Question

In designing a sprayed seal, the objective is to determine an application rate for the bitumen so that the aggregate is partially embedded in the bitumen. Describe how the following factors influence the design calculations for the bitumen application rate, and the effect of changing each of these factors. a) Average Least Dimension (ALD) of the aggregate. b) The surface texture of the surface to be sealed

Answer 1

Ans a) Average Least Dimension(ALD) of aggregate is the smallest perpendicular distance between two parallel plates through which the particle just pass . It is necessary to determine ALD because it helps to calculate application rate of Bitumen . The volume of voids between aggregate after rolling and spreading will be minimum if ALD is calculated and mix is designed according to that because the aggregate after spreading and traffic compaction adopt a position whereby their least dimension is vertical. Aggregates with less ALD helps to produce optimum mix and high spread rate with minimum voids while the aggregate with large ALD require lower spread rate to make it settle with the help of rolling.

Ans b) In order to prevent excessive aggregate loss , about 70% of aggregate should be embedded in the surface to be sealed .If embedded aggregate is less than 70% than majority of aggregate will be chipped off from seal under loading and compaction..To achieve this 70% embedded aggregate goal , it is necessary to know surface texture of surface to be sealed. Rough textured surface usually support the aggregate penetration.If surface texture of surface to be sealed is smooth then it may be difficult to achieve 70% or more than 70% aggregate embedded into surface