Physico-Chemical and Thermal Transformations of Wood of Long-Term Natural Ageing

In this paper, the physicochemical and thermal transformations of long-term naturally aged wood are investigated. The results obtained indicate a significant loss of chemical and thermal stability of wood composite as a result of natural aging with hydrolytic destabilisation of the lignocarbohydrate complex, as well as disturbance of the morphological structure of the material. It is shown that lignocarbohydrate materials of long-term natural ageing are characterised by abnormal intensity of the charring process and heat release, as well as increased tendency to smouldering combustion. A new hazard, previously not taken into account in fire resistance standards and assessments, has been discovered – a decrease in the fire resistance of long-life wooden structures. The significant influence of the factor of operation time is caused by the increase in the charring rate of wooden structures. Thus, for a load-bearing wooden beam with a service life of 150 years, the charring rate increases on average by 1.8 times compared to modern softwood structures. It has been experimentally established that changes in physical, chemical and mechanical properties of long-life wood under the influence of high temperatures or fire can lead to a reduction in the fire resistance limit of a wooden structure due to the loss of load-bearing capacity by more than 2 times.