Yukio Hama

Estimation of Shrinkage Behavior and Stress of Expansive Concrete on Buildings

In this study, Based on the constructed model in advance, we suggested the macro prediction method of shrinkage cracking reduction in concrete using expansive additives, and the method was verified. In addition, extended application of model to building, the strain of walls and slabs on building was estimated by model and the generated stress was estimated thereby comparing this with the result by existing method to verify the model’s applicability and the validation of our model. From examination of theoretical model for concrete using expansive additives to examination for building levels, furthermore suggests the macro prediction method for shrinkage reduction and cracking control effects was can be supply practical data in application of expansive concrete and utility in the future.

Influence of Environmental Conditions on Pore Structure Change in Mortar with Various Types of Cement

The main aim of this study is to investigate the variation of pore structure and frost resistance in mortar subjected to different environmental conditions and for different exposure times. Mortar specimens were prepared by using three types of cement, which are ordinary Portland cement, fly ash cement, and ground granulated blast furnace cement. Various environmental conditions which are drying, wetting, and drying/wetting cycles were applied to specimens in laboratory, after casting mortar specimens followed by initial curing for 4 weeks in water at 20°. The pore structure modification was evaluated by mercury intrusion porosimetry (MIP) method. It was clarified that the pore structure change can be affected by the studied factors, which are exposure drying temperature, exposure drying duration, and cement type. Furthermore, equations which can predict the pore structure changes was derived based on the experimental results.

EFFECTS OF NORMAL AIR TEMPERATURE CHANGE ON APPLICABLE PERIOD OF COLD WEATHER CONCRETING AND MATURITY

This report deals with the effects of normal air temperature obtained from 3 measurement periods(1961-1990,1971-2000,1981-2010) on change of applicable period of cold weather concreting and maturity related to construction plan. According to the results of this study, it made clear that applicable period of cold weather concreting based on latest normal value is shorter than the previous period which are described in JASS5-2009. And maturity based on latest normal value is also bigger than the maturity based on previous normal value.

RESISTANCE TO FROST DAMAGE AT EARLY AGE AND STRENGTH DEVEROPMENT AT LOW-TEMPERATURE ON CONCRETE USING VARIOUS RECYCLING MATERIALS

This paper reports the results of the experiment on resistance to frost damage at early age and strength development at low-temperature on concrete using various recycling materials.Results show compressive strength to prevent frost damage at early age can be set at 5N/mm2, which is equal with normal concrete in any case. Low-temperature strength development of concrete using high-strength artificial aggregate, electric arc furnace oxidizing slag aggregate and normal eco cement is equal with normal concrete.

A SURVEY ON COLD WEATHER CONCRETING TO PRACTICAL PERSONS IN HOKKAIDO AND TOHOKU REGIONS AND A PROBLEM WITH THE RECOMMENDATION FOR PRACTICE

The cold weather concreting recommandation for practice of AIJ is utilized by many practical persons. However, about mixing plan or curing plan, estrangement from the field results data was pointed out, and so I carried out a survey for the purpose of grasping the actual situation. In addition, as for the compounding plan technique, it turned out that in Hokkaido region they had much adoption of standard curves of sixth document in the recommendation for practice. When I compared this standard curve with the field results data and the laboratory data, I pound the estrangement at early age was wide, so it is necessary to review this curve.