Asphalt mastics, mortars and concrete

Mastics. Plastic substances which are produced using combination of organic binder with fine powder-like or fibred fillers are categorized as mastics. Fine powdered mineral matters – limestone, dolomite, chalk, talc, tripoli powder, ash, cement, etc. are used as powder-like fillers; low sorts of asbestos, mineral wool, etc - as fibred fillers. Mastics can consist of 10 – 70% fillers, depending on the function and peculiarities of the components.

The name of mastics usually specifies the kind of binder, applied: bitumen, tar, rubber-bitumen etc. Depending on the method of application mastics may be categorized as hot or cold.

Hot mastics are applied with previous warming-up to 130-180°С. They harden quickly as a result of diminishing viscidity of binder at cooling and have high water resistance and adhesive capacity.

At the same time its application involves a number of difficulties: by the danger of working with hot materials, enhanced adhesiveness, by the necessity of heating of transport devices and etc. These difficulties are absent with the application of cold mastics which allows waterproofing work to be mechanized, increase their productivity and improve the labour time. Furthermore, cold mastics allows getting a more lubricating skim and more economy with respect to the cost of organic binders. Cold mastics are mixtures of organic binders, thinned with solvents, or water-emulsion pastes with mineral fillers. Petrol, ligroin, white spirit, kerosene, oil butter, etc. are applied as solvents. At the normal ambient temperature, cold mastics are applied without heating, their hardening progresses due to evaporation of solvent or water evaporation.

Depending on the required function, mastics are divided into roofing, waterproofing, pressurizing, spackling, lining, etc.

For roofing mastics are used for agglutination of roll materials and waterproofing of roofs, the basic indexes are heat-resistance and stretchability.

Bitumen compositions have got the widest application among roofing mastics.

Tar mastics are applied for gluing on tar paper materials. Tars and their mixtures with polymers serve as binders in it.

Waterproofing mastics are applied for waterproofing plaster creation and filling of deformation joints. Major requirements for waterproofing mastics are small values of water saturation and swellings, sufficient deformability.

The basic requirements for the hot waterproofing asphalt mastics are presented in Table 15.3.

Table 15.3

Physical-mechanical indexes of waterproofing asphalt mastics

For waterproofing of plasters and arrangement of unroll roofs, cold asphalt mastics are widely used. They are produced by mixing bitumen pastes with mineral fillers. They have enhanced water saturation in comparison with hot asphalt mastics; however, the process of water absorption is halted with the lapse of time. The advantages of cold asphalt mastics are: enhanced durability and heat-resistance, possibility of high mechanization of works. Among bitumen-polymeric mastics the most widespread are: bitumen-rubber, bitumen-latex and bitumen-epoxy composites.

Asphalt concrete. Asphalt concrete is the name for material which is produced as a result of consolidation of compacted and rationally composed mixture of asphalt binder and mineral aggregates. Asphalt binder is the mixture of bitumen with mineral filler – micronized powder. Sand and crushed stone or gravel is used as mineral aggregate.

Asphalt concretes are classified according to structural features – grain and porosity, the temperature at a packing, physical state and function. Depending on the maximal fineness of grains of aggregates in the mixture, asphalt concretes may be distinguished as: coarse-grained (to 40 mm), medium-grained (to 25 mm) and fine-grained (to 15 mm). Maximal fineness of aggregates should not exceed 0.6–0.7 thickness of asphalt coverage. In the absence of in-bulk grains of coarse aggregates (more than 3–5 mm), the material is called sand asphalt concrete or asphalt mortar. For porosity less than 5% asphalt concretes are considered as dense and more than 5% - porous asphalt. Depending on the temperature of mass at packing asphalt concrete may be distinguished as hot, warm and cold asphalt concretes. The first are packed at a temperature of the masses not below 120°С, the second - not below 60°С. Cold asphalt concrete is packed at the temperature masses 25-30°С and ambient air not below 10°С. The positive feature of hot asphalt mixtures is high-rate of hardening, and cold is the protracted storage.

