For pavement seals the following materials are used:
• asphalt layers;
• stress absorption membranes (“SAMIs”) (see Fig. 13.37); and
• junction sealing material.
SAMIs act over an old cracked pavement surface, sealing the cracks against water ingress. They often provide a small degree of differential horizontal movement between an old and a new pavement layer so that the relative movements of the parts of the old pavement either side of a crack do not cause a stress concentration in the new, overlying, pavement layer at the same point. Without this ability, a crack in the new layer can quickly form immediately above the old crack — a problem known as “reflection cracking”. Water can then, very quickly, re-enter the road and the overlay will not act as an effective seal (e. g. Fig. 13.38).
