XRD patterns for mixtures without the GO admixture (in blue)
indicate the presence of calcite (C) as a predominant crystal
phase. We attribute this to paste decalcification by NaCl and
accompanying carbonation of concrete.23 In comparison, the
pastes of mixtures with the GO admixture showed a decrease
in calcite (C) peaks and an increase in portlandite (P) peaks,
indicating the beneficial role of GO in reducing carbonation
during salt weathering. The fly ash + GO concrete showed the
best performance in the salt exposure cycles, apparently
because GO facilitated the formation of margarite (M) and
clinotobermorite (CT) as well as semicrystalline C-S-H (I)
and C-A-S-H gels.23 The improved resistance to salt attack in
the fly ash mixtures also stems from the large amount of
network structures (Q3 and Q4 Si) in the geopolymer.22 This
contrasts to the chain structures (Q1 and Q2 Si) predominant in
Pervious concrete specimens were exposed to FT cycles or
cycles of wetting in a 3.0 wt% NaCl solution followed by
drying in air. The transverse resonance frequency was
employed as the indicator of changes induced by such
exposures. While the FT cycling caused rapid physical
damage to the specimens, the salt exposure caused a slow
A GO admixture at 0.02% by weight of binder dosage
significantly improved the resistance of the tested concrete
mixtures to FT damage. The FT resistance of GO-modified
fly ash pervious concrete cured for 28 days was comparable
to the FT resistance of cement pervious concrete cured for
14 days. The best FT resistance was demonstrated by the portland
cement mixture with the GO admixture (cured for 14 days).
The GO admixture also slightly improved the resistance of
the tested concrete mixtures to salt weathering. Fly ash
pervious concretes showed a better resistance to salt
weathering than their cement counterparts due to continued
hydration of fly ash-based binder and the different chemistry
of fly ash pastes.
The authors acknowledge the funding support by the U.S. Department
of Transportation (USDOT) Center for Environmentally Sustainable
Transportation in Cold Climates, American Coal Ash Association
Educational Foundation, and Washington State University (WSU)
Office of Commercialization. The authors thank Luis Gerardo Navarro,
Kafung Wong, Pizhong Qiao, and Zhidong Zhou at WSU for their help
with freezing-and-thawing tests. Boral, Lafarge, BASF, and W.R. Grace
kindly donated constituent materials for this study. Jing Zhong at Harbin
Institute of Technology helped with the fabrication of the graphene
oxide used in this work. The technology described herein is disclosed in
United States Patent Application 20180257989A1, Fly Ash Cementitious
Compositions, Sept 13, 2018.
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