First of all, let me tell you what this thread is NOT. It is not intended to make you a concrete expert, since I'm not one. It is not going to give you a lot of techniques on finishing, since there are members on here that have spent years on the opposite end of the chute as I am. It will hopefully take some of the apprehension out of ordering and placing concrete yourself.
What is Concrete?
Concrete, in its most basic form, is a mixture of water, course aggregate (3/4" and 3/8" rock), fine aggregate (sand), and cement (Portland, Flyash, Slag, etc.). Modern concrete almost always contains chemical additives, such as mid-range and high-range water reducers, air entrainment, shrinkage reducers, accelerators, and retarders (I'll get to those in a moment).
The rocks and sand make up the bulk of the actual mass of the concrete, with the water and cement binding everything together. The different mixtures of these ingredients determine a lot of things, such as the strength of the different mixes.
Once the water hits the cement, the hydration process starts, and the clock starts ticking. You've got about two hours to get the concrete where you want it.
So, What You're Saying, Is That Its Not Just Flat And Gray?
Well, yes and no. It ends up that way, but ordering from your local concrete supplier will be easier (and you'll sound like a professional!) if you know what kind of concrete is best for what you're doing.
So Get To It: What Kind Should I Order?
Geez, be patient. We'll focus on two basic types, a 3/4" rock mix and a pea gravel mix.
First, we need to determine what you're doing. Pea gravel mixes won't have any 3/4" rock in them, so they are used for decorate concrete, such as stamped patios, exposed aggregate driveways and sidewalks, and garage floors with radiant heat. They're generally more expensive than 3/4" rock mixes (no, I don't know why), so they aren't used when not necessary.
For almost everything else, a 3/4" rock mix will work fine. Things like foundation footings and walls, basic driveways, sidewalks, garage floors, piers, all that jazz, a 3/4" mix works great. It finishes just as good as a pea gravel mix, without the extra cost.
Should I Get a Truck Or a Bunch of Bags?
That depends on how strong your back is. A concrete mixer loaded with 10 yards is equivalent to 500 (!) 80lb bags of Quikrete. At $3.65 per bag at Home Depot, that works out to $1825 (before sales tax), or about double what the truck would cost. That doesn't figure in the extra time it takes, since it would take you all day to mix that much in a portable mixer (which also costs money to rent), and labor ain't cheap. If you order a 10 yard truck, it could be poured out in 15 minutes, as opposed to 8-9 hours.
If your job is less than one yard, you may want to look at bags. Concrete companies will charge a short load fee (since that truck isn't making much money hauling one yard), and that brings costs up. Its still a lot easier, but less cost effective, to order a truck.
How Much Do I Need?
Concrete is sold by the cubic yard 3x3x3. It is almost never placed 3ft thick, so for a slab, you measure L (ft2) x W (ft2) x H (in2) / 324. Or, you can go here:
Concrete Calculator
and let a computer do it for you. If you order a truck, get at least a half yard more than what you think you need. There are many variables (grade variances, concrete sticking to the inside of the drum, etc.) which make getting the exact amount difficult. If you have to use a concrete pump, get at least a yard more.
You Said You Would Explain The Additives, But You Haven't Yet
Good Lord, you are impatient. So, without further ado:
Water Reducers (mid-range and high-range) - These are chemicals that, as the name suggests, increase the plasticity of concrete without using excess water (they make it wetter). Since the ratio of water to cement is a major factor in determining the strength of your concrete, the less water used, the better. You won't need to know much about these when ordering, since the mix will already be designed with them in there. Usually, though, the truck will have extra high-range with him, so if you want it a lot wetter than he brought it, he can add extra. The general rule of thumb is a gallon of high-range will increase the slump of a full load 2". Of course, there are many other factors, but the cool part about it is you can have the mix more workable, and it won't effect the strength.
