To determine the strength and quality of the cement used in the building, quality tests are performed on the material. Based on its performance and durability, cement can be used for a variety of purposes.
The following tests are conducted on cement in the laboratory are as follows:
- Fineness Test
- Consistency Test
- Setting Time Test
- Strength Test
- Soundness Test
- The heat of Hydration Test
- Tensile Strength Test
- Chemical Composition Test
1. Cement fineness test
The pace of hydration, the rate of heat evolution, and the rate of strength development are all governed by the fineness of the cement. The surface area increases and the development of strength are accelerated with finer grains. Sieve testing or an air permeability test can be used to determine the cement’s fineness.
Sieve Test- The cement is sieved continuously in a circular and vertical motion for 15 minutes as part of the sieve test, which breaks up air-set lumps. For regular cement, the residue that remains on the sieve is weighed and should not be more than 10%. Rarely is this test applied to fineness.
Air Permeability Device by Blaine –The specific surface, which is defined as the total surface area in sq. cm/g of cement, is determined using Blaine’s Air Permeability Test. Finer particles have a larger surface area.
2. Cement consistency test
This test is carried out to determine the cement setting times using the Vicat’s apparatus, a common consistency test device. The water content that allows a Vicat plunger with a 10 mm diameter and 50 mm length to penetrate depths of 33-35 mm within 3–5 minutes of mixing is the standard consistency of cement paste.
Three times must pass the test, with the amount of water added to the cement each time changing from 24 to 27% of the cement’s weight. This test should be carried out at a constant humidity of 20% and temperature of 25°C or 29°C.
Cement’s initial setting time and final setting time are determined using Vicat’s instrument.
Initial Setting Time: A needle with a 1 mm square tip is utilized for this test. The needle is permitted to pierce the paste (a mixture of water and cement as per the consistency test). The first setup time is defined as the amount of time needed to penetrate 33-35 mm of depth.
Final Setting Time: When the paste reaches the desired hardness, the needle can only pierce the paste 0.5 mm deep. The final setup time is defined as the point at which the needle does not pierce more than 0.5 mm.
3. Strength test of cement
Cement’s strength cannot be determined solely by looking at the cement. Instead, a cement-to-mortar ratio of 1:3 is used to indirectly define the strength of cement. The cement’s strength at a particular time is what determines this mortar’s compressive strength.
4. Soundness test of cement
Le Chatelier’s apparatus is used for this test to find out if cement contains uncombined lime and magnesia.
5. Heat of Hydration Test
Chemical reactions cause heat to be created as cement is hydrating. Concrete could reach a high temperature of 50°C as a result of this heat. Low-heat cement must be used in large-scale construction to prevent problems.
Also read about- Commonly Used Types of Cement and Their Uses in Construction
Hydration test equipment
This test is conducted using a calorimeter that uses the concept of calculating heat gain. According to the study’s findings, low-heat cement shouldn’t produce 65 calories per gram in 7 days or 75 calories per gram in 28 days.
6. Tensile Strength of Cement
A cement-mortar briquette is used in a tensile testing machine to conduct this test. In the mould, a briquette is created using a 1:3 cement-sand mixture that has an 8% water content.
Tensile Strength Instrument- A temperature of 25°C or 29°C and a relative humidity of 90% is used to cure this mixture for 24 hours. Six briquettes are examined after 3 and 7 days to determine their average strength.
7. Chemical Composition Test
The quantity of various cement ingredients is measured using a variety of assays. The specifications are as follows and are based on IS: 269-1998:
- It should not be less than 0.66 for the percentage of alumina to iron oxide.
- The ratio of the percentage of alumina, iron oxide, and silica to the lime saturation factor (LSF), also known as the ratio between the percentages, should not be less than 0.66 and not more than 1.02.
- Maximum ignition loss should not exceed 4%.
- The maximum allowed total sulfur concentration is 2.75%.
- Insoluble residue should not weigh more than 1.50% of the total weight.
- Magnesium content shouldn’t be higher than 5%.
Onsite Tests of Cement
On construction sites, the cement should be tested before being mixed:
1. Cement Color Test
There shouldn’t be any differences in the cement’s color. It should be a consistent tint of light greenish grey.
2. Lumps
There shouldn’t be any firm lumps in the cement. These lumps are created by the atmosphere’s moisture content being absorbed. In buildings, lumpy cement bags should be avoided.
3. Cement Adulteration Test
When you rub the cement between your fingertips, it ought to be smooth. If not, sand has been added throughout the adulteration process.
4. Float Test
Before sinking, cement granules should float freely in water for a while.
5. Date of Manufacturing
Because cement loses strength over time, it is crucial to verify the date of manufacture. It is preferable to use cement within three months of when it was manufactured.
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