International Concrete Abstracts Portal

The authors have proposed a partially pre-cooling system for massive structures, such as gravity concrete dams. It is discussed in this paper how the effectiveness of the proposed method is discussed using the finite element analysis. In the ordinary pre-cooling system, pre-cooled concrete is placed in the entire region (width and depth) of a massive structure. In the proposed system , pre-cooled concrete is placed only in the surface layer. In order to evaluate the effectiveness of this system, a thermal stress analysis was conducted by the finite element method. The key parameters were the dimensions of the cooling system and cooling temperatures. The results show that the proposed system is rather effective than the conventional cooling system in terms of the thermal stress condition of massive concrete structures. In addition, the cost benefit is adequately expected.

A study on application of recycled concrete for structural concrete was carried out under the concept of life cycle assessment (LCA) for environmental management of construction utilizing recycled products. Such products are often discarded, when existing electric power plants are rebuilt or upgraded in order to meet increasing power demands. In pursuing the reuse of these recycled materials, the basic policy was composed of three items: (1)the assurance of quality; (2)the reduction of environmental impact; and, (3)construction cost. The study is divided into two main parts: feasibility study on the reuse of recycled concrete and, experimental study on the quality of recycled aggregate and recycled aggregate concrete. This quality o Paper aper presents the result of the experimental study on the recycled aggregate and recycled aggregate concrete. Based on the investigation and the analysis of results, valuable data were obtained regarding concept and practice as to the reuse of construction debris based on LCA.

It is essential that concrete structures should withstand the conditions for which it has been designed for long periods of time. The lack of durability may be caused either by the environment to which the concrete is exposed or by the concrete itself. In this study, the resistance to freezing and thawing of high-slag content concrete(HSC concrete), which is one of the external causes, have been discussed for the purpose of utilizing the ground granulated blast furnace slag (GGBS) as an ingredient of cement. The slag content in cement ranged from 0 to 9.5 % by weight of total cementitious materials and the fineness of slag was 816 m*/kg. The resistance of air entrained (AE) concrete with a slag content of 70% was superior or comparable to that of slag free concrete, whereas AE concretes have questionable performance in the case of slag content of 85%, and have less ability in the case of 95% slag content with respect to freezing and thawing resistance. HSC concretes could have satisfactory high resistance to freezing and thawing by using an air-entraining high range water-reducing admixture(AEHW admixture), even if the slag content was 95%. Then, the concretes with AEHW admixture, which is called SP concrete, would be recommended for freezing and thawing conditions with respect to the use of HSC concrete.

Concrete creep and shrinkage strain obtained in constant temperature and constant humidity room are different from those observedinthe actual condition. Most of creep and shrinkage strain prediction equations predict the creep coefficient and shrinkage strain under the constant temperature and constant relative humidity. The effects oftemperaturehistory andrelativehumiditychange of atmosphere are not consideredinthese equations. In this study, the effect of the change of atmosphere condition on creep and shrinkage strain is discussed. It is shown that the concrete creep and shrinkage strain in actual ambient are influenced by casting season of concrete. Creep and shrinkage strain of concrete cast in winter aremuchbigger than those in summer. The significance to consider the effect of environmental change on concrete creep and shrinkage strain is emphasized in this paper.

The development and evaluation of chemical admixtures requires experimental verification of many admixture samples in the laboratory prior to testing the most promising formulations in concrete. Since quantities of new admixture formulations are usually limited, it is necessary to carry out small-scale tests on fresh cement pastes and mortars. The large number of test methods used by individual researchers makes it difficult to compare results from different laboratories. In an attempt to solve this comparability problem, an advanced methodology for testing of water-reducing admixtures has been developed and is discussed in this paper. This methodology is based on studying the properties of fresh cement-water systems, namely pastes and mortars, with or without the addition of a chemical admixture. It includes and modifies some traditional tests such as the Vicat test for cement pastes and the flow test for cement mortars plus some more recently developed tests such as the mini-slump test. It also includes some new test methods such as the torque test and the mini-flow test. The applicability of the new set of test methods was examined during the evaluation of lignosulphonates as water-reducing admixtures for concrete. The determination of rheological properties, air-entrainment and set-retardation was conducted on cement pastes and mortars. The values describing the plasticity/fluidity, air content, and time of setting were obtained by different methods and under different conditions. The results were then compared and their interpretation is discussed. The methodology presented here is suitable for preliminary evaluation of concrete admixtures. Incorporation. of these test methods into national and international standards is suggested.