Asphalt concrete mixtures depending on workability may be stiff, plastic and poured. Diminishing the stiffness of the mixtures leads to difficulty in the placement of mass, its compacting is however facilitated.

Depending on the functional requirements asphalt concretes are classified as: road, aerodrome, decorative and hydraulic. Hydraulic asphalt concrete is intended for permanent work in water. That is why it should have enhanced water impermeability, water resistance, elasticity and heat-resistance.

Viscid road bitumen are used for making hot asphalt concrete. Thus more viscid asphalts are applied if it is required to provide enhanced heat-resistance and water resistance of coverage. In warm mixtures, bitumen of reduced viscidity are used and also liquid bitumen which thicken quickly and those, which thicken with medium speed. Cold asphalt concrete is prepared on the basis of liquid bitumen which thicken with middle speed or slowly. For asphalt concrete, used in damp-proofing, it is more effective to use bitumen-polymeric binders.

An important component of asphalt concretes is the filler, which improves the basic properties of material, connects the bitumen on the surface and structures it. Mineral filler is instrumental in increasing the density of asphalt concrete (Fig. 15.2) and the reduction of bitumen consumption. The fine powders from such materials - limestones, dolomites and asphalt rocks are applied as fillers. Sometimes pulverized industrial wastes are also used. The content of clay particles in the filler must be no more than 5%. The optimum dispersion of powder, is that at which its specific surface measures 4,000-5,000 cm²/g. Mineral powder, produced from rocks, which contain acidic compounds, does not have the necessary positive influence on bitumen. An effective method of improvement of the filler quality is its activation by treatment with bitumen and surfactant matters in the process of grinding.

Heat and crack resistance of asphalt concrete is considerably improved by addition of 2-3% fibred filler( – low-grade asbestos). Surplus asbestos results in a negative effect such as: increased porosity and reduced water resistance of concrete.

Sand and crushed stone or gravel used for asphalt concrete is mainly the same, as those used for cement concretes. It is thus important to create such grain-size distribution of the mineral part of asphalt concrete which would provide minimum voidage of the mixtures.

Among the methods of proportioning asphalt concrete mixtures the most widespread is the method of that involves the use of dense mixtures curves, which includes determination of grain-size distribution of the crushed stone, sand and filler; the choice of the proportion of mineral materials with condition of 100 % total content of all fractions: setting of approximate amount of binder with next correction by the trial batches and researching of specimens.

In Table 15.4 approximate compositions of sand and fine-grained mixtures, recommended for hydraulic asphalt concrete are presented.

Table 15.4.

Composition of hydraulic asphalt concretes by mass %

The basic properties of asphalt concrete are closely related to its structure, which is determined by the structure of mineral part, by the features of mineral materials and their interaction with bitumen.

The physical-mechanical properties of asphalt concrete are related, first of all, with its density. So the maximum density correlates to the maximum strength of material. Influence of moisture on asphalt concrete increases with the increase of the amount of connected pores. The volume of these pores can be correlated with the amount of water absorption.

Bitumen has the most high viscidity and strength in the saturated state, i.e., in the area of contact with the surface of mineral components. Increasing the unabsorbed bitumen-free amount results in structure weakening and strength decreasing (Fig. 15.3) of asphalt concrete. However a certain amount of free bitumen is needed for a granting of plasticity and corrosive resistance to the asphalt concrete.

The ratio between strength at the normal temperature and strength at a temperature 50°С is called the heat-resistance coefficient whilst the ratio between the indexes of strength at 20 and 0°С is called the elasticity coefficient. Shear deformations take place due to insufficient heat-resistance, which cause dulling of asphalt concrete on the slopes. Deformability and crack-resistance are reduced due to insufficient elasticity at low temperatures. Additions of some polymers and special rubbers improve structural and mechanical property of asphalt concretes. Rubbery polymers in the amount 2-3% introduced to the mass of bitumen increase the interval of plasticity of asphalt concrete mixtures up to 100-120°С, decrease the temperature of fragility by 10-20°С, considerably improve their elasticity over a wide range of temperatures, and improve a range of other properties. To ensure good resistance to temperature of asphalt concrete ,it is important also to provide optimum content of mineral filler in it.

