Introduction, Classification, Standards, Uses of Bitumen

Bituminous materials

Asphalt material is composed of some extremely complex polymer hydrocarbons and these hydrocarbons of non-metallic (oxygen, sulfur, nitrogen) derivatives of the black or black-brown solid, semi-solid or liquid mixtures, hydrophobic materials, dense structure, almost completely insoluble in water, does not absorb water, has good waterproof, so widely used in civil engineering waterproof, moisture and seepage; asphalt belongs to the organic cementing materials, and sand, stone and other mineral mixes have very good bonding ability, the resulting asphalt concrete is the most important pavement material for modern road projects. Material, and sand, stone and other mineral mixtures have a very good bonding ability, made of asphalt concrete is the most important pavement material for modern road projects.

Petroleum asphalt composition and structure

1. Elemental composition

Petroleum asphalt is composed of a variety of hydrocarbons and non-metallic (oxygen, sulfur, nitrogen) derivatives of the mixture, the elemental composition of the main carbon (80% ~ 87%), hydrogen (10% ~ 15%); the rest are non-hydrocarbon elements such as oxygen, sulfur, nitrogen, etc. (<3%); in addition, there are some trace elements of metal.

2. Component composition

Usually the asphalt is separated into a few chemical properties similar to its engineering performance has a certain connection with the chemical composition of the group, these groups are called “components”. China's current regulations have three-component analysis and four-component analysis of two kinds of methods.

Petroleum asphalt three-component analysis of petroleum asphalt separated into oil, resin and asphaltene three components.

(1) oil for the light yellow transparent liquid, giving asphalt fluidity, the amount of oil content directly affects the asphalt softness, crack resistance and construction difficulty. China's domestic asphalt in the oil often contains wax, in the analysis should also be separated from the oil, wax. The presence of wax will make the asphalt material at high temperatures become soft, resulting in the phenomenon of flow; at low temperatures will make the asphalt become brittle and hard, resulting in cracking. Because the wax is a harmful component, it is often used to improve the performance of asphalt dewaxing method.

(2) resin for the reddish-brown viscous semi-solid, high temperature sensitivity, melting point below 100 ℃, including neutral resin and acidic resin. Neutral resin so that asphalt has a certain plasticity, mobility and adhesion, and its content increases, the adhesion of asphalt and elongation increases; acidic resin content is not much, but the activity is large, can improve the asphalt and other materials, improve the asphalt wetting, asphalt can be emulsified.

(3) asphaltene for the dark brown solid particles, heating does not melt, it determines the asphalt adhesion, viscosity and temperature stability, as well as the hardness of asphalt, softening point. Asphaltene content increases, the viscosity and adhesion of asphalt increases, hardness and temperature stability.

Petroleum asphalt technical standards

Petroleum asphalt technical standards will be divided into different types of asphalt and standard (grade), in order to choose. At present, petroleum asphalt is mainly divided into three categories: road petroleum asphalt, construction petroleum asphalt and ordinary petroleum asphalt.

In the classification of asphalt grade, is based on the asphalt penetration, ductility, softening point and other indicators. Needle penetration is divided into asphalt grade of the main indicators. For the same variety of petroleum asphalt, the larger the grade, the corresponding viscosity is smaller (the larger the value of the penetration), the better the ductility (the greater the plasticity), the greater the temperature sensitivity (the lower the softening point).

Selection of petroleum asphalt

Selection of petroleum asphalt should be based on the nature of the project (housing, roads, corrosion), local climatic conditions, the project site (level, underground) and other factors to be considered. As a result of high grade asphalt than low grade asphalt containing more oil, anti-aging ability, so in order to meet the requirements of the premise, should try to choose a high grade of petroleum asphalt, in order to ensure that there is a longer service life.

(1) road petroleum asphalt road petroleum asphalt is divided into heavy traffic petroleum asphalt, light traffic petroleum asphalt, emulsified petroleum asphalt, liquid petroleum asphalt and modified asphalt. Road project selection of asphalt materials should be considered traffic and climate characteristics. High-temperature areas in the South should choose high-viscosity petroleum asphalt to ensure that the summer asphalt driveway has enough stability, not rutting, etc.; and cold areas in the north should choose low-viscosity petroleum asphalt to ensure that the asphalt driveway at low temperatures still have a certain degree of deformation capacity, to avoid cracking.

2) construction of petroleum asphalt construction of petroleum asphalt needle penetration is smaller (viscous), high softening point (heat resistance is better), but less elongation (less plastic), mainly used for the manufacture of oil paper, linoleum, waterproofing coatings and asphalt embedded joints and so on. Most of them are used in building roofing projects, underground waterproofing projects, trench waterproofing, anti-corrosion projects and pipeline anti-corrosion projects. The use of asphalt made of thicker film, increasing the sensitivity to temperature; at the same time, the black asphalt surface is a good heat-absorbing body, generally in the same area of asphalt roofing surface temperature than other materials are high; asphalt roofing to achieve a surface temperature of 25 ℃ ~ 30 ℃ higher than the highest local air temperature. In order to avoid summer flow, the softening point of asphalt materials for general roofing should also be higher than the maximum temperature of the roof in the region 20 ℃ ~ 25 ℃, you can choose No. 10 or No. 30 petroleum asphalt. For example, Wuhan, Changsha asphalt roof temperature of about 68 ℃, the softening point of asphalt should be selected in 90 ℃ or so, low summer easy to flow; but should not be too high, otherwise the winter low-temperature easy to be hard and brittle, and even cracking. Some parts that are not easily affected by temperature, or lower temperature areas, such as underground waterproofing vapor barrier, etc., can choose a higher grade of asphalt, such as No. 60 or No. 100 asphalt. Therefore, the choice of petroleum asphalt according to the region, the project environment and requirements.

