Study of the Treatment of Construction Joints in Concrete Using Water Jet Method

本研究的目的是研究水射流切割对硬化混凝土表面处理的效果，并找出施工缝的粘结强度。采用抗弯强度比来评价施工缝的强度。将有施工缝试件的抗折强度与不带施工缝试件的抗弯强度之比作为抗折强度比，竖向施工缝的抗弯强度比一般低于水平施工缝，这是由于混凝土渗水形成薄水层而导致混凝土失去粘结性能所致。研究表明，采用旋转射流切割方法，垂直施工缝的抗弯强度比可达到80%~90%，且表面处理的压痕深度保持在规定值。从试验结果可以看出，规定深度的适宜取值为7 mm以上，表面处理深度主要受压缩机水压的影响，抗折强度比不受粗骨料类型和旧混凝土水灰比的影响。在实心梁和接缝梁试验中监测了声发射信号。获得了声发射事件的个数、幅度分布和波形，并显示出以下趋势。当载荷接近失效载荷时，声发射事件数和长波长集中在梁中心附近。但大振幅分布和频率不受施工缝的影响。

The aim of this study is to investigate the effectiveness of water jet cutting for the surface treatment of hardened concrete and to find out the bond strength of construction joints. The flexural strength ratio was used to evaluate the strength of construction joints. The ratio of the flexural strength of the speciments with construction joints to the strength of the specimens without construction joints was regarded as the flexural strength ratio.The flexural strength ratios for vertical construction joints are generally lower than the horizontal construction joints because of being caused by the loss of adherence properties of concrete due to the formation of a thin water layr by bleeding. This study showed that the flexural strength ratio of the vertical construction joints were obtained ranging 80% and 90% when a rotary jet cutting methed was used and the depth of the indentations of surface treatment maintained a specified value. It can be seen from the experimental results that the suitable value of specified depth is more than 7mm.The depth of surface treatment is mostly affected by the water pressure of the compressor.The flexural strength ratios were not affected by the type of coarse aggregate and the water-cement ratio of old concrete.AE signals were monitored during the tests of solid beams and jointed beams. AE events counts, amplitude distributions and wave form were obtained and the following tendencies were showed. AE event counts and long wave lengths were concentrated around vicinity of center of the beam as the load is close to the falure load. But large amplitude distributions and frequency were not affected by the construction joints.