Why how and what makes concrete go hard?

Question

I know cement goes hard when mixed in the right quantities with sand, chipping and water but WHY?

Answer 1

Cement and concrete are different.

Cement is made by heating limestone with small quantities of other materials (such as clay) to 1450°C in a kiln. The resulting hard substance, called ‘clinker’, is then ground with a small amount of gypsum into a powder to make ‘Ordinary Portland Cement’, the most commonly used type of cement (often referred to as OPC).

Portland cement is a basic ingredient of concrete, mortar and most non-speciality grout. The most common use for Portland cement is in the production of concrete. Concrete is a composite material consisting of aggregate (gravel and sand),

Concrete solidifies and hardens after mixing with water and placement due to a chemical process known as hydration. The water reacts with the cement, which bonds the other components together, eventually creating a stone-like material.

The reactions are highly exothermic and care must be taken that the build-up in heat does not affect the integrity of the structure.

Answer 2

Instead of cutting and pasting from Wiki (without quoting my source), I will just give you the link and you can read the full article yourself.  It's good stuff.

Really, who would say "highly exothermic"?!?

Answer 3

wikipedia:

In the most general sense of the word, a cement is a binder, a substance which sets and hardens independently, and can bind other materials together. The name "cement" goes back to the Romans who used the term "opus caementicium" to describe masonry which resembled concrete and was made from crushed rock with burnt lime as binder. The volcanic ash and pulverized brick additives which were added to the burnt lime to obtain a hydraulic binder were later referred to as cementum, cimentum, cäment and cement. Cements used in construction are characterized as hydraulic or non-hydraulic.

The most important use of cement is the production of mortar and concrete - the bonding of natural or artificial aggregates to form a strong building material which is durable in the face of normal environmental effects.

Cement should not be confused with concrete as the term cement explicitly refers to the dry powder substance. Upon the addition of water and/or additives the mixture is no longer referred to as cement but concrete, regardless if aggregates have already been added or not.

Chemistry:

http://www.uvi.edu/Physics/SCI3xxWeb/Str...

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Answer 4

The quick hardening component of cement is Tricalcium Silicate, which when mixed with water forms two crystalline structures -calcium silicate hydrate and calcium hydroxide. There are other calcium silicates that also have similar reactions that provided additional long term hardness.

2 Ca3SiO5 + 7 H2O ---> 3 CaO.2SiO2.4H2O + 3 Ca(OH)2 + heat

Answer 5

The hardening of concrete is caused by a chemical reaction between the cement and the water. The sand and gravel added to the mix are to bulk up the mixture and make it less brittle by providing convoluted fracture paths.

Answer 6

Those answers are good, but yada yada yada.

What I want to do is make 2.5 ton limestone blocks.  I want to use calcium and water, and sunlight and some electrodes and the Thompson effect.  

Any ideas?

Answer 7

It is down to a chemical in  cement called V1 agra.