Laboratory tests of cement
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Laboratory tests of cement are very important to test in cement quality tests. The name of the laboratory test on cement is
1) Standard Consistency Test.
2) Setting Time Test.
3) Strength Test.
4) Soundness Test.
5) The Heat of Hydration Test.
6) Chemical Composition Test.
Read more: Types of Cement in Different category
1)Standard Consistency Test (Laboratory tests of cement)
The laboratory tests of cement for finding out initial setting time, final setting time and soundness of cement, and strength a parameter is known as standard consistency has to be used. it is pertinent at this stage to describe the procedure of conducting a standard consistency test. the standard consistency of a cement paste is outlined as that consistency that may allow a Vicat plunger having a ten-millimeter diameter and fifty-millimeter length to penetrate to a depth of 33-35 millimeters from the highest of the mold. The appartus is called Vicat Appartus. This equipment is used to search out out the percentage of water needed to provide a cement paste of standard consistency. the standard consistency of the cement paste is sometimes called normal consistency (CPNC). the subsequent procedure is adopted to search out standard consistency. Take regarding five hundred gms of cement and prepare a paste with a weighed amount of water (say twenty-four % by weight of cement) for the primary trial.
The paste must be prepared in a standard manner and filled into the Vicat mold within 3-5 minutes. after filling the mold, shake the mold to expel air. a standard plunger, ten-millimeter diameter, fifty millimeter long is connected and brought all the way down to touch the surface of the paste within the test block and quickly discharged permitting it to sink into the paste by its own weight. Take the reading by noting the depth of penetration of the plunger. Conduct a 2d trial (say with twenty-five percent of water) and determine the depth of penetration of the plunger.
Similarly, conduct trials with higher and better water/cement ratios until such time the plunger penetrates for a depth of 33-35 millimeters from the highest. that specific percentage of water that enables the plunger to penetrate only to a depth of 33-35 millimeters from the highest is thought because the percentage of water needed to provide a cement paste of normal consistency. This percentage is sometimes denoted as ‘P’. The test is needed to be conducted at a constant temperature (27° + 2°C) and constant humidness (90%).
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2) Setting Time Test (Laboratory tests of cement)
The laboratory test of cement has been made for the setting time of cement as initial setting time and final setting time. It is difficult to draw a rigid line between these two arbitrary divisions. For convenience, initial setting time is regarded as the time elapsed between the moment that the water is added to the cement, to the time that the paste starts losing its plasticity. The final setting time is the time elapsed between the moment the water is added to the cement and when the paste has completely lost its plasticity and has attained sufficient firmness to resist certain definite pressure.
In actual construction dealing with cement paste, mortar, or concrete certain time is required for mixing, transporting, placing, compacting.
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3) Strength Test (Laboratory tests of cement)
The Laboratory tests of cement compressive strength of hardened cement are that the most significant of all the properties. Therefore, it's not surprising that the cement is always tested for its strength at the laboratory before the cement is employed in necessary works. Strength tests don't seem to be created on neat cement paste due to difficulties of excessive shrinkage and later cracking of neat cement. The strength of cement is indirectly found on cement sand mortar in specific proportions. quality sand is used for locating the strength of cement. It shall conform to IS 650-1991. Take 555 gms of normal sand (Ennore sand), 185 gms of cement (i.e., the ratio of cement to sand is 1:3) in a non-porous enamel tray and mix them with a trowel for one minute, then add water of quantity.
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| Soundness Test of cement |
4) Soundness Test (Laboratory tests of cement)
The Laboratory tested of cement after setting mustn't undergo any appreciable change of volume. Certain cement has been found to undergo a large expansion after setting causing disruption of the set and hardened mass. This will cause serious difficulties for the durability of structures when such cement is used. The testing of cement's soundness ensures that the cement does not show any appreciable subsequent expansion is of prime importance.
The unsoundness in cement is due to the presence of excess lime that could be combined with acidic oxide at the kiln. This is also due to inadequate burning or insufficiency in the fineness of grinding or thorough mixing of raw materials. It is also likely that too high a proportion of magnesium content of calcium sulfate content may cause unsoundness in cement. For this reason, the magnesia content allowed in cement is limited to 6 percent. It can be recalled that to prevent flash setting, calcium sulfate is added to the clinker while grinding. The quantity of gypsum added will vary from 3 to 5 percent depending upon C3A content. If the addition of gypsum is more than that could be combined with C3A, excess of gypsum will remain in the cement in a free state. This excess of gypsum leads to an expansion and consequent disruption of the set cement paste.
5) The heat of Hydration Test (Laboratory tests of cement)
The Laboratory tests of cement reaction of cement with water are exothermic. The reaction of cement with water is exothermic. The reaction liberates a considerable quantity of heat. This heat is called heat of hydration. The study and control of the heat of hydration become important for the construction of concrete dams and other mass concrete construction. Different compounds hydrate at different rates and liberate different quantities of heat. On mixing cement with water a rapid heat evolution lasting a few minutes occurs. This heat of evolution is probably due to the reaction of the solution of aluminates and sulfates.
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6) Chemical Composition (Laboratory tests of cement)
The chemical test of cement detailed discussion has been given earlier regarding the chemical composition of cement. Both oxide composition and compound composition of cement have been discussed. At this stage, it is sufficient to give the limits of chemical requirements. The various chemical compositions of all types of cement.
The ratio of the percentage of lime to the percentage of silica, alumina, and iron oxide, when calculated by the formulae.
Not greater than 1.02 and not less than 0.66.
The above is called lime saturation factor percent.
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