25 + 10
Figure 1. Bituminous waterproofing layer.
Two 400 × 280 × 75mm thick Hyson Cell pavements with a 4mm rubber bitumen waterproofing layer sandwiched at the neutral axis of the combined structure.
10mm pegs @ nominally 600c / c both ways if slope greater than 1 in 1.
10mm pegs @ nominally 1 000c / c both ways if slope less than 1 in 1.
achieved with the correct mix, this can be degraded to as little as 50m ² per day if 19mm stone is added to save costs on the fill. The savings of the cost of the fill are therefore more than offset by the poor workability of the mix, totally putting the brakes on productivity. It is also very difficult to achieve a satisfactory finish with large aggregate present. The grout mix should generally be a‘ pumpable mix’, even if pumps are not used.
River sand should be used with no other aggregate added. this on site, by adding a few small packets of the Hyson Cells superplasticiser / retarder to the truck. This modified the slump to 120 – 130 mm( for the slopes) without adding water and so consequently without reducing the strength of the mix.
The quantity of additive required was arrived at by careful trial and error, so that it was not overdone. Adding the plasticiser on site also enabled the contractor to remain in control and make small adjustments on an as-required basis.
False economy of crusher dust At Phalaborwa, the ready-mix plant added crusher dust to the mix while the floor was being cast. Production was satisfactory, and the presence of the crusher material was not noticed at that time. However, when construction of the walls began, problems were immediately encountered and Jannie Meintjies of Süllwald Bouers called Hyson Cells to the site. After assessing the situation, it was found that when the crusher dust was discontinued and the Hyson special plasticiser / retarder was added, the contrast in improved production was remarkable.
Control of the grout mix
Cost benefit of Hyson plasticiser Phalaborwa showed that the workability of the mix is critical to production and to the finish that can be achieved. The use of the plasticiser / retarder supplied by Hyson Cells is very cost efficient. Production on the walls that was initially 75m ² per day while the crusher dust was present, was improved to 550m ² with the crusher dust removed and the flow ability controlled by adding the Hyson Cells plasticiser. The plasticiser only adds about 2 % to the direct cost of the grout. Meintjies was quickly converted and thereafter, the additive became part of the standard routine.
On-site modification of mix The technique that was adopted was to order the grout from ReadyMix with a standard slump of 90 – 100mm, but to modify
16 Water Sewage & Effluent July / August 2018