Materials (Concrete)

Concrete and cement:

(the following informative notes on materials are all from 'Materials for Builders & Architects' by Arthur Lyons)

Cement: Cements are materials that act as adhesives. However, I will use this as the binding agent that is used to make mortar and concrete. Joseph Aspdin created the patent for OPC in 1824. This kind of cement was made from clay and limestone.

Lime: There are two types of limes – hydraulic and non-hydraulic. Hydro, I believe, has something, well, a lot, to do with water? Hence it is easy to assume that one type of lime reacts with water. Non-hydraulic limes would then react with CO2 from the air. Lime was used as a type of mortar by the Romans, who probably took the idea from the Greeks. However, lime-based mortar is not used as commonly today, because of OPC (Ordinary Portland cement).

Hydration of cements: For instance, OPC is hydraulic. It starts to harden (sets) due to various chemical reactions between the cement and water. (A minimum of 0.23 of water/cement ratio is required to hydrate all the cement.) Setting starts instantly when water is added to the cement. The actual hardening is a gradual process that takes days at a decreasing rate. This actually takes quite a long time. However, 28 days is an often-mentioned period after which the cement should have strengthened ‘enough’.

Concrete: Aggregates: Aggregates form most of concrete. The aggregates used can affect the crushing strength, size, shape, etc of the concrete. There are 3 types of aggregates: lightweight, dense or high-density. Having each type of aggregate should make stronger concrete than using a single type. When water is mixed with this dry composite, which enables it to be shaped (typically poured) and then solidified and hardened into rock-hard strength through a chemical process known as hydration. The water reacts with the cement, which bonds the other components together, eventually creating a robust stone-like material.

CaCO3 + H2O => Ca(OH)2 + CO2 => CaO +H2O => CaCO3 ? ? ( I have absolutely clue why this would make it harder etc.) Check this link:

Physical properties of concrete: Creep is the long-term deformation of concrete under load. This is directly dependant with Young’s Modulus of Elasticity (stress/strain). Additionally heat and moisture can affect the size of concrete, which might affect structures if not taken into account.

Reinforced Concrete: Concrete, like most masonry blocks, is very strong in compression but weaker in tension. Hence concrete can be reinforced with steel to make it strong in both compression and tension. Generally compression happens at the point where load is applied and tension on the opposite side of this point (in a beam). Concrete has relatively high compressive strength, but much lower tensile strength.