The original idea of the use of aggregate as an inert filler can be extended to the inclusion of large stones unto 300 mm size in a normal concrete, thus the apparent yield of concrete for a given amount of cement is increased. The resulting concrete is called ‘Plum Concrete’ .
These large stones are called ‘plums’ and used in a large concrete mass. The volume of plums should not exceed 20 to 30 % of the total volume of the finished concrete and they have to be well dispersed throughout the mass. This is achieved by placing a layer of normal concrete, then spreading the plums, followed by another layer of concrete and so on. Care must be taken to ensure that no air is trapped underneath the stones.
The plums must have no adhering coating. Otherwise, discontinuities between the plums and the concrete may induce cracking and adversely affect permeability.
Purpose of plum concrete:
Plum concrete is a special type of concrete which is usually done where the surface is uneven and to minimize the costing of concrete.
Practical Example:- below footings of residential buildings where in a small portion where the slope of ground below single footing is 1:10 to 1:50 in that case to save the cost of concrete plum is usually preferred. This finally leads to minimize the construction cost of building in all.
Uses of plum concrete:
- Plum concrete is used at the water channel beds
- It is used mostly in mass concrete works like concrete gravity dams or bridge piers In such cases pieces of rock about 150 mm in size are used as coarse aggregates to mix a plum concrete.
- It is used at side slopes of the embankment to provide a protective layer to earthen foundations and bases.