According to this article, translucent concrete will be hitting the market quite soon.

Thousands of optical glass fibers form a matrix and run parallel to each other between the two main surfaces of every block,” explained its inventor Áron Losonczi. “Shadows on the lighter side will appear with sharp outlines on the darker one. Even the colours remain the same. This special effect creates the general impression that the thickness and weight of a concrete wall will disappear.

via linkbunnies