Another successful seminar roadshow was organised by the Concrete Society of Southern Africa recently, focusing on the many aspects of concrete floors and slabs on grade.
The seminar, chaired by the CEO of the Society, John Sheath, was held on 4 consecutive days in Durban, Port Elizabeth, Cape Town and Johannesburg, where both local and overseas industry experts in concrete flooring, presented the latest developments in systems, design, measurement, materials, construction and trouble-shooting.
Watch the video overview here, courtesy of Concrete.TV:
First to speak was Ian Buchanan, Royal Consulting Services who, in his own inimitable style, described the current approaches used to measure both level and flatness of concrete floors. The use of a 'straightedge' for example, he suggested is an inappropriate and unenforceable specification, still inflicted on the construction industry today, because it is impractical; it has no fixed application method; it has no definition of number of tests and is open to a variety of interpretations.
Ian continue by recommending the use of the United Kingdom Concrete Society's Technical Report 34, incorporating European Standards for both free movement and defined movement floor areas.
He described the different requirements in this report under each floor usage type, covering permissible tolerance values, results analysis, and measuring equipment now available and used.
Worked examples were illustrated to assist delegates in understanding the need for level and flat floors in industrial applications. Also discussed was the method by which a floor constructed to a Free Movement (FM) flatness and level specification, could be converted to accommodate a Very Narrow Aisle (VNA) retrieval and storage system.
He concluded by stating that of all the materials used in an industrial building, the only "living" element which is shaped, is the concrete used in the construction of the surface bed. We get one chance to get it right, so USE THAT CHANCE WISELY!
Next, delegates had the privilege of listening to Darryl Eddy, Regional Managing Director of Twintec, based in the UK and responsible for all technical, commercial, sales and marketing activities for sub-Saharan Africa, and for all Twintec Group's Research and Development activity.
Darryl's presentation focused on 'jointless' steel-fibre reinforced concrete (SFRC) floors, and covered a comprehensive range of issues such as the demands of a modern warehouse, design and engineering considerations, current and potential applications and how 'jointless' SFRC floors are constructed. This was well supported by numerous successful case studies from many parts of the world, including South Africa.
The solutions to many of the challenges facing warehouse operators currently, he felt are to:
• Reduce the number of formed joints
• Increase reinforcement level
• Minimise shrinkage
• Armour the formed joints
• Eliminate sawn contraction joints
• Select appropriate flatness specification
• Increase surface hardness
• Provide detailing that is 'industrial floor slab' specific
Darryl concluded that SFRC suits the demands of a modern warehouse and it can be used in any industrial application anywhere. SFRC floors offer many benefits such as the elimination of sawn induced joints; a reduction in overall life cost; improved efficiency and operator comfort; greater flexibility; reduced maintenance costs; reduced programme times and improved tolerances.
Good design guidance exists to validate SFRC, but, Darryl emphasised that it must be delivered by experienced contractors working to the requirements of TR34 specification.
The next topic to be presented was the 'jointless' shrinkage-compensated concrete system by Peter Norton, Concrete Laser Flooring. Peter began his presentation by describing some of the many problems that property owners and operators experience with curled joints in conventional jointed floors. For example – damaged hyster wheels, load spillage, slower traffic, repair costs, etc.
The 'jointless' shrinkage-compensated system has three pillars:
• Anti-shrinkage concrete
• High steel fibre reinforcement throughout
• Total Quality Management
Peter explained that the use of an anti-shrinkage admixture in the concrete mix provided a force greater than the force of normal drying shrinkage, and therefore, no cracking develops and no joints are needed. This was illustrated in graphical form.
Special steel fibres were used and the concrete is fully saturated with fibres occurring in the mix every 15 mm. This provides much better tensile strength and strain-hardening performance. During the mixing process, the steel fibres are literally 'blown' into the mixer, thus giving a consistently even spread and avoiding any balling of the fibres in the mix.
The fibres are all aligned when originally packed, and this also helps to achieve even fibre distribution in the concrete mix.
In terms of Total Quality Management, improved quality control techniques are adopted using checklist-based procedures. A fully-owned laboratory tests the cement, aggregate and admixture cocktail, whilst concrete testing includes flexural, shrinkage and compression. In addition, computerized measuring of the floor is carried out with 'Rack Track' after the pouring, and printed daily reports are produced showing achieved surface tolerances.
