Dr. Rajeev Goel, Principal Scientist, Dr. S.K. Sharma, Principal Technical Officer, and Dr. P Lakshmy, Sr. Principal Scientist, CSIR-Central Road Research Institute, Mathura Road, New Delhi

Introduction

Before carrying out any testing of the concrete structures using NDT methods, visual inspection of the structure is a must. Visual inspection is not confined to the surface, it also include examination of bearings, joints, etc. and documentation of the present status of the structure. Material deterioration is often indicated by surface cracking and spalling of concrete. The cracks pattern will provide information for the cause of cracking.

Core test is one of the best methods to assess the present strength of concrete in the structure. However, an accurate estimation of the equivalent cube strength corresponding to a particular core result must take into account the effect of length-to-diameter ratio which requires a suitable correction factor. The main limitations of this test are those of high cost, inconvenience, damage and localised nature of the results. The properties of in-situ concrete vary within a structural member due to differences of compaction, curing, workmanship etc. Non-destructive testing as well as load tests is also used to assess the present conditions of the concrete structure.

Detailed inspections/investiga- tions of various distressed bridges were carried out by authors and repair and rehabilitations measures were suggested. In this paper, two different case studies have been presented, in which approach to assess the cause(s) of the distress is given so that suitable repair and rehabilitation measures can be suggested.

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