The paper presents a study of the resistance of connections of load-bearing laminated wood structures using domestic melamine-urea-formaldehyde adhesives (MMFC) to cyclic temperature and humidity influences. The method of cyclic tests is described. An assessment is made of the resistance of MMFC to temperature and humidity influences and the compliance of the selected adhesive with the requirements established for the production of long-span load-bearing structures.

Keywords: melamine-urea-formaldehyde adhesives, wooden structures, resistance of adhesive joints to cyclic temperature and humidity influences, strength

The paper presents a study of the water resistance of joints of load-bearing laminated timber structures using domestic melamine-urea-formaldehyde adhesives (MMFC). The high relative strength of samples dried after soaking and boiling above that established for the increased water resistance group is shown. An assessment of water resistance for three formulations is given, the dynamics of crack growth due to the influence of the moisture factor of MMFC.

Keywords: melamine-urea-formaldehyde adhesives, wooden structures, water resistance of adhesive joints, strength

The problem of maintaining the exact ratio between the components in mixtures based on oxychloride cement is described. This problem is solved by the use of additives plasticizing or water-reducing action. The results of studying the effect of the type of additives on the mobility of mixtures and the strength of hardened oxychloride cement pastes are presented. The positive effect of the use of additives based on naphthalene and melamine sulfoformaldehyde was shown. The negative effect of additives based on lignosulfonates on the strength of oxychloride cement pastes has been established. Assumptions about the reasons for the low efficiency of additives based on polycarboxylate esters are indicated. The positive influence of the plasticizing effect of additives on the homogeneity of the microstructure of oxychloride cement pastes is shown. An assumption about the reasons for the increase in strength when using additives based on naphthalene and melamine sulfoformaldehyde is made.

Keywords: oxychloride cement, Sorel cement, plasticizer, water reduction, additive, modification, structure, strength

This article presents the results of a study of the tendency of composites based on magnesium oxychloride cements to deformation changes. The dependence of the degree of deformation of light magnesian concretes on the conditions of their hardening has been determined. The main factors influencing the deformation of light magnesia concretes have been established. The influence of hardening conditions on the intensity of deformation changes is shown. Revealed the reasons causing uneven deformation of light magnesia concrete. A method for the manufacture of light magnesia concretes has been determined, which prevents their uneven deformation and subsequent violation of the geometry of the structure. It has been established that the introduction of modifier additives, such as cellulose ethers, helps to reduce the delamination of concrete magnesia mixtures, improve their homogeneity and reduce the unevenness of deformation changes over the sample volume.

Keywords: magnesium oxychloride cement, volumetric deformations, shrinkage, expansion, warpage, hardening conditions