High Performance Concrete

High Performance Concrete and the acronym HPC have become more fashionable in recent years. These are made using the same technologies as that used for ordinary concrete except that the materials used were carefully selected and controlled. The potential of High Performance Concrete has not yet been fully exploited. Today, the definition of HPC has expanded to encompass both durability and strength.

High Performance Concrete meets special performance and uniformity requirements that cannot always be achieved routinely by using conventional materials and normal mixing, placing and curing practices.

Ingredients of HPC:

1. Cement
2. Fine Aggregates
3. Coarse aggregates
4. Water
5. Chemical admixtures
6. Mineral admixtures

Cement: It should develop as dense as it can. This leads to loss of workability due to rapid and large release of heat of hydration.

Fine aggregate: The grain size distribution of fine aggregate within the limits specified for ordinary concretes is generally acceptable.

Coarse aggregate: The higher the targeted compressive strength, the smaller the maximum size of coarse aggregate should be.

Water: It is essential to have compatibility between the cement and the admixtures along with water.

Chemical Admixtures: Chemical Admixtures improve workability of the mix with a considerable decrease of water requirement.

Water reducers: They contain certain organic molecules known for their dispersing properties. 

Superplasticizers:They are powerful in dispersing cement particles

Retarders: They cause faster loss of workability. 

Air entrainers: They increase workability and resistance to deterioration due to freezing and thawing action.

Mineral admixtures: They react with lime generated during hydration of cement in the presence of water and form calcium silicate hydrate.

Silica fume: It is not necessary for compressive strengths under 75 Mpa, most cements require to achieve 100 Mpa.

Fly ash: It is a generic term to define a term within broad limits. It is generally suitable for HPC.

Slag: Slag or ground granulated blast furnace is the by-product of the manufacture of pig iron in a blast furnace.

Properties of Fresh concrete:

1. Sensitivity to variations in dosages of admixtures
2. Effect of methods of mixing of ingredients
3. Ambient temperature
4. Method of measurement of workability
5. Rate of retention of workability

Durability and Strength Properties of HPC: Stresses due to loading may result in unacceptable creep, deflection, capacity or cracking.

Mechanical Properties of HPC:

1. Compressive strength
2. Stress-strain behaviour
3. Modulus of rupture and splitting tensile strength

Durability Characteristics of HPC: It is more durable than ordinary concrete.

Special Concretes: They are meant to give high performance for special requirements.

Air-entrained high performance concrete: They are used to improve freeze-thaw durability and scaling resistance in severe climatic conditions.

Light weight concrete: The principle reason for low permeability and excellent durability is due to absence of cracks in the transition zone.

Heavy weight concrete: They are mainly used when building huge counter weights or shields for radioactive gamma rays.

Slurry Infiltrated Fibre Concrete: It is prepared by infiltration of low viscosity cement into a bed of steel fibres, which are pre-packed in forms.

Projects of HPC:

1. Water Tower Place, Chicago

2. Norways Gulfaks Offshore plat form
3. Hasan II mosque, Casablanca

Conclusions:

1. The use of HPC will increase world wide to make economic and durable concrete.
2. Reduction of cement content means emission of less carbon dioxide, which is a positive aspect for a good environment.
3. There are few applications where high strength concrete is absolutely necessary.