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

Drying Phase
The residual solution in the specimens at the end of the drying phase reduced to zero for the Silane-1 and Coating-1 combination as compared to 0.05% for the combination of Silane-2 with Coating-1 when immersed in water. However Silane-2 with Coating-1 proved to be a better combination over Silane-1 with Coating-1 when immersed in 15% NaCl solution as it drained out all the solution at the end of the drying phase. Corrosion of reinforced concrete is very much influenced by the diffusion phase (Cady et. al. 1984) and hence the immersion process should govern the selection of the coating type to be used for protecting structures.

cigmat2.png
Figure 2: Weight change kinetics in water followed by drying for concrete coated with Silane-1 and Coating-1

cigmat3.png
Figure 3: Weight change kinetics in water followed by drying for concrete coated with Silane-2 and Coating-1

cigmat4.png
Figure 4: Weight change kinetics in 15% NaCl solution followed by drying for concrete coated with Silane-1 and Coating-1

cigmat5.png
Figure 5: Weight change kinetics in 15% NaCl solution followed by drying for concrete coated with Silane-2 and Coating-1

Finite element modeling of the weight change
The effect of mass transfer coefficient of the coating material on the weight change of coated concrete cylinder was also studied by using the finite element method. A commercially available finite element program was used for the modeling. Due to the symmetry the concrete cylinder was modeled as a 2D axis symmetric model. The concrete diffusion coefficient (Dconc = 15x10-12 m2/sec) was obtained based on the test results (Vipulanandan et al. 2011). Three node linear triangular elements were used. The finite element mesh configuration with triangular elements used in this study is shown in Figure 6. Mesh sensitivity analysis was performed by varying the number of elements from 8,365 to 15,462. The prediction (weight change with time in Figure 7) converged with a minimum of 12,792 elements onwards. Hence a total number of 12,792 elements were used for detailed analyses. The model was solved to get the degree of saturation and normal diffusive flux at different instants with time. In Figure 7, the finite element model prediction of weight change is compared to the experimental results and the agreement was very good.

cigmat6.png
Figure 6: Finite element model used for modeling the weight gain of coated cement concrete cylinder

Buyer's Guide