex methods by multiple regressive analysis using single method, re-bound hammering and ultrasound velocity, there are a little differences by specimens, but it is considered that it shows 0.2%～11.0% of decisive coefficient compared to ultrasound velocity method and 0.2%～9.8% of decisive coefficient compared to re-bound hammering and complex method may estimate more accurate strength than single method. 5) As a result of comparing error rates between conventional suggested equations and this estimation equations, there are a little differences by age, but error rate of this study was reduced to 0.3%～15.5% compared to conventional equations by re-bound hammering, 0.6%～18.6% by ultrasound velocity method and 0.6%～34.2% by complex method and it is judged that it is desirable to be used for concrete using admixture and fiber 6) Since application of existing expression of normal concrete against concrete using admixtures and fiber causes error rate, this study suggests the following estimation expression depending on the kind of admixtures and fiber of concrete using them and position of non-destructive experiment.