Clarification of fracturing mechanism by expansive cement agent and basic examination far making an alarm unit to predict an accidental discharge using acoustic emission monitoring

氧化钙（CaO）基膨胀水泥，也被称为“非爆炸性爆破剂”，已广泛用于破坏大块岩石和混凝土结构。为了弄清其断裂机理，我们在200 mm和300 mm立方的砂浆试件中心钻一个直径为50 mm的孔，在孔内注入氧化钙基膨胀水泥，对其进行了断裂实验。在宏观裂纹产生之前，AE（声发射）源聚集在试件外侧，而不是孔附近，说明宏观裂纹起源于试件外侧，然后向内扩展。膨胀压力在井眼切向产生拉应力，但在井壁处应力最大，且随距井眼距离的平方成比例减小。另一方面，由于孔的加热引起的热应力在试样的外部是拉伸的，但在孔附近是压缩的。由此可见，热应力对氧化钙基膨胀水泥造成的裂缝影响较大，至少对没有裂缝的岩石或混凝土块而言是如此

Calcium oxide (CaO)-based expansive cement, also known as "non-explosive demolition agents", has been widely used to fracture massive rocks and concrete structures. To clarify its fracture mechanism, we made an experiment to fracture a mortar specimen of 200 mm and 300 mm cubic by setting calcium oxide-based expansive cement in a 50 mm diameter hole bored in the center of the specimen. AE (acoustic emission) sources clustered in outside of the specimen rather than vicinity of the hole just before macroscopic cracks generated, suggesting that macroscopic cracks originated at the outside of the specimen and then extended inward. Although the expansive pressure causes tensile stress in tangential direction of the hole, the stress is the maximum in the hole wall and decrease in proportion to square of the distance from the hole. On the other hand, thermal stress due to heating of the hole is tensile in the outside of the specimen but it is compressive in the vicinity of the hole. Thus, it could be concluded that thermal stress has large effects in the fracture caused by calcium oxide-based expansive cement, at least, in a rock or concrete block without preexisting crack