June 26 and 27 were red-letter days for the Wood Technology Society (WTS) and its parent association the Institute of Materials, Minerals and Mining (IOM3) as it played host to Timber 2018. This was the first scientific conference held by the WTS and marked 10 years since the last conference of this type held by WTS’s predecessor, the Institute of Wood Science.
As might be expected, the conference attracted delegates from across the wood science disciplines and also included chemists, physicists, engineers, architects and construction specialists.
The first day kicked off with presentations on timber structures. Stephan Zaugg, of Swiss timber and steel construction company Zaugg AG Rohrbach, showcased a recent project to build parking for automotive logistics company, COTRA Autotransport.
The project called for parking spaces for 1,600 vehicles plus 200 holding bays over three storeys (plus roof parking) and a net area of around 23,000m2. The site had to remain fully operational during construction, so offsite prefabrication was key.
Construction in concrete was ruled out as it would have required pile foundations – problematic in ground with a high water table (1-1.5m below the surface). With a lightweight timber structure a flat foundation system could be used, which also had a cost benefit.
The modular structure included inter-storey slabs of five-ply cross-laminated timber (CLT) covered with two layers of mastic asphalt with a separation layer and sealing membrane. The structure also includes glulam slab joists resting on V-shaped glulam pillars. In total the project used 3,400m3 of CLT, 30m3 of BauBuche glulam and 1,1,00m3 of laminated timber of various strength classes. Architect Audley English, founder of Buildeco, also looked at structural timber, specifically C24 and LVL. He said the construction industry needed to innovate if it was to accept the government’s challenge of increasing house starts and he offered an alternative approach to timber frame and CLT. His company’s utilises a patented system based on mass production manufacturing techniques machined from either solid C24 softwood for the frame or, more recently, from LVL.
“This British invention and method of construction is the only three-dimensional building system that uses 2D flat-pack cassette panels that, once assembled, form a 3D post-tensioned structure, stronger than equivalent offsite structures,” he said. The same cassette panels are used to form walls, floors, ceilings and roofs and are connected by common structural 3D locking lugs. The result is a very strong, pre-tensioned monocoque structure, which is locked together using one simple hand tool – an oversized Allen key.
Mr English added that his company is currently using this system for buildings up to four storeys. “The future is to demonstrate that building up to 40 storeys is possible by utilising this 3D panel system,” he said. Adrian Campbell, founder and director of changebuilding, gave an engineer’s perspective on key knowledge gaps in the use of mass timber – glulam, LVL and CLT.
One immediate knowledge gap he raised was the lack of data available on the overall scale of delivery of mass timber building compared to other forms of construction.
“While it is recognised that mass timber is far from a mainstream construction material, there is still an interest in knowing the overall scale of use in the market to get a perspective on the ‘headroom’ of possible new markets and relevance of benefits,” he said.
Another question concerned sustainability.
“We’re focused on sequestered carbon during service life but what are the scenarios for mass timber at end of service life and how does that effect the total scenario for timber?” he said.
“My view is that we don’t have much idea how to disassemble a building and make use of it again so we don’t have full circularity.”
Mr Campbell went on to say that engineering graduates – even those who wanted to adopt timber into design projects – had limited information about the basic quality of the products, the variety of products and their best application.
He said that industry must aim to make their knowledge more openly known about and incorporated and avoid over specialisation of the topic that would be a barrier to broader adoption.
The second group of presentations drilled down into wood properties.
Martin Ansell presented the research of PhD student Chee Beng Ong who had studied the bending properties of finger-jointed Malaysian dark red meranti (DRM) in order to determine its suitability for the manufacture of glulam.
“The motivation for the work was to develop uses for plantation grown Malaysian DRM,” said Dr Ansell. “In recent years the Malaysian government, with support from local timber industries, has initiated and actively promoted activities related to the use of timber in construction.”
The effect of end pressure when bonding and variation in density on the bending strength (modulus of rupture – MOR) were investigated, as was the influence of the cross-sectional area and the orientation of finger-joints on the MOR.
Results showed that the bending stiffness of DRM pieces was not affected by fingerjointing, leading to the conclusion that finger-jointed DRM shows strong potential for the production of structural glulam beams.
Peter Macdonald, an MRI physicist by training, presented a model of softwood geometry that can be used for multiscale modelling of the longitudinal movement of water through spruce on behalf of Robin Adey-Johnson. The work is part of a four-year engineering doctorate project.
Previous results obtained from a high resolution X-ray CT scan and subsequent image analysis of a large number of Norway spruce tracheids (elongated cells that provide support and upwards conduction of water and dissolved minerals in all vascular plants) were used to produce a model that can represent the variability in wood anatomy found within a timber joist or log. The aim was to produce a model capable of describing the variability that occurs naturally in wood, rather than an idealised structure, so that realistic behaviour can be expected.
A model for the micro-mechanical characterisation of wood fibres was the paper presented by PhD student Stephen Garrett, who is sponsored by Huntsman Polyurethanes.
