Element Losses from Cement Paste in Acidic Environment
Jeewoong Kim and C. Vipulanandan
Department of Civil and Environmental Engineering
University of Houston, Houston, TX 77204-4791
Phone: 713-743-4291; E-mail: jkim10@Bayou.uh.edu
Abstract
This study investigated the corrosion of cement paste in hydrochloric acid. Tests were
performed to estimate the leaching of elements such as calcium during the chemical attack
by hydrochloric acid (1% and 3%) on pure cement paste. Elements leached from cement paste
during immersion were measured using atomic absorption spectroscopy. Weight loss of the
specimen occurred and elements in the solution by leaching from the specimen increased
with immersion time. Visual observation showed the pattern cracks resulting from the
volume change of the specimen.
Introduction
Acidic environment caused by industrial wastes or chemical residues in the ground could
influence the durability of the Portland cement concrete. When the cement binder in the
concrete is exposed to an acid, the corrosion process starts. During the acid attack the
elements leached from the cement paste has not been quantified. It is important to take
into account the chemical and physical mechanisms that occur on the cement paste during
exposing to an aggressive environmental condition. The chemical analysis of the cement
paste resulting from the attack of the paste with hydrochloric acid help us to know the
chemical mechanisms of corrosion process in acid attack.
Objective
The objectives of this study are (1) to investigate the corrosion of cement paste in
hydrochloric acid by monitoring the weight change of the specimen and (2) to investigate
the elements leached from the cement paste during the acid attack.
Testing Program
A total of 30 cylindrical specimens of f 1.5 ´ 3.5 inches with W/C ratio of 0.4 cured in
moist environment for 28 days before testing. Ordinary Portland cement was used for all
the specimens. Specimens were fully immersed in de-ionized water, 1% and 3% hydrochloric
acid solutions in plastic jars. The solutions were replaced everyday with fresh ones and
the constant pH was maintained. This procedure provided an accelerated simulation of the
acid attack on cement pastes. Each specimen was removed from the jars, cleaned thoroughly,
inspected and weighed. Each solution was corrected and the atomic absorption test was
performed to measure the leached elements.
Results and Discussion
All specimens in the acid solution showed "pattern crack" type resulting from
the volume change in the specimen. During the leaching period notable weight loss occurred
in samples in 3% and 1% acid solution. Highest weight loss was measured in 3% solution
(Fig 1.). Using atomic absorption spectroscopy (AAS), ionic concentrations of calcium,
silica, and aluminum were determined (Fig 2. & 3.).
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Conclusion
The following conclusions can be advanced based on the test results of this study:
1. Due to acid attack, pattern cracking occurred on the surface of the cement paste within
12 hours of immersion.
2. Significant weight loss was observed during the test period.
3. The amount of element leached from the specimen due to acid attack was quantified.
Acknowledgment
This work was supported by the Center for Innovative Grouting Materials and Technology
under grants from the City of Houston, National Science Foundation (CMS-9526094) and
various industries.
References
J. H. Kong, J. G. Orbison, Concrete deterioration due to acid precipitation, ACI Materials
Journal, March-April 1987, pp. 110 - 116.
J. I. Alvarez, et al, Methodology and validation of a hot hydrochloric acid attack for the
characterization of ancient mortars, Cement and Concrete Research, vol. 29, 1999, pp. 1061
- 1065.