Purpose of Admixtures

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In continuation with Admixtures article, let us understand the functions

Functions of Admixtures

Concrete admixtures have various functions and they are as follows:

(a) To  increase  the rate  of strength development at early ages – calcium chloride is the most widely  used accelerator,                              

(b) To retard the initial setting time while pumping concrete over a long distance,

(c) To  increase the workability without changing the water content – pozzolana such as fly ash is used,

(d) To increase the strength,

(e) To  increase  the  resistance  to  freezing  and  thawing  – vinyl  resin  is  an  air entrainment admixture which is used for this purpose,

(f) To decrease heat evolution,

(g) To increase water tightness,

(h) To decrease capillary flow of water, and

(i) To decrease rate of bleeding and segregation. 

Chemical admixtures are various types and they are:

(a) Accelerating admixture – A substance that increases the rate of hydration of hydraulic cement, reduces the setting time, or in other words, increases the rate of strength development.

(b) Retarding admixture – A substance which delays the setting time of cement paste.

(c)   Water – reducing admixture – A substance which either increases the workability of freshly mixed mortar or concrete without increasing water-cement ratio or maintains workability with reduced water-cement ratio.

(d) Air – entraining admixture – A substance that causes air to entrap/Cd in the form of tiny bubbles in mortar or concrete during mixing to increase its workability and resistance to freezing and thawing.

(e)  Super plasticizing admixture   – A   substance that has very high workability with a large decrease in water content (at least) for a given workability. High range water reducing admixture (HRWRA) is also referred to as a superplasticizer.

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Types of Cement

Dear Readers,

As you are well aware that without Cement modern infrastructure is not possible or even unimaginable now. Cement is a critical component in the construction of buildings, roads and other brick-and-motor creations and it plays vital role in construction Industry. Cement is a grey colored powder that resembles ash in texture. It is a binding substance that is used to harden and set two materials, typical bricks or rocks together. Before using it, cement is mixed with water and other materials in varying ratios and placed between two substances as “glue”. 

It’s time to learn about the many types of cement available in the market to cater to different construction purposes. Cements are broadly classified into two categories – Hydraulic and Non-Hydraulic, depending on how they react to the presence of water.

Hydraulic Cement: This cement gets hardened in a very short span and are widely used in construction industry for saving time and effort.

Non-Hydraulic Cement: They have a very long setting period and can only work in dry conditions. Non-hydraulic is not practical for commercial constructions, as they cannot be used in sites that are open to weather challenges.

Selection of cement based on suitability for different concrete construction is important for durability considerations of structures. Thus, making wise choice of cement type for specific construction site that prevents structure from deteriorating and saves much repair and rehabilitation cost later. 

A wide variety of cement types are available in market, which are suitable for use under certain conditions due to its unique properties. They are as follows.

    1. Ordinary Portland cement (OPC)

    2. Portland pozzolana cement (PPC)

    3. Rapid hardening Portland cement (RHPC)

    4. Low Heat Portland Cement (LHPC)

    5. Portland Slag Cement (PSC)

    6. Sulphate-resisting Portland Cement (SRPC)

    7. Hydrophobic Portland Cement (HPC)

Other Types of cements are based on its either unique property or its application.

    1. High Alumina Cement

    2. Quick-setting Cement

    3. White Cement

    4. Coloured Cement

    5. Air Entraining Cement

    6. Expansive Cement

    7. Extra rapid hardening cement

    8. Super sulphated cement

    9. Oil-well Cement

    10. Ultra-high strength concrete (UHSC)

Ultra-high strength concrete (UHSC) is the latest spectacular development in the domain of Portland cement-based materials.

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Concrete Admixtures

 Dear Readers,

Concrete is widely used in civil engineering and construction. In the concrete mixing process or before the concrete mixing can make the concrete hardening, mixing better materials, called concrete admixtures.

Various types of admixtures are used in concrete to enhance the performance of concrete. Concrete admixture is defined as the material other than the aggregate, water and cement added to the concrete. Admixtures are artificial or natural, and it may be added to the concrete mix, just before or during the mixing, to change one or more properties of the concrete in the plastic or hardened state as required in our structure. 

The successful use of admixtures depends on the proper combination of ingredients and concrete. Most admixtures are supplied in ready-to-use liquid form and are added to the concrete at the factory or construction site. Some additives such as pigments, extenders, and pumping agent, etc., used only in extremely small amounts, generally from the vessel manually pre-measured ingredients.

Types and Functions of admixtures are as Follows.

There are two types of admixtures:

Mineral admixtures 

Chemical admixtures

(1)    Mineral admixtures 

Followings are the types of Mineral admixture:

Fly ash

Silica fume

Ground granulated blast furnace slag

Rice husk ash

(2)    Chemical admixtures 

Chemical admixtures are various types, and they are:

Accelerating admixture

Retarding admixture

Water – reducing admixture

Air – entraining admixture

Super plasticizing admixture

Special Admixtures based on the application

Pozzolanic Admixtures

Damp-proofing Admixtures

Gas forming Admixtures

Air detraining Admixtures

Alkali Aggregate Expansion Inhibiting Admixtures

Anti-washout Admixtures

Grouting Admixtures

Corrosion Inhibiting Admixtures

Fungicidal, Germicidal, Insecticidal Admixtures

Coloring Admixtures Bonding Admixtures