Raw materials .1 Aggregate evaluation

URE 6 Bond lowing point

5. Loading

3.1 Raw materials .1 Aggregate evaluation

① Water absorption and specification of aggregate

Water absorption contrast of the two types aggregates is shown in Fig.1 below.

Fig. 1. Water absorption contrast.

Two kinds of aggregates were screened in accordance with the France sieve and GB mesh sieve, results are shown in Fig. 2 and Fig. 3.

Fig. 2. Specification of the two types aggregate (GB mesh sieve).

Fig. 3. Specification of the two types aggregate (French mesh sieve).

From the contrasts of aggregate size and water absorption, it can be found that 1#

and 4# of basalt are obviously coarser than that of limestone, passing percent at the sieve size of 0.075mm of basalt is significantly higher, and the remaining has no significant difference. But from the water absorption of aggregate in comparative perspective, Xinjiang basalt water absorption is larger than that of Jiangsu limestone by about 1%. In order to ensure sufficient asphalt film thickness, attention should be paid to asphalt dosage adjustment during the mixture design.

For an in-depth analysis of aggregate characteristics and its influence on the durability high modulus asphalt mixture design, detailed comparative analysis on aggregate shape, surface texture and other indicators were carried out using AIMS.

(Hainian, Lei and Zhanping 2012; Hainian, Peiwen and Shitong 2008).

② Aggregate particle shape（Form 2D）

Aggregate particle shape is characterized by 2D shape index, the calculation method is as Eq. 1.



^−Δ

=

= Δ

+ 



 



 −

=^{θ θ}

θ θ

θ θ θ 360

0

2

Form R

R D R

(1) Where: Rθ -- radius for the aggregate particles in the theta angle;

Δθ -- for angle micro increment, especially when the aggregate is round, shape index is 0.

Shape index were divided into four grades from 0~20, the smaller the index, the aggregate shape is closer to circle. The evaluation criteria is shown in Table 1.

Table 1. Shape Index Valuation Criteria.

Valuation Criteria Low Moderate High Extreme Shape Index Range 【0, 6.5】 （6.5, 8】 （8, 10.75】 （10.75, 20】

Shape index of the two typical aggregates were compared at the two key sieve

size of 4.75mm and 0.075mm, the results are shown in Fig. 4.

Fig. 4. Different aggregates shape index comparison of same size.

From the view of 4.75mm in size aggregate, basalt aggregate shape is more evenly distributed, except for extreme shape, the other stalls were evenly situated;

The vast majority of the limestone aggregate shape is more regular (shape index below 8 account for 85%), while there are 2.3% of the aggregate belonging to the extremely irregular shape. Basalt aggregate irregular shape ratio is about 7% higher than the limestone in sieve size of 0.075mm

③The coarse and fine aggregates angularity

In AIMS the aggregate angularity describes the characteristics of particle edge sharpness according to the ratio of 0-10000. The evaluation index is expressed by using angular gradient representation. The calculation formula is as Eq. 2.



⁻

= − +

= − ³

1

1 3

3 /

1 ⁿ

i i

n i

GA θ θ

(2) Where: θ--for an orientation angle on edge point;

N--the total number of points;

i--edge of the i-th point of the aggregate particles edge.

According to different shapes of aggregates, the value of GA is from 0 to 10000, when the shape is round the GA value is 0, the evaluation criteria is listed in Table 2.

Table 2. Aggregate Angularity Evaluation Criteria.

Evaluation Criteria Low Moderate High Extreme Shape index range 【0, 2100】 （2100, 3975】 （3975, 5400】 （5400, 10000】

Aggregates angularity tests were carried out of several key sieve selected, the results are shown in Fig. 5.

Fig. 5. Comparison of different aggregates angularity index of same size.

It can be found that at 9.5mm in size the two kinds of aggregate angularity distribution makes little difference: the vast majority of coarse aggregate angularity is at medium level. The larger difference is aggregate in size of 4.75mm and below, which shows Xinjiang basalt aggregate angularity is better, that is conducive to reducing the incidence of flow deformation of the mixture, but it may also increase the difficulty of the mixture compaction construction. The mixture made of Xinjiang basalt aggregate requires to properly increase the compaction effort.

