Cylinders from mixes with silica fume
Cylinders from mixes with silica fume
(OP)
I have read in the silica fume's mfg. data sheet that Silica fumes react with free lime to form calcium silicate hydrates, which is responsible for the strength of concrete. Could this be an explanation to why i'm getting higher compressive strength reults on cylinders cured in tanks (which contain lime) than cylinders cured in my moist room???





RE: Cylinders from mixes with silica fume
It is more likely that your tank conditions are better controlled than your moisture room. Just a couple of degrees cool in the curing process will cause a strength reduction...not much, but enough to vary the strength between the two methods of curing. Further, the tanks provide true 100% relative humidity, whereas the moisture room might vary a bit.
RE: Cylinders from mixes with silica fume
I feel the immersed samples would be more realistic of the real world since the concrete in place does have pressure or enhancement from the silica fume or the natural long term process of carbonation that can increase the strength.
Testing and curing processes are tightly controlled but can only go so far to predict the properties of the materials in the real world. This is a constant problem to balance a strict, repeatable process and yet be realistic. Concrete is relatively easy to test on a long term basis (except for durability) because the real results are better than lab tests. - This is always a concern when being involved in writing ASTM procedures and practices. Some procedures and practices are good for research and others for real world conditions.
RE: Cylinders from mixes with silica fume
RE: Cylinders from mixes with silica fume
the comparisson was cylinders to cylinders. I was suprised to see 1000 psi difference between 2 sets of cylinders taken from the same wheelbarrow.End treatment the same, size of sample the same and age @ test the same.The only difference was tank vs moist room.
RE: Cylinders from mixes with silica fume
If you had different curing, you must have had different handling and preparation of samples. - What was the age of the cylinders? The chemistry of cement hydration over time can get very complex, especially when less common materials are introduced.
Dick
RE: Cylinders from mixes with silica fume
RE: Cylinders from mixes with silica fume
Depending on your w/c ratio, it may be that the moist room is preventing loss of moisture from within the concrete where the tank is providing a constant source of external water to help hydrate particles that may otherwise run out of water for hydration.
RE: Cylinders from mixes with silica fume