The supporting structure in any pavement design is provided by the base and sub-base materials.
Colto requirements state that the aggregate for base and sub-bases should be derived from hard, sound and durable rock.
Note: CAS-SA does not use approved target grading to produce a product
Approved target gradings are determined by laying a trail section using material that complies with Colto requirements. Before compacting, several samples of the material in situ are taken and subjected to analysis. The resultant grading curve is then classified as the approved target grading for that project and all future grading results are appraised against this target.
To achieve good workability, compaction and density, the hardness and particle shape of aggregate used in road layer works are very important.
Soluble Salt Requirements:
Colto recommends the following on-site:
For quartzite, tillite, shale and G1 to G4 materials, measure the soluble salts against pH or electrical conductivity.
- Use material if the pH is > 10 after treatment at the crushing plant, and subsequently remains = 8,0.
- The pH is < 6,0 treat with lime until the pH = 10,0 before use
For Natural gravel and other crushed aggregates, use material if the electrical conductivity (EC) is 0,15 Sm-a, but pay particular attention to design and construction if the pH =6,0
- pH = 6,0 the EC is 0,02 Sm-a and sulphates are not a problem, use the material. If not, analyse the material in accordance with the customer’s instructions and submit a proposal for approval.
- Where the salinity of water added for compaction causes the salinity of the material to increase, determine soluble salinity within 24 hours to compaction before a prime coat is applied.