🕑 Reading time: 1 minuteVarious tests on Hardened Concrete is done to ensure the design strength of concrete and quality of concrete construction is achieved.
- Tests on Hardened Concrete
- Destructive Tests on Hardened Concrete
- Non-Destructive Tests on Concrete
- Chemical Tests on Hardened Concrete
Tests on Hardened ConcreteThe test conducted on hardened concrete can be classified into two main categories:
- Destructive Tests on Concrete
- Non-destructive Tests on Concrete
- Chemical Test on Concrete
Destructive Tests on Hardened ConcreteThe common destructive tests conducted on concrete are: The main destructive tests on hardened concrete are as follows.
1. Concrete Cube TestConcrete Characteristics is determined by characteristics compressive cube strength test of concrete.For cube test two types of specimens either cubes of 15cm X 15cm X 15cm or 10cm X 10cm x 10cm depending upon the size of aggregate are used. For most of the works cubical moulds of size 15cm x 15cm x 15cm are commonly used. These specimens are tested by compression testing machine after 7 days curing or 28 days curing. Load should be applied gradually at the rate of 140 kg/cm2 per minute till the Specimens fails. Read More:Cube Test on Concrete
2. Tensile Strength TestThe concrete structures are highly vulnerable to tensile cracking and hence the determination of tensile strength of concrete is very important. The tensile strength of concrete structures is determined by:
2.1 Split Cylinder TestHere, the tensile strength is determined indirectly. The test is performed based on IS: 5816 – 1970. The test specimen employed is 30cm x 15cm which is placed over a compression testing machine.The load is applied over the specimen diametrically and uniformly through the cylinder length till the cylinder undergoes failure. The failure of the cylinder will be along the diameter in vertical direction. Between the specimen and the loading plates, plywood strips are placed to avoid direct stress due to direct point of application. The tensile stress formed with the progress of load will split the cylinder into two halves. The splitting takes place along the vertical plane. This is caused due to the indirect tensile stress caused. Let the tensile stress created that results in splitting be ft . If ‘P’ is the compressive load at the failure, “L” is the cylinder length and diameter of the cylinder being ‘D’,
2.2 Flexure TestThe guidelines for performing the flexure test are as per BS 1881: Part 118: 1983. Here a concrete beam specimen of dimension 15x15x75 cm is loaded. The span of the beam specimen must be three times the depth. As shown in the figure below, equal load application is done at one-third distance from the end supports. The reactions are equal at the support. The bottom beam fiber experiences an increase in stress with the increase in load application. The increase of stress is at a rate of 0.02 MPa & 0.10 MPa. For low strength concrete, we make use of low rate and for high strength, we use high rate. 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. Modulus of Rupture is given by,
3. Core Strength TestCylindrical 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.
Non-Destructive Tests on ConcreteThe main non-destructive tests for strength on hardened concrete are as follows.
- Rebound Hammer (Hardness Test)
- Ultrasonic Pulse Velocity Test
- Pull Out Test
- Penetration Resistance
- Other non-destructive tests
3.Pull Out TestThe pull-out test will determine the force that is required to pull out a steel rod specially shaped from hardened concrete to which the steel was cast. Pulling out of steel is done with a cone of concrete that has a slope of 45 degrees. The force required to pull the concrete out is related with the compressive strength of the concrete.
5. Other non-destructive testsEquipment has been developed to measure
- Crack widths and depths
- Water permeability and the surface dampness of concrete
- Depth of cover and the location of reinforcing bars
- The electrochemical potential of reinforcing bars and hence the presence of corrosion
Chemical Tests on Hardened ConcreteA complete range of chemical tests is available to measure
- Depth of carbonation
- The cement content of the original mix
- The content of salts such as chlorides and sulfates that may react and cause the concrete to disintegrate or cause corrosion of the reinforcement
- Alkali Content