Building a Concrete Driveway
Making a concrete driveway requires a great deal of heavy labor and careful planing but if done correctly can provide many, many years of service. Concrete driveways can be finished in dozens of different colors and designs making that driveway unique. The most critical requirement to a good solid concrete drive is the sub-base beneath. Extremely wet or soft soils will cause shifting of the bearing materials and thereby assure future failure of the finished concrete itself. If your substrate is dry or has had proper under drainage installed, placement of a leveling course of suitable material is then required. Generally this course of material is at least six inches thick when compacted and rolled. DOT spec Item 304 provides a great sub base and is available at most stone quarries. Man made Item 4 which consists of graded sand and gravel can be substituted in areas that do not have a granite type rock source. Man made item 4 must have proper under drainage in place as it is more susceptible to rain or ground water wash outs. Once the sub-base has been placed and compacted the next thing is to assure the finished slopes are what you want the top of your concrete to adhere to. Make sure the finished grades slope away from buildings, do not cause any ponding areas and will cause all captured water to run to the area you wish it to go.
Layout the finished driveway using your pins and string line setting the string to the top elevation of the concrete for the driveway itself. Taking extra time here to get it right will make setting your wood forms a great deal faster and more accurate later on. Once all the string lines are in place take a good look at what you have created. Do curved areas have nice and smooth lines? Are the square areas actually square? Are all the slopes correct? Make the adjustments now. Install your wood forms making sure they can handle the pressure from the concrete.
Now plan the concrete pours. If the driveway is very large, pouring it all at once is not practical.
Even with lots of professional help that does it every day, pouring 100 yards of concrete in one day and then finishing it is a daunting task. A sudden rain shower or broiling sun can cook the concrete or destroy the finished surface. Carefully watch the weather for the day of the pour. Concrete panels should not be poured larger than twenty or twenty-five feet in length and fifteen feet wide.
Expansion joint material is placed between panels to absorb expansion and contraction of the concrete due to changing temperatures. Caulking these joints prevents water form getting between the slabs. In warm climates it prevents weeds from growing, in cold climates it prevents ice from forming between the slabs and cracking them.
Access for the ready mix trucks is always a consideration as well. You want to avoid driving the trucks inside the forms if at all possible. If the driveway is to have reinforcing bars it prevents any truck access. If only welded wire mesh or fiber reinforcement is being used a good crew can pour a panel, set an expansion joint form and, install the mesh and then continue with the next panel without delaying the pour. Like they say, do not try this at home. If you are working with a few inexperienced friends, keep the pours manageable in size. If you are using colored concrete or intend to use a stamp on the surface keep the pours even smaller.
Driveway concrete should be at least 3000 pound strength, but 4000 pound is preferable for only a few dollars more per yard and it will take a great deal more weight. Edges at roadways where a car will transition for concrete to asphalt should have a double reinforcing bar installed horizontally along the lip on the edge to prevent cracking and chipping.
Once the concrete is placed a power trowel is used to provide a smooth surface without polishing it like a floor in a building. Different trowel blades provide different finishes. Commonly used on a driveway are float finish blades. Many people like a broom finish surface and this also can be adjusted to be as heavy or light as desired.
