Portland cement is a water cement obtained by grinding clinker with a suitable amount of gypsum or raw crystallized calcium sulfate.
The reason for adding calcium sulfate to clinker will be explained below.
It is a composite product, which is mainly composed of calcium, aluminum and iron silicates, and is obtained from the thermo-chemical reaction of calcareous and clay materials in a cement kiln at a temperature of 1300 to 1500 ° C.
Portland cement is a hydraulic or aqueous binder, ie it is hard due to mixing with water and chemical reaction with it.
This action is called hydration and is accompanied by heat production.
In general, Portland cement is obtained from four main compounds including Fe2O iron oxide 3, Al2O aluminum oxide 3, SiO2 silicon oxide and CaO calcium oxide. Which are represented by the symbols, F, A, S and C, respectively.
Alkalis include sodium and potassium oxides, which often enter cement with clay compounds. And due to the alkali-silica reaction (ASR) and the long-term degradation of concrete, their value must be controlled and in principle do not allow their values to exceed 1%.
The main phases of Portland cement
It is one of the main components of cement and has a small amount of hydration. And after the first week, it plays an important role in the compressive strength of concrete. For this reason, this step is more common in slow-setting cements than other types of cement.
This material is another major component of Portland cement and has a high hydration rate and plays an important role in the compressive strength of concrete in the first week.
This part of Portland cement also has a high rate of hydration and together with tricalcium silicate plays an important role in the initial regulation of concrete. One of the disadvantages of this phase is that it is easily sulfated after hydration, and if you are exposed to sulfates, it gives calcium sulfoaluminate, which increases the volume and damage of concrete.
This phase has the lowest amount of cement and its effect on concrete is less than other phases.
The ratio of these steps varies depending on the type and application of cement.
Reason for adding gypsum to clinker and grinding it with clinker:
Due to the high rate of hydration, the tricalcium silicate (C3S) and tricalcium aluminate (C3A) phases are added to the calcium sulfate (gypsum) to reduce their hydration rate and reduce the hydration heat dissipation.
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