His work is focused on MDF and adhesives and aims to empirically determine the stiffening effect of the glue on the fibre.
Mr Garrett was swiftly followed by Qiushi Peng, from the University of Sheffield’s School of Architecture whose work explores the chemical composition and mechanical behaviour change on new and ancient pine during heat treatment in vacuum and air.
The third section of the day focused on the wood value chain and had its roots in home-grown timber.
Dan Ridley-Ellis from the Centre for Wood Science and Technology at Edinburgh Napier University summarised the current status of strength grading of UK-grown timber – something of a dark art given the variation of properties from species to species, country to country, from tree to tree within the same forest and even within the same tree.
Dr Ridley-Ellis covered visual grading grades and strength class assignments; grading machines with approved settings for machine control; the species, size ranges and strength class combinations covered; and grade determining properties of UK specific strength classes.
In his conclusions he said that timber grading in Europe is developing quickly, with new machines and updates of standards and new visual grading assignments and machine grading settings being added regularly.
He also said he could foresee a time when the timber frame or CLT manufacturer would carry out the grading, rather than the supplier, which would help reduce the volume of timber being rejected for construction purposes.
“There are grading machine settings for UK-grown timber that exceed both the common expectation and the current industrial practice,” he said. “As machine grading becomes more accessible to building fabricators it opens up more potential for wider and more efficient use of the domestic forest resource.”
Morwenna Spear of Bangor University’s BioComposites Centre followed with highlights of an as yet unpublished project entitled ‘Timber as a biogenic carbon: its joint roles in bioenergy and carbon sequestration’.
The key trend, said Dr Spear, is that demand for timber is set to increase. More people are building with timber for all sorts of reasons, including its excellent carbon profile, its renewability and sustainability. The demand for timber for bioenergy is also increasing.
“This gives rise to a need to evaluate the volumes of timber available for different uses as we move towards a future where there is increased reliance on timber as a renewable structural material and as a potential source of bioenergy,” she said.
As buildings become more energy efficient the importance of the carbon associated with the construction materials would come to the fore more and Dr Spear expects there to be an increasing interest in the carbon profile of materials in the built environment to assist attainment of greenhouse gas targets.
She added that she expects to see Environmental Product Declarations (EPDs) integrated into BIM in the future.
Psychologist and environmental scientist Caroline Greenslade is now a PhD student at the University of Surrey’s Centre for Environment & Sustainability. Her research is sponsored by the Economic & Social Research Council and the Forestry Commission and is exploring the reasons why the volume of woodland in the south-east – specifically Surrey and West Sussex, which are the most wooded counties in England – is not matched by the processing capacity in the region.
There is a huge amount of stock still standing in England’s woodlands, she said. In fact 400,0003 of timber could be removed every year for the next 40 years without reducing the overall standing stock. The situation is most acute in the south-east, which has 25% of the national total of ‘overdue’ wood biomass.
Ms Greenslade’s research has identified 50 factors currently restricting increased woodland management across the supply and demand network in the south-east. These include human factors such as a reluctance to cut down trees, weak consumer demand signals and an unreliable supply chain. Bangor University’s Athanasios Dimitriou continued the home-grown theme with his presentation on adding value to UK-grown timber in construction.
Dr Dimitriou maintains that UK softwood is often seen as lower quality than imported softwoods because of their lower grading strength, however, “UK-grown softwoods like Sitka spruce are often under graded in an attempt to minimise the rejected timber and maximise the sawmills’ production efficiency”. He added that there is potential use for spruce in high value products such as glulam and CLT “which might balance the economic inputs and benefits”.
Dr Dimitriou also suggested that a forestry approach of selecting appropriate species for future plantation planning could open up a large market for locally-grown construction timber products.
Day one of the conference wound up with a look at coatings and adhesives.
Stephen Uphill from Accsys Group, the manufacturer of Accoya, explained the research the company had carried out in the performance of coatings on modified wood.
This included an outdoor set up in Arnhem in the Netherlands, where more than 1,000 panels of various timber species with different coatings were assessed for weathering performance.
“Typically all coatings systems showed similar trends,” said Dr Uphill. “Coatings applied to Accoya and MEDITE TRICOYA EXTREME performed better than on other timber species due to the increased dimensional stability of these substrates and consequential lower stresses on the films themselves.”
Dr Radek Bragança of Bangor University’s BioComposites Centre presented on bio-based adhesives for the wood-based panel industry. His work is focusing on natural, bio-based alternatives to currently used amino-based adhesives, such as lignin, tannin, protein, starch and derived molecules.
Wrapping up the day, Dr Dimitriou presented the findings of Nyle Parker, a research student at Cardiff University’s School of Engineering & Physics. His research into ‘broadband dielectric measurement and simulation of e-field curing system’ is looking into radio frequency (RF) curing of adhesives in products such as glulam and CLT.
