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<< Click to Display Table of Contents >> Bond |
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The bond between the sub-base and the concrete slab not only has an important effect on the curling stress in the slab but also on the permeability of this interlayer to water and thus erosion of the sub-base as well as the development of crack spacing in the reinforced concrete pavements (CR and UT). Bond is critically important if very thin slabs are placed on top of existing pavements as part of a rehabilitation action. Well-bonded slabs result in reduced curling, lower stress in the slab and a lower risk of voids developing between sub-base and slab. The following table gives a guideline to the factor that can be assigned to bond between slab and subbase:
Sub-base Type |
Stiffness E (mPa) |
Bond Factor* |
New asphalt: No stripping |
2500 - 8000 |
8 - 10 |
New asphalt: medium strip |
1200 - 2500 |
3 - 5 |
New asphalt: high strip |
400 - 1000 |
0 - 1 |
Old asphalt: no strip |
2000 - 7000 |
4 - 6 |
Old asphalt: medium strip |
800 - 1200 |
1 - 3 |
Old asphalt: high strip |
250 - 600 |
0 - 1 |
Strong concrete |
30000 - 50000 |
0 - 1 |
Medium strength concrete |
15000 - 30000 |
0 - 1 |
Weak concrete |
8000 - 15000 |
0 - 1 |
Newly cemented G1 & G2: C1 |
2500 - 9000 |
3 - 5 |
Old cracked C1 |
200 - 1000 |
1 - 3 |
Newly cemented G3: C2 |
2000 - 4500 |
3 - 5 |
Old cracked C2 |
200 - 800 |
0 - 1 |
Newly cemented G4 & G5: C3 |
1000 - 2500 |
3 - 5 |
Cracked cemented G4 & G5: C3 |
120 - 500 |
0 - 1 |
Newly cemented G6 & G7: C4 |
1000 - 2500 |
2 - 4 |
Old cracked & weathered C4 |
80 - 400 |
0 - 1 |
Best quality crushed stone: G1 |
300 - 1000 |
6 - 8 |
High quality crushed stone: G2 |
150 - 800 |
4 - 6 |
Base quality gravel: G3 |
100 - 700 |
2 - 4 |
High quality sub-base gravel: G4 |
80 - 500 |
1 - 3 |
Sub-base quality gravel: G5 |
70 - 300 |
0 - 2 |
Selected quality gravel: G6 |
60 - 200 |
0 - 1 |
Good quality gravel: G7 |
50 - 180 |
0 - 1 |
Natural gravel: G8 |
40 - 140 |
0 |
Sandy soil: G9 |
30 - 190 |
0 |
Clay soil: G10 |
15 - 50 |
0 |
*Note: If the surface of the sub-base is smooth and oily, use the lower values for Bond and if the surface is textured (milled or rough) use the mean or higher suggested values for Bond.