Tenli Waters and Professor W. Spencer Guthrie, Civil and Environmental Engineering
The purpose of this project was to evaluate the effectiveness of nano-lithium silicate sealers for protecting concrete parapet walls against chloride ingress along highways where deicing salts are applied as part of regular winter maintenance.
For this research, testing was performed on parapets of bridges F799, F800, and on a non-bridge barrier-wall along Mountain View Corridor. Bridge F799 was located at 8200 South and F800 was located at Dannon Way. Testing was performed on the west side of F799, east side of F800, and the west side of the traveled way for the non-bridge barrier wall.
For this research, there were four possible treatment combinations chosen and two surface treatment products were used. The treatments selected were chosen by the provider of the surface treatment products. The two surface treatment products were Transil Plus and silane, Hydrozo 100. No treatment was applied to the initial section, specified as site D in the study. The next section, which was to the right of the previous section and defined as site C, received a treatment of one coat of Transil Plus. One coat of silane and then a top coat of Transil Plus was applied at the next section, defined as site B in the study. For the non-bridge location in this study an additional treatment type was applied consisting of one coat of silane and one coat of Transil Plus on both sides of the barrier wall. The final treatment defined as site A, coating both sides of the barrier wall, was not performed at the parapets due to the potential of discoloration on the exterior face of the parapet. The Utah Department of Transportation wanted to maintain the aesthetics of the parapet locations of the study.
Schmidt hammer testing was performed at each combination of location and treatment type. Three rebound numbers were recorded for testing performed in 2013 and 2014. Site locations for 2014 were measured 12 inches to the right relative to the test location of the previous year. Schmidt hammer testing consisted of contacting the surface of the concrete with the hammer oriented perpendicular to the concrete surface. As force was applied the spring of the hammer was released and the hammer impacted the concrete surface. For each impact of the hammer a given rebound number was observed and recorded. Perpendicular orientation of the Schmidt hammer during testing was maintained for two reasons; first, to apply full impact of the hammer normal to the concrete surface and second, to account for the angle of the oriented hammer used to determine corresponding compressive strengths.
Chloride sampling was performed at each location for each surface treatment and treatment combination being investigated. Samples were collected in both 2013 and 2014. Samples were obtained in two lifts of 0.5-in. each, to respective depths of 0.5-in. and 1in. Drilling to these individual depths was accomplished using two different drill bit sizes, the larger size of 1.5-in.-diameter was used for the more surficial lift and the 1.0-in.-diameter bit was used for the deeper lift. Drilling in this manner reduced the risk of cross contamination caused by scraping of the shallower lift during drilling operations of the deeper lift. After drilling was completed at each depth the pulverized concrete powder was collected in bags and transported to the BYU Highway Materials Laboratory. There, each concrete powder sample was analyzed using laboratory titration in general accordance with AASHTO T-260-97 (Sampling and Testing for Chloride Ion in Concrete and Concrete Raw Materials). A target weight of 1.0 oz was chosen for the samples and then each sample was oven dried for 24 hours. The samples were then digested using nitric acid and hydrogen peroxide to release the acid-soluble chlorides. Each solution was then filtered, and the filtrate was titrated with silver nitrate. The measured chloride percentage was then multiplied by a concrete density of 150 pcf, which is a common value for concrete, and converted to units of lb Cl-/yd3 of concrete.
A fixed effects analysis of variance (ANOVA) with interactions was used in the investigation of the test results involving independent and dependent variables in the Schmidt and chloride concentration analyses. Distance from the lane line to the vertical wall tested was accounted for as a covariate. The Schmidt hammer and chloride concentration data were analyzed separately.
There was an observed difference in the Schmidt hammer numbers with respect to age. Schmidt hammer numbers were not found to be different in this analysis with respect to site. The increase in Schmidt hammer numbers is attributed to the expected increase in concrete strength with increased time. The results do not show an increase in strength related to a densification effect of surface treatments.
Treatment A, one coat of silane and a topcoat of Transil Plus applied to both sides of the vertical wall, had a lower chloride concentration than treatment D, no treatment. The significance of the effect of Treatment A on chloride concentration may have been influenced by the design of the study and the limited data involving treatment A. The data showed that treatment B, one coat of silane followed by a topcoat of Transil Plus, reduced the amount of chlorides more than the other treatments. Treatment C, one coat of Transil Plus, was observed to have lower chloride concentrations than treatment D, no treatment. However, the difference between treatment C and treatment D was not found to be statistically significant.