In the Philippines wood-wool-cement board (WWCB) is made in both small and large factories by mixing wood-wool (shavings) from low-quality wood, additives and Portland cement. The result is a building panel that resists water, fungi, termites and fire, and is easy to work. This high-value product uses thin logs unsuitable for sawing. It also provides employment for small communities.
The WWCB industry is expanding in the Philippines. However, most Australian plantation eucalypts and acacias are not used, partly because their wood-wool has not been evaluated for WWCB, and partly because one of the commonest species, Acacia mangium, contains carbohydrates and extractives that must be removed by soaking before the cement will cure properly. Manufacturers would be encouraged to use Australian trees if they were informed on how to select the best species and provenances, how long to soak the wood, how wet and what size the shavings should be, what is the best ratio of wood to cement, and how much 'accelerator' should be added to set the cement.
The project's aim was to improve the suitability of Acacia mangium for use in WWCB, firstly by identifying the provenances and families whose extractives do not interfere with the cement's curing process, and secondly, by measuring changes in A. mangium after different storage times.
Researchers assessed which of the major eucalypt and acacia species planted throughout Asia were compatible with the cement and thus useful for making WWCB. They sampled eucalypts and acacias growing in Australia and in the Philippines by taking two small cores of solid wood at two heights to determine tree characteristics. They ground some cores, leached them with cold water and analysed the leachates. They then kneaded cement with dried sawdust, testing samples that had been leached and also the effects of adding accelerating chemicals. After measuring the setting reactions and strengths of the resulting blocks, they classified the trees by the degree to which they inhibited the cement.
The best combinations of wood-cement ratio, wood soaking time and pre-treatment method, along with type and amount of additives, were determined for WWCBs that would be manufactured from eucalypts and acacias. Project staff then manufactured and compared boards made at pilot scale from eucalypts, acacias and species native to the Philippines. The boards were tested to determine whether or not to debark before the wood-wool is cut, what were the optimum pre-soaking times, the effects of incorporating various accelerators or rice hull ash into the cement mixture, and what were the best of several ratios of wood to cement. The boards were bent to measure elasticity, rupture and toughness. They were also immersed in water to measure absorption and swelling, buried to test resistance to termites and rot, and tested for their ability to withstand fire and long-term weathering.
This project contributed significantly to the depth of scientific knowledge and practical experience required to foster the development of a viable WWCB manufacturing industry in the Philippines. The results from early research into the compatibility of important plantation species of acacias and eucalypts with Portland showed that most eucalypt species grown in the Philippines would be suitable for wood-cement boards, overcoming a fundamental lack of information about utilisation options for plantation-grown wood.
The researchers found that certain varieties of Acacia mangium were moderately well suited for wood-cement composites and, more importantly, the research demonstrated that good-quality WWCBs could be manufactured from any A. mangium wood supply with an appropriate combination of billet postharvest storage, soaking of wood-wool and/or pre-treatment of wood-wool with simple inorganic compounds that neutralise the effect of heartwood on cement setting.
Product development research from the project (carried out mostly at FPRDI in the Philippines) resulted in a selection of medium-weight WWCBs ranging from 450 to 900 kg/m3 in density and 8 to 50 mm in thickness. These are suitable for a range of non-load-bearing applications, including walls, roofing and flooring in housing and emergency-shelter construction. They are best manufactured in a ratio of 60% cement to 40% wood by weight, from strands measuring 3 to 5 mm in width, 0.3 mm in thickness and anywhere from 300 to 500 mm in length.
Strand alignment of the surface layers has been shown to significantly improve panel stiffness and reduce the propensity for creep deformation with time under its own weight. However, since this must be done by hand it slows down productivity and adds to product cost. Such products are therefore being designed to suit specific, higher performance applications such as flooring. While strand alignment is still in the research-and-development phase at FPRDI, the research on the optimisation of the basic board manufacturing process, including correct wood/cement ratios, billet pre-storage to reduce soaking time, and mat quality, has been successfully transferred to WWCB plants, often in combination with simple mat internal reinforcement using stiffer materials.
Project research also benchmarked the quality of commercially produced WWCB products in the Philippines and evaluated the performance of surface coatings for exterior panelling. Wide variation was found in product physical properties, particularly strength and stiffness, thereby providing focus areas for product improvement through subsequent research. The simplest and most effective coatings to extend the service life of WWCB panels are fine concrete render or stucco, which significantly reduce moisture-induced thickness swell of WWCB. Elastomeric paint is another finish that maintains the surface of WWCB while protecting it from weathering and staining, however it is more expensive than cement render. Elasto-polymers are also now commonly mixed with cement render to give the surface finish greater flexibility and resistance to moisture.
Subsequent ACIAR-funded project activity resulted in the development of product performance standards for WWCB along with building codes for one- and two-storey structures containing WWCB wall, floor and roofing systems. These are in the process of being formalised through the Philippines Bureau of Product Standards (Department of Trade and Industry).
This project laid the foundation knowledge necessary for the development and growth of the WWCB industry in the Philippines to help meet the need for low-cost, locally produced building materials. It has demonstrated that low-density plantation-grown wood, which is unsuitable for applications requiring the use of solid sawn wood, can be used to manufacture WWCBs at relatively low cost and with natural durability in tropical conditions.
The Philippines is the first country to adapt a material, hitherto manufactured and used only as light-weight, non-structural sound-insulating panels for interior use, to a wide range of structural and non-structural applications in housing and commercial buildings. The ACIAR-sponsored project enabled them to effectively build on this foundation to expand the range of tree species known to be suitable for cement-composite manufacture, to improve product quality and develop new products.
Links:
[1] http://www.aciar.gov.au/country/Philippines
[2] http://www.aciar.gov.au/programarea/Forestry