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Capping Layer

13 replies [Last post]
Wed, 2007-07-11 01:58
Rick Aquino
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Hi All,

I’m a Mechanical Engineering graduate but struglling to do a road schedule project, would you mind telling me what is a capping layer (how it is done after sub grade or base course, what is emulsion in a road construction? is it being done after the sub-grade or the capping, and how about "tack coat" is it the same as asphalt coating?

Thanks..
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Tue, 2007-08-14 08:52
#1
ashraf alawady
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Thank you for these important infomation .
i have stated what we have in our specification and standards.
i will try to investigate the subject more and i will come back if if successe to gather any additional infomation.
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Tue, 2007-08-14 02:12
#2
Clive Randall
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I am sorry I do not agree, the capping layer caps the substrate and is before the sub base see below


"A typical Road Pavement consists of several layers, consisting of different types of materials chosen for their particular properties, such as:-
Smooth ride, impervious to water, skid resistance, texture, load spreading ability/strength, drainage etc

===============wearing course============= 40mm. H.R.A./SURFACE COURSE (WEARING COURSE)
:::::::::::::::basecourse::::::::::::::::: 60mm. BINDER COURSE (BASECOURSE)
xxxxxxxxxxxxxxx roadbase xxxxxxxxxxxxxxxxx 100mm. BASE (ROADBASE)
ooooooooooooooo sub-base ooooooooooooooooo 150mm. TYPE 1-UNBOUND MIXTURE (GRANULAR SUB-BASE)
+++++++++++++ capping layer ++++++++++++++ 100mm. CAPPING of min 15%CBR
////////////// subgrade ////////////////// min 3% CBR

This gives a total road pavement thickness of 450mm., the thickness usually regarded as the minimum needed to be resistant to frost damage.


The link is here

http://www.highwaysmaintenance.com/design.htm

Hope this helps

Or this
http://www.worldhighways.com/pressreleases/article.cfm?recordID=35
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Tue, 2007-08-14 01:44
#3
ashraf alawady
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May be but we are following BS standareds and i believe that the capping layer terminology should not be varied and from the name of this layer as capping mean the top layer or the end layer and it should not be between the layers.
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Tue, 2007-08-14 01:31
#4
Clive Randall
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The capping layer terminology appears to be in variance between the UK definition and the Egyptian definition.

In the UK the capping layer is material placed between the subase and formation.
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Tue, 2007-08-14 00:43
#5
ashraf alawady
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Tack coat is:
emulsified asphalt diluted with an equal quantity of water (1:1).
it shall be applied to a previously laid asphalt layers ( base course or binder course).
the rate of application is 0.3 liters to o.6 liters per square meter.
the application tempreture for the tack coat shall be between 10 deg. c and 60 deg. c
after application the surface shall be allowed to be dried (fo 2 hours approx.).

Capping layer is :-
aggregate sub-base materials mixed with 4% cement and the thick of this layer can be 150 0r 200 mm .
it should be laid on the vere after the completion of all asphalt layers on the carriage way and shoulders in order to protect the verge and to act as stabilizing layer .
so the predessor for this activity is completion of asphalt weaing couse and comletion of the verge construction.
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Tue, 2007-08-07 05:44
#6
Clive Randall
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Joshaf
Have you got a problem???

If a company is tendering or constructing a road it would appear appropiate to plan it with an engineer who has relevant experience!

That is why the question on why a mech eng was planning a roads project was asked.

Respect for what we do is related to how well we do it. If we dont understand what we are doing we cannot do it well

init
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Tue, 2007-08-07 05:35
#7
Bill Joshaf
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May be they have only mech eng in their Company.

Can u do planning for ShutDown Plant being Civil Planner (if you are really ) I donot think so........
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Tue, 2007-08-07 05:35
#8
Bill Joshaf
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May be they have only mech eng in their Company.

Can u do planning for ShutDown Plant being Civil Planner (if you are really ) I donot think so........
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Thu, 2007-08-02 02:04
#9
Clive Randall
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Tack coat is a bitumen spray applied prior to asphalt over the subase binding the ashpalt top the sub base

Why is your company asking a mech eng to do road planning????
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Wed, 2007-08-01 05:59
#10
Rick Aquino
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Hi Stuart,

Thank you so much for the answer,thank you, it is really a big help

Regards
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Tue, 2007-07-31 18:21
#11
Stuart Johnson
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Rick,
In basic terms, in road construction a capping layer is a depth of generally oversized hardcore required beneath the sub base when ground condition testing has determined the CBR is too low. The CBR is the California Bearing ratio and scales the compactibility of the existing ground.

A capping layer will be approx 200mm in depth and will be compacted in 50-100mmlayers using a twin drum seated roller.

The capping layer is the lowest level of the road construction. the sub base will be approx 150-200mm followed by binder course of 20mm dense bitumen macadam followed by 40-60mm of 10mm surface course.

I took this next bit froma manual extract, hope it helps:

"for subgrades the CBR less than 15%, the manual states that the maximum thickness of aggregate layer (capping or sub-base) shall be 150mm, and for a subgrade of CBR less than 3%, the first layer of aggregate placed (as capping or sub-base) shall be at least 200mm thick. Possible measures to be taken for cases where the subgrade is particularly soft (CBR less than 2%) are also given in the manual."

Well hopefully that helps,

Stuart Johnson
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Wed, 2007-07-11 02:43
#12
Rick Aquino
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Hi Mr. Chan,

Thank you for the advice, unfortunately, i have no resources at this moment, actually what i am doing right now is an advance scheduling, our skilled people will be coming by next month from different country, although it is already in my plan to ask them , i just took an opportunity to ask all of you guyz, maybe someone out there would give at least an exact answer to my question.

Cheers.
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Wed, 2007-07-11 02:24
#13
KongChung Chan
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You will be far better off to ask your subbies and foremen. They will be the people who will be actually doing that and whose knowledge you require to understand the process that you then model electronically.

By being nice to them, they may even go on to do the planning for you. After all, if you are planning for them, shouldn’t you know the details from them to do that planning?

Let them talk, and listen to them and encourage them. They will tell you and may sketch for you the schematics of the work that you can then pop into the computer that you can claim all for your own.
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