Seal coat,prime coat and tack coat

Here is a brief explanation of important terms used In road construction i.e, seal coat, tack coat, and prime coat.

1. CE-311L Transportation Engineering- || Lab

2. Introduction: PRESENTED BY: MUHAMMAD ARIF REG NUM# 18PWCIV5179 CLASS NUM# 170 PRESENTED TO: ENGR.MANZOOR ELAHI I

3. Tack coat (Bitumen bond) Introduction: A tack coat is an adhesive material applied between layers of the asphalt concrete that is laid down for road construction. The adhesive when applied correctly, helps to prevent the degradation of the road by keeping the asphalt concrete layers together. Fig shows the application of a tack coat over a pavement

4. Cont.…….. What is tack coat made of? It is an asphalt emulsion. The trick is to take the very sticky, thick, bituminous asphalt and grind the particles very finely. This is done in what is called a colloidal mill. Tack coats are a necessity when it comes to the construction of roads today, but one question remains, how much tack coat is needed for proper bonding? The amount of tack coat applied is significant to the effectiveness of the tack coat as well as the quality of the road over time. Many different considerations go into the application of the tack coat, such as the method of application, the amount of tack coat used, and the cost of it. With the importance of the tack coat, it is essential to know how to apply it. A tack coat has many ways it can be applied but has different effects The main challenge is to find a very effective method that also keeps the cost down.

5. Methods: A sprayer typically applies the tack coat with a multitude of different nozzles and nozzle angles. Fig. shows a truck with mounted nozzles spraying the tack coat onto the pavement. Most likely, the many different ways that the sprayers are configured and made directly affect the amount of tack coat put down and directly affect the durability of the road. When applying the tack coat, the trucks must go at a constant speed to get a uniform application of the tack coat on to the asphalt concrete pavement. If too little is applied, then the tack coat is not sufficient but add too much and it gets expensive A truck applying the tack coat onto the pavement

6. Equipment used for tack coat A tack coat truck . This is a man applying a tack coat with just a hose

7. Tack Coat Application Rate Calibration Method A: Weighing Pads Method B: Volume-based Calculations Weighing pads used to see how much tack coat has been applied

8. Optimum Application of Tack Coat A lightly applied tack coat A heavily applied tack coat An appropriately applied tack coat

9. Summary In conclusion, the tack coat is an essential aspect of the road-building process and is necessary to prolong the lifetime of the roadway. Along with its importance for the lifetime of the roadway, the way the tack coat is applied is significant as well. The tack coat has many different parameters that must be met to be applied most effectively such as the application rate of the tack coat, the surface the tack coat is being applied to, and the temperature of the tack coat and of the environment the tack coat is being applied. Once applied adequately then the tack coat will ensure a longer-lasting roadway that will far outlive a roadway without a tack coat.

10. Seal coat: Seal coating is the process of applying a liquid product over an existing asphalt pavement in a manner that seals the surface and fills small voids and cracks as protection against the elements. Left unsealed, sunlight, wind, and water will gradually cause asphalt to harden and oxidize, and as it becomes more brittle, cracking can occur. Over the space of a few years, asphalt paving can be seriously damaged if it is not periodically sealed. sealing can help prevent damage from freezing water as well as salts and road chemicals. Sunlight and wind are also highly damaging to asphalt in warmer climates. Seal coat usually provides friction to vehicles and water proofing. The minimum thickness of the seal coat required is  20mm for bitumen pavement

11. How Seal Coating Works There are different forms of seal coating material, but all methods work by a process of cleaning and patching the existing surface, then coating the entire surface of the asphalt with a liquid sealer that forms an impenetrable barrier once it is dry. With the surface seal coat intact, the underlying asphalt is protected from the effects of water, wind, and sunlight that can degrade and harden the asphalt and cause it to crack and crumble. How Often to Seal-Coat The seal coating process can is normally first applied one year after the initial pavement has been placed to allow proper cure and wear of the surface. After this, it's recommended that you have driveways and parking lots seal coated every two to three years for normal use, or every year if the pavement experiences heavy traffic.

12. Benefits of Seal Coating Extends the life of the driveway and parking lot by preventing the asphalt from hardening and crumbling It creates an attractive, uniform coat over the pavement, especially if crack and holes are properly filled before seal coating is applied. Sealing protects the driveway from salts, chemicals, and moisture from entering the pavement. Seal coating is a cost-effective way of repairing or surfacing the existing pavement, extending the life of the pavement and driveway.

13. Prime coat A prime coat is an application of a low viscosity asphalt to a granular base in preparation for an initial layer (or surface course layer) of asphalt. The purpose of the prime coat is; to coat and bond loose material particles on the surface of the base, to harden or toughen the base surface to provide a work platform for construction equipment, to plug capillary voids in the base course surface to prevent migration of moisture, and to provide adhesion between the base course and succeeding asphalt course. After applying the prime coat, it must cure for a minimum of 48-72 hours before asphalt is placed, with no rain in the forecast. for a normally clean environment, a  coat of up to 50 microns is considered adequate. For a dusty or humid location requiring constant servicing and cleaning, a thicker coat, say, up to 70–80 microns, is considered to be adequate. 

14. Purpose of prime coat: Coat and bond loose material particles on the surface of the base. Harden or toughen the base surface to provide a work platform for construction equipment. Plug capillary voids in the base course surface to prevent migration of moisture. Provide adhesion between the base course and succeeding asphalt course.