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Showing posts from March, 2014

Construction Steps for Cement Concrete Pavement

Hi,
Concrete pavements are rigid pavements having very high flexure strength as compared to flexible pavements. Concrete pavements can be constructed using two different methods:

Alternate Bay methodContinuous bay methodIn alternate bay method, concrete pavement slab are laid on whole width of pavement in alternate bays.In continuous bay method, concrete pavement slabs are laid continuously only on one bay and another bay is open for the traffic.  Generally the second method of continuous bay, is preferred over alternate bay method because, traffic movement is allowed while it is restricted in the first. Also, the alternate empty spaces invites the rainwater collection and create in-convenience to the construction work.
Various steps for the construction of concrete pavements: Preparation of Sub-grade and Sub-basePlacing of formsBatching of material and MixingTransporting and Placing of ConcreteCompaction and FinishingFloating and Straight EdgingBelting, Brooming and EdgingCuring of Cem…

Road user Characteristics (Traffic Characteristics)

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Hi,
According to S.K.Khanna and S.E.G.Justo from book Highway Engineering, Traffic Engineering is the branch of engineering which deals with the improvement of the traffic performance of road networks and terminals. For achieving that we have to perform systematic traffic studies, analysis and then its engineering application.

First of the most important scientific study is the study of the traffic characteristics. Traffic can be classified into two classes: Road Users.Vehicular traffic. In this post I will discuss the road user characteristics that effect the traffic performance.
Road user characteristics Human beings performing different roles in the traffic are most important elements of the traffic and so we have to study their characteristics and behavior. Various roles of human are such as driver, pedestrians, cyclists etc. The physical, mental and emotional characteristics of human beings affect their ability to operate motor vehicle safely or to service as a pedestrian. Hence i…

Length of Summit Curves (Vertical curve)

Hi,
 Today, I am going to put here the details and engineering behind the length of the Summit Curves required for the vertical alignment of the highways.


Design criteria for the length of Summit Curves:      Summit curvesare the vertical curves having convexity upwards. These curves are introduced for the driving comfort and aesthetic purposes. In summit curves we do not need any transition curves because centrifugal acceleration is not acting laterally outward or inward but, its acting upward.  So, rate of introduction of providing the super-elevation is not the criteria. If we provide the circular curve without the transition curve and since centrifugal force is upward, driver will not face the sudden jerk.  The main criteria for the design of the length of the summit curves is the sight distance.
Length of the road is governed by the stopping sight distance and the overtaking sight distance.


On the basis of the Stopping sight distance(SSD): Suppose length of the transition curve is…

Grade Compensation at the Horizontal Curves on Highways

Hi,

Grade or Gradient is  the ratio of vertical rise or fall of the road center line with respect to its length. It has to be provided for the vertical alignment of the road. When we provide gradient to the road, vehicle has to apply more power to overcome the component of the gravity force. More the grade more effort it required.

At the horizontal curves the effective tractive effort of the vehicle is reduced because of the turning angle. Suppose 'T' is the tractive effort of the vehicle, and the turning angle of the front wheel is '@' then the tractive effort in that direction will be less.

There will be a loss of tractive effort equal to (T-T.cos.@). This loss in the tractive effort has to be compensated at the horizontal curves by reducing the grade.

According to IRC, a grade compensation  of,  (30+R/R), maximum 75/R  has to be provided for the grades more than 4%.
No grade compensation is required for the lower values of the the grade.
Here, R is the radius of th…

Steps for Construction of Earth roads

Hi, today I am going to share with you the steps which are necessary for the construction of the earth roads:

General : First of all what is an earth road? Earth road is a type of road whose whole pavement section is constructed with the locally available earth material preferably. Borrow pits are located at the nearby sites preferably outside the land width  where, the required earth is available.

