CIGMAT Report: Center Studies Concrete Coatings And Repair Methods For Corroded Steel Piles

By C. Vipulanadan, PhD, P.E., professor and director of Center for Innovative Grouting Materials and Technology (CIGMAT) and Texas Hurricane Center for Innovative Technology (THC-IT), Department of Civil and Environmental Engineering, University of Houston | October 2012, Vol. 67 No. 10

Performance of the silanes and coatings could be evaluated by monitoring the weight change of coated concrete specimens immersed in corrosive environment. This change in weight of coated concrete could be used as a measure for degree of deterioration of the concrete, and hence, the prediction of the weight change is very important for predicting the service life of coated concrete. Mathematical modeling of the weight change phenomenon can help in determining the coating parameters, which could be used in evaluating the effectiveness of coating materials. To evaluate the quality of concrete in resisting water intake a diffusion model for concrete cylinders without coating was developed by Mebarkia and Vipulanandan (1995). A thin film model has been developed by Vipulanandan and Liu (2002a) to evaluate the performance of coating during the immersion phase. These models were used in this study to investigate the performance of treated concrete with coatings and silanes.

Research objective

The overall objective of this study was to investigate the effectiveness of combining sealers with coating to protect the concrete from chloride and moisture intrusion. Two silanes, (Silane-1 and Silane-2) with a latex coating (Coating-1) were used. The specific objectives were as follows:
1. Evaluate the treatment with silane, with and without latex coating, in controlling the water and 15% sodium chloride solution diffusion/infiltration (Immersion Test for 21 days) and exfiltration/breathing (Drying Test for 21 days) in concrete .
2. Model the wetting process using the finite element method.

Materials used

Cylindrical concrete specimens (3-inch diameter x 6-inch height) were obtained from an on-site concrete batch plant used for constructing a bridge across a causeway. The concrete used was classified as class F concrete by the Texas Department of Transportation. Concrete specimens (cylinders) had an average unit weight of (based on 20 specimens) 140 pcf (22 kN/m3) standard deviation of 0.9 pcf, (0.14 kN/m3) COV of 0.62%, and an average compressive pulse velocity of 4070 m/s. The average 28-day compressive strength of concrete was 36.5 MPa. The water and 15% salt solution absorption in 21 days into the concrete were 1.64% and 1.53% respectively (Table 1). There was notable difference in the weight change during the drying phase for concrete that was in water compared to the 15% salt solution (Table 1).

Table 1: Immersion and Drying Test Results for Uncoated Concrete

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