The structural reuse of Pinus Radiata in New Zealand

Abstract

Masses of used Copper chromium arsenic (CCA) treated timber is deposited into landfill from light timber framed building deconstruction every year. This research explores the structural integrity of CCA treated timber and the feasibility of its re-use within the construction industry. To answer this question an appropriate methodology has been designed to achieve quality results. The first part of the methodology was to identify the profit margin for pinus radiata through communicating with individuals in the current market. This market all works around the concept that to reuse there needs to be a significant buying community as it needs to generate MONEY. Through doing this it was identified that only a few companies in New Zealand reuse CCA treated timber and the ways of which it is re-used varies greatly between companies. Some firms pull the nails out due to health and safety reasons, while others leave them in due to the overall cost of the sale. This gives a good understanding on what everyone is doing across the country and allows for the sale market to be set at $2.00 a meter, which if done correctly comes in at around $0.16 a meter of profit.

The next part of the methodology required a physical assessment of material itself in order to establish its structural integrity and identify other potential barriers to its reuse. This section covered all other possibilities to pinus radiata focusing on the different timber which have the same properties, and focus on separate treatments which will also conduct the same issues as CCA. This all found that there is much research to consider, which placed New Zealand in an area of profit, as any of these documents could be the focus point and all could eventually relieve CCA from the industry.

Existing research identifies how the use of CCA treated timber can be prevented, but does not consider the diversion of existing treated timber being deposited into landfill. The lack of research into the re-use of CCA treated timber is the main barrier found in this thesis. This required the series of events which occur between building deconstruction and deposition into landfill to be clearly defined, before they could be changed. The changes to how CCA treated timber is processed after deconstruction has the potential to divert the material from landfill for re-use. The primary addition to this process was an assessment of the strength which it holds. To accomplish this a three point bending test was carried out on each member, finding the alternate strength and the modulus of elasticity (MOE). These two figures could then be directly compared to NZS 3603:1993 timber structural standards allowing their long term history of testing to be the comparative point (New Zealand Government, 1993).

With the two figures it was found that all of this material strength was 91% above the minimum strength grading of SG6, and 55% above the next area of SG8, which is the most commonly used framing timber. Although through doing this there was hope for the material to present themselves with a way of finding the general strength with minimal tools, this is not present in the research.

The most important finding of this research is that CCA treated timber is strong enough to be placed straight back into the construction industry and re-used for light timber frame construction. Future research is needed into the additional education required of builders in order for them to confidently re-use the timber in construction.