Is it possible to create exposed-aggregate walkways with enough rock at the surface to make pedestrians think they're walking on gravel paths? Ahal Contracting Co., St. Louis, proved the task can be done when its crews placed 40,000 square feet of exposed-aggregate walkways for the Missouri Botanical Garden's Boxwood Garden and the Kemper Center for Home Gardening. The four different concrete mix designs used for the project contained aggregate concentrations higher than those found in the typical exposed-aggregate mix.
To achieve uniform aggregate exposure on each of the project's 5-inch-thick walkways, crews sprayed surface retarder on the slab immediately after placing and finishing the concrete, and then covered the slab with polyethylene sheeting. The next day, they removed the sheeting and washed the concrete surface to remove cement paste from the top of the aggregate. To protect their handiwork, workers applied a waterproofing sealer 28 days after concrete placement. Completed in April 1995, all the exposed-aggregate walkways have withstood the test of time admirably, impressing the garden's visitors with their beauty as well as their durability.