Importance of Testing Cement before Construction

 

         Importance of Testing Cement before Construction

These different methods for testing the strength of Cement are important to ensure that the Cement used in construction meets the necessary standards and is able to perform its intended function.

Testing Cement before construction is important for several reasons:

Quality assurance: Cement tests ensure that the Cement used in construction meets the necessary quality standards. It helps to ensure that the Cement is of the required strength, durability, and other properties necessary for its intended use.

Safety: Cement tests ensure that the Cement used in construction is safe for use. It helps to prevent accidents and failures that could occur due to the use of substandard Cement.

Cost-effectiveness: Testing Cement helps to make sure that the right quantity of Cement is used for a particular application. This can help to avoid wastage and reduce costs.

Durability: Testing Cement helps to ensure that the Cement used in construction is durable and able to withstand the intended load and environmental conditions.

Compliance: Cement tests help to make sure that the Cement used in construction complies with relevant industry standards and regulations. This is important for ensuring that the construction project meets legal requirements and is safe for use.

In summary, testing Cement before construction is important for ensuring the quality, safety, cost-effectiveness, durability, and compliance of the construction project. It is a necessary step in the construction process that should not be overlooked.

 

                                         DETERMINATION OF FINENESS OF CEMENT BY SIEVIE

Theory:

Cement is obtained by grinding various raw materials after calcinations. The degree to which cement is ground to smaller and smaller particles is called fineness of cement. The fineness of cement has an important role on the rate of hydration and hence on the rate of gain of strength and also on the rate of evolution of heat. Finer cement offers a greater surface area for hydration and hence the faster development of strength although the ultimate strength is not affected. Fineness also provides more cohesiveness to concrete and avoid separation of water at the top of concrete (called bleeding). However, increase in fineness of cement increases the drying shrinkage and cracking of the concrete. Fineness of cement is tested either by sieving or by determination of specific surface using air-permeability apparatus. The specific surface is defined as the total surface area of all the particles in cm² per one gram of cement. Although determination of specific surface is more accurate to judge fineness of cement, it is rarely used except for specific purpose. In contrast sieving is most commonly used method to determine fineness of cement and is quite good for field works.

Objective: Determination of fineness of cement by dry sieving. Reference: IS 4031 (Part-1):1988. Apparatus: IS-90 micron sieve conforming to IS: 460 (Part 1-3)-1985; Weighing balance; Gauging trowel; Brush. Material: Ordinary Portland cement

Procedure: 1. Weigh accurately 100 g of cement to the nearest 0.01 g and place it on a standard 90 micron IS sieve.

2. Break down any air-set lumps in the cement sample with fingers.

3. Agitate the sieve by giving swirling, planetary and linear movements for a period of 10 minutes or until no more fine material passes through it.

4. Collect the residue left on the sieve, using brush if necessary, and weigh the residue.

5. Express the residue as a percentage of the quantity first placed on the sieve to the nearest 0.1 percent.

6. Repeat the whole procedures two more times each using fresh 100 g sample. 2

 Observations:

Sl. No	Weight of sample taken (W) (in g.)	Weight of residue (R) (in g.)	%age of residue = 𝑅 ̸ 𝑊 × 100	Average % of residue
1
2
3
4

Result: Percentage residue of cement sample by dry sieving is ___________ percentage.

Conclusions: The given sample of cement contains less than/ more than 10% by weight of material coarser than 90 micron sieve.

Therefore it satisfies/ not satisfies the criterion as specified by IS code. Precautions:

Discuss about the precautions to be taken while conducting this experiment

                   ADVANCE STUDY/KNOWLEDGE

The fineness of cement has a direct impact on the rate of hydration. Finer cement particles have a greater surface area, which allows for faster chemical reactions between the cement and water during the hydration process.

Specifically:

Finer cement particles have a larger surface area per unit volume compared to coarser particles. This increased surface area provides more sites for the hydration reactions to take place.

