Hello.

 

I recently did an experiment for a science fair in which I tested the effects of fly ash in concrete on the strength of the concrete. I tested 0%, 25%, and 50% amounts of fly ash in the concrete. All of the research I've collected says that fly ash increases the strength of concrete. However, my results displayed the opposite. My control group of just Portland cement and no fly ash was the strongest and the 50% concentration of fly ash was the weakest. Each test group underwent hydration for a time of 3 days. Any ideas of why this happened?

 

Thanks!

I'm not necessarily an expert, but a quick search turned up this:

 

The quality of fly ash is important--but it can vary. Poor-quality fly ash can have a negative effect on concrete. The principle advantage of fly ash is reduced permeability at a low cost, but fly ash of poor quality can actually increase permeability. Some fly ash, such as that produced in a power plant, is compatible with concrete. Other types of fly ash must be beneficiated, and some types cannot be improved sufficiently for use in concrete.

Link

 

It could be that the quality of fly-ash your'e using is increasing permeability of the concrete, which certainly wouldn't be good for the strength

I'm not necessarily an expert, but a quick search turned up this:

 

Link

 

It could be that the quality of fly-ash your'e using is increasing permeability of the concrete, which certainly wouldn't be good for the strength

 

Ah, thanks for the input and link. I was looking for info on varying qualities of fly ash and affect on strength. Thanks again.