20 Dec Structural integrity essential to survival
Previously damaged buildings stand a much lower chance of retaining essential structural integrity in order to survive a fire event, reflects Jamie Hutchison, Marketing Executive, Belzona UK and as concrete is a globally popular construction material in the world, when a repair is needed reducing downtime and maintenance costs are top priorities.
Concrete is the most widely used construction material in the world, with a vast range of regular uses and under a compressive load, concrete is one of the best building materials around. However, this does not mean it is completely invulnerable to damage. Much like the deterioration of steel through rusting, moisture has many detrimental effects on concrete. Problems such as freeze-thaw or spalling/cracking are a result of contributing factors from moisture. Freeze-thaw occurs when moisture inside concrete freezes and expands, causing a big issue. The cyclic loading caused by the constant expansion and contraction can break the concrete down, eventually resulting in failure.
Damage can also occur from too little moisture during cure, which causes the concrete to dry out too quickly, leading to cracking, spalling and loss of structural integrity. Additional problems such as carbonation, chemical attack, and impact can all result in further damage to concrete.
When a repair is needed, reducing downtime and maintenance costs are top priorities. Yet, there can be situations where applications aren’t straight forward, such as overhead and vertical repairs. Using traditional or alternative concrete repair methods can mean more time and costs associated with a repair. Formwork or shuttering can be required to mould the material into shape and provide support during and after the application. Not only does this extend the maintenance period, but it also introduces further labour and material costs.
Epoxy-based, composite concrete repair solutions offer superior performance and application benefits compared to traditional and alternative concrete repair methods. Its lightweight properties allow repairs to take place without the need for installation of formwork/shuttering for overhead and vertical repairs. The mechanical properties are also superior with higher impact resistance and higher levels of adhesion. In addition, concrete can take up to 28 days to achieve full strength. During the cure period, controlled measures are needed in order for the concrete to achieve the required strength.
Strict moisture levels are required in order to prevent rapid evaporation of water during the curing process to reduce the risk of a weakened product and likelihood of future cracking. Ideally, composite concrete repairs achieve a full mechanical cure in as little as 12 hours. Once applied, these polymeric repair materials can be left to cure without the need of extra attention or strict environmental controls.
The most innovative of composite concrete repair systems introduces a further performance benefit in the form of fire resistance. Particular areas such as tunnels, metro/subway systems and high-rise buildings, are more susceptible to smoke and concentrated heat, which can dramatically increase the risk of environmental damage and threat to life. Additionally, subterranean structures can encounter further problems as a result of ground movements and subsidence.
Water penetration can also cause issues for concrete structures leading to corrosion of embedded steel reinforcement, and concrete breakdown and spalling. These added factors can result in severe damage before a fire even begins. In the event of a fire, due to the rapid heat build-up, entrapped moisture can expand leading to cracking, spalling and failure of the concrete which introduces additional safety concerns and risks. Already damaged buildings or structures stand a much lower chance of retaining the structural integrity they need in order to survive a fire event. For these reasons, maintaining the integrity of existing structures is essential and should be a priority.
A fire in a confined space, such as a tunnel or underground parking garage, can generate much higher temperatures than one in an open space, due to containment and reflection of the heat and can cause significant damage to concrete resulting in severe structural damage. The generation of smoke can significantly hamper rescue services attending the blaze. This has been reported in a number of fire in tunnels, car parks and commercial buildings.
With temperatures reaching over 1000°c, severe deterioration of the concrete can lead to a huge loss in structural integrity. This amount of heat does not only have an impact at the surface of a material but also affects underlying structures. Due to the high temperatures, heat transfer through a material means objects beneath the surface are also exposed to elevated temperatures and can thermally degrade. For example, the mechanical properties of embedded steel reinforcement will begin to deteriorate due to the extreme heat of a fire, resulting in loss of structural integrity.
In the event of a fire, it is essential to extend the period of time in which it takes for the fire to take hold and delay the onset of structural deterioration in order to allow for persons to safely evacuate. Buildings and structures that have been subject to fire damage need to be closed for a prolonged amount of time to allow for repair. In the worst of cases, buildings and structures may need to be completely demolished. This creates a wide number of economic and environmental consequences.
To eliminate such dangers, we have developed the Belzona 4141FR as a fire-resistant, lightweight repair composite for the rebuilding and protection of damaged vertical and overhead concrete surfaces. It has received a Euroclass Classification of B – s1 d0 which means that in the event of a fire, the material has a very limited heat release and flame spread, as well as producing little or no smoke. In addition, the classification denotes there are no flaming droplets or particles shed from the product during combustion.
During fire testing, the system was exposed to temperatures of up to 1900°c (3450°F) for periods of 30 minutes, with no significant damage or loss of material. This material does not contribute to the spread of flame. It was also tested alongside a standard polymeric concrete repair material to show the difference in flame spread and smoke production. Using a propane torch, both materials were exposed to a flame at a temperature of 1980°c (3600°F), for a continuous period of 60 seconds.
As shown above, the difference in fire resistance is pronounced. The results of the side-by-side test demonstrate that Belzona 4141FR produces minimal flame spread and smoke with no loss of material when compared to the alternative material which shows significant burning. Additionally, as a solvent-free material, it is ideal for both internal and external masonry, experiencing no shrinkage during cure.
Fire still remains to be one of the most serious potential risks to buildings and structures thus a safety-conscious, fire-resistant composite concrete repair system must form an essential part of the construction tool kit. With concrete being such a widely used construction material, continued research and development has led to significant efforts into creating a safe and easy to use system for the rebuilding and protection of damaged vertical and overhead concrete surfaces. Without the need for formwork/shuttering, downtime can now be significantly reduced, whilst also allowing for an easy and quick application, even with basic tools. From high-rise buildings and car parks to metro stations and tunnels, a long-lasting, cost-effective solution for any type of building and structure can be sourced.