ndt presentation short

7/31/2019 NDT Presentation Short

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The major objective of this virtual meeting is to introduce the standards developedy u comm ttee 09.64 o omm ttee 09 on oncrete an oncrete

Aggregates.

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There are additional references to provide more information on the methods to bescusse . wo o t ese re erences are reports y omm ttee 228 on

Nondestructive Testing of Concrete. ACI 228.1R covers methods to estimate in-place strength, and ACI 228.2R deals with other nondestructive test methods.

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ASTM C215 is a laboratory method for measuring the resonant frequency of testspec mens. wo met o s may e use : orce resonance an mpact resonance.

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This is a schematic of the forced resonance method. The specimen is vibrated aterent requenc es an t e amp tu e o t e v rat on s measure . meter

indicates the vibration amplitude. When the applied frequency is the resonantfrequency, the amplitude of vibration will be at its maximum value.

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This shows the principle of the impact resonance method. The specimen is struckw t a sma ammer an t e resu t ng v rat on s measure y a trans ucer. esignal is analyzed and the resonant frequency of the specimen is determined. Theimpact method is simpler and faster to use than the forced resonance method.

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The method allows for measuring the resonant frequency for three vibrationalmo es: ong tu na , exura , an tors ona . rom t e measure requency, t eshape, and the mass of specimen, we can calculate the dynamic modulus ofelasticity.

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The method is used to monitor changes to specimens exposed to deteriorationmec an sms.

The dynamic modulus is greater than the static modulus measured by ASTM C469.

Results depend on how specimen is made.

Results from different specimens should not be compared.

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This shows an example of a system for the impact resonance method. On the rightare t e resu ts o t ree tests. e grap s are amp tu e versus requency an t epeak corresponds to the resonant frequency. The test has excellent repeatability.

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ASTM C597 measures the time for a pulse of vibrational energy to travel over anown pat engt .

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The instrumentation includes two transducers held on opposite sides of a member.grease- e mater a s use to coup e t e trans ucers so t at t e v rat ona

energy enters the member. The control unit includes a pulser and a timer. Thepulser excites the transmitter and the timer measures the travel time. The pulsevelocity is calculated from the travel time and distance between the transducers.

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This is an example of an instrument for measuring travel time. The two graphsustrate ow trave t me s measure . en t e s gna n t e rece ver reac es a

threshold level, the timer shuts off and the elapsed time is displayed on the unit. Theunits are in microseconds.

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The direct path is the best method, but when it is not possible a semi-direct path isaccepta e ut t e e ect ve pat engt s not nown prec se y an t e amp tu e othe received signal is reduced.

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The pulse velocity is a function of the elastic constants and density of the concreteas n cate y t e equat on.

The method is useful to assess the uniformity and relative quality of concrete in astructure.

Moisture content affects the velocity.

There is a minimum specimen size that can be tested, which is based on thefrequency of the transducers.

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Path length has to be measured accurately and good coupling is needed.

Not reliable for estimating strength or assessing in-place elastic modulus.

The method can be used in the field and in the laboratory.

Need to avoid bars aligned with travel path.

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This shows how the method is used to assess uniformity. A grid is marked onoppos te aces o t e mem er. easurements are one at eac gr po nt.

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We plot the velocity contours and the uniformity can be assessed. Note thatn most mem ers t e ottom w ave a g er ve oc ty ue to ettercompaction.

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Test Method C803/C803M measures the resistance to penetration of a steel rod or asma er p n t at s r ven nto t e concrete. t can e use to est mate n-p acestrength using a previously established strength relationship.

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This shows the driver and the probe that will driven into the concrete. The driver is agun.

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This shows the two types of probes that are used, and the explosive charge used tor ve a pro e nto t e concrete.

The upper probe is for lightweight concrete or low strength concrete.

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The driver has to be pressed against a template in order to be fired.

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This shows the probe after it has been embedded into the concrete. The exposedengt o t e pro e s measure . e stronger s t e concrete, t e greater s t eexposed length.

