DURABILITY OF CONCRETE MATERIALS FORCOMPONENTS OF HIGH RISE STRUCTURES

Abstract

Globally, concrete is the most widely used construction material after water. Conventional concrete has traditionally been designed on the basis of 28 day compressive strength and may not meet the functional requirements of concrete structures like resistance to environmental & chemical attack, impermeability, shrinkage cracks, etc. This generally impacts the maintenance free service life of the structure. Normally in developing countries, concrete is specified in a prescriptive manner e.g. M-50. No other parameters for durability and performance are specified including the service life of the structure. As a result of this many times concrete meets the standard basic parameters but fails in meeting durability parameters or requirements. To counter the above requirements a shift to High Performance Concrete (HPC) is desirable. HPC should not be confused with High strength concrete. HPC is an engineered concrete meeting special combinations of performance and uniformity requirements that cannot always be achieved routinely using conventional constituents and normal mixing, placing and curing practices. It includes concrete that provides high strength, high early strength, ease in pumping and placement with or without vibration, resistance to segregation and bleeding, volume stability and resistance to shrinkage. It also enhances resistance to sulphate attack, alkali silica reaction, carbonation, chloride & corrosion induced disruption, low permeability and diffusion, high modulus of elasticity and lower creep coefficient, improved toughness, impact and abrasion resistance, enhanced resistance to freeze and thaw attack, higher durability and lower service life of structures. This article deals with the various durability aspects of High Performance Concrete in terms of mix design approach, testing & performance evaluation. As a case study this article emphasises on M80 free flow high performance concrete for shear columns & core walls and M40 temperature controlled concrete for raft foundations of high rise structures, which highlights the durability aspects holistically. The following criteria will be discussed in the article pertaining to ease of placement by using free flow or self-compacting concrete, Temperature controlled concrete for reducing core temperature and reducing the effect of thermal stresses on concrete and long term mechanical properties, which include Modulus of elasticity, drying shrinkage & creep in concrete.