Masters Degrees (Forest and Wood Science)

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Browsing Masters Degrees (Forest and Wood Science) by Author "Chatukuta, Sylvester"

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    Evaluation of sawmilling and cross-laminated timber processing value chain integration
    (Stellenbosch : Stellenbosch University, 2022-04) Chatukuta, Sylvester; Wessels, Brand; Muller, Barry; Stellenbosch University. Faculty of AgriScience. Dept. of Forest and Wood Science.
    ENGLISH ABSTRACT: Current high prices for CLT in South Africa are a deterrent to its adoption as a construction material. This prospect is further exacerbated by the predicted lumber shortages in the coming years. As such it is imperative to consider development of innovative, lower cost CLT manufacturing processes, underpinned by raw material optimization. This research investigated the integration of manufacturing of lumber and CLT with the aim of reducing the unit cost of CLT as a product. Arguably the best potential for cost reduction of lumber is the increase of volume recovery during the sawmilling process. Two ways in which volume recovery increases can be achieved include the production of random width boards and increasing the wane allowance on boards. The objectives of this study were: (1) To evaluate the potential increase in volume recovery when an SA Pine sawmill include random widths and increased wane allowance in its sawing strategy (both random widths and increased wane products can potentially be used as raw materials for CLT manufacture), and (2) to investigate the effect of increased wane allowance on SA Pine CLT strength and stiffness performance. To achieve the objectives; the research branched into three separate studies. Firstly, benchmarking of the Simsaw 6 sawmill software was performed to quantify the difference between simulated volume recovery and real-world volume recovery. Secondly, structured random widths (RW) and increased wane (IW) allowance scenarios were simulated to evaluate increase in volume recovery possible. Lastly, ten CLT panels of varying crosswise lamella wane surface area were manufactured and tested to destruction according to the American National Standards Institutes (ANSI) (2018) PRG-320 and EN 16351 (2015) specifications. This was done to determine whether increased wane allowance had an effect on CLT bending performance. Preparation of the panels closely mirrored commercial CLT fabrication. Results from the sawmill benchmarking trial show that Simsaw 6 predicted real world sawmill yields. For small logs, the software overestimated log volume recovery by between 1,4% to 2,4% with a mean of 2,01% volume recovery overestimation. The software overestimated the real-world sawn logs volume recovery with between 1,3 to 3,7%, with a mean of 2,13% for large logs. For the small and large logs combined, the simulation results were on average 2,07% higher than real sawn results. Increased wane allowance (IW) and increased wane allowance combined with random widths (IW+RW) showed significantly improved volume recoveries in all log classes. Using the maximum wane permitting scenario of (thickness =75%, width =50% and length =100%), the simulated volume recovery was interpolated to real-world sawmill volume recovery, as a weighted average of simulated yields. Maximum mean weighted volume recovery for a typical small-log sawmill was 63.5% for the increased wane combined with random widths scenario (IW+RW), followed closely by increased wane (IW) scenario at 61.5 % respectively. These volume recovery results indicate very high improvements compared to the current volume recoveries attained in typical sawmills in South Africa. Ten sample CLT panels were manufactured and tested to failure and mechanical bending properties were determined. Prominent failure mode of the bending tests was the brittle tension failure, ensuing from the CLT bottom longitudinal layer. The measured knot properties on the middle section of the CLT panels were correlated with the MOE and MOE values; however, no significant correlation was noted. The experimental bending stiffness of each CLT panel was then compared with its predicted mechanical properties based on the shear analogy method for loads perpendicular to plane based on the global stiffness measurements. The comparisons between predicted and experimental results for the three wane groups, despite small sample size, show close similarity. Results from the severe wane category demonstrated that the inclusion of substantial wane percentage in CLT within the crosswise lamellas did not influence the bending stiffness of the CLT panel. A comparison between the experimental bending moment of the sample CLT panels and predicted bending moment of manufactured CLT panel was performed. The calculated experimental bending moment (FbS) results varied between 7.2 and 12.5 N. mm whilst the predicted bending moment for S5 CLT (FbSeff) was 2.2 N.mm. Of the five severe wane panels, two had an FbS value lower than 10 N.mm/m. Of the five moderate and no-wane panels, none had values lower than 10 N.mm/m. It, therefore, seems as if the severe wane might have resulted in lower FbS values. If present, the magnitude of this effect still seems to be fairly small. It is likely that the lower bonding area due to gaps caused by wane was responsible for the perceived lower FbS values. Overall, the results show a good indication of the potential use of wane edged boards in CLT production. CLT manufacturing with increased wane allowance boards resulted in high utilization of lower value lumber, therefore increased value extraction per single log. As attested by the successful design, testing and validation of the experimental work undertaken in this research, value chain integration seems to hold much potential to reduce the cost of CLT in South Africa.