Fly Ash, Really Only Advantages? - The Issues and Discussion of Modern Concrete Science - page 117

Fig. 9.12 The actual influence of ash floating in high fly ash cement concrete

quality of concrete in the crucial loading parts will directly impair the safety and
lifetime of structures (Fig. 9.12 ).
Moreover, in the construction of roof, surface slurry will peel off from concrete
when excessive

fly ash is added, and this phenomenon is called “ dusting, ” which

will impair the water-proof property and lifetime of the roof.

9.3 Summary

1. It is revealed from above engineering cases that, in the construction of runway
of airport, it is unsuitable to add fly ash 20 % more than and not allowed to add

fly ash 30 % more than the amount of a concrete mix, or the quality of concrete
will seriously decrease, leading to uselessness of the structures. Most of tech-
nicians and engineers working in the construction

field believe that the amount

of adding fly ash into a concrete mix should not exceed 30 % [ 4 ] in constructing

highway, or quality problems of cracks and plate-broken will appear. The
conclusion accords with our results from constructing airport (thereby,

the

requirements for adding fly ash not more than 20 % into a concrete mix in

China s standards before 2005 are well-founded). Consequently, we draw a

conclusion that concrete with excessive addition of

'

fly ash is not suitable for
constructing such structures as road and highway that require abrasive resistance
and impermeability. Moreover, a case in England is frequently cited by Chinese
experts: In the extension construction of Garwick airport in England, the con-
crete prepared by adding

y ash
reached 46 %. Pictures taken after 4 years clearly showed that the runway could

fly ash or not was compared, and the amount of