Reinforced concrete structures are one of the most durable and robust structures around us where cement and concrete history can be traced to early civilizations. Cementitious compounds or substrates have been use as mortar for the Great Wall of China and other structures in early Chinese civilization. The Romans initiated the use of concrete for superstructures before the Chinese and specialized in marine concrete which can set underwater. The use of concrete among the Greeks are less prolific than the Romans. Modern day cement was invented in 1824 by Joseph Aspadin and this cement is known as Portland cement.

2. Although it is generally accepted that concrete is robust and durable, the main issue with the use of reinforced concrete for construction is the susceptibility of reinforcement bars in reinforced concrete to corrosion. When concrete lost its passivity in several ways and due to the ingression of detrimental elements, reinforcement bars will start to corrode. The reduction of surface area and pitting will result in reduction of overall tensile strength. Therefore, reinforced concrete structures will always have a thin layer called "cover" which will protect reinforcement bars and concrete infill.

3. Concrete structures are similar to other structures made of wood, steel and aluminum where degradation will take place after some time. Thus, in most design literatures, limits are set and typically categorized as serviceable limit and ultimate limit. When a structure about to lapse its serviceable limit; rehabilitation, rejuvenation and repair is/are required. For reinforced concrete structures, the guideline to conduct such remedial works are based on BS EN 1504 with 10 parts which highlight 11 principles and various methods. One have to understand that these 10 parts do not exclusively tied to the 11 principals but relevant to methods.

4. BS EN 1504 may have the list of remedies for concrete repairs and rehabilitations, however the outcome of selecting the right principals and methods rely heavily on prognosis and performed diagnoses. In certain instances, diagnoses and prognosis may not resolve to the use of solution(s) provided in BS EN 1504. Hence, a professional engineer or technologist has to recognize the actual scenario and may make normative referencing to other specifications.

It is certainly a rare case when issues are not detectable through procedures as prescribed in BS/MS EN 13791, BS EN 12390 and MS1242. Misleading and oversimplified methodologies and tools for diagnosis are often the root cause of incomplete prognosis. This can only be tackled through statistical analysis as I reckoned in my recommendations to JKR practice through multivariate statistical analysis (DOI: 10.1088/1757-899X/1229/1/012003). In this particular journal article, my case study indicates the actual culprit in diminished concrete strength which can only be detected through Scanning Electron Microscope (SEM) Petrography and X-ray diffractometers.

5. When prognosis directs the utilization of the right solution for the use of extending the structure lifespan, method should be determined based on the principal(s) and the application should comply with BS EN 1504.

Similar method could reappear in different principals and this can provide more than a single purpose when applied. Principals are divided into two categories; protection of concrete and protection of reinforcement bars. A method may provide protection for both in some instances. Principal 1 to Principal 6 protect the concrete and Principal 7 to Principal 11 protect the reinforcement bars.

(To be continued)