## 1 Introduction  
Laminated veneer lumber (LVL), one of the most important engineered wood products (EWPs), offers all the superior advantages of the parent wood as well as improved properties due to its laminated structure. LVL is manufactured by bonding together rotary peeled or sliced thin wood veneers under heat and pressure. Prior to lamination, the veneers are glued, and the grain of each veneer is oriented in the same direction. This makes LVL stronger, straighter, and more uniform than the parent wood and overcomes some of wood's natural drawbacks such as strength-reducing knots [1]. LVL can be used for exterior and interior applications including beams, lintels, purlins, truss chords, stairs, and furniture applications [2]. The manufacture of LVL currently almost fully depends on the use of synthetic adhesives, mainly based on formaldehyde (e.g., urea formaldehyde (UF) and phenol formaldehyde (PF)) as a binder due to its low cost and sufficient properties. Formaldehyde-based adhesives have dominated the application over the last 80 years and are still dominating the field of wood products bonding [3]. LVL produced using formaldehyde-based adhesive causes a serious challenge for further development and application of products made of LVL [4]. The formaldehyde can irritate the eyes, as well as the respiratory and nervous systems, and possibly lead to cancer and leukemia [5; 6]. Hence, the allowed level of formaldehyde emission from wood products has been limited by the announcement of the International Agency for Research on Cancer and Environmental Protection Agencies in various countries, forcing companies to reduce formaldehyde emission in their products. In addition, LVL may not be sufficiently resistant to fire and decay to be used for exterior applications, unless treatment or protection is provided. A lot of effort has already been made toward minimizing the aforementioned issues [3; 7; 8]. However, most of these approaches could result in an obvious increase in cost and complexity of the preparation process. In this context, mineral binders have shown great potential in replacing the conventional synthetic binders for the production of EWPs [9; 10; 11]. The use of a mineral binder as an adhesive for the bonding of veneer, apart from the fact that the mineral components are formaldehyde-free, has several other advantages compared to using synthetic adhesives. Mineral binders are resistant to fire, extreme temperature, acids, mildew, and fungi [10; 11; 12]. Geopolymer (M\({}_{n}\)[-(Si-O\({}_{2}\))\({}_{z}\)-Al-O-]\({}_{n}\)_-_w_H\({}_{2}\)O, M=Na, or K) is an emerging class of binding materials made by pozzolanic powder activated by an alkaline solution [13; 14]. Pozzolans are defined as materials containing high amounts of silicon dioxide (SiO\({}_{2}\)) and aluminum oxide (Al\({}_{2}\)O\({}_{3}\)) that are either raw or calcined natural materials [15; 16]. A three-dimensional amorphous aluminosilicate network is formed due to the geopolymerization process through the linking of SiO\({}_{4}\) and AlO\({}_{4}\) by sharing their oxygen atoms in a high alkalinity environment [17; 18]. Although numerous studies have been dedicated to the reinforcement of the geopolymer matrix with wood [10; 19; 20], only a few studied the potential of geopolymer as a binder for solid wood bonding [21; 22; 23]. A few studies have also been devoted to the use of geopolymer as a binder to produce wood-based products [9; 24; 25; 26]. No literature is available on the use of geopolymer binder to manufacture engineered wood products such as LVL. Adequate adhesion between two materials (similar or dissimilar) is of great importance for determining the final application of resultant products. The requisite adhesion strength between the materials stems from the intrinsic adhesion forces across the interface of materials, as well as the toughness of adhesive joints [6; 27].