Construction Diagnostic Centre Pvt. Ltd.

Karve Road, Pune, Maharashtra

We are involved in lending excellent Pile Integrity Testing services to the clients. Based in Maharashtra (India), we provide Pile Integrity Testing services in case of defective pile shaft necking, discontinuity of concrete, intrusion of foreign matter and improper toe formation due to contamination of concrete at base with soil particles, washing of concrete due to high water current, adoption of improper construction method, poor quality control on concreting etc.

Cracks can also be a cause of failure, so if pile integrity can be assessed before completion of pile caps, then this will go a long way towards certification of pile integrity. Our Pile Integrity Testing is a quick procedure that enables number of piles to be examined in a single working day. This method provides information about continuity, defects such as cracks, necking, soil incursions, changes in cross section and approximate pile lengths ( unless the pile is very long or the skin friction is too high).

In this test, a small metal / hard rubber hammer is used to produce a light tap on the top of the pile. The shock traveling down the length of the pile is reflected back from the toe of the pile and recorded through a suitable transducer / accelerometer ( also held on the top of the pile close to the point of impact) in a computer disk for subsequent analysis.

The primary shock wave which travels down the length of the shaft is reflected from the toe by change in density between the concrete and the sub strata. However, if the pile has any imperfections or discontinuities within its length these will set up secondary reflections which will be added to the return signal. By a careful analysis of the captured signal and knowledge of the conditions of the ground, age of the concrete etc., a picture of the location of such problems can be formed.

Principle & Procedure :

• Hammer impact on the surface and a receiver monitors reflected stress wave. Time domain analysis used to determine travel time.
• Based on One Dimensional Stress Wave approach, a low strain integrity testing
• The pile head motion is measured as a function of time. The time domain record is then evaluated for pile integrity.
  

Significance and use :

• Suitable for - Slender structural elements like structural columns, driven concrete piles, cast in place concrete piles, concrete filled steel pipe piles, timber piles.
• Evaluation of Pile integrity and pile physical dimensions i.e. cross-sectional area, length, continuity, and consistency of the pile material
• Piles shall be trimmed to cut off level or sound concrete level before the test with all laitance removed.
• For Pile Dia. > 500 mm take additional reading
• Apply Impact within a distance of 300 mm
• Filter the signal to eliminate High & Low frequencies
• In a few cases where piles are too long or skin fiction is high, low strain method does not provide sufficient information particularly the toe reflection. In such cases high strain method can be used by giving higher impact energies
• The cast-in-situ piles should not be tested normally before 14 days of casting as per IS code & not before 7 days as per ASTM.
• The reasonably correct assessment of Stress Wave Velocity of pile concrete is essential as an input.
• A Complementary Ultrasonic Pulse velocity test may be carried out at the head of the pile in order to arrive at the speed of sound propagation.
• The test being a low cost and speedy, it is recommended to carry out testing of 100 % piles. The further tests such as Dynamic or Static Load tests may be decided upon the results of Pile Integrity Tests.

Limitations :

• Evaluation is approximate and not exact.
• No information about load carrying capacity of pile.
• It does not provide information regarding verticality or displacement in position of piles.
• Minor deficiencies like local loss of cover, small intrusions or type of conditions of materials at the base of piles are undetectable.
• Integrity testing may not identify all imperfections, but it can be useful tool in identifying major defects within the effective lengths.
• The test may identify minor impedance variations that may not affect the bearing capacity of piles. In such cases, the engineer should use judgment as to the acceptability of these piles considering other factors such as load redistribution to adjacent pile, load transfer to the soil above the defect, applied safety factors and structural load requirements.
• Soil stiffness or founding on rock of similar density as the pile, will attenuate the signals such that there will be little or no toe reflection.
• The low strain integrity method is applicable to cast-in-situ concrete bored and driven piles. Conclusive results are rarely obtained in case of segmented precast reinforced concrete driven piles or precast piles in prebored holes.
  

