A STUDY OF COMPRESSIVE STRENGTH & NDT RESULTS FOR DIFFERENT CONCRETE MIXES

Abstract

The non destructive tests (NDT) are used to determine the compressive strength of concrete. The relationship between the measured, mechanical or physical and the compressive strength is generally not unique. This arises from the diversity in the existing relations between the measured characteristic and the factors affecting the concrete strength, i.e. water cement ratio, age, aggregate content, effect of steel fibres, curing conditions, type of cement used, degree of compaction etc. In order to improve the significance of the NDT concrete strength correlation by at least two different non destructive tests should use. The aim of the present work is to check the validity of rebound hammer and ultrasonic pulse velocity for assessing concrete strength, which are widely used in structural field. The NDT are compared on basis of sensitivity of measurements and scatter of results. An extensive series of tests was carried out to obtain a correlation of the NDT results with compressive strength for parameters given below. Fourteen concrete mixes has been prepared for test. Total I21 nos of cubes and three columns has been prepared for the test. NDT and destructive testing has been done on each specimen. In this study both the well known NDT techniques, Rebound hammer and Ultrasonic Pulse Velocity (UPV) method were adopted. The parameters which affect the compressive strength of concrete, used in thi study ar'ater cement ratio of the (1. ~ s concrete FA : CA ratio in the mix proportion, volume fraction of steel fibres and improper ,h p p 'ti curing. Four water cement ratios has been used in this study. Among these four water cement ratios, for first two types the cubes are tested continuously upto 12t1 and rest of the cubes were tested upto 4th week. Three columns of different percentages of steel has been prepared to observe the effect of steel on pulse velocity. For each column three cubes of same mix as the column specimen, has been prepared to observe the variation of UPV through concrete with steel and without steel. In case of improper curing four type of improper curing has been used and they are curing for first week only, no curing for first week and curing after that, no curing for first two weeks and curing after that, and no curing at all. For these conditions how the quality of concrete in terms of strength changes has been observed. Detail results for various parameters are given in chapters 4 and 5. The conclusions drawn from this study are useful.