Q: I have a mature Silver Maple tree adjacent to my concrete driveway. I believe the roots of the tree are shallow and have lifted (or prevented the uniform settling of) the driveway over its 40-year life. The result is that the driveway has large, uneven cracks roughly parallel to the edge of the drive nearest the tree.
I want to replace the driveway, but I do not want to: (a) hurt the tree, or (b) just end up with the same cracking over time. Are there any solutions?
A: Since you don't want to damage the tree, I think your options are somewhat limited.
If you decide to replace the driveway, you will need to take special care not to damage the roots when you remove the old concrete. Once the old concrete is removed, see if you can add enough sand and/or gravel to the subgrade of the driveway to provide a couple of inches of cover to the existing tree roots. This will result in raising the finished elevation of your driveway by a few inches, but if this does not create other problems, it might allow you to repair your driveway and keep your tree. However, if the tree continues to grow, you may see cracks reappear in the same area of the new driveway, in spite of the 'cushion' you have installed over the roots.
To minimize potential cracks in the area of the tree, I would recommend adding additional reinforcement to the concrete in this area by installing a grid of 1/2" rebar on 12 inch centers. This will help hold any cracks that do occur from spreading apart, and minimize faulting of the slab.
If the area around the tree is not in the main traffic pattern of your driveway, consider not replacing the concrete in this area. If you need this part of the drive for your traffic pattern, one other alternative to consider would be using pervious concrete in the area adjacent to the tree (See our web site for more info on pervious concrete). This would benefit the tree by allowing more water to reach the root system, and still provide a surface that cars could drive over. Keep in mind that pervious concrete can not be reinforced, so you still risk cracks from the roots, but the pervious concrete will probably provide a little more flexibility than regular concrete, and may be a little less susceptible to cracks for this reason.