About GTM rubber modified asphalt concrete pavement construction

Summary: waste tire rubber powder particles mixed into the asphalt concrete layer in the form of wear, improved pavement performance, extending the pavement life, saves the life of the road repair and maintenance funds and maintain a good level of service roads, but also recycling of waste tires to be so, reduce the pressure on the environment, and has broad application prospects. This article focuses on analysis of asphalt concrete using GTM method with the ratio test, then the construction of key technologies.

Keywords: GTM method, powder asphalt concrete mix design, construction

1GTM powder status and characteristics of asphalt concrete
1.1GTM powder asphalt concrete pavement Profile
Waste tire crumb rubber asphalt is processed into powder particles greater than 15% of blending into the asphalt to go, then add modifiers or other polymers and has been the way with cementitious material.

GTM crumb rubber asphalt concrete is to use the U.S. Corps of Engineers rotating shear test machine (GYRATORY TESTING MACHINE, referred to as the GTM for Mixture design, the use of crumb rubber asphalt mixture production, the paving, rolling obtained by forming asphalt pavement . GTM for asphalt mix design, in 1978, included in the American ASTM standards, was amended in 2003, it's possible to simulate the actual effect of cars on the road, so as to reasoning approach to the design asphalt mixture, the shear strength of asphalt mixture is greater than the shear stress suffered, and to strain control in the appropriate context, can reduce the heavy traffic asphalt pavement rutting occur under, over, pro package and other damage.

The company's beginning in 2009, combined with geographical features of Anhui Province, and gradually promote the use of the new technologies, new materials, .2010 in Bengbu City Road South Exit Highway S207 mussels renovation project, Bengbu City, Dragon and other several road projects around Lake Engineering applications, with good results. powder asphalt concrete regional climate and wide applicability, Anhui province Jieke application for new construction and renovation of various grades of roads and urban road surface layer of the structure.

1.2 Features
1.2.1 improved road performance
Rubber Powder for Asphalt Asphalt concrete help to improve the high temperature stability, fatigue resistance, water stability and low temperature properties such as road performance, improved surface quality, longer service life.

1.2.2 reduce the construction cost
Compared to ordinary asphalt and SBS modified asphalt, asphalt rubber powder can reduce the cost per ton of 50 to 70 yuan.

1.2.3 energy saving
recycling of waste tires, reduce its environmental pressures, in line with our current construction of a conservation-oriented society and the development of circular economy policy is an effective way of recycling, have a high social benefits. Reducing urban road traffic noise have significant effect.

2 Process Principle
GTM method using mix design and construction quality control as standard, GTM rotating compaction density is generally Marshall compaction density of 1.02 to 1.04 times, which can be effectively avoided due to indoor molding method and molding method of construction does not match the actual cause degree of compaction over one hundred, and raise the standard of compaction, thus further improving asphalt pavement performance.

Crumb rubber asphalt concrete construction points of production, transport, paving, rolling four stages, the most central aspect is the temperature control and the choice of rolling way. Crumb rubber asphalt temperature than ordinary asphalt construction increased 20 ~ 25 ℃, than other asphalt increased 10 ~ 15 ℃. powder dosage of not less than 15% (or 17.6% in mixed (Mixed, this article describes the method to be used in the finished powder mixed asphalt.

3 construction points
3.1 Mix Design
3.1.1 GTM Asphalt Mixture Design Principles
Mix design pressure is expected by the design unit road transport vehicles in accordance with a representative of the vehicle tire pressure to determine the ground. Designed dense-graded asphalt mixture powder-cement ratio should be controlled within the range of 1.2 to 1.6, using GTM to determine the best equilibrium good asphalt content and standard density, gradation using a continuous dense-graded asphalt mixture.

3.1.2 GTM mix design testing procedures
GTM Test Method mix design using three-step method, into the target mix design stage, the production mix and production mix design validation phase.

Goals with the design phase: the actual use of raw materials after passing inspection, the mix design, excellent mineral aggregate gradation, determine the design asphalt content, the rutting test, low temperature bend test, such as freeze-thaw test split mix design testing, meet the requirements as a target mix for the mixing plant to determine the proportion of cold feed silos, feed rate and test mix used.

Production with the design phase: According to the target mix to determine the proportion of cold material and feed rate, in the hot silo reclaimer for material grading tests, should be expected to take the heat for each thermal material hopper release, with loaders to fully take over the venue into the mix hardened, take a representative for the heat storage material gradation tests to determine the hot mix silo. and take the target amount of asphalt mix design and + -0.3% in three asphalt content tests and test mix for GTM, GTM through indoor tests and sample test mixing machine, integrated product mix to determine the optimum asphalt content and density standards, which determine the optimum amount of asphalt mix design with the goal difference between the results value not greater than + -0.2%, while the appropriate choice of mesh size and angles, as far as possible the feeding hopper of the general heat balance.

Validation phase of the production mix: mixing machine according to production test results mix mix, paving the test section, and sampling to verify the GTM, and drill core from the road testing the size of voids, which determine the production of standard mix. Test mix test shop items must be legal, construction, supervision and other parties concerned to implement the relevant units, which determine the mix of standards must be approved by the supervising engineer. The standard mix of mineral aggregate gradation in the synthesis should include at least 0.075mm, 2.36mm , 4.75mm, and the nominal maximum size of the sieve through rate is close to optimal Engineering design of the grading range values, and to avoid the 0.3 ~ 0.6mm at a "hump." mix of established standards, should again rutting test and water stability test.

