Rajib B. Mallick, Distinguished Professor of the Ralph White Family, Civil and Environmental Engineering, Worcester Polytechnic Institute (WPI), Massachusetts, USA, Veeraragavan Amirthalingam, Professor of Civil Engineering, IIT Madras Hot mix asphalt (HMA) is mainly composed of mineral aggregate and asphalt binder.

They are heated and mixed at high temperature (~150oC) in the factory, and placed together with the paver at a low but sufficiently high temperature (~140oC) ), and before the temperature drops below a certain level (usually 90-100oC) with roller compaction. Due to the increased stiffness, once the temperature of the mixture drops below about 90oC, compaction usually becomes very difficult.

This change in stiffness is the result of the change in the stiffness of the asphalt binder, which behaves as a viscous material at high temperatures and as a viscoelastic material in most other temperature ranges. The carefully designed and constructed HMA pavement provides a durable, smooth and waterproof surface at a relatively low cost. HMA (also known as asphalt) pavements do not need to create joints like ordinary Portland cement concrete (PCC) pavements.

However, unless trapezoidal paving is used, longitudinal seams will appear between adjacent paving lanes. During the first pass of the paver, the first lane is constructed. When placing adjacent channels, the first channel is already cooled and is called the cold side of the joint.

The second channel is often referred to as the hot side of the joint. During the compaction of the cold lane edge, the road surface is not constrained, so the density near the edge is lower (higher clearance) compared to the area far from the edge. There is a restriction when compacting the edge (hot side) of the adjacent lane because it is placed next to the cold seam. Due to problems at the joint and on both sides of the joint, the density directly in the joint is almost always lower than that of the asphalt mixture away from the joint.

The low-density joint area is the “Achilles’ heel” of other well-structured pavements because it may allow water and debris to enter the pavement quickly and may cause subsequent disintegration and premature damage

News Source : NBM&CW