Cement . A coworker says wet cement weighs the same as dried concrete I disagree whos right?

Answer 1

Your coworker is correct. Setting concrete is a chemical reaction which incorporates the water into its molecular structure. There is no evaporation of the water involved. The "drying" is the result of the chemical reaction that makes the water become part of the molecular structure.

Here is the reaction. Observe that the only product that is given off is heat: (there is an additional reaction for dicalcium silicate that is much the same)

Tricalcium silicate + Water--->Calcium silicate hydrate+Calcium hydroxide + heat

2 Ca3SiO5 + 7 H2O ---> 3 CaO.2SiO2.4H2O + 3 Ca(OH)2 + 173.6kJ

http://www.cement.org/basics/concretebasics_lessonfive.asp

The only loss of mass is the very insignificant amout of water that evaporates. On a humid day this is truly insignificant, and one trick of many concrete finishers to strengthen concrete is to keep it wet while it is setting- this actually strengthens the concrete because it keeps the water from evaporating. It is possible to pour concrete underwater. It sets up just fine.

Answer 2

Depends on how picky you are. Some of the water WILL evaporate, so there will be SOME weight loss; just not a lot.

Also, because your talking about weight and you didn't specify location, if the dry concrete was on the moon, and the wet cement was on the earth; then the dry concrete WOULD weigh less. If you had specified mass that would be a different story. (I know it's dumb, but it's a good way to screw with your coworker)

Answer 3

Only a fraction of the water in wet cement evaporates. Most of the water undergoes a chemical reaction, becoming part of the hard cement (it sets)

So a certain volume of cement becomes lighter as it sets. However, most cemets also shrink as they dry, also reducing the volume.

In a nutshell, the specific gravity of cement does not change much as it sets (and dries)

Answer 4

It must weigh more. Cement does not just dry. It actually chemically incororates water molecules into the calcium oxide chemical, and other constituents that make cement. (there is a hydration reaction). That is why cement it covered by a layer of , for example burlap, and is kept wet to encourage the reaction. The hydration stengthens the cement. By adding water the cement must gain mass and volume.
Dan.

Answer 5

moist cement will weigh extra. As water receives into the porous aspects of the dry cement block and could upload to the load. there'll be no strengthen contained in the quantity of the block.

Answer 6

Wet cement has a lot of water content, therefore it weighs more.
When it's allowed to dry and settle, quite a bit of the water has evaporated by then, lessening its weight.

You're right.

Answer 7

you are, as wet cement contains water which will have some degree of evaporation in the drying process thus reducing the original weight.

Answer 8

I would think that wet cement would weigh more than dry because it has less air...but I'm not at all sure.

Answer 9

Concrete always has excess water that bleeds off or evaporates. So the Weight will change.

Answer 10

You are right. The water evaporates, and is gone...so the difference is the weight of the water.