A pozzolana is a natural or artificial material containing silica in a reactive form. By themselves, pozzolanas have little or no cementitious value. However, in a finely divided form and in the presence of moisture they will chemically react with alkalis to form cementing compounds.

Fly ash has little cementing property when only water is added, its reactivity could be activated by OH [2,3], in ordinary Portland concrete, the pozzolanic reaction is very slow due to the low OH content. The replacement of part of cement and lime with fly ash in cement–lime mortar will consume a mass of calcium hydroxide (lime), at the same time the pozzolanic reaction will be activated due to the high OH content in mortars. 

Use of Fly ash in Concrete & Its 11 impacts
Use of Fly ash in Concrete & Its 11 impacts


Fly ash as Pozzolanic Material

Pozzolanas must be finely divided in order to expose a large surface area to the alkali solutions for the reaction to proceed. 

Examples of pozzolanic materials are volcanic ash, pumice, opaline shales, burnt clay and fly ash. 
The silica in a pozzolana has to be amorphous, or glassy, to be reactive. 

Fly ash from a coal-fired power station is a pozzolana that results in low-permeability concrete, which is more durable and able to resist the entrance of deleterious chemicals. 

The first reference to the idea of utilizing coal fly ash in concrete was by McMillan and Powers in 1934 and in subsequent research 

When coal burns in a power station furnace between 1250°C and 1600°C, the incombustible materials combine to form spherical glassy droplets of silica (SiO2 ), alumina (Al 2O3 ), iron oxide (Fe2 O3 ) and other minor constituents.

Application of Fly ash in Construction

The positive effects while use of fly ash in concrete have resulted in numerous applications in construction industry due to sustainable and restorative approach towards deleterious effects. 

In the construction sector, the fly ash is used 
  1. in the production of cement as an additive-material, 
  2. in production of concrete instead of some of the cement or instead of some of the fine aggregate
  3. as a base and sub-base material in highway construction
  4. as a filling material in dams, in retaining walls, 
  5. for production of light construction materials 

(ACI Committee 1987; Erdogan 1997). 

Fly Ash and Pozzolanic Reaction 

When fly ash is added to concrete the pozzolanic reaction occurs between the silica glass (SiO2 ) and the calcium hydroxide (Ca(OH) 2) or lime, this is a by-product of the hydration of Portland cement. The hydration products produced fill the interstitial pores reducing the permeability of the matrix. 

Roy (1987) states ‘the reaction products are highly complex involving phase solubility, synergetic accelerating and retarding effects of multiphase, multi-particle materials and the surface effects at the solid liquid interface’. 

The reaction products formed differ from the products found in Portland cement-only concretes. A very much finer pore structure is produced with time presuming there is access to water to maintain the hydration process. Dhir et al. (1986) have also demonstrated that the addition of fly ash improves the dispersion of the Portland cement particles, improving their reactivity. 

Little pozzolanic reaction occurs during the first 24 hours at 20°C. Thus for a given cementitious content, with increasing fly ash content, lower early strengths are achieved. Taylor (1997) explains the hydration processes involved in some detail. 

The presence of fly ash retards the reaction of alite within the Portland cement at early ages. However, alite production is accelerated in the middle stages due to the provision of nucleation sites on the surface of the fly ash particles. 

The calcium hydroxide scratches the surface of the glassy particles reacting with the SiO2  or the Al2O3 –SiO  framework. 

The hydration products formed reflect the composition of the fly ash with a low Ca/Si ratio. 
Clearly the surface exposed for reaction is greater, the finer the fly ash; additionally, the higher the temperature, the greater the reaction rate. 

At later ages the contribution of fly ash to strength gain increases greatly, provided there is adequate moisture to continue the reaction process. 

