# Step for determining the quantity of bitumen & aggregates for road surface dressing

This construction video tutorial sheds light on the detail method to workout the quantity of bitumen and aggregates toward road surface dressing (Top Layer of the road).

The area of the road is taken as, Area = 20m^{2}

The density of the road surface dressing on top should taken as 12 mm and it is demoted as T_{C}

Here, the value of T_{L} is unknown. T_{L} denotes loose thickness that should be maintained after compaction

T_{L} is based on the following factors :-

Initial Voids = 50% (existence or air or air pockets i.e. gaps in aggregates)

Final Voids = 20%

Wastage = 10%

Suppose that Bitumen will fill 60% of the final voids.

T_{C} is defined as compacted thickness

To determine the thickness of T_{L}, the following formula is used :-

T_{C} = 50% in T_{L} + 20% in T_{C}

Now convert the value to decimal by dividing with 100 = 0.5 T_{L} + 0.2 T_{C}

T_{C} ? 0.2 = 0.5 T_{L} = 0.8 T_{C} = 0.5 T_{L}

T_{L} = 1.6 T_{C}

putting the value of compacted thickness, we get

T_{L} = 1.6(12) = 19.2mm

So, loose depth is 19.2 mm

Now, after adding 10% wastage, we get = 19.2mm + 19.2(0.1) [convert to decimal value by dividing with 100]

= 21.12mm

So, loose thickness should be 21.12mm to attain 12mm compacted thickness

To get more details, watch the following video tutorial.

Video Source: F&U-FORYOU