ConCrax 2012 Seminar
Selection of the right topics and speakers are two of the most critical success factors when running a seminar roadshow and ConCrax was a great example of getting these two criteria right. Demand for places at the event was brisk in all centres and nearly 470 delegates attended to hear of the latest thinking with regards to cracking in concrete
President, Billy Boshoff set the scene for the seminar in his keynote address which covered the causes of cracking, how to prevent it and understanding the fundamentals of cracking. He followed this with a detailed overview of Plastic Cracking, Corrosion Cracking, ASR and Sulphate Attack.
Prof Mark Alexander (Mike Otieno in PE and Durban) talked on cracking related to drying shrinkage, creep and thermal effects. The presentation included the causes and effects of different types of shrinkage - autogenous, carbonation, plastic and drying; factors affecting the onset of creep; various causes of thermal cracking of concrete and a brief overview of the repair options for cracked concrete.
In conclusion, Prof Alexander stated that:
- the main cause of concrete cracking is the presence of restraints – internal or external
- creep can be beneficial to structures – Tensile relaxation
- internal thermal cracking may not be visible but can be very dangerous!
- cracking can lead to durability problems e.g. reinforcement corrosion
- the repair of cracks must be carried out in good time using the correct material and procedure.
Peter Gage from Jones & Wagener provided an engineer’s perspective of concrete cracking, focusing on structural cracking - flexural, shear and detailing. Talking on bending cracking in particular he stated that concrete floors on the ground can be designed without reinforcing. In this instance the bending capacity of concrete is relied on. “With the advance in materials and design methods over the last half century or so, the capability of the materials is pushed into the realm where cracking is “normal”.
He talked on design and the acceptable limits for cracking, and detailing for crack limitation, referring to the national design codes currently in use in both South Africa and Europe. Concrete cover of the reinforcement was also dealt with very comprehensively.
Next to present was Chris Howes from Port Elizabeth who was able to give the delegates an insight into the contractor’s challenges on site with concrete cracking. His very practical approach to the issue highlighted the many aspects of concrete that have to be considered by the contractor in order to reduce or eliminate cracking. The concrete specification and mix design; joint layout and design; consistency of concrete supply; protection from the elements and finishing of the surface, were just some of topics covered. In conclusion, he reiterated that good planning can minimise or eliminate concrete cracking, thus avoiding a lot of time, cost and aggravation at the end of the day.
Wayne Smithers of Sika in his presentation on causes, remedies and materials, described in some detail the process of repairing cracks in concrete structures using crack injection systems. Although not new to the industry the materials currently available for such processes have advanced considerably. These can be epoxy, polyurethane, polyacrylate or cement microfine based.
Generally speaking, resin-based injection materials offer good adhesion to concrete, mortar, stone, steel and wood. They are used to fill and seal voids and cracks in structures such as bridges and other civil engineering buildings, industrial and residential buildings, e.g. columns, beams, foundations, walls, floors and water retaining structures. They not only form an effective barrier against water infiltration and corrosion promoting media, but also structurally bond the concrete sections together.
This presentation was followed by a journey with Gordon Mowatt of Spec-con through a short, non-academic, light-hearted presentation, to share with delegates some of the experiences, both good and bad, which relate to a specialist contractor’s involvement through the diagnostic phase to the final repair of cracked concrete.
“As a specialist contractor, when asked to fix concrete cracks, we often find ourselves”, he said, “tasked with the highly complicated, scientific and technologically challenging procedures in preparing the specialised crack repair materials, for example: adding component A to component B and mixing it up for the allotted time period.
This seemingly basic undertaking appears to be beyond the ability of most “run of the mill general contractors” and has resulted in the emergence of the Specialist Approved Contractor.
Of particular interest to delegates was the overview given by the speaker on diagnosing, testing and monitoring of concrete cracks, as well as the available crack repair solutions currently available.
The last speaker on the seminar was George Evans, Concrete Technologist of the Cement and Concrete Institute, who presented, in his own inimitable style the concrete industry’s view of cracking in concrete. He described the definition of cracks, the different types, their significance, assessment, underlying causes and prevention.
At the end of proceedings thanks were expressed by the Seminar Chair (CEO, John Sheath in Johannesburg and President, Billy Boshoff at the coastal events) to the speakers, the sponsors, the Organising Committee and the delegates for their support of the ConCrax 2012.