Civil Construction Materials Q&A

1. In shaking the sieve, which is preferable – horizontal or vertical motion?

The horizontal motion is preferable for shaking the sieve. Besides performing uniform istribution to the aggregate, it prevents collision between aggregates and sieve container that happens to break the particles into smaller parts. This increase the accuracy of the sieve result obtained. In addition, horizontal motion allows lesser dust escaped into the air compared with the vertical motion.

2. Should the amount of the shaking time be the same for all specimens?

Different specimens has different amount of the shaking time required. It is determined by type of samples used assuming the number of sieves used is fixed. Fine aggregate consumes more time compared to coarse aggregate. The main reason of this concept does not lie on the mesh size nor amount ratio but the weight of those tiny particles. Basically, mesh sizes used are always reasonable to its particle sizes. Imagine if the image of course aggregate with its suitable mesh was minimized, it becomes the picture of fine aggregate with its mesh just that the amount of particles are more likewise to the number of openings increased for fine aggregate. The ratio had become equal in this case.

However, the weights of particles subject to same shaking force applied made the different especially for shaking in vertical motion. Fine particle can be thrown higher than coarse particle with same force applied meanwhile lands slower than coarse particle when they are both in the air due to its lightness. Thus it needs longer time for each and every tiny particle to reach its receiver.

3. How would the grading of the aggregates for both coarse and fine, affect the workability and compressive strength of concrete?

Larger aggregate has smaller surface area compared to the finer aggregate which leads to lesser water needed for its mixture process. Generally, the amount of water added into the mixture is the main key to concrete’s workability and compressive strength. It will increase the workability of concrete somehow reducing its compressive strength.

Workability of concrete is defined as the ability of a fresh concrete mix to fill the form or mold properly with the desired work and without reducing the concrete’s quality.

Thus to reach optimum result for construction purpose, a well graded soil is needed as smaller size particles are to be filled into the voids between larger size particles in the concrete to reduce its porosity meanwhile achieving maximum compressive strength. Well graded soil consist various sizes of particle which prevents concrete to fail.