CONSTRUCTION MATERIALS
GROUP PROJECT – NON-DESTRUCTIVE TESTING REPORT
Abdul Rahman Hilmi Name
:
Siti Rozanadia Zainudin Suresh Rao SCM 010 – 010 – 412 412
Student ID
:
SCM 016 - 722 SCM 012 - 898
Course
:
BEng (Hons) Civil Engineering
Subject Name
:
Construction Materials
Subject Code
:
ECV 3223
Lecturer
:
Ms. Salmaliza
Submission Date
:
22 / 02 / 2012
Pile Integrity Test Introduction Integrity of a foundation should be tested after installi ng the piles to see if the foundation piles can support the load and transfer it to the piles without any problem, if there is any problem can be solved before building the construction. The problems that can affect the foundation piles are necking, voids, cracks, concrete flush out . Those problems will come from the way of mixing, ratio problems, quality of the materials and installation. For installation the piles, the driven piles while installing it needs to be hit causing the pile an overstressing and maybe it will cause damage or cracks that can‟t be seen underground. Thus, a specific test is used to detect the problems by using the pile integrity test. Pile integrity test is a test that can be tested on the foundation to see either the piles of the foundation have a defect and can‟t apply its job or no by detecting the defec ts based on wave propagation theory. In this test, a special hand held hammer will be hit on the pile to create a low strain, impact wave that are compressed then travel down to the pile by a constant wave speed (same high strain dynamic testing). There is an accelerometer or geophone placed on top of the pile to measure the impact done by hammer. If there is a significant reflection on the wave means that a problem detected on the tested pile. And to know where the location of the problem in the pile is, it can be estimated from the putative wave speed and the s ize estimated from the magnitude of the early reflection. This test is also used as a length determination of the pile constructed on the ground. This test is have several names like sonic test, low strain dynamic test and low strain integrity test.
Objectives The main objective in the testing is to provide information about: a) Physical dimensions of the pile b) Pile continuity c) Consistency of material in the pile Pile Integrity Test Methodology Pile Integrity Test is also called Low Strain Dynamic Test which is a test being conducted to assess the condition of piles and shaft. As opposed to Dynamic Load Test which applies a heavy mass of drop weight, Pile Integrity Test incorporates a sm all weight hand-held hammer as one of the apparatus.
Figure: Pile Integrity Test Kit The test is carried out by attaching accelerometer on top of the pile where it is connected to the collector (test instrument), as the pile head is being tapped by the hammer, a compressive wave is generated. When the travelling compressive wave encounters any deformation or change in pile cross section or the concrete quality, it will generate an upward tension wave which is then observed at the top of the pile. The velocity recorded along with the subsequent reflections from the pile toe or pile discontinuities are graphically displayed by Pile Integrity Test instrument. Engineers will interpret the visual based on fluctuation of the graph to look for pattern of significant changes to cross section of the piles. From there, engineers will determine whether there are no cracks or deformation on the pile and also the quality of concrete of the pile is at satisfactory level.
Figure: Pile Integrity Test on Bored Pile
Figure: The graph on the display fluctuates as the pile is tapped by hammer
Figure: Sample of Result of Pile Integrity Test
Apparatus
The test is performed using digital data acquisiti on equipment called the PIT-Collector. The equipment shall have the following minimum requirements:
The analog to digital resolution shall be at least 24 bits, The sampling frequency shall be at least 25,000 Hz. Data shall be stored such that additional processing or further wave analysis is possible. Data shall be displayed in the field for evaluations of preliminary data quality and interpretation. The equipment shall allow attachment of a motion sensing device capable of measuring acceleration, velocity or displacement due to the impact of the pile top with a hand held hammer.
A hand-held hammer and accelerometer is also require to perform this test.
Procedures 1. Low strain integrity testing should only be carried out on cast-in-situ piles after 7 days or more from the data of pile casting unless otherwise approved. 2. The contractor shall ensure that the pile head shall be clean, free from water, laitance, loose concrete, over spilled concrete and blinding concrete and be re adily accessible for the purpose of testing by the specialist engineer. 3. An area on the pile head is cleaned and the accelerometer (which is connected to the PIT-Collector) is attached onto the pile by an adhesive medium (Vaseli ne or grease). 4. A hand-held rubber tip hammer is impacted on to the pile top to generate a “low strain” compressive impact wave. The PIT-Collector will graphically display the velocity records.
