*Article* **Steatite Powder Additives in Wood-Cement Drywall Particleboards**

**Viet-Anh Vu 1, Alain Cloutier 1,\*, Benoît Bissonnette 2, Pierre Blanchet 1and Christian Dagenais 1,3**


Received: 23 September 2020; Accepted: 23 October 2020; Published: 29 October 2020

**Abstract:** The objective of this study was to develop a new drywall wood-based particleboard as an alternative to gypsum board. Various development iterations have led to the use of wood particles, steatite powder and Portland cement. The resulting outcome shows that screw withdrawal resistance was improved by 37% and bending properties by 69% compared to gypsum board of a similar density (0.68–0.70). The raw surface of the boards is of good quality and comparable to the paper-faced surface of gypsum board. Furthermore, the reaction to fire was evaluated through bench-scale test with a cone calorimeter. The investigated particleboard did not reveal visual signs of combustion after 20 min when exposed to a radiant heat of 50 kW/m2, while burning of the overlay paper of gypsum board occurred at about 57 s, suggesting that wood-cement-steatite powder particleboard could be classified as a quasi non-combustible material.

**Keywords:** steatite; wood particles; Portland cement; fire performance

#### **1. Introduction**

Steatite (also known as soapstone or soap rock) is a type of metamorphic rock. It is primarily composed of mineral talc, rich in magnesium. Its main component is hydrated magnesium silicate:Mg3Si4O10(OH)2. As it is relatively soft because of its high talc content, it has been used as carving material for thousands of years. This stone is soft, dense, heat-resistant and has a high specific heat capacity [1]. Steatite can be pressed into complex shapes before heating. It is also used in the paint industry, particularly in marine paints and protective coatings for ceramics due to its high electrical resistivity [2]. Due to its electrical characteristics, steatite is mostly used in electrotechnics. In the world market, steatite with more than 92% brightness, less than 1.5% CaCO3 and less than 1% Fe2O3 is preferred for exports [3].

Many studies have been carried out to evaluate the performance and applications of wood-cement composites because of their low cost and important contribution in mitigating the housing problem in developing countries [4]. Indeed, many studies have shown that wood-cement boards, could be used for ceilings or walls covering [5,6]. The most important advantages of wood–cement boards are their high resistance to insect, fungi, decay, acoustic waves and fire [6,7]. In fact, the sugars present in wood can inhibit cement setting. Therefore, the main problem in wood-cement board design is the compatibility between wood and cement [6]. The effect of wood on cement setting depends on several factors, among which harvesting season and wood species have the higher impacts [8]. Several special cement-based mortar containing additions of fine powder such as steatite [9], glass [10] and wood ash [11] have emerged.

The replacement of cement with steatite powder (SP) decreases setting time of cement and increases mortar cube compressive strength, but the consistency of the binding material increases [2]. The replacement of cement with SP was reported to result in improvements of the mortar microstructure, up to maximum replacement rates of the order of 20% by weight [12].

Gypsum boards (GB) are widely used in North America building construction for interior partitioning. Gypsum boards consist of calcium sulphate in the form of dihydrate crystals with overlay paper on both sides. The board core is a non-combustible material. It contains nearly 21% chemically combined water which is slowly released as steam when submitted to high levels of heat. Because steam does not exceed 100 ◦C at normal atmospheric pressure, it effectively retards the transfer of heat and the spread of fire [13,14]. Even after complete calcination, when all the water has been released from its core, GB continue to serve as heat-insulating barriers. When installed in combination with other materials such as walls and ceiling assemblies, GB serve to protect building elements from fire effectively for prescribed durations. While GB fails the flaming criteria for determining the non-combustibility of materials due to the paper overlay [15], it is typically an accepted material for non-combustible construction in most building codes due to its good fire performance. However, the paper overlay plays a vital role in the mechanical resistance of GB [16]. Besides, it appears that construction wastes from this material are a problem [17], which is aggravated by its extensive use. Economic pressures and environmental concerns are some of the driving forces of today's industrial development. Hence, many research projects are being conducted for increasing the utilization of waste materials in order to decrease threats to the environment and to streamline existing waste disposal and recycling methods by making them more affordable [17]. On the market, several alternatives to gypsum have been used such as plastic panels, plywood, fiberboard and veneer plaster.

The aim of the present study was to evaluate the mechanical, physical and thermal properties and reaction to fire of wood-cement particleboards incorporating SP as a supplementary cementing material, intended as an eco-responsible alternative to the GB. In this study, two in three of the raw materials used for particleboard production, wood particles and SP, are secondary low-cost products from lumber production and mineral extraction of steatite.

### **2. Materials and Methods**
