Vertase FLI Completes Innovative Peat Stabilisation Trials

Vertase FLI has recently completed innovative peat stabilisation trials using Ordinary Portland Cement (OPC) and combustion waste materials (wastes destined for disposal unless a more sustainable method of re-use can be found). The trials confirmed strength gains within peat using OPC-combustion waste mixtures that were in excess of those observed using traditional OPC-sand mixtures, whilst offering the added benefits of greater handleability and sustainability. The potential to reduce the quantity of OPC when combining with combustion waste materials could offer significant cost savings to future projects.

Construction of infrastructure over land containing peat and peaty soil has long been a challenge to geotechnical engineers working on civil engineering schemes. An obvious solution is to excavate and relocate the peat deposits allowing for the infilling of the resultant void with geotechnically competent materials. However, the costs to undertake this are typically prohibitively high meaning that an alternative solution has to be found whereby the peat can remain in situ.

One such solution which has been widely explored by geotechnical engineers is the addition of OPC to improve the geotechnical properties of peat and peaty soil, typically in significant quantities (e.g. 300 kg/m3). The curing of the cement enhances the compressive strength and bearing capacity of the material to values which are more in-keeping with the requirements of proposed infrastructure.

However, OPC is a primary product manufactured from raw materials (calcareous and argillaceous materials such as limestone or chalk, and from aluminium oxide, silica oxide, ferric oxide and magnesium oxide found as clay or shale). Its production, which involves quarrying and heating of materials to high temperatures has a significant carbon footprint and is cited to contribute up to 10% of the worlds carbon dioxide emissions. It is therefore unsurprising that there has been an impetus within the geotechnical community to identify additives/bulking agents that can be combined with the OPC to reduce the required cement addition while still imparting the required geotechnical improvement to the peat.

Additives and bulking agents used commercially have traditionally included sand or similar granular materials. Sand is understood to play a vital role in enhancing the bonding in cementitious reactions by filling voids and providing a skeleton. OPC-sand mixtures have been shown to impart equal to or superior geotechnical properties to peat when compared to OPC alone.

As a remediation contractor offering sustainable remediation strategies to our clients, we have a vested interest in sustainability issues whilst still delivering the required geo-environmental and geotechnical improvements to land that are required by all project stakeholders. When approached by an environmental consultancy to undertake some geotechnical stabilisation trials on peat, we have therefore gone beyond the use of standard OPC-sand mixtures and explored the use of combustion waste materials (by-products from industrial combustion processes) as an additive/bulking agent to the OPC. Unlike sand, which is also a primary product, combustion wastes are destined for disposal unless a more sustainable method of re-use can be found and agreed with Regulators.

Our peat stabilisation trials using OPC-combustion waste mixtures demonstrated significant strength gains within the peat relative to unamended samples. Twenty-eight day CBR results of up to 11% were achieved with moderate additions of the mixture, offering the potential for significant cost advantages to the project relative to the more widely commercially adopted OPC-sand mixtures. Furthermore, the increased handleability of the OPC-combustion waste mixture (by virtue of its consistency) and its reduced carbon footprint represent significant advancements in the geotechnical improvement of peat, which we feel are worthy of sharing with the wider geotechnical and earthworks community. Finally, diverting a waste material from disposal by identifying innovative and sustainable methods of re-use can be considered a key responsibility imparted onto us all during our gradual transition from a consumer to a circular economy – a frontier that we are keen to push at VertaseFLI.

A more detailed technical report regarding the peat stabilisation trials can be viewed here.

If you have any questions about the methods or indeed enquiries for geotechnical stabilisation works, please get in touch with Ian Burton (iburton@vertasefli.co.uk) or Duncan Scott (dscott@vertasefli.co.uk) and we shall be happy to discuss further with you.