Technical above mentioned components of the cement. This melting and reacting of the raw material is also called point of incipient fusion. The raw material fuses to form the different components depending upon the temperature and heat absorbed. When the mixture of the raw materials is poured into the kiln, the outer or peripheral particles of the mixture are subjected to maximum temperature and energy, so bigger molecular components( like C 4AF) are formed after fusion reaction by absorbing greater amount of energy. Similarly, the core of the mixture is subjected to a comparatively lesser energy and temperature, so smaller molecular components( like C 2S) is formed by absorbing comparatively lesser amount of energy.
When the fusion reaction is completed, the final product is gradually cooled to avoid the absorption of water molecules from atmosphere so that it maintains its amorphous form. After cooling, around 3 % of CaSO 4 is added to the cement to avoid instant setting or flash setting of cement paste.
to form H 2SO 4 and CaO, which makes the water acidic. Initially a colloidal or suspended solution of cement( dark liquid) is formed due to this acidic environment. Because of this C 4AF and C 3A are unable to react with water instantly and so the energy and plasticity of the solution remains for a small duration called initial setting time. During this small duration, the traces of alkalis present in the cement neutralise the acidic environment. After this initial setting time, a neutral environment is formed, which is suitable for the reaction between the components of cement & water. Thus the reaction starts with water and this reaction is termed as Hydration of cement.
In the above graph, the reaction with water of the different components of cement with the
Properties of Cement Components
From the above paragraphs, it is clear that, the bigger molecules have formed with higher energy and so they have higher affinity to water and they react as well as solidifies faster as compared to smaller sized molecules. So if there is no CaSO 4, then on the addition of water to cement, C 4AF will be first to react and solidify within a fraction of second, releasing the energy it had absorbed to get fused, C 3A will be the second, C 3S will be third and C 2S will be the last.
But due to the presence of CaSO 4, the above reaction is delayed. When water is added to cement, CaSO 4 reacts with water immediately passage of time is shown. Theoretically, the component shall start reacting after initial setting time( when a neutral environment, suitable for reaction is formed) and should set instantly without any delay but due to the following reason the reaction or hydration