STRUCTURAL on the importance of concrete repair
STRUCTURAL’s Chris Hill and Sibtain Kapadia explain why, given the Middle East’s unforgiving natural environment, it is vital that regional developers take steps to protect their assets
Salt, heat, and time: these factors dominate the Middle East’s natural environment. They are also the three main ingredients necessary for the deterioration of our most commonly used building material – concrete.
Although an extremely versatile material, concrete is far from perfect. In essence, it’s akin to a big, hard sponge, which has the potential to fail in a harsh environment like that of the UAE. Luckily, there are many ways to protect concrete structures, even after they have been constructed.
We should start by noting that concrete is a system of materials working together to the best of their individual abilities. Reinforcing steel, for example, carries tensile loads on an element, while the concrete itself absorbs compression forces. If a system is overloaded, the concrete will begin to crack because – although inherently strong in compression – it leaves much to be desired in terms of tension. An effective combination of materials is essential if a building is to remain stable in the longer term.
If left unchecked, damage to a system’s components can result in major issues connected to concrete decline and repair.
Firstly, reinforcing steel is present in all structural elements. Perhaps surprisingly, the salt, heat, and time – which we know cause concrete to deteriorate – actually cause most damage to steel. When steel corrodes and begins to fail, its corresponding concrete section fails with it because the components are unable to work in tandem. The majority of concrete deterioration that we see in the Middle East is typically the result of damaged steel.
Secondly, concrete will always crack; this is an inherent characteristic of the material. In fact, without some cracking, the tensile stresses in an element would not be passed on to its reinforcing component. As such, a designer’s primary objective when it comes to concrete is to minimise and control the areas in which the material can crack.
In turn, what we need to watch out for in buildings are the areas where concrete cracking is patterned, or extensive in length, width or depth. These are indications of ill repair or overloading and, when they occur, a specialist repair solution may well be necessary to protect a structure. Put simply, an expert needs to come in to handle the negative effects of salt, heat, and time.
Salt is a major contributor to concrete deterioration. Groundwater in the Middle East is often highly saline, and can lead to a variety of problems. On a visible level, salt stains in parking garages and other sub-grade structures can cause aesthetic damage. But more importantly, on a material level, these salts are ions with the potential to corrode reinforcing steel.
Corrosion is an irreversible chemical reaction that, if left unattended, actually accelerates over time. Many people will have witnessed this process in the form of buildings that look fine for years, but then quickly develop cracks, concrete delamination and, eventually, spall their concrete cover to expose severely degraded steel. This process is further catalysed by the Middle East’s high ambient temperatures and humidity, which represent ever-present threats that can propel concrete systems along the road to ruin.
While repairs can be conducted after concrete spall has occurred, it is advisable to take steps to control corrosion beforehand. Methods like impressed current cathodic protection (ICCP) can help to halt reinforcement corrosion, and extend a building’s life cycle by decades.
Developers, contractors, consultants, and occupants can also collaborate at an early stage by using an ICCP system to minimise the adverse effects of a structure’s continued use. The same benefits will not result from reactionary repairs, which may require the replacement of reinforcements, not to mention not to mention concrete and finishes. Ultimately, once a structure begins to fall apart, the level of impact on all parties tends to grow more burdensome as the years go by.
This leads us to the last of the region’s concrete-related concerns: time. Over time, the natural protection that concrete offers to its reinforcement breaks down. At present, there aren’t enough older structures – of 30 years and above – for this to be considered a widespread problem in the Middle East. However, this will not always be the case.
The time-related challenges facing our industry today are largely connected to the pace of construction; essentially, a lack of time. When put under excessive time pressure, the associated risks of misplacing reinforcements, improperly placing concrete during casting, missing revisions to drawings, and adjusting layouts during construction, all increase.
Each of these concerns comes with its own set of direct impacts, but all lead to the same result: a concrete system that is unable to fully support its intended loads. When this happens, measures must be taken to augment the building’s capacity so that it corresponds with final demand.
Such augmentation typically takes the form of concrete strengthening. There are many ways to strengthen a structure; concrete enlargements and carbon-fibre reinforced polymer (CFRP) systems are among the most common. Both systems require the original element and the new material to work together as a single composite section.
With regards to the former, pressurised form and pump concrete enlargements can help to ensure composite action. In terms of the latter, or other methods similar to CFRP, a well-defined and disciplined approach to quality assurance and quality control (QA/QC) can also ensure proper interaction between the old and the new.
Either way, a specialist contractor should be enlisted in order to help navigate the repair landscape. For existing buildings, which entail many more constraints than new-build projects, the repair and strengthening of concrete require lots of reverse engineering and project collaboration in order to increase the structure’s strength and lifespan.
If you’d like to learn how to ensure that your concrete assets are stronger and last longer, visit structuralme.com and register for STRUCTURAL’s upcoming Yas Island Engineering Seminar, which will take place on 23 February, 2017.