Atsushi Teramoto

Shrinkage and Creep Performance of Recycled Aggregate Concrete

With the growing emphasis on sustainability in the concrete industry, there has been a renewed interest in the use of recycled concrete as aggregate in new concrete. Recycled aggregate concrete is not a new concept, but it is normally met with resistance due to reduction in strength and an increase in drying shrinkage. The organizations that allow for recycled concrete aggregates in concrete give few guidelines. One of the common requirements is that the recycled aggregates should be soaked prior to use. The goal of this study was to investigate how the initial moisture state of the aggregates affect the creep and shrinkage properties. Tests included free shrinkage of prisms, restrained shrinkage ring tests and an actively restrained tensile creep test. By using the recycled concrete aggregate at or near SSD conditions, the mixtures were workable and had lower free shrinkage. The recycled aggregate mixes did have higher tensile creep but this is not detrimental in paving applications where it would work to prevent shrinkage cracking.

QUALITY ESTIMATION METHOD ABOUT FOREIGN-MADE CEMENT USED CONDUCTION CALORIMETER

The purpose of this research is to clarify the characteristic features of the foreign-made cement, and to develop the simple estimation method by a small amount of cement sample. At first, the authors analyzed chemical composition and mineral composition based on X-Ray Fluorescence and X-ray diffraction and others. Then, they tested the physical properties and the heat of hydration by conduction calorimeter, and examined about correlation of the strength and heat of hydration. As the results, foreign-made cement had difference the kind of plaster and admixture (lime stone, blast furnace slag, fly ash, natural pozzolan and so on). Furthermore, it becomes clear that they had correlation between early strength and early heat of hydration. In addition, they had correlation between strength since 28 days and the quantity of SiO₂. It shows that, if early quantity heat of hydration is measured, it can estimate from early compressive strength to long term compressive strength in accuracy for quality estimation.本研究では海外で製造されたセメントの簡易な品質評価手法を開発するため、化学組成、鉱物組成を分析ののち、物理試験と水和発熱量測定を行い、物理特性と水和発熱量の相関について検討を加えた。その結果、石膏の種類、混合材の種類が異なる海外のセメントにおいて、初期の圧縮強さと総発熱量、圧縮強さ比とSiO₂量の間には相関があることが明らかとなり、材齢初期の水和発熱量を測定することで、初期から長期の圧縮強さが予測できる可能性が示された。

Temperature dependency of autogenous shrinkage of ultra high-strength concrete

In this contribution, temperature dependency of autogenous shrinkage of ultra high-strength concrete whose binder is premixed silica fume cement with W/B=0.15 is investigated. Experimental factors are temperature of fresh concrete and elevated temperature history that are emulating difference of temperature history due to placing season. As a result, following conclusions are obtained 1) autogenous shrinkage of ultra high-strength concrete has two stages from the point of view of a rate of shrinkage, i.e., earlier age (stage1) and later age (stage2), 2) lower temperature of fresh state increase autogenous shrinkage at stage.1, 3) higher temperature develop larger autogenous shrinkage, especially over 40oC at stage2. 2 EXPERIMENTAL PROCEDURES 2.1 Materials and Mixture Proportions Table 1 lists the materials used for this experiment. The types of fine aggregate and coarse aggregate are that used for general UHSC. In this study, coarse aggregate is comminuted with a maximum size of 5mm, because specimen size is fixed as 10x60x370 mm to avoid distribution of temperature in specimen. The mix composition of this experiment is shown in Table 2.Water-to-binder ratio is fixed with 0.15 in both cement paste and mortar. 2.2 Experimental equipment for measurement of autogenous shrinkage -600 -500 -400 -300