HIGH STRENGTH ANDHIGH PERFORMANCE CONCRETE

Presented ByAHSAN RABBANICIVIL ENGINEERING DEPARTMENTREC RAIPUR

INTRODUCTIONStrength of a material is defined as the ability to resist stress without failure.It is important to note that High strength and High performance concrete are not synonymous.Concrete is defined as High strength concrete on the basis of its compressive strength measured at a given age.In early 1970s any concrete mixture that showed 40MPa or more compressive strength at 28 days were design as High strength concrete.Later 60-100MPa concrete mixture were commercially developed and used in the construction of high rise buildings and long span bridges in many parts of the world.

Why do we need high strength concrete?To put the concrete into service at much earlier age, for example opening the pavement at 3-days.

To build high rise buildings by reducing column sizes and increasing available spaces.

For the same magnitude of loading longer spans and fewer beams.

To satisfy the specific needs of special applications such as durability, modulus of elasticity and strength.

The definition of High Performance Concrete is more controversial.

Mehta and Aitcin used the term HPC for concrete mixtures possessing high workability, high durability and high ultimate strength.

ACI defined HPC as a concrete meeting special combinations of performance and uniformity requirements that cannot always be achieved routinely using conventional constituents and normal mixing, placing, and curing practice.

WHAT IS HIGH PERFORMANCE CONCRETE ?

These concrete almost always has a higher strength than normal concrete.

However, strength is not always the primary required property.

For example, a normal strength concrete with very high durability and very low permeability is considered to have high-performance properties.

Typically, such concretes will have a low water-cementing materials ratio of 0.20 to 0.45.

CONTD..

Concrete that last longer and possess the following salient features is called High performance concrete (HPC).-High workability-High strength-High early strength-High durability-High modulus of elasticity-Toughness and impact resistance-Volume stability.-Ease of placement.-Compaction without segregation.

CONTD..

MATERIAL REQUIREMENT FOR HPC

MaterialRequirementsCement-Portland CementWater-Potable tap water having pH 7.3.Fine Aggregate-Sand with rounded particle shape.-Higher FM(around 3)Coarse Aggregate-Smaller maximum size(10-12 mm) is preferred.-Angular and crushed with a minimum flat and elongated particles - Higher CA/FA ratio than that for normal strength concrete.Admixtures (chemical & mineral) - Type of admixture depends on the property of the concrete to be improved - Optimum dosage Overall basic considerations Quality materials - Improved quality of cement paste as well as aggregates - Denser packing of aggregates and cement paste

HIGH STRENGTH CONCRETE MATERIAL

MaterialPrimary ContributionPortland CementCementing Material/DurabilityBlended Cement

Cementing Material/Durability/High StrengthFly Ash/Slag/Silica FumeCalcined ClaySuper plasticizer Flow abilityHigh range water reducerReduce Water-cement ratioRetardersControl settingAcceleratorsAccelerate SettingCorrosion inhibitorsControl Steel corrosionPolymerDurability

BENEFITS OF HPCHigh Performance Concrete is a specialized series of concretes designed to provide several benefits in the construction of concrete structures:

Performance BenefitsCost and other BenefitsEase of placementLess materialEarly High strengthReduced Maintenance Seismic ResistantExtended Life Cycleconsolidation without affecting strengthEffective Utilization of Industrial Waste Speed of ConstructionImproved Durability

APPLICATIONSBridgesHigh Rise BuildingsTunnelsPavementsNuclear Structures