what it is the reason for fly ash replacement limits?
what it is the reason for fly ash replacement limits?
(OP)
Looking at Table 4.2.2.9 of ACI 301 (or Table 4.2.3 of ACI 318), there are limits for fly ash, slag, silica fume, etc, for concrete subject to DEICING chemicals.
Does this mean for concrete NOT subject to DEICING (i.e. most indoor concrete), there are NO replacment limits for fly ash, etc.? And where can I read about the REASON for the limits and why?
Thanks guys!
Does this mean for concrete NOT subject to DEICING (i.e. most indoor concrete), there are NO replacment limits for fly ash, etc.? And where can I read about the REASON for the limits and why?
Thanks guys!






RE: what it is the reason for fly ash replacement limits?
RE: what it is the reason for fly ash replacement limits?
RE: what it is the reason for fly ash replacement limits?
1. Fly ash needs cement to react with it to form the desired chemical compounds. Replace too much cement with fly ash and concrete properties degrade. With the proper ratio, the concrete is "better" than with cement alone.
2. Concrete gets it's strength from the large aggregate. Within reason, the more large aggregate the stronger the concrete. However a full range of aggregate sizes is needed to fill the spaces between the large aggregate. Fly ash is both microscopic and spherical. These two properties are an ideal addition to the concrete mix. However, use too much, and the mix now has too much small aggregate.
Here is one of the best documents that I have seen concerning the advantages of fly ash in concrete:
http:
www.SlideRuleEra.net![[idea] idea](https://www.tipmaster.com/images/idea.gif)
www.VacuumTubeEra.net
RE: what it is the reason for fly ash replacement limits?
Mr. Simons advocates the mix be designed for the desired properties, without fly ash, and then fly ash is used as a Mineral Additive. His argument (which I am in general agreement with) is sufficient heat of hydration, setting time, early strength development and such issues must be obtained in many instances. Replacing cement with fly ash may produce an inadequate concrete.
Mr. Simons does use a fair bit of fly ash in most mixes. He states the NMDOT stipulates that a minimum of 20% be used, with no restrictions on the maximum amount!!!!
The NMDOT concrete mixes reportedly use the w/c to proportion the mixtures for the desired early properties and then use w/cm to develop the longer-term properties.
This seems logical to me.
RE: what it is the reason for fly ash replacement limits?
thanks for the tech data...very informative
RE: what it is the reason for fly ash replacement limits?
RE: what it is the reason for fly ash replacement limits?