SCC 2013 Seminar
SELF COMPACTING CONCRETE …...the way of the future
Members and guests were exposed to a day of both technical and practical presentations at the recent Self-Compacting Concrete seminar road show – SCC Seminar 2013, organised by the national office. Events were held in Durban, Port Elizabeth, Cape Town and Johannesburg.
Delegates at SCC Seminar 2013
In his opening address, John Sheath, CEO of the Concrete Society and Chair of the seminar, described self-compacting concrete (SCC) as an innovative concrete material which is highly flowable, non-segregating that can flow into place, fill the formwork, and encapsulate the reinforcement without any mechanical consolidation. “Because of its characteristic fresh properties”, he said, “It has the potential to dramatically alter and improve the future of concrete placement and construction processes”.
He went on to say that the objective of the seminars was to bridge the gap between research and practice; link science with practical application and describe a number of projects and types of applications where SCC had been used successfully.
First to present was Brenton Brouard from Chryso SA who described the various component materials required to ensure a successful SCC. He covered chemical admixtures, cements, fillers and aggregates, detailing their attributes and role in overall mix design.
This was followed by a very lively presentation by George Evans representing the Cement and Concrete Institute who gave very sound advice to delegates on the specification, testing and performance of SCC. Tests include:
- Filling ability/Flowability
- Passing ability (through the reinforcement)
- Segregation Resistance
- Compressive Strength
- Dimensional Stability
He emphasized that self-compacting concrete was all about the production and placing of the flowable material, as once in the form or mould, it was then conventional concrete with the standard requirements in terms of strength, stability and durability. The highlight of the presentation was the pouring of the 140 slender columns that surround the Soccer City Stadium, all of which were cast using SCC. The challenges had been the complex shape and angle of the columns, as well as the fact they contained 860kg per m3 of steel reinforcement. “They simply could not have been constructed with conventional concrete”, he concluded.
Being such a liquid and free-flowing material, SCC requires special attention when it comes to the formwork used. Vaughan Burgess from Form-Scaff presented some sound technical advice when he described the pressures involved in casting SCC, particularly when it came to the rate of pouring the concrete.
He cited some examples of where insufficient time had been allowed for earlier pour layers to gain any strength before the next pour, resulting in too high a pressure in the formwork and subsequent bursting out of all the liquid concrete.
His final word to the delegates was - “Slow down - resist the temptation to cast the concrete as quickly as possible.
Stephan Zeranka, a PhD student at Stellenbosch University presented the results from his work carried out so far on the use of steel fibres in self-compacting concrete.
He showed that the superior workability of self-compacting concrete (SCC) can be used to improve the uniform dispersion and effective utilisation of fibres, which is necessary for the wider and reliable structural use of fibre-reinforced concrete (FRC). Combined benefits of SCC in the fresh state and properties of FRC in the hardened state are possible. This can lead to new possible fields of application, he concluded.
Moving to a more practical presentation Hennis van Zyl from Lafarge presented his experiences with a proprietary self-compacting concrete system. The successful projects he described, all in South Africa, illustrated some of the many advantages of using this type of concrete placement – e.g. speeding up project time, passing highly congested reinforcement, getting into limited access areas and providing excellent architectural finishes.
Architectural SCC at the Menlyn Podium in Pretoria
The afternoon session began with a presentation by Professor Rainer Haldenwang of the Cape University of Technology, ho reported on work carried out ion the effect of superplasticisers on the reproducibility of SCC. By way of background he took delegates through a précis of the theory of Rheology which provided some fascinating details about the deformation and flow of matter. This included details of the use of rheometers that can be used to measure the rheology of concrete.
Prof. Haldenwang went on to describe the research work that his B.Tech students had carried out on the rheology of concrete mixes containing different superplasticisers, and then summarising the reproducibility results.
An engineer’s perspective was presented by Ric Snowden of Arup (Pty|) Ltd in Cape Town and Port Elizabeth, whilst Pheku Montwedi, also from Arup, presented in Durban and Johannesburg. Delegates were taken through the use of high slump concrete (not SCC) on two projects – the K29/N14 Interchange Bridge and the precast segments for the Gautrain viaducts. In both cases it was shown that if SCC had been used on these projects, many of them would not have been experienced. Ric Snowden was very supportive of the principle of SCC and suggested that engineers should in future be specifying this where appropriate.
Gautrain viaduct precast segment
The final presentation of the seminar was a comprehensive look at projects around the world that had successfully used SCC in their construction. Daniel van der Merwe, Architect from C&CI illustrated the use of this unique material in a multitude of architectural structures. These ranged from churches and libraries to music halls and residences in Europe, Asia and South America.
All projects had used SCC very successfully and illustrated the incredible finishes that this material can offer. Daniel stressed however, that when deciding upon fair-faced SCC through formwork, design objectives should be communicated. The formwork pattern plan, formwork sheeting jointing, sheeting type - and porosity, planning of joints and corners, formwork anchors and spacers should all be defined.
Agreement should be reached on sample or test surface panels which are costed for separately- and which also become the reference for assessment criteria.
In his closing remarks, the seminar Chair, John Sheath expressed his thanks to the speakers, the sponsors, the head Office staff and the delegates for their support for and their participation in the SCC seminar.