L. Huang, A.M. Sha*, F. Ma, Z.Z. Liu and X.L. Zou. Chang an University, China. August 3, 2015

Transcription

1 L. Huang, A.M. Sha*, F. Ma, Z.Z. Liu and X.L. Zou Chang an University, China August 3, 2015 ISSAEST, Fairbanks, AK, USA, August 2-5, 2015

2

3 The national or local standards of the asphalt stabilized aggregates just provides a simple climate zone and specifications of construction. The application and construction in this area are facing with unprecedented problems. The applications in cold and high altitude region (Qinghai-Tibet Plateau) reported can obviously provide a useful experience to make sure the pavement with high service levels. The practice could be also very helpful to improve the national or local standards related with this issue.

4 This section is from the southern of the Bayan Har Mountains, ended at the north Qinghe.

5 Meteorological data of the main counties nearby the test section Location Maduo County Qingshui River Chengduo County Yushu County Average air pressure Annual mean air temperature( C) Annual mean highest air temperature ( C) Annual mean lowest air temperature (C) Extreme maximum temperature ( C) Extreme minimum temperature ( C) Long year average precipitation (mm) Daily maximum precipitation (mm) Long term average evaporation (mm) Most large snow depth (cm) Most large freezing depth (m) Average wind speed (m/s) Monthly mean wind speed in winter (m/s) Most wind speed (m/s) Dominant wind direction NE WNW W

6 Origindestination K ~ K K ~ K K ~ K K ~ K Upper layer AC-13C, 4cm AC-13C, 4cm AC-13C, 4cm AC-13C, 4cm Lower layer AC-16C, 5cm AC-16C, 5cm AC-16C, 5cm AC-16C, 5cm Base ATB-25, 12cm ATB-25, 18cm ATB-25, 18cm ATB-25, 18cm Sub-base Cushion Pavement Structure of the test section 4% cement treated crushed aggregates, 24cm graded gravel, 20cm 2% cement treated crushed aggregates, 18cm, graded gravel, 20cm graded crushed aggregates, 18cm graded crushed aggregates, 20cm geocell reinforced graded crushed aggregates, 18cm graded crushed aggregates, 20cm Length/m

7 Raw materials: Asphalt binder The binder used in this test section is Karamay110# asphalt, whose technique properties is detailed in Table. The results of asphalt Test items unit Test results Specificatio n Penetration 25 C, 100g, 5s 0.1mm T Ductility 15 C, 5cm/min cm >100 T Softening point (Ring ball) C 44.4 T Relative density (15 C) T Viscosity (135 C) Pa s T Viscosity (175 C) Pa s T

8 Raw materials: Aggregate Four types of aggregated (provided by Zhalongqiong Quarries) with a gradation of 0~3mm, 3~5mm, 5~10mm, 10~30mm were used in the test sections.. Test results of aggregate Test items Test values Requirements Specification Crushing value (%) T Needle and plate particle content (particle diameter> 9.5mm) (%) T Needle and plate particle content (particle diameter<9.5mm) (%) T Particle, <0.6mm Liquid limit (%) 21.5 <28 T Plasticity index 5.6 <9 T

9 Raw materials: Mineral filler The mineral filler used in this study was produced in Huashixia, and the Table shows the main technique properties of the filler. Technique properties of the mineral filler Test items Unit Test value Specificatio n Density g/cm T Moisture content % 0.4 T Hydrophilic coefficient 0.77 T

10 The passing rate of the aggregate used in this study is shown in the Table. Passing rate of the aggregates Mineral aggregate Passing proportion (%) #(10-30mm) #(5-10mm) #(3-5mm) #(0-3mm) Mineral powder Raw materials: Aggregate

11 Raw materials: Asphalt stabilized aggregates The gradation of the asphalt stabilized aggregates used in this study is shown in the Table. Gradation of the asphalt treated crushed aggregate Gradation type Passing proportion (%) Upper limitation Lower limitation Mean value Composite gradation

12 To obtain the best engineering performance of the asphalt stabilized aggregates, the optimal asphalt content (OAC) was determined by the large scale Marshall test, in which the cylinder specimens (Φ mm) were measured. Results of the large-scale Marshall test Test items Unit Requirements construction criterion design criterion Nominal maximum aggregate size mm Specimen size mm Φ Φ Φ Double-sided beat numbers number Porosity % 3~6 3~6 4~6 Stability, KN Flow value mm 1.5~4 measured measured Asphalt saturation % 55~70 55~70 55~70 nominal maximum design air voids ATB-40 requirement aggregate size Voids in mineral % aggregate,