·         The faster hydration of finer cement allows for quicker development of strength in the early stages of cement setting and hardening. The higher surface area accelerates the initial chemical reactions.

·         Finer cement also results in a more homogeneous and dense hydration product distribution within the cement paste. This improves the overall strength and durability of the hardened cement.

·         However, excessively fine cement can also lead to challenges, such as increased water demand, higher heat of hydration, and increased risk of drying shrinkage. There is an optimal fineness range for cement based on the intended application.

In summary, increasing the fineness of cement generally increases the rate of hydration, leading to faster initial strength gain, but must be balanced against potential drawbacks of very fine cement particles.

 

                      Advantages and disadvantages of Fineness of Cement

The disadvantage of high fineness, include: - The cost of grinding to a higher fineness is considerable. - The finer the cement the more rapidly it deteriorates on exposure to the atmosphere during bad storage. - Finer cement increases the surface area of its alkalis – leads to stronger reaction with alkali- reactive aggregate – cracks and deterioration of concrete. - Finer cement exhibits a higher shrinkage and a greater proneness to cracking. - An increase in fineness increases the amount of gypsum required for proper retardation because, in finer cement, more C3A is available for early hydration (due to the increase of its surface area). Fineness of cement is tested in two ways:

(a) By sieving.

(b) By determination of specific surface (total surface area of all the particles in one gram of cement) by air-permeability apparatus. Expressed as cm² /gm or m² /kg.

Generally Blaine Air permeability apparatus is used.

a) By sieving: Weigh correctly 100 grams of cement and take it on a standard IS Sieve No. 9 -90 µ microns). Break down the air-set lumps in the sample with fingers. Continuously sieve the sample giving circular and vertical motion for a period of 15 minutes. Mechanical sieving devices may also be used. Weigh the residue left on the sieve. This weight shall not exceed 10% for ordinary cement. Sieve test is rarely used due to clogging sieves opens with cements particles.

b) By Blaine test Principle of this method is in observing the time taken for a fixed quantity of air to flow through compacted cement bed of specified dimension and porosity. Volume of cement bed in the cell can be found by it with mercury before and after putting cement on it then determine the difference between two weights, this difference divided by mercury density in room temperature to obtain volume of cement bed. Repeat this for twice at least and use the average value of volume in following equations, also the weight of cement used in cell must be with porosity equal to 0.5 ± 0.0005.

                                                                         W= 3.15 V ( 1 – e )

Which: 3.15 = specific gravity of cement W= weight of cement V = volume of cement bed e = porosity of cement bed Place the perforated disc on the ledge at the bottom of the cell and place on it a new filter paper disc. Place the sample of standard cement weighted (W) with knowing surface area, in the cell. Place a second new filter paper disc on the levelled cement. Insert the plunger and press it gently but firmly until the lower face of the cap is in contact with the cell. Then air pumped inside the tube raise the level of the manometer liquid to that of the highest etched line. Close the stopcock and the manometer liquid will begins to flow. Start the timer as the liquid reaches the second etched line and stop it when the liquid reaches the third etched line. Record the time, t .The procedure repeats three times for standard sample and tested one. The surface area then can be calculated by      Which: S = specific area of tested cement sample ( cm² \gm) Ss = specific area of standard cement ( cm² \gm ) T = average time for tested sample Ts = average time for standard sample.

Correction factor of a sieve

A correction factor is a factor multiplied with the result of an equation to correct for a known amount of systemic error.

Although many numerical evaluations are likely to be precise, you may not always arrive at a specific conclusion in terms of measurements. This is because multiple factors can come into play, resulting in skewed conclusions. Oftentimes the need for evaluating these uncertain factors is a necessity.

This process of evaluating factors that lead to uncertainty in measurement results is known as uncertainty evaluation or error analysis. Error analysis is dependent on correction factors, which are designated calculations implemented to evaluate uncertain factors in measured results

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