Comparison of Ordinary Concrete & Fly ash Concrete Chemical Properties
Comparison of Ordinary Concrete & Fly ash Concrete Chemical Properties (source

Effects of Using Fly ash in Portland Cement Concrete

In a normal concrete Calcium Hydroxide produced during hydration reaction is not put into much use. Whereas if we use fly ash, the fly ash will convert the CH into CSH. We know that CSH gel is the one responsible for the strength of the concrete.

The use of fly ash in portland cement concrete (PCC) has many benefits and improves concrete performance in both the fresh and hardened state. Fly ash use in concrete improves the workability of plastic concrete, and the strength and durability of hardened concrete. Fly ash use is also cost effective. When fly ash is added to concrete, the amount of portland cement may be reduced.

All the effects of fly ash on properties of concrete are discussed in detail. 

Permeability of Fly ash Concrete
Permeability of Fly ash Concrete (Source: https://www.fhwa.dot.gov/pavement/recycling/fach03.cfm)
You might also like to read :- 

Reduced Heat of hydration 

Due to increased replacement of fly ash with the proportion of cement in concrete mix design. Fly ash is able to reduce the heat of hydration very effectively. 

The hydration of Portland cement compounds is exothermic. The introduction of fly ash to replace a proportion of cement in concrete influences temperature rise during the hydration period. 

The rate of pozzolanic reaction increases with increasing temperature, however the peak temperatures in fly ash concrete are significantly lower than equivalent PC concretes. 

Increased Setting Time & Form work Striking Time

Using fly ash in concrete will increase the setting time compared with an equivalent grade of PC concrete. There is a period before the hydration of fly ash concrete commences, but is has been shown by Woolley and Cabrera (1991) that the gain in strength, once hydration has started, is greater for fly ash concrete. 

When 30 per cent fly ash is used to replace PC in a mix, the setting time may be increased by up to 2 hours. 

This increased setting time reduces the rate of workability loss. However, it may result in finishing difficulties in periods of low temperature. 

In compensation, it will reduce the incidence of cold joints in the plastic concrete. 

Formwork striking times at lower ambient temperatures may have to be extended in comparison to PC concrete, especially with thin sections. 

However, in practice vertical formwork striking times can be extended without this affecting site routines, e.g. the formwork are struck the following day. For soffit formwork, greater care has to be taken. 

Better Elastic Modulus & Lower Creep

The elastic modulus of fly ash concrete is generally equal to or slightly better than that for an equivalent grade of concrete. 

The greater long-term strength for fly ash concretes gives lower creep values, particularly under conditions of no moisture loss. These conditions may be found in concrete remote from the cover zone of a structure. Where significant drying is permitted the strength gain may be negligible and creep of OPC and fly ash concretes would be similar. 

Lower Tensile strain capacity

Tensile strain capacity of fly ash concretes has been found to be marginally lower, and these concretes exhibit slightly more brittle characteristics (Browne, 1984). There is possibly a greater risk of early thermal cracking for given temperature drop, partially offsetting the benefits of lower heat of hydration in the fly ash concrete. 

Coefficient of thermal expansion

The type of coarse aggregate used largely influences the coefficient of thermal expansion of concrete. Replacement of a proportion of cement with fly ash will have little effect on this property (Gifford and Ward, 1982). 

Effect of Fly ash on Curing

Hydration reactions between cement and water provide the mechanism for the hardening of concrete. The degree of hydration dictates strength development and all aspects of durability. If concrete is allowed to dry out hydration will cease prematurely. Fly ash concrete has slower hydration rates and the lack of adequate curing will affect the final product. 

Thicker sections are less vulnerable than thin concrete sections because heat of hydration will promote the pozzolanic reaction. 

Resistant to Alkali–silica reaction Effects

Alkali–silica reaction (ASR) (Concrete Society Technical Report 30, 1999) is potentially a very disruptive reaction within concrete. ASR involves the higher pH alkalis such as sodium and potassium hydroxides reacting with silica, usually within the aggregates, producing gel. 

