ndt level 0 rebound hammer material

8/19/2019 NDT Level 0 Rebound Hammer Material

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FAKULTI KEJURUTERAAN AWAM

UNIVERSITI TEKNOLOGI MARA

PASIR GUDANG LABORATORY MANUAL

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COURSE CIVIL ENGINEERING MATERIALS

COURSE CODE ECS 256

LEVEL OF OPENNESS 0

CATEGORY TRADITIONAL

DEGREE OF OPEN-ENDED (%) 0

PERIOD OF ACTIVITY 1 WEEK (WEEK 1)

TITLE NON-DESTRUCTIVE (NDT) MEASUREMENT OF CONCRETE

1.0PREAMBLE

1.1 Introduction

The traditional methods of conducting laboratory activities will not be able to provide theavenue for students to enhance independent learning activities and inculcate creativity andinnovation. Level 0 is fully prescriptive where problem, ways & means and answers areprovided to the students. However it is still necessary especially to first and second yearstudents.

In this laboratory activity students will be exposed to the types of non-destructive test thatcan be applied to the concrete in order to identifying deficiencies in concrete.1.2 ObjectiveThe objective of the test is:- To identify deficiencies in concrete where to investigate the strength of the structuralconcrete member1.3 Learning Outcomes At the end of the laboratory activity, students would be able to:

1. Organize and conduct non-destructive laboratory experiment.2. Classify the strength according to standard.3. Analyse data correctly and present in typical format.4. Work in a group to produce technical report.

1.4 Theoretical BackgroundConcrete is one of the most widely used construction materials for a wide variety of

structural and architectural elements. But concrete can suffer from several forms of in-service deterioration. The most common deterioration modes are corrosion-induceddelamination and spilling. The corrosion process is driven by moisture and oxygen thatcan permeate the concrete. Freeze-thaw damage can also deteriorate in-serviceconcrete. This is a progressive deterioration of the concrete material caused by theentrance of water (into the concrete pores) that subsequently expands when it freezes,introducing tensile stresses that can cause concrete to crack. Freeze-thaw damage leadsto a generalized deterioration of the concrete strength properties, widespread cracking,spilling, and eventually loss of section.

In addition to in-service deterioration, construction related factors can undermine concretedurability. These include low cover, honeycombing, and voids. Discontinuities introducedduring construction can lead to poor durability, reduced load carrying capacity, and poor

aesthetic quality of the finished concrete.

Non-Destructive (NDT) measurement provides cost-effective and reliable methods foridentifying deficiencies in concrete. NDT test methods are used to determine hardened






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concrete properties and to evaluate the condition of concrete in deep foundations,bridges, buildings, pavements, dams and other concrete construction.

Several types of NDT that are commonly use include:

i. Rebound Hammer testii. Ultra Sonic Pulse Velocity or Pundit testiii. Rebar locator testiv. Half-cell testv. Windsor probe

Every method of non-destructive test have its own boundary and which mean the methodcannot afford an accurate and consistence result for difference cases and to detectdifferent defect.

The NDT methods are applied to concrete construction for four primary reasons:1. Quality control of new construction;2. Troubleshooting of problems with new construction;

3. Condition evaluation of older concrete for rehabilitation;4. Purposes; and5. Quality assurance of concrete repairs.

NDT can access parameters such as:i. Densityii. Strengthiii. Surface hardness

It is able to check the quality of workmanship and structural stability as it can also detectvoids and cracking in concrete or other materials.

NDT technologies are evolving and research continues to enhance existing methods anddevelop new methods. The report is intended to provide an overview of the principles of

various NDT methods being used in practice, and to summarize their applications andlimitations. The emphasis is placed on methods that have been applied to measurephysical properties other than the strength of concrete in structures, to detect flaws ordiscontinuities, and to provide data for condition evaluation.

2.0PROBLEMSTATEMENT

The group is required to carry out non-destructive test following the procedures outline andsubsequently analyse the data and present it in a proper technical format.

3.0WAYS &MEANS

3.1 Apparatus3.1.1 UPV/ PUNDIT Test

Pundit test equipment, pencil, ruler and concrete elements specimen (cracking line).

