Various Laboratory Tests on Cement and the Parameters Measured

Cement is a leading building material in various construction applications. Knowing the high demand for this building material, we have multiple cement manufacturers around the world, each assuring high quality and strength. But as consumers, we cannot take their word for granted! This insists we conduct various tests on cement to ensure the quality and usability of the cement we purchase. 

This article briefly enlists each test on cement, the methodology used, and the parameters tests. As numerous tests are there, explaining each test with a detailed procedure is beyond the scope of this article. We will be providing links to each test procedure that will lead you to a detailed article. 

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Laboratory Tests on Cement

1. Fineness Tests on Cement

Fineness tests on cement determine the mean size of the cement grain in the given sample. The greater the fineness, the greater the surface area of each particle, greater the rate of hydration.

The Fineness Test on cement is determined either by:

1. Sieve Analysis: The test determines the amount of cement particles regained on a standard sieve. The cement sample is allowed to pass through a series of standard sieves. As per Indian standards, the amount of cement retained on a 90 μm sieve must not exceed 10%. 
2. Surface Area Test: An air permeability test is conducted to determine the surface area of the cement particles. It is performed by any of the two apparatus - Lea and Nurse Air Permeability Apparatus and Blain Air permeability Apparatus. The test determines a specific surface in Blaine (m²/ kg). The minimum specific surface for OPC should not be less than 2250 cm²/kg.

2. Consistency Test on Cement

A consistency test of cement is conducted to determine the amount of water needed to create a cement paste with a specific consistency. The test apparatus used for this is the Vicat apparatus. 

The standard consistency of cement paste is defined as that consistency that will permit a Vicat plunger having 10 mm diameter and 50 mm length to penetrate to a depth of 33-35 mm from the top of the mold ( or up to a point of 5 to 7mm from the bottom of the Vicat's mold).

3. Setting Time Test on Cement

Setting time test on cement determines the time required for the plastic cement to solidify. The test is conducted using the Vicat apparatus. 

The initial setting time may be defined as the time taken by the paste to stiffen to such an extent that the Vicat's needle is not permitted to move down through the paste to within 5 ± 0.5 mm measured from the bottom of the mold.

The final setting time is the time after which the paste becomes so hard that the angular attachment to the needle, under standard weight, fails to leave any mark on the hardened concrete. 

For Ordinary Portland Cement, the initial setting time must not be less than 30 minutes and the final setting time should be around 10 hours. 

4. Specific Gravity of Cement

The specific gravity of cement is defined as the ratio of the density or mass of the cement to the density or mass of a reference substance. So, by knowing the specific gravity, we can tell how a material will behave in water and whether it's good for certain jobs, like building. And we also know to keep cement dry to prevent it from getting ruined.

Specific Gravity of cement is calculated using the Le Chatelier Flask method. This method can be done either at the site or in the laboratory. 

The specific gravity value of cement is around 3.17, while that of Portland blast furnace slag and Portland pozzolan cement may have specific gravities near 2.90. 

5. Soundness Test on Cement

The soundness test measures the expansion of hardened cement paste to determine if it's prone to excessive expansion. The test helps identify potential issues with cement before it's used in construction.

The soundness test of cement can be determined by two methods:

1. Le-Chatelier method: This test uses a special apparatus to measure how much cement expands when placed in water.
2. Autoclave Method: This test applies pressure to the sample. It's sensitive to both lime and magnesia, and is used when the cement contains more than 3% magnesia.

The value of soundness of cement must not exceed 10 mm for ordinary, rapid hardening and low heat Portland cements.

6. Compressive Strength of Cement

Compressive strength tests on cement help to determine the strength of cement thus concluding how much cement is required to achieve the necessary strength.

The compressive strength of cement is determined using cube tests on cement mortar cubes. Compression testing machine or universal testing machine is used for testing. Test 3 cubes for compressive strength for each time period as per detailed specifications. Such as 3 cubes for 3 days test, 3 cubes for 7 days test, and 3 cubes for 28 days test.

The compressive strength of good Portland cement and standard sand mortar cement at the end of 3 days should not be less than 11.50 N/mm2 and at the end of 7 days should not be less than 17.50 N/mm2. 

7. Tensile Strength Tests on Cement

While cement is primarily known for its compressive strength, understanding its tensile strength is crucial for various applications. Tensile strength measures a material's resistance to pulling forces.

While there isn't a direct tensile test for cement, indirect methods are employed to assess its tensile strength, using: 

1. Split Tensile Test: A standard cylindrical specimen of cement mortar is placed horizontally in a compression testing machine. A compressive load is applied along the diameter of the cylinder, causing tensile stresses to develop along the axis of the cylinder. The tensile strength is calculated based on the load at failure and the dimensions of the specimen.
2. Flexural Strength Test: A beam-shaped specimen of cement mortar is supported at both ends and loaded at the center. The tensile stress is calculated based on the load at failure, the span of the beam, and the cross-sectional dimensions.

The typical range of concrete's tensile strength is between 10% and 15% of its compressive strength.

8. Heat of Hydration Test on Cement

The heat of hydration test of cement measures the amount of heat generated when water and cement react. The test uses a calorimetric apparatus to measure the temperature change when cement samples are mixed with acid solutions.

The heat of hydration of low-heat Portland cement is 65 calories per gram or less after 7 days and 75 calories per gram or less after 28 days is 272kJ/kg.

 

9. Chemical Composition Test on Cement

A chemical composition test of cement measures the amount of various chemical compounds in cement, such as silica, alumina, iron oxide, calcium oxide, and magnesium oxide.

An X-ray fluorescence (XRF) spectrometer is a tool used to analyze the chemical composition of cement in a non-destructive, quick, and accurate way. XRF is a preferred method for cement analysis because it can be used at various stages of cement production, from the quarry to the finished product.