Estimation of Concrete Compressive Strength ofFulbaria Super Market -2, Block -B, Gulistan, Dhaka.by Combined Method (Ultrasonic Pulse Velocity andRebound Index).

Address: House No. 193/A, Road No. 1, New DOHS, Mohakhali, Dhaka-1206.

Phone: 02-8831756

Email: info@dzignscape.net, rcclab@dzignscape.net

Index

1.0 Pulse Velocity Test

1.1 Fundamental principle

1.2 Equipment for pulse velocity test

2.0 Measuring with Ultrasonic Instrument

3.0 Transducer arrangement

4.0 Preparation

5.0 Rebound Hammer Test

6.0 Testing Equipment Details

7.0 Strength Conversion Literature & Codes

8.0 Results

1.0 PULSE VELOCITY TEST

1.1 Fundamental principle

A pulse of longitudinal vibrations is produced by an electro acoustical transducer, which isheld in contact with one surface of the concrete under test. When the pulse generated istransmitted into the concrete from the transducer using a liquid coupling material such as greaseor cellulose paste, it undergoes multiple reflections at the boundaries of the different materialphases within the concrete. A complex system of stress waves develops, which include bothlongitudinal and shear waves, and propagates through the concrete. The first waves to reach thereceiving transducer are the longitudinal waves, which are converted into an electro signal by asecond transducer. Electronic timing circuits enable the transit time T of the pulse to bemeasured.

Longitudinal pulse velocity (in km/s or m/s) is given by:

V=L/T

Where,

V is the longitudinal pulse velocity,

L is the path length,

T is the time taken by the pulse to traverse that length.

1.2 Equipment for pulse velocity test

The equipment consists essentially of an electrical pulse generator, a pair of transducers, anamplifier and an electronic timing device for measuring the time interval between the initiationof a pulse generated at the transmitting transducer and its arrival at the receiving transducer. Twoforms of electronic timing apparatus and display are available, one of which uses a cathode raytube on which the received pulse is displayed in relation to a suitable time scale, the other usesan interval timer with a direct reading digital display. Time equipment should have the followingcharacteristics. It should be capable of measuring transit time over path lengths ranging fromabout 100 mm to the maximum thickness to be inspected to an accuracy of 1%. Generally, thetransducers used should be in the range of 20 to 150 KHz although frequencies as low as 10 KHzmay be used for very long concrete path lengths and as high as I MHz for mortars and grouts orfor short path lengths.

High frequency pulses have a well-defined onset but, as they pass through the concrete, becomeattenuated more rapidly than pulses of lower frequency. It is therefore preferable to use high

frequency transducers for short path lengths and low frequency transducers for long path lengths.Transducers with a frequency of 50 KHz to 60 KHz are suitable for most common applications.

2.0 Measuring with Ultrasonic Instrument

The Ultrasonic Instrument can be used several applications including the following:

Pulse velocity measurement Path length measurement Surface velocity measurement Crack depth measurement Estimating the dynamic elastic modulus of samples (with the shear wave transducer) Ultrasonic Instrument only. Estimating compressive strength using pulse velocity alone

or in combination with a rebound hammer.

3.0 Transducer arrangement

Three transducer arrangements are commonly used.

Wherever possible use the direct arrangement as this ensures the maximum signal transmissionbetween the transducers. The semi-direct arrangement is less sensitive the distance between thecenters of each transducer.

The indirect method is particularly useful for determining crack depth, surface quality or in thecase when only one surface is accessible.

4.0 Preparation

Basic preparations are common to each application. The distance (path length)

Between the transducers should be measured as accurately as possible. It is very important toensure adequate acoustic coupling of the transducers to the surface under test. A thin layercouplant should be applied to the transducer and the test surface. In some cases it may benecessary to prepare the surface by smoothing it.

For compound measurements and uniformity, testing a test grid should be drawn out on thesurface.

Rebar's affect the ultrasonic measurements as the signal will travel faster through the rebar thanthrough the concrete. The location of rebar should be determined.

The standard measuring producer is:

Apply the couplet. Positions the transducers. Perform the measurement. Repositions the transducers (Compound measurements only) Save the result.

5.0 Rebound Hammer Test

Rebound Hammer Test is done according to ASTM C 805. The steel hammer (Control, ModelNo 58-C0181/G) impacts, with a predetermined amount of energy, a steel plunger in contactwith a surface of concrete, and the distance that the hammer rebounds is measured.

The instrument should be hold firmly so that the plunger is perpendicular to the test surface.Gradually push the instrument toward the test surface until the hammer impacts. After impact,maintain pressure on the instrument and, if necessary, depress the button on the side of theinstrument to lock the plunger in its retracted position. Read the rebound number on the scale tothe nearest whole number and record the rebound number. Take ten readings from each test area.No two impact tests shall be closer together than 25 mm (1 in.). Examine the impression madeon the surface after impact, and if the impact crushes or breaks through a near-surface air voiddisregard the reading and take another reading.

