By:Er. Vishnu Prasad PaudyalNEC Regn. #:5304/Civil/A

Asstt. Professor, PECDec. 08, 2014

A Presentation onNDT of Concrete

Contents:Non destructive tests( NDT)—An Introduction Simple & Effective techniques to Evaluate the

existing structures for their durability & strength. Easy & Quick Process. No damage to the structures Economical Provides reliable data Certified by the Codes & Standards. Internationally valid practice Limitations: Does not provide absolute value

of strength as the concrete is not actually loaded.

Destructive tests:Time consuming & complex procedure.Expenditure for sampling & preparationReinstatement of damaged portion

required.Involves Field tests & Lab analysi.sMore reliable than NDT.

Objective of NDT:To determine the Elastic modulus .To evaluate DensityTo evaluate StrengthTo determine cracks & voids To observe the reinforcement

arrangements.To evaluate Quality & Workmanship.To determine Surface hardness .To determine surface absorption.

Different Tests of NDT:Rebound hammer test.( Schmidt hammer)

[IS 13311, Part II]Ultrasonic Pulse velocity ( UPV)tests.[ IS

13311, Part I]Core tests [ IS 516, ASTM C 42/41)Corrosion assessment test.Bar locator & Cover meter.Carbonation test.

Tests & Purpose:Rebound hammer: To estimate compressive

strength & surface hardness.UPV test: To measure homogeneity , uniformity,

compactibility, presence of cracks / voids[ To measure the durability]

Core test: To evaluate the situ comp. strength of concrete.

Corrosion Assessment : To know the extent & rate of corrosion in reinforcements.

Bar locator & Cover meter: To know the status of re-bar & extent of cover.

Carbonation: To evaluate the extent of carbonation.

Rebound hammer:Principle: The rebound of an elastic mass

depends on the hardness of the surface against which the mass impinges.

The rebound number is an arbitrary measure since it depends on the given spring & on the size of the mass.

The compressive strength is estimated through correlation between rebound number from charts displayed in the body of the hammer.

The test is sensitive to the presence of aggregate & voids immediately underneath the plunger.

Should take 10 to 12 readings over the area.

Rebound hammer [SCHMIDT hammer]

Interpretation of the Results:

Factors affecting test Results:Type of CementType of aggregateSurface condition & moisture contents.Curing & age of concrete.Carbonation of concrete surface.Proper use of equipment.

Ultrasonic Pulse Velocity ( UPV) test:Principle: the velocity of sound in a solid material v, is

a function of the square root of the ratio of its modules of elasticity e,to its density σ.

The apparatus generates a pulse of vibrations at an ultrasonic frequency which are transmitted by transducer in to the concrete member .

The vibrations are received & converted to an electric signal by second transducer.

These signals are fed through an amplifier to a cathod ray oscilloscope.

The time taken by the pulse to travel through the concrete is measured by an electrical timing- unit.

Knowing the length of the path travelled the concrete , the pulse velocity is calculated.

Findings of UPV test:Correlation of pulse velocity & strength as a

measure of concrete quality.Detection of presence & approximate

extent of cracks , voids & other imperfection in concrete.

Factors affecting Test Results:Smoothness of concrete surface under test.Influence of path length on pulse velocity.Temperature of Concrete.-5 ⁰ -30⁰---Ideal 30 ⁰ -60 ⁰ ----

Reduction up to 5 %. Below 5 ⁰----Increase up

to 7.5%• Moisture condition : UPV is proportional to

the moisture condition.• Presence of reinforcement steel.

Core Test:[ Partially destructive]Cores from the hardened concrete are taken by

drilling .The samples are than conducted visual inspection

& other tests for determining comp. strength.Cores also used to measure density, water

absorption, indirect tensile strength.Through chemical analysis , concrete composition

can also be found out.Precaution : 1.Reinforcement bars should be

avoided . 2. Proper choice of core location .

Carbonation test:Objective: 1.To assesst he pH of the concrete. 2.

Extent of corrosion. Chemical used:Phenoltholene solution ( Colorless below a pH

of 8.2 & is pink /purple at a pH greater than 10.)

Factors affecting test results:Dark Concrete.SaturationExtent of drilling.

Factors affecting test:Cover thickness may be affected by the

adjacent re- bar.Magnetic effects from the aggregates or

matrix of the concrete.Roughness of the surface.Cross section ,shape of the bar.

THANK YOU!!!!Any questions pl?????