PARAMETRIC STUDY OF NON-DESTRUCTIVE TESTING OF CONCRETE

Abstract

Nondestructive testing of concrete is inevitable tool in estimation of field strength of concrete, but the test results are very much affected by lots of parameters of the concrete. The aim of this study is to determine how much variation in strength is occurring, if it is obtained using Rebound hammer method instead of conventional cube compressive testing, when different parameters are changed in the concrete. Also, the experimental findings of the Ultrasonic pulse velocity (UPV) test on concrete cubes during progressive compressive loading are reported in this work. The concrete cubes were tested in progressive compression till failure, during which the pulse velocity recorded at each increment of the load. It was observed that cracks started earlier for the higher strength concrete (low water-cement ratio), than the lower strength (higher water-cement ratio) concrete. This is evident from decrease of pulse velocity earlier during the progressive compression testing. Also addition of Fly Ash has reduced the cracking at the earlier stage of compression. Improper compaction and delayed casting has lead to cracking at earlier stage and they progressed faster. Silica fume and brick aggregate concretes showed cracking at earlier stage. Experimental results showed that when concrete is poorly compacted, the difference between Rebound hammer readings and compressive strength is very high (16 % of difference in readings at 28 days for a density ratio of 0.945 is reported). For segregated concrete specimens and delayed casting, a same phenomenon was observed. Addition of Fly Ash increased the difference between Rebound strength and compressive strength. Then facts demonstrated the usefulness of the UPV test for anticipatory failure in concrete structures and usefulness of Rebound hammer test in determining compressive strength of concrete.