Cement is the binding material used in the construction works. Cement is the composition of the following:
Percentage in cement
The durability and strength of cement depend upon the components present in the cement.
Properties of Cement
The properties of cement can be categorized into two types namely physical properties & chemical properties.
Physical Properties of Cement
It is the biggest factor for undeterrable strength of cement. Higher fineness leads to higher strength. Higher fineness denotes that there is more area for cement water reaction resulting increase in strength. Fineness in cement is achieved by grinding the clinker during the process of production.
The capacity of not changing of properties of the material like change in volume; when water is added upon it is soundness. Material with high soundness has a higher strength. So cement should also have high soundness. Cement should be the cause of high soundness in mortar and concrete.
Few reasons for unsoundness are :
1. Excessive use of Gypsum in cement.
2. Excess of Lime
3. Burned Less
4. Excessive magnesia content
Some of the tests carried out for ensuring the soundness are:
a. Le Chatelier Test
b. Autoclave Test
Uniformity in the nature of the material leads to higher consistency. So, cement should have high consistency. Consistency in the strength is the cause of uniformity nature of the material.
In other words, the flowing ability of cement paste is called consistency. Vicat Test is carried out to measure the consistency of cement.
4. Setting Time
When water is added to cement; it hardens and sets. Setting time may depend upon uniformity of cement, water-cement ratio, presence of admixtures, etc. The initial setting time of the cement should not be less and the final setting time should not be high.
Best initial and final setting time for cement is given as:
Initial Setting Time: 30-45 Minutes
Final Setting Time: Below 10 Hours
5. Heat of hydration
The chemical reaction between cement and water is called the heat of hydration. When water is added on cement, heat is generated. This can affect the quality of cement because excessive hydration leads to undesired strength. Hydration depends upon the water-cement ratio, uniformness, temperature of curing, etc.
The heat of hydration is mostly affected by C3S and C3A.
6. Strength of Cement
Compressive, tensile and flexural strength plays a vital role in the durability and quality of cement.
Factors affecting the strength of cement are:
a. Water-Cement ratio of a mix.
b. Cement-Fine aggregate ratio
c. Curing Conditions
d. Size and shape of a specimen
e. The manner of moulding and mixing
f. Loading conditions
g. Age of cement
Chemical Properties of Cement
If the lime is used more than 65 %; it may result in the problem of expansion.
Excess use of alumina quickens the setting time but weakens the cement.
c. Sulfur Trioxide
If the amount of Sulfur Trioxide used is more then the cement become unsound in nature.
d. Iron oxide
It is also called Ferric Oxide. It is responsible for the colour of the cement.
Silica provides high compressive strength, abrasion resistance and bond strength to cement.
The high amount of alkali use leads to difficulty in the regulation of setting time and low amount leads to discolouration of cement.
If the magnesia is used in high amount then it results in unsoundness and uneconomical.
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