Question

1. What are the oxides used for manufacturing of cement and their range of percentages?

2. What are the principal chemical compounds of cement and their range of percentage ?

3. List the different Portland Cement Types and their specific properties and use.

4. For controlling cement quality, some physical properties need to be verified.

What are the properties shall be tested for cement quality?

5. What is the effect of cement fineness on concrete property?

6. Explain the effect of shape and surface texture of an aggregate influence the paste requirement for concrete mix. 

           

Answer 1

1. The following oxides are generally used for manufacturing of Cement and their approx composition limits for Ordinary Portland Cement is given below.

Oxide	% Composition
Calcium Oxide (CaO)	60-67
Silicon Oxide (SiO2)	17-25
Aluminium Oxide (Al2O3)	3.0-8.0
Iron Oxide (Fe2O3)	0.5-6.0
Magnesium Oxide (MgO)	0.1-4.0
Alkalies (K2O, Na2O)	0.4-1.3
Sulphur Oxide (SO3)	1.3-3.0

2. The Principal chemical compounds of Cement and their percentage composition range for a Typical Portland Cement is given below.

Name of Compound	Abbreviated Formula	% Composition Range
Tricalcium silicate	C3S	50-60
Dicalcium silicate	C2S	15-20
Tricalcium aluminate	C3A	10-12
Tetracalcium aluminoferrite	C4AF	7-10

3. Different Portland Cement Types

         a. Ordinary Portland Cement :- This cement is classified into 3 grades, namely 33 grade, 43 grade, 53 grade depending upon the strength of cement at 28 days. This is generally used in all general construction works. However, the manufacture of OPC is decreasing across the world on account of the popularity of blended cement in view of lower energy consumption, environmental pollution, economic and other technical reasons.

           b. Rapid Hardening Cement :- This cement is similar to OPC but it develops strength rapidly. So also called as high early strength cement. This cement develops at the age of 3 days, the same strength as that is expected of OPC in 7 days. It is used in pre-fabricated concrete construction, where formwork is to be removed early for re-use elsewhere, Road repair works etc.

            c. Sulphate Resisting Cement :- OPC is susceptible to sulphate attack. To overcome Sulphate attack, the use of cement with low C₃A is suggested. This Sulphate Resisting Cement has low C₃A and comparatively low C₄AF. This cement is used in the when Concrete is to be used in marine condition, in foundation and basement where soil is infested with sulphate, in the construction of Sewage treatment works.

            d. Portland Slag Cement :- This cement is obtained by mixing Portland cement clinker, gypsum and granulated blast furnace slag. This cement has reduced heat of hydration, refinement of pore structures, reduced permeability etc. This cement is used in the construction works in the coastal regions.

            e. Portland Pozzolana Cement :- It is prepared by intergrinding OPC clinker with 10 to 25% of pozzolanic materials. This cement is used for hydraulic structures, mass concrete structures like dam, bridge piers etc, marine structures.

4. Tests for Cement Quality

1. Fineness Test
2. Soundness Test
3. Heat of Hydration Test
4. Setting Time Test
5. Strength Test

5. Effect of Cement Fineness on Concrete Property

       The fineness of cement has an important bearing on the rate of hydration and hence the rate of gain of strength. Finer cement provides a greater surface area for hydration and hence faster the development of strength.

6. Shape :- The shape of aggregates is an important characteristic as it affects the workability of concrete. Flat particles in concrete aggregates will have objectionable influence on the workability, cement requirement, strength and durability. Excessive flaky aggregate makes very poor concrete.

Texture :- The adhesion between cement paste and aggregate is influenced greatly by the surface texture of the aggregate. As surface smoothness increases, contact area decreases. A smooth particle has less contact area hence a highly polished particle will have less bonding area with a matrix than a rough particle of same volume.