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

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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.