④Aggregate surface texture (Texture)

Using aggregate surface texture value to reflect the coarse aggregate surface texture depth, the formula is as Eq. 3.

( )

( )

²

3

1 1

, ,

3

1

 

= =

=

i N j

j

i x y

N D

TX (3) Where: D--decomposition functions;

n-- the number of decomposition levels;

N--total number of tests in a single capture images;

i--1,2,3 ....

j-- microwave index;

x,y -- positional coordinates for coefficient

Aggregate surface texture value are assessed according to the range of 0 to 1000, specific evaluation criteria is shown in Table3, specially aggregate surface close to be smooth and polishing, its texture value closer to 0.

Table 3. Aggregate Surface Texture Evaluation Criteria.

Evaluation Criteria Low Moderate High Extreme Shape index range 【0, 200】 （200, 500】 （500, 750】 （750, 1000】

The two kinds of aggregates surface texture values are shown in Fig. 6.

Fig. 6. Surface texture values contrast of two kinds of aggregates It can be seen from Fig. 6, at sieve size of 9.5mm the two kinds of aggregates coarse aggregate surface texture are quite different, reflected as: basalt aggregate surface texture even deeper, in case of forming the same film thickness of the asphalt ,the basalt aggregate needs more asphalt than limestone, which can help to improve the mixture performance of anti water damage, while the premise is to be sure aggregate dry enough when the mixture is being produced.

⑤Flat / Elongated aggregate（Flat & Elongated，Flat or Elongated）

The aggregate used in the production of mixture must be controlled its value of flat / elongated, which avoid strength losing and skeletal structural instability because of aggregate being too flat and elongated to broke.

AIMS uses the flat ratio and elongated ratio to describe, defined as follows:

Flat ratio = dS/dI; Elongated ratio = dI/dL;Flat and thin value: L/S=dL/dS; Flat or elongated (F or E): dI/dS or dL/dI> 1,2,3 ... ...

Where: dS, dI, dL denote respectively the aggregate shortest (thickness), intermediate (width) and maximum (length) dimensions.

The Flat & Elongated of the two kinds of aggregates are shown in Fig. 7~Fig. 8.

Fig. 7. Comparison of Flat & Elongated aggregate about the two kinds of aggregates.

Fig. 8. The envelope comparison of Flat/ Elongated aggregate between the two kinds of aggregates.

Some basalt aggregate set outside the 1:6 envelope at sieve size of 4.75 mm, which is more flat, attention should be paid to control the aggregate amount of 4.75mm ~ 9.5mm in size during mixture design.

⑥Corse aggregate angularity texture value (CAAT)

CAAT is used to describe the coarse aggregate angularity and surface texture. the formula is as Eq. 4.

CAAT=10*TX+0.5*GA (4) Evaluation criteria of coarse aggregate CAAT value is shown in Table 4.

Table 4. Evaluation Criteria of CAAT Values .

Evaluation Criteria Low Moderate High Extreme

CAAT range of values ≤3050 （3050,6987.5】 （6987.5,10200】 （10200,15000】

CAAT test results of the two kinds of coarse aggregate are shown in Fig. 9.

Fig. 9. Comparison of CAAT value about the two kinds of aggregate.

It can be seen from Fig. 9, the test conclusions are close to the GA and TX test results, that indicate the Xinjiang basalt aggregate surface is more rough, which is beneficial to increasing the friction and enhancing the interference effect of aggregates, and making the aggregate not easy to slip, it is conducive to the formation of stable graded skeleton (Hainian and Peiwen 2009).

3.1.2 Hard paving grade asphalt

The index of hard asphalt HBP20 used in this paper meet the European EN13924 standard Class2 about 15/25 asphalt technical requirements (EN12591；EN 12597), its key performance indicators is listed in Table 5.

Table 5. Hard Paving Grade Asphalt Performance.

Item Unit HBP20 Technical Requirements Penetration (25℃, 5s, 100g) 0.1mm 22 15～25

Penetration index (PI) - -0.58 - Softening point (R&B) ℃ 65.5 55～71 Dynamical viscosity(60℃) Pa·s 3580 >550

Flash point ℃ 321 ≥235

Solubility % 99.75 >99

After TFOT

Mass changes % 0.01 <0.5

Residual penetration ratio at 25℃ % 69.2 >55