Fundamentals of Concrete Protection - Extending Service Life of New Structures and Protecting Distressed Structures

Introduction

Sunny Surlaker
RCC is one of the most versatile and widely used construction materials on account of its mouldability and designable durability. Due to harsher pollution and extreme requirements of construction practices, it's performance and durability is greatly affected. The concrete is said to be durable when it can withstand design exposure conditions, over its service life with little deterioration. Durability is a function of the quality and quantity of cover to the reinforcement. Considering practicality of construction coupled with completion deadlines, it becomes virtually impossible to cast specified cover in terms of quality and quantity. The outermost layer of concrete therefore becomes the weakest one. A combination of the porous nature of concrete and a weak cover lead to diffusion of detrimental materials like water, CO2, chlorides and SO2 into concrete. These materials or a combination thereof, lead to loss of passivity and corrosion of the steel and ultimately deterioration of the concrete, which leads to weakening of the RCC structure as a whole.

Very simply, concrete has two tendencies that render it susceptible to water and pollutants. Concrete has porosity due to capillarity and concrete will crack. Porosity of concrete and cracking can be minimized using good mix design, production and placing techniques, however it cannot be eliminated entirely. Therefore durability of concrete can only be enhanced by use of apt protective coatings that can form a physical and a chemical barrier against ingress of water, chlorides, CO2 and SO2. Paints and other decorative coatings are designed for aesthetic purposes and normally not for protection of concrete against carbonation, chloride attack, UV radiations and for crack bridging properties.

The same principle is applicable to repair of concrete structures as well. Since cover is the first line of defense to inhibit corrosion, the repair and rehabilitation is recreation of cover with a high protection quotient.

Concrete Protection thus becomes a key Step in PREVENTING repairs of structures and helps enhance the life of suitably repaired distressed structures. It is thus fitting for this practice to be incorporated for new structures and most certainly used to protect repaired structures.

NBMCW February 2014