5. Testing method depends on the shape of the pile. For square piles, testing point is located at the middle of the pile where the hammer impact is focused about a quarter distances away from the accelerometer.
6. For spun piles (piles with hollow section in the middle), testing should be carried out in 3 equally spaced out points where the hammer impact should not be too close to the accelerometer.
7. For cast-in-place piles or bored piles, testing should be done as in the configuration below:
8. The make-up of a pile should be properly checked to see whether the failing zones lie in the joints at the pile or along the pile body.
Analysis of Test Results – Pile Integrity Test After raw data in accelerometer is obtained, the acceleration values are integrated to obtain velocity signals. The velocity signals are then plotted against time. The velocity against time graph is displayed on reflectogram which is the device connected to the accelerometer. In general, a sharp deflection on the graph indicates a change in impedance which means there is a significant change in the pile cross section while a gradual and slower change is due to the soil. In respect to the reflectogram, an impedance decrease resulting in positive wave which usually indicates presence of soft toe, while impedance increase resulting in negative wave indicates hard toe. Below are typical reflectogram on different pile profile:
Figure: Typical Reflectograms
Limitations - Pile Integrity Test There are some limitations to Pile Integrity Test whereby reflection of wave may not be detected if small and gradual changes to cross section of the pile existed. The 2 figures shown below explain type of pile defects not detectable in Pile Integrity Test and ones that are detectable.
Figure: Defects Not Detectable in Pile Integrity Test
Figure: Defects Detectable in Pile Integrity Test
Ultrasonic Pulse Velocity Test (UPV) Introduction This test is done to assess the quality of concrete by ultrasonic pulse velocit y method as per IS: 13311 (Part 1) – 1992. The underlying principle of this test is the method consists of measuring the time of travel of an ultrasonic pulse passing through the concrete being tested. Comparatively higher velocity is obtained when concrete quality is good in terms of densit y, uniformity, homogeneity etc. Applicable On: ( Beams, Bridge Decks, Elevated Slabs, Shaft Tops and Walls ) Test For: ( Cracks, Delaminations, Honeycomb, Velocity vs. Strength Correlation with Cores and Void ) Objectives
Determine the quality and condition of surface and interior concrete in t he dry or underwater.
Locate Honey Combs and Voids in Concrete
Locate Cracks in Concrete, Ceramics, Masonry or Stone
Determine Fire Damage Extent in Concrete or Masonry
Crack Depth Determination
Determining Young's Modulus ( with optional Shear Wave Transducers )
Find Hidden Areas of Rotting Woodultrasonic
Predict strength of early age concrete
Methodology The UPV methodology relies on direct arrival of compressional waves, which are generated by sources with resonant frequencies ranging from 50 to 150 kHz. The highest resonant frequency sources/receivers are typically used with thinner structural members for higher resolution and smaller anomaly identification. The test is performed by positioning the source and receiver on either side of the area, then the source sends a compressional wave through the region, and the receiver records the full waveform on the other side. The position of the two transducers can be varied such that direct, semi-direct, and indirect tests can be performed, which aids in mapping out the volume of the defect. Further tests can be performed if the user wishes to generate a 3-D rendering of the volume. This is done by testing many different “paths” through the medium and then using a tomographic inversion program to generate a model.
