Maintenance of Concrete Structures for Durability of RCC Members
Modern concrete is known for its durability and can provide long service life when properly proportioned and placed, especially under normal conditions. However, many older concrete structures were constructed using early concrete technology and have already been in service for over 50 years, often under harsh conditions. These structures require regular inspections to ensure that they are being properly maintained to retain their serviceability.
It is crucial for managers and foremen of operation and maintenance crews to understand that deferred maintenance for concrete structures is not cost-effective. Delaying or neglecting necessary maintenance can result in expensive repairs or even replacement of otherwise usable structures, as demonstrated in Figures 1 and 2. Therefore, it is essential to promptly provide the proper maintenance to ensure the longevity and performance of concrete structures.
Fig.1 : Lack of maintenance has resulted near loss of irrigation structure
Fig. 2: Deferred maintenance has allowed freezing and thawing deterioration to seriously damage the structure
There are certain portions of exposed concrete structures in freezing climates that are more vulnerable to weathering and deterioration. These include the top 2 feet of walls, piers, posts, handrails, parapets, curbs, sills, ledges, copings, cornices, corners, and surfaces in contact with water or spray during freezing weather. However, preventive maintenance, such as weatherproofing treatment with concrete sealing compounds, can considerably improve the durability and serviceability of these surfaces and prolong their lifespan.
Choosing the right protective treatment depends on accurately assessing the exposure environment. While some concrete sealing compounds and coatings may perform well in essentially dry environments, they may not be effective in the presence of water, as in the case of bridge curbs, railings, stilling basin walls, and piers. Results from freezing and thawing tests of concrete specimens protected by various sealing compounds and coatings, such as linseed oil, fluorosilicates, epoxy and latex paints, chlorinated rubber, and waterproofing and penetrating sealers, indicate that proprietary epoxy formulations, siloxane and silane formulations, and high molecular weight methacrylate formulations are particularly effective in resisting deterioration caused by repeated freezing and thawing in the presence of water. However, it’s important to note that no formulation can completely “waterproof” concrete, as they cannot prevent treated concrete from absorbing water and becoming saturated under conditions of complete and long-term submergence.
Concrete sealing compounds are typically not applied on new concrete construction, except for hand-placed mortar restorations of deteriorated concrete. These treatments are commonly used on older surfaces when visible evidence of weathering appears, preferably in the early stages of deterioration before it advances to a stage where it cannot be easily arrested. Early signs of weathering may include fine surface cracking close to edges and corners, pattern cracking, surface scaling or spalling, and shrinkage cracking. By treating these vulnerable surfaces early on, later repairs can be avoided or postponed for a longer period of time.
In the past, linseed oil-turpentine-paint preparations were widely used for concrete deterioration caused by weathering. However, the term “linseed oil treatment” has caused misconceptions that a simple coating of boiled linseed oil would protect concrete from weathering, which is not the case. The recommended treatment used to involve multiple steps, such as acid washing surface preparation, 48-hour drying, and application of two or more coats of a hot linseed oil-turpentine mixture followed by two or more coats of white lead paint, with the first coat thinned with linseed oil and turpentine. However, modern concrete sealing compounds are much simpler to apply and provide superior protection to the concrete, making the use of linseed oil-turpentine-oil paint system no longer recommended.