(3) ordinary petroleum asphalt Ordinary petroleum asphalt wax content of up to 20% to 30%. When the asphalt temperature reaches the softening point, it is easy to produce the phenomenon of flow; asphalt in the penetration of paraffin will also make the asphalt bonding layer of heat resistance and bonding force is reduced. Therefore, it is generally inappropriate to use ordinary petroleum asphalt in the project.

 

Coal asphalt

Coal asphalt is a product of coal distillation (coal tar) obtained through reprocessing. According to its application in the project requirements of different, according to the consistency can be divided into two categories of soft coal asphalt (liquid, semi-solid) and hard coal asphalt (solid).

Coal asphalt is composed of aromatic hydrocarbons and their oxygen, sulfur, carbon derivatives of the mixture, the main elements for the C, H, O, S and N, coal asphalt elemental composition is characterized by the “hydrocarbon ratio” than petroleum asphalt is much larger. Coal asphalt chemical components of the analysis method is similar to petroleum asphalt, can be separated into: oil, soft resin, hard resin, free carbon C1 and free carbon C2 five components; which contains naphthalene, anthracene, phenol and other hazardous substances in the oil, its content must be restricted.

Coal asphalt and petroleum asphalt, compared with the following differences in technical properties: lower temperature stability; better adhesion with mineral aggregates; climate stability is poor, aging fast; corrosion resistance, can be used for wood and other surface anticorrosion treatment. The technical indexes of coal asphalt mainly include: viscosity, distillation test, water content, toluene insoluble content, naphthalene content, phenol content and so on. Among them, the viscosity of coal asphalt, is the evaluation of the quality of coal asphalt the most important indicators, but also divided into coal asphalt grade based on its test method is similar to petroleum asphalt.

The main technical properties of coal asphalt are worse than petroleum asphalt, less used in construction projects; but its anti-corrosion properties are good, so it is suitable for underground waterproofing layer or as anti-corrosion materials.

Modified asphalt

Modern civil engineering not only requires asphalt with better performance, but also requires a longer service life, but the asphalt material by the environment, easy to aging. Through a variety of technical measures, in the traditional asphalt materials, add other materials to further improve the performance of asphalt, known as modified asphalt. The purpose of modification is to improve the rheological properties of asphalt materials, extend the durability of asphalt, etc., to improve the adhesion of asphalt and aggregates; applications and waterproofing project asphalt, the most important modification purpose is mainly the first two points.

Way to improve the rheological properties of asphalt

Improve the rheological properties of asphalt in many ways, the modification effect is better with the following types of modifiers:

(1) resin modifiers

Used as asphalt modified resin is mainly thermoplastic resin, commonly used polyethylene (PE), polypropylene (PP), atactic polypropylene (APP), phenolic resins, natural rosin and so on. They can improve the viscosity of asphalt, improve high-temperature stability, while increasing the toughness of asphalt; but the improvement of low-temperature performance is not obvious.

(2) rubber modifier

Rubber is an important modifier of asphalt, asphalt and asphalt has a good miscibility, and can make asphalt with rubber has many advantages, such as high-temperature deformation is small, low-temperature flexibility, etc.. Commonly used rubber modified asphalt mainly includes: chloroprene rubber modified asphalt, butyl rubber modified asphalt, recycled rubber modified asphalt, styrene-butadiene rubber modified asphalt. Among them, styrene-butadiene rubber modified asphalt performance is very good, can significantly improve the elasticity of asphalt, elongation, high-temperature stability and low-temperature flexibility, fatigue and aging resistance and other properties, mainly for the production of waterproofing roll-roofing or waterproofing coatings.

(3) rubber and resin blend modifiers

At the same time with rubber and resin to improve the properties of petroleum asphalt, asphalt can make both rubber and resin properties, and lower cost. Preparation, the use of raw material varieties, ratios, production process is different, you can get a lot of different performance products, mainly coils, sheets, sealing materials.

(4) micro-filler modifiers

In order to improve the adhesive properties of asphalt and heat resistance, reduce the temperature sensitivity of asphalt, usually adding a certain amount of mineral micro-fillers. Commonly used are fly ash, volcanic ash, shale powder, talcum powder, lime powder, mica powder, diatomaceous earth and so on.

(5) fiber modifiers

In the asphalt mixed with a variety of fiber substances, asphalt can be significant high-temperature stability, while increasing the low-temperature tensile strength. Commonly used fiber substances are: a variety of synthetic fibers (such as polyethylene fiber, polyester fiber) and mineral asbestos fibers.

Ways to extend the durability of asphalt

Currently to improve the durability of asphalt methods, mainly mixed with some of the more expensive chemical additives, such as antioxidants, etc.; but the use of antioxidants, must be identified through the test on the effectiveness of its technology. Currently the most effective additives to improve the durability of asphalt for the special carbon black, carbon black pre-treatment of additives, can be formulated “carbon black modified asphalt”.