Masumi Inoue

Effective Crack Control of Concrete by Self-Healing of Cementitious Composites Using Synthetic Fiber

Although concrete is one of the most widely used construction materials, it is characterized by substantially low tensile strength in comparison to its compression strength, and the occurrence of cracks is unavoidable. In addition, cracks progress due to environmental conditions including damage by freezing, neutralization, and salt, etc. Moreover, detrimental damage can occur in concrete structures due to the permeation of deteriorating elements such as Cl− and CO2. Meanwhile, under an environment in which moisture is being supplied and if the width of the crack is small, a phenomenon of self-healing, in which a portion of the crack is filled in due to the rehydration of the cement particles and precipitation of CaCO3, is been confirmed. In this study, cracks in cementitious composite materials are effectively dispersed using synthetic fibers, and for cracks with a width of more than 0.1 mm, a review of the optimal self-healing conditions is conducted along with the review of a diverse range of self-healing performance factors. As a result, it was confirmed that the effective restoration of watertightness through the production of the majority of self-healing products was achieved by CaCO3 and the use of synthetic fibers with polarity, along with the effect of inducing a multiple number of hairline cracks. In addition, it was confirmed that the self-healing conditions of saturated Ca(OH)2 solution, which supplied CO2 micro-bubbles, displayed the most effective self-healing performance in the surface and internal sections of the cracks.

SEARCH FOR MIX PROPORTIONS OF CONCRETE FOR PAVEMENT IN EARLY TRAFFIC OPENING IS POSSIBLE AND ITS PRACTICALITY

The curing period of concrete pavement is longer than that of asphalt pavement. This aspect of concrete pavement has resulted in preventing the wide-spread use of concrete pavement. In this report, the mix proportion of paving concrete with an early opening for traffic and good workability was examined by using chemical admixture. Herein the authors report, that the objective of both workability and early age strength could be attained by using a high early strength Portland cement. This study details the contribution of two materials such as high range water reducing agents and nitrite type accelerator used in combination. Finally, they report the application of the proposed composition in concrete pavement, showing improved performance in workability of ready-mix concrete. In addition, the long term durability of concrete was confirmed. The corroboration of results implicated the possible utilization of concrete pavement. コンクリート舗装ではアスファルト舗装に比べ養生期間が長く，交通開放までに時間がかかる．それがコンクリート舗装普及への最大の弊害となっている．そこで本研究では，混和剤からのアプローチにより早期交通開放可能かつ十分な作業性を確保できうる舗装用コンクリートの配合を探索した．その結果，早強ポルトランドセメントを結合材として，亜硝酸塩系の硬化促進剤と成分の異なる2種の高性能減水剤をバランス良く併用することにより，作業性および早期強度発現性の両方の目標を満足できることが明らかとなった．また，実用性を重視した舗装用コンクリートへの適用について，試験施工を通じて評価を行い，生コンの運搬・作業性およびその後の耐久性に問題がないことを確認でき，実用化への可能性を導いた．

Volume Change of Limestone and its Effects on Drying Shrinkage of Concrete

Recently, the cracks of concrete by drying shrinkage become one of the problems in the construction industry in Japan. The drying shrinkage decreases when the concrete is produced with limestone aggregate. However, it is not clear why the drying shrinkage is decreased. The purpose of this study is to clarify the relation between the drying shrinkage of concrete and the limestone aggregate. In this study, the experiments about the strength, elasticity and drying shrinkage of concrete and the physical properties and shrinkage of coarse aggregates were conducted. It is thought that the volume change of aggregates affects directly the drying shrinkage in concrete.