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