In this paper, development of a nonlinear vibro-acoustic modulation technique based on non-contact piezoelectric sensors was investigated to detect the crack progression of concrete cracking caused by thermal treatments. Experimental results show that defined ultrasonic nonlinear parameter is in agreement with the accumulation of thermal crack. The phase velocity of Rayleigh wave and resonance frequency of vibrations were measured and compared with ultrasonic nonlinear parameter to validate the sensitivity of developed method. X-ray Computed Tomography (CT) technique is applied to visualize microstructure of thermal damage. The CT images show that proposed nonlinear parameter is reliable and well correlated with the microstructural defects of concrete specimen. Due to the advantage of removable characteristic of non-contact ultrasonic measurements, the developed non-contact nonlinear wave modulation method could be promising for quick and convenient damage assessment of concrete structures in engineering practice.