Development of Roofing Tiles Support Made from Bituminous Plywood

: In this study, a new design of roof support was investigated to improve the system of roof coverings with roofing tiles. Usually, wood frames or slabs are often used as support for roofing tiles, which presents many disadvantages such as the expensive cost of the slabs and sometimes inefficient Corresponding wood frames. The new design proposed in this study uses the technique of Kodjo Attipou wood frames, but by interposing between the frames and the roofing tiles, a barrier is made of bituminous plywood. The barrier is composed of plywood 1.22 m in width, 2.44 m in length and 4 mm in thickness. The plywood is covered with a cloth of cotton fibers, impregnated in petroleum bitumen fluidized by kerosene. A test of permeability was conducted and has shown good results after 3 weeks of imbibition in water. The new composite material obtained can then serve as intermediate support in the system of roof coverings with roofing tiles and wood frames.


Introduction
In the West African sub-region and particularly in Togo, various materials such as straw ( Fig. 1 and 2), metal sheets, tiles made of fibers, cement, baked clay, or mortar cement are used for roof coverings (Wallonie, 2016;Youcef and Bahia, 2011). The support used with these materials was generally wood frames (Fig. 3). The use of wood frames is widespread but its deformation and vulnerability to attack of insects cause often operating inconvenience of the roof (Picard, 1992). It is also noticed, especially with the roofing tiles resting directly on wood frames (Fig. 4), that under brutal effect, shocks of heavy loads break the roofing tiles and cause leaks of the roof. To overcome these drawbacks, support made of reinforced concrete is often realized before laying the tiles (AFNOR NF P84 204-1-1 Reference DTU 43-1). This technique results in an additional cost.
Therefore, it is of interest to investigate alternative roof coverings that are efficient and economic. The present study is within the framework of promoting the use of local and environment-friendly materials Lolo et al., 2017;Banakinao et al., 2016;Drovou et al., 2015;Keita et al., 2014;Sorgho et al.,2014;Pasch and Pizzi, 2002;Lefeu and Francy, 1999). The new design of roof coverings proposed in this study uses layers of bituminous plywood, at different proportions and different compositions, with fibers of cotton, as intermediate support between the wood frames and the roofing tiles, to guarantee the waterproofing of the roof.

Tools and Equipment
The tools and types of equipment used for the manufacture of bituminous plywood and permeability tests were: Brushes, scissors, hot plate, tares, water tank, ball unit and ring, penetrometer bitumen, and viscometer.

Materials
To manufacture the bituminous plywood, four raw materials were used: The fabric of fibers of cotton used for this study was the type used for bagging wheat flour. The choice of wheat flour bag is due to the fact painters usually use it as oil painting canvases and it is well-known that oil paints resist for a long time on fabrics of fibers of cotton. Since bitumen is a product derived from petroleum and contains a given percentage of oil, it can be then weather resistant on this type of bag. However, a systematic prior washing of fabrics of fibers of cotton with soap, followed by a high clean water rinse was done before the application of the impregnation layer.
Fluidized bitumen is a bitumen-based liquid obtained by dissolving road bitumen in a hydrocarbon solvent of petroleum origin (NFT 65-002). For the waterproofing of the substrate, a grade 60/70 of road bitumen was used, which is fluidized at 65% with kerosene, and a petroleum diluent with a kinematic viscosity of 1.25 mm 2 /s at 40•C.
To assess the influence of the size of the granulometry of the sand on the hygroscopic behavior of the bituminous plywood, sand with three different moduli of fineness was used to manufacture three different series of bituminous plywood.

Methodology for Manufacturing Bituminous Panels
Waterproof plywood was made, on which bitumen was applied, alternated by sand and fabric of fibers of cotton. The methodology was realized in six (06)  fluidized at 150 • C was applied at 0.068 g/cm 2 ( Fig. 9) 5. A compacted layer of sand was then applied. The mass of the sand used depends on its modulus of fineness, i.e., 0.073 g/cm 2 for coarse sand with a modulus of fineness of 2.9, 0.04 g/cm 2 for medium sand with a modulus of fineness of 2.4 and 0.003 g/cm 2 for fine sand with a modulus of fineness of 2. Therefore, three series of panels were obtained (Fig. 10) 6. A final layer of bitumen of grade 60/70 fluidized at 150C was applied at 0.068 g/cm 2 over the compacted layer of sand (Fig. 11) The manufactured bituminous panels were subjected to a test of water absorption to assess their hygroscopic behavior. In addition, seven untreated plywood panels were made for comparison purposes.

Test of Water Absorption
For each different modulus of fineness of sand, seven (07) samples of treated and untreated panels (seven rectangular panels 30 × 30 cm) were manufactured. There were four (04) series of seven panels for the test. After weighing each panel, the treated face was gently soaked in a rectangular tank of water of dimensions 1 × 2 m, filled to 2/3 (Fig. 12). The untreated face of the panels was preserved from any contact with water. The untreated panels were also imbibed in water at the same moment. The seven samples of each series were imbibed in water for twelve (12) days.
After every twenty-four (24) h, the panels were taken out of the water, cleaned carefully, and then weighed. This operation was repeated until the weight of the panel between two successive weighings hardly varied. The quantity of water absorbed was calculated for each panel and the mean value of the seven panels of each series was determined. Knowing the surface of contact of the panel with water (30 × 30 cm 2 ) and the duration of water absorption and assuming that the absorption is uniform over the entire surface of contact, the coefficient of permeability was calculated according to the following formula Eq. 1: where, Pe is the coefficient of permeability (m/s); Q is the quantity of water absorbed (m 3 ); A is the surface of contact and D is the duration of absorption (s).

Tests Conducted on the Materials used
To characterize the sand, two tests were conducted: the particle size analysis according to the standard NF P 94056 and the test of the sand equivalent according to the standard NF P 94-054.

Results of Tests Conducted on the Sand
The granulometric curves of the different sands are presented in Fig. 13. As expected, the percentage of sand" passing through" the sieve increases while the modulus of fineness decreases.
The results of the different tests on sands are summarized in Table 1. The absolute density and the apparent density of the sands tested are quite similar. The Mf1 and Mf3 sand contain more fine elements than the Mf2 sand.

Amount of Water Absorbed and Coefficient of Permeability
The curves in Fig. 14 show the variation in the quantity of water absorbed by each series of panels as a function of the imbibition time. Those curves indicate that on the tenth day of imbibition, all panels of the three processed series are saturated with water. The untreated panels are saturated at the seventh and are completely immersed while the treated panels still float on the water. The results are presented in Table 2.
The total quantity of water is measured at saturation, i.e., on the seventh day for the untreated panels and the tenth day for the treated panels. Table 3 presents the different coefficients of permeability of the panels (Fig. 15).

Conclusion
This study shows an improvement of the system of roof coverings by introducing a new design of roof support. An alternative to classic roof coverings using roofing tiles directly laying on wood frames was proposed. The new technique proposed can guarantee the waterproofing of the roof support.     A new composite material, bituminous plywood, was obtained by adding different layers of road bitumen (of grade 60/70), fabrics of fibers of cotton, and sand at specific modulus of fineness (2.9, 2.4, and 2) on plywood with fluidized bitumen. The new composite material was placed between the wood frames and the roofing tiles to form the new system of roof coverings. The test of water absorption conducted on the manufactured panels shows a permeability of about 3.47 × 10 −10 m/s. These panels are then classified in the category of water-impermeable materials.
Bituminous plywood can be used as an alternative to slabs in the system of roof coverings, to strengthen the roof against water infiltration and to ensure the durability of the construction as well as a low-cost roofind system.