Blast-furnace slag is generally used as a partial replacement material for Portland cement, usually on the basis of a direct weight-for-weight replacement and generally in the order of 30-50% by weight. For general use, a maximum blast-furnace slag content of about 40% is recommended. Up to this limit, the compressive strength of concrete at 28 days is comparable to that of ordinary Portland cement concrete with the same cement content. (paraphrased from Ryan, W.G. and Samarin, A., Australian Concrete Technology, Longman, Melbourne, 1992).
Are there any particular properties you're trying to obtain for your slab-on-ground by introducing blast-furnace slag to the mix?
Blast-furnace slag blended cement concrete tends to have better pumpability and can be used in mass concrete applications to reduce the peak temperature rise and tendency to crack due to heat development.
Suggest you discuss with your ready-mix or blast-furnace slag supplier. They are the real experts.
Thanks for the reply, I have spoken with the supplier. Using it in a slab-on-grade reduces the cement content, and delays the strength gain, two properties that are beneficial in an overall strategy for reducing shrinkage cracks. With grade 120 slag, you actually can get higher compressive and flexural strengths from the concrete, after the initial delay in strength gain. These are also properties that are beneficial for a heavily loaded slab-on-grade. It also produces a whiter concrete, which the architects like.
I designed slag-grinding plant for a client. I got an education on slag from them. It is a great material. The benefits are numerous when slag is used in concrete. They used 50:50 slag:cement mixes not only for the slabs, wall, footing and grade beams. They also used for the slip forming of the 50-foot diameter silos. They also used the mix for the pavement.
My clients web site (they are British company that has one plant in Florida) is
The main problem with slag in slabs on grade is that the lower strength gain meas you cannot access the poured area for a few more days. If you are working to a relaxed programme then great it should be good.
My experience is that contractors want to get back on the slab as soon as possible. Some years ago we were given the task of assessing data on an ultra-high strength concrete which would enable the slab to be trafficked within 24 hours. The heat generation was very high and needed to be controlled with lots and lots of reinforcement. It was used on commercial projects but I've no further information on the process as I moved jobs!
I have heard anecdotes that slag cement is more prone to plastic cracking but this probably is not a problem for a power floated slab??
Lufti's link is good. I'd say that Civil and Marine are probably the clear market leader here in the UK.
