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

以碱骨料反应为重点进行的试验分析得出以下结论：(1)碱硅反应影响结构岩心膨胀特性研究。对21个外观严重变质的碱硅反应影响桥墩进行了分析。在21个桥墩中，有6个的核心扩展超过1000×10^6。它们的累积裂纹密度超过1m/m^2或更大，显示出严重的损伤。因此，1000×10^6的核心展开可以作为asr影响结构恶化管理和评价的参考值。(2)对实际结构ASR损伤的定量评价从受ASR影响的实际结构中得到岩心开裂行为与抗压强度的关系。结果表明，裂纹密度增大至8.0 m/m2，但仍保持了设计抗压强度的80%左右。(3)碱骨料反应钢筋断裂模拟试验采用1/8比例尺试件模拟实际结构，试件内含膨胀混凝土进行ASR膨胀模拟试验。钢筋的断裂被很好地再现，断裂面表现为与实际结构的断裂面相似的脆性断裂。钢筋的肋形对钢筋的裂纹扩展有显著的影响。通过对比现有钢筋（8φ）与原钢筋（2φ）不同肋形钢筋，发现现配钢筋的混凝土膨胀裂纹扩展范围小于钢筋直径的5.0%，而原配钢筋的混凝土膨胀裂纹扩展范围高达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%.