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Archive for June, 2007
concrete surface flaking
Posted by Lee from Maysville, KY, US on June 22, 2007
I have a problem with surface of my concrete driveway flaking off.
Eight months after concrete was poured, the top eighth inch is flaking off, in a lot of different places. There are a lot of spots you can see that are loose and will flak off.
Can you tell me what could have caused this problem, Also I would like to know if a topping of some kind can be used, If so what kind of
topping would be best, And how to prepare surface before appling a topping. My contractor tells me he is going to fix it, But he dose not seem to know just what to do.
THANKS FOR ANY ADVICE YOU CAN GIVE
Dear Lee,
Some one had asked a very similar question few months back. Please scroll back 2 pages on the link were questions are answered on this website and you can read the reply to that question. (http://expert.concreteproducts.com/admixtures/page/3/)
Apart from that answer such problems also occur sometimes due to alkali- aggregate reactions, if the aggregate used is reactive or if the pavement is damaged due to freeze thaw.
thanks
sealers
Posted by Dick from Everson, WA, US on June 4, 2007
Can I apply a lithium based sealer to colored and acid stained concrete? I am currently constructing 16″ x16″ x3′ columns for a decorated fence and I want to protect it from all weather conditions
Thank you
Dick Dykstra
Lithium based sealers are generally applied to structures affected from alkali-silica reaction. So far, I have not heard them being used for any other kind of protection.
Try to use mineral admixtures like flyash , slag or silica fume in your concrete mixes and try to maintain a low water to cementitious ratio for your concrete with the help of a high range water reducer. Cure the concrete well after construction. This will certainly improve the durability of your columns. For additional protection you can use a silane based colorless water repellent sealer.
Redosing of concrete with High Range Water Reducers.
Posted by Ron from Sydney, OT, AU on June 4, 2007
Hi Bruce,
My name is Ron Maloney. I work for a government department in Australia (Roads and Traffic Authority).My branch delivers new roads and bridges to the state.
The question Is what do you think of redosing of high strength concrete ?.
The concrete has had the water reducer added at the plant and hauled for approx. 1 hour. The slump is reverting, and is to old to retamper. The contractor would like to redose to improve the slump. What do you think?
Re-dosing of admixtures in concrete mixes is fairly common for normal strength mixes, especially when the ambient temperature is high which cause high slump loss.
In your case for high strength mixes, I would say it would be safe to re-dose, if the concrete has not lost its workability completely. I think re-dosing a concrete having a slump of above 2” should not be a problem, but this is only a good guess I can make based on my experience.
If re-dosing is something you think you will anticipate regularly, I would recommend you to do a couple of lab trial mixes, in which you should re-dose the concrete mixes with admixtures when the slump has dropped to different levels and observe if they have any negative influence of re-dosing on strength, air and permeability.
At site, higher the slump before re-dosing, the better it is. Never re-dose if you feel the concrete has started to take initial set..
Also while re-dosing always try to re-dose using only a pure superplasticizer which contains no retarder. This is to avoid excessive retardation. Under no circumstances with high strength concrete would I re-dose more than once.
Goodluck
How many 60 lb bags needed to cover a space of 28″X28″X3″?
Posted by John from Lancaster, CA, UM on June 3, 2007
How many 60 lb bags of premix cement NEEDED to cover a space of
28″ X 28″ X 3″ . Am using a wheel barrel to mix it in however, don’t know when to stop mixing , that is, using the water of course?
Please help me….am new to this, hard breaking back work and sweatty type of work, but it has to be done.
Also pouring cement in between 2″ X 3″ (measure above).
Counted about 15 squares of 28X28X3 and I figure about 75 sacks of premix cement…Am I way off?
Thank you,
John
Generally companies selling premix cement bags mention the amount of mortar or concrete produced by a bag of premix cement for a given quantity of added water. So look for the coverage on the premix bag.
The volume of the space you are trying to cover is 28” x 28” x 3” = 1.36 cubic foot. If the manufacturer claims a 60 lbs bag produces 0.42 cubic foot of concrete for a given water content, you will need 3.29 lbs of premix cement per hole. So, for 15 such holes you will need roughly 48 number of 60 lbs bags. But again, this is for an assumed amount of water, if the amount of water you add change, your yield will be different.
Alternately you can bring 3 or 4 bags to fill one space to get an estimate of how many bags are need to cover the remaining hollow spaces.
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