Water, Sewage & Effluent July August 2018

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 15 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

Water, Sewage & Effluent July August 2018 | Page 17