Water, Sewage & Effluent July August 2018 | Page 17
Correct use of materials is critical to the final finish and to
the speed of construction. Hyson Cells offers support on
mixes using in situ sands and the advice was followed by
Süllwald Bouers.
No large aggregate
Construction workers and concrete suppliers are both
familiar with cost saving that can be achieved with
conventional concrete, by using large aggregate as a filler
material. However, with Hyson Cells, this is not the case.
The flow characteristics of the grout determines the speed
of construction and, while more than 200m² per day is easily
Materials
pores of the grout block itself, as well as thoroughly sealing
the tiny shrinkage cracks between the cast in situ blocks.
Used together with Hyson Cells, the priming coats would
probably prove adequate on their own, but the bitumen layer
is built up to 3–4mm and a final layer of undiluted Waterblok
is applied to provide an additional ‘reserve’ of waterproof
material. This reserve of impermeable bitumen will be forced
into any openings that may result from any movement of the
underlying flexible paving structure because of loads owing
to head of water or trafficking.
The bitumen layer is protected against mechanical
damage, UV degradation, and drying out by the second,
upper layer of Hyson Cells. If not protected, the bitumen
could otherwise peel, especially if it was walked on or
trafficked by vehicles. The upper Hyson Cells layer is
more than a protecting skin: it is a heavy-duty trafficable
pavement, and this allows the dam to be cleaned of silt,
using big mechanical scrapers and trucks.
These pegs were used as supports for horizontal formers that allowed the workers to walk without having to stand on the empty cells. The
long pegs had to be cut to prevent puncturing vehicle tyres later.
Water Sewage & Effluent July/August 2018
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innovations
is required, it is feared that possible subsidence could
cause the joints between the cast blocks to open and so
cause leaking.
With the ‘double-liner bitumen sandwich’, (a) the
encapsulated bitumen layer provides an impermeable
seal, (b) the bitumen is placed on the ‘flexible paving’
bottom layer of Hyson Cells, and (c) the top layer of
Hyson Cells provides protection to the bitumen liner
and distributes the wheel loads of vehicles used for
mechanical removal of silts.
The main purpose of the bottom layer of Hyson Cells
interlocking block paving is to serve as a flexible surface
on which the bitumen emulsion is applied. In the event of
subsidence of the subgrade, the segmented block paving is
only slightly deformed. The blocks tend to rotate and lock
up and so distribute the stresses and limit deformation.
Small-scale controlled cracking and bridging take place
instead of uncontrolled wide cracks, accompanied by large
displacements that would occur with an un-reinforced
conventional concrete slab.
The bitumen layer is 100% waterproof. Waterblok
rubberised waterproofing compound is a mineral-filled
emulsion of a refined grade of bitumen that contains a high
percentage of rubber latex. It is a water-based emulsion
and requires no heating. A high percentage of rubber latex
imparts considerable elasticity to the dried film and it can
accommodate the relatively small displacements of the
underlying Hyson Cells layer on which it is applied. It is non-
toxic to water (SABS 1217) and is unaffected by even 30%
sulphuric acid.
Thin coats of diluted bitumen emulsion are brushed on
to prime the surface. The bitumen therefore penetrates the