*2.4. Preliminary Work*

A preliminary test program was conducted to evaluate the effect of SP when used in partial replacement of cement in a mixture of wood particles and cement. Seven mixtures were investigated, the variable being the fraction of cement replaced by SP. The mixing sequence used with a mortar mixer (HOBART A-120, Hobart Canada Inc, Don Mills, ON, Canada) is presented in Table 2.


**Table 2.** Mixing Sequence.

Unsurprisingly, the presence of steatite was found to increase the amount of water necessary to produce mixtures with adequate workability. The quantity of water required was estimated according to ASTM C1437 [24] to make sure that all mixture have the same workability value as P1 (Table 3). Assessing the workability and bending strength of mixtures with different percentages of SP was intended to determine the maximum amount of SP that could be used in the mixture without affecting negatively the mechanical properties of the particleboard in comparison with those of the reference wood-cement particleboard and GB. Only cement and wood particles were selected to prepare the control mixture (P1), while six other mixtures were prepared by incorporating SP at replacement rates of 10, 15, 20, 30, 40 and 50% respectively (P2 to P7).

**Table 3.** Mass ratio of steatite powder, cement and water used for the seven mixtures considered.


Preliminary mechanical results have shown that the replacement of cement by SP in WCSP has a significant impact. The three-point bending test results at 3, 7, 14 and 28 days of moist curing show that the bending strength of the sample particleboards increases with the curing time as expected for Portland cement-based systems, although it does not increase much beyond the age of 14 days. A density change test revealed that the weight of all particleboards was stable after 14 days of curing. The study of Vu et al. [8] has also shown that the difference of bending resistance between the particleboard cement-wood-wood ash at 7 and 28 days of curing time, was not significant (4.2% max.). In the freshly consolidated particleboard, the heavier SP particles tend to settle in the bottom, yielding non-uniform characteristics across the thickness of the board. This segregation results in non-isotropic particleboards with different bending MOR depending on which side is subjected to tension stress during the test. These preliminary results have shown that particleboards with 15% of the cement replaced by SP (P3) is optimum, with the best mechanical properties obtained among the six tested mixtures. Indeed, the study of P. Kumar et al. [12] shown that the replacement of SP should be maintained below 20%.
