February 14, 2021
Optimised Concrete Hardstanding Designs Without Mesh
Moving away from traditional mesh reinforcement provided significant project time and cost savings for the concrete hardstanding service yards for the new Next Plc Distribution Centre, South Elmsall, West Yorkshire.
Adept Consulting Engineers structural design for the external service yard concrete pavements initially opted for traditional mesh reinforcement. However, conversations with Danley concerning possible optimisation of materials and labour resulted in a rethink and the decision to use Danley’s Strategic Reinforcement™ Design. This value engineered solution offered potential installation cost savings of over 15%, increased productivity and a more sustainable solution.
Although proven and used overseas for over 20 years. the Next project is a first for the UK. The strategy combines ground supported flatwork designs incorporating Danley tapered plate dowels including PD3® dowel cradles for sawn-free movement joints and Danley® dowels for construction joints.
Martin Langan, Technical Consultant at Adept Consulting Engineers, said: “In the UK, mesh reinforcement is the most common method used to reinforce concrete service yard slabs. However, following a technical seminar from Danley we were intrigued about the possible benefits of a method widely used in North American that omits the use of mesh.”
The approach involves removing the steel from the mid-panel and putting it at the joints, the strategic controlling of cracks can maintain the structural integrity of concrete slabs and the use of tapered plate dowels allows for slab shrinkage and lateral movement. The long-term serviceability and durability of concrete ground supported slabs is delivered most effectively through management of the natural behaviour of concrete. As most failures and deterioration of concrete slabs occur at the joints, Danley’s Strategic Reinforcement™ Design optimises materials and labour by creating a joint design layout for the specific application, and placing steel where it provides the most benefit, which is at the joints for reliable load transfer. Therefore, all mid-panel reinforcement is eliminated. The result is superior long-term joint stability with minimised joint spalling and reduced out-of-joint panel cracks.
Langan continued: “Impressed by the potential performance, sustainability and cost saving benefits, we decided to trial the Strategic Reinforcement™ Design on the high bay extension at Next, South Elmsall.”
The original specification detailed a 200mm C35A concrete slab with mesh throughout and joints spaced at 7m x 5m panels. At the contraction joints, H16mm diameter dowel bars at 300mm centres were proposed. The Danley design specified thinner 165mm PAV2 concrete slabs, no mesh, and joints spaced on a 4m x 4m grid. The smaller panels allow more controlled cracking of the concrete within the joints to relieve shrinkage stresses that develop during the curing process. 10mm thick Danley dowels were used at the construction joints and 10mm thick PD3® dowel cradles used at the sawn contraction joints. The combined effect of smaller panels and the superior load transfer efficiency of the tapered plate dowels with free movement at the joints minimises stresses within the concrete. In comparison to the original specification, this resulted in 17.5% less concrete by volume, contributing to reduced costs, improved concrete delivery logistics, and the reduction of CO2 emissions.
Paul Turner, Director at QED Construction, commented: “When Adept informed us of their decision to use the Danley Strategic Reinforcement™ Design, this method was very new to us. I have been in the trade for a long time and this is the first time I had heard of it. However, it was clear that this was going to offer us huge benefits in terms of faster and easier installation, improving performance whilst lowering cost.
The elimination of mesh meant that we required one less labourer and that we didn’t need to set up the day before. It also meant less steel to use and less load to carry. For every 120 – 150m2, we saved around half a day’s work. On the first day of the job, we set up the PD3 Dowel Cradles and Danley® Dowels following the issued designs issued. The installation was fast, easy and straightforward, and it was simple to use the PD3® cradles as a cutting guide to saw the joints.”
QED Construction realised an installed cost saving of 17%. The reduced slab thickness for this project resulted in eight fewer deliveries and there was an 80% reduction in steel by weight, further reducing carbon emissions.
15“We were particularly impressed by the Danley® Dowels,” continued Turner. “It eliminates the need for drilling or processing of timber formwork that is required with traditional steel dowel bars, and the plastic sleeves made stripping off the formwork much easier, saving us a couple of hours each pour. We also found it easier to keep the dowels level upon installation. We now use Danley® Dowels as standard across all of our current projects, the time-saving and performance benefits are exceptional. For projects that we have tendered for, we now propose the Strategic Reinforcement™ Design to the structural engineers.”
Matt Craven, Project Manager at Harris CM, the main contractor on the project, said: “At the beginning, the main concern for all parties was the elimination of the traditional mesh. For us, it’s about finding the right solution for the client and the warranty it comes with. Danley took us through the whole process, were very hands-on and observed all of the work while the project was ongoing.”
The Strategic Reinforcement™ Design complies with Concrete Society TR66 Rev 1: External in-situ Concrete Paving, ACI 330.2R-17: Guide for the Design and Construction of Concrete Site Paving for Industrial and Trucking Facilities and ACI 360-R-10: Guide to Design of Slabs-on-Ground.