It may not detect :

• The toe reflection when the L/D ratio roughly exceeds 20 (In hard soils) to 60 (In very soft soils)
• Progressive changes in cross-section
• Minor inclusions and changes in cross-section smaller than 25% .
• Variations in length smaller than 10%.
• Features located below a crack or a major (1:2) change in impedance
• Debris at the toe
• Deviations from the straight line and from the vertical.

We are known for providing reliable Load Testing services to the clients. Based in Maharashtra (India), we provide load testing of building & bridge components in case of the strength of concrete is below the acceptable norms, structural design data is not available, load carrying capacity of the flexural member needs to be assessed, the members is to be subjected to a higher loads, the members are noticed to have cracks, deflections, the structure is damaged due to fire, earthquake, blast, corrosion etc., and change in use of structure. IS – 456 – 2000 recommends that Load Testing of flexural members should be carried out in such case where the core test results do not satisfy the requirements.

The Load Test for Building is carried out as per IS – 456. For Bridges Load test is carried out in accordance with IRC – SP – 51 – 1999, the load test can be performed by either loading with simulation of specific IRC vehicle (IRC – 37) or by other type of static load which produces the design forces. Load Test Procedure as per IS – 456- 2000. The  structure  should  be  subjected  to a load  equal to  full  dead  load  of  the  structure  plus  1.25  times  the imposed  load  for  a period  of 24  h and  then  the  imposed load  shall  be  removed.

Based in Maharashtra (India), the firm is acknowledged for lending accurate Rebound Hammer Testing services to the clients. This test is used for checking the strength of concrete since 1940.The test is based on the principle that the rebound of an elastic mass depends on the hardness of the surface against whichmass strikes.The plunger of hammer is strongly and steadily pressed against the concrete surface at right angles until the spring loaded mass is triggered from the locked position. The spring controlled mass rebounds and the extent of such rebound depends upon the surface hardness of concrete. The distance traveled by the mass as a percentage is defined as rebound number.

Influence of Test Conditions :

The test is significantly influenced by following factors :

• Type of Cement : Concrete made with high alumina cement can give strength 100 % higher or that with supersulphated cement can give 50 % lower strength than that with ordinary Portland cement.
• Type of Aggregate : The influence of aggregate type and proportion can be considerable.
• Surface condition & Moisture content : Trowelled & floated surfaces are harder than moulded surfaces. Exposed aggregate surfaces are unsuitable for this methods. A wet surface will give rise to underestimation of strength of concrete by about 20 % lower than calibrated under dry condition.
• Curing & Age of concrete : The relation between hardness and strength varies as a function of time, subsequent curing and exposure condition will further influence this relationship. But this effect can be ignored for concrete up to 3 months old.
• Carbonation of Concrete surface : Concrete exposed to atmosphere will normally form a hard carbonated skin. The strength predicted for carbonated concrete may overestimate up to 60 %.

• Application :

  The rebound hammer method may be used for

  • Assessing the likely compressive strength of concrete with the help of suitable calibration charts.
  • Assessing uniformity of concrete
  • Assessing the quality of concrete in relation to specified standard requirements.
  • Assessing the quality of one element of concrete to another.

  • Reliability & Limitations :

    The test determines the hardness of the surface only. The impact of hammer is sensitive to the surface layer of about 25 to 50 mm only. The reliability of this test as alone, for compression strength is less, but it can generally indicate uniformity of concrete.

    The rebound hammer results are very sensitive to the spring constant, thus after a use of hammer for about 15000 impacts, it is recommended to calibrate the hammer on Anvil.

    The influence of aggregate type and proportion can be considerable. Thus it is strongly recommended that every lab, NDT consultant using rebound hammer shall develop their own graphs for compressive strength verses Rebound number, and shall not use blindly, the graphs given by manufacturers.

    The probable accuracy of prediction of concrete strength in laboratory level is 15 % and that of structure is 25 %. It is recommended to use of Rebound hammer along with ultrasonic concrete testing or core test.