Maintenance of Concrete Structures for Durability of RCC Members
Modern concrete is a very durable construction material and, if properly proportioned and placed, will give very long service under normal conditions.
Many concrete structures, however, were constructed using early concrete technology, and they have already provided well over 50 years of service under harsh conditions. Such concrete must be inspected regularly to ensure that it is receiving the maintenance necessary to retain serviceability.
Managers and foremen of operation and maintenance crews must understand that, with respect to concrete, there is no such thing as economical deferred maintenance. Failure to promptly provide the proper necessary maintenance will simply result in very expensive repairs or replacement of otherwise useful structures.
Figures 1 and 2 demonstrate the folly of inadequate or inappropriate maintenance.
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
These two structures now require replacement at a cost tens of times greater than that of the preventive maintenance that could have extended their serviceability indefinitely.
Experience has shown that there are certain portions of exposed concrete structures more vulnerable than others to deterioration from weathering in freezing climates. These are exposed surfaces of the top 2 feet of walls, piers, posts, handrails, and parapets; all of curbs, sills, ledges, copings, cornices, and corners; and surfaces in contact with spray or water at frequently changing levels during freezing weather.
The durability of these surfaces can be considerably improved and serviceability greatly prolonged by preventive maintenance such as weatherproofing treatment with concrete sealing compounds.
Selecting the most satisfactory protective treatment depends to a considerable extent upon correctly assessing the exposure environment. Concrete sealing compounds and coatings that provide good protection from weathering in an essentially dry environment may perform poorly in the presence of an abundance of water such as on some bridge curbs and railings, stilling basin walls, and piers.
Freezing and thawing tests of concrete specimens protected by a variety of concrete sealing compounds and coatings, including linseed oil, fluorosilicates, epoxy and latex paints, chlorinated rubber, and water-proofing and penetrating sealers indicate that proprietary epoxy formulations, siloxane and silane formulations, and the high molecular weight methacrylate formulations clearly excel in resisting deterioration caused by repeated freezing and thawing in the presence of water.
None of these formulations, however, will totally “waterproof” concrete. That is, they will not prevent treated concrete from absorbing water and becoming saturated under conditions of complete and long-term submergence.
Except for hand-placed mortar restorations of deteriorated concrete, concrete sealing compounds are ordinarily not applied on new concrete construction. The treatments are most commonly used on older surfaces when the earliest visible evidence of weathering appears.
That is, the treatment is best used before deterioration advances to a stage where it cannot be arrested. Such early evidence consists primarily of fine surface cracking, close and parallel to edges and corners.
The need for protection also may be indicated by pattern cracking, surface scaling or spalling, and shrinkage cracking. By treatment of these vulnerable surfaces in the early stages of deterioration, later repairs may be avoided or at least postponed for a long time.
Linseed oil-turpentine-paint preparations have been widely used in the past for concrete deterioration caused by weathering. These preparations, when applied correctly, have been effective. The terminology “linseed oil treatment,” however, has caused many users to believe that a simple coating of boiled linseed oil would protect concrete from weathering. Such is not the case.
The treatment recommended consisted of a number of steps including 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, the first of which was thinned with linseed oil and turpentine.
The modern concrete sealing compounds are much simpler to apply and provide superior protection to the concrete. The use of the linseed oil-turpentine-oil paint system is no longer recommended.