The Constructor

Plum Concrete: Applications and Procedure of Laying

Plum Concrete

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Plum concrete, also termed cyclopean concrete or rubble concrete, is a mixture of wet concrete and a plum (large size, strong, and clean natural coarse aggregate or boulders of roughly 300 mm size or larger). Plum occupies approximately 30-40% of the total mass of concrete.

The addition of plum to concrete reduces the heat of hydration as it prevents the use of an excess quantity of cement without compromising on strength.  

Plum concrete is mainly used where mass concreting is required, as in the construction of gravity dams, embankments, filling of deep or uneven areas, foundations, etc. So, it is an economical alternative to conventional concrete.

Figure-1: Plum Concrete

Plum (Aggregate) Properties

The plum that is used to produce plum concrete needs to comply with the ASTM standard. Its desired properties are:

  1. The size of natural stone or boulders, i.e., plum, is approximately 150 mm, 200 mm, 300 mm, or larger. The size is selected based on the project, availability of materials, and engineering decisions.
  2. Angular-shaped stones are favorable for producing plum concrete.
  3. The plum should be clean and free from oil, dirt, or other harmful materials that may compromise proper adhesion or bonding with concrete.
  4. It should be of good quality, sound, durable, and free from segregation, seams, cracks, and other structural defects or imperfections.
  5. Plum should also be free from the worn or weathered and rounded surface.

How to Place Plum Concrete?

  1. Spray water on the surface on which plum concrete is to be placed. After that, spray anti-termite compound, which is essential for the foundation of a structure.
  2. Place a minimum of two layers of concrete to ensure that the bottom of boulders is embedded in concrete to eliminate voids at the bottom.
  3. Next, the natural stones are placed carefully making sure that they are not dropped into concrete. The distance between two boulders or a boulder and a form should not exceed 50 mm.  
  4. The concrete placement is carried out layer by layer until the required level is attained.
  5. The thickness of each layer should not be greater than 900 mm.
  6. Curing of plum concrete should be done for a minimum of seven days.  
Figure-2: Placement of Plum Concrete at the Foundation Base

Applications of Plum Concrete

  1. Level deep pits or uneven surfaces at the bottom of foundation excavations to reduce construction costs. In this manner, the bottom level or bed of foundation is reached using low-cost but strong materials.  
  2. Construct the base of concrete footings and foundations.
  3. Rubble concrete is employed in areas where massive concrete placement is required, for instance, concrete dams, bridge piers, side slopes, and barriers.
  4. Plum concrete, produced by mixing 150 mm boulder size and cement content of at least 173 kgm3, has been used to construct an actual dam.
  5. Reduce the cost of large thickness Portland cement concrete.
  6. It is used for the construction of machine foundations where a large mass of concrete is required for the safety of the foundation and machine.
  7. It is used for the construction of beds of water channels
Figure-3: Plum Concrete for Sloping or Uneven Surface

FAQs

What is plum concrete?

Plum concrete, also termed cyclopean concrete or rubble concrete, is a mixture of wet concrete and a plum (large size, strong, and clean natural coarse aggregate or boulders of roughly 300 mm size or larger). Plum occupies approximately 30-40% of the total mass of concrete.

What are the applications of plum concrete?

Plum concrete is mainly used where mass concreting is required, as in the construction of gravity dams, embankments, filling of deep or uneven areas, foundations, etc. So, it is an economical alternative to conventional concrete.

What are the characteristics of aggregate used for plum concrete?

1. The size of plum could be 150mm, 200 mm, 300 mm, or larger
2. The shape needs to be angular
3. Clean from any dirt
4. Hard, durable, sound, and free from cracks and structural defects

Read more:

How to choose quality coarse aggregate for concrete construction?

How aggregate affects the mix design of concrete?

How long does concrete take to cure?

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