膨張材を収縮低減剤によってスラリー化した混和材料によるひび割れ低減方法
膨張材を収縮低減剤によってスラリー化した混和材料をアジテータ車に後添加する新しいひび割れ低減方法に関して検討した。スラリーを後添加する混練方法での拘束膨張量は膨張材のみを使用する場合に比べて大きく、スラリー化しても膨張材と収縮低減剤の併用効果があった。また、膨張材や収縮低減剤を、予めセメントや水に置換して混練する従来法とスラリーを後添加する混練方法の違いが硬化特性に与える影響は小さかった。実機レベルでのスラリーの添加を鑑みてアジテータ車で練り混ぜた結果、空気量の調整には注意が必要であったが、120秒間の高速攪拌でスラリーをベースコンクリートに均質に混ぜることができた。検討したひび割れ低減方法は、膨張材や収縮低減剤の活用の自由度を高め、膨張材の練混ぜ不足の問題解決や品質向上にもつながるものと考えられる。
Cracking Reduction Method Using Admixture Slurried with Expansive Additive and Shrinkage Reducing Agent
A new cracking reduction method has been discussed. Admixture slurried with expansive additive and shrinkage reducing agent is post-added into fresh concrete in an agitator vehicle. If the slurry is post-added to fresh concrete, restrained expansion ratio is greater than that using an expansive additive only. A combined effect of expansive additive and shrinkage reducing agent is recognized even if admixture is slurried with expansive additive and shrinkage reducing agent. Comparing a traditional blending method, in which expansive additive and shrinkage reducing agent are replaced by cement and water in advance, with a new blending method in which slurry is post-added, the effect of difference in blending method on hardened concrete is small. Considering that the slurry is added in practical work, the mixing by an agitator vehicle revealed that slurry can be homogeneously mixed with base concrete by the high-speed agitating for 120 seconds, although the careful adjustment of the amount of air is needed. The author assures that the new method, discussed here to reduce cracking, will enhance the flexibility of the use of expansive additive and shrinkage reducing agent. The new method will also solve the insufficient mixing of expansive additive and will improve the quality of expansive concrete.
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