Question: Where did I see information about slabs made of concrete that is porous enough for water to drain straight down through it?

This would be an advantage in parking lots in our area because it would minimize the loss of water by runoff.

Answer: We published an article beginning on page 685 of the September 1983 issue called "Porous Concrete Slabs and Pavement Drain Water."

The article tells about applications in many parts of the world, gives examples of mix proportions, and describes the kinds of bases, subbases and drainage systems used with the porous concrete. The porosity in the concrete is achieved by using coarse aggregate and no fine aggregate. Sometimes other materials are added to the mix, such as fly ash or an adhesive admixture. The concrete can be placed with rakes or slipforming equipment and finished with vibratory screeds or rollers. Troweling is undesirable. Further details are given in the article.