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AfzalWaseem 2007-Civil-87

PARTIALLY DESTRUCTIVE TESTSThe more recently introduced partially destructive tests. In the latter

category the pull-off test involves bonding a circular steel probe to theconcrete surface using an epoxy resin adhesive which is strongerthan concrete in tension. By measuring the load required to cause atensile failure in the concrete the equivalent compressive strengthcan be estimated by using an appropriate calibration graph. Thispaper summarizes the results of tests carried out over the past nineyears and includes a comparison with other partially destructivemethods which are currently available. The results of field tests,carried out during the construction of a multi-storey parking garage,are reported as well as two case histories relating to commercial

applications. In all instances the viability and accuracy of this in-situtest method have been proven.Journal ACIDocument Name: SP82-17Author(s): A.E. Long and A. McC. Murray

NON-DESTRUCTIVE TESTING OF CONCRETEThe standard method of evaluating the quality of concrete in buildings

or structures is to test specimens cast simultaneously forcompressive, flexural and tensile strengths. The main disadvantagesare that results are not obtained immediately; that concrete inspecimens may differ from that in the actual structure as a result ofdifferent curing and compaction conditions; and that strengthproperties of a concrete specimen depend on its size and shape.

Although there can be no direct measurement of the strengthproperties of structural concrete for the simple reason that strengthdetermination involves destructive stresses, several non- destructivemethods of assessment have been developed1. These depend onthe fact that certain physical properties of concrete can be related tostrength and can be measured by non-destructive methods. Suchproperties include hardness, resistance to penetration by projectiles,rebound capacity and ability to transmit ultrasonic pulses and X- andY-rays. These non-destructive methods may be categorized aspenetration tests, rebound tests, pull-out techniques, dynamic tests,

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Submitted to Sir. Ali Ahmed Destructive and Non Destructive testing Methods

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radioactive tests, maturity concept. It is the purpose of this Digest todescribe these methods briefly, outlining their advantages anddisadvantages.

Penetration TestsThe Windsor probe is generally considered to be the best means oftesting penetration. Equipment consists of a powder-actuated gun ordriver, hardened alloy probes, loaded cartridges, a depth gauge formeasuring penetration of probes and other related equipment. Aprobe, diameter 0.25 in. (6.5 mm) and length 3.125 in. (8.0 cm), isdriven into the concrete by means of a precision powder charge.Depth of penetration provides an indication of the compressivestrength of the concrete. Although calibration charts are provided bythe manufacturer, the instrument should be calibrated for type of

concrete and type and size of aggregate used.Limitations and Advantages.The probe test produces quite variable results and shouldnot be expected to give accurate values of concrete strength. It has,however, the potential for providing a quick means of checking qualityand maturity of in situ concrete.It also provides a means of assessing strength development withcuring. The test is essentially non-destructive, since concrete andstructural members can be tested in situ, with only minor patching ofholes on exposed faces.

Rebound TestsThe rebound hammer is a surface hardness tester for which anempirical correlation has been established between strength andrebound number. The only known instrument to make use of therebound principle for concrete testing is the Schmidt hammer, whichweighs about 4 lb (1.8 kg) and is suitable for both laboratory and fieldwork. It consists of a spring-controlled hammer mass that slides on aplunger within a tubular housing.

The hammer is forced against the surface of the concrete by thespring and the distance of rebound is measured on a scale. The testsurface can be horizontal, vertical or at any angle but the instrumentmust be calibrated in this position.Calibration can be done with cylinders (6 by 12 in., 15 by 30 cm) ofthe same cement and aggregate as will be used on the job. Thecylinders are capped and firmly held in a compression machine.

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Submitted to Sir. Ali Ahmed Destructive and Non Destructive testing Methods

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Several readings are taken, well distributed and reproducible, theaverage representing the rebound number for the cylinder. Thisprocedure is repeated with several cylinders, after which compressivestrengths are obtained.Limitations and Advantages.The Schmidt hammer provides an inexpensive, simple and quickmethod of obtaining an indication of concrete strength, but accuracyof 15 to 20per cent is possible only for specimens cast cured andtested under conditions for which calibration curves have beenestablished. The results are affected by factors such as smoothnessof surface, size and shape of specimen, moisture condition of theconcrete,type of cement and coarse aggregate, and extent ofcarbonation of surface.Journal ACI

Document Name: CBD-187Author(s): R.F. Feldman

DESTRUCTIVE TEST

Can be done for testinga) Compression strength concrete

- Cube testb) Tensile strength of concrete

- Direct Tension Test- Split-Cylinder Test- Flexural Test

c) Flexural StrengthCube Test

Concrete cube testing is a primary quality compliance check onthe specified design characteristic compressive strength ofconcrete mix supplied to the site. Concrete cube is prepared byplacing 3 layer of concrete in the mould. Each layer is compacted

using rod for 35 times. Then it is cured in a tank of water for 7, 14and 28 days. On the 7th day, cube will be taken out forcompressive strength test.

SPLIT CYLINDER TEST (ASTM 496)1. A cylinder specimen of minimum 2-in. (50mm) dia, placedwith its axis in a horizontal plane.

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2.Then it is subjected to a uniform load along the length of thespecimen.

3.Logically, the load will split to 2 parts (P), so the tensilestrength can be calculated as

ft = 2P / ldl = length of the cylinder

d = diameter of the cylinder

4. The type and shape of coarse aggregate particles also affect thetensile strength.5. Split Cylinder Test to determine the tensile strength of concrete bysplitting cylinders of the concrete in a compression testing machine.

References

Topic Partially Destructive TestingJournal ACIDocument Name: SP82-17Author(s): A.E. Long and A. McC. Murray

Topic Non Destructive TestingJournal ACIDocument Name: CBD-187Author(s): R.F. Feldman

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Submitted to Sir. Ali Ahmed Destructive and Non Destructive testing Methods