13 The OAC could be determined based on the data in the Table in which five asphalt contents were investigated. Test results of large scale Marshall test Asphaltaggregate ratio(%) Theory relative density Integrated relative density VV (%) VFA(%) VMA (%) MS (kn) FL (0.1mm)

14 As a result, the optimal asphalt content (OAC) and corresponding technical targets are concluded, as shown in the Tables. Optimal asphalt content and density Asphaltaggregate ratio (%) Theory relative density (g/cm 3 ) Integrated relative density (g/cm 3 ) VV (%) VFA (%) VMA (%) MS (kn) FL (0.1mm) Mixture type Aggregate mix proportion optimal asphalt content Proportion (%) 1# 2# 3# 4# Mineral powder Asphaltaggregate ratio (%) ATB

15 main procedures Practice and application Construction preparation Mechanical debugging Mixture mixing Roller-Compaction. Mixture spreading Mixture transportation Acceptance monitoring

16 During the construction of the asphalt stabilized aggregates in the test section, the machinery allocation is as detailed as Table. Machinery allocation Equipment Number Remark Intermittent mixing Plant 1 possessing production capacity Asphalt paver 3 Bitumen-spraying car 1 Tandem steel wheel vibrator roller (13t) 2 Wheel roller(26t) 2 Dump truck 13 charging about 40t per car Synchronous surface dressing machine 1

17 Practice and application Mixture producing and transportation The mixtures (ATB-25 asphalt mixtures) were mixed for 45s. Generally, it takes about 30 minutes to produce asphalt stabilized aggregates to fill a dump truck under a normal condition the distance was about 6.3 ~ 10.7 km, which needs about 25 ~ 30 minutes to transport the mixtures. Temperature requirement of asphalt stabilized aggregates Heating temperature of asphalt Heating temperature of mineral aggregate Factory temperature of mixture Storage temperature of mixture Discarded temperature of mixture 150 C~155 C 180 C~185 C 165 C~170 C 10 C >185 C

18 Practice and application Paving procedure The field paving equipment is showed below Tandem steel-wheel vibrator roller Rubber-wheel roller Asphalt paver

19 Practice and application Paving procedure The rolling strategy of machines, temperature controlling is detailed in Tables Rolling strategy of machines and temperature controlling Rollin g proces s Initial pressur e Repres s Final pressur e Type of roller two 13t tandem steel wheel vibrator roller (static pressure) two 26t wheel roller(vibration) two 13t tandem steel wheel vibrator roller (static pressure) Running speed(km/h) Rollin g cycles Rolling tempera ture( C) 2 to to 5 8 to to 6 2 to Requirement of rolling temperature Producing and mixing temperature ( C) 165 C ~170 C Arriving temperature ( C), 160 Spreading temperature ( C), 155 Initial compacting temperature ( C), 150 Re-compacting temperature ( C), 140 Final compacting temperature ( C), 120 Final temperature Wheel roller 115 of the surface ( C), Tire roller 105

20 Field measurements Compactness The core samples were taken from the field test sections, as shown in Figs. The thickness and compactness of core samples can be found in Table. Detection results of compactness Base type Thick ness Requir ement Compa ctness Requir ement Coring samples in the field K ~K (12cmATB) K ~K (18cmATB) K ~K (18cmATB) K ~K (18cmATB)

21 Field measurements Deflection Detection results of deflection Base type K ~K K ~K K ~K633K ~K Deflection

22 Field measurements Test conclusion and analysis thin. 1) Insufficient and uneven thickness The smoothness of sub-base is inadequate. the edge of the asphalt stabilized aggregates may be The differences of compaction thickness. 2) Insufficient and uneven compactness the segregate during charging, moving, discharging and paving. Temperature reducing because the roller did not compact in time. The limitation of roller machines caused the rolling speed could not keep up with the paving speed.

23 Existing problems Temperature caused segregation Gradation caused segregation Un-compacted core sample Surface segregations after compaction

24 Strategies

25 The low temperature, great temperature difference, severe freezethaw cycles and short construction period in cold and high altitude regions affect the construction of asphalt stabilized aggregates. This case study provides a reasonable guidance for asphalt stabilized aggregates in cold and high altitude regions. It suggests that the asphalt stabilized aggregates should obtain suitable compositions and structures based on the material optimization and optimal mixture design. Besides, effective and efficient temperature control, construction technology and organizing manage could guarantee the engineering performance of mixtures.

26 Feng Ma PH D, Associate Professor Vice Chair of Highway Engineering Department, Highway School, Chang'an University, China (+86)