INSIGHT
By trial – and ( minimal ) error
By TCI , with further info from Bryan Perrie
Poor quality concrete is wasteful — and dangerous , warns The Concrete Institute and advises that trial testing , correct curing , and mock-ups form part of quality control
Concrete of inferior quality wastes time and money , ruins contractors ’ reputations — and could be dangerous to users of substandard structures , warns John Roxburgh , lecturer at The Concrete Institute ’ s ( TCI ) School of Concrete Technology . Roxburgh says it has sadly become a fact of life that the contracting fraternity pleads poverty when it comes to doing a project properly — but then ends up having to find funds to fix disasters later . “ In concrete works , this is especially true : by not getting the job right the first time , the contract is going to run over time and costs will escalate drastically ,” he states . Roxburgh says concrete quality typically encapsulates three elements :
• First , the concrete must perform structurally . It should have the correct strength and required deformation properties .
• Second , it should be aesthetically pleasing . “ Of course , there will be many cases where aesthetics is irrelevant , such as in foundations . But in exposed concrete , appearance will be important and will often be the only way a client will judge a contractor ’ s work . Attractive concrete calls for precision of work and a good off-shutter finish .”
• Last — and this is the element of quality often overlooked — is how well the concrete will perform over time within the environment in which it has been placed . Durable concrete will have a low maintenance cost over its life cycle .
“ Poor quality concrete can be disastrous in terms of finances , reputation , and the safety of users of the structures .”
John Roxburgh – TCI
“ So how does a contractor produce quality concrete ? The quote by the American war hero , William A . Foster , sums it up beautifully . Foster said : ‘ Quality is never an accident ; it is always the result of high intentions , sincere effort , intelligent direction and skilful execution .’ To produce quality concrete , having the correct intentions is just the first step — doing the necessary preparations is even more important . “ The correct concrete mix design to meet the required strength , durability , and workability requirements must be
TCI formulated . And a suitable mix design can only be found by trial testing . Mockups of the formwork — which represent the shape of the actual formwork in the project — should be made . The concreting teams should practice on these mock-ups to develop the correct placing techniques and to ensure the correct surface finish to the concrete . “ For concrete with high durability , good site practice is vital , and this should include a thorough curing regime . Curing can never be rushed .
26 - CEC April 2018