any theories on the stress wave propagation in concrete?

1) A starting point is Buck Schreyers paper on 1-D waves in inhomogeneous media.  The reference is :

"One-Dimensional Elastic Waves in Inhomogeneous Media" by Howard L. Schreyer, ASCE J. Engineering Mechanics, vol. 103, no. 5, 1977, pp. 970-990.

2) You can also look at the paper by George Gazetas called " Vibrational characteristics of soil deposits with variable wave velocity", International Journal for Numerical and Analytical Methods in Geomechanics, vol. 6, issue 1, pp. 1-20, 1982.

3) A slightly more mathematical paper is the one by George Papanicolou and co-workers called "Transport equations for elastic and other waves in random media", Wave Motion, Volume 24, Issue 4,
December 1996,
Pages 327-370.  The doi is doi:10.1016/S0165-2125(96)00021-2 .

A google search on "Elastic wave random media" will give you a huge range of papers on the subject. 

-- Biswajit 

You may check out Jacob Lubliner's book "Plasticity Theory." There's a chapter on wave propagation in elastic-plastic material (not a complex media like rock or concrete, but should be a good start). This book is now reprinted by Dover, with a low price.