Pull out test

Principle of Test : Involve the measurement of the force requirewd to extract a metal insert from within the concrete against a reaction ring .

- Because of its shape , the steel rod is pulled out with a cone of the concrete .
- The concrete is simultaneously in tension & in shear , the generated lines of the cones running at about 45 degree to the direction of pull .

- The pull-out force is then related to the compressive strength of the concrete .
- The most reliable method of obtaining the strength of concrete in a structural member is the cutting of cores for subsequent preparation & crushing in a laboratory .

- Cores are to be of 50 to 200mm diameter & at least 100mm depth .

- After trimming & capping to provide parallled end faces , cores should be stored in water for at least 48 hours prior to testing .

- Besides compressive strength test , cores can be tested for the following :

• Visual inspection for surface conditions , depth of deterioration , fractures , unsual deposits , colouring or staining , voids & other features . 
• Tensile strength . 
• Transverse , longitudinal & torsional frequencies . 
• Static modulus of elasticity 
• Chemical tests on mix proportions , chloride content & other properties . 
• Concrete cores are partially destructive & care shouyld be taken to ensure that the integrity of the structure is not adversely affected by the coring .