C. B. Wessels

C. B. Wessels
Stellenbosch University | SUN · Department of Forest and Wood Science

About

57
Publications
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425
Citations

Publications

Publications (57)
Article
In this research, the effect of wood preservatives and wood properties on one-component polyurethane bond performance in Pinus patula laminates was investigated through shear and delamination tests. Concentration levels of 2 and 4% of chromated copper arsenate (CCA), and 1.67 and 3.30% of disodium octaborate tetrahydrate (DOT) were used. Different...
Article
The prospect of manufacturing durable structural laminated wood with copper and boron-based preservative-impregnated Eucalyptus grandis wood was previously investigated but revealed adhesive-bond performance below standard requirements. In this study, bonding process factors, viz. mechanical pretreatment (surface planing) and bonding pressure in co...
Article
Full-text available
In this study, the variation of collapse and shrinkage both radially and along the height of trees was investigated and their relationships with warp in the sawn boards as well as the basic physical properties of wood (density, moisture content, permeability, extractives contents and heartwood/sapwood ratio) were determined. Seventy trees of Eucaly...
Article
The fundamental factors responsible for the complexities in adhesive bonding of preservative-treated wood are predominantly wood species, preservative composition, and adhesive system. It is post-effect of these factors that process variables such as assembly times and bonding pressure exert secondary influences on adhesive-bond development in pres...
Article
Full-text available
Before round timber can be profitably used in construction, it needs structural characterization. The visual grading of Eucalyptus grandis poles was integrated with additional parameters developed by multivariate regression analysis. Acoustic velocity and dynamic modulus of elasticity were combined with density and pole diameter in the estimation o...
Article
Warping is a frequently encountered defect in wood products which is evaluated in different ways by various sawn timber product standards. However, there are weaknesses in the current evaluation methods especially when comparing warp in different board lengths. The objective of the work described in this paper was to develop a theoretical model of...
Article
The effect of copper azole impregnation, wood density, adhesive spread rate, mechanical pre-treatment, open and close assembly times, bonding pressure, and press duration on melamine-urea–formaldehyde-bond performance of Eucalyptus grandis joints was investigated. The results obtained showed that the shear strength was mainly affected by copper azo...
Conference Paper
This study investigated the treatability of the sapwood and heartwood of sawn Eucalyptus grandis with copper-azole (CuAz) and disodium octaborate tetrahydrate (DOT) water-borne preservatives towards improving its durability for enhanced use in structural solid wood applications. The results obtained showed that, at a moisture content of 12 ± 1%, sa...
Article
The traditional visual estimation of wood failure percent (WFP) in shear-failed adhesive-bonded joints is often marred by inconsistencies and produces results with large variations between examiners. This method of determining WFP has also been criticized as inaccurate and subjective. Therefore, an alternative method with improved accuracy and more...
Article
In recent times, mass timber products have encouraged renewed interest in wood as raw material for more sustainable building and construction. However, durability concerns due to wood susceptibility to biodegradation could curtail this interest. Hence, there is a need for more durable wood products in emerging structural applications including the...
Article
Full-text available
Round timber is often used for hydraulic engineering works, but the strength grading of round logs is not as well developed as that of sawn timber. The advantages of using defined strength classes, as well as the proper selection of the raw material, could be applicable to hydraulic works as well. In this study, the methods and rules developed for...
Article
The Eucalyptus genus is the most widely planted hardwood worldwide. It is, however, mostly used for low value products as a result of various wood quality problems. Splitting and distortion of wood due to growth stresses is arguably the most critical quality issue for this genus. In this research, the effect of water availability on the peripheral...
Article
Full-text available
The objectives of the work described in this paper were to present concept processing pathways for manufacturing high value, green-glued finger-jointed Eucalyptus engineered products and review existing research related to these engineered products. Additionally, critical knowledge gaps that need to be addressed in future research were identified....
Article
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We investigated the South African log resource availability and the potential global warming impact of an increasing wood-based residential building market. We have shown that, with the use of wood resources currently exported as chips, as well as planting trees in areas that have been earmarked for afforestation, a sustainable residential building...
Article
Key message An increase in the stiffness of lumber with a decrease in initial tree spacing was confirmed for Pinus patula Schiede ex Schltdl. & Cham. The underlying properties of microfibril angle, wood density and knot frequency explained 71% of the variation in lumber stiffness. Tree spacing also influenced wood properties independent of radial g...
Article
Full-text available
Rapid growth rates and the accompanying reduced rotation ages of forest plantations have resulted in increased proportions of juvenile wood. Growing space markedly influences growth rate and may be manipulated by stand density management. The objective of this study was to evaluate the effect of stand density on the modulus of elasticity (MOE), mod...
Article
This research provides an economic analysis of different management regimes of Pinus patula plantations destined for saw log production based on land expectation value (LEV). The effect of initial planting density on wood quality is considered in the economic evaluation. Different planting densities (403, 1097, 1808 and 2981 stems per hectare [spha...
Article
