Fracture of the reinforcing bars and deterioration mechanism due to Alkali Silica Reaction

（1）碱硅反应（ASR）影响下桥墩芯样的膨胀特性研究对21个外观严重劣化的ASR影响下桥墩进行了分析。在21个桥墩中，有6个的核心膨胀超过1000×10^6。它们显示出严重的损坏，累积裂纹密度超过1 m/m^2或更高。因此，1000×10^6的岩心膨胀率可作为受ASR影响的结构物劣化管理和评估的参考值。(2)ASR对实际结构损伤的定量评价从实际结构中得到了受ASR影响的芯样的开裂行为与抗压强度之间的关系。结果发现，裂纹密度增加到8.0米/平方米，但约80%的设计抗压强度被保留。(3)碱骨料反应引起钢筋断裂的模拟试验采用1/8比例的模拟实际结构的试件，并在试件中加入膨胀混凝土，进行了模拟ASR膨胀的试验。钢筋断裂被很好地再现，断裂面表现出类似于在实际结构的断裂面中观察到的脆性断裂。研究还发现，钢筋的肋形状对这些钢筋的裂纹扩展有显着的影响。根据现有钢筋（8φ）和具有不同肋形状的旧钢筋（2φ）的比较，在现有钢筋的情况下，混凝土膨胀引起的裂缝扩展小于钢筋直径的5.0%，而旧钢筋的裂缝扩展高达80%。

The following conclusions were drawn from the experiment and analysis focusing on the alkali aggregate reaction :(1) Research on the expansion characteristics of cores sampled from alkali silica reaction (ASR)-affected structuresAnalysis was conducted on 21ASR-affected piers having seriously-deteriorated appearances. Of the 21 piers, six had a core expansion of over 1000×10^6. They showed serious damage exceeding a cumulative crack density of 1m/m^2 or more. Therefore, the core expansion of 1000×10^6 can be used as the reference value for the management and evaluation of deterioration of ASR-affected structures.(2) Quantitative evaluation of ASR damage to actual structuresThe relationship between cracking behavior and compressive strength of cores was obtained from ASR-affected actual structures. It was found that the crack density increased up to 8.0 m/m2, but about 80% of the design compressive strength was retained.(3) Experiment simulating fracture of reinforcing bars due to alkali aggregate reactionsAn experiment simulating ASR expansion was conducted using 1/8 scale specimens modeling actual structures and containing expansion concrete within the specimens. Fracturing of reinforcing bars was well reproduced and the fractured planes showed brittle fracturing similar to that observed in the fractured planes of actual structures. It was also found that the rib shape of reinforcing bars has a significant effect on the crack propagation of those bars. According to the comparison of present bars (8φ) and the former bars (2φ) having different rib shape, cracks caused by concrete expansion propagated for less than 5.0% of the bar diameter in the case of present-reinforcing bars, but that of former reinforcing bars was as large as 80%.