Page 131 - SAPEM-Chapter-10-2nd-edition-2014

South African Pavement Engineering Manual
Chapter 10: Pavement Design

9. STRUCTURAL CAPACITY ESTIMATION: CONCRETE BLOCK PAVEMENTS
The methods that are available for designing concrete block pavements are described in detail in Concrete Block
Paving Book 2: Design Aspects published by the Concrete Manufacturers Association (CMA, 2007). The methods are
divided into the following four categories:
• Equivalent thickness concept
• Catalogue design method
• Research based design methods
• Mechanistic design methods (Lockpave and blokPAVE)

9.1 Equivalent Thickness Concept
The equivalent thickness concept assumes that the pavement can be designed with established flexible pavement
design procedures, and that the blocks and bedding sand substitute an equivalent part of the conventional design.
Table 55 gives a summary of the various values of equivalent substitution used in Argentina, Australia, UK and USA.
Using the equivalency factor, the block pavement is designed with well-established flexible pavement design
procedures, incorporating a measure of subgrade strength, such as the Californian Bearing Ratio (CBR).

Table 55. Summary of Various Factors of Equivalent Substitution

Country Concrete Block Paving is Equivalent to…
Argentina 2.5 times thickness of granular subbase
Australia 2.1 – 2.9 times thickness of crushed rock base
1.1 – 1.5 times dense graded asphaltic concrete
USA Corps of Engineers 165 mm cover
2 – 2.85 times thickness of granular base
United Kingdom 225 mm of soil cement
160 mm of rolled asphalt

This design approach assumes that block paving responds to traffic in a similar manner to conventional flexible
pavements and that, consequently, there is no impediment to the use of established design procedures. However,
this is not strictly correct. The advantages particular to block paving, such as the development of progressive
stiffening and lockup, the ability to tolerate large transient deflections, and the ability to spread the load, thus
reducing the stress below the bedding sand, are not recognized.

The equivalent thickness concept is not generally used in South Africa for designing block pavements.

9.2 Catalogue Design Method

With the catalogue design method, the blocks and base thickness are selected based on experience of road
construction on subgrades similar to that under consideration. Where experience is extensive, as in Europe, this
simple approach can yield satisfactory results. The design procedures are often presented as a design catalogue,
which encapsulates local knowledge, but tends to make little distinction between different subgrade conditions or
wheel loads.

In South Africa, these design manuals are based on catalogue designs:
• Draft UTG2 (1987): Structural Design of Segmental Block Pavements for Southern Africa
• Guidelines for the Provision of Engineering Services in Residential Townships. (Community Development,
1983.)

In all cases, the road is classified in terms of traffic volume (cumulative E80s), traffic type (residential or industrial)
and climatic conditions. Once the road has been classified, the catalogue can be used to select the pavement design.
Figure 54 is a typical design taken from UTG2. The material classes specified for the pavement design are as per
TRH14. The catalogue method lacks flexibility in that only subgrade strength of CBR = 10 or 15 is accommodated,
and often yields a less than optimal pavement design. Experience with the catalogue in Figure 54 is that the
pavement structures are thinner than required.

Section 9: Structural Capacity Estimates: Concrete Block Pavements
Page 120