Figure 3.1: Pundit Test Equipment






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Procedures (PUNDIT)

i. Preparing for use: Before switching on the “V” meter, thetransducers should be connected to the sockets marked “TRAN” and “REC”.

the “V” meter may be operated with either: a. The internal batteryb. An external batteryc. The A.C. line

ii. Set reference: A reference bar is provided to check theinstrument zero. The pulse time for the bar is engraved on it. Apply a smearof grease to the transducer faces before placing it on the opposite ends of thebar. Adjust the “SET REF” control until the reference bar transit time isobtained on the instrument read-out.

iii. Range selection: For maximum accuracy, it is recommended thatthe 0.1 microsecond range be selected for path length up to 400 mm.

iv. Pulse velocity: Having determined the most suitable test pointson the material to be tested, make careful measurement of the path length

“L”. Apply couplant to the surfaces of the transducers and press it hand ontothe surface of the material.

v. Do not move the transducers while a reading is being taken, as this cangenerate noise signals and errors in measurements.

vi. Continue holding the transducers onto the surface of the material until aconsistent reading appears on the display, which is the time in microsecondfor the ultrasonic pulse to travel the distance “L”.

vii. The mean value of the display readings should be taken when the units digitbetween two values.

Pulse velocity = (Path length / Travel time)viii. Separation of transducer leads: It is advisable to prevent the two

transducer leads from coming into close contact with each other when thetransit time measurements are being taken. If this is not done, the receiver

lead might pick-up unwanted signals from the transducer lead and this wouldresult in an incorrect display of the transit time.

3.1.2 Rebound Hammer

Rebound Hammer – a spring-loaded steel hammer which when released strikes a steelplunger in contact with the concrete surface.Test anvil – a 6 inch diameter by 6 inch long high-carbon steel cylinder hardened toRockwell 65-67C. Abrasive stone – silicon carbide of medium grain texture.

Figure 3.2: Concrete Test Hammer

Procedures (rebound hammer)

1. Before commencement of a test, the rebound hammer should be tested against thetest anvil, to get reliable result, for which the manufacturer of the rebound hammerindicates the range of readings on the anvil suitable for different types or model.Check the hammer reading with the testing anvil before and after testing.






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2. Firmly hold the instrument in a position that allows the plunger to strike verticallydownward against the test anvil and verify that the rebound hammer provides therebound number specified. Be sure to follow the same procedure as for testing thesubsequent concrete test surface. Note that the test anvil shall be placed on a solid

surface, e.g., concrete floor.3. Grind and clean the concrete surface using the abrasive stone.4. Firmly hold the instrument in a position that allows the plunger to strike

perpendicularly to the concrete test surface.5. Gradually increase the pressure on the plunger until the hammer impacts.6. Examine the impression; if the impact crushes or breaks through a near surface void,

discard the reading.7. After impact, record the rebound number to the nearest whole number. The mean of

each set of reading shall be calculated using all the readings.

3.3 Data Acquisition

Table 3.1: Comparative Hardness for Rebound Hammer

Average Rebound Quality of Concrete

> 40 Very good

30 – 40 Good

20 – 30 Fair

< 20 Poor and / or delaminated

0 Very poor and / or delaminated

Table 3.2: Classification of Concrete Grading for Pundit Test

Pulse Velocity(m/second)

Quality of Concrete (Grading)

Above 4.5 Excellent

3.5 to 4.5 Good3.0 to 3.5 Medium

Below 3.0 Doubtful

Report

1) Report the test date, type of concrete, and estimated unconfined compressive strength.2) Hammer orientation, i.e., downward, upward, horizontal, or at a specific angle.3) Average rebound number to the nearest whole number.

A1 B1 C1 D1 E1

A2 B2 C2 D2 E2

A3 B3 C3 D3 E3

A4 B4 C4 D4 E4 A5 B5 C5 D5 E5

4.0RESULTS

4.0 Results, Analysis and ConclusionThe group is required to submit the technical report of the laboratory results highlighting the

data acquisition process, analysis carried out and the relevancy of the set-out output to achievethe objective.

Determine. Find related formula to calculate these parameter:1. the pulse velocity, V;2. the modulus of elasticity, E and;3. the mass density, ρ.

Figure 4.1: Example Sample Cracking Line at Wall / Column / Slab






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a. The results of rebound hammer on the elements were analysed by determine theaverage value of each point.

Structure

element

Grid

No.

Reading

(Rb)

Compressive load

(N/mm2)

Remark /

commentWall A1

B2

C3

D3

E4

Average

Classification

Table 4.1: Rebound Hammer Data Table

b. The results of Ultrasonic Pulse Velocity (UPV)/ PUNDIT Test on the elements wereanalysed by determine the average value of each point.

Structureelement

GridNo.

SpecimenDefects

(visual inspection)

SpecimenDimension

Time, t(µs)

PulseVelocityV = L / t

(m/s)

Remark/comment

Wall A1

B2

C3

D3

E4

Average

Classification

Table 4.2: UPV/PUNDIT Test Data Table

*The format of the report is left to the creativity and discretion of the group.The report must be submitted 7 days after the completion of the test.

ndt level 0 rebound hammer material

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