We know aggregates are inert filler in concrete as it is expected not to participate aggregate in any chemical reaction. As inert property is desired, we have to choose material that is not chemically reactive, any impurity like alkali, chloride etc. can result severe problem in concrete.
We have discussed maximum allowable size of aggregate for structural concrete. When large amount of mass concrete is required, we can use large stones as aggregate in normal concrete. The objective is to produce relatively large amount of concrete for given cement content. This type of concrete is called cyclopean concrete.
The large size of stones is termed as plums. The size of stones may be up to 1 ft. (300 mm). But
Stone size ≤ 1/3 X (Least dimension of concrete mass).
There has restriction with volume of plums; this is
Plums volume ≤ (20 ~30) % of volume of finished concrete.
The plums should be dispersed rationally throughout the concrete mass.
The construction procedure is-
A normal concrete layer is placed on desired surface and then plums are spread on this thoroughly. Another layer of concrete is placed above spread plums.
Each layer of concrete is placed in such way that each plum has at least 4 in (100 mm) concrete around it. Problem may arise with entrapped air beneath stones. Care has to be taken to avoid air void to work entire section of cyclopean concrete as one unit.
No adhering coating on plums is allowed as discontinuities in bond between plums and surrounding concrete may produce cracking and concrete becomes permeable.
Now let’s consider about economy of cyclopean concrete; obviously it reduces significant amount of cement but need more labor than normal concrete. It also breaks down continuity of normal concreting work. Now-a-days, labor cost is very high and ratio of labor cost to cost of saved cement is carefully investigated to ensure economy of the project. In many case it is not economical and this type concrete is selected for only special projects.