Anti-Stripping Agent for Bituminous Mix

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Anti-stripping agents are used for bituminous mixes and materials to ensure adhesion between bitumen and aggregates (hydrophilic), even when submerged in water.

Material Requirement

The anti-stripping agents shall consist of fatty acid amines having a long hydrocarbon chain. These agents should conform to the chemical and physical requirements as detailed in the table below:

Sl No	Test	Method	Limit
1	Appearance	Visual	Liquid/Solid
2	Odor	Smelling	Agreeable
3	Specific gravity 27oC	IS: 1202-1978	0.860-1.03
4	Pour point oC Maximum	IS: 1448	42
5	Flashpoint (COC) Minimum	IS: 1448	150
6	Water content percent Vol. Maximum	IS: 1448	1
8	Total base value mg KOH/g minimum	ASTM D 664	200
9	Nitrogen content percent Wt. minimum	Elemental Analyser	7
10	Stripping value with bitumen containing 1 percent Wt. anti-stripping compound at 40oC, 24 hours	IS: 6241	No stripping
11	Underwater coating test	IS: 6241	Complete Coating
12	Thermal stability at 163oC, 5 hours	IS: 6241	Should not lose its efficacy
13	Boiling water test percent minimum coating	ASTM D 3625	95
14	Retained Marshall Stability percent minimum	Marshall Stability Test	75

Storage and Handling

1. Anti-striping agents shall be properly stored in closed containers made of steel or aluminium.
2. The containers made of zinc, copper, polythene, PVC, and most types of rubber are not suitable for use.
3. Most of the anti-stripping agents cause irritation when in contact with human skin and are irritating to the eyes.
4. Protective gloves for hands and goggles for the eyes shall be used while handling them, especially in the case of liquid anti-stripping agents.

1. Use in Sprayed Work

a. Additive Dosage

The required dosage shall be determined depending on the aggregate's nature and size (stepping value). While the recommended minimum dose of an anti-stripping agent for sprayed work is given in the table below, the actual dosage shall be determined in the laboratory depending upon the site conditions.

Aggregate stripping value	Dose of the anti-stripping agent in percent by weight of bitumen	Dose of the anti-stripping agent in percent by weight of bitumen	Dose of the anti-stripping agent in percent by weight of bitumen	Dose of the anti-stripping agent in percent by weight of bitumen
	Surface dressing with precoated aggregate	Penetration Macadam/Built-up spray grout	Surface Dressing with uncoated aggregate	Liquid seal coat
0-25	0.5	0.6	0.7	0.8
25-50	0.6	0.7	0.8	1.0
50-100	0.8	1.0	1.0	1.0

b. Mixing Procedure During Construction

1. The anti-stripping agent supplied in liquid, solid, or concentrated form shall be thoroughly mixed with liquid bituminous material or directly with bitumen.
2. When used with straight run bitumen, the correct dose of the anti-stripping agent shall be mixed in a hot bitumen tank boiler.
3. The two constituents shall be agitated till the anti-stripping agent is thoroughly mixed.
4. The dose of the anti-stripping agent shall suitably be increased if the binder is to remain in the bitumen boiler for a longer period.

Use In Premix Work

a. Additive Dosage

The required dosage shall be determined depending on the aggregate's nature and size (stepping value). The recommended minimum dose of an anti-stripping agent for sprayed work is given in the table below:

Aggregate stripping value	Dose of the anti-stripping agent in percent by weight of bitumen	Dose of the anti-stripping agent in percent by weight of bitumen	Dose of the anti-stripping agent in percent by weight of bitumen
	Void content 3-5 %	Voids content 5-10 %	Voids above 10 %
0-25	0.3	0.4	0.5
25-50	0.4	0.5	0.6
50-100	0.6	0.8	1.0

b. Mixing Procedure During Construction

1. The required amount of the anti-stripping agent shall be poured into the hot bitumen tank and stirred or circulated to ensure a homogenous mix for 15 to 30 minutes.
2. It is important to employ a stable anti-stripping agent or to increase the dose to the expected degradation.
3. Alternatively, the right dose should be pumped into the bitumen line using a pump.
4. The agent is mixed with bitumen before being sprayed on the aggregate in the mix, thus there is no need for a separate mixing period for the agent and bitumen.
5. To make the newly placed surface skid-resistant, precoated chippings are pushed into the hard surface while the mix is still hot in rolled asphalt and bitumen mastic surfacing activities.
6. These chippings shall be pre-coated with bitumen treated with an anti-stripping compound.

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