1 Aggregate Primary function: TRH 3 : Surface Seals for Rural and Urban Roads Components  Resistance to abrasion of base  Transfer of wheel load to pavement structure  Skid resistance  Structure for accommodating binder (water proofing)  Protection of binder from UV Additional characteristics:  Light absorbing qualities to reduce glare  Differing texture or colour to define areas

2 Aggregate : Factors affecting performance: TRH 3 : Surface Seals for Rural and Urban Roads Components  Shape  Nominal size  Grading  Hardness, durability, abrasion  Porosity / absorption  Cleanliness, dust content  Spread rate

3 Aggregate : Factors affecting performance: TRH 3 : Surface Seals for Rural and Urban Roads Components  Shape – affects interlock and thus stability  Shape and size – affects void content / macro texture, binder application  Grading – affects interlock, contact area, noise  Strength – affects breakdown during construction and service  Wear – affects abrasion or polishing / micro texture (skid resistance)  Porosity – affects absorption of lighter fraction of binder (durability)  Cleanliness – affects adhesion

4 TRH 3 : Surface Seals for Rural and Urban Roads Components Warning Seal design method is based on strict standards w.r.t size, shape and grading. Changes to these standards could lead to current design approach being inappropriate with possible reduced performance.

5 Binder function: TRH 3 : Surface Seals for Rural and Urban Roads Components  Waterproof pavement structure  Retain aggregate Performance influenced by:  Adhesion properties  Cohesion properties

6 Binder factors affecting seal performance: TRH 3 : Surface Seals for Rural and Urban Roads Components  Binder type and properties  Grade of binder  Spray rate  Viscosity at application  Stiffness, R & B ??

7 Binder type: TRH 3 : Surface Seals for Rural and Urban Roads Components Penetration grade Cut-backSABS Emulsion Homogeneous modified (PMB) Non-homogeneous modified (Bit-rubber) Modified emulsions (various grades and binder content Cutting back of binder – NOT generally recommended

8 Factors influencing selection of binder: TRH 3 : Surface Seals for Rural and Urban Roads Components  Purpose of application i.e. tack coat, penetration spray etc.  Min. temp. at application and early life  Min. temp. during service life  Max. temp. during service life  Road geometry e.g. gradients, tight curves etc.  Traffic  Pavement deflection  Aggregate characteristics

9 TRH 3 : Surface Seals for Rural and Urban Roads Components Properties of polymer modified binder for hot sealing applications

10 TRH 3 : Surface Seals for Rural and Urban Roads Components Properties of polymer modified emulsions for surface seals

11 TRH 3 : Surface Seals for Rural and Urban Roads Components Properties of bitumen-rubber for use in surface seals and asphalt