20.5.1. Temperature

The effect of temperature on asphalt pavements is different from that of concrete pavements. Temperature affects the resilient modulus of asphalt layers, while it induces curling of concrete slabs.

This chunk discusses how temperature influences two key types of pavement materials: asphalt and concrete. For asphalt pavements, increased temperatures impact their resilient modulus, which is a measure of how much the material will deform under load. Higher temperatures can lead to a softer and more workable asphalt mix. Conversely, concrete slabs respond to temperature changes by curling—this is due to the temperature differences between the top and bottom surfaces of the slab. This differential thermal expansion can create stress within the concrete, leading to potential cracking over time.

Imagine a rubber band; when it's warm, it stretches more easily, reflecting the softer state of heated asphalt. In contrast, think of a pancake that's hotter on one side—if one side cools faster than the other, it could curl up, similar to how concrete might curl with temperature changes.

In rigid pavements, due to the difference in temperatures of top and bottom of slab, temperature stresses or frictional stresses are developed.

In rigid pavements, the temperature can cause stresses because the top and bottom surfaces of the concrete slab heat and cool at different rates. These differences lead to expansion and contraction, which in turn create internal stresses—known as temperature stresses. If these stresses exceed the material's tensile strength, it can result in cracks and other forms of distress in the pavement.

Consider a metal spoon left outside on a hot day. As one end heats up and expands while the other stays cooler, the spoon bends slightly. Rigid pavements behave similarly under temperature changes—if the conditions cause enough stress, they can crack, just like the bending spoon.

In flexible pavement, dynamic modulus of asphaltic concrete varies with temperature.

The dynamic modulus of asphaltic concrete is a measure of its stiffness and performance under traffic loads. This property changes with temperature—hotter temperatures typically lead to a lower dynamic modulus, meaning the material is softer and more susceptible to deformation under traffic loads. Conversely, cooler temperatures increase the dynamic modulus, making the material stiffer and more resistant to deformation. Proper understanding of this relationship is crucial for pavement design, as it influences how the pavement will perform over its lifespan.

Think of how a gummy bear behaves differently at room temperature compared to being chilled in the fridge. At room temperature, it’s soft and squishy (low stiffness), but in the fridge, it becomes firmer and holds its shape better. Asphalt behaves similarly; it becomes softer in heat and stiffer when cooled, affecting its performance under traffic.

Frost heave causes differential settlements and pavement roughness. The most detrimental effect of frost penetration occurs during the spring breakup period when the ice melts and subgrade is in a saturated condition.

Frost heave refers to the upward movement of soil caused by freezing and expansion of moisture in the soil. This movement can lead to uneven surfaces in pavements, termed differential settlement. In the spring, as ice melts and soil becomes saturated from melting ice and snow, the subgrade may weaken, leading to further instability in the pavement structure and increasing roughness and deformation across the pavement surface. This process emphasizes the importance of proper drainage to mitigate issues related to frost heave.

Consider how ice cubes might push the lid of a cooler as they expand. Likewise, when soil freezes and expands, it pushes up against the pavement, leading to bumps and uneven surfaces, much like how the cooler's lid might warp if enough ice is packed in underneath.

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