6.0 Testing Equipment Details

Ultrasonic Pulse Velocity

Name: Control PULSONIC Ultrasonic Pulse AnalyzerCountry of Origin: ItalyModel No: 58-E4900Frequency: 50 KHzCalibration Time: 57.3 micro secondTransmitter Output: 2500 V

Ultrasonic Pulse Velocity Analyser

Rebound Hammer

Hammer Brand: Control Digital Concrete HammerCountry of Origin: ItalyModel No: 58-C0181/G

Rebound Hammer

7.0 Strength Conversion Literature & Codes

The compressive strength of the test specimen is found using the following relationship

where,

RILEM-NDT4 (1993), f'c (Mpa) = Ct*0.0048552*(UPV)2.6*(RI) 1.4

Di Leo and Pascale (1994),f'c (Mpa) = Ct *0.026132*(UPV)2.446*(RI)1.058

Gasparik (1992), f'c (Mpa) = Ct *0.02860*(UPV)1.850*(RI) 1.246

where,

fc = Compressive Strength of Concrete in MPa

Ct = Ct refers to multiplicative correction co-efficient is the ratio of the Core

UPV= Ultrasonic Pulse Velocity in km/s

The following literature and codes have been used in this report

1. Ultrasonic Pulse Velocity Test (ASTM C 597)2. Rebound Hammer Test (ASTM C 805)3. RILEM, The International Union of Laboratories and Experts in Construction Materials,

19934. Di Leo A., Pascale G. (1994) Prove non distruttive sulle costruzioni in cemento armato,

Convegno prove non distruttive par laffi dabilita e la sicurezza delle strutture civile,Saie94, Giornale AICAP.

5. Gasparik J. (1992) Prove non distruttive nellEdilizia, Quaderno Didattico, AIPND,Brescia.

8.0 Results

Name of the Project: Fulbaria Super Market -2, Block -B, Gulistan, Dhaka.

Table 1: Test Points with respective points Ultrasonic Pulse Velocity (UPV) and Rebound Index (RI) Value

SLNo.

SampleID

Member Ultrasonic Pulse Velocity Results UltrasonicPulse

Velocity(km/s)

AverageUltrasonic

PulseVelocity(km/s)

ReboundHammer

Results(RI)Average

Value

ID/Type Location UPV IDSIZE /

Distance(mm)

TIME (microsecond)

1 TP 1 Column (C1) 3rd FloorHP000471 914.4 233.2 3.921

3.952 35.70HP000473 914.4 229.6 3.983

2 TP 2 Column (C2) 3rd FloorHP000474 914.4 223.7 4.088

4.092 35.30HP000475 914.4 223.2 4.097

3 TP 3 Column(C3) 3rd FloorHP000476 914.4 223.4 4.093

4.075 33.70HP000477 914.4 225.4 4.057

4 TP 4 Column(C4) 3rd FloorHP000483 914.4 245 3.732

3.685 30.40HP000484 914.4 251.4 3.637

5 TP 5 Column(C5) 3rd FloorHP000481 914.4 264.3 3.460

3.484 28.90HP000482 914.4 260.6 3.509

6 TP 6 Column(C6) 3rd FloorHP000479 914.4 303.9 3.009

2.975 29.30HP000480 914.4 310.8 2.942

7 TP 7 Column(C7) 3rd FloorHP000486 914.4 229.7 3.981

4.011 31.40HP000487 914.4 226.3 4.041

8 TP 8 Column(C8) 3rd FloorHP000490 914.4 266.8 3.427

3.404 34.20HP000491 914.4 270.4 3.382

9 TP 9 Column(C9) 3rd FloorHP000488 914.4 249 3.672

3.608 33.10HP000489 914.4 258 3.544

Test References:ASTM C 805 & ASTM C 597

Limitation:Rebound Number Values may vary due to the surface smoothness and plaster is not removed

Table 2: Combined Method to find the Compressive Strength of Concrete

SlNo Sample Id

UPV(km/s) RI (#)

f'c ; RILEM-NDT4(1993) f'c (Mpa); Leao & Pascale (1994) f'c (Mpa);Gasparik (1992)

Mpa psi Mpa psi Mpa psi1 TP 1 3.952 35.70 25.80 3741.404 33.09 4798.195 31.27 4533.879

2 TP 2 4.092 35.30 27.81 4031.738 35.61 5162.747 32.88 4768.066

3 TP 3 4.075 33.70 25.78 3737.565 33.56 4865.699 30.80 4465.776

4 TP 4 3.685 30.40 17.18 2490.781 23.53 3411.356 22.49 3260.648

5 TP 5 3.484 28.90 13.83 2005.558 19.44 2818.991 19.03 2759.671

6 TP 6 2.975 29.30 9.35 1355.988 13.41 1943.729 14.46 2096.052

7 TP7 4.011 31.40 22.41 3248.879 29.96 4343.584 27.39 3971.237

8 TP8 3.404 34.20 16.48 2389.926 21.95 3182.634 22.49 3260.703

9 TP9 3.608 33.10 18.32 2655.995 24.45 3544.807 24.04 3486.445

Reference Literature:RILEM-NDT4 (1993), f'c (Mpa)= Ct*0.0048552*(UPV^2.6)*(RI^1.4)Di Leo and Pascale (1994),f'c (Mpa)= Ct*0.026132*(UPV^2.446)*(RI^1.058)Gasparik (1992), f'c (Mpa)= Ct*0.02860*(UPV^1.850)*(RI^1.246)

*Ct = 1*Ct refers to multiplicative correction co-efficient is the ratio of the CoreCompressive Strength and Design Strength

Developed & Prepared By:

Sal Saad Al Deen TaherB.Sc Engineer (Civil, CUET)Junior Structural Engineer

Limitations:Combined method requires core strength to find the actual relationship.