The Relationship of Ferroan Dolomite Aggregate to Rapid Concrete Deterioration, HR-266, 1987
Authors
Publication date
1 January 1987
Publisher
Abstract
Some of Iowa's 13,200 miles of portland cement concrete (pcc) pavement
have remained structurally sound for over 50 years while others have suffered
premature deterioration. Research has shown that the type of coarse aggregate
used in the pcc is the major cause of this premature deterioration.
Some coarse aggregates for concrete exhibit a nonuniform performance history.
They contribute to premature deterioration on heavily salted primary roadways
while providing long maintenance-free life on unsalted secondary pavements.
This inconsistency supports the premise that there are at least two mechanisms
that contribute to the deterioration. Previous research has shown
that one of these mechanisms is a bad pore system. The other is apparently a
chemical reaction.
The objective of this research is to develop simple rapid test methods
to predict the durability of carbonate aggregate in pcc pavement.
X-ray diffraction analyses of aggregate samples have been conducted on
various beds from numerous quarries producing diffraction plots for more than
200 samples of dolomitic or dolomite aggregates. The crystalline structures
of these dolomitic aggregates show maximum-intensity dolomite/ankerite peaks
ranging from a d-spacing of 2.884 angstroms for good aggregates to a d-spacing
of 2.914 angstroms for nondurable aggregates. If coarse aggregates
with known bad pore systems are removed from this summary, the d-spacing values
of the remaining aggregates correlate very well with expected service
life. This may indicate that the iron substitution for magnesium in the
dolomite crystal is associated with the instability of the ferroan dolomite
aggregates in pcc pavement