Placing reinforcing bars cap#2

Apuntes

Placing reinforcing bars Cap #2: concrete and reinforced concrete. Topic: definitions. 1. Concrete: is a mixture of one part cement, of about 1-1/2 to 2-1/2 parts fine aggregate (usually sand) and of about 3 to 5 parts coarse aggregate (such as gravel, crushed stone or blast-furnace slag), and clean water. By varying the proportions of the mixture, concrete with different crushing strengths may be obtained. These strengths can be varied from about 3,000 to 10,000 pounds per square inch, and higher. The mixture is plastic, and in normal temperatures will set up firm in hours (known as an initial set), will be self-supporting in a few days, and will attain its full rated strength in a specified length of time, usually 28 days. Concrete is strong in compression, but relatively weak in tension and shear. 2. High-early strength cement: is sometimes used in concrete where a faster rate of hardening is required. It will cause the concrete to attain about the same strength in about one-half or one-third of the time required with ordinary cement. 3. Air-entraining cement: creates tiny air voids (bubbles) in the con-crete, resulting in a more plastic mixture which is easi...