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Bruce Strickland
National Marketing Manager
Sika Corporation
(800) 933–SIKA
Bruce has over 30 years experience in the admixture industry. In his career, he has held positions in product development, marketing, sales and sales management. Bruce has also spent time in...more»»
Type G admixtures
Posted by Frank from Abu Dhabi, OT, AE on March 25, 2007
Bruce,
We have a mix design using type G admixture to improve the slump/workability and retardation of settting time for marine piling works (ie barged concrete). Is it acceptable to redose on site with the same Type G admixture to increase not only the slump but the time allowed for placing even though the specifications require a maximum time of 1.5 hours?
A Type G admixture can be used for re-dosing in specific cases. The factors influencing would be the amount of admixture added while re-dosing, the slump of concrete before re-dosing and target slump. Re-dosing will cause retardation, the extent of retardation would depend on the ambient temperature. At higher temperatures re-dosing will have less influence on retardation.
I would advice you to contact the admixture company from whom you are buying the admixture, provide him the mix design details and ask their opinion about this matter.
If the purpose of re-dosing is just to increase the slump and you are not looking for a longer slump retention, the best option would be to re-dose using a Type F admixture.
Use of slag in road building
Posted by Sandra from Ann Arbor, MI, US on March 24, 2007
Many years ago, when my house was being built, slag was used by the builder on a particularly soggy area of the approach to the building site, to allow vehicular access. It was extremely effective. Our unpaved driveway is long (1/8 mi.) and we have a chronic problem with potholes. I would like to try using slag to fill these areas. What are your thoughts on the use of slag in road building and maintenance, and where can I buy slag in the vicinity of Ann Arbor, MI?
I don’t think I can give an accurate answer to this question with the information provided. It would appear that the builder used something other than the slag we use in concrete. My best guess is that he used something like crusher run from an aggregate supplier. Perhaps a call to someone in Michigan to find out their defination of “slag” would help.
Efflorescence on exterior & interior basement walls
Posted by Robert from Cottleville, MO, US on March 20, 2007
Hi, my name is Robert Sims
I have a villa that is 6 months old. Foundation poured in July or August 2006. We now have efflorrescence on both the exterior and interior walls. The builder brought in a Technical Service Engineer to take a look at it and give me a report on it.
He checked the compressive strength in numerous places with a Swiss Impact Hammer. The results were 4710psi. He gave the build instructions on cleaning it up and sealing the walls.
A couple of questions that weren’t answered are;
Can this cause damage to the rods or metal ties in the foundation that would cause weakening in years to come?
Can this cause corrosion in the concrete itself which would be a problem later.
My electrical box is attached to the wall in question, should this be removed and cleaned and sealed behind. Can this eat into the metal and wiring?
Can this re-occur?
Do you know of a company in my area to use for a second opinion?
Thank you for any assistance you can give me in this matter.
God Bless
Bob
If the wall is made of concrete blocks, then there shouldn’t be any issue of corrosion, but if they are made of reinforced concrete, efflorescence can cause corrosion.
Efflorescence occurs when free calcium hydroxide from the concrete is transported by water through the capillaries to the surface of the concrete. On the surface calcium hydroxide reacts with carbon dioxide in the air to form an insoluble material calcium carbonate (white deposit).
The migration of calcium hydroxide to the surface creates channels through which harmful materials like chlorides; contaminated water can enter the concrete and react with the steel to cause corrosion.
During corrosion the steel rusts and expands, which may lead the concrete to spall.
Efflorescence if present should be cleaned and the concrete surface should be sealed with a penetrating sealer (coating). There are products available for this in the market. Do a google search for “Stopping efflorescence” for more information.
Electrical Duct Banks
Posted by REN from SAN JOSE, CA, US on March 14, 2007
Who makes Fluidized thermal backfills ( low thermal resistivity) for electrical duct banks in the San Francisco Bay area?
I am sorry I do not know who supplies such materials in San Francisco. If there is any organization/associations which represents such materials you can contact them for local suppliers.
You can try to look for this information using a search engine like google. Search "Fluidized thermal backfill" or "Electrical duct banks + San Francisco" etc and you might be lucky.
Good luck.
Foam Concrete 1
Posted by Moti from Kuwait, OT, KW on March 13, 2007
Is there any minimum thickness requirement for Foam Concrete. If there is, how much is it? If the thickness of foam concrete is about 25 to 30 cm, please advise if any reinforcement is required.
Foam concrete can be used for many different applications. The specifications for foam concrete would be project specific and depend on the purpose for which it is used.
Also, you might have to contact a structural engineer if you want to know if any reinforcement is required or not for your foam concrete application.
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