This gel has a high capacity for absorbing water from the pore solution causing expansion and disruption of the concrete. Some greywacke aggregates have been found particularly susceptible to ASR. The main source of the alkalis is usually the Portland cement or external sources. 

Fly ash does contain some sodium and potassium alkalis but these are mainly held in the glassy structure and not readily available. Typically, only some 16–20 per cent of the total sodium and potassium alkalis in fly ash are water-soluble. 

Many researchers have shown that fly ash is capable of preventing ASR. Oddly, the glass in fly ash is itself in a highly reactive fine form of silica. It has been found that the ratio of reactive alkalis to surface area of reactive silica is important in ASR. 

The recommendations (BSI 5328 amendment 10365, 1999) within the UK require a minimum of 25 per cent BS 3892 Part 1 fly ash to prevent ASR. For coarser fly ashes, a minimum of 30 per cent fly ash may be required to ensure sufficient surface area to prevent ASR. 

Small quantities of fine fly ash with low-reactivity aggregates and sufficient alkalis may be more susceptible to ASR if the pessimum silica–alkali ratio is approached. Even when total alkalis within the concrete are as high as 5 kg/m 3 , fly ash has been found (Alasali and Malhotra, 1991) able to prevent ASR. 

The addition of fly ash reduces the pH of the pore solution to below 13 at which point ASR cannot occur. The use of low-alkali cements has a similar effect. 

Effects of Fly ash on Carbonation of concrete

As fly ash pozzolanically reacts with lime, this potentially reduces the lime available to maintain the pH within the pore solution. However, fly ash does reduce the permeability of the concrete dramatically when the concrete is properly designed and cured. 

When designing concretes for equal 28-day strength the slow reaction rate of fly ash usually means that the total cementitious material is often increased. This increase partially compensates for the reduction in available lime. Coupling this with the lower permeability leads to the result that the carbonation of fly ash concrete is not significantly different from Portland cement-only concrete of the same grade (28 days) 

Resistant to Freeze–thaw damage

Fly ash concrete of the same strength has a similar resistance to freeze–thaw attack as Portland cement concrete. Dhir et al. (1987) reported on the freeze–thaw properties of concrete containing fly ash. 

They used nine fly ashes of various sieve residues. All mixes were designed to give equal 28-day strengths. Freeze–thaw was assessed using an 8-hour cycle of 4 hours at –20°C and 4 hours at +5°C. Ultrasonic pulse velocity (UPV) and changes in length were used for the assessment of freeze–thaw performance. 

They found, as have other researchers, that adding fly ash reduces freeze–thaw resistance unless air entrainment is used. However, Dhir found that only 1.0 per cent of air entrained in the concrete gave superior performance compared with plain concrete irrespective of the cement type. 

It is clear that the less permeable and denser the mortar matrix is within the concrete, the less space is available to relieve the pressures associated with the expansion of freezing water. 

Resistant to Sulfate attack

Fly ash concrete can increase the resistance to sulfate attack. Deterioration due to sulfate penetration results from the expansive pressures originated by the formation of secondary gypsum and ettringnite. 

The beneficial effects of fly ash have been attributed to a reduction of pore size slowing penetration of sulfate ions. Less calcium hydroxide is also available for the formation of gypsum. 

The smaller pore size of fly ash concrete reduces the volume of ettringnite that may be formed. One of the major constituents of cement that is prone to sulfate attack, tricalcium aluminate (C A), is diluted since a proportion of it will have reacted with the sulfates within the fly ash at an early age. 

WAPDA is currently looking for competent, dedicated, dynamic and self-motivated personnel for the following positionson contract basis extendable on account of satisfactory performance.

Junior Engineering (CIVIL) in department of GM (C&M) Water

  • Pay Scale: BPS (17) 
  • No. of Post: 62 
  • Qualification : B.Sc. (Civil Engineering) or equivalent from HEC recognized university 
  • Note: The discipline will be considered as per registration with PEC
  • Age limit (years): 33
62+ Job vacancies in WAPDA from all Pakistan Provinces March, 2018
62+ Job vacancies in WAPDA from all Pakistan Provinces March, 2018

How to apply for this Job?

