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Cement is very important binding material. It is mostly used to make cement mortar and concrete. Cement has a property to get hardened and to achieve strength within a short period of a time in presence of water. It is therefore very important for us to know in how much time cement will set and in how much time we will have to use the cement.
When water is mixed with cement, the paste is formed and remains in the plastic state for a first few minutes. During these first few minutes the paste can be mould in any required shape due to its plasticity.Within this specific time reaction continues between cement and water. During this reaction, paste loses its plasticity and gets hardened. Afterward, moulding the hardened paste in the desired shape becomes difficult. This early time of the hardening of cement paste is known as “Setting Time of Cement”.
Setting time is defined as a specified time required for concrete or mortar to change from liquid state to plastic state and plastic state to solid state so that surface becomes sufficiently rigid to withstand a definite amount of pressure. It is necessary to place and consolidate the concrete or the mortar before initial setting started and do not disturb till the final setting of mortar or concrete has taken place.
Courtesy - 123rf
Setting time of cement usually depends on various factors, such as the type of cement, fineness of cement, chemicals, sand, availability of ambient temperature during casting, presence of certain type of salts, the percentage of water etc. For example, setting time of cement is longer during winter or in cold area due to low temperature.
Setting time is usually differentiated as initial setting time & final setting time. This mean that if the initial setting time of cement is 30 minutes, the cement mortar or concrete must be placed in position within 30 minutes of adding water. If delayed, mortar or concrete will lose strength. If delayed due to some unavoidable circumstances, either you have to reject cement/concrete or add additional cement depending upon delay.