Comparison Between Coarse Aggregate Shape Factors and Resulting Mix Properties Using Conventional and New Universal Gauge Instruments

The aggregate shape factors, such as flakiness and elongation, separately dealing with thickness and length respectively, as well as in combination and angularity number, play a vital role in the properties of resulting granular, as well as bituminous, mixes. These properties are determined using a set of IS sieves, such as 50, 40, 31.5, 25, 20, 16, 12.5, 10 and 6.3 mm and, based on this, the upper limits for their presence in mixes have been specified. However, in mixes, the aggregate gradation consists of sieves, such as 26, 19.5 11.2 mm, etc. This indicates that sieves used for shape factors' determination and actual use are different, which needs rethinking. It is expected that the shape factors and mix properties determined by the conventional sieve instruments may be different from those determined using actual sieves. It was therefore attempted to design and fabricate a single, simple and inexpensive new instrument, referred to in the paper as Universal Gauge, to determine the aggregate sizes and compare with those determined by conventional instruments. It was also attempted to compare the Marshall test properties of semi-dense bituminous concrete mixes using the same aggregate with shape factors determined by the two approaches separately. It was found that the results obtained from the two approaches are different.