Housing in Southern Africa May 2015

Cement & Concrete

on concrete slump and flow. Chryso Southern Africa is a mar- ket leader in concrete and cement admixtures and ancillary products. Due to the latest developments in admixtures, modern concrete is now attaining unparalleled levels in important areas, such as mechanical performance, workability and dura- bility,” says Sepotokele. The global trend amongst precast product manufacturers is to use SCC as an alternative to conventional vibrated concrete (CVC). With its extremely high workability (flow is measured rather than slump), SCC does not require post-cast vibration, whichmeans a greatly reduced noise level in the precast yard. Technical specialist, George Ev- ans at PPC, in conjunction with Chryso, was primarily responsible for formulating the specific design mix that Rocla is using for its SCC. Rocla began experimenting with SCC in 2012, mainly due to the complex forms it had to replicate for several of its products such as the Alfabloc retaining wall system, REBLOC road barriers and wing walls for stormwa- ter outlets. “SCC is ideal for all of our wet-cast applications. Typically our wingwalls are extremely thin walled – in some cases they are only 80 mm thick. Our Alfablocs, which are literally cast in the shape of an ‘A’, also require com- plex, thin-walledmoulds. It is difficult to achieve this with CVC. Hence the main reason for incorporating SCC into our production as it gave us the ability to take on more complex projects and allow us to broaden our product range,” says Jason Roberts, civil technologist at Rocla. “We had to look at redesigning our SCC mix when we changed our material supplier. You cannot simply change the cement and sand and expect to get the same product. SCC is a lot more sensitive. It is almost a new animal in terms of concrete,” says Roberts. Chryso Southern Africa now sup- plies six of Rocla’s 12 plants with a rangeof products, fromsuperplasticis- ers and accelerators to mould release oils. Sepotokele attributes the success of the project to the close working relationshipachievedbetweenChryso Southern Africa and Rocla. He says, “Our aim is to provide tailor-made so- lutions for thespecificapplicationsand requirements of our clients. Working withprogressive clients likeRocla also serves toadvanceconcrete technology in South Africa.” ■

Admixtures

Construction chemicals specialist, Chryso Southern Africa, is supplying precast product manufacturer Rocla with its CHRYSO Optima 203 and CHRYSO Quad 20 admixtures for use in self- compacting concrete (SCC).

C HRYSO Optima 203 is a new generation, high range wa- ter reducing/superplasticis- ing admixture, based on modified polycarboxylate technology. “This admixture is formulated primarily to achieve high workability with a wide range of cements, which lends itself

to the sophisticated requirements of SCC mix design,” says Kabelo Sepotokele from Chryso Southern Africa. Sepotokele explains, “Quad 20 is a stabiliser that features a unique for- mulation to increase the viscosity of cement paste, with a limited impact

May 2015