Specification for Prime Coat and Tack Coat

Prime Coat | Tack Coat | Application Rate | Site Testing | Asphalt | Bitumen | Roads

1. Prime Coat 

The prime coat shall be applied and shall consist of the MC-70 confirming to project specification, International Specification like AASHTO, Saudi Aramco Standard, Indian Standard Specifications.

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Role of Prime Coat :

The requirement for furnishing and applying a prime coat to a previously constructed sub-base or aggregate base course, highway shoulders, or concrete pavement, to provide the bond for a superimposed bituminous course.

Clearing Surface :    

Before the application of the prime coat, the aggregate base surface shall be cleaned of all loose dirt and other objectionable materials by means of approved mechanical sweeper or blower and or hand broom.
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Application :

• The prime coat shall be applied only when the surface is dry. 
• Areas to be primed shall be as shown on the Drawing and including 200mm widths outside the edges of the pavement lin.

• 

  Prime Coat application

  The atmospheric temperature is 16℃  or above. Prime Coat shall not be applied when the weather is foggy or rainy or in a sandstorm.
• The Prime coat shall be applied uniformly to the surface of the base using a pressure distributor at a rate between 0.65 and 1.75 kg per square meter (For Oman, Standard Specification for Road and Bridge Construction 2010 application rate is 0.8  - 1.75 kg per square meter ) and at a temperature between 50℃  to 80℃  for MC-70 and at a temperature between 65℃  and 105℃ for MC-250.
• Hand spraying will be approved only for priming small patches or inaccessible areas that cannot be primed by the normal operation of the pressure distributors.

Prime Coat application by Tanker

Curing : 

The prime coat shall be permitted to cure until the penetration into the underlying surface has been approved by the QA QC Engineer of the client. But not less than 24 hours.

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2. Tack Coat

The tack coat shall be of RC-250 conforming to o project specification, International Specification like AASHTO, Saudi Aramco Standard, Indian Standard Specifications.

Role of Tack Coat :

The requirement for furnishing and applying a 

tack coat to a previously constructed sub-base or aggregate base course, highway shoulders, or concrete pavement, to provide the bond for a superimposed bituminous course.

Application of Tack coat: 

Tack Coat Application

The tack coat shall be applied on paved surfaces and vertical surfaces, such a concrete, which will be in contact with the asphalt paving by means of bitumen distributor at a maximum rate of 0.25 liters per square meter or as directed by the client representative. Tack coats shall not be placed during rainy weather, nor when the moisture on the surface to be paved would prevent proper bond, nor when the atmospheric temperature is less than 16℃, nor when the temperature of the surface on which the material is to be placed is less than 16℃.

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Site Testing of Prime Coat and Tack Coat  :

1. 

   Temperature fixed 

   Temperature tests shall be done on-site before applying Prime Coat. The temperature gauge is fixed on the backside of the prime coat tanker. Temperature shall be checked visually at the site and reported by Third Party Technician.

Temperature between 50℃  to 80℃  for MC-70 and at a temperature between 65℃  and 105℃ for MC-250.

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2. Prime Coat Application Rate Test shall be done by a third party technician at the site.  
   
   

Procedure :

• A Board of 30cm X 30cm shall be taken and weight it.
• Place the board on a prime coat spraying location.

• 

  Board For Prime Coat

  Run the prime coat tanker over the board at the time of spraying.
• The tanker will spray the prime coat on board.
• After spraying weight the board again with the sprayed prime coat on the board.
• And determine the spread rate of prime coat/tack coat as following :
• Note - Numbers of test and frequency of test for prime coat and tack coat are dependent upon the quantity of work general 1 test for 500mtrs and minimum one test for each work.

Determination	Unit	Test No.
		1 (Prime Coat)	2 (Tack Coat)
Size of Board	m	.30 X .30	.30 X .30
Area of Board (A)	m2	.090	.090
Initial Weight of Empty Board (W1)	kg	.360	.365
Final Weight of Board After Application of Prime Coat/Tack Coat(W2)	kg	.462	.385
Weight of Prime Coat/ Tack Coat in  W3 = (W2 - W1)	kg	.102	.020
Rate of Spread of Prime Coat/Tack Coat	kg/m2	1.13	0.22
Specified Limit	kg/m2	0.65 to 1.80	Max .025

Board for Prime Coat Test

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Method of Measurement :

The bituminous prime coat and tack coat shall be measured by the square meter of the areas shown on the cross-section at the appropriate rate specified by the Engineer.