CIGMAT Report: Update From This Unique, Industry-Specific Ongoing Research Program

By C. Vipulanadan, PhD, P.E., professor of Civil Engineering, director of CIGMAT and the Texas Hurricane Center for THC-IT | September 2010 Vol. 65 No. 9
1) Macro-cells 2) Macro-holes in the Macro-cell walls 3) Macro-cell walls. Fig. 1: Microstructure of a polyurethane grout.

When selecting the coating systems to solve concrete corrosion problems, their performance and installation must be implicit. Restoring concrete with coatings requires considering concrete surface conditions (strength and moisture content) and the porosity of the concrete. The minimum recommended surface strength of concrete for using coatings is in the range of 1.4 to 1.75 MPa (200-250 psi) [Soebbing, 1996]. A sufficient quantity of water at the concrete surface can react with the coating material and affect the setting and the adhesion of the coating systems. The surface moisture will depend on the porosity of the concrete and hydrostatic pressure due to the water table. Coatings can debond and blister if the hydrostatic pressure exceeds the tensile adhesion of the coating material. Concrete deterioration can range from slight etching or partial loss of surface cement binder to complete loss of cement binder. Complete binder loss yields exposed coarse aggregates and reinforcing steel, which will further accelerate corrosion, cracking and spalling of the concrete.

There is limited information in the literature on the performance of coated concrete wastewater facilities and the results are not conclusive on the durability of coated materials. Several coating materials were studied by Los Angeles County and the results show that only a low percentage of coatings performed well under their testing conditions [Render et al. 1994]. Consequently, it is essential to identify good coating materials for protecting the wastewater facilities against corrosion.

Since several factors in the field can affect the performance of coating, it is vital to identify the key factors through controlled experiments where critical variables are studied one at a time. A testing program has been developed for evaluating coating materials for concrete and clay brick rehabilitation.

The objective of the coating test protocol was to evaluate the performance of coating materials for various wastewater rehabilitation projects. Specific objectives are as follows: (a) to develop a full-scale testing facility to evaluate the application and performance of coatings on a concrete surface under hydrostatic pressure; (b) to evaluate the chemical resistance of the coated concrete and clay bricks with and without holidays; and (c) to determine the bonding strength of the coating material to concrete and clay bricks.

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