What is the procedure and formula of core cutting test of concrete and bituminous?

Answer 1

(hope this help)

75mm, 100mm or 150mm diameter cores are taken on site using state of the art core cutting machines. Cover meter is used to locate the reinforcement steel before core cutting. This prevents structural damage to the RCC member by avoiding the reinforcement. These cores are dressed in our lab and tested using standard compression testing methods to determine compressive strength and arrive at equivalent cube strength of concrete.

IS Codes applicable: IS : 456 / IS : 516 / IS : 1199

Applications:

Assessment of strength.

Study of aggregates used in the mix design.

Assessing probable causes of failures/problems.

Equipment Used:

Core cutter.

Core compression testing machine.

Test basis:

A core sample is the actual representation of the material used in the structural element. When processed and subjected to load, it fails at a particular load, giving a fair idea of its compressive strength.

Methodology:

Step1: Reinforcement Mapping.

By using a special instrument, based on eddy currents, the reinforcements are mapped in the structural member.

Step 2: Core cutting.

Cores are taken using special diamond cutters of 75 mm, 100 mm or 150 mm diameter. Locations are selected to avoid steel so as to minimize the damage to the structure.

Step 3: Dressing.

The edges of the core are smoothend using grinding and cutting wheels and epoxy mortar is applied on both sides for capping. This ensures that the ends are approximately at 90% to the axis and are within 0.05 mm plane ness.

Step 4: Immersion in water

The core samples are immersed in water for 48 hours. The cores are weighed before and

after immersion.

Step 5: Compression testing.

The cores are then subjected to compression forces on compression testing machine. The breaking point is observed.

Step 6: Reporting.

Based on the lab report, sizes of the core etc. an equivalent cube strength is calculated for the concrete applying necessary correction factors. The density, core strength and equivalent cube strength are reported.

Influencing factors:

Core diameter and length (h / d ratio)

Proper capping and hydration of the cores as per IS code.

Old/new/Mixed (jacketed) concrete.

Understanding results:

The result is normalized for comparison with compressive test results of a standard cube. This is done so that the cube results can be compared with the core results. Standard correction factors as per IS code are used for this purpose. This value may not be the same as the core strength.

Following are the factors which affect the compressive strength of extracted concrete cores:

Size of stone aggregate: If the ratio of diameter of core to maximum size of stone aggregate is less than 3, a reduction in strength is reported. For concrete with 20mm size aggregate, 50mm dia core has been tested to give 10% lower results than with 10mm dia cores.

Presence of transverse reinforcement steel: It is reported that the presence of transverse steel causes a 5 to 15% reduction in compressive strength of core. The effect of embedded steel is higher on stronger concrete and as its location moves away from ends, i.e. towards the middle. However presence of steel parallel to the axis of the core is not desirable.

H/D ratio: This has been already discussed above. However its value should be minimum 0.95 and maximum 2. Higher ratio would cause a reduction in strength.

Age of concrete: No age allowance is recommended by the Concrete Society as some evidence is reported to suggest that in-situ concrete gains little strength after 28 days. Whereas others suggest that under average conditions, the increase over 28 days' strength is 10% after 3 months, 15% after 6 months. Hence it is not easy to deal the effect of age on core strength.

Strength of concrete: The effect in reducing the core strength appears to be higher in stronger concretes and reduction has been reported as 15% for 40 MPa concrete. However a reduction of 5 50 7% is considered reasonable.

Drilling operations: The strength of cores is generally less than that of standard cylinders, partly as a consequence of disturbance due to vibrations during drilling operations. Whatever best precautions are taken during drilling, there is always a risk of slight damage.

Site conditions vis-a-vis standard specimens: Because site curing is invariably inferior to curing prescribed for standard specimens, the in-situ core strength is invariably lower than the standard specimens taken and tested during concreting operations.

Engineer Muhammad Mubashir

Refrences

http://theconstructor.org/concrete/core-sampling-and-testing-of-concrete/2865/

http://www.aaryanengineers.com/core_testing.html