Various tests on Hardened Concrete is done to ensure the design strength of concrete and quality of concrete construction is achieved.
Normal tests on Hardened Concrete:
The main destructive tests on hardened concrete are as follows.
(a) Cube test: Compressive strength of hardened concrete is done by cube test. More details about Compressive strength tests on Concrete Cube.
(b) Tensile splitting test on concrete cylinders
(c) Flexure test
A plain concrete specimen is tested to failure in bending. The theoretical maximum tensile stress at the bottom face at failure is calculated. This is termed the modulus of rupture. It is about 1.5 times the tensile stress determined by the splitting test.
(d) Concrete core test:
Cylindrical cores are cut from the finished structure with a rotary cutting tool. The core is soaked, capped and tested in compression to give a measure of the concrete strength in the actual structure. The ratio of core height to diameter and the location where the core is taken affect the strength. The strength is lowest at the top surface and increases with depth through the element. A ratio of core height-to-diameter of 2 gives a standard cylinder test. Read more: Core Sampling and testing of concrete.
The main non-destructive tests for strength on hardened concrete areas follows.
(a) Rebound hammer (hardness) test
The Schmidt hammer is used in the rebound hardness test in which a metal hammer held against the concrete is struck by another spring-driven metal mass and rebounds. The amount of rebound is recorded on a scale and this gives an indication of the concrete strength. The larger the rebound number is, the higher is the concrete strength.
(b) Ultrasonic pulse velocity test
In the ultrasonic pulse velocity test the velocity of ultrasonic pulses that pass through a concrete section from a transmitter to a receiver is measured. The pulse velocity is correlated against strength. The higher the velocity is, the stronger is the concrete.
(c) Other non-destructive tests
Equipment has been developed to measure
1. Crack widths and depths
2. Water permeability and the surface dampness of concrete
3. Depth of cover and the location of reinforcing bars
4. The electrochemical potential of reinforcing bars and hence the presence of corrosion
Chemical tests on Concrete:
A complete range of chemical tests is available to measure
1. Depth of carbonation
2. The cement content of the original mix
3. The content of salts such as chlorides and sulphates that may react and cause the concrete to disintegrate or cause corrosion of the reinforcement