Method The instrument has an easy to view display (320 by 240 pixels). The backlit for daylight use, makes field work easier and faster, since the operator can identify good results in seconds without the problems related with the sun light reflection on the screen. The signals can be recorded in the instrument for review on the screen or for transfer to a PC. Typically, the 54 KHZ transducers are used for concrete test ing, the signal wavelength is about 75mm ( 3 inches ). Finer materials require higher frequencies for optimum resolution. The basic V-Meter contains a transmitter, a receiver and a very accurate high speed electronic clock. The transmitter generates an electrical pulse which when applied to a transmitting transducer, converts the electrical energy into a pulse of ultrasonic mechanical vibration. This vibration is coupled with the specimen under test by placing the transducer in contact with the specimen. At another selected point on the specimen another receiving transducer is coupled by mechanical contact. Each transmitted pulse of energy registers on the high speed clock. Conventional UPV testing requires access to two surfaces, preferably two parallel surfaces such as the top and bottom surfaces of a slab or the inside and outside surfaces of a wall. This test can be performed, however, using the indirect method which does not require access to two surfaces. The first energy wave reaching the receiving transducer is converted back to an electrical signal and turns off the clock. The elapsed time is displayed on the LCD in 0.1 microsecond increments. The unit can also display and store the resulting waveform. This ensures the operator that a proper acoustic contact has been made with the surface of the material under test. In defect areas, the compressional wave velocity is slower than in sound areas and signal amplitude is often lower. For stru ctural members containing large, severe voids, signal transmission may be completely lost. In some defect ar eas, such as honeycombs, the compressional wave velocity may be almost the same as in sound areas, but distortion of the signal (filtering of high frequencies) ma y be used as an indication of a honeycomb defect. The standard transducers for the V-Meter are made for a 54 KHz high Q resonant frequency with a stainless steel housing. The connector is a ninety degrees to the face of the transducer to facilitate operation and getting proper acoustic contact. A push button and special cable are added to the reciever in order to store data while taking readings. The data can later be uploaded to a computer via the software. An adaptor is provided to utilize the reciever with standard co-axial cable. The ultrasonic transducers are typically used in one of three configuartions, direct, semidirect and indirect mode. Direct is the most sensitive method as the receiving transducer will receive maximum energy from the transmitted pulse. Since the longitudinal pulses leaving the transmitter are propagated mainly in the direction normal to the transducer face. The travel time is affected by the concrete condition along the thickness of the member. Semidirect transmission is performed with transducers on adjacent faces. This is the next preferred method. Finally, In-Direct the least preferred with the transducers on the same face. This should be used only when it is impossible to have access to two faces of the material under test. The received amplitude of the method, for the s ame path length, is only about 2% of that
received signal when using the direct method. Testing for shear waves can only be performed with the In-Direct method, with both transducers on the same face as the specimen under test. Apparatus The apparatus for ultrasonic pulse velocity measurement shall consist of the following; 1. 2. 3. 4.
Electrical pulse generator. Transducer – one pair Amplifier. Electronic timing device.
Procedures Procedure to determine strength of hardened concrete by Ultrasonic Pulse Velocity. i) Preparing for use: Before switching on the „V‟ meter, the transducers should be connected to the sockets marked “TRAN” and ” REC”.The „V‟ meter ma y be operated with either: a)the internal battery, b) an external battery or c) the A.C line. ii) Set reference: A reference bar is provided to check the instrument zero. The pulse time for the bar is engraved on it. Apply a smear of grease to the transducer faces before placing it on the opposite ends of the bar. Adjust the „SET REF‟ control until the reference bar transit time is obtained on the instrument read-out. iii) Range selection: For maximum accuracy, it is recommended that the 0.1 microsecond range be selected for path length upto 400mm. iv) Pulse velocity: Having determined the most suitable test points on the material to be tested, make careful measurement of the path length „L‟. Apply couplant to the surfaces of the transducers and press it hard onto the surface of the material. Do not move the transducers while a reading is being taken, as this can generate noise signals and errors in measurements. Continue holding the transducers onto the surface of the material until a consistent reading appears on the display, which is the time in microsecond for the ultrasonic pulse to travel the distance „L‟. The mean value of the display readings should be taken when the units digit hunts between two values. Pulse velocity=(Path length/Travel time) v) Separation of transducer leads: It is advisable to prevent the two transducer leads from coming into close contact with each other when the transit time measurements are being taken. If this is not done, the receiver lead might pick-up unwanted signals from the transmitter lead and this would result in an incorrect display of the transit time.
Interpretation of Results
The quality of concrete in terms of uniformity, incidence or absence of internal flaws, cracks and segregation, etc, indicative of the level of workmanship employed, can thus be assessed using the guidelines given below, which have been evolved for characterizing the quality of concrete in structures in terms of the ultrasonic pulse velocity.
Dye Penetrant Inspection (DPI) Dye penetrant inspection (DPI) can also be referred as liquid penetrant inspection (LPI), is a method vastly used and the most cost efficient method to locate surface-breaking defects in all non-porous materials. The penetrant may be applied to all non-ferrous materials and ferrous materials; although for ferrous components magnetic-particle inspection is often used instead for its subsurface detection capability. LPI is used to detect casting, forging and welding surface defects such as hairline cracks, surface porosity, leaks in new products, and fatigue cracks on in-service components. Materials used
Basic materials needed for a simple dye penetration test are;3 aerosol spray cans, some lint free cloths, and adequate visible light(UV). Penetrants are classified into sensitivity levels.
