Que4.17. Explain the colorful types of tests for compressive strength and tensile strength of concrete.
Answer Following are the colorful test used for determining compressive and tensile strength
1. Concrete cell Test Concrete specific is determined by characteristics compressive cell strength test of concrete.
ii. For cell test two types of samples either cells of 15 cm × 15 cm × 15 cm or 10 cm × 10 cm × 10 cm depending upon the size of total are used.
iii. For utmost of the workshop boxy moulds of size 15 cm × 15 cm × 15 cm are generally used.
iv. These samples are tested by contraction testing machine after 7 days curing or 28 days curing. cargo should be applied gradationally at the rate of 140 kg/ cm2 per nanosecond till the samples fails.
2. Tensile Strength Test
i. The concrete structures are largely vulnerable to tensile cracking and hence the determination of tensile strength of concrete is veritably important.
ii. The tensile strength of concrete structures is determined by Split cylinder test.
Flexure test.
3. Core Strength Test Cylindrical cores are cut from the finished structure with a rotary slice tool.
ii. The core is soaked, limited and tested in contraction to give a measure of the concrete strength in the factual structure.
iii. The rate of core height to periphery and the position where the core is taken affect the strength.
iv. The strength is smallest at the top face and increases with depth through the element.
v. A rate of core height- to- periphery of 2 gives a standard cylinder test.
Que4.18. Describe the flexure test and split tensile test of concrete.
Answer Flexure Test
1. The guidelines for performing the flexure test is as per BIS 1881 Part 118 1983.
2. Then a concrete ray instance of dimension 15 × 15 × 75 cm is loaded.
3. The span of the ray instance must be three times the depth.
4. As shown in theFig.4.18.1 equal cargo operation is done at one third distance from the end supports. The responses are equal at the support.
6. The increase of stress is at a rate of0.02 MPa and0.10 MPa.
7. For low strength concrete we make use of low rate and for high strength we use high rate.
8. The theoretical outside tensile stress at the nethermost face at failure is calculated.
This is nominated the modulus of rupture. It’s about1.5 times the tensile stress determined by the splitting test.
2. The test instance employed is 30 cm × 15 cm which is placed over a contraction testing machine.
3. The cargo is applied over the instance diametrically and slightly through the cylinder length till the cylinder undergoes failure.
4. The failure of the cylinder will be along the periphery in perpendicular direction.
5. Between the instance and the lading plates, plywood strips are placed to avoid direct stress due to direct point of operation.
6. The tensile stress formed with the progress of cargo will resolve the cylinder into two halves. The splitting takes place along the perpendicular aeroplane. This is caused due to the circular tensile stress.
Que4.19. Explain the colorful way involved in evaluation of compressive strength of concrete from medication to testing of sample.
Answer Following are the step for cell testing
1. cell Casting Measure the dry proportion of constituents( cement, beach and coarse total) as per the design conditions. The constituents should be sufficient enough to cast test cells.
ii. Completely mix the dry constituents to gain the invariant admixture.
iii. Add design volume of water to the dry proportion( water- cement rate) and mix well to gain invariant texture.
iv. Fill the concrete to the mould with the help of vibrator for thorough contraction.
Finish the top of the concrete by trowel and tapped well till the cement slurry comes to the top of the cells.
2. Curing
i. After some time the mould should be covered with red gunny bag and put unperturbed for 24 hours at a temperature of( 21 ± 2) °C.
ii. After 24 hours remove the instance from the mould.
iii. Keep the instance submerged under fresh water at 27 °C. The instance should be kept for 7 or 28 days. Every 7 days the water should be renewed.
iv. The instance should be removed from the water 30 twinkles previous to the testing.
v. The instance should be in dry condition before conducting the testing.
vi. The cell weight shouldn’t be lower than8.1 kg.
3. Testing
i. Now place the concrete cells into the testing machine( centrally).
ii. The cells should be placed rightly on the machine plate( check the circle marks on the machine). Precisely align the instance with the spherically seated plate.
iii. The cargo will be applied to the instance axially.
iv. Now sluggishly apply the cargo at the rate of 140 kg/ cm2 per nanosecond till the cell collapse.
v. The maximum cargo at which the instance breaks is taken as a compressive cargo.
4. computation Compressive Strength of concrete = Maximum compressive cargo Cross sectional area.
Que4.20. Describe the non destructive testing of hardened concrete.
Answer Non-Destructive Tests on Concrete The mainnon-destructive tests for strength on hardened concrete are as follows
1. Rebound Hammer( Hardness) Test
i. The Schmidt hammer is used in the answer hardness test in which a essence hammer held against the concrete is struck by another springdriven essence mass and rebounds.
ii. The quantum of answer is recorded on a scale and this gives an suggestion of the concrete strength.
iii. The larger the answer number is, the advanced is the concrete strength.
2. Ultrasonic Pulse Velocity Test
i. In the ultrasonic palpitation haste test the haste of ultrasonic beats that pass through a concrete section from a transmitter to a receiver is measured.
ii. The palpitation haste is identified against strength.
iii. The advanced the haste is, the stronger is the concrete.
3. Pull Out Test
i. The pull out test will determine the force that’s needed to pull out a sword rod especially shaped from hardened concrete to which the sword was cast.
ii. Pulling out of sword is done with a cone of concrete that have a pitch of 45 °.
iii. The force needed to pull the concrete out is related with the compressive strength of the concrete.
4. Penetration Resistance Test Penetration resistance tests on concrete offers a means of determining relative strengths of concrete in the same structure or relative strength of different structures.
ii. Because of nature of accoutrements , it can not be anticipated to yield absolute values of strength.