In this study the effect of planting density on the stem form of Pinus patula trees was investigated. Four different spacing treatments of 403, 1 097, 1 808, and 2 981 stems per hectare (spha), and four stem form properties viz. stem deviation, taper, sinuosity and ovality, were assessed on the lower nine metres of the tree stem. The results showed...
Article
Only 1% of South Africa’s total land area is used for forestry with 51% of that being used for Pinus and 40% for Eucalyptus species. A shortage of adequate structural sawn timber has been forecast where Pinus species is the predominant raw structural material and Eucalyptus is mainly used for pulp production. Young, engineered Eucalyptus grandis ha...
Article
The objectives of this study were (1) to analyse different testing methods for evaluating face-bonding quality of cross-laminated timber from Eucalyptus grandis timber bonded with a one component polyurethane adhesive and (2) to evaluate the effect of different processing variables on the face-bonding quality of cross-laminated panels. A 3 × 2 fact...
Article
Full-text available
This study reviews, from a South African and developing world perspective, green building rating tools and life-cycle assessment methods with a focus on wood constructions. Based on existing studies, it seems as if the well documented environmental benefits of using wood is not sufficiently reflected in the green building rating systems reviewed. A...
Article
Full-text available
The predominant plantation hardwood species in South Africa Eucalyptus grandis is, despite relatively good strength and stiffness properties, seldom used for lumber production due to low dimensional stability, splitting, and cracking of the wood. As critical defects often develop or aggravate during the drying process, the edge gluing of Eucalyptus...
Article
Improved growth rates and shorter rotation ages have caused a reduction in the stiffness of structural lumber from South African-grown pine plantations. Microfibril angle (MFA) and wood density are known to be two wood properties that influence wood stiffness. Therefore, the objective of this study was to determine the effect of planting spacing of...
Article
Faster growth and reduced harvesting ages are causing a reduction in the stiffness of lumber from South African grown pine plantations. The objective of this study was to determine whether increased planting densities of Pinus elliottii would result in improved stiffness of its sawn lumber and whether it would affect other relevant lumber propertie...
Article
Full-text available
The exploitation of Eucalyptus grandis lumber as structural material may take advantage of the finger-jointing and edge-gluing of the boards while they are still wet, so as to reduce the natural susceptibility of the species to warp and split during drying. But the strength grading needed for structural uses, usually performed on dried lumber, shou...
Article
Full-text available
South Africa was the first country in Africa to implement a locally developed green building rating tool and has a growing number of rated green building projects. The method of life-cycle assessment can help to compare and assess the environmental performance of building products. At present, more than 70% of all sawn timber in South Africa is use...
Article
Full-text available
Information on the external shape, internal properties and defects of a tree is important for the forest and wood-processing industries. Resin pockets are internal defects, associated with some softwood species, and are especially undesirable in furniture, joinery and veneer products. In this study, we propose a new lower-cost method for measuring...
Article
A study was undertaken to evaluate the quality of the timber produced by Pinus elliottii × Pinus caribaea var. hondurensis (PECH) and the Pinus patula × Pinus tecunumanii low elevation (PPTL) and high elevation (PPTH) hybrids and their parent species for both kraft pulp and sawn-timber production. Trees were taken from unthinned tree improvement tr...
Article
Four experiments were established on the semi-arid west coast plain of South Africa during the 1990s. The trails tested the survival and growth of several eucalypt species and hybrids, some of which were established in a climate that is drier than their natural distribution range. The aridity indices (AI; defined as mean annual precipitation [MAP]/...
Article
Full-text available
Southern Africa, and specifically its western parts is dominated by low rainfall areas, and it is expected that the rainfall in most of these parts will in future decrease further due to climate change. Woodlots of fast-growing, non-invasive tree species can provide the opportunity to produce wood and release the pressure on natural woodlands, whil...
Article
The objectives of this study were to develop and assess a method of using tree ring measurements in standing pruned Pinus patula trees for modelling the knotty core of the pruned section of a tree and to assess variability in knotty core diameters in the tree stem. A total of 170 trees from 17 compartments on a wide variety of growth sites from the...
Article
Full-text available
South Africa is a timber-scarce country that will most probably experience a shortage of structural softwood lumber in the near future. In this study the concept of using young, green finger-jointed Eucalyptus grandis lumber was evaluated for possible application in roof truss structures while the timber is still in the green, unseasoned state. Dry...
Article
Full-text available
Faster growth and reduced harvesting ages is causing a reduction in the stiffness of lumber from South African grown pine plantations. The objective of this study was to determine whether higher planting densities of Pinus radiata from the Southern Cape, South Africa, could be used as a management intervention to increase the stiffness of its sawn...
Article
The main objective of this study was to determine which property, of the six strength and stiffness properties used in structural timber design, was the most influential in the design of nail-plated roof trusses. Thirty recently completed nail-plated roof truss designs were randomly selected from three roof truss manufacturing plants and a total of...
Article
Full-text available
For wood manufacturers around the world, the single biggest cost factor is known to be its raw material. Maximum volume recovery of this raw material is, therefore, of key importance for the industry. The wood products industry consists of several interrelated manufacturing steps for converting trees into logs and logs into finished lumber. Each op...