Sub-grade and the surface of the earth roads are given larger camber of 1in 33 to 1 in 20 because they need faster drainage to be safe from the moisture. A maximum value of camber of 1 in 20 is the limit because higher camber will result in the formation of cross ruts and corrosion of pavement soils.

Specifications of Materials: The earth material used for the construction of earth roads are termed as satisfactory if they possess the following properties:
Base Course                         Wearing Course

Clay content                       <5%                                      10 to 18%S…

Highway Compaction Equipment

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Hi,
 There are various types of compaction equipment:

RollersRammerVibratorsRollers: Rollers are vastly used in the highway construction for compacting the sub-grade and other layers. They are again of three types:Smooth wheeled rollers:  These are used for compacting granular soils and specially useful where crushing is required. Smooth wheeled rollers generally vary from 4 to 22 tonnes in their weight. 2. Pneumatic Tyre rollers: These are used for compacting the silty and sandy soils and not preferred for clayey and granular soils. 3. Sheep's foot rollers: These rollers are having hollow cylindrical wheels having sheep's foot shaped projections on their surfaces. They are suitable for compacting the clayey soils, specifically where needing action is required and along with them smooth wheeled rollers may be used for giving a smooth surfacing to top surface.Rammers: Rammers are used where rollers are not suitable due to the area constraints. They are mechanically operated usi…

Highway Excavation Equipment

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Hi, how you doing? Today I am going to post here what I learnt about the highway construction equipment.

As we know that highway construction at field can be broadly classified into two phases:

 Excavation or preparation of sub-grade.Pavement layers construction. In the phase of the excavation or preparation of the sub-grade we need two types of equipment: Excavation equipmentCompaction equipment In this post I will discuss the excavation equipment. Types of excavation equipment that is to be used depends upon the type of the soil and availability of the equipment. Various equipment used in general for the excavation of the sub-grade are Bull DosserScraperPower ShovelDrag-lineClam-shellsHoeBulldozer  Bulldozer is a crawler equipment used to push and haul the earth material up a distance of 100 m using its front blade and a ripper attached at its rear.
 Bulldozer is a versatile equipment because it can be used in undulating ground or level ground, can be used for various building constru…

Design of Dowel bars - Rigid Pavements.

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Hi,
How you doing? Let's discuss the design of the dowel bars. So, what are dowel bars first?

Dowel bars  Dowel bars are steel bars, generally round in shape,  and are used in the expansion joints which, are provided in the concrete pavements(rigid pavements) to allow the expansion of the concrete slab.
The main function of the dowel bars is to transfer the wheel load from one slab to the adjacent slab through the shear and bending moment.

Dowel bars are embedded on both the slabs, and on one slab there is a dowel cap which provides space for the bar to occupy it when there is expansion in both slabs.
This empty space is filled with some easy to contract material so, that it may adjust its volume according the need of the dowel bar.

Design of Dowel bars:
In order to design the length and diameter of the dowel bar we have to check its failure under the action of wheel load on the pavement slab.
Failure may occur in three ways:

Failure of the dowel in shearFailure of dowel bar in flex…

Bitumen Penetration Test to Find out its Grading.

Hi,

We know that penetration test is one of the important tests, which is performed to test the grade of the Bitumen. You might be looking this article to jot down the theory and procedure of the test into your laboratory/practical notebook or might be checking just to refresh your knowledge. If you have one of these reasons, reading this article surely is going to help you in fulfilling the purpose. So, here we go:

AIM:  To find out the consistency/hardness of the Bitumen and thereby to find out its grade using the Bitumen penetration test.

APPARATUS: 
Standard Penetration test apparatus with all the accessories such as, needle, weight and timer.Heaterwater bath with temperature control, maintained at 25° ± 0.1 °C, containing not less than 10 litres of water.Accessories to the Standard penetration test are:
Container: flat bottomed cylindrical metallic dish having 55 mm diameter and 35 mm depth.Penetration Needle: A straight, highly polished cylindrical hard steel rod having a diameter …