6.6 : Compacting Factor test

The compacting factor test is a method used to assess the workability of concrete. It is especially suitable for concrete mixes containing aggregates up to one and a half inches in size. This test involves specialized equipment consisting of two truncated cone-shaped hoppers and a cylinder, all with polished interior surfaces to minimize friction.

The procedure begins by placing concrete into the upper hopper without any compaction. Once filled, the bottom door of this hopper is opened, allowing the concrete to flow into the lower hopper. After the lower hopper is filled, its bottom door is then opened to let the concrete fall into the cylinder positioned below it. Excess concrete is then stricken off to level the surface.

During the test, a steel rod may be used to gently poke and dislodge any concrete that may get stuck in the hoppers. The weight of the concrete within the cylinder is recorded, and its density when partially compacted is calculated. For comparison, the fully compacted density of the concrete is determined by filling the same cylinder with concrete in four layers and tamping each layer thoroughly to ensure maximum compaction.

The compacting factor is calculated as the ratio of the density of the partially compacted concrete to the density of the fully compacted concrete. This ratio provides a numerical value that indicates the workability of the concrete, with different levels of the compacting factor reflecting varying degrees of workability. This test is crucial for understanding how the concrete will behave when placed in molds or forms during construction projects.