Even though concrete is one of the most popular construction materials; however, it also has many cons in use at the same time such as a severe deterioration after subjected to fire exposure. Nowadays, fire accidents occur easily in all over the world including Thailand and almost of structural concrete under fire incidents were diminished, i.e. the mechanical properties caused by a decomposition of chemical compound and changes in physical structure. A series of experiment is conducted for macroscopic specimens in burning process conforming to standard temperature – time curve of ASTM E119, then they are cut in order to investigate the attenuation of chemical properties on less than 0.15 mm diameter powder sample, physical properties on 5 mm cubic and mesoscopic samples for mechanical properties test. The relationships between chemical – physical and physical – mechanical properties are compared with numerical simulation considering the effect of chemical and physical properties on mechanical properties. Based on the results of the current study, the proposed numerical simulation can be used to assess the changes of material model as a function of the residual chemical compound content of mortar samples after high temperature treatment.