Thursday, May 15, 2014

Failures in Rigid Pavements


With the reference of the book titled as 'Highway Engineering,'  by S.K.Khanna and C.E.G.Justo, I created this post, which covers the failures in rigid pavements. If you have the book, please consult the book, because that would be a better option. Failures in cement concrete pavements are recognized mainly by the formation of the structural cracking.

Failures occur due to two factors:
(a) Deficiency of the pavement materials.
(b) Structural in-adequacy of the pavement system.

  • Deficiency of the Pavement Materials:
  1. Soft aggregates
  2. Poor workmanship in joint construction
  3. Poor joint filler or sealer material
  4. Poor surface finish
  5. Improper and insufficient curing.
Here are the various defects that creep in due to the causes above:

  1. Dis-integration of the cement concrete
  2. Formation of cracking
  3. Spalling of joints.
  4. Poor riding surface
  5. Slippery surface
  6. Formation of shrinkage cracks
  7. Ingress of surface water and further progressive failures.
  • Structural in-adequacy of Pavement System:
Inadequate sub-grade support, less pavement thickness would be major cause of developing the structural cracking in pavements. Following are the causes and types of failure which develop:

  1. Inadequate pavement thickness
  2. In-adequate sub-grade support and poor sub-grade soil
  3. Incorrect spacing of joints.
Above would give rise to the failures of the following types:

  1. Cracking of the slab corners
  2. Cracking of the pavement longitudinally
  3. Settlement of slabs
  4. Widening of joints
  5. Mud Pumping.
Now here are the typical pavement failures which occur in the rigid pavements and will be discussed here is details:

  1. Scaling of the cement concrete
  2. Shrinkage cracks
  3. Spalling of joints
  4. Warping cracks
  5. Mud Pumping
  6. Structural cracking

  • Scaling of Cement Concrete:

Whenever there is deficiencies in the concrete mix or presence of some chemical impurities may result into the scaling of the cement concrete. Also when excessive vibrations are given to the mix, cement mortar will come on top during the construction and thus with use the cement mortar gets abraded exposing the aggregates of the mix. This makes the pavement surface rough and shabby in appearance.
  • Shrinkage Cracks: During the curing operation of cement concrete pavement immediately after the construction, the shrinkage cracks normally develop. The placement of cracks are in longitudinal as well in transverse direction.
  • Spalling of Joints:
Sometimes when pre-formed filler materials are placed during the casting of pavement slabs, the placement is somehow dislocated and filler is thus placed at an angle. The concreting is completed without noticing this faulty alignment of the filler material. Thus this forms an overhang of a concrete layer on top side and the joint later on shows excessive cracking and subsidence.

  • Warping Cracks:
If the joints are not well designed to accommodate the warping of slabs at edges, this results in development of excessive stresses due to warping and the slab develops cracking at the edges in an irregular pattern. Hinge joints are generally provided for relieving the slabs of warping stresses. There is no structural defect due to warping cracks if proper reinforcement is provided at the longitudinal and transverse joints as it takes care of the structural in-adequacy.



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