Benefits of this system are claimed to be: no shrinkage = less joints; less joints = better customer satisfaction; better concrete = more durable floor; durable floor = better life-cycle costs.
Paul Heymans, Amsteele Systems introduced a newly-formed company, PT-Pave, which he explained was a joint venture between Chris Howes Construction and Amsteele Systems, formed to offer the industry a complete package in post-tensioned concrete pavements.
He defined post-tensioning as the "counteraction of concrete's natural weakness in tension by strengthening and reinforcing the concrete with the use of high tensile steel cables, which exert a compressive force onto the concrete member and providing an uplift force between supports". Paul went on to describe the material requirements for the bonded slab post-tensioning, which included the multi-strand steel cables, anchors, ducts and grout, followed by the materials for unbonded slab post-tensioning – single strand steel cable, polyethylene coating, anchors and wedges.
Some of the many applications that Paul described were floors for distribution centres, warehouses, refrigerated stores, bulk storage facilities, bulk container facilities, raft slabs, reservoir floors and even tennis courts.
Full coverage of the design aspects, installation, concrete placement and post-concreting activities (e.g. stripping curing, and tensioning) were presented. Some cost comparisons were made with other forms of concrete floor construction, and whilst PT floors will never compete with an unreinforced slab situation, they are very economical compared with conventional reinforced concrete floors and in some cases with fibre-reinforced concrete.
Paul stated that post-tensioning optimizes the cost of subgrade preparation due to the PT pavement's strength and stiffness. The system uses an optimum combination of post-tensioning, slab thickness and concrete tensile strength to produce a cost-effective slab on grade solution, and is one of the most durable and robust methods of pavement construction in general, and on poor ground.
Delegates were promised something completely different by the next presenter, Johan Coetzee, World of Decorative Concrete and he certainly fulfilled his promise. Focusing on polished concrete (which, by the way is not the same as ground and sealed concrete), Johan took delegates through the grinding and polishing process in quite some detail, highlighting the pitfalls that many inexperienced contractors face, due mainly to a lack of knowledge of the process.
Some of these included leaving straight edge marks and footprints; bad and inconsistent mixing; bad placing; bad infill work; insufficient rebar cover and general bad workmanship. All these defects he attributed in one way or another, to unskilled applicators, sub-standard materials and/or a lack of knowledge of the product by the Applicator, Specifier and even the supplier.
It did not help either, he suggested, not having a formal Code of Conduct in place for decorative concrete.
Johan had clear messages for the engineers, the architects and quantity surveyors, setting out design and specification requirements that would ensure successful polished concrete and decorative concrete in general. He concluded his presentation by showing images of successful, completed projects that highlighted that dull, grey floors can be transformed into beautiful, easy-clean, environmentally-friendly and durable surfaces.
Final presenter of the day was Bryan Perrie, Managing Director of The Concrete Institute who described the common failures in concrete floors and how to specify to prevent them. He began by citing the results of some research that the Institute had carried out on the level and types of enquiries that the organisation had handled over the past 40 years.
During this time, he stated problems with concrete floors failing represented the highest incidence of enquiries, site visits and reports, and despite numerous interventions, not much has changed – there is still a strong need for education.
Bryan covered typical defects that are experienced with concrete floors and slabs, the three main categories being surface, joint and structural. Each one was dealt with in some detail:
He also went into a lot of detail describing the various design-related and construction-related causes of these defects. Research had shown, he confirmed, that 40% of problems were caused by design/detailing issues, whilst 60% were construction-related.
Bryan continued with an overview of how specifying could be improved in order to mitigate a lot of the problems experienced. Aspects mentioned were factors affecting performance, subgrade support, concrete quality and thickness, designing for joints, workmanship and finishes.
A golden rule that Bryan put forward was "do not specify anything that cannot, or will not, be measured".
Our sincere gratitude goes to Lafarge South Africa who were our National Sponsors for this whole event.
Thank you also the many companies who displayed their products and services at the seminar. These were:
• Royal Consulting
• Samson Technologies
• Amsteele Systems
• CLF Flooring