Page 20 - Microsoft Word - 20120528 Unesco study

2.3.3 Constructions
For this study standard constructions are used, based on practice. The standards for traditional
constructions are given by the SCT. These constructions are calculated by PowerCem
technologies as described in this paragraph. With this information the standards for RoadCem
based construction are designed.
Therefore, for all road and soil types, 2 constructions are designed:
- 1 traditional construction.
- 1 RoadCem construction.

Calculation methodology:
The constructions are calculated using an iterative process. Construction is assumed on the
basis of previous experiences. The construction will be checked on possible failure
mechanisms. To optimize the chosen construction, the following variables can be changed:
- Types of materials used.
- Physical parameters of the materials.
- Dimensions of the layers.

The calculation steps are summarized below.

Step 1: Determination of loading
First the expected loads on the road have to be assumed. For this study these values depend
on the road type. A distinction is made for the heaviest load which can occur, and the standard
repeating loads. This information is defined by the SCT.

Step 2: Determination of stresses and strains
Using the computer program BISAR the strains and stresses in the construction will be
determined. BISAR is a linear elastic calculation program which uses the stiffness and viscosity
of the materials to calculate the stresses and strains on the most critical points of the
pavement construction.

Step 3: Control of the maximum stresses and strains
In step 1 the stresses and strains are calculated on the critical points. These strains and
stresses have to be checked with the parameters of the material, i.e. Is the material able to
absorb the stresses and strains? For most materials these properties are made available by the
supplier.

Step 4: Fatigue properties
The most common failure mechanism of a road construction is the result of repeating loads, in
general the passing of trucks. There is a significant difference in this failure mechanism,
comparing a RoadCem pavement construction and a traditional construction.
For a traditional construction, there are 2 standard failure mechanisms:
1. Repeating strain in the bottom of the asphalt layer will lead to crack’s. These cracks
will reflect to the surface. The quality of the road will be significantly reduced and
structural maintenance will be required.
2. In a pavement construction with a limited depth of asphalt, there will be permanent
deformations in the unbound layers below. The deformations will reflect on the
surface with crack’s appearing which will require structural maintenance

Both of these scenarios have to be checked.

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