The safest bet for any concrete mix is four-two-one: four parts crushed rock, two parts sand, and one part cement. The four-two-one mix, obviously, has seven parts. Conveniently, when mixing concrete, the ratio can be mixed on any range of scales. For example, if you only have a small amount of concrete to mix, it's okay to use three parts sand and two parts cement - that's still a safe mix. If you have a lot more cement than sand, though, you should probably use five parts cement to one part sand.
The key thing about concrete is consistency. If you add too much water, the concrete will be sloppy and runny; if you don't add enough, it'll be dry and crumbly. Concrete needs to be moist but not wet - not fully hydrated, yet not so far along in the curing process that it won't drip when you tap it. This is why most concrete mixes include some form of alcohol or other solvent to accelerate the drying process and eliminate any hint of moisture within the mixture.
As long as you follow basic concrete safety guidelines (such as wearing protective clothing and using personal protection equipment), there is no concrete that is toxic to humans. However, concrete production uses chemicals to reduce friction between materials during the mixing process, which can cause some concrete fumes to appear. These fumes are composed of carbon dioxide and organic compounds such as ethanol and methyl methacrylate.
The concrete ratio varies on the strength you want to attain, but as a general rule, a basic concrete mix would be 1 part cement to 2 parts sand to 4 parts aggregates. A foundation mix of one part cement, three parts sand, and six parts aggregates can be employed. As with any concrete project, more or less cement, sand, and/or aggregate may be required depending on the desired consistency and strength.
Concrete is a mixture of water and cement that sets into a solid mass when mixed together. Concrete can be colored or plain, smooth or textured. It can be used for floors, walls, and other structures. Concrete is easy to work with and durable; it can be repaired if needed. Its durability makes it useful for applications where other materials fail quickly, such as in roads and bridges. However, concrete needs constant maintenance to stay attractive and functional.
There are many ways to mix up concrete, but the most common methods are with a shovel and trowel or with a mixer. For simple tasks, like putting down a base for a garden bed or driveway, using a shovel and mixing bowl is sufficient. For larger projects that require more control over the concrete's consistency, a mixer is recommended. There are two types of mixers: hand-mixing beaters and powered mixers. Both types use different techniques but produce similar results.
Half of the cement, sand, and aggregates (for a concrete mix alone) should be measured. Using half of the mixture now will keep it from drying out before you get a chance to use the rest. You may combine the remaining half afterwards. If using cement, add it while stirring.
Mortar is the same as concrete with the addition of water. The amount you need depends on how thick you want your wall to be. One option is to buy a package of prefabricated mortar boards. These are small cones that you drill holes in and stick into the ground to create a stable surface upon which to build. You then pour a thin layer of mortar into the holes and spread it around with a small rod or brush. The mortar will set into a solid board when it dries.
You can also make your own mortar. Mix one part portland cement to three parts sand in a bowl or other container. Add enough water to form a paste-like substance. Let it cure for at least 24 hours before using.
If your mortar does not set properly, it means there was too much air in the mixture. Remove any large lumps of sand or gravel before adding the water. This will help prevent "shot" or broken pieces of concrete from getting into your mortar.
1 tablespoon cement A three-part mixture of sand, sand, and sand, and sand, sand, and will yield a concrete mix with a compressive strength of about 3000 psi. Mix water with the cement, sand, and stone to create a paste that will bind the materials together until the mixture solidifies.
2 bags of #30 gravel 1/4 inch or larger If you want your driveway to look good, let it harden for at least one day before using it. The time required depends on the temperature out there but usually isn't more than a week or two. If you drive over the surface often, however, you'll need a surface that can withstand some wear and tear. A concrete driveway does not require any special treatment other than cleaning up debris left behind by gravel and allowing the mixture to cure properly before using it.
3 bags of #40 gravel 1/4 inch or larger If you want your driveway to look good, let it harden for at least one day before using it.
This concrete mixture ratio of 1 part cement, 1 part sand, and 3 parts aggregate yields a concrete mix with a compressive strength of 2500 to 3000 psi. When water is mixed with the cement, sand, and aggregate, it forms a paste that binds the ingredients together until the mixture hardens. The amount of water required depends on the type of cement used. Portland cement requires more water than lime-based cements like portland cement concrete.
For optimum performance, concrete should be mixed as close to the job site as possible. Concrete that is mixed in a central location will set up more slowly because there is no flow and heat from nearby mixing bowls or barrels. This allows the mixture to reach a stable temperature more quickly, which improves its workability and reduces cracking.
The best mixing method for portland cement concrete is by hand. The concrete mixer truck can also be used for small jobs but for larger projects a hand mixer is recommended because it gives you better control over the quality of the mix. Hand mixing requires more effort up front but leads to better concrete properties down the road.
For most applications, air entrained concrete is used instead of plain old wet concrete. Air entraining agents (AEAs) are added to concrete to increase its air content and reduce its density. This makes the concrete easier to pump and pour, and also helps it cure faster.
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