Aggregates are inert granular materials such as sand, gravel, or crushed stone that are used in concrete together with water and portland cement. Coarse aggregates are any particles greater than 0.19 inch in diameter, but most commonly vary between 3/8 and 1.5 inch in diameter. Fine aggregates are defined as particles smaller than 0.19 inch, and usually range from 0.075 to 0.125 inch in diameter.
The three main ingredients of concrete are water, cement, and aggregate. Concrete is a hydrophilic material that attracts water molecules inside its structure where they dissolve the cementing material. As the water evaporates, it leaves voids inside the concrete that lead to deterioration. This process is called "carbonation." Concrete also absorbs oxygen from the air which causes oxidation. The oxidized surface layer peels off and falls away when the concrete is placed beneath a roof or covered with another material. This protective layer is called an "epoxy" skin.
The ratio of cement to water should be approximately $0.45$ per $100$ gallons ($17.1$ L) for a general-purpose concrete. Higher ratios of cement to water increase the strength and durability of the final product. Lower ratios may produce a concrete that sets up more quickly, but this may be desirable if you need the concrete to act as a binder instead of a structural element.
Fine aggregates are often sand or crushed stone with a diameter of less than 9.55mm. The most frequent aggregate size used in construction is 20 mm. In mass concrete, a greater size, 40 mm, is more typical. Larger aggregate sizes need less cement and water. This is called the "agglomeration effect". The larger the particle, the longer it can be carried by the flow of water to the bottom of the mold.
Cement is the common name for calcium carbonate, a major ingredient in rock that has been transformed under heat and pressure into a hard, brittle substance that we call concrete. Cement is made from limestone or clay and coal ash. When mixed with water, cement begins to harden almost immediately, giving it its solid character. However, it takes about three years for it to mature enough to withstand structural loads.
Concrete is a mixture of cement, gravel, and water. The type of cement you use affects the color and texture of the finished product. Concrete can be colored using various substances including powders and liquids. Concrete was originally made with the whole coarse aggregate (gravel) being mixed with the cement and water before the mixture was placed in the mold. Today, pre-mixed concrete is available in all colors, textures, and shapes.
Fine aggregates are often made of natural sand or broken stone, with the majority of particles passing through a 3/8-inch screen. Coarse aggregates are any particles greater than 0.19 inches in diameter, but often vary between 3/8 and 1.5 inches. As a result, aggregate selection is a critical step. If you use fine aggregate in your concrete, it should make up at least 30 percent of the total material budget. If you use coarse aggregate, that number drops to 20 percent.
The size of the aggregate affects the strength and other properties of the concrete. Concrete mixes usually include several different sizes of coarse and fine aggregates to achieve the desired consistency. The ratio of coarse to fine aggregate affects how much water is required for the mix to reach its full strength. For example, if you double the amount of coarse aggregate, you need only half as much time to pour the concrete.
Concrete that contains more coarse aggregate will not flow as easily. This can be an advantage when placing concrete in large projects where smooth surfaces are needed, such as roads or parking lots. Coarse aggregate also makes for stronger concrete. The air inclusions between the grains of coarse aggregate help prevent cracking from occurring inside the slab.
Coarse aggregate is available in two main types: natural and manufactured. Natural coarse aggregate comes from rocks such as gravel, cobbles, and boulders that are left over after quarrying for finer materials.
The typical diameter range used is between 9.5mm and 37.5mm. The most frequent aggregate size used in construction is 20mm. In mass concrete, a greater size, 40mm, is more frequent. Coarse aggregates are usually larger than 37.5mm.
The density of dry gravel is about 80% of that of water. The percentage will be lower if it contains any clay or silt. The higher the proportion of rock, the lower the density will be. For example, sand has a density of 2kg/m3 while granite has a density of 25kg/m3.
Concrete has a density of 1150kg/m3. This means that, for a given volume, you need much more coarse material than fine.
Bricks and blocks have a density of 900-1100kg/m3.
As far as fire resistance is concerned, the key factor is the thickness of the material. The thicker the wall, the better it will resist heat and flame. Thicker walls are also more resistant to mechanical damage from being hit by vehicles or objects dropped from above.
Thickness is also important in relation to insulation.
Sand, gravel, crushed stone, slag, or rock dust are examples of aggregates (or mineral aggregates). To construct pavements, properly chosen and graded aggregates are combined with the cementing medium asphalt. The primary load-bearing components of an asphalt-concrete pavement are aggregates. Other ingredients such as superplasticizers, antidegradants, and air-entraining agents are also added to improve the performance of the final product.
Asphalt is a mixture of bitumen, which is a heavy black viscous liquid that is derived from crude oil, and aggregate. The term "asphalt" comes from the Greek word for rosin, which is a sticky resin extracted from pine trees. In fact, old asphalt roads still contain some resins even though they are now made of petroleum products instead of rosin.
Bitumen is a thick, sticky substance found inside large bodies of water under extreme pressure. It is made up of long chains of molecules called paracrystals that overlap each other like shingles on a roof. These chains are made up of carbon atoms linked together by chemical bonds that can be broken and re-formed many times without losing its basic structure. Bitumen is very resistant to heat and cold, rain and snow, but it will melt if exposed to the sun for a long time.
The largest use of bitumen is probably in road construction.
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