Inland Branch Technical Seminar: The concrete wisdom of world-renowned Professor Pierre-Claude Aїtcin
Some 50 members and guests of the Inland Branch were treated to presentations by Professor Pierre-Claude Aïtcin, world authority on concrete technology, innovation and construction. Pierre-Claude Aïtcin, is Professor Emeritus of the Université de Sherbrooke, Canada, known and recognized for his visionary qualities, ability to innovate and social commitment, is a role-model for the engineering profession.
During his first brief visit to South Africa Professor Aitcin visited colleagues at the University of Witwatersrand, technical staff at PPC Cement, presented at Concrete Society techincal meetings in Johannsburg and Cape Town and finally, before spending some personal time touring the country, his colleagues at the University of Cape Town.
Two presentations were given to the Inland Branch members entiled: "The sky’s the limit" and "The Science and Technology of Concrete Admixtures".
The sky’s the limit
The first presentation covered the history of concrete technology for high-rise buildingsduring the last fifty years, when concrete technology has made great progress, largely due to the control of concrete rheology through the use of superplasticizers and viscosity modifying admixtures. Thus, concrete rheology is no longer depending only on water, but rather on a judicious balance between water, superplasticizer and viscosity modifier dosages.
Professor Aïtcin went on to say that before the 1970’s, it was impossible to produce concretes having, at the same time, both a slump of 100 mm and a w/c ratio lower than 0.40, due to the limited performance of the lignosulfonate-based water reducers that were then the only dispersing admixtures available on the market.
But, as soon as the very efficient dispersing properties of polymelamine sulfonates and polynaphtalene sulfonates were discovered in Germany and Japan, respectively, it became possible to decrease the w/c ratio below 0.40 while at the same time increasing its slump up to 200 mm.
More recently, a new type of admixture, known as a viscosity modifying admixture (VMA), has been developed to control concrete rheology. VMA is now used when pumping concrete, for underwater concreting and in self-consolidating concrete.
These two innovations resulted in a significant advantage for concrete over steel for the construction of high-rise buildings: it is no longer necessary to use cranes to raise and place concrete; concrete can be pumped from the first to the highest floor. Thus, concrete was pumped up to 586 metres using a single pump during the construction of Dubai’s Burj Khalifa.
He then illustrated step by step, how the construction of high‐rise buildings has evolved from entirely steel structures to entirely concrete structures, by describing the construction of some landmark structures built from 1968 to the present time.
In concluding his first presentation, Professor Aïtcin stated that due to the development of powerful dispersing admixtures and viscosity modifying admixtures, it is now possible to build very efficiently and economically high-rise concrete structures. Thanks to entrepreneurs who challenged the limits of the use of concrete, this became possible with progressive learning over the years of how to pump high strength concretes “up to the sky”.
The Science and Technology of Concrete Admixtures
This presentation was based on Professor Aïtcin’s book with that title.
The book presents admixtures from both a theoretical and practical point-of-view. The authors emphasize key concepts that can be used to better understand the working mechanisms of these products by presenting a concise overview on the fundamental behaviour of Portland cement and hydraulic binders as well as their chemical admixtures.
It also discusses recent effects in concrete in terms of rheology, mechanics, durability, and sustainability, but never forgetting the fundamental role played by the water/binder ratio and proper curing in concrete technology.
Part One presents basic knowledge on Portland cement and concrete.
Part Two deals with the chemical and physical background needed to better understand what admixtures are chemically, and through subsequent sections present discussions on admixtures technology and two particular types of concrete, self-consolidating and ultra-high strength concretes, with final remarks on their future.
In conclusion, Prof Aïtcin predicted that in the future the interaction between particular cements and particular superplasticizers will be more and more complex because:
- commercial cements will be blended cements
- alternative fuels will be used more and more
- different sources of calcium sulphate will be used
The presentations were followed by a lively question time and the Chairman of the Inland Branch, Roelof Jacobs thanked Prof Aїtcin for sparing the time to visit the branch. He also thanked PPC for their generous sponsorship of the day which made the event possible.
(Click on images to enlarge)