Precast concrete produced in the industry is advantageous in a sense that it meets certain requiring standards and thus is easy to manage, and it saves construction period by shortening concrete curing time in the field. Nevertheless, studies on the strength evaluation of PC material by steam curing have rarely been done. In addition，as concrete becomes of high strength, it is speculated that relevant steam curing temperature history is also required. Therefore this study is on the steam curing method in manufacturing precast concrete products, and cement mortar has been used for experiments to exclude the possibility that concrete aggregate granularity and aggregate shape change may affect on strength development by cement hydration. In addition, this research is to provide the fundamental information of industrial manufacture of PC member by suggesting the optimal steam curing condition. The optimal steam curing condition has been investigated from the relations between temperature history condition and strength development, via modifying temperature patterns in various ways such as pre-tirne, curing maximaI temperature, maximaI temperature maintenance time which are factors that affect on high strength concrete product in steam curing.

Concrete is most widely used construction material in the world. Its superior properties make it a suitable material for utilization. Modern age concretes are more durable and have high strengths as compared to old age concretes. However, these high strength concretes presents high shrinkage at early-ages, which is due to low water/binder (w/b) ratios. Keeping in view this problem, this research study is conducted. Mortars were made with cement and silica fume as binders with incorporation of two different size ranges of tea waste particles. Setting time, flow and chemical shrinkage of fresh mortars were investigated. The results showed that the addition of saturated tea waste particles reduced the chemical shrinkage at early ages as compared to the mixes without tea waste particles.

본 연구에서는 선별파쇄 골재 등 부순 골재에 포함된 토분함유량 규정치를 정하는 연구의 일환으로써 골재 토분이 모르타르의 기초적 특성에 미치는 영향을 분석하였다. 토분함유량이 증가할수록 유동성과 휨강도는 감소하고, 공기량은 증가하며 압축강도는 1 % 전후에서 증가하는 경향도 나타났으나 전반적으로 감소하였다.

In this research, in order to improvement the performance of the two-component mixed aggregate mixed with fine granite fine aggregate and seawater, the examination of the effect of reject ash on the cement mortar according to the change of substitution rate was done. As a result, it was found that the effect of improving the compressive strength is more effective when the rejection ash is replaced by 5% in the mixed aggregate than in the case of using the high quality aggregate.

In this study, hydration heat, autogenous shrinkage and compressive strength of the specimens has been verified with moisture supply on the hardened cement paste depending upon the difference in moisture condition of the fine aggregates. The result showed that, autogenous shrinkage was significantly reduced and also the compressive strength was improved due to the continuous moisture supply regarding on fine aggregates.

In this research, in order to improvement the performance of the two-component mixed aggregate mixed with fine granite fine aggregate and seawater, the examination of the effect of reject ash on the cement mortar according to the change of substitution rate was done. As a result, it was found that the effect of improving the compressive strength is more effective when the rejection ash is replaced by 5% in the mixed aggregate than in the case of using the high quality aggregate.

In construction sites there are many cases that concrete is cured in a dry condition, without being moistured, after form have been removed. Consequently such curing condition causes cracks on concrete. In this study is to observe when applied ERCO(Emulsified Refined Cooking Oil) coating on concrete surfaces after removal of form, affects water evaporation and Shrinkage of high-strength mortar.

In this study, experimental research was carried out to study the high strength RC exterior beam-column joints regions, without the shear reinforcement, using high ductile fiber-reinforced mortar. Test results showed that specimen BCJNSP1.0 were increased th maximum load-carrying capacity and showed stable hysteresis behavior and satisfactory crack pattern in comparison with th specimen BCJNS without shear reinforcement in the beam-column joint region.

In this study, experimental research was carried out to study the high strength RC exterior beam-column joints regions, without the shear reinforcement, using high ductile fiber-reinforced mortar. Specimens designed by retrofitting the exterior beam-column joint regions of existing reinforced concrete building showed a stable mode of failure and an increase in shear strength capacity due to the effect of enhancing dispersion of crack control at the time of initial loading and bridging of fiber from retrofitting new high ductile materials during testing.

본 논문에서는 반복하중이 작용하는 고강도 모르타르 충전식 슬리브 철근이음의 강성에 대한 합리적인 검토를 하기 위하여 100여개 고강도 모르타르 충전식 슬리브 철근이음의 실험데이터를 이용하여 슬리브 철근이음이 보유하고 있는 구조인자가 반복 하중이 작용하는 슬리브 철근이음의 강성에 미치는 효과를 파악하였고, AIJ 규준에 정해져 있는 강성 등급을 충족시키는 최소한 의 조건에 대하여 평가한 결과, SD350과 SD400 철근을 매입한 모르타르 충전식 주물 슬리브 철근이음에서 fg*(L/d)가 470MPa 이상이 된다면 AIJ 규준의 SA급 강성, fg*(L/d)가 340MPa 이상이 된다면 AIJ 규준의 A급 강성을 최종파괴형식과 슬리브 형상에 상관없이 확보할 수 있는 것으로 나타났다. 또한 SD500 철근을 매입한 모르타르 충전식 슬리브 철근이음에서 주물슬리브와 강관 슬리브를 사용한 경우는 fg*(L/d)가 400MPa 이상이 된다면 AIJ 규준의 A급 강성을 확보할 수 있는 것으로 나타났다.

본 연구에서는 고강도 모르타르 충전식 기계적 슬리브 철근이음에 대한 단조가력 하에서의 강성을 보다 적절하게 평가하기 위하여, 슬리브 철근이음의 주요한 구조요소가 미치는 단조가력 하에서의 철근이음 강성에 대한 영향을 검토하였고 AIJ 규준에서 설정한 단조가력 하에서의 슬리브 철근이음에 대한 강성 기준과 비교평가하였다. 이것을 위하여 단조가력을 실시한 국내외 189여개 고강도 모르타르 충전식 기계적 슬리브 철근이음의 실험데이터를 조사하고 그 실험결과를 분석하였다. 그 결과, AIJ 규준에서 규정하는 목표 강성을 확보하는데 필요한 fg(L/d)의 한계값을 철근의 종류와 슬리브의 종류에 따라서 각각 제시하였다.

본 연구에서는 보다 자유로운 형상의 슬리브를 만들 수 있는 구상흑연 주철을 이용하여 보다 효과적으로 구조성능을 발휘하면서 SD500 고강도 철근에 적합하게 개발된 모르타르 충전식 슬리브 철근이음을 대상으로 실물크기의 19개 실험체를 제작하여 반복가력실험을 실시하였다. 그리고 강도, 강성, 슬립을 중심으로 한 구조성능에 대하여 본 실험의 주요한 변수에 따르는 영향을 분석하고, 국내기준을 비롯한 주요기준의 요구 성능과 비교하였다. 본 연구결과에서는 SD500 고강도 철근용으로 개발한 모르타르 충전식 슬리브 철근이음은 반복하중이 작용하는 경우에 대하여 국내기준을 비롯한 주요기준에서 요구하는 구조성능을 보유하고 있는 것이 확인되었고, SD500 고강도 철근용 모르타르 충전식 슬리브 철근이음에 대한 구조설계 기준 정립에 필요한 정량적인 기술 데이터를 제시하였다.