five main categories : plasticisers , superplasticisers , air-entrainers , accelerators , and retarders .
CEC : Briefly , what are the individual characteristics of these admixtures ? NS : When plasticisers are added to the concrete mix , they enhance workability by repelling binder particles and distributing the particles more evenly throughout the concrete . Superplasticisers can reduce the required water content of the concrete mix by 15 – 20 %. Air-entrainers introduce bubbles into the concrete mix to provide maximum protection against freezing and thawing , and increase workability when the mix lacks fines . Accelerators speed up the chemical reaction of the cement and water and consequently , the rate of hydration , improving the setting or early gain in the strength of concrete . Retarders , on the other hand , slow the chemical reaction of cement and water , providing longer setting times and slower initial strength gain .
CEC : When did the construction industry become converted to the role that admixtures can play to enhance performance and durability ? Was there substantial early resistance ? NS : It was during the 1980s that admixtures really started to be regarded as an essential part of concrete mix design . In the early years , there was scepticism from some quarters , but as the industry has advanced — and been able to really measure the benefits of admixtures — there are very few projects on which admixtures are not included in the concrete mix design today .
CEC : Is there a particular facet of the construction operations that particularly benefit from the use of admixtures in the concrete ? NS : Many precast operations now use self-compacting concrete ( SCC ), which is a highly flowable type of concrete that spreads into the form without the need for mechanical vibration . It is a nonsegregating concrete that is placed by means of its own weight . With careful mix design , SCC admixtures produce a concrete that is fully flowing and self-compacting and can be placed with no vibration . SCC functions in the same manner as superplasticised , flowing concrete but does not need any compacting effort . It is also less susceptible to bleed and segregation . Admixtures – specifically superplasticisers – produce fluid SCC that is cohesive with high flow retention . SCC is also extremely pumpable . The towering pylons of the Nelson Mandela Bridge in Johannesburg were , for example , filled with SCC based on a superplasticiser supplied by Chryso .
CEC : What exactly was ‘ new ’ in Chryso ’ s New Generation range of admixtures that have been around for a few years now ? And how radically did these relatively ‘ green ’ chemicals change the fortune of admixtures not only in this country , but worldwide ? NS : The new generation admixtures are based on specific raw materials or polymers ( poly carboxylates ). These raw materials and formulations radically improve the performance of the admixture in terms of water reduction / workability retention and strength development compared to traditional or old generation admixtures . A key benefit for Chryso is that we produce our own raw materials for the formulation of our New Generation products .
CEC : Which sectors of the construction industry are the main users of your admixtures ? NS : Ready-mix concrete users mainly use admixtures to adjust the workability retention of concrete ; precast users use admixtures to speed placing and setting times so that they can get faster turnaround time of the moulds and improved surface finishes ; and for on-site mixing for new construction , different admixtures are used to meet a project ’ s specific needs .
CEC : How important is the advisory role and after-sales service in the admixture industry ? NS : Accurate dosing is essential to fully capitalise on the benefits of admixtures . Dosage rates and admixture selection are determined through a series of trial mixes to optimise concrete properties . This is why it is vital for suppliers of admixtures to provide detailed guidelines to assist with the design of mix proportions and admixtures dosages . As for after-sales service , Chryso has recently substantially expanded its laboratory testing facilities with the opening of a new Centre of Excellence in Jet Park . The Centre features ultra-modern equipment and temperature control systems to offer cement , concrete , and construction systems technology as an added-value service to customers . The Centre ’ s testing and advisory service to customers is the most comprehensive of its kind available in the South African admixtures industry and can provide tailor-made solutions to match specific applications and customer requirements . This service is provided free of charge to Chryso customers . nn
TECHNOLOGY
The towering pylons of the Nelson Mandela Bridge in Johannesburg were filled with self-compacting concrete , based on an admixture supplied by Chryso .
CEC April 2018 - 23