International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395-0056
Volume: 09 Issue: 07 | July 2022
p-ISSN: 2395-0072
www.irjet.net
Review on Impact Echo Technique for Concrete Exposed to High Temperature Apoorva Upadhye1, Dr. P. S. Patil2 1PG
Student, Department of Civil Engineering Department of Civil Engineering, Rajarambapu Institute Of Technology Islampur, Maharashtra, India ---------------------------------------------------------------------***--------------------------------------------------------------------2Professor,
Abstract - Impact echo is a non-destructive method for
loss of water of hydration. After 1200 ℃ concrete starts to melt. From 600 ℃- 1400 ℃concrete structurally is not useful.
evaluation of concrete based on the stress waves generated by impact which transmits through the structure and gets reflected by internal flaws. Impact echo can be used to measure the thickness in concrete slabs and plates approved by (ASTM Standard C 1383-98a, and I.S 15987: 2013). It is preliminary used to determine the extent of flaws such as voids, honeycombing, cracks, delamination and debonding in plain, reinforced and post tensioned concrete structures. Impact echo is a reliable method for locating variety of defects. Recently, Impact echo method is estimating its application in determining the dynamic modulus of elasticity as well as the assessment of thermally deteriorated concrete.
When concrete is exposed to fire it has non-uniform properties in the cross section of members. The degradation mainly occurs at near-surface layer. Due to change in temperature corresponding to strains creates incompatibility between cement paste and aggregates which leads to microcracks. Since the microcracks has a significant effect in defining the true strength of material it is necessary to analyze the damage severity. To take a decision on the possibility of further operation of facility after fire accident, Post fire assessment of concrete quality is relevant. Ensuring the safety of concrete structures, early detection of internal defects and accurately characterizing defect is important.
Key Words: Impact-echo, Stress waves, thermally deteriorated concrete
1.1 NON-DESTRUCTIVE TEST:
1.INTRODUCTION
Over all these years, number of non-destructive techniques have been developed and applied for detecting the internal flaws and defects of concrete structures. Non-Destructive testing is carried out to predict the lifetime of structure and risks connected with the further usage of it. The most important advantage of NDT is that after testing, the structure remains undamaged. The NDT methods include Rebound Hammer test, ultrasonic pulse velocity, ground penetration radar, impact echo, etc. Among these different techniques Impact-echo (IE) method is most popular one to detect the cracks and delamination of concrete structures. The impact echo method was invented at U. S. National Bureau of standards (NBS) in 1980, and developed at Cornell University, New York from 1987-1997. The first successful attempt of this method was in geotechnical engineering which evaluated the integrity of concrete piles and caissons.
Concrete is a heterogeneous mixture of aggregates, cement and water, and a noncombustible material. In spite of the fact that concrete is noncombustible, it experiences the negative effect on mechanical properties when exposed to high temperatures during fire. The increase in temperature affects the cement paste as well as aggregates. It is well known that during heating, Aggregate grains expand and the cement paste experiences shrinkage. Change in volume over time which decreases the dimension of concrete is known as shrinkage. The shrinkage of cement paste is related with evaporation of water from pores during heating process as a well as with dehydration of hydrates i.e (C-S-H gel) Aggregates normally occupy 40–60 % of the volume in concrete, the behavior of concrete at high temperatures is strongly dominated by properties of the aggregate used.
How Impact Echo Works: An impact produced by steel ball against the concrete structure, is used to generate the stress waves that propagates into structure and gets reflected by internal flaws and defects. The displacements which are caused by the reflection of these stress waves are obtained from the transducers which is adjacent to the impactor. The resulting displacement versus time is recorded in time domain, which are transformed to frequency domain by Fast Fourier Transform technique which gives the plot of amplitude versus frequency. Multiple reflections of stress waves on surface are used to determine the location of flaws
When concrete is exposed to high temperature it degrades the Physical (evaporation), Chemical (dehydration) and Mechanical (compressive strength, damage, spalling, cracking) properties. The main changes occur primarily in the hardened cement paste. As the temperature increases in concrete to 100℃free water from the capillary pore system of hardened cement paste will be evaporated. In the range of 100 ℃- 400 ℃the cement paste loses physically bond water, while at temperatures above 400 ℃chemically bound water will be lost and explosive Spalling is observed. At 800 ℃total
© 2022, IRJET
|
Impact Factor value: 7.529
|
ISO 9001:2008 Certified Journal
|
Page 1989