This paper describes study on evaluation method of particle size and penetrability of ultrafine cement grout. Proposed method to evaluate particle size (digital image method) provided larger particle size than the result obtained by the conventional granulometry. The results by digital image method well coincided with penetrability of grout into cracks indicating that the proposed digital image method was right measure to evaluate the particle size of ultra fine cement grout. The proposed method was applied to evaluate the difference between single and double mixings of grout. The result clearly indicated the difference and it can be said that the double mixing was superior for ultrafine cement grout.