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This is a cylinder that was cut in half after a penetration test. The initial energy oft e pro e s a sor e y r ct on, energy to racture t e coarse aggregate, anenergy to fracture the mortar. Of these, only the fracture of mortar is related toconcrete strength. For equal concrete strength, penetration is affected by theaggregate type.

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The penetration method can be used to assess uniformity or locate deterioratedconcrete.

It can be used to estimate strength with a previously established relationship.

As mentioned, penetration is affected by aggregate type.

Surface damage has to be repaired for tests on exposed surfaces.

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This is an example of a strength relationship. Penetration was measured on a slabspec men an t e compress ve strengt was measure us ng compan on cy n ers.At different ages the penetration was measured and sets of cylinders were testedfor compressive strength

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This shows how aggregate type affects the strength relationship. For a given valueo expose engt , t e ar er t e aggregate t e ower w e t e concrete strengt .Thus is it very important to use same coarse aggregate to develop the strengthrelationship as will be used in the concrete to be placed in structure.

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ASTM C805/C805M is the rebound number test, which measures the rebound of amass t at str es a stee ro n contact w t t e concrete sur ace.

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This slide shows a rebound number test being performed. The button is used tore ease t e nstrument rom t s oc e pos t on an to oc t e nstrument a ter arebound test so that the rebound number can be read.

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This shows the operation of the rebound hammer. As the instrument is pushed, aspr ng attac e to t e ammer s stretc e . e ammer s re ease an str es t eshoulder of the rod in contact with the concrete. The mass rebounds and therebound distance is measured on a scale from 10 to 100. The test specimen has tobe firmly supported so that it does not move during the test.

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The rebound number is read on the scale. The numbers represents the percentageo t e or g na stance rom t e ammer to t e s ou er o t e ro . o a re ounnumber of 41 means the rebound distance is 41 % of the original distance.

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This slide illustrates the effects of near surface conditions on rebound number. Anaggregate part c e e ow t e sur ace w resu t n a g re oun ; w ereas an a rbubble below the surface will result in a low rebound number. A rough texturedsurface will reduce the rebound number. A dry or carbonated surface layer willincrease rebound number. The first two conditions can be taken care of by ignoring

outliers. The latter two factors result in systematic errors.

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The rebound hammer is a good tool for assessing uniformity.

To estimate in-place strength, the strength relationship has to be developed bymeasuring strengths of cores from the structure.

As mentioned there are several factors that affect the rebound number.

Rebound may be affected by the instrument that is used.Not suitable for acceptance or rejection of concrete.

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Here is an example of a strength relationship based on cores taken from thestructure. or t s examp e, t e scatter s g er t an or t e pro e penetrat on testexample that was shown.

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For the cast-in-place tests, the insert is attached to formwork and concrete isp ace .

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When in-place strength is to be estimated, supporting hardware is removed, and thensert s pu e out us ng a tens on ac react ng aga nst a ear ng r ng.

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Load is increased until a conical fragment is extracted. The maximum force attainedur ng t e extract on s use to est mate t e n-p ace compress ve strengt . e

reaction ring forces the failure to occur in well defined and repeatable pattern.

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On the left, we see the pullout test being performed. In this case, the insert wasp ace n t e top sur ace o t e s a . y turn ng t e an e, a tens e orce pu s onthe shaft of the insert. On the right is the conical fragment that is extracted.

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The strength relationship must be established for the concrete to be used.

The method can be used during construction to determine if the in-place strength issufficient for different construction activities.

The post-installed test can be used on existing structures.

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Consideration should be given to the fact that the bottom of a placement will havegreater strengt .

Because of the size of the insert that is commonly used, strength in the outer 25 mmis estimated.

Careful planning is required so that tests will provide the best information.

Not applicable to other types of pullout tests that do not produce the same failuremechanism.

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The strength relationship can be established by casting a set of cylindersan cu es. our nserts are p ace on t e aces o t e cu es.