Air Entrainment - Concrete naturally is about 1-3% air, or little voids in the material. This is fine for concrete that isn't exposed to freeze/thaw cycles, such as interior slabs or underground footings. However, for outdoor concrete (patios, driveways, sidewalks, etc.), you need more air voids because it will expand and contract. For this, an air entrainment additive is used to bump up the percentage to about 5-6%. The DIYer only needs to know to make sure the mix "has air" when he or she orders the concrete. The mix will already be designed with the proper amount in mind.
Accelerators - If you want your concrete to set up faster, order accelerator. There are two types, calcium chloride and non-CC. Calcium is cheaper, but can't be used with steel (rebar or mesh) because it is corrosive. If you want accelerator and are using steel reinforcement, you must get non-CC. I would recommend the DIYer not use accelerator, since it cuts the margin of error down. It is more for the professional who knows what they're doing and would like to be done quicker.
Retarder - A retarding chemical gives you about an extra 45 minutes to work with your concrete, which gives you a bit more of a margin of error. It also helps if you live in a remote area that is far from a concrete supplier, or if you can only con one friend into help you.
My Supplier Asked Me What Slump I Want. What is Slump?
Slump is a measure of how wet the concrete is when still in its plastic (semi-solid) state. A concrete tester fills a 12" tall metal cone with concrete. When he pulls up on it, the concrete inside falls down because of gravity (not just a good idea, its the law), and the slump is a measure of how far it falls. The most common slump is 4", but this differs depending on application. A dryer slump would be used in footings (2-3") so the concrete doesn't ooze out the bottom of the forms, whereas a wetter slump (5-6") would be used when doing most flatwork (driveways, sidewalks, etc.) because it makes it easier to work with and finish nicer.
If you want your concrete wetter, the driver will add 1 gallon per yard per inch of slump. So if you have about a 4" slump and want a 5, add 10 gallons to a 10 yard load. Easy as pie.
If you want it dryer, tough beans. All you can do is wait. Have the driver stop his drum for about ten minutes and then look again.
Anything Else?
Oh, probably. Feel free to ask questions in this thread, but perhaps if you have questions about finishing or other placing issues, a professional finisher could start a thread to that effect.
What is Concrete?
Concrete, in its most basic form, is a mixture of water, course aggregate (3/4" and 3/8" rock), fine aggregate (sand), and cement (Portland, Flyash, Slag, etc.). Modern concrete almost always contains chemical additives, such as mid-range and high-range water reducers, air entrainment, shrinkage reducers, accelerators, and retarders (I'll get to those in a moment).
The rocks and sand make up the bulk of the actual mass of the concrete, with the water and cement binding everything together. The different mixtures of these ingredients determine a lot of things, such as the strength of the different mixes.
Once the water hits the cement, the hydration process starts, and the clock starts ticking. You've got about two hours to get the concrete where you want it.
So, What You're Saying, Is That Its Not Just Flat And Gray?
Well, yes and no. It ends up that way, but ordering from your local concrete supplier will be easier (and you'll sound like a professional!) if you know what kind of concrete is best for what you're doing.
So Get To It: What Kind Should I Order?
Geez, be patient. We'll focus on two basic types, a 3/4" rock mix and a pea gravel mix.
First, we need to determine what you're doing. Pea gravel mixes won't have any 3/4" rock in them, so they are used for decorate concrete, such as stamped patios, exposed aggregate driveways and sidewalks, and garage floors with radiant heat. They're generally more expensive than 3/4" rock mixes (no, I don't know why), so they aren't used when not necessary.
For almost everything else, a 3/4" rock mix will work fine. Things like foundation footings and walls, basic driveways, sidewalks, garage floors, piers, all that jazz, a 3/4" mix works great. It finishes just as good as a pea gravel mix, without the extra cost.
Should I Get a Truck Or a Bunch of Bags?
