The paper is devoted to computer and experimental simulation of US (ultrasonic) signal propagation in acoustic solids with micro-structure. Any change in the percentage of flaws or pores influences considerably the value of the ultrasonic wave speed. The theoretical analysis is based upon the Ray Tracing algorithm. We calculate numerically the full path of each ray from the transmitter to the receiver, in its multiple reflections between the surfaces of the internal obstacles. The natural experiments are performed in a water basin with some arrays of equal metallic round rods. This simulates the US evaluation of the mechanical properties of concrete. The computer modeling allows us to construct the envelope of the US signal registered at the receiving transducer. Then we simulate the dependence of the wave speed versus porosity. There is a sufficiently good accordance between numerical and experimental results.