Article
Reduction in the rotation ages of softwood saw-log plantations in South Africa is causing increased proportions of low stiffness sawn lumber at final harvest. It has been shown for some species that the microfibril angle (MFA) of the S2 layer of tracheids is strongly related to the modulus of elasticity (MOE) of wood, even more so than wood density...
Article
In the water-scarce environment of South Africa, drought-tolerant eucalypt species have the potential to contribute to the timber and biomass resource. Biomass functions are a necessary prerequisite to predict yield and carbon sequestration. In this study preliminary biomass models for Eucalyptus cladocalyx, E. gomphocephala and E. grandis × E. cam...
Article
Full-text available
Pinus patula is the most intensively planted conifer in the tropics and subtropics. The increased proportion of corewood that results when rotation ages of pine plantations are shortened has become a wood quality factor of growing concern worldwide. The purpose of this study was to develop empirically based models for predicting the flexural proper...
Article
Full-text available
The objective of this study was to examine the variation in and intercorrelation among wood properties determining the suitability of 16- to 20-year-old South African-grown Pinus patula trees for structural timber. A total of 1 112 sawn boards from 340 logs, 170 trees and 17 different compartments were examined. Sawlogs were taken from two height l...
Conference Paper
Full-text available
This paper looks at how to model and link two important cutting operations in the South African pine wood industry. The model is proposed to help answer the question: given the current log supply - what should some of the decisions, specifically machine settings, be for the two cutting centres to try and meet market demand at a minimal cost. The fi...
Article
Full-text available
In this study sawn timber from 16- to 20-year-old Pinus patula trees were obtained from a wide variety of sites along the Mpumalanga escarpment in South Africa. The objectives of this study were to assess the efficiency of the current visual and mechanical grading rules on this timber and to evaluate the potential of some indicator properties to be...
Conference Paper
In many softwood sawmills logs are positioned in front of the primary breakdown saw according to predetermined rules such as centering the log and/or positioning the plane of maximum curvature vertically. However, if one wants to optimise this positioning process in terms of value recovery there can be tens of thousands different log positions to c...
Article
Full-text available
The accurate prediction of the mechanical properties that can be expected from timber from standing trees has many benefits for the growers and processors of trees. It includes support in tree breeding selection, tree processing allocation decisions, site and silvicultural research and processing production planning. A number of methods have been d...
Article
Full-text available
The objectives of this study were to determine the bending strength and stiffness properties of young Pinus elliottii x P. caribaea var. hondurensis timber from the Southern Cape, South Africa, and to evaluate the predictability of these properties from acoustic measurements on standing trees, logs and their sawn boards. The timber has good bending...
Article
Automated three-dimensional log scanning and positioning systems in a sawmill have a limited time available to reach an optimal positioning solution before primary breakdown sawing starts. In this study a search algorithm (tentacle algorithm) was developed for this task and was empirically evaluated in terms of its ability to find an optimal or clo...
Article
In a case study at a local sawmill, the authors analysed the cost and production information and designed a managerial accounting system using Activity Based Costing (ABC) techniques. With ABC, activities are viewed as the fundamental cost objects and the cost of a product is derived as the sum of the costs of all the activities needed to manufactu...
Article
Full-text available
The reintegration of South Africa into the global economy and technological change on many fronts has increased the need for investment in human capital to make South Africa's industry globally competitive. This paper describes how a partnership was formed between government, industry and educators in South Africa and Canada to develop university-l...
Conference Paper
Full-text available
The objective of this study was to develop and assess the methodology of using tree ring measurements in standing pruned Pinus patula trees for modeling the knotty cores of the pruned section of a tree. A total of 170 trees from 17 compartments on a wide variety of growth sites from the Mpumalanga escarpment were selected and destructively sampled....
Article
The frame saw is a popular primary and secondary log breakdown saw in South Africa. In this study a theoretical model for estimating the maximum feed speed of a frame saw is derived. Contrary to earlier models, the actual blade speed is used as a variable in the derivation. The chip holding capacity of the saw gullet is used as the limiting factor...
Article
One of the challenges when optimizing the positioning of a log in front of the primary breakdown saw is the limited time available for software to reach a solution. In this study, the distribution of optimal log positions in front of the primary breakdown saw, some variables that influence the software solution time, as well as the effect of positi...
Conference Paper
Full-text available
The opportunity exists for sawmills sourcing their logs from intensively managed softwood plantations to indude quality information as well as log and product volume in their production planning process. A destructive sampling procedure and three integrated software systems were developed and can be used to optimize profit of the timber manufacturi...
Article
The opportunity exists for sawmills sourcing their logs from intensively managed softwood plantations to include quality information as well as log and product volume in their production planning process. A destructive sampling procedure and three integrated software systems were developed and can be used to optimize profit of the timber manufactur...

Projects

Project (1)
Project
This is a long term research aim, which tries to further the understanding of how biotic and abiotic stress influences tree growth, allocation and wood properties