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Pinus maximinoi is a species that can potentially be deployed commercially to provide structural timber and poles for the South African market. The objective of this study was to investigate the flexural properties of sawn timber and poles of P. maximinoi from young plantations of the Southern Cape. A total of 60 trees and 150 logs for the sawmill study were obtained from two research trials on the Longmore estate in the Humansdorp area (13.7 years old), and on the Kruisfontein estate close to Knysna (9.0 years old). Some 74 poles from the same compartments were removed and tested in bending. The P. maximinoi sawn timber had excellent bending properties, superior to sawn timber from other South African Pinus species, tested at similar radial positions in previous studies. Analysis of variation showed that site, log height and board radial position had a significant influence on the modulus of elasticity (MOE) of sawn timber. Multiple regression analysis showed that board MOE can be predicted using a model including tree taper, time-of-flight measured with Treesonic and wood density (model R2 = 0.87). The P. maximinoi poles complied with the mean MOE national standard requirement SANS 457-2 of 9 000 MPa but not with the fifth percentile (bending strength) modulus of rupture (MOR) requirement of 34 MPa. This study and other research, however, showed that the national standard requirement for MOR of poles might be too high for current log resources in South Africa. The investigation into the bending and other properties of P. maximinoi sawn boards and poles showed extremely positive results. Based on this wood quality study of P. maximinoi, it is certainly a very promising species for deployment in the Southern Cape and potentially other regions in South Africa. [ABSTRACT FROM AUTHOR]

South Africa is a water scarce country with minimal natural forests. Plantation forest species such as the Mexican tropical hard pine, Pinus patula Schiede & Deppe ex Schltdl. & Cham., was introduced into the country to satisfy local fibre demand. Today, the majority of pine plantations in South Africa are found in the Mpumalanga province. The province has diverse growing conditions in relation to climate and soil properties. Sample plots were established in even-aged P. patula plantations and stratified according to soil parent material and altitude. Growing conditions of each sample plot were characterised according to climate and soil properties. A total of 540 sample trees were measured for height, diameter, density, and latewood content. The sample trees were harvested to produce 2690 logs. The logs were milled, and the resultant lumber was graded according to density, dynamic modulus of elasticity, and modulus of rupture. Annual maximum temperature had the most significant impact on tree growth, while rainfall correlated with wood density and latewood content of standing trees. However, annual maximum temperature and tree height had a negative relationship with the recovered lumber properties and dimensional stability. Spring rainfall appeared to be the most important factor influencing lumber twist and this was possibly due to the associated larger juvenile core present in the trees. [ABSTRACT FROM AUTHOR]

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), modulus of rupture (MOR) and other selected properties of young (16–20 years) South African-grown Pinus patula lumber. Thirty-seven trees from two commercial stands were processed into 71 logs, cant sawn into lumber and tested for MOE, MOR, wood density and distortion. The first stand was planted at 1334 stems ha−1 and thinned to 827 stems ha−1 at age 11. The second stand was planted at 1667 stems ha−1 and was unthinned. Lumber from a previous study on 17 different commercial stands from more conventional (lower) stand density management regimes was also analysed using linear mixed-effect models. Only lumber from the 1667 stems ha−1 stand conformed to the requirements for structural use and had a considerably higher mean MOE of 8967 MPa compared to 7134 MPa for the 1334/827 stems ha−1 stand and 5556 MPa for the more conventional stands. MOR values were adequate for all stands. Unlike previous studies on other species, slenderness did not seem to have a profound effect on the MOE of the lumber from these P. patula trees. Stand density management therefore has the potential to increase lumber stiffness of P. patula and should be considered as a forest management intervention for wood quality improvement by saw-log growers in South Africa. [ABSTRACT FROM AUTHOR]

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 lumber. A secondary objective was to determine the effect of planting density on other relevant properties including warp, knots, density, and modulus of rupture (MOR). Lumber properties of 61 Pinus radiata trees from four different spacing treatments from a 20-year-old spacing trial were recorded. Results indicated that initial planting density had a highly significant effect on the MOE(edge) of sawn lumber. There was a large increase in MOE(edge) of lumber from 403 spha to 1097 spha. However, MOE(edge) did not increase significantly with planting densities higher than 1097 spha. Initial planting density also had significant effects on the number and size of knots and the MOR of lumber. These results did not follow the same trends as previously found on New Zealand-grown Pinus radiata. [ABSTRACT FROM AUTHOR]

