Studies on Methods to Assess the Quality of the Surface Layer of Concrete

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1. Establishment of test methods and assessment of concrete quality.The convenient assessing methods of concrete quality were introduced, which were applicable on site and composed of non-destructive tests on surface strength and surface durability. Two kinds of pull-off and pull-out strength tests for the former strength and three kinds of permeability tests applying Figg's method for the latter durability were proposed.2. Influencing factor on test results.Two strength tests and there permeability tests well reflected the change of concrete quality due to the change of water cement ratio, the age and so on. However, permeability values required the correction o f moisture content, and the maximum size of coarse aggregates greatly affected the estimated strength. The coefficients of variation were up-most 20% for the former strength tests and 30% for the latter permeability tests.3. Application of proposed tests for quality control and maintenanceTwo strength tests are available to estimate the structural strength of concrete as well as the change of near surface strength due to freeze-thaw action, carbonation and other causes. In special, the propose d pull-off strength test is promising for estimating the strength in a aribitary depth. Three permeability test data were closely related to the porosity change of concrete and also available to judge the change of surface concrete quality. However, the more detailed study was needed to set up the threshold values determining the deterioration of concrete.