Applicants can fill in the prescribed from Pakistan testing service website (http://pts.org.pk) .
Candidates shall submit application forms duly filled in along with test fee of Rs. 170/- in favor of Pakistan testing service, copy of CNIC and two recent passport size photographs directly to PTS through courier on the address mentioned on Application form on or before 3rd April, 2018.

We are here sharing you all the job openings and vacancies for civil engineering graduates in WAPDA.

This Civil Engineering Jobs in  WAPDA, Water & Power Development Authority is best opportunity for Fresh BSc Civil Engineer. All Civil Engineering jobs in Punjab, KPK, Sindh, AJK, FATA,  is collected from different Newspapers on every Sunday and shared for our viewers so that that can apply for the job and get the employment in WAPDA C&M Water  as Junior Civil Engineer. These Jobs are for the Building Engineering So you must have experience in Building and Highways 

We have prepared a group on Facebook where you can get the alerts about Jobs in WAPDA If you know any job opportunity in Government Sector both permanent Jobs and Jobs on contract basis you can contact us, you can inform us about the job.

If you are a fresh or experienced civil engineer living in Pakistan and seeking Civil Engineering Job in Water & Power Sector than don’t post or share your CV here as we are not a part of the department and we are just sharing it so that you can get the opportunity to apply for this job.

As a civil engineer and construction expert, you’d be familiar with a lot of common beam types and kinds but did you know there are a lot of uncommon types of beams you don’t know.

Or in other words there are many uncommon types of beams you should know and in this post I’d be sharing all those uncommon structures that are rarely used but are unique, special, scarce and interesting.


I’ll not be messing you up in structural mechanics or theory of structures and I’ll not classify the beams based on the restraints and supports or type of loading or type of material used. I’m talking about some scarce types of beams based on their functionality and purpose.

So, I am actually a lover of Building Drawings and Construction management;

The history of construction is already bursting with wooden beams, stone beams, metal beam. Do you know what is a collar beam or a flitch beam?

Han? No?

1. What is Collar beam? 

These are actually the most common types of beams used in the historical cultural heritage museums and old buildings.   A collar beam, like the word, “collar” is a horizontal beam that are used to join two rafters in a roof of a building of hip shaped. Collar beams are compression beams that actually act like a frame for the roofing construction.

Now you’d be burning to know what is flitch beam? Right?

What is Collar beam?
What is Collar beam? Pic Credit : http://chestofbooks.com

2. What is Flitch beam?

Flitch beam which is also sometimes referred as flitched beam is actually a compound beam i.e. made up wood and steel plate. A vertical steel plate is sandwiched between two wooden beams to make a flitched beam. The flitch beams are mostly used in wood-frame structure.

Flitch Plates (Pic credit: https://manifoldrecording.com) 

3. What is Primary and Secondary beams?

Primary and Secondary beam are usually used in a slab supported by beams and a frame structure. The slab is directly supported by the secondary beams which are those rested on the primary beams. Primary beams is the one that runs from column to column and act as a main frame beam at floor levels.
Primary & Secondary Beams (pic credit: https://engineering.stackexchange.com) 

4. What is a conceal or hidden beam?

You know about T-beam; the top flanges of the t-beam are actually concealed or hidden in the thickness of the slab so it appears as rectangular beam but it is actually designed as t-beam. So concealed beams or hidden beams are the ones that are actually hidden in the to slab or roof slab.

conceal or hidden beam
conceal or hidden beam (pic credit: http://www.openingtolovenow.com) 

5. What is a drop beam?

Drop beam is actually a typical T-beam; it is called drop beam because it is thicker than the slab and showing under the roof deck but from top it is leveled with the top deck slab.
drop beam
drop beam

6. What is a coupling beam?

Coupling beam is like a stiffner beam that is used effectively when two shear wall or other elements subjected to lateral loads are strapped and joined. The coupling beam is used to decrease overturning effect and thus improve the stiffness of a system.

