Underground Construction - January 2022 - 38

CIGMAT Report
TABLE 7. Weight changes in coated concrete specimens during 15 percent NaCl wetting cycle
Percentage Weight Gain in Wetting Time (Days)
Coatings
Coating-1
Silane-1
Silane-1 and Coating-1
Silane-2
Silane-2 and Coating-1
Remarks
1
0.5 percent
0.2 percent
0.5 percent
0.1 percent
0.5 percent
Silane-2 had the lowest
weight change
4
1.8 percent
0.4 percent
1.6 percent
0.15 percent
1.2 percent
Coating-1 had the highest
weight change
10
2.0 percent
0.6 percent
2.0 percent
0.18 percent
1.4 percent
Silane-1 had the second
lowest weight change
21
2.0 percent
0.7 percent
2.1 percent
0.2 percent
1.5 percent
Weight changes were sensitive
to the type of coating
Remarks
Highest change in weight.
Second lowest change in weight.
Second highest change in weight.
Lowest change in weight.
Performed better than composite
coating Silane-1 and Coating-1.
Of all the coatings investigated, Silane-2
had the lowest weight change
Test results are also summarized in TABLE 7:
* Weight increase in 15 percent NaCl solution after 21days,
for specimens coated with Silane-1 was 0.7 percent, compared
to 0.2 percent for specimens coated with Silane-2.
* Similarly, weight increase for specimens coated with Silane-1/
Coating-1 combination was 2.1 percent, compared to 1.5 percent
for Silane-2/Coating-1 combination.
* Weight gain of specimens coated with Coating-1 was similar to
the Silane-1/Coating-1 combination, which reinforces the fact
that Coating-1 governed the solution uptake where it was used.
* However, the Silane-2/Coating-1 combination was more eff ective
in resisting the solution intake in all cases, compared to Silane-1/
Coating-1 combination.
FIGURE 11: Change in weight for concrete in 15 percent NaCl solution
coated with Silane-1 and Coating-1
Results of the drying phase are compared in FIGURES 2, 3, 4
and 5. Most of the weight changes were observed during the fi rst
six days, when the testing water and salt solutions evaporated.
Residual solution at the end of the drying phase reduced to zero for
the Silane-1/ Coating-1 combination, compared to 0.05 percent for
the Silane-2/Coating-1 combination, when immersed in water.
However, Silane-2 with Coating-1 proved to be a better
combination than Silane-1 with Coating-1, when immersed in
15 percent NaCl solution, as it drained out all the solution at the
end of the drying phase.
Corrosion of reinforced concrete is very much infl uenced by
the diff usion phase (long-term); hence, the immersion process
should govern the selection of the coating type to be used for
protecting structures.
FIGURE 12: Weight change in 15 percent NaCl solution coated with
Silane-2 and Coating-1
combination was 2.3 percent, compared to 1.21 percent for
Silane-2/Coating-1 combination.
* Maximum weight gain was observed for specimens coated with
Coating-1, compared with any other combination. Th is implies
that Coating-1 absorbed more water and governed the water
intake for cases where Coating-1 was the outer layer.
In the 1.5 percent NaCl solution, relationships between the
percent weight change and time for coated specimens are shown in
FIGURES 11 and 12 for Silane-1 and Silane-2, respectively. Th e same
weight changes were observed in the fi rst four days, as in the water
wetting phase.
38 JANUARY 2022 | UCONonline.com
Conclusions
Applicability of two commercially available silanes, combined
with a latex-based coating, in resisting absorption of water
and 15 percent NaCl solution was investigated. Th e following
conclusions are advanced:
1. A relatively quick test method (21 days of immersion
followed by 21 days of drying) was eff ective in identifying
the diff erences in performance.
2. Silane-2 alone preformed the best in water and in the 15 percent
NaCl solution, clearly identifying its use with reinforced concrete
piles and columns in the causeway bridge along the coast.
3. Based on analyses of the results, just the immersion test can
be used to evaluate the performance of coatings for concrete
under diff erent environments. *
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