Determine the fluctuation range of construction grading permit, according to the standard mix and quality management requirements in the allowable fluctuation range of the sieve, with the development of construction with the level control to check the production of asphalt quality standards established by the design with than in the construction process shall not be changed. the production process should strengthen the tracking and detection, and strictly control the quality of materials approach, in case of material changes and has been tested and graded asphalt mixture, GTM specification does not match the requirements, should be re- mix design.

3.2 Construction Preparation
Road construction before the deck should be dry and clean, the measurement of construction ambient temperature, air temperature should be not less than 10 ℃, the surface temperature should be not less than 15 ℃, rain and wind not construction.

3.3 Asphalt Mixing Process Links to free download http://www.hi138.com using DG-4000S-type batch asphalt mixing plant for mixing, mixing time is determined according to the test mix 50S (dry mix Time 6S, wet mixing time, 44S, mixing plant by plate printing online testing, to avoid the low content of less than 0.075mm particle phenomenon, mixing plant hot bin dosage of 5 # positions: 4 # positions: 3 # positions: 2 # position: 1 # positions: slag = 27%: 21%: 19%: 12%: 17%: 4%, the amount of asphalt layer is below 4.4%, the top layer of 5.1% crumb rubber asphalt using asphalt road 70 # asphalt.

GTM normal construction of asphalt concrete temperature range
3.4 Transportation of asphalt concrete, paving process
3.4.1 paver leveling mode operating conditions and
Using ABG423 and LTU90SC echelon paving paver, paver two apart 10 ~ 30m, close to the front carved with the host, to fight a wide paver 8m, due to the higher median curbs, tightrope more difficult by the decided to field studies in the curbs on the left side of the laying of aluminum bar, painted on the curbs on the paving line at any time to adjust, balance beam to walk the middle, near the shoulder of the Vice-machine, the width of paver fight 7.5m, the middle of the paver good level, take the "sled", set up steel wire used for leveling the left, two paver paving layer vertical joints using thermal seams.

3.4.2 truck unloading material way
Paver three transport vehicles before paving can begin when the vehicle away from the paver stopped at 10 ~ 30cm, paver to avoid collision, the process of discharging gap hanging on material transport vehicles, rely on paver drive forward, back material, the first starting from the top not too high, feed hopper to be filled by the paver, slowly and evenly to the paver hopper discharge, when discharging the mixture to avoid overflow.

3.4.3 paving temperature
Two paver with 15 dump truck cycle operation, the paving material transport vehicles to reach the scene, there is someone with a plug-in digital thermometer to measure and record each vehicle mixture of material temperature and paving the scene temperature.

3.4.4 paving speed and initial vibration compaction method
Choose paving paver speed 2 ~ 2.5m/min, so slow and uniform, uninterrupted paving. Paver in place, the first warm-up 40 to 50 minutes so that the screed temperature reaches 100 ℃ or more, beginning paving, a personal check thickness and flatness, as the vibration frequency and amplitude matched ram, so paving the surface layer have sufficient initial strength to determine the hammer 3.

3.5 Technology to eliminate pavement segregation
Paver screed to do warm-up, and vegetable oil, wipe the end of the screed, the screed at the end is not rough.

Paver adjust to the best working condition and adjust both ends of the spiral distributor automatic material level, causes the feed door opening, the rate of chain plate and screw feeder speed to match the distributor, screw distributor of mixture slightly above the surface of spiral distributor 2 / 3 degrees, the screed plate to the mixture before in the whole wide range of highly consistent, to avoid the phenomenon of segregation occurs paving layer.

Remain uniform in the paving process forward, to minimize the number of close fighting, fighting close to shorten the time, to avoid paving close fight segregation phenomenon.

3.6 compaction of asphalt mixture
Rubber modified asphalt concrete are particularly sensitive to temperature, such as rolling too slowly, the temperature dropped asphalt powder compaction is very difficult, so using the compaction program: initial pressure with 2 sets of double-drum roller in accordance with the two side by side paver paver paver width followed by the shoulder belt to grab at the RCC, RCC is 2 times the number of times, roller compacted using vibration forward and backward vibration, adhere to the "high-frequency, low-amplitude, time rolling "principle, speed control described in the following table:
Asphalt compaction program table (each paver
Temperatures are in the initial pressure above 160 ℃, re-pressing temperatures were above 140 ℃, rolling end temperature is not lower than 120 ℃.

3.7 asphalt concrete surface layer of loose Shop coefficient
By paving the bearing layer under the front elevation measuring point, paving the same measuring point elevation, and after rolling the same measuring point elevation of the test calculation, repeated than for verification, the measured coefficient of 1.2 pine shop.

3.8 treatment of construction joints
Vertical construction joints using thermal seams, leaving the front paver temporarily rolling 10 ~ 20cm wide, as part of the elevation plane after the shop, and a 10cm layer of paving around the overlap to form in the hot joints to the final rolling to eliminate cross-stitch seams.

Horizontal construction joints with flat seams, kerf time paving mixture compacted in the end not yet completely cooled before hardening. With three-meter straightedge along the vertical position, in the paving section of the end of the ruler was a cantilever state, to share ply with the ruler to set joint position of disengagement with the artificial plane together to form a vertical joint surface, and coated with asphalt, until the next horizontal construction with roller compacted. compacted compaction roller is located has been road, miss the new overlay 15cm or so, then every pressure again, move to the new overlay 20cm or so, until all of the new overlay, and then to the vertical rolling. transverse horizontal seams at the required smooth, tight.

4 Conclusion
September 2010, the Bengbu Municipal Transportation Agency's technical appraisal, as well as in Anhui Science and Technology Information Institute search for new Technology, rubber modified asphalt construction Technology