This could well be boring ... but I just can't stand it.... Water is the
agent that activates Portland cement...
What happens is this... the particles of portland will actually grow fur....
for lack of a better word.... think of it like the fuzzy wuzzy was a bear
soap we had as kids..... the more water the more hair.... to a point.... the
hair latches on to other hairs in the particle next to it and that is what
causes the Cementing of aggregates...( sand and gravel ) together...
If you have to much water and not enough parts of cement there won't be
enough of this bonding.... if you have to much cement and not enough water
the hair won't grow.... both will have a lack of strength. Super strong
slabs are made from LOTS of Portland Cement and JUST the right amount of
water.... As long as your still mixing the cement you can add more water
or cement to get the right consistency right up until you pour it.... and
Yep you can actually add portland right to the top if you have a bit to much
water.... after you set it.... but keep in mind your little fury particles
are way to far apart to have any real strength in the actual slab because of
extreame water content.
The time it takes for this hair to grow and then bond together is considered
set time..... and as long as you keep the hairs apart by movement you can
actually extend the set time by an hour or so.... ( notice the little drums
running while the truck drives to your house )
or your back aching while you run your mortar hoe back and forth mixing it
up... ( a proper hoe is like a garden hoe with two large holes in it....)
Cracking isn't from expansion but from Contraction... Cement shrinks as it
gets hard..... especially those pourly mixed slab's.... but any large
concrete slab is going to crack.... and the rebar is going to simply hold it
together when the crack occurs..... I don't trust Fiberglass to hold it
together so I am not a fan of Fiber reinforced concrete....
Tooth paste is a term I use for consistency alot.... but milk shake works as
well..... the actual term is Slump.... which means how high a given amount
of cement will stand when poured on a flat surface..... Hence the term 2"
slump or 6" slump.... the higher it stands the less water it has in it.....
As for finishing what your doing is bringing the cream to the top by
floating the area with a " Bull Float "....( soulds like Bull to me... oh
nevermind ) this cream is mostly portland and water and is much easier to
level the gravel... you can actually do the same thing by continuously using
your skreeting board in a verticle as well as horizonal motion....
Troweling is done once the water has evaporated to the point that the top
cream is just workable... but barely.... and adding a sprinkle of water from
a coke bottle often helps in getting that fine finish most of us would want.
Drying time..... The boards can be removed in about 8hrs.... no need to
wait as long as they don't press down vertictly on the slab anywhere... I'd
recommend waiting until the next day personally.... no need to wait any
longer..... the Curing of concrete is a NON liniar deal.... it gets about 85
percent of it's strength in those first 24 hrs..... the next 10% in the
following 6 day's.... then cures for a total of 56days.... after that there
is no perceptable change in it's strength over time. So basically you can
build on a green slab in 3-7 day's with no problems because it's mostly
there....
Okay now there was MORE then you ever wanted to know about concrete.....
Keith ( damn if you got this far without a delete button I'm proud of you...
.... )
/// unsubscribe/change address requests to majordomo@autox.team.net or try
/// http://www.team.net/mailman/listinfo
/// Archives at http://www.team.net/cgi-bin/wilma/shop-talk
|