Emulsions, paste. Composite binders

Along with bitumens and tars, water emulsions, which are the dispersible systems in which the shallow particles of organic binders (lesser than 1 µm) are evenly diffused in water, are also used in construction. The manufacture of stable emulsions is possible due to application of surfactant additions – emulsifiers. Water-soluble high molecular compounds and soaps of alkaline metals (saponated rosin, fatty acids, lignosulphonates and other) are used as emulsifiers. The mechanism of emulsifier action consists in adsorption on the particles of bitumen or tar and formation of protective shields which are instrumental in maintenance of dispersed particles in the hanging up state.

The emulsion variety is the so-called emulsion pastes, emulsifier of which is superfine hydrophilic mineral powders (lime, clay, tripoli powder and other like that).

In Table 15.2 the characteristic compositions of bitumen emulsive pastes, applied for cold asphalt mastics are presented.

Emulsions and pastes do not contain volatile solvents; they can be used to coat both dry and wet surfaces. Upon evaporation of water the dispersible phase of emulsions coagulates and homogeneous coverage appears.

Bitumen and tar emulsions and pastes are widely used in road and hydraulic engineering construction. Pastes are used as a binder for cold asphalt mastics.

For making emulsions and pastes the viscid oil bitumens are used. The technological process consists in heating and mixing of the initial components in the special mixers.

The improvement of the properties of bitumen and tar materials can be attained by application in the form of composite binders: tar-bitumen, rubber-bitumen, bitumen- and tar polymeric.

Table 15.2

Recommended compositions of bitumen pastes

Binders which are formed by the combination of bitumen with tar or pitch, have the advantages of both components: enhanced biostability and atmospheric resistance, high adhesive capacity, less sensitivity to temperature drops and etc. The most widespread are composites which have a 65-70% bitumen and 25-30% tar.

Rubber matters are effective additions for increasing the elasticity, softening temperature, durability and longevity of the bitumen. Hence, by combining rubber and bitumen in the ratio of 1:1, the relative lengthening improved by more than 200%, elasticity – by almost 3 times, resistance to breaking by 0.8 MPa, the softening temperature to 120°С, and the brittle temperature reduces down to - 20°С.

Content of rubber in rubber-bitumen binders, as a rule, is in the limits from 5 to 30%, thus its optimum concentration grows to the extent of decline of viscidity of bitumen. The ordinary ground up rubber from old motor-car overlays, and also wastes of production are used for making the binder. Production of rubber-bitumen binder consists in melting of the ground rubber with bitumen at a temperature 160–200^оС and continuous interfusion within 1-2 hours to complete homogenization. With respect to mechanical influence, molten bitumen rubber is devulcanized and acquires high plasticity.

A number of bitumen composites with additives of latex, polyethylene, epoxies have been developed. Bitumen-polymeric compositions have higher heat-resistance, mechanical strength and deformative ability, especially at subzero temperatures. They both are produced by mechanical method - by treatment of the mix on rollers and method of alloying at temperatures ranging from 160-190°С.

Date: 2015-12-18; view: 922