7. What is a Pergola beam?

It is actually a purely architectural beam that is projecting out of the slab as cantilever sometimes to create a DIY effect of pergola.
Pic credit : http://decoholic.org

Pic credit : http://decoholic.org

8. What is Grid or or Joist beams?

Grids are actually joist beams that are constructed in a waffle slab making an orthogonal assembly. The joists or grid beams increases the stiffness of the waffle slab making it able to span larger lengths to meet architectural requirements.

9. What is Portal Beam?

Portal beam is actually a part of a portal frame. Portal frame construction is typically used in industrial warehouses where large open spans are required at low cost followed by a pitched roof. In portal frame the vertical columns are connected by horizontal beams or trusses called portal beams.

So that’s all I hope this post is an amazing and interesting for you; it is, actually for me. If you have any question regarding these uncommon and scarce types of beams than please comment below.

The valuing of variations in any project are lifeblood of a project provided they are properly settled in terms of fair and properly evaluated Star Rates. So actually you want to know "what are star rates".  

In unit price contract the Bill of Quantities (BQ or BOQ) is provided by the employer through his consultants but the quantities quoted in there are only estimated and not final. The difference between estimated quantities and executed quantities depends on the complexity of the structure as well as the fair judgment and experience of the party preparing the BOQ. The contractor, in the bidding phase, quote unit rate or unit price against each item of work involved thereby building up the total contract price. 

What are Star Rates?
What are Star Rates? 


In this post we will be going to discuss about :- 

During the execution of works the actual quantities are jointly measured and verified by the Engineer for interim payment purpose. During the final measurement stages any variation from the original works or any additional works the rate of which are not agreed in the initial BOQ unit price contract would be submitted as Variation Order or Rate analysis for the approval of the Engineering & the Client. These new rates quoted by the Contractor other than the rates quoted in Contract are termed as Star Rates. These star rates are mostly used in agreements with sub-contractors and are seldom in case of entire construction project. 

What are Star Rates? 

As per above discussion we are now able to define "what are star rates" - 

Star Rates are the rates jointly agreed by the Engineer and Contractor for valuing of any instructed variations from the contract quantities quoted in the BOQ during bidding stages of the Contract. 

What is Re-Measurement Contract? 

These types of Contracts are also sometimes referred as Re-measurement Contracts. In this types of Contract typical drawings are generally used during bidding stages. The scope and quantities for the works involved in Re-measurement contracts are easily adjustable thus disputes are reduced. But sometimes the large changes in quantities, sometimes, require deep negotiations to resolve. 

Arguably , this type of contract is fair with the employer at risk for total quantities and the Contractor at risk for fixed unit price. Disputes situations are reduced because the final contact sum is based on a final re-measurement rather than being based on preliminary quantities set at tender but large quantity changes (>15-25%) can lead to increase or decrease in unit prices which can cause some intense negiotiations to settle.

For these types of projects where star rates are involved; the works involved are to breakdown completely which require excellent quantity surveying and reporting capabilities of the staff involved. The Estimation Engineer or Quantity Surveyor must have bulk experience for preparation of BOQs and verification of Quantity Witness Reports (QWRs) and IPCs.  

One example of the star rate can be; like there is a work for installation of some mechanized part in a building at some elevation or level but as the project is carried out, the level or elevation is increased thereby making the installation difficult and dangerous. In such situation the contractor can prepare a Star Rate for such work keeping in view the original unit price in original contract. 

Requirements for Star Rate 

Any of the Star rates submitted by the Contractor in Re- Measurement Contract are considered acceptable if the rates are: 

- A built up rate which can be assessed by raw materials cost, labour cost and preliminaries plus reasonable overheads and profits, but no major special material involved [special material cost less than or equal to 30% of lumpsum price.] 
- Equal to or close to the term rate of similar nature or unit rate employed by the government authorities -Housing Authority etc. BUT NO MORE THAN 15% difference. 
- Equal to or close to 15% rate previously employed in other lumpsum contract competitive with the quotations from alternative contractors. 

