385
4000.045
Petersen, Perry H.
Book on Concrete by Waddell
Article
1964
Post 1964
31-1 thru 31-7
Y
Lightweight concretes include those made with (1) lightweight aggregates; (2) foamed cementitious matrix, the end product usually known as cellular concrete; (3) gap-graded natural or lightweight aggregates wherein the sand fraction is usually omitted; and (4) combinations or variations of the above. The range in lightness in weight extends from a high of 120 pcf to a low of about 10 pcf. Structural lightweight concrete is generally in the range of 120 to 85 pcf. Semistructural, insulative, and/or fill concrete usually weights from 85 to 50 pcf, whereas the least dense concretes (50 pcf and less) are employed solely as heat insulation. Some lightweight concretes made with cementitious binders other than portland cement require autoclaving or high-pressure steam curing in order to cause hydration to take place. Thus this one type is limited solely to precast shapes, slabs, planks, and the like, and these have a structural capacity sometimes greater than that indicated by the density of the concrete. However, lightweight concretes are mixed, placed, handled, and cured in a manner and by methods conventional to the concrete industry, and with little modification. Furthermore, lightweight concrete is often used as a complete and suitable substitute for normal-weight concrete even though it is light in weight. Its cost per cubic yard may be greater, but it reduces the dead load as well as contributes to heat insulation. The decreased dead load results in reduction of the size of footings, the number of piles required to support the structure, and the size of the foundation walls, columns, beams, and floor thickness; this reduction in mass of concrete (bulk as well as density) will result in savings that may far offset the increased cost of the concrete. Furthermore, the heat-insulation value of the lightweight concrete may be sufficient in itself, thereby eliminating need for additional insulative material.