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Asphalt aggregate

Asphalt aggregate

Asphalt mixture is a composite material, mainly composed of asphalt, coarse aggregate, fine aggregate, mineral powder, and some also add polymer and wood cellulose; by these different quality and quantity of materials mixed to form a different structure, And have different mechanical properties.

Definition

The asphalt mixture is a general term for the mixture of the mineral and the asphalt binder. According to the material composition and structure is divided into continuous gradation, intermittent gradation mixture. According to the composition of the ore material and the size of the gap is divided into dense grading, semi-open with, open grade with the mixture. According to the size of the nominal maximum particle size can be divided into special coarse (nominal maximum particle size greater than 31.5mm), coarse grain (nominal maximum particle size is equal to or greater than 26.5mm), medium (nominal maximum diameter of 16mm or 19mm) , Fine particles (nominal maximum diameter of 9.5mm or 13.2mm), sand type (nominal maximum particle size less than 9.5mm) asphalt mixture. According to the manufacturing process is divided into hot mix asphalt mixture, cold asphalt mixture, recycled asphalt mixture.

Structure

According to the principle of grading composition of the asphalt mixture, the structure can be divided into three categories:

(1) Suspension - dense structure

This kind of asphalt mixture filled with the pre-aggregate of the secondary aggregate (slightly larger than the secondary aggregate size) has a large density, but since the aggregates are fed by the secondary aggregate and the asphalt mortar The structure has a large cohesion c, but the internal friction angle Φ smaller, high temperature stability is poor.

(2) skeleton - void structure

The proportion of coarse aggregate in this structure is large and the fine aggregate is little or no. The coarse aggregates can be interlocked to form a skeleton; however, the fine aggregate is too easy to form voids between the coarse aggregates. The internal friction angle Φ is higher, but the cohesion c is also lower.

(3) skeleton - dense structure

A larger number of coarse aggregates form a spatial skeleton, and a considerable amount of fine aggregate fills the gap between the skeletons to form a continuous gradation. This structure not only has a higher internal friction angle, but also a higher cohesive force.

The asphalt mixture of the three structures has a significant difference in stability due to the density ρ, the porosity VV, and the mineral gap VMA.


Main materials and properties

asphalt

China's industry standard "urban road construction and quality acceptance norms" CJJ1-2008 provides: urban road pavement layer should be preferred to use A-class asphalt (that can be applied to all levels, any occasion and level). Do not use coal tar pitch.

Its varieties are road oil asphalt, soft coal asphalt and liquid petroleum asphalt, emulsified petroleum asphalt. All kinds of asphalt in use, should be based on traffic volume, climatic conditions, construction methods, asphalt surface type, material sources, etc. selected. Multi-layer layer selection of asphalt, the general upper layer is appropriate thicker asphalt, the lower layer or the connection layer is appropriate with thin asphalt. Emulsified petroleum asphalt according to the solidification rate can be divided into quick coagulation, in the condensate and slow condensate three, for the treatment of asphalt surface, asphalt through the road surface, asphalt mixture at room temperature and layer, layer and seal layer.

Asphalt for asphalt mixes should have the following properties:

(1) has a large consistency: characterization of the bond size, that is, under certain conditions of temperature consistency;

(2) has a large plasticity: the "degree of extension" that is, under a certain temperature and external force deformation without cracking capacity;

(3) has sufficient temperature stability: that is, asphalt temperature sensitivity is low, the summer is not soft, winter is not brittle;

(4) has a good atmospheric stability: heat, anti-aging ability;

(5) has a good water stability: strong ability to resist water damage.

Coarse aggregate

(1) coarse aggregate should be clean, dry, rough surface; quality technical requirements should be consistent with "urban road construction and quality acceptance norms" CJJ 1-2008 the relevant provisions.

(2) coarse aggregate and asphalt have good adhesion, with hydrophobic.

