Page 3 - W M Donald Newsletter - Edition Nine

IF YOU WANT TO MAKE YOUR SITE MANAGER’S LIFE EASIER, TRY A LITTLE DLC
There is a tendency to think of innovation as involving new technology, advanced materials or AI. However, the majority of innovations involve two existing ideas in a new combination, or an existing product, service or process in a new application. A good example of the latter is the work currently being undertaken by W M Donald, in partnership with Leiths, to develop Rigabond.
Many of the housing developments on which W M Donald is active consume considerable amounts of suitable upfill materials simply to achieve ‘competent ground’. Often this material cannot be sourced within the site and has to be imported. Competent ground, in this context, means ground which is stable and has sufficient bearing capacity to bear the loads imposed by domestic housing.
Dry lean concrete (DLC)
Dry lean concrete (DLC) has been around for a long time and was used extensively during World War 2 as a cheap and effective substrate for military runways. DLC generally comprises an imported or site-won granular material blended with Ordinary Portland Cement and PFA (Pulverised Fuel Ash). The ratio of cement and PFA to aggregate is calculated based on the aggregate’s particle size distribution, moisture content and the desired product strength. Typically, 80 - 150kg of cement with 20% PFA is added per cubic metre of DLC. Crucial to the final strength of DLC is that it is blended at the optimum moisture content for that specific mix. This results in a very low slump material when compared to traditional lean mix concretes that have much higher water contents and plasticisers to aid flowability. The low slump and moisture content allow the material to be delivered to site by traditional tipper trucks, discharging to stockpile for later use rather than a concrete tanker discharging direct to point of placement.
Rigabond DLC
The ‘inventive step’ in Rigabond is to use Type 1 sub base as the base aggregate in the DLC mix. The properties of the single source Type 1 material are known, and strength tests have already been carried out therefore the results are predictable and repeatable. As the archive of test data grows, this material will become a popular product on housing developments as a direct replacement for lean mix concrete or structural fill platforms.
Currently, Rigabond has only been used on a case-by- case basis as there is currently no general standard accepted by NHBC. W M Donald and Leiths have been working with consulting engineers, Fairhurst, to test the new material and ensure it is fit for purpose with the ultimate goal of having Rigabond accepted by NHBC. Two of the questions that are currently being addressed are how we demonstrate adequate product compaction in the trench and Rigabond’s behaviour when subjected to long-term water saturation.
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