If the star rates cannot be assesed/approved by the above methods, a negotiation can be made and the final unit rate approved by the director in the writing. Otherwise , star rates items must be taken out for tendering. 

Guideline for Star Rates in FIDIC

The above assessment method should be released to all term contractors for information.
The FIDIC – based contracts, which is mostly the case, the valuing of variations is properly documented. The Clause 51.1 of FIDIC gives six situations where the contractor is authorized to recover the surplus costs that are arising by the instructed variations, provided that the variation has not resulted from the Contractor default. 

The FIDIC clause 52.1 guides the Engineer how to value variations – the top priority is given to the rates that are given in the contract. In the event of disagreement, the Engineer can fix the rates that are appropriate, in his opinion, by notifying the contractor accordingly, with a copy to the employer.     

PERT is an acronym of Program evaluation and review technique, it is a project network analysis that was developed by the U.S Navy in 1950s to facilitate the management of large and complex projects. The management of the project will involve the planning and the control of the projects.

The individual components of the projects are mentioned out as the scope through charts. These charts are arranged in a logical order. These will be arranged such a way that proper relationship is shown and expressed through this chart.

Advantages and Disadvantages of PERT
Advantages and Disadvantages of PERT

Time & Cost in PERT?

The PERT technique is event oriented project evaluation technique, where the time and cost of each event, that comprise a project is taken into consideration. Each event in PERT is specified to understand the resources and the time that is required to complete that project.

PERT is implemented in projects  that  are non-  repetitive. So these are not developed based on a historic background as in the case of CPM (Critical path Method).

PERT gain many advantages that help the project management team achieve their goals with efficiency. But every method will have some disadvantages too.

Here, we will discuss the advantages and disadvantages of the PERT.

 Advantages of the PERT

The main advantages of PERT are:

1.  PERT analyze the uncertainties and possible solution of the project. Hence, the project manager will know the defects and issues in the project execution. This will hence help in solving the pitfalls faced in the project planning. Unexpected surprises and wastage due to these issues can be avoided and minimized to a large extend. PERT analysis will help in determining all the essential factors that will help in the execution of a successful project.
2.  PERT provides tools that will help in forecasting the schedule and changes due to any unexpected impacts. Most of the potential changes, that have high involvement in the project completion can be identified early so that preventive measures can be taken.
3.  PERT identifies the most critical activities in the chart and give more focus for them. This controlling on critical activities will help in utilizing the resources effectively.
4.  PERT enables constant review along with their updation based on the daily reports and the feedback received from the subordinates. In order to ensure

that the process to be done systematically, all the management levels shall be vigilant and involved.
5.  PERT  helps  in  improving  the  communication  system  followed  in  the
organization. The personal role of every individual in the project is represented through a task relationship graph. This clearly states the roles and the responsibilities of each individual.
6.  PERT is more used in the planning of large projects which is unique in
nature. The project is divided into events. Every event in a PERT chart is defined based on the:
➢   Time required for the completion of the event
➢   What precedes the event?
➢   What succeeds the event?
7. PERT collects information from all parts of the department to bring up the best chart for the projects. This will directly or indirectly help in bringing proper coordination of the project thus helping the decision-making process during critical situations. The PERT process will involve the combination of data that is both quantitative and qualitative which will facilitate proper coordination of the project.

