Fly ash is used as a substitute for Portland cement in concrete as it has pozzolanic
Simply drying the ash does not restore its pozzolanic
As a general observation, all the foamed concrete mixes with an OPA content showed strength development through the ages hinting the existence of a pozzolanic
Wisener describes GeoKrete as a factory blended, fiber reinforced, cementitious-like repair mortar synthesized from pozzolanic
materials comprised mostly of recycled fly ash industrial byproducts, enhanced with a mono crystalline quartz aggregate.
Apparently in this case, the hydration type is mostly pozzolanic
, but after 28 days of curing the process is hindered due to the lack of silicates and aluminates.
In particular, using Class F FA, even if it does not readily exhibit self cementing characteristics, upon PC or lime addition, pozzolanic
reactions take place leading to the formation of calcium silicate hydrate gel (CSH) (Dermatas, Meng 2003).
Many scientists agree with idea that pozzolanic
materials (silica fume, fly ash, metakaolin, blast furnace slag) can improve structure of concrete and decrease permeability to moisture of cement matrix and interfacial transition zone.
However, the use of pozzolanic
materials lead to various disadvantages including: increased setting time; slow rate of strength development; prolonged period of curing; increased water demand; increased superplasticizer dosage; and placing problem (Ghrici et al.
Silica dioxide and ash that are similar to other pozzolanic
substances, can improve the strength of concrete through Ca[(OH).
Many studies have been carried out recently on producing a highly pozzolanic
material from calcination of paper sludge under controlled condition (10), (12).
activity of feedlot biomass (cattle manure) ash.
Obviously, gap-graded blending with a pozzolanic
admixture (rice husk ash served as reference) leads to fractionalization in the pore network.