Materials and methodsThe hydration times and hydration temperatures at 20 ~ are determined according to Sandermaan and Kohler (1964). The equipment used to measure hydration times at 83 ~ has been described somewhere else (Simatupang et al. 1995). Circular cement-bonded particleboards specimens with a diameter of five cm and target thickness of 12 mm were made from larch or poplar ~ood particles. Each specimen was made from 6.3 g (oven dry) wood particles. 18.9 g binder and an effective water/binder ratio of 0.40 (Simatupang 1973). The required aluminum sulfate was dissolved in water. Metakaoline was obtained by calcination of kaolinite (Riedel de Haen, Germany) at 750 ~ for six h. The material was cooled in a desiccator and stored in air-tight containers before use. Portland cement was a PZ 45F. The properties have been published in former literature, see Simatupang and Neubauer 1993. A blender with two counter-rotating twirling-sticks was used for blending the furnish for three specimens. The furnish was then divided in three parts and each part was manually filled in a 5 cm high circular wooden form with a diameter of 50 ram. Six of such holes were drilled in a 25 x 15 x 5 cm wood block. A 38 mm high wooden disc with a diameter of 49 mm, inserted in each hole, was the distance bar to predetermine the board thickness. The wooden forms and disc were coated before use with liquid paraffin to prevent sticking. The filled wooden block, which rested on a plywood plate, was then placed in a hydraulic press. Pressing time was 24 h at ambient conditions. After demotding the particleboard specimens were stored 28 d at 20 ~ and 65% RH before testing. The shear strengths were determined according to .After testing the cement particleboard specimens were ground passing a 200 mesh sieve, dried and stored in air-tight containers before use. The filtrate of 2 g ground material, soaked in 20 ml bidistilled water for 15 min, was used for the pH measurements. Calcium hydroxide was determined according to Shebl et al. (1988)~ Cement-bonded fiberboards were made from recycled newspaper fibers. The properties of these fibers have been published elsewhere (Takats and Simatupang 1993). Blending the fibers with water and binder was accomplished with a household hand-mixer modified according to the following method. In a 15 cm long copper tube with 10 mm diameter, various holes were drilled. Six cm long steel nails with sharp ends, were inserted in the holes until it protrude from the tube, and soldered. The quirl was connected to the central shaft of the hand-mixer. Make water was firstly mixed with the fibers. Blendig was continued after dosing the binder. The fluffy furnish showed no lumps. To make a 18 x 18 cm board with a thickness of 6 mm and a target density of 1.4 g/cm 3, 18.7 g fibers (oven dry) and 187.3 g binder were required. The effective water/binder ratio was 0.35. The mat was manually formed into a wooden form.Four mats were placed on a 50 x 50 stainless steel caut. Distance bars of 6 mm predetermined the thickness. A...