A Self-Learning Manual - Institution of Engineers Mauritius

A Self-Learning Manual
Mastering Different Fields of Civil Engineering Works (VC-Q&A Method) Vincent T. H. CHU
Robert P. Cooper (1986)).
3. What is the function of a sand layer underlying paving
slab/interlocking blocks? (S2)
Normally after the laying of sub-base layer of the paving slab/interlocking
blocks, a 30mm thick sand bedding is screeded and tamped over the
pavement area. Then paving slabs are laid horizontally with joints of
2-3mm wide and are laid in uphill direction. After completing the laying of
paving slabs, sand used for filling joints is spread over the surface of the
units and brushed into the joints such that all joints are completely filled.
The paving slabs are then bedded into final position by using plate
vibrators.
The sand layer serves the same purpose of normal blinding layer under
concrete structure:
(i) Provide a level and flat surface for the paving slab/interlocking blocks
to lay on;
(ii) Protect the foundation (i.e. underground subgrade and sub-base layer)
against adverse outside conditions (e.g. bad weather) during
construction of the laying work of paving slab/interlocking blocks.
4. Can the sand bedding be omitted in paving block pavement? (S2)
In the paving block pavement, it normally consists of the following main
elements: sub-base, sand bedding and paving blocks. Sub-base is the
main structural element to take up traffic load and spread it into larger area
so that the traffic stress is small enough for subgrade to sustain. Sand
bedding is used for providing correct line and level for paving blocks to lie
on. To achieve this, screeding of bedding layer is implemented so that the
paving blocks could be laid directly on it without the need of further leveling.
The large range of particle sizes associated with sub-base renders it
unsuitable to provide a uniform surface with correct level for paving blocks
to lie on.
5. Should sand layer or cement sand be used as bedding of precast
concrete paving units? (S2)
Cement sand is a mixture of cement and sand and it acts as a cohesive
mass once mixed. Normally, a 20mm to 30mm sand layer is laid
underneath precast paving block units. However, in locations of steep
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