In Calculating Specific Gravity for Both Fine and Coarse Aggregate, the Density of The

Discussion

In calculating specific gravity for both fine and coarse aggregate, the density of the aggregate is compared to the density of water. For instance, our coarse aggregate has a specific gravity of _____. This was calculated by taking the weight of the coarse aggregate, ___, and dividing it by the weight of water of the same volume. The weight of the water of the same volume was found to be ____. It was calculated by taking the weight of the aggregate in water, ____ , and subtracting that weight from the weight of the aggregate. The important principle is that the aggregate weight in air minus the aggregate weight in water yields the weight of a sample of water of the same volume.

We found that the specific gravity for the SSD aggregate is greater than the specific gravity for the dry aggregate. This makes sense, because the SSD aggregate contains more water than the dry aggregate .

The specific gravity for both dried and SSD needs to be known. The dry specific gravity is the specific gravity of the aggregate after it has been dried thoroughly for a relatively long period of time, for example, in the desert. The SSD specific gravity is the specific gravity of the aggregate when it is dry to the touch, but still retains moisture inside it. Aggregates can be used in either state, so both specific gravities must be known.

The fineness modulus was calculated to be _____. This valuenumerically represents the fineness of an aggregate. It is calculated by summing the cumulative percentage retained on the sieves of size 6”, 3”, 1.5”,3/4”, 3/8”, #4, #8, #16, #30, #50 and #100, and then dividing by 100.

It is important for the aggregate gradation to be within certain gradation limits. This is because the aggregate must be well-graded, instead of gap-graded or uniform-graded. When the aggregate is gap-graded, it may be missing a few sizes of aggregate. If it is uniform-graded, it may all be the same size. When the aggregate is not well graded it can cause the strength of the concrete batched with this aggregate to decrease

A problem that we encountered was removing fine aggregate stuck in the wire screens in sieves. This problem may cause measured weights to be incorrect.

Through this lab, we learned how to take an accurate sample of aggregate, as well as how to do a slump test.

Results

Fine Aggregate Sieve Analysis

Specific Gravity and Absorption of Fine Aggregate

Moisture Content of Fine Aggregate

Coarse Aggregate Sieve Analysis

Specific Gravity and Absorption of Coarse Aggregate

Moisture Content of Coarse Aggregate

Dry Rodded Unit Weight of Coarse Aggregate

Fineness modulus

The calculation is as follows: (____+_____+_____+ + + +____)/100

coarse aggregate has a specific gravity of _____. This was calculated by taking the weight of the coarse aggregate, ___, and dividing it by the weight of water of the same volume. The weight of the water of the same volume was found to be ____. It was calculated by taking the weight of the aggregate in water, ____ , and subtracting that weight from the weight of the aggregate.