Disadvantages of PERT

1.  PERT is a time-oriented method. Time will be the main concern required for the completion of a particular project activity. This will clearly demand for the time duration required for the completion of each activity. As PERT deals with unique project and unique construction method, the time allocation is a difficult task.
2.  PERT method of project planning will consume large amount of labor. This is the case, both in management side and execution side. As time is the main target, the management won’t hesitate to invest money.
3.  PERT Planning will require the collection of fresh data for the fresh project.
This will make the data collection procedure a tedious process. Sometime this will make the data collected to be less accurate. This will bring inaccuracy in time and the cost that is estimated for the events and the total project. High chances of biasing are the end results of such issues.
4.  PERT method won’t work good if the main project is a combination of two
projects, that will require the sharing of resources.
5.  The changes in the preceding event or the succeeding event will result in the failure of the whole method.
6.  The  PERT  charts  becomes  more  complicated  with  the  increase  in  the
activities, as there will be dependent tasks in hundreds.
7.  PERT method is expensive in nature
8.  PERT is a combination of predictions as there is no past history to compare with. This predictions will result in the inaccuracy of the project.

No trial and error method is followed for this issue. All assumptions put forward have to be justifiable and have a reason before their implementation.


1.  Operations Research, Sivarethinamohan
2.  Project Planning and Control with PERT & CPM, Dr. B.C. Punmia & K.K.

The shear strength of the final asphalt product is affected by the quality of the asphalt prime coat applied. 
Asphalt Prime Coat is also termed as emulsified asphalt, water diluted asphalt and Cutback aliphatic spray. Recently I have got the chance of working on a highway project somewhere in a mountainous cold-weather region. 

And I was amazed after finding the impact of climate on construction activities and materials used therein. The use of MC 30 cutback asphalt prime coat was a surprise factor for me but after finding its properties and features I was surprised and decided to share my experience with you. 


By going through this article you will be able to understand :- 
  • What is Asphalt Prime Coat? 
  • Functions of Asphalt Prime Coat
  • Why Asphalt Prime Coat is needed?
  • Qualities of a good Asphalt Prime Coat? 
  • Application of Asphalt Prime Coat in Cold Weather & Cut Back primers? 
  • Process of Applying Asphalt Prime Coat

What is Asphalt Prime Coat?

Asphalt Prime coat is actually a low viscous slow-setting grade of asphalt emulsions that are diluted with water and applied between the non-stabilized bases including but not limited to Water Bound Macadam (WBM) and succeeding asphalt course.

What is Asphalt Prime Coat?
What is Asphalt Prime Coat? 

Also Read

Functions of Asphalt Prime Coat

The functions and advantages of the Asphalt Prime Coat are as follows:- 

Plug in the Capillary Voids

The above stated heading is actually the main objective in addition to the other objectives of the asphalt prime coat. So the asphalt prime coat is applied as water proofing layer on the base course so as to protect the underlying layers from wet weather and thereby avoiding any migration of moisture across layers. 

Integrity of the Granular Baser

The second most important objective of the asphalt prime coat is to bind the loose material in the base course by coating the material particles and thus hardening and toughening the base surface to provide a work platform.  

Binder for intermediary layers

The granular base course cannot directly adhere with the succeeding HMA (Hot mix Asphalt) and will therefore can cause shear failure if the thickness of the asphalt is not adequate. So in order to have proper adhesion with the base course the asphalt prime coat or primer must be sprayed on it.  

To Reduce Dust

As stated above, that due to primer coat the fines in the base course are confined within the base layer either granular or WBM. The confinement of these fines would produce an environmental friendly impact making construction activities more human friendly and dust free. 

Why Asphalt Prime Coat is needed? 

I am glad you asked this question as it is the question of this century lolz. Anyhow, as per my experience, the main need of the asphalt prime coat is because of the failure of the asphaltic emulsions (HMA) to wet the granular base course thereby creating a poor adhesion. Emulsions having high binder content or quick set slurry are always susceptible to such outcomes. And then came this superficial adhesion agent called asphalt prime coat. 

 Qualities of a Good Asphalt Prime Coat / Primer 


All the objectives of the prime coat can only be met if it is penetrated, enough. By enough it means completely up to the depth of the base course but usually it is found that penetration of 1-2 cm is enough.  A good quality primer or prime coat chemical must be composed of small particles that are having low surface tension in an emulsion allowing it to penetrate into the capillary voids. 

