Corrosion and Protection of Reinforced Concrete
Concrete is the most widely used material of construction in the world (and the second most used material by mankind after water) (Miller, 2018). Concrete is strong in compression but weak in tension and so much of the concrete is reinforced, usually with steel. The steel reinforcement can take the form of conventional carbon steel (black steel), prestressing steel, post-tensioned steel, and steel fibres, and its widespread utility is primarily due to
the fact that it combines the best features of concrete and steel. The proper- ties of these two materials may be compared below (Table 1.1).
The properties of the materials thus complement one another and so by combining them together a composite that has good tensile strength, shear strength, and compressive strength combined with durability and fire resis-tance can be formed. Typical properties of reinforcing steel and concrete might be (Table 1.2).
So that the strains at failure (if the stress strain curves were linear) are approximately 2 × 10–3 for the steel and 8 × 10–6 for the concrete. Consequently, when the steel is operating at or near its yield point the concrete must be cracked and so different forms of prestressing have been developed to ensure that the cracking is controlled to an appropriate level.
The properties of the materials also complement each other in that the properties of the steel can be modified by alloying and working to vary its strength and corrosion resistance, the properties of the concrete can be modified to facilitate the building of the structure by changing the ease with which it can be formed into the required shape and the penetrability of the final structure to aggressive agents that might attack the steel. In this chapter attention, will be focussed on the structure of concrete and the way in which its properties are controlled by its components, the cement, the aggregate, the mixing water, and admixtures.
1.2 THE STRUCTURE OF CONCRETE
Basically, concrete consists of mineral aggregate held together by a cement paste, so that if we consider a normal mix it will consist of cement, sand (fine aggregate), coarse aggregate and water (and often other admixtures) which are mixed together to form eventually a hard, strong material. The primary binding agent in concrete is cement. The water reacts with the cement to make a cement paste which then hardens and binds the aggregate together to make the solid concrete and the cured composition of the conrete may be represented by the proportions shown in Figure 1.1.