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The photo shows a cube being made with an insert on each face. At regulart me nterva s, we measure t e strengt o at east two cy n ers an at east8 pullout tests. At least 6 strength levels should be used.

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Here is an example of a strength relationship for a specific concrete. Note that the 6strengt eve s are we str ute . e manu acturer s recommen e re at ons p salso shown, and it is consistent with the relationship obtained for this specificconcrete mixture.

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The maturity method allows us to estimate the in-place strength based onmeasur ng t e n-p ace temperature an us ng a prev ous y esta s e strengtrelationship.

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The maturity rule states that samples of the same concrete subjected to differentcur ng temperatures w ave approx mate y equa strengt t ey ave t e samematurity index. The maturity index is the number calculated from the measuredtemperature. There are two ways to calculate the maturity index:

Temperature-time factor

Equivalent age at reference temperature

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The white curve represents the in-place temperature history of the concrete.

The temperature-time factor is the area between this curve and a datumtemperature, and it can be approximated as indicated by the equation.

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The maturity method is useful as a tool to estimate in-place strength duringconstruct on to eterm ne w et er concrete s strong enoug or app y ngconstruction loads or stopping curing.

It can also be used as a planning tool to estimate strength development under non-standard curing temperatures.

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There are important limitations:

Moisture must be present for hydration, so it only applies when concrete isbeing cured.

It does not account for the effects of early-age temperature on long-termstrength

Because we only measure temperature, the maturity methods needs to besupplemented by other indications of potential strength of the concrete in thestructure.

Accuracy depends on using the correct maturity function.

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This slide summarizes how the maturity method is used. First, we have to establsiht e strengt -matur ty re at ons p or t e concrete m xture. en we p acetemperature sensors in the structure and measure the temperature history. When astrength estimate is required, we read the maturity meter, and estimate the strengthfrom the strength-maturity relationship.

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Here we see specimens being cured for determining the strength-maturityre at ons p. ome spec mens are connecte to matur ty meters. t regu ar t meintervals, we read the meter and measure the strength of at least two specimens. Inthis case, beams are also being tested.

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Here is an example of a strength-maturity relationship. Note that thestrengt s are even y str ute . s curve s or a spec c concretemixture.

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Here we see an engineer reading the maturity meter to determine if the concrete isstrong enoug to remove t e ormwor .

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The last method to be discussed is the impact-echo method for measuring thet c ness o p ate- e e ements. mpact-ec o s anot er met o ase on stresswaves.

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The impact-echo method uses a short duration impact to create a stress wave thattrave s nto t e concrete an s re ecte rom t e oppos te sur ace. e trans ucermeasures the surface motion and by signal analysis we can determine the depth ifwe know the wave speed in the concrete.

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The method may be used to measure thickness of plate structures.

There is systematic error in the computed thickness because of the digital data thatis recorded.

We need to consider wave speed variability within structure.

The maximum and minimum thickness that can be measured depends oninstrumentation; limits need to be established for the instrument that is used.

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Some other limitations:

The method is not applicable when overlays are present.

The concrete surface needs to be air dry.

The sub-base has to have a slower wave speed than the concrete.

It should not be used if the structure is subjected to other impacts during testing.

It cannot be used when there is high electrical noise unless instrumentation is wells e e .

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A plate is a structure in which the two lateral dimensions are at least six times thet c ness.

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Two procedures are needed to measure thickness. Procedure A is used toeterm ne t e wave spee an roce ure s use to measure t e

thickness frequency.

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This shows how the wave speed is determined by using two transducers andmeasur ng t e t me t ta es or t e stress wave to trave rom one trans ucer to t eother transducer.

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Then we do tests at various points to measure the thickness frequencies andca cu ate t e t c ness s ev se as erent s ze mpactors to create mpactswith different durations. The duration has to be matched with the thickness your aretrying to measure. Smaller thickness requires a smaller impactor.

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Thank you for your attention, and thank you to all the individuals in ASTM ando om a or ma ng t s sem nar poss e. w e g a to answer quest ons.

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