Usually in a common primer the asphalt emulsifier is diluted with water making a dispersion of discrete particles. But the emulsifier actually increases the surface tension and thus avoiding penetration. 

 Curing / Setting

It is required for the Primer to completely cure before covering the base course with the Hot Mix Asphalt (HMA). Through experiments it is found that the emulsified asphalt cures earlier than the MC or SC cutbacks. But earlier curing or setting would make handling and application difficult which is always a problem for the cold areas. And therefore thinning and heating is a pre-requisite for such primers. 


The primer must be completely absorbed within the base course but if after 24 hours the primer is not absorbed it must be removed by blotting with sand. 

Primer in Cold Weathers & Cutback Asphalt Primers

Mostly in colder regions, the asphalt prime coat is often deleted by increasing the thickness of the HMA. But it is the responsibility of the designer to judge and advice the optimum option to either delete the asphalt prime coat or use the cutbacks. Cutbacks asphalt asphalt prime coat bitumen consists of penetration grade asphalt cement and a diluent or cutter of medium volatility like kerosene. The cutback agent or cutter is added to reduce or cutback the viscosity of the bitumen. The mixture thus obtained is often termed as cutback bitumen. Medium Cure Cutbacks penetrated deeper than the conventional emulsified asphalts diluted with water but the efficient functioning of cutbacks primer requires it to be mixed properly with the granular base. .

Process of Applying Asphalt Prime Coat

  1. Cleaning and Clearing of the Base Surface. 
  2. Sprinkling water over the base surface to ensure good penetration of the emulsion or prime coat but avoid over watering. 
  3. Spraying of the Prime Coat using the standard emulsion sprayer that is already properly calibrated. 
  4. Allow penetrating and drying. Usually traffic must not be allowed for more than 24 hours but if traffic must use the road a thin layer of sand can be spread. 
  5. Final surfacing is done on the next day.

So whats Next...??

So I have tried to elaborated enough on Asphalt Prime Coats, its types, features, how to apply it etc. But may be I have missed something which you may know. So why not share your experience with the world. So talk about asphalt prime coat. 

Saad Iqbal

{picture#https://3.bp.blogspot.com/-XZIy9ZMfPN8/Un4OZ_kOBrI/AAAAAAAAAMU/mGCOrK2TE7g/s320/1467370_565639096843077_167871782_n+-+Copy.jpg} Hi there, I am Saad Iqbal from Pakistan - Founder of Iamcivilengineer. I am Currently Working in a Consultancy Firm as Junior Engineer and am a Passionate blogger and a Civil Engineer from UET Taxila, Pakistan. {facebook#https://facebook.com/imsharing} {twitter#https://www.twitter.com/iamcivilengg} {google#https://plus.google.com/u/0/107498623703455203528} {pinterest#https://www.pinterest.com/iamcivilengg/civil-engineering-iamcivilengineercom/} {youtube#https://www.youtube.com/user/imsharingdottk}


{picture#https://3.bp.blogspot.com/-XZIy9ZMfPN8/Un4OZ_kOBrI/AAAAAAAAAMU/mGCOrK2TE7g/s320/1467370_565639096843077_167871782_n+-+Copy.jpg} Hi there, I am Saad Iqbal from Pakistan - Founder of Iamcivilengineer. I am Currently Working in a Consultancy Firm as Junior Engineer and am a Passionate blogger and a Civil Engineer from UET Taxila, Pakistan. {facebook#https://facebook.com/imsharing} {twitter#https://www.twitter.com/iamcivilengg} {google#https://plus.google.com/u/0/107498623703455203528} {pinterest#https://www.pinterest.com/iamcivilengg/civil-engineering-iamcivilengineercom/} {youtube#https://www.youtube.com/user/imsharingdottk}
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