Service life is the period of time a structure is able to perform optimally without major unforeseen maintenance or repair. Concrete structures are designed with projection of their service life which is usually between 75 and 100 years.
Though concrete reinforced with high quality iron rod is regarded as durable, and long-lasting, the main challenge has always been how to design and construct new concrete structures that will perform during their design service life with minimum maintenance and repair. Another issue is how to maintain or extend the service life of existing concrete structures so they can continue to serve their intended purpose.
This is why it is important to constantly assess the safety and service life of existing structures to identify the rate of deterioration or potential repair as early as possible. Without proper maintenance, corrosion is inevitable. A detailed assessment will show if the structure meets requirements or not. This will help ascertain if its service life can be extended as replacing structures is very expensive.
Owners and designers should pay attention to service life expectation of the structure during the design phase. The contracts and specifications should have a definition of how the service life should be measured. The effect of various design options should also be assessed in order to make decisions to optimize service life performance. To achieve the optimum balance between service life, functional performance, initial cost and maintenance costs, all the players in the design, construction and maintenance process must be fully integrated.
Anticipating/Predicting Service Life
Research has shown that many infrastructures are kept in service longer and with larger loads or stress than expected at the design stage even when they are exposed to agents of deterioration such as chlorides, sulphate attack, sewage, freeze-thaw, abrasion, erosion, cavitation and others.
Apart from the design-related factors and others that can be avoided either before or during construction, some factors that determine the service life of a structure are environmental and are beyond the control of the owners and designers. Some of these factors are listed above.
There are some tools that assist designers to predict the service life of a structure when designing it. One of these is numerical modelling which is used to predict the corrosion period of iron rods, the primary mechanism of concrete deterioration.
It allows design options to be tested under various environmental conditions after which rational decisions can be made to improve durability at reasonable cost.
There is another mode that allows for the estimation of the time to first repair with a comparison of initial costs and maintenance costs.
Achieving Service Life
It is possible to achieve 100-year service life of a structure requires an integrated approach. Modern design standards, which address the service life objectives, have been adopted into building codes and specifications. Various tools used to improve the durability of structures and reduce maintenance are now available.
Various quality control procedures to improve construction practices and durability of structures have also been developed by contractors.
Other Preventive Measures
Another measure to ensuring that concrete structures achieve their service life is the use of high quality corrosion-resistant iron rod which is available in various forms. This will reduce maintenance costs ensure that no major repair is needed for a very long time. The service life of concrete structures is largely determined by fatigue phenomena, which in turn depend on the traffic load to which the structure is subjected.
More so, there is need to establish the expectations of owners with respect to maintenance responsibilities at the design stage of the project.
The possibility of extending the service life of reinforced concrete structures is hinged on the understanding of the main causes of deterioration, their influence on service life, and taking proactive maintenance and repair steps during reinforced concrete service life when repair costs are relatively low. There should be active monitoring and maintenance programme so that the condition of reinforced concrete elements can be reviewed at regular intervals. Early detection of problems and prompt action can minimize repair costs.