Azobe

The African wood type azobe remains indispensable in garden and civil engineering products. It has unique mechanical properties such as hardness, strength, impact and friction resistance, wear resistance and high durability, combined with large available dimensions. It is particularly used in harsh conditions, such as in locks, bridges and other hydraulic engineering works. It is an exterior wood type in its own right, although it is also used for robust constructions such as company floors and wagon floors and as garden wood products such as planed posts and sheet piling.
The import of azobe hardwood is not large in comparison with the total wood import to the Netherlands. However, azobe hardwood has acquired a reputation for a number of specific applications. It fulfils a prominent role in wet marine construction in particular and is a material that is difficult to replace by anything else. Neither in the application phase nor in the decomposition phase is it harmful to the environment.

Growing regions
Azobe comes from the tree with the botanical name Lophira alata. The broadleaf tree grows in the entire coastal region of West Africa, from Liberia to Zaire (but very widely).The total growing area, in which azobe occurs alongside other tree species, amounts to over 40 million hectares. Hardwood Discount imports mainly from Cameroon.  Azobe is one of the characteristic species of the rainforest, but also in the savannas to southern Sudan and Uganda, it is a familiar sight. In certain areas it grows in groups, sometimes in the form of entire stands. The growing area is very diverse. The tree can be found both in forest stands on the mountain slopes and in the low-lying coastal areas, up to the marshy mangrove forests. Azobe is a real pioneer that has grown up strongly due to human intervention. The population moved into the forest, cleared the land and after some time left for another place. Then nature took its course, and azobe emerged as one of the first trees. In the original forest, on the contrary, hardly influenced by people, the tree is less common.

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Cameroon has about 20 million hectares of forest, 18 million hectares of which are tropical rainforest; the forest cover is under severe pressure from rapid population growth. As Africa's largest producer of timber, the country is also the main supplier of hardwood azobe. Of the 300 suitable commercial timber species that grow there, 30 are of commercial importance, such as azobe, ayous, ilomba, sipo, sapeli, iroko and tali. The forest sector contributes 10% to GNP and employs about 55,000 people. The new Forest Act (1994) contains the requirements for forest exploitation and, together with a large number of decrees and regulations, ensures sustainable conservation. Active involvement of the local population is part of the forestry policy.

The World Bank sees this forestry legislation as an example for the region. In addition to many small companies, fifteen large (international) companies are active, all working on sustainable forest management. They must submit a management plan to the Department of Environment and Forests within three years of acquiring a concession. The concession rights are valid for 15 years; renewal follows upon proven good management. Annual inventories are mandatory. In reality, only hardwood azobe trunks with a diameter of 80 cm or more are harvested (officially, this is permitted from a diameter of 60 cm). The selective harvest amounts to an average of one tree per hectare. The products that hardwood discount manufactures in the azobe wood type are: raw poles, decking boards, sheet piling, fence poles, raw beams and rules.


Tree description
Azobé is quite undemanding in terms of soil and environment. The tree grows well in mineral soils, in places where the soil has been disturbed: in secondary forests and along roads, railways and open spaces. It behaves like a real pioneer in the early stages. During the first growth phase, it is a typical light wood species; when older, it becomes a (semi-)shade wood species. Under favourable conditions, it shows very rapid growth while maintaining high density and corresponding strength and durability. The annual extra growth in width is about 1-1.5 cm. The tree reaches an average height of 40 m (maximum 50 m), with a diameter of 80-150 cm at breast height. The trunk is quite narrow and symmetrical, with a somewhat swollen foot. The stem length is about 25-30 meters. The wood has a density of 1,100-1,300 kg/m3 in the wet state and 900-1,100 kg/m3 in the dry state. As a so-called sinker, it is always transported by land or boat.

Wood description

Azobé is very strong, hard and durable. There is a clear colour difference between the heartwood and the sapwood. The sapwood, usually 10-20 mm thick, has a light pink to grey-yellow colour that gradually changes to light red-brown. The heartwood is red-brown; under the influence of light, the colour turns dark red to deep red-brown to chocolate brown; sometimes it has a violet glow. Between the sapwood and the heartwood is an orange-brown intermediate zone of 60-90 mm with slightly fewer properties than the heartwood, the so-called transitional wood. The sapwood is not suitable for use. The FSC-certified azobe from Cameroon is also being offered, partly due to the efforts of Dutch timber importers and/or concession holders. One concession holder has set up a traceability process to guarantee the legality of its timber. 

After inspection by an independent certification organisation, this timber is offered with an OLB (Origine et Légalité des Bois) certificate. Gabon and Congo Brazzaville are also important producers of azobe. In Gabon, West Africa's pioneer in sustainable forest management, 1.48 million ha of forest have been certified and, since 2002, admitted to the Dutch Keurhout system. The country has been accepted as a pioneer member by the PEFC (Programme for Endorsement of Forest Certification Schemes), in which over thirty country systems from six continents are represented. In Congo-Brazzaville, a lot of work is being done on forest certification, among other things on the basis of FSC rules. It is likely that sustainably produced wood from this country will soon be available with a certificate on our market.

