Deterioration of Iowa Highway Concrete Pavements: A Petrographic Study.
Deterioration of Iowa Highway Concrete Pavements: A
Petrographic Study.
(7086 K)
Stutzman, P. E.
NISTIR 6399; 84 p. December 1999.
Available from:
National Technical Information Service
(NTIS), Technology Administration, U.S. Department of
Commerce, Springfield, VA 22161.
Telephone:
1-800-553-6847 or 703-605-6000;
Fax: 703-605-6900.
Website: http://www.ntis.gov
Order number: PB2000-100135
Keywords:
highways; concretes; deterioration; aggregates; air
voids; cracking (fracturing); ettringite; freeze thaw;
microstructure; petrography
Abstract:
Major highway concrete pavements in Iowa have exhibited
premature deterioration attributed to effects of
ettringite formation, alkali-silica expansive reactions,
and to frost attack, or some combination of them. These
pavements were constructed in the mid-1980s as
non-reinforced, dual-lane, roads ranging in thickness
between 200 mm and 300 mm, with skewed joints reinforced
with dowels. Deterioration was initially recognized with
a darkening of joint regions, which occurred for some
pavements as soon as four years after construction.
Pavement condition ranges from severe damage to none,
and there appeared to be no unequivocal materials or
processing variables correlated with failure. Based upon
visual examinations, petrographic evaluation, and
application of materials models, the deterioration of
concrete highway pavements in Iowa appear related to a
freeze-thaw failure of the coarse aggregate and the
mortar. Crack patterns sub-parallel to the concrete
surface transecting the mortar fraction and the coarse
aggregate are indicative of freeze-thaw damage of both
the mortar and aggregate. The entrained air void system
was marginal to substandard, and filling of some of the
finer-sized voids by ettringite appears to have further
degraded the air void system. The formation of secondary
ettringite within the entrained air voids probably
reflects a relatively high degree of concrete saturation
causing the smaller voids to be filled with pore
solution when the concrete freezes. Alkali-silica
reaction (ASR) affects some quartz and shale in the tine
aggregate, but is not considered to be a significant
cause of the deterioration. Delayed ettringite formation
was not deemed likely as no evidence of a uniform paste
expansion was observed. The lack of field-observed
expansion is also evidence against the ASR and DEF modes
of deterioration. The utilization of fly ash does not
appear to have affected the deterioration as all
pavements with or without fly ash exhibiting substantial
damage also exhibit significant filling of the entrained
air void system, and specimens containing fly ash from
sound pavements do not have significant filling. The
influence of the mixture design, mixing, and placing
must be evaluated with respect to development of an
adequate entrained air void system, concrete
homogeneity, long-term drying shrinkage, and
microcracking. A high-sand mix may have contributed to
the difficult mixture characteristics noted upon
placement and exacerbate concrete heterogeneity
problems, difficulty in developing an adequate entrained
air void system, poor consolidation potential, and
increased drying shrinkage and cracking. Finally, the
availability of moisture must also be considered, as the
secondary precipitation of ettringite in entrained air
voids indicates they were at least partially filled with
pore solution at times. Water availability at the base
of the slabs, in joints, and cracks may have provided a
means for absorbing water to a point of critical
saturation.
Building and Fire Research Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899