to blister. For example, if an air pocket beneath a

membrane adhered to a deck at 5 lbf/in. (875 N/

m) is heated from 70 to 140F (24 to 67C), a 5.2-

top of blister)

in. (13.2-cm) radius would be the smallest void that

could blister (Fig. 3a). However, if the air beneath

Equation 2 explains that the smaller the void,

the membrane is continually water saturated, the

the less likely it is to develop into a blister:

critical void would reduce to 2.25 in. (5.7-cm) ra-

dius (Fig. 3b). Of course, higher bond strengths

(2)

are more resistant to blistering, but one must real-

ize that heat, the driving force of blisters, softens

the adhesive and diminishes peel strength. Thus,

where *r *is void radius. That is, it requires more

the 5-lbf/in. force used in the above analogy is

internal pressure (heat) to expand a small void

considered conservative, even though some mem-

than to expand a large one.

branes adhere more tightly to concrete at room

Figure 3, developed from eq 2, illustrates this

temperature.

concept. It consists of four graphs, each composed

The situation changes as soon as the membrane

of three curves, where each curve represents peel

strength plotted against temperature and critical

is topped with hot pavement. In this case the void

immediately heats up to 250F (146C) or more and

size. Each graph defines the smallest void expected

12

10

8

6

10 lbf/in.

4

5 lbf/in.

2

1 lbf/in.

0

12

10

8

6

4

2

0

100

150

200

250

300 100

150

200

250

Temperature (F)

Kh

001

5