Sustainability
Azobé is considered as a very durable wood type. This is confirmed by the large quantities applied for many decades under the most severe conditions. The heartwood belongs to durability class 1/2, in (sweet) water applied to class 1; research according to NVN-ENV 807 (Wood preservatives - Determination of the effect against soft rotting fungus and other soil inhabiting micro-organisms) indicates that the transition wood also belongs to class 2. It is well resistant to attack by earthworm in both brackish and saline water.

Quality standards

The quality of wood is determined in our country by the series of standards on the quality requirements for wood (KVH 2000), which sets requirements for the main external characteristics such as the thread course, knots, cracks and deformations. In this range there is for azobe NEN 5480 (Quality Requirements for Wood - Wood type azobe). This distinguishes between quality classes A, B and C, which are aligned as closely as possible with the common commercial qualities. Class A makes the highest demands on strength and/or appearance. Since 2003, the European strength classes according to EN 338 (Timber for structural applications - Strength classes) have been in use. The most important strength class for azobe, corresponding to quality class A/B, is D60, as mentioned in NEN 6760.

Processing

Although azobe has a high density and is very hard, with the right tools it is relatively easy to work. Of course, the required strength and processing time are higher than for lighter and less hard wood species. The round wood is usually sawn with a band saw. If you work it dry, the saws and chisels will be considerably dulled. The wood can be turned quite well. It can also be planed, even though it is quite heavy. Because of the strong cross grain, a small chip angle must be maintained during machine planing in order to obtain a smooth surface. Radially sawn, it is difficult to split, tangentially easy. Freshly sawn azobe has a typical tannin smell, which disappears after a while. It is difficult to bend. Due to its hardness and the risk of splitting, it is advisable to pre-drill when nailing and screwing. This should be done quietly, otherwise the wood will carbonized. Like similar heavy and hard wood species, it is difficult to glue it with the usual types of glue. TNO, Dutch Ministry of Waterways and Public Works and a number of wood companies are working on tests to be able to wet glue hydraulic timber species such as azobe.

Finishing
Given its high natural sustainability, azobe does not need to be treated. Although it does age untreated and therefore acquires a beautiful patina, there are also applications where the red-brown colour is preserved. It is advisable to use non-film forming, coloured finishing agents; these should be reapplied periodically as working can cause hairline cracks to appear in the surface.

Outdoor applications
Especially thanks to its mechanical properties such as hardness and strength, azobe is widely used in civil engineering, and in recent years increasingly in garden products. Hardwood Discount also has specifically chosen for Azobe hardwood in the following products; azobe poles, azobe decking, azobe sheet piling, azobe fence, azobe beams, shoring. The many possibilities of azobe wood make it the perfect choice for all outdoor applications.

Supply
Azobe wood is delivered in a constant, flawless quality. Besides, heavy dimensions (0.8-1.5 m) in long lengths (4-12 m) are available. Some of it is still imported in log form and sawn here in the country. However, a shift is taking place towards the production countries. Specific standard sizes in table form cannot be given for this type of wood. It is still mainly sawn to specification in the so-called specification wood and in azobe posts, azobe planking, azobe sheet piling, azobe fences, azobe beams, azobe revetment and in the specification one can include: 'azobe of sustainability class 1/2, with document for sustainable forest management or at least of demonstrable legality'.

Drying

From fresh to dried, azobe shows considerable shrinkage. It therefore requires a very slow drying process. Sawn azobe is mainly processed wet. This means that the centre-to-centre distances and the right thicknesses have to be taken into account in the construction. Also, due to its sometimes nervous behaviour, it is wise not to assume too large free spans and, in the case of deck wood, to use sufficient thicknesses (from approximately 40 mm). In order to prevent end cracks in (round) timber of heavy dimensions, the ends are often smeared with a wax emulsion. 

Especially in gallery constructions. Other very favourable properties play a role here: high wear resistance, high impact strength and low friction resistance. In particular, it can be used under harsh conditions, i.e. damp situations and high loads. This makes it suitable for hydraulic engineering works such as bridges and bridge decks, lock gates, jetties, fenders, dams, sheet piling, purlins, mooring posts, sleepers, friction bars and switchwood. Furthermore, it is used for dragline fences, picket fences, bulkheads, garden wood and park benches. When dried (to approx. 20-25%) it can be used as a noise barrier. Wickerwork of thin azobe is used for sheet piling, corbels and zinc pieces, road foundations and garden fences.


Interior applications
Its use indoors is more limited. Its hardness and wear-resistance, however, make it especially suitable for company floors. Due to the many cross-threads, the friction and splitting resistance is high. For this reason, it is used for wagon floors, lift shafts, brake blocks and stair treads. Other applications include support structures for heavy machinery and - because of its resistance to acids and chemicals - for installations in chemical factories. The high density provides relatively favourable fire-retardant properties. In the classification of its contribution to fire propagation, it can therefore be classified as class 2 without further investigation. It is therefore highly qualified as fire-resistant cladding for steel or concrete columns; it can also be used itself as fire-resistant column in housing construction, which is very common. A special feature is that the wood species serves as rail for the rubber-tyred metro trains in Paris.

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