Sulfate attack monitored by microCT and EDXRD: Influence of
cement type, water-to-cement ratio, and aggregate
N.N. Naik
a
, A.C. Jupe
a
, S.R. Stock
b
, A.P. Wilkinson
c
, P.L. Lee
d
, K.E. Kurtis
a,
*
a
School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
b
Institute for Bioengineering and Nanoscience in Advanced Medicine, Northwestern University, Chicago, Illinois, United States
c
School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia, United States
d
Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois, United States
Received 28 May 2005; accepted 7 June 2005
Abstract
X-ray microtomography (microCT) and spatially resolved energy dispersive X-ray diffraction (EDXRD) were used in combination to
non-destructively monitor the physical and chemical manifestations of damage in Portland cement paste samples subjected to severe sodium
sulfate attack. Additional measurements of expansion and compressive strength were made on complementary mortar and cement paste
specimens. Specifically, the influences of cement type (ASTM Types I and V), water-to-cement ratio (0.485 and 0.435), and the presence of
aggregate on the rate and forms of damage were examined. As expected, Type V cement samples exhibited less cracking and expansion than
the Type I cement samples. EDXRD indicated an anticorrelation between ettringite and gypsum in the near-surface region for Type V
samples, which may be associated with crack formation. An unanticipated result for Type I cement pastes was that cracking was apparent at
earlier exposure times and progressed more rapidly for samples with w / c of 0.435, than for those with w / c of 0.485. Possible mechanisms
for this behavior are proposed. The presence of aggregate particles resulted in a more rapid rate of cracking, as compared to the corresponding
cement paste sample.
D 2005 Elsevier Ltd. All rights reserved.
Keywords: Concrete; Diffraction; Durability; Gypsum; Ettringite; Expansion; Tomography; X-ray
1. Introduction
The resistance of Portland cement concrete to external
sulfate attack is governed by many parameters related to
materials selection and mixture proportioning. These
include cement composition, water-to-cement ratio (w / c),
use and proportion of supplementary cementing materials,
characteristics of the aggregate (e.g., maximum size), and
the use of chemical admixtures, among others. w / c and
cement composition, in particular, are two key factors
affecting the sulfate resistance of concrete mixtures [1 –4].
Also, the addition of aggregate is well known to lead to
increased permeability in concrete as compared to cement
paste. As each of these three parameters can be controlled
during the design of the concrete mixture, the influence of
cement type, w / c, and the presence of aggregate are of
particular interest in understanding the progress of sulfate
attack.
However, considerable uncertainty remains in optimally
selecting and proportioning materials for sulfate resistance
in concrete [5–8]. For the most sensitive and critical of
applications – hazardous waste containment vessels con-
taining sulfate-rich materials or buried in sulfate-containing
soils – these deficiencies become safety issues. For more
typical applications, such as hydraulic structures or housing,
these deficiencies are economic and environmental sustain-
ability issues.
Thus, for both critical and typical applications where
sulfate exposure is expected, laboratory testing may be
warranted to characterize the sulfate resistance of potential
0008-8846/$ - see front matter D 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.cemconres.2005.06.004
* Corresponding author. 790 Atlantic Dr., Atlanta, GA 30332-0355,
United States. Tel.: +1 404 385 0825; fax: +1 404 894 0211.
E-mail address: kkurtis@ce.gatech.edu (K.E. Kurtis).
Cement and Concrete Research 36 (2006) 144 – 159