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Types of cements

January , 19th 2019 | Author: Hasan Shirazi PE (@) Read: 1668 times

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There are two broad categories of cements based on setting characteristics i.e. Hydraulic and Non-Hydraulic Cements.

Hydraulic Cement sets in the presence of water due to hydration reaction between cement and water. After setting it develops resistance against deterioration from water. (Example of Hydraulic Cement: OPC)

Non Hydraulic Cement cannot set in the presence of water and needs to be dry to set. It requires Carbon dioxide for carbonation reaction to proceed which causes strength gain. (Examples of Non-Hydraulic Cements: Lime, Gypsum)

As per ASTM three separate standards exist for specifying Hydraulic Cements.

ASTM C150 defines Portland Cement types as follows:

Cement Type: Description

·         Type I: Normal (OPC)

  • Type II: Moderate Sulfate Resistance
  • Type II(MH): Moderate Heat of Hydration (and Moderate Sulfate Resistance) 
  • Type III: High Early Strength
  • Type IV: Low Heat of Hydration
  • Type V: High Sulfate Resistance (SRC)

If Air entrainment is required then letter A is added in the end e.g. Type IA is Ordinary Portland Cement (OPC) with Air Entrainment Properties.

For blended hydraulic cements – specified by ASTM C595 – the following nomenclature is used:

Cement Type: Description

·         Type IL: Portland-Limestone Cement (5% to 15% Limestone)

  • Type IS: Portland-Slag Cement (Max. 95% Slag: GGBFS)
  • Type IP: Portland-Pozzolan Cement (Max. 40% Pozzolan: Fly Ash, Silica Fume, Metakaolin etc.)
  • Type IT: Ternary Blended Cement (Less than 70% of Blend consisting of Limestone + Slag + Pozzolan); with Limestone (15% max.) and Pozzolanic material (40% max.)

The amount of blended material is specified as percentage in the nomenclature, for example:

Type IP(20) would have 20% Pozzolan mixed with Type-I cement

Type IT(S20)(P15) would have 20% Slag and 15% Pozzolan mixed with Type-I cement

Type IT(P20)(P15) would have 20% of one type of Pozzolan and 15% of another type of Pozzolan mixed with Type-I cement.

If Air Entrainment is required then letter A is added in the end e.g. Type IP(20)A would be Type-I cement with 20% Pozzolan and having Air Entrainment properties. Other desirable properties mentioned below like HE, LH, HS, R etc. can also be added at the end if so required.

Due to the fact that Slag reacts with water in much the same way as cement, it can be added in much larger quantities than Pozzolans, which do not contribute in hydraulic reaction but rather react with Calcium Hydroxide in the hydrated cement to modify cement properties. While Limestone is just a filler and does not contribute towards strength of cement mix hence, its allowable replacement ratio is the least.

The reason for producing blended cement is that it improves the quality of concrete as compared to Portland cement. As a comparison Portland Slag Cement (PSC) blend has several advantages over Type-V (SRC) cement e.g.:

1.      PSC gives protection against Sulphate as well as Chloride attack while SRC only gives protection against Sulphate attack. This is particularly useful in coastal environment.

2.      PSC results in more durable and superior concrete.

3.      PSC gives protection against ASR.

4.      PSC has low heat of hydration and higher long term strength.

5.      PSC is cheaper than SRC.

Cements can be specified based on their performance characteristics according to ASTM C1157 as follows:

Cement Type: Description

·         Type GU: General Use

  • Type HE: High Early-Strength
  • Type MS: Moderate Sulfate Resistance
  • Type HS: High Sulfate Resistance
  • Type MH: Moderate Heat of Hydration
  • Type LH: Low Heat of Hydration
  • Type R: Low Reactivity Cement (for resistance to alkali-silica reaction)

This third type of standard can be adopted when Performance based Specification is to be specified.

 

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Who we are
Hasan Shirazi PE . Professional Civil Engineer with experience in design, supervision and management of Major Highways, Buildings and Infrastructure Projects in Pakistan and Malaysia. Preparation of General Specifications and Composite Schedule of Rates and their various revisions for National Highway Authority.
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