Pavement 1 Flashcards
what contributes to pavement strength
thickness layer configurations in-situ cbr construction quality moisture material
What contributes to the granular layer
interlock ability,grading,crushing strength, particle shape
water content, cohesion
what is the worst case for aggregates?
No size distribution
angular > rounded
Why is compacting past the optimum bad?
compacting past the maximum point is bad because over compaction collapses the voids, causing water to enter.
Why does clay suck?
Particles absorb water, the absorbed water pushes the plates over each other, clay swells when wet and shrinks when dry
clay and water = shear failure
Why do we use bitumen/ asphalt?
works well on road, material behaves like Elastoplast
What is the worst case scenario for bitumen?
Slow moving, hot day
Describe some typical bituminous design
Stone mastic asphalt = singly graded, reliance on aggregate contact, not much bitumen content. Used for rutting but needs strong support
Continuous graded= crack resistant but prone to rutting
Stabilization : modify chemical properties
What are the two assumptions for structural analysis?
pavement and the sub grade are linear elastic, homogeneous and isotropic
Why is the subgrade important?
supports the loads imposed by the traffic, determines the structural capacity
What determines the subgrade strength?
insitu measurements at representative moiseture and loads
What are the critical locations?
vertical compression on top of sub grade and horizontal tensile strains at the bottom of the stabilized layer ( inc cemented
granular layer has none, strength specified by
what are ways to improve pavement strength?
improve the stiffness increase thickness change configuration try to avoid stabilized due to cracking is stabilized, ensure support
what are some typical ways water enters pavement?
1) seepage from higher ground
infiltration into the pavement via cracks or holes
infiltration into the shoulder and transfer
vapor movements and soil suction
movement of water from the lower soil layers
Evaporation
How does water affect pavment strength?
Fills up the voids, therefore reduces the contact between aggegates. This reduces the interlocking strength. Additionally, infiltration of water in the subgrade such as clay is bad because the subgrade will move up and down due to moisture shrinkage.
