Previous studies show that the fly ash geopolymer concrete cured at room temperature can be significantly improved if mixed into a small dosage of ordinary Portland cement. However, this modified material has rarely been compared with the traditional fly ash geopolymer concrete, cured at high temperature and not mixed with any ordinary Portland cement. In order to meet the needs of practical engineering applications, the basic mechanical properties, including Poisson,s ratios, were tested and compared between two different materials, i.e., the thermally cured fly ash polymer concrete without cement and the room temperature cured fly ash geopolymer concrete with a small dosage of cement particles. Also, to clarify the mechanism in results of the mechanical tests, the microscope and chemical elements tests, including SEM, EDS, XRD, FTIR and CT, are performed. The results show that the mechanical properties of room-temperature cured fly ash polymer concrete containing a little cement are close to those of thermal cured FGC without cement particles. Before compressive failure of prism specimens, the lateral to the vertical strain ratio is close to 1.0, exhibiting a significant lateral deformation capability. After adding 8% cement particles, the degree of polymerization reaction at room temperature is close to that of high temperature curing measures without cement. In forming a more reasonable microscopic pore structure, the samples cured at room temperature are better than those cured at high temperatures.