Water Resistant Concrete
Is it possible to protect Reclamation concrete structures from damages due to freeze-thaw action and undesirable chemical reactions from reservoir water intrusion?
What is the best research strategy to investigate ways to prevent water intrusion resulting in freeze-thaw damages and undesirable chemical reactions in concrete?
Need and Benefit
Many of Reclamation's facilities are made out of concrete and are situated in regions where temperature extremes annually reach below and above the freezing point of water. For older facilities, there is a need to protect the concrete from the physical weathering process of freeze-thaw.
Frequently, freeze-thaw damages are found at Reclamation facilities at or near the water surface. Since Reclamation facilities are water delivery structures, they are typically in continuous contact with water and prone to the damages from repeated water freeze-thaw cycles. Underwater inspections carried out by Reclamation scuba divers frequently confirmed this. Concrete surfaces well below or above the water surface are usually free from damages, but those at or near the water surface often have freeze-thaw damages. Good examples of this can be found at the powerplants at Green Mountain Dam (in Colorado) and Seminoe Dam (in Wyoming).
In addition to freeze-thaw damage, water-intrusion chemical reactions may also cause similar expansion stress on the concrete. For example, gypsum formation may occur within the concrete matrix. Carbonate is replaced by sulfate from the reservoir water, changing calcite crystals to anhydrite, which in the presence of water, changes to gypsum. Gypsum is a larger molecule trying to occupy the same amount of space left behind by the calcite crystal, resulting in enormous pressure buildup in the concrete.
Modern concrete uses a process of air entrainment, which is the intentional creation of tiny bubbles within the concrete. An air-entraining admixture agent, typically a surfactant, is mixed with the concrete to create these air bubbles. Most of the air bubbles then survive during the hardening of the concrete. The primary purpose of this process is to relieve the pressure exerted by water freezing and improve the durability of the hardened concrete. The air bubbles compress a little, so the air bubbles act to absorb stresses caused by water freezing. This process was first introduced in the 1930s, and most of Reclamation's newer structures are well protected from the freeze-thaw weathering process. However, older Reclamation structures were not created with air entrainment and require alternative forms of protection.
Coating, membranes, and sealants are sometimes used to waterproof concrete. There are many different types of coatings, membranes, and sealants. However, since they are applied to the surface of the concrete and not into the matrix of the concrete, they are still subjected to weathering action and may deteriorate over time. Cracking and water seepage past the barrier can still occur. Preliminary investigations in preparation of this scoping proposal indicate that chemical formulations that actually penetrate the concrete matrix and form crystallization reactions to become an inherent part of the concrete matrix offer the best strategy in protecting the concrete from water intrusion damages caused by freeze-thaw and undesirable chemical reactions.
In this scoping project, we will carry out literature reviews and market research to investigate commercially available and research products (i.e., lithium silicates) that have the ability to "waterproof" concrete within the matrix of the concrete itself. These products act as crystallization reactions within the cracks, capillaries, and pores to prevent further water intrusion and repeated freeze-thaw damage. In addition, electrokinetic transport may be used to first drive out retained water and undesirable crystals (i.e., gypsum) and then drive in desirable crystallizing products. Such a method of concrete protection would add more years to the durability of our older Reclamation concrete structures and save costs associated with repairs and maintenance.
Bureau of Reclamation Review
The following documents were reviewed by experts in fields relating to this project's study and findings. The results were determined to be achieved using valid means.
Completion Report - X0919 Water Resistant Concrete (final, PDF,
By Kevin Kelly
Report completed on May 30, 2014