Chemical analysis at cement testing lab of hardened concrete can provide a wealth of information about the mix constituents and possible causes of deterioration. Standard methods can be used to find the cement content and original water/cement ratio, but many other properties can also be established; Cement Content and Aggregate Cement Ratio, Cement Content and Pulverised fuel ash/fly ash (pfa) content, Cement Content and Slag content, Water/Cement Ratio, Aggregate Grading, Determination of the presence of High-Alumina Cement (HAC)
The most common strength test, compressive strength, is carried out on a 50 mm (2-inch) cement mortar test specimen. The test specimen is subjected to a compressive load (usually from a hydraulic machine) until failure.
The fineness of cement has an important bearing on the rate of hydration and hence on the rate of gain of strength and also on the rate of evolution of heat. Greater fineness increases the surface available for hydration, causing greater early strength and more rapid generation of heat. Cement fineness play a major role in controlling concrete properties. Fineness of cement affects the place ability, workability, and water content of a concrete mixture much like the amount of cement used in concrete does.
Heat of Hydration
When cement is mixed with water, heat is liberated. This heat is called the heat of hydration, the result of the exothermic chemical reaction between cement and water. The heat generated by the cementâ€™s hydration raises the temperature of concrete.
Loss On Ignition
This test helps in determining the inorganic analytical chemistry, particularly in the analysis of minerals. It consists of strongly heating (“igniting”) a sample of the material at a specified temperature, allowing volatile substances to escape, until its mass ceases to change.
Initial setting time is the time that elapsed from the instance of adding water until the paste ceases to behave as fluid or plastic. Whereas final setting time referred to the required for the cement paste to reach certain state of hardness to sustain some load.
Soundness refers to the ability of a hardened cement paste to retain its volume after setting. Lack of soundness is observed in the cement samples containing excessive amount of hard burnt free lime or magnesia.