Thermal spalling of concrete is a common phenomenon that occurs due to high temperatures. Concrete is a durable and strong material, but it can be damaged when exposed to high temperatures. Thermal spalling is the process of concrete cracking and breaking apart due to the expansion of moisture within the concrete when it is heated. This phenomenon can lead to structural failure and can be a significant safety hazard.
There are several factors that can contribute to thermal spalling of concrete, including the type of cement used, the aggregate composition, the water-cement ratio, and the temperature gradient. When concrete is heated, the moisture trapped inside begins to expand, and the concrete may crack and spall. This phenomenon is more likely to occur in concrete with a high water-cement ratio or a low cement content, as these concretes have a higher porosity and allow for more moisture to be trapped inside.
Thermal spalling can also occur when there is a large temperature gradient across the concrete. For example, if one side of the concrete is exposed to high temperatures while the other side is still at a lower temperature, the differential expansion can cause the concrete to crack and spall.
To prevent thermal spalling in concrete, several measures can be taken during the design and construction phases. One of the most effective methods is to use a low water-cement ratio and high-quality cement to reduce the amount of moisture that can be trapped inside the concrete. The use of air-entrained concrete can also help to reduce the amount of water that can freeze and expand during temperature changes.
Another approach to preventing thermal spalling is to use thermal insulation to reduce the temperature gradient across the concrete. This can be achieved by incorporating insulation materials into the concrete, or by placing insulation materials over the concrete surface.
In this article, Thermal Spalling of Concrete Explanation is given. This is the in-depth article for Thermal Spalling of Concrete.
Spalling is considered as one of the most complex and poorly understood phenomenon occurred at high temperatures. (Khoury 2000; Tenchev and Purnell 2005) Mostly it is assumed that this phenomenon occurs at high temperature but it can be observed at early ages of fire (Canisius et al. 2003) and at a temperature of around 200 °C.
If the spalling is severe, it might have destructive consequences on the strength of reinforced concrete structures. Spalling can expose the steel reinforcement to the fire by reducing or even eliminating the layer of concrete cover over it, resulting in the strength of reinforcement is reduced and overall deterioration of whole structures takes place.
Spalling also reduces the physical strength of reinforced structures by reducing the cross-section of the member. Reduced cross-section results in increased stress on the other parts of the member due to imposed loading.
Spalling of fire-damaged bridge pier reduces cross-section and exposes the reinforcement
Spalling is an important phenomenon, as it takes place at comparatively small temperatures; even any other deleterious effects of heating takes place on the strength of concrete.(Fletcher et al. 2007) Spalling occur due to the involvement of high thermal stresses in the member/structure either due to rapid temperature change or buildup of high pressure resulting from moisture evaporation and concrete is unable to release these high thermal stresses.
It results in the development of the fracture and later on the removal of material from the surface in the form of hunks. So in general it can be concluded that moisture content of at least 2% and sudden change in temperature are prerequisite for spalling within the material.
(Schneider 1988) In the present age, the world is shifting towards the use of “high-strength” or “high performance” concrete with the advent of technology. Compressive strength of “high strength” or “high-performance” concrete is significantly higher than normal-strength concrete. Despite of higher compressive strength it is noticeably moisture absorbent and less porous. It is harder for water molecules to leave the concrete surface as it has generally less water content and hence the water-cement ratio. It is occasionally claimed that lower porosity of high-strength concrete makes it more prone to spalling as lesser porosity helps in achieving high pressure inside the member. (Hertz and Sørensen 2005) However, the research in the recent years shows contraction to this by performing tests that indicate “high-strength” or “high-performance” concrete possess higher spalling resistance, (Ali et al. 2004) which means that the improved tensile properties efficiently counter the growth in activities that encourage the affinity of spalling