Feasibility of using fly ash as binder in coarse and fine aggregates for bases (FHWA-OK-86-8) 2125
Abstract
Aggregate-fly ash mixes consisting of fine aggregate
bases (FAB), coarse aggregate bases (CAB) and Class C fly ash
additions of 15, 25 .and 35% were tested in compressive and
flexural strength for curing periods of up to six months.
X-ray diffraction (XRD) was employed to study the mineralogical
composition of the mixes and identify the fly ash hydration
products. Scanning electron microscopy (SEM) was used to
verify the XRD findings and study the microstructural developments
in the mixes.
The compressive strength of the mixes varied considerably
during the first week of curing but exhibited better uniformity
in later ages. The variation was attributed to the
massive formation of ettringite. Later, when ettringite was
transformed to monosulfoaluminate and the CAH, CASH and CSH
hydration phases form, the strength of the mixes gained
uniformity and magnitude. After a month's curing the mixes
presented little resistance to flexural failure but in 90 days
the flexural strength level was substantial. The mixes were
characterized as stiff but structurally flexible and ??
flexural design approach was devised. SEM observations
indicated packing and densification of the mix matrix with
time, as the hydration products form skeletal matrices in the
mixes, resulting in better strength. The study establishes
the dual role of the fly ash as a filler and a chemical agent
(binder).