I was trying to find water/powder ratio (powder here means cement+slag) for normal consistency using Vicat's apparatus (about 6mm from bottom). But with increase in replacement by GGBS from 0% through 60% is leading to a almost proportional increase in water demand.
While I find some other papers claiming a decrease in water demand with increase in replacement due to much slower hydration of GGBS as compared to OPC. How do you suggest should I justify my observation?
(I don't have Particle Size Distributions as of now but both the cement and the GGBS are commercially available from the market)
The demand of water to achieve standard consistency depends on the specific surface area of the powder. If, with the replacement of cement by slag, you have an increase of water demand, it means your slag have greater specific surface area than cement (or, in other words, your slag is finer than your cement). Commercially available slags have different fineness, which can be higher or lower than that of a specific cement. In the cases where water demand decreased with the replacement ratio of cement by slag, coarser slag or finer cement most probably were used (so slag was coarser than cement). The rate of hydration doesn't play a role in consistency test because the test is performed significantly before the initial setting time.
By the way, in my tests, I have the similar experience - with the replacement ratio of cement by slag the flow of mortar decreases. Although the decrease is small, it is proportional to the replacement level.
i AM NOT SURE BUT IT MAY ALSO DEPEND ON THE CHEMICAL COMPOSITION OF GGBS. Probably gypsum has some role to play in water requirement.
i AM NOT SURE BUT IT MAY ALSO DEPEND ON THE CHEMICAL COMPOSITION OF GGBS. Probably gypsum has some role to play in water requirement.
I found the following relavant infofrom this link.
http://library.modot.mo.gov/RDT/reports/Ri99035/or06008.pdf
In general, the use of GGBFS will retard setting time. However, experiences have been mixed in regard to setting time. Duos and Eggers found that setting time was a function of the amount of cementitious material and mixing/curing temperatures. In general, setting time of richer mixes at 23˚ C [73˚ F] was not significantly affected by increasing amounts of slag. However, leaner mixes at 40˚F exhibited slower setting as slag content increased. Bush et al.
found little change in setting times with 25 and 50% GGBFS contents. Saika et al.25 found that although initial setting times were not impacted much by slag replacement, final setting times increased. Hogan and Meusal
found that both initial and final set times were not affected appreciably. ACI 2334
states that slag mixes tend to have longer initial setting times by one half to one hour.
i AM NOT SURE BUT IT MAY ALSO DEPEND ON THE CHEMICAL COMPOSITION OF GGBS. Probably gypsum has some role to play in water requirement.
I found the following relavant infofrom this link.
http://library.modot.mo.gov/RDT/reports/Ri99035/or06008.pdf
In general, the use of GGBFS will retard setting time. However, experiences have been mixed in regard to setting time. Duos and Eggers found that setting time was a function of the amount of cementitious material and mixing/curing temperatures. In general, setting time of richer mixes at 23˚ C [73˚ F] was not significantly affected by increasing amounts of slag. However, leaner mixes at 40˚F exhibited slower setting as slag content increased. Bush et al.
found little change in setting times with 25 and 50% GGBFS contents. Saika et al.25 found that although initial setting times were not impacted much by slag replacement, final setting times increased. Hogan and Meusal
found that both initial and final set times were not affected appreciably. ACI 2334
states that slag mixes tend to have longer initial setting times by one half to one hour.
i AM NOT SURE BUT IT MAY ALSO DEPEND ON THE CHEMICAL COMPOSITION OF GGBS. Probably gypsum has some role to play in water requirement.
I found the following relavant infofrom this link.
http://library.modot.mo.gov/RDT/reports/Ri99035/or06008.pdf
In general, the use of GGBFS will retard setting time. However, experiences have been mixed in regard to setting time. Duos and Eggers found that setting time was a function of the amount of cementitious material and mixing/curing temperatures. In general, setting time of richer mixes at 23˚ C [73˚ F] was not significantly affected by increasing amounts of slag. However, leaner mixes at 40˚F exhibited slower setting as slag content increased. Bush et al.
found little change in setting times with 25 and 50% GGBFS contents. Saika et al.25 found that although initial setting times were not impacted much by slag replacement, final setting times increased. Hogan and Meusal
found that both initial and final set times were not affected appreciably. ACI 2334
states that slag mixes tend to have longer initial setting times by one half to one hour.
Try to add small amount of water reducing admixture to obtain the same consistency with the same water content but at different % of GGBS.
Regards,
Valeria
- Badges
- Science topic