Slag in the mix design
Slag in the mix design
(OP)
I have had a few mix designs come across my desk that are using GGBF slag, around 40% of the cementious material if I remember correct (at home right now). What are the consequences of substituting slag for Portland? I have access to the MCP 2002, and I can read that all day long and may never read what some of you who have used this or permitted its use will know. What are your opinions and experiences with slag in the mix?





RE: Slag in the mix design
Federal Highway Administration
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EPA
http://www.epa.gov/cpg/products/cement.htm
Environmental Council of Concrete Organizations
http://www.ecco.org/pdfs/EV18.pdf
www.SlideRuleEra.net
RE: Slag in the mix design
In the UK cement replacement products are often used, especially in water retaining structures. PFA and GGBS take longer to hydrate compared to OPC and thus the peak heat of hydration for concrete with some cement replacement material is lower then a pure OPC concrete. This can lead to substantial savings in rebar to limit early age thermal cracking.
One drawback is that as the blended cement takes longer to hydrate the rate of strength gain of the concrete can be slower which may increase formwork stripping times (this could have serious effects if the mix is used on large multistorey framed buildings), however with 40% GGBS replacement the rate of strength gain should not be affected that much.
This link is for a ggbs manufacturer and gives some guidance on the effects of using GGBS.
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I've got a few useful documents in pdf format that I could send to you. Whats the easiest way to do this? Do you know of any file sharing websites.
RE: Slag in the mix design
As patswfc it is often used (along with pfa) as a method of reducing the overall temperatures generated during hydration as it replaces the OPC in the mix. It also leads to a denser more durable concrete. From memory you can go to about 30% maximum cement replacement with PFA and up to about 60-70% replacement with GGBS. I'm not sure of the chemistry behind it though.
A word of warning, while it may be benficial from a design point of view I have been caught out by its use before. Some contractors dont like it as it can extend formwork stripping times. This can cost more in terms of schedule can often be greater than any material savings reinforcement, particularly if its a small job.
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RE: Slag in the mix design
RE: Slag in the mix design
RE: Slag in the mix design
One submittal item we generally request from the supplier is a strength gain curve. They are not always willing to supply that (mostly because they don't have them for some of their mix designs, and because that presents another potential liability for them if the mix doesn't follow the curve reasonably closely), but it doesn't hurt to push for it.
At one time, Rinker was the leader in your area for backup info. They would readily supply info for my requests. Since I haven't been involved day-to-day in your area in about 10 years, I'm not sure how much info is available from the suppliers.
If you're active in the Central Florida Chapter of ACI, you might bring that up as a topic for one of your meetings.
RE: Slag in the mix design
RE: Slag in the mix design
RE: Slag in the mix design
RE: Slag in the mix design
RE: Slag in the mix design
regards,
RE: Slag in the mix design
RE: Slag in the mix design
RE: Slag in the mix design
www.slagcement.org
RE: Slag in the mix design
And no one has mentioned the environmental benefits. Everytime I get the question of "why do we need this stuff in the mix" from the contractor or redi-mix supplier, I describe the durability and engineering benefits, plus I don't feel guilty adding in "because it's the right thing to do". Our industry ignores it (mostly) but cement is a big part of a big problem - and requiring GGBFS is one relatively painless way engineers can make a significant difference. Most contractors, architects, and owners will agree that it's the right choice once they know that 1. it doesn't really cost any more, 2. it makes a better final product (by the way, architects like the whiter color that results), and 3. it is an environmentally consciencious choice.