For people who don't know the difference between cement, mortar and concrete:
Cement is a substance used for producing mortar and concrete. It's never used on its own. It is a "binding agent". Note that the term "cement" is often not used correctly in everyday speech, with people talking about gluing bricks together with cement, when bricks are actually glued together with mortar.
Mortar is the glue between bricks. You can see it between the bricks in any brick wall. It is produced by mixing cement with sand. This results in a paste which hardens after being applied to a brick.
Concrete is a substance that can be put into any shape, and then hardens. The bricks in a brick wall can be made from it. (More examples?) It is produced by mixing cement with sand and gravel (which are larger rocks).
There is also reinforced concrete, which the Romans didn't have. While concrete by itself can in principle be moulded into any shape, this can sometimes fall apart after hardening. Reinforcement refers to putting the concrete around metal wiring, which allows for more versatile shapes while maintaining stability.
Reinforced concrete in part is designed to provide structural strength under tension forces. Concrete is stable in compression but has weak resistance to tension. Pretensioned reinforced concrete permits longer unsupported spans but even vertical concrete can benefit from reinforced bars, to prevent spalling. (I believe). Not all reinforcing steel has to be tensioned to be useful, that's a technique for long spans.
More like reinforcing bars, rather than reinforced bars. And technically the overwhelming majority of what is sold today are actually deformed reinforcing bars, since the intentional addition of ridges on the outside of the bar helps the concrete adhere as compared to smooth mild steel.
>There is also reinforced concrete, which the Romans didn't have. While concrete by itself can in principle be moulded into any shape, this can sometimes fall apart, even after hardening. Reinforcement refers to putting a concrete around metal wiring, providing more versatility.
Not a correction per se, but some further explanation.
The reason for reinforcement is because concrete is strong in compression and weak in tension - in fact for design purposes we disregard its tensile capacity entirely. What reinforcement does is handle the tensile stresses in a structural member. When a beam, column, or slab bends it often (based on the load placed and structural design) creates tension on one side and compression on the other, so we put the rebar in the structural member close to the tension side, or on both sides if there may be tension on both sides.
In slabs reinforcing may also be used in some capacity just to limit cracking in an otherwise non structural capacity. In certain kinds of designs it may also provide confinement to the concrete which can be important for structural analysis reasons that are too technical to get into here (plastic hinging especially in earthquake design, etc).
We have different kinds of reinforcement, depending on the need of the project, but for the most part we use steel because its reasonably durable, has similar temperature expansion properties to concrete (imagine if your concrete got cold and shrunk more than things embedded in it, or grew so much the things embedded in it weren't attached anymore), its behaviour is well understood, and it is reasonably priced.
The design of steel reinforcing in concrete is also done in a way that reduces the likelihood of sudden failures, so that if something does happen, it happens slowly and with plenty of warning.
There are alternative reinforcing materials that may be appropriate in some very specific situations, but civil engineering moves very slowly and adoption is slow because risk is high. Fiber Reinforced Polymer (FRP) and Glass Reinforced Plastic (GRP) are examples of these. They may have much higher tensile stress capacity per unit of area, and also are less susceptible to corrosion, but they cost a lot, their failure modes are sudden, greater deflections under load, and each may have other tradeoffs like worse compressive behaviour, or worse fire resistance, etc.
There's a small trend towards stainless steel rebar. It's expensive, but is now used for concrete structures near salt water.
Epoxy coated rebar turned out to be a mistake. One scrape in the epoxy and it starts rusting. Exposure to UV prior to installation can damage the epoxy coating. Currently banned in Quebec.[1]
epoxy coated rebar has not been banned in quebec, rather the transportation agency has decided not to allow it in their projects. You are free to use it if you'd like on your own projects. Other provinces still allow it in bridge decks, and you will find the requirements for the materials and material handling/repair in their standard specifications.
Though most concrete is reinforced with steel rebar, it can be reinforced with all sorts of other materials to strengthen it under different conditions & loads: glass rods, plastic meshes, fibres, carbon nanotubes, etc.
Portand is the cheap stuff- like the $6 Quikrete bag at Home Depot. CSA is more expensive, but also available at Home Depot- look for the "Rapid Set" brand (Rapid Set Cement All is like $28 a bag).
It's kind of awesome, it's so fast you can sculpt vertically with it. You use more water with it than Portland, it starts out more mud-like. It tends to be preferred for repairs.
There are many types of even just portland cement, or portland cement with additives. Early strength development, sulfate resistance, air entrainment (trapping little bubbles of air in the concrete so that it cracks less in freeze thaw cycles), different heats of hydration, etc.
Well, technically, you can use cement instead of mortar (wet, but without sand). As far as I understand, sand is more like a neutral filler, to save money on cement. Various other things can be used to fill as well, like gravel. Sometimes even empty plastic bottles (reduces material and weight) are suitable (just make sure they don't float up). If one got very smooth bricks (e.g. precisely cut aerated concrete), then it might make sense, as there's very tiny amount of mortar (or even glue) is needed anyway.
If the sand is properly coarse, it can add strength. However, finding coarse sand is increasingly difficult, resulting in misuse of smooth sand (from error or being defrauded).
Tangent: coarse sand is also important for certain types of septic systems to function properly.
But yeah, you can make concrete blocks and build stuff with those. They are usually larger than clay bricks. In my country, the stuff used for building is mostly concrete bricks filled with small air bubbles air so that it is lighter and also insulates better.
Cement is a substance used for producing mortar and concrete. It's never used on its own. It is a "binding agent". Note that the term "cement" is often not used correctly in everyday speech, with people talking about gluing bricks together with cement, when bricks are actually glued together with mortar.
Mortar is the glue between bricks. You can see it between the bricks in any brick wall. It is produced by mixing cement with sand. This results in a paste which hardens after being applied to a brick.
Concrete is a substance that can be put into any shape, and then hardens. The bricks in a brick wall can be made from it. (More examples?) It is produced by mixing cement with sand and gravel (which are larger rocks).
There is also reinforced concrete, which the Romans didn't have. While concrete by itself can in principle be moulded into any shape, this can sometimes fall apart after hardening. Reinforcement refers to putting the concrete around metal wiring, which allows for more versatile shapes while maintaining stability.
Feel free to provide corrections.