# Effect of Primary Spruce Lamella Aging on the Bending Characteristics of Glulam Beams
## 1 Introduction  
Glued laminated (glulam) beams and similar wooden composites, e.g., cross-laminated timber (CLT), overlayed materials, laminated wood-nonwood composites and multiwood composites (COM-PLY), are commonly used in structural engineering, furniture, sport, musical and decoration products [1]. In glulam, the defects in the sawn timber are cut out, and lamellas with a thickness of \(\leq\)50 mm are bonded together [2]. Glulam beams can be made from coniferous woods (Douglas fir, larch, Norway spruce, hemlock, Southern pine, etc. ), broadleaved woods (azobe, beech, doussie, keruing, padouk, red map, resak, etc. ), as well as densified low-density woods (batai, poplar, etc.) [2; 3; 4; 5], preferentially using thermosetting glues such as polyurethane (PUR), resorcinol-formaldehyde(RF), phenol-resorcinol-formaldehyde(PRF), melamine-formaldehyde(MF) or urea-melamine-formaldehyde(UMF). In Europe, the Norway spruce is the most common wood species used for glulam [2; 5; 6]. The final quality of glulam beams is influenced by many factors: (1) the wood species, whether it is used in its natural state or after chemical, thermal, mechanical or biologicalmodifications, and what are its typical structural characteristics and properties, e.g., the density and porosity, the type and amount of extractives, the pH value, roughness, free surface energy, moisture content at bonding, tension and compression strengths, elasticity, and resistance to pests, fire and weathering; (2) the glue type and its physical-chemical characteristics, e.g., the molecular weight, viscosity, surface tension, chemical reactivity, resistance to water and total durability; and (3) the technology of gluing, e.g., the spread rate of glue and its open time and the pressing diagram used [7; 8; 9; 10; 11; 12; 13; 14]. The applicability of structural gulam beams depends mainly on their mechanical properties and resistance to biological damage, fire and weathering. Today, when new sources of wood are limited, preparation of gulam beams from older wood products previously aged in various environments is actual. During the demolition and reconstruction of buildings, a large amount of construction waste is generated, including wood waste. This usually ends up in municipal waste landfills, while only a small part of it is reused in the form of recycling [15; 16] or for energy production [17]. In general, to increase the efficiency of the use of waste materials, a method of cascading resources was developed [18]. This is a method in which the efficiency of the use of a material resource is increased through its gradual or repeated use for several applications in individual consecutive cascading steps. By applying cascading in practice, the efficiency of the use of wood raw materials can also be increased, and thus, trees and wood stocks in the forest can be saved. The theoretical concept of wood cascading was first described by [PERSON] [19]. Subsequently, the studies by [PERSON] et al. [20; 21], [PERSON] et al. [22] and other researchers emphasized the environmental and economic advantages of this method for wood recycling in practice. Currently, despite all of the favorable aspects of the cascading method, wood waste is primarily used for the production of particleboards [23], cement chipboards [24] and possibly other types of agglomerated materials [25]. However, during their production, it is necessary to first chip the waste wood material, which does not fulfill the basic principle of cascading. In order to maximize efficiency, it is necessary to achieve the greatest possible number of cascading steps, and in the first steps, wood particles from the waste material, even larger than wood chips, should be used. So far, relatively few workplaces have dealt with such research, and most of the research has focused on the production and testing of the properties of CLT panels from recycled solid wood [26; 27].