Fine aggregates in SCC / Normal concrete

Fine aggregates is a key component in SCC as well as normal concrete, it gives volume to the cement mortar without which the concrete will segregate very easily.

Fine aggregates used for concrete can be of different types as well as grades, some broad classification of fine aggregate is stated below:

•          Natural / River sand – These are produced naturally by weather disintegration of rocks & which has been deposited by stream/river or glacier agencies.
•          Crushed Stone sand – As the name suggests, it is a man made product, produced by crushing hard stones.
•          Crushed Gravel Sand - It is also a man made product, produced by crushing natural gravels.

The use of fine aggregate is dependent upon the availability of a particular type of sand at that area. If river sand in available it is generally used, if not any other alternative that is easily available may be used. Based on the aggregates available a concrete mix design shall be determined by trial before starting concreting work.

As per the attached grading chart Fine Aggregates of all zones can be used to produce concrete, but Zone II is the most commonly used, Zone I, III & IV shall be used cautiously as coarser / finer grains would give a different impact on the workability of the concrete. Trials to be finalized, with satisfactory results of V-box, U-Box, J-ring tests as well as flow test in case of SCC concrete. During an ongoing project, the fine aggregate shall be tested per truck load to ensure that only nominal variation between the truck loads is accepted or as to store it in different slot for different application of sand in that project.

Another test that should be carried out at every intake of sand is to check the moisture content of that particular lot, it provides the value we need for moisture correction during creation of batch sheets used at batching plant. The process is to take a finite weight of the sample (say W₁) heat that in an oven & then weight again (say W₂). Now the difference between the weight’s is the amount of moisture present in that given sample (X = W₁ – W₂). Percentage moisture content is calculated by (X / W₁ x 100).