our church parking lot has a very impermeable soil, currently grassed but not totally. during heavy rains it floods (ponds).
we need to grade the area to allow for drainage but also want to cover areas where grass does not grow well. we considered concreting the entire lot but found the cost to be extremely expensive.
we have heard of crushed asphalt and also porous asphalt. are they different and which would either be OK to use?
do we need a sub-base other than the in-situ materials with either?
Crushed asphalt simply refers to old asphalt pavement that has been crushed into small pieces, typically about 3/4 inch, and can be used as sub-base for new pavement. This is similar to crushed concrete.
Porous pavement is the more common term for porous asphalt. This requires a special preparation of the asphalt pavement so there are holes in the pavement that allow water to drain through. The same technique can be used to create porous concrete. It is more expensive than standard pavement. In your case, it would not work well, since you state that you have essentially impervious soil underneath your pavement, so water that percolated through the pavement would pool underneath the pavement, and above the soil, and would damage the pavement.
Regardless of what type of pavement you use, you need a sub-base that typically consists of 6-12 inches of crushed stone or crushed concrete. This provides drainage underneath the pavement. In the case of porous pavement, you typically need more stone underneath the pavement, typically 12-24 inches, since all the water that percolates through the pavement is temporarily stored in the sub-base until it percolates away underground.
what Dan said ...... as always excellent advise
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