Now a days, structures are being built for design life of more than 100 years. Durability parameters are more stringent. Combination of OPC, GGBS, Fly Ash may give better results.
But many consultants do not allow above combination.
Dear Yatin,
As a researcher, I have been well-informed about the benefits of using supplementary cementitious materials (SCM) but as a consultant, I am still bound by conservatism at the workplace.
To answer your question, the role of alkali to activate fly ash (FA) and GGBS must be understood (For more info on this you can read a paper on my profile). Such a mixture of OPC, FA and GGBS is not recommended because the calcium hydroxide alkali produced by OPC is insufficient to activate large amounts of FA and GGBS. Therefore, unactivated FA and GGBS do not serve its intended purpose as a binder.
Hope this answers your question,
Th major issue with using ternary binders such as fly ash + slag + cement is the need for having three silos at batching plants. It is expensive and not practical for the majority of concrete suppliers.
In the US ternary mixes are becoming more common. It is being used because the mixes are more dense and have lower permeability as measure by surface resistivity testing. The above comment on costs is legitimate, but not necessarily a barrier.
Directly & indirectly, I am a part of various projects where binder is quadra blend (OPC + FA + GGBS + Alccofine). As per design trials by clients, this combination gives best durability for concrete structures.
Moreover, there is composite cement in existence which is a combination of OPC clinker + fly ash + GGBS
Having had hands on exposure; I don't see any technical reasons for not using fly ash & GGBS in same mix.
Resistance from design engineers seems to be out of fear of not achieving strength in required time frame as fly ash & GGBS are thought to be slow strength developers. But with the help of new age additives like Alccofine, this limitation also has been addressed successfully.
Thanks Samuel, Mr Mohammadi, Mack, Jafer for your contribution.
Does this mean incorporating additives in OPC + FA + GGBS mixture is key to succeeding in their utilization.
Concrete produced with fly ash has best resistance against high temperature when compared with GGBS and Rice husk.
- Badges
- Science topic