Sample Lab Aggregates

The objective of these experiments is to determine specific gravity, absorption capacity, and fineness modulus of a f ine aggregate sample and to plot a gradation curve for the sample. The scope of the experiment was limited to one aggregate sample only. In determining the SSD and oven-dry weights needed for calculation of specific gravities, a conical mold was used to reach an SSD condition and the sample was later dried in an oven. Sieve analysis determined the particle size distribution by sifting the aggregate through a series of eight sieves of different sixes by use of a mechanical shaker.

Part B used sieves to d etermine the r elative size of particles in the aggregate. Specific gravity is the ratio of the mass of a given volume of material to the mass of an equal volume of water. The water c ontent of a concrete mixture can a ffect its strength, durability, and cost. The fineness modulus is an i ndex n umber that is roughly proportional to the average si/e of the particles in a g iven aggregate, w hich a ffects a mixture’s gradation. Gradation is the distribution of particle si/c w ithin a given sample of material and affects economy, d urability, workability, and shrinkage in concrete.

Loose sand was cleaned from around the base and the m old was r emoved by l ifting it v ertically. When the sand slumped slightly, it i ndicated that it had reached a s urface dry c ondition. If the sand retained the mold shape, it i ndicated the sand was in a wet c ondition. This process was repeated u ntil an appropriate slump indicated SSD c ondition had b een achieved (Figure 4). Figure 2: Conical mold f illed with sand Figure 3: Sand tamped with rod Figure 4: Slump indicated SSD condition 3. 4. 5. A pproximately 400 g of the SSD aggregate was t aken. The exact w eight of SSD sample (D) was recorded.