If you are going to install a concrete driveway you have to make sure that you put in expansion joints. These are necessary because because concrete expanses and contracts depending on the temperature. If your driveway was one big slab it would crack, the expansion joints prevent this from occurring by giving the concrete room to expand. Installing expansion joints is fairly easy if you know what you are doing.
The first thing that you have to do in order to install expansion joints in your concrete driveway is to determine where they are needed. As a general rule you are going to want to limit each section of concrete to being no bigger than a 4 foot by six foot slab. This however requires a lot of joints and most people think that it destroys the look of the driveway. You can get around this problem by using steel grids to strengthen the concrete which means that you can have larger sections. If you do this your best bet is to put one expansion joint down the center and then have them going horizontally every six to eight feet.
It is also important to realize that how closely you need to space your expansion joints will depend on the concrete that you are using. High quality concrete is much stronger than low quality concrete and it does not need as many expansion joints. It is therefore a good idea to ask your concrete supplier how many joints they recommend for their product.
When it comes time to actually install the expansion joints there are basically two options that you can use. The first is to put wooden slats in between each section of concrete. These slats will then need to be removed once the concrete is hard enough that it will not flow in and fill the slats. In order to make sure that you can get the slats out you will need to spray them with a flight agent that keeps the concrete from sticking to them. This approach makes it easier to ensure that your joints are straight but it does take more time because of all the prep work that is involved. It also offers the disadvantage of requiring quite a bit of wood which adds to the expense of your driveway.
The other option that you have for putting in expansion joints is to simply use your trowel while you are smoothing the surface. To do this as soon as you have poured the concrete and smoothed the surface you will want to take your trowel and make the joints. The big issue that you will have here is making sure that they are straight, it is usually best to run a piece of string from on side of the driveway to the other attached to wooden spikes along the edge of the driveway that you can follow to stay in a straight line. The other big thing is to make sure that you get your joints to the right depth, they should be a quarter of the thickness of the slab. So if you have a four inch slab you need your expansion joints to go down 1 inch.