Contd. from Part 1 …..
( https://civilconstructionresourcez.wordpress.com/2012/01/10/roads-with-flexible-pavement-part-1/ )
In Part-1 the basic structures of flexible road pavement, road formation etc. have been discussed. In this post some more important and practically relevant matters on flexible road pavement are discussed. Construction of these pavement involve the following important aspects:
* Preparation of sub-grade level as per drawings, specifications etc.
* Material testing and delivery to the construction point.
* Blending, screening of pavement materials to meet the prescribed quality requirements as and when necessary.
* Compaction method and procedure.
* Spreading and compacting of layers.
* Tolerances for various layers such as base and sub-base courses.
* Designing of bituminous mix for bituminous seal.
* Construction of bituminous seal as per requirements.
* Preparing a trial pavement section in order to be assured that the entire operation involving all the aspects or stages is good enough and the final product is upto the expectations.
Some important quality test requirements mainly as per BS, American standards as well as some specifications in Gulf are mentioned below.
Some important pre-construction tests on materials are: a) Atterberg limits b) California Bearing Ratio or CBR c) Particle size analysis d) Flakiness index e) Abrasion loss f) Sodium sulphate (NaS04) or Magnesium sulphate (MgS04) soundness g) Sand equivalent h) Friable particles etc.
Granular sub-base: These materials consist of well graded natural gravel and sand or crushed rock. These may be naturally available or may be produced by screening and blending. AASHTO grading classifies granular sub-base materials into 3 groups i.e., class A, class B and class C depending on percentage of sample s passing through AASHTO sieves.
Some other quality requirements for granular sub-base materials are: liquid limit (maximum 25), plasticity index (max. 6), loss by abrasion (max. 50%), CBR (min. 30%), sand equivalent (min. 25). It is also desirable that in grading analysis, the fraction passing through 75 micron sieve should not be more than two third of that passing through 425 micron sieve.
Aggregates base course: Materials for this course are also divided into 3 classes, i.e., class A, class B and class C depending on percentage of sample passing through AASHTO sieves. Some more important quality requirements for base course materials are: liquid limit (maximum 25), plasticity index (max. 6), loss by abrasion (max. 40%), CBR (min. 80%), sand equivalent (min. 30), Na or Mg soundness (max. 12% or 18% respectively), friable particles (max. 25%).
More salient quality requirements on pavement construction will be discussed in the next post (Part-3). The link is https://civilconstructionresourcez.wordpress.com/2012/01/13/roads-with-flexible-pavement-part-3/