(3) for the urban expressway, the trunk of the asphalt surface layer of coarse aggregate crushing value of not more than 26%; water absorption of not more than 2.0%.

(4) coarse aggregate should have a good particle shape, close to the cube, multi-angular, needle-like content of not more than 15%.

Fine aggregate

(1) fine aggregate should be clean, dry, no weather, no impurities, quality technical requirements should be consistent with "urban road construction and quality acceptance norms" CJJ 1-2008 the relevant provisions.

(2) fine aggregate should be above the sand particle size, mud content of less than 3% to 5%; have sufficient strength and wear resistance.

(3) hot mix grade asphalt mixture in the amount of natural sand should not exceed 20% of the total aggregate, SMA, OGFC should not use natural sand.

Filled with sand

(1) filled with sand Application of limestone or lime slurry in the strong rock and other hydrophobic stone by grinding the powder, the powder should be dry, clean, fineness to meet the requirements. When the use of cement, lime, fly ash as filler, the amount should not exceed 2% of the total mineral aggregate.

(2) urban expressway, trunk road asphalt surface should not use fly ash as filler.

(3) Asphalt mixture with the quality of mineral powder technical requirements should be consistent with the "urban road construction and quality acceptance norms" CJJ 1-2008 the relevant provisions.

Fiber stabilizer

(1) wood fiber technical requirements should be consistent with the "urban road construction and quality acceptance" CJJ 1-2008 the relevant provisions.

(2) should not use asbestos fibers.

(3) fiber stabilizer should be 250 ℃ high temperature conditions are not bad.


Hot mix asphalt mix main type

Ordinary asphalt mixture

AC type asphalt mixture, suitable for urban secondary roads, auxiliary roads or sidewalks and other places.

Modified asphalt mixture

(1) Modified asphalt mixture refers to the addition of rubber, resin, polymer, ground rubber powder or other filler and other additives (modifier), so that the performance of asphalt or asphalt mixture can be improved Of the asphalt mixture.

(2) Modified asphalt mixture Compared with AC type asphalt mixture, it has high high temperature anti-rutting ability, good low temperature anti-cracking ability, high resistance to abrasion and long service life.

(3) modified asphalt mixture surface for urban expressway, trunk road.

Asphalt mahut (king + emperor) fat crushed stone mixture (referred to as SMA)

(1) SMA mixture is a kind of asphalt, mineral powder and fiber stabilizer composed of asphalt mastic binding material, filled in the intermittent skeleton formed in the mixture.

(2) SMA is a discontinuous graded asphalt mixture, the proportion of coarse aggregate above 5mm is as high as 70% ~ 80%, the amount of mineral powder is 7% ~ 13% ("powder ratio" exceeds the limit of 1.2 ); Asphalt dosage is more, up to 6.5% to 7%.

(3) SMA is currently used at home and abroad more anti-deformation ability, better durability of the asphalt surface mixture; for urban expressway, trunk road.

Modified (asphalt) asphalt mastic mixture (SMA)

(1) the use of modified asphalt, material ratio using SMA structure.

(2) has a very good high temperature anti-rutting ability, low temperature resistance to deformation and water stability, and the construction depth, anti-skid performance, anti-aging properties and durability have greatly improved.

(3) for traffic flow and the rapid growth of the frequency of passenger cars continue to increase the axle weight, strict implementation of the one-way exercise of the urban expressway, the main road.

Technical indicators

Asphalt mixture density

Refers to the asphalt mixture at room temperature under the conditions of the dry mass per unit volume, expressed in t / ㎥. [1] 

The relative density of asphalt mixture

The ratio of density and water density of compacted asphalt mixture under the same temperature is not dimensioned. [1] 

Theoretical Maximum Density of Asphalt Mixture

In order to calculate the porosity of the asphalt mixture, it is assumed that the compacted asphalt mixture specimen is the maximum density in the ideal state of the mineral material (including the gap of the mineral material itself) and the asphalt, ㎥ said.