Cement, water, fine aggregate (sand), and coarse aggregate are the four primary components of concrete (rock). Cement is the binding agent that gives concrete its strength; it contains silica and alumina as its main components. Water plays two key roles in cementing materials together: It helps prevent the solid particles from drying out too quickly, and it also helps make certain minerals in the cement hydrate (i.'ts hard to explain but bear with me) - if you freeze fresh concrete, for example, it will keep its plasticity even after thawing because some of the water has frozen into small crystals that protect the cement from breaking down. Sand and gravel add weight to the concrete and provide more surface area for the cement to bond with. The finer the sand or gravel, the more surface area there is to create a strong concrete.
Coarse aggregates are used in concrete to increase its weight and make it easier to handle during construction. Coarse aggregates include natural stones such as granite and marble, which have pores and cracks that can hold water within them. This allows any moisture in the air to enter the stone and be taken up by it. As the stone dries out, it releases this water back into the surrounding soil.
Concrete is made composed of lime (CaO), cement, water (H2O), sand, and many other ground-up rocks and minerals. All of these elements are combined. They are added to the concrete mixture to boost its strength. The cement is not chemically bound to the rocks and gravel. It stays in the concrete while the calcium ions from the lime combine with oxygen atoms from water to make a hard surface that protects the rock beneath it.
Lime is the main ingredient in cement. It comes from limestone, which is the main component of mortar and brick. Limestone contains some carbon dioxide (CO2) when it first forms into a rock. As it gets older, more carbon dioxide is absorbed into it from the air. This causes it to become brown or yellow.
When limestone is heated in a kiln, the carbon dioxide is driven off. The leftover material is pure calcium oxide (lime). This can be mixed with small amounts of other ingredients to create cement. There are two types of cement used in construction: ordinary portland cement and high-performance cements.
The chemical reaction that occurs when cement is mixed with water produces a solid substance that has great mechanical properties. Cement does this by using the limestone powder as a source of calcium and the silica particles from the sand to form calcium-silicate hydrate (C-S-H). As long as there is enough water, the process will continue indefinitely.
Concrete is made up of cement, sand, aggregates, and water. "Pasta" is a Portland cement and water combination. Concrete is therefore a combination of paste, sand, and aggregates, however rocks are occasionally used in lieu of aggregates. The word "concrete" comes from the Latin concretus, meaning "solidified."
Concrete can be mixed by hand or with equipment. The two main types of mixers used for concrete are the open bucket mixer and the closed drum mixer. Open bucket mixers use buckets or other containers to mix the ingredients together while drums rotate and blades inside the drum mix the concrete.
An electric drill fitted with a mixing blade can be used as an alternative to an open bucket mixer. This method produces a rougher mix but it's faster than using buckets. Drills should not be used to mix wet concrete because the vibration will cause the wet ingredients to split off the seeds (i.e., gravel) that are embedded in the concrete.
A concrete pump is used to inject water into the dry ingredients to create a slurry that can be transported to a work site. Pumps vary in size from 50-100 gallon capacity for home use to 1500-3000 gallon capacity for commercial applications.