Water resistance of asphalt concrete is characterized by the ratio between ultimate compression strength of water-saturated and dry specimens at 20°С, and also water absorption and swelling under vacuum. Increasing the density, improvement of bitumen coupled with mineral components, positively influence the water resistance. Water resistance also depends on the amount and chemical composition of bitumen and the mineral powder. In hydraulic asphalt concrete the content of bitumen and powder is recommended to be 1-2% higher, than for road asphalt concrete. The basic technical requirements for the properties of hydraulic asphalt concretes are presented in Table. 15.5.

Table 15.5

Properties of hydraulic asphalt concrete

Asphalt mixtures are made on the specialized enterprises of stationary or temporal movable type (Fig. 15.4). Such basic operations are included in the technological cycle of hot asphalt mixtures production: drying, heating of aggregates to 160-200°С, separating them into fractions; preparation of mineral filler in the mill unit; melting of bitumen in melting tank at temperatures between 150-190°С, dosage and careful mixing of all components.

Readymade road concrete mixtures with the temperature 140-160°С is transported on industrial site, where it is specially placed with a mechanical paver and is compacted by static and vibrating rollers, surface vibrators and other special vibratory compactors. Bases under an asphalt concrete should be compacted, dry and plane, to provide good coupling and take up the operating loadings without considerable deformations. If it is required, the base is treated by insecticides.

For asphalt concrete revetments of hydraulic structures for the purpose of improving water impermeability, the surface treatment with hot bitumen, emulsion or asphalt mastics is conducted and it is sprinkled with coarse-grained sand.

Roll materials

Roll materials are supplied in rolls of 10–30 m long. They are divided into basic roll materials, which are produced by impregnation of bases (the cardboard, glass fabric, etc) by organic binder (Fig. 15.5) and unsupported, which are made by rolling of mixtures binder with fillers. Basic and unsupported roll materials are applied for the installation of roofs and damp-proofing. Specific requirements, which are advanced for roofing materials are in respect to its atmospheric- and thermal resistance, to waterproofing, water-impermeability, deformability, and biostability. A roof carpet from roll materials for industrial and civil buildings is used in three - five layers as a roofing carpet. For arranging of overlays one material with improved physical-mechanical properties are used. For lower layers one - sarking felt can be used.

Surface waterproofing from roll materials is also used as multi-layered coverage and is the most widespread.

Basic roll materials are divided into uncovering and covering. The first are produced from dipping bases without next application of covering layer; second - by application on the dipping basis from both sides of protective covering layers, which provide enhanced technical properties and longevity of materials.

Asphalt paper and sarking felt which are produced by the impregnation of paper with oil bitumens are the widespread roofing material. Asphalt paper basis is a roofing carton with mass 300-350 g/cm², made from the mixture of rag, waste-paper and fibred wood-pulp. It is used mainly for the roofs of temporary structures, and also for vapor sealing. Asbestos paper serves as the basis for sarking.

Ruberoid is divided into roofing and lining depending on setting. The first one serves for arranging of overlay of roofing carpet, second one is for lower layers of roofing carpet and waterproofing of structures.

Waterproofing properties of the roll materials are improved considerably by the replacement of roofing cardboard with fiberglass materials and metallic foil.

The nonwoven fabric made of chaotically placed fiberglass, and agglutinated by polymers is used as the basis for glass-ruberoid. Alfol and bitumen-polymeric binders are used for the manufacture of special roll materials, intended for roofs making and waterproofing of structures.

The pitch paper is applied mainly for arranging of the roofs of temporary buildings, for vapor sealing, as lining material and for damp-proofing of foundations.

Rubber-bitumen materials are high-quality roll materials. They are produced by the use of bitumen-rubber binder, fillers and admixtures. By comparison to an ordinary ruberoid, rubber-bitumen materials differ in terms higher extensibility, lesser water saturation, rot-resistance and flexibility.

Date: 2015-12-18; view: 1179