Autogenous Shrinkage Behavior Research Articles

Autogenous shrinkage of high performance concrete containing mineral admixtures under different curing temperatures

The present study investigated experimentally autogenous shrinkage behaviors of high performance concrete (HPC) containing fly ash (FA) and blast-furnace slag (BS) exposed to different isothermal temperatures. The deformation of concrete specimen after initial setting was determined using a modified method which is based on non-contact measurement technique. The results indicated that the method can precisely monitor non-load induced deformations of HPC mixtures. The inclusions of BS and FA resulted in significant increase and decrease of autogenous shrinkage of HPC, respectively. While both the rate and the magnitude of autogenous shrinkage for almost all mixtures were increased with rise of curing temperature, extents of the influence were varied with water–binder ratio, composition of cementitious materials and age. It is noted that although the equivalent age equation was widely applied to evaluate temperature dependence of mechanical properties of cement-based materials, its applicability on autogenous shrinkage of HPC was questionable. In addition, on a trial and error basis, a modified autogenous shrinkage equation was performed in terms of numerical fitting of the measured data.

Temperature dependence of autogenous shrinkage of silica fume cement pastes with a very low water–binder ratio

Ultra-high-strength concrete with a large unit cement content undergoes considerable temperature increase inside members due to hydration heat, leading to a higher risk of internal cracking. Hence, the temperature dependence of autogenous shrinkage of cement pastes made with silica fume premixed cement with a water–binder ratio of 0.15 was studied extensively. Development of autogenous shrinkage showed different behaviors before and after the inflection point, and dependence on the temperature after mixing and subsequent temperature histories. The difference in autogenous shrinkage behavior poses problems for winter construction because autogenous shrinkage may increase with decrease in temperature after mixing before the inflection point and with increase in temperature inside concrete members with large cross sections.

A PROPOSAL OF PREDICTION MODEL FOR AUTOGENOUS SHRINKAGE OF ULTRA HIGH-STRENGTH CONCRETE

In this paper, a prediction model for autogenous shrinkage of ultra high-strength concrete which include silica fume was proposed by using mixture rule and autogenous shrinkage behavior of cement paste with low water-to-binder ratio. The proposed autogenous shrinkage model consists of two parts with regard to the rate of autogenous shrinkage. Characteristic autogenous shrinkage of ultra high-strength concrete which is rapid autogenous shrinkage up to about 1 day, is expressed by a function of water-to-binder ratio and temperature of fresh concrete. And reaction activity of silica fume in high temperature is expressed by apparent activation energy. The proposed model is evaluated by a comparison with previous data, and it has about accuracy of 30%.

EVALUATION OF CRACKING POTENTIAL OF HIGH-STRENGTH CONCRETE BASED ON MIX DESIGN AND REAL ENVIRONMENTAL CONDITIONS

High-strength concrete using various types of cement, considering mix design and real environmental conditions, was studied on the cracking potential. As a result, behavior of autogenous shrinkage in portland cement concrete showed a change from shrinkage to expansion at the temperature peak under temperature-history cure, but it remained in shrinkage in the blast furnace slag cement concrete. The cracking potential in concrete subject to temperature-history cure was higher than that in concrete under other conventional cure, and stress strength ratio was independent of cure condition. An estimation method for the age of cracking was shown by evaluating strain of reinforcing bar on tensile loading.

고로슬래그를 함유한 콘크리트의 자기수축 특성

초록 · 키워드 목차 오류제보하기 등록된 정보가 없습니다. ABSTRACT1. 서론2. 실험 연구3. 실험결과 및 분석4. 자기수축 예측 모델5. 결론참고문헌요약

Effects of microstructure on restrained autogenous shrinkage behavior in high strength concretes at early ages

Fluorescence microscopic examinations were conducted to identify damages induced by restraining autogenous shrinkage. Characteristics of fluorescent areas and their correspondence to autogeneous shrinkage behavior of high strength concretes were discussed. Silica fume concrete exhibited a greater creep potential when loaded at very early ages. The microstructure in sealed concretes with an extremely low water/binder ratio was porous. The vicinity of aggregate grains was more porous and weaker than the bulk matrix in sealed concretes. In addition, sealed silica fume concretes contained many unhydrated cement particles which were profiled by thin gaps between the core cement particles and the surrounding cement paste matrix. These features of microstructure were not observed in water ponded concretes. The detected fluorescent areas may be defects caused by selfdesiccation and autogenous shrinkage. The flaws had little effects on the development of strength. However, the presence of thin gaps around remnant cement particles may increase creep deformation to relieve internal stresses.

Effects of microstructure on restrained autogenous shrinkage behavior in high strength concretes at early ages

Effects of microstructure on restrained autogenous shrinkage behavior in high strength concretes at early ages