Visible penetrants are normally seen red in colour, they represent the lowest sensitivity. The smaller defects can be identify wen the emit brilliant yellow-green colour. The fluorescent penetrants are done in darkened environment. The dye contains two or more colours which will unleash themselves when the ultraviolet (UV) shown to them. Factors affecting the test
When selecting a sensitivity level one must consider many factors, including the environment under which the test will be performed, the surfac e finish of the specimen, and the size of defects sought. One must also assure that the test chemicals are compatible with the sample so that the examination will not cause permanent staining, or degradation. This technique can be quite portable, because in its simplest form the inspection requires only 3 aerosol spray cans, some lint free cloths, and adequate visible light. Stationary systems with dedicated application, wash, and development stations, are more costl y and complicated, but result in better sensitivity and higher samples through-put.
Below are the main steps of Liquid Penetrant Inspection: 1. Pre-cleaning:
The test surface is cleaned to remove any dirt, paint, oil, grease or any loose scale that could either keep penetrant out of a defect, or cause irrelevant or false indications. The cleaning methods may include solvents, alkaline cleaning steps, vapor degreasing, or media blasting. The main idea is we need a clean surface where any defects present are open to the surface, dry, and free of contamination. 2. Application of Penetrant:
The penetrant is then applied to the surface of the item being tested. The penetrant is given a "dwell time" to soak into any flaws (generally 5 to 30 minutes). The dwell time depends on the penetrant which is used, material being tested and the size of each flaws. As we know the smaller flaws will need a longer penetration time. 3. Excess Penetrant Removal:
The excess penetrant should be removed from the surface. The removal method is determined by the type of penetrant used. Water-washable, solvent-removable, lipophilic postemulsifiable, or hydrophilic post-emulsifiable are the common penetrant removals. Emulsifiers represent the highest sensitivity level, and chemically interact with the oily penetrant to make it removable with a water spray. When using solvent remover and lintfree cloth it is important to not spray the solvent on the test surface directl y, because this can remove the penetrant from the flaws. If excess penetrant is not properly removed, once the developer is applied, it may leave a background in the developed area that can mask indications or defects. In addition, this may also produce fals e indications severely to your ability to do a proper inspection. 4. Application of Developer:
After excess penetrant has been removed, a white developer is applied to the sample. Several developer types are available, including: non-aqueous wet developer, dry powder, water suspendable, and water soluble. Choice of developer is detemined by penetrant‟s compatibility and by inspection conditions. When using non-aqueous wet developer (NAWD) or dry powder, the sample must be dried prior to application, while soluble and suspendable developers are applied with the part still wet from the previous step. NAWD is commercially available in aerosol spray cans, and may employ acetone, isopropyl alcohol, or a propellant that is a combination of the two. Developer should form a semi-transparent, even coating on the surface. The developer draws penetrant from defects out onto the surface to form a visible indication, commonly known as bleed-out. Any areas that bleed-out can indicate the location, orientation
and possible types of defects on the surface. Interpreting the results and characterizing defects from the indications found may require some training and/or experience. 5. Inspection:
The inspector will use visible light with adequate i ntensity (100 foot-candles or 1100 lux is typical) for visible dye penetrant. Ultraviolet (UV-A) radiation of adequate intensity (1,000 micro-watts per centimetre squared is common), along with low ambient light levels (less than 2 foot-candles) for fluorescent penetrant examinations. Inspection of the test surface should take place after a 10 minute development time. This t ime delay allows the blotting action to occur. The inspector may observe the sample for indication formation when using visible dye. It is also good practice to observe indi cations as they form because the characteristics of the bleed out are a significant part of interpretation characterization of flaws. 6. Post Cleaning:
The test surface is often cleaned after inspection and recording of defects, especially if postinspection coating processes are scheduled.
Aerosol Cans
Dye penetration steps
Conclusion Nondestructive testing is a form of materials testing used when the materials being examined cannot be destroyed in the process of testing. This t ype of testing is used when permanently changing the material during testing is not an option for any number of reasons from safety to expense. In some cases, it may reveal the need for more thorough testing methods, some of which could cause permanent alteration or damage. Turning to nondestructive testing first can save money and increase efficiency on a project. People can also use techniques like covering something in a penetr ant and then imaging it. If the material is sound, the penetrant will lie on the surface. If there are cracks, holes, and other issues, it can seep inside, spreading through the material. This will not endanger the substance, and the penetrant can be easil y removed after testing. Nondestructive testing also includes standard activities like weighing and measuring the material, collecting information about how light refracts off it, and using chemical sniffing to learn more about its composition.