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 properties of the wood produced from relatively young P. patula trees. Models were based on the properties of standing trees, and their effectiveness was evaluated at board, tree, and compartment levels. Sample material was obtained from 170 P. patula trees, 16-20 years old, established in 17 compartments on the Mpumalanga escarpment of South Africa. Multiple regression models were developed, which managed to explain 68, 60, and 95 % of the variation in the dynamic modulus of elasticity (MOE) on individual boards, trees, and compartments levels, respectively. At compartment level, 80 % of the variation in the 5th percentile MOR value could be explained by the model. Sensitivity analyses showed that site index at base age of 10 years, acoustic time of flight, wood density, and ring width were influential variables in the MOE models. The models indicated that tree slenderness during early growth seems to play a major role in determining the dynamic MOE and MOR of lumber. This is in agreement with Euler's buckling theory and the bending stress theory. The results from this study indicated that the MOE and MOR of lumber can be accurately predicted on especially a compartment level. The predictive models developed can be used as management tools to improve operational decisions around tree breeding, silvicultural practices, and rotation ages. [ABSTRACT FROM AUTHOR]

Different types of loading due to traffic may act on bridges. The focus of this paper is on normal traffic loading according to the South African specification TMH7 (Committee of State Road Authorities 1988). TMH7 represents the code of practice for the design of highway bridges and culverts in South Africa. The aim of the paper is to provide additional insight into the effect of normal traffic loading patterns on the flexural analysis of skew bridges. This is necessary since TMH7 does not explicitly specify application patterns for normal traffic loading. Only the intensity of normal traffic loading is specified and it should be applied to yield the most adverse effects. In this paper a set of so-called "standard application patterns" are investigated and compared with the application patterns that yield the most adverse effects. The patterns are compared for flexural effects in selected design regions of the bridge deck. Numerical experiments were performed and are presented for a typical single-span bridge deck. The results of the numerical experiments are compared as the angle of skew of the bridge deck increases. [ABSTRACT FROM AUTHOR]

[Display omitted] • Successfully developed coal/ceramic composites of structural importance. • C=O and H 2 bond in the coal discards enhanced bonding with the preceramic polymer. • The developed coal/ceramic composites were stable up to 550 °C. • Flexural & compression strength of the composites in the range of 27.51–36.46 MPa & 83.78–208.50 MPa. • Coal discard rich in mineral does not result in higher strength composites. The mining and processing of coal are accompanied by the accumulation of a substantial volume of discard that threatens the environment. Also, the continuous harvesting of natural resources such as clay to produce building materials is not environmentally sustainable. In this study, various South Africa coal discard was blended with a polysiloxane preceramic polymer resin and thereafter pyrolyzed to produce coal/ceramic composites. The physicomechanical properties of the composites were evaluated using various ASTM standard test methods. The thermal stability, mineralogy, and functional group properties of the raw materials and the composites were checked using TGA, XRD, and FTIR respectively. The results suggest that carbonyl functional groups and hydrogen bond in the coal discard promoted bonding with the preceramic polymer, therby improving the physicomechanical properties of the composites. XRD results showed that the total intensity of the diffraction peaks in the coals discards declined after pyrolysis of the blend of coal discard and the preceramic polymer. This suggests the amorphization of the crystalline phases in the coal discards. The developed composites displayed water absorption and flexural strength as low as 1.94–10.1% and 27.51–36.46 MPa respectively. The remarkable mechanical properties of the composites suggest that the coal composites produced in this study could be applicable in the construction industry. However, more tests like impact strength, thermal conductivity, etc. are required to fully characterize the properties of the coal composites. [ABSTRACT FROM AUTHOR]

Low-cost wood–plastic composites (WPCs) were developed from invasive trees and recycled low-density polyethylene. The aim was to produce affordable building materials for low-cost social housing in South Africa. Both raw materials are regarded as waste materials, and the subsequent product development adds value to the resources, while simultaneously reducing the waste stream. The production costs were minimised by utilising the entire biomass of Acacia saligna salvaged from clearing operations without any prior processing, and low-grade recycled low-density polyethylene to make WPCs without any additives. Different biomass/plastic ratios, particle sizes, and press settings were evaluated to determine the optimum processing parameters to obtain WPCs with adequate properties. The water absorption, dimensional stability, modulus of rupture, modulus of elasticity, tensile strength, and tensile moduli were improved at longer press times and higher temperatures for all blending ratios. This has been attributed to the crystallisation of the lignocellulose and thermally induced cross-linking in the polyethylene. An increased biomass ratio and particle size were positively correlated with water absorption and thickness swelling and inversely related with MOR, tensile strength, and density due to an incomplete encapsulation of the biomass by the plastic matrix. This study demonstrates the feasibility of utilising low-grade recycled polyethylene and the whole-tree biomass of A. saligna, without the need for pre-processing and the addition of expensive modifiers, to produce WPCs with properties that satisfy the minimum requirements for interior cladding or ceiling material. [ABSTRACT FROM AUTHOR]