That depends on how strong your back is. A concrete mixer loaded with 10 yards is equivalent to 500 (!) 80lb bags of Quikrete. At $3.65 per bag at Home Depot, that works out to $1825 (before sales tax), or about double what the truck would cost. That doesn't figure in the extra time it takes, since it would take you all day to mix that much in a portable mixer (which also costs money to rent), and labor ain't cheap. If you order a 10 yard truck, it could be poured out in 15 minutes, as opposed to 8-9 hours.
If your job is less than one yard, you may want to look at bags. Concrete companies will charge a short load fee (since that truck isn't making much money hauling one yard), and that brings costs up. Its still a lot easier, but less cost effective, to order a truck.
How Much Do I Need?
Concrete is sold by the cubic yard 3x3x3. It is almost never placed 3ft thick, so for a slab, you measure L (ft2) x W (ft2) x H (in2) / 324. Or, you can go here:
Concrete Calculator
and let a computer do it for you. If you order a truck, get at least a half yard more than what you think you need. There are many variables (grade variances, concrete sticking to the inside of the drum, etc.) which make getting the exact amount difficult. If you have to use a concrete pump, get at least a yard more.
You Said You Would Explain The Additives, But You Haven't Yet
Good Lord, you are impatient. So, without further ado:
Water Reducers (mid-range and high-range) - These are chemicals that, as the name suggests, increase the plasticity of concrete without using excess water (they make it wetter). Since the ratio of water to cement is a major factor in determining the strength of your concrete, the less water used, the better. You won't need to know much about these when ordering, since the mix will already be designed with them in there. Usually, though, the truck will have extra high-range with him, so if you want it a lot wetter than he brought it, he can add extra. The general rule of thumb is a gallon of high-range will increase the slump of a full load 2". Of course, there are many other factors, but the cool part about it is you can have the mix more workable, and it won't effect the strength.
Air Entrainment - Concrete naturally is about 1-3% air, or little voids in the material. This is fine for concrete that isn't exposed to freeze/thaw cycles, such as interior slabs or underground footings. However, for outdoor concrete (patios, driveways, sidewalks, etc.), you need more air voids because it will expand and contract. For this, an air entrainment additive is used to bump up the percentage to about 5-6%. The DIYer only needs to know to make sure the mix "has air" when he or she orders the concrete. The mix will already be designed with the proper amount in mind.
Accelerators - If you want your concrete to set up faster, order accelerator. There are two types, calcium chloride and non-CC. Calcium is cheaper, but can't be used with steel (rebar or mesh) because it is corrosive. If you want accelerator and are using steel reinforcement, you must get non-CC. I would recommend the DIYer not use accelerator, since it cuts the margin of error down. It is more for the professional who knows what they're doing and would like to be done quicker.
Retarder - A retarding chemical gives you about an extra 45 minutes to work with your concrete, which gives you a bit more of a margin of error. It also helps if you live in a remote area that is far from a concrete supplier, or if you can only con one friend into help you.
My Supplier Asked Me What Slump I Want. What is Slump?
Slump is a measure of how wet the concrete is when still in its plastic (semi-solid) state. A concrete tester fills a 12" tall metal cone with concrete. When he pulls up on it, the concrete inside falls down because of gravity (not just a good idea, its the law), and the slump is a measure of how far it falls. The most common slump is 4", but this differs depending on application. A dryer slump would be used in footings (2-3") so the concrete doesn't ooze out the bottom of the forms, whereas a wetter slump (5-6") would be used when doing most flatwork (driveways, sidewalks, etc.) because it makes it easier to work with and finish nicer.
If you want your concrete wetter, the driver will add 1 gallon per yard per inch of slump. So if you have about a 4" slump and want a 5, add 10 gallons to a 10 yard load. Easy as pie.
If you want it dryer, tough beans. All you can do is wait. Have the driver stop his drum for about ten minutes and then look again.
Anything Else?
Oh, probably. Feel free to ask questions in this thread, but perhaps if you have questions about finishing or other placing issues, a professional finisher could start a thread to that effect.