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