Evaluation

Determination of Degradation

The determination of the degradation was based on the rating scheme provided in ISO 4628-4 [5] with additional rating criteria introduced to determine the influence of minute surface cracks (see Tables 4 and 5 as well as Fig. 2).

Evaluation of Degree of Degradation

The degree of degradation (QS-value) is based on the product of the rating of Quantity (Q) and Size (S) of cracks as shown in Eq 1. The approximate rela­tionship between the QS-value and the surface condition is indicated in Fig. 3. The digital photos of the cracked sealant surfaces given in Fig. 4 illustrate the effectiveness of the QS-value to assess the state of degradation of the sealant.

QS(t) = Q(t) X S(t) (1)

where QS(t) is the QS-value after t months, Q(t) is the rating of Q after t months, and S(t) is the rating of S after t months.

TABLE 4—Crack rating index of quantity.

Rating

Quantity of Cracks (Q)

0

None

0.5a

Trace

1

Very few

2

Few

3

Moderate

4

Considerable

5

Dense

aNewly introduced rating.

TABLE 5—Crack rating index of size.

Rating

Size of Cracks (S)

0a

Not visible X 100 magnification

0.3a

Only visible under magnification up to X 50

0.5a

Only visible under magnification up to X 30

1

Only visible under magnification up to X 10

2

Just visible with normal corrected vision

3

Clearly visible with normal corrected vision

4

Large cracks generally up to 1 mm wide

5

Very large cracks generally more than 1 mm wide

aNewly introduced rating.