STAR Cement's product range includes the following.
 
  1. OPC – TYPE I – Bulk and Bag / 50kg
  2. SRC – TYPE V – Bulk and Bag / 50kg
  3. MSRC – TYPE II – Bulk
  4. Blended Cements – Bulk 
 
All of the above complies to well-known international norms like BS / EN / ASTM. 
 
A test certificate can be made available on request.

Types of Cement

Classification of Cement

Cement produced in the market are widely classified into three categories as below:

- Portland Cements - Ordinary Portland Cement or Sulphate Resisting Portland Cement.
- Blended Cements - Like Slag Cements, Fly Ash cements, Pozzolana Cement etc.
- Special Cements - Depending on customers needs and mostly named as High Early Strength cement, Regulated Set Cement, Low Heat Cement, Low Alkali Cements, Expansive Cements, High Alumina Cements, White Cement, Oil Well Cement, Water-Proofing Cement etc. 

Portland Cement

The most commonly produced cement in the market is the Ordinary Portland Cement and Sulfate Resisting Cement and the properties are given below. The main difference between the Ordinary Portland and Sulfate Resisting Cement is the C3A content. In Sulfate Resistaning Cement this value is lower and due to this the concrete is not attacked by sulphates in normal concentrations. It has low heat properties as well.

Preferred analysis of Ordinary Portland Cement (Type -I) Conforming to ASTM C - 150

Blended Cements
 
Blended or composite cements are cement products ground from a blend of Portland Cement Clinker and a substitute material. This material can be a naturally occurring rock-like a pozzolan or limestone, or an industrial by-product like granulated blast furnace slag or fly ash.

Portland Slag Cement
 
This type of cement is made by intergrinding Portland Cement Clinker and granulated blast furnace slag. Normally 30 – 50 % slag is added with clinker and gypsum to produce such cements.
Normally Slag Cement will have slightly lower strength in the earlier period compared to Ordinary Portland Cement, but the later strengths are nearly equal to that of ordinary cement. The heat of hydration is much lower and hence slag cement can be used in mass concrete structures. Since the sulphate resistance property is also good, slag cements can be used in seawater construction. In addition, the slag cement improves the workability of concrete to certain extent.

Portland Pozzolana Cement
 
Portland Pozzolana Cement is made by grinding clinker and gypsum with pozzolans. Pozzolana is a natural or artificial material containing silica in reactive form. Pozzolanic material is commonly found in – volcanic ash, opline shales and cherts, calcined clay, burnt clay, fly ash, silica fume, rice husk and granulated slag.
The rate of strength development depends on the activity of the pozzolanic material. As a rule, pozzolonic cement develops strength slowly with, longer curing period, but nominal stregth is obtained at later days.
Since pozzolans are cheaper compared to clinker, cost-effective clinker can be produced. It has comparatively lower heat of hydration and it can be useful for mass construction. Pozzolana cements also show good resistance to sulphate attack and some other corrosive agents.
The most widely used pozzolana cement is the Fly Ash Cement. Fly ash is available in large quantity as a waste product, in fine, usually spherical shaped particles and can be introduced directly to the separator of the cement mill. The spherical and the glassy particles of the fly ash have a favourable effect on the cement properties. Good quality fly ash reduces the water requirement and improves the workability of the concrete.

Quality of Cement

The quality of cement is judged by its performance in combination with water as a binder in a material and it includes properties like setting behavior, strength development, heat development, volume stability and durability. It is very essential to ensure that the contribution to these properties of the cement is kept at a certain level and with variations as small as possible to meet the demand expressed in the standard specifications and to comply with the wishes and needs of the market.
These factors are associated with the characteristics of the materials being used for the cement viz. Clinker, Gypsum and Additives, and how they are altered during grinding and storage.

Setting
 
Setting refers to stiffening of a cement paste, which changes in character from a plastic or flowing mass into a rigid material. The time elapsing before this takes place is dependent on several factors including temperature, water to cement ratio and characteristics of the cement itself.
A generally accepted standard method for assessing the setting time of a cement paste is the Vicat Needle method. The initial setting-time is the time elapsed when the needle cannot totally penetrate the sample any longer, and the final setting-time is when the needle cannot penetrate into the paste at all.
The key factor in setting is the amount and reactivity of Gypsum. If too little gypsum is present to prevent the rapid hydration of the aluminate paste, quick or false set can occur. Besides giving too short handling time will normally impair the subsequent strength development.
On the other hand if too much Gypsum is present in a dehydrated, reactive form an early stiffening, caused by precipitation of Calcium Sulfate Dihydrate, can occur. This is called false set. But in most cases, the cement paste can be made to fluid again by further mixing, after which the paste will show normal setting and strength development behavior.
The factors, which influence setting, are:
- The temperature at testing.
- The amount and reactivity of C3S
- The amount and reactivity of C3A
- The content of soluble alkali.
- The fineness of the cement.
- The reactivity of the Gypsum.

Strength
 
The most important property of a Portland Cement paste is its strength development characteristics. It depends on several factors including the mix proportions, temperature, humidity conditions, size and shape of the test specimen. The time chosen before testing is usually 1,2,3,7 and 28 days.
The early strength is dominated by C3S and C3A while, C2S and C4AF contribute to the late strength development.
Uncombined CaO in clinker will not have any influence in the strength, but high content will have lower C3S, which may reduce the strength.
The alkalis and sulphates are very important factors in strength characteristics of a clinker. Depending on SO3 content, the alkali will be present in all the four clinker phases, partly as readily soluble alkali and alkali sulphate. The later part is known to have a marked influence on strength development.
Other minor components in the clinker minerals can modify the hydraulic activity. Additive of fluoride and sulphate to raw meal has shown not only to improve its burnability considerably, but also produce clinker of higher reactivity.
Gypsum is added to the cement to prevent early stiffening, but it also has a marked influence on strength development.There is an optimum SO3 content, which yields maximum strength.
A decisive factor for cement strength is the fineness of the cement. Normally the increased fineness will give increased strength level in the earlier strength development.
Pre-hydration of cement clinker can occur:
- As a result of incorrect internal water cooling in the cement mill
- When storing very hot cement in a silo
- When clinker and especially cement is exposed to humidity.
All the above can lead to reduced reactivity of the clinker minerals and hence impair strength development of cement.

Hydration
 
The hydration of the clinker minerals in Portland Cement results in development of heat. The C3S and C3A phases dominate the heat development characteristics as their hydration reactions are fast and are combined with the highest specific heat development. The heat of hydration is an important factor. It can be helpful in cold concreting or can be troublesome in mass concreting. Other factors like alkalies, certain minor components and degree of pre-hydration also influence the rate of hydration of the clinker.

Soundness
 
Soundness in cement means excessive expansion during hydration of pastes, mortar and concrete. Such expansion cause cracks and consequently reduces strength and durability. The chemical reactions involved with expansion in cement pastes are:
- The formation of ettringite from C3A and SO3
- The hydration of hard-burned free CaO
- The hydration of crystalline MgO.
The limit for MgO should be less than 5%. The range for SO3 shall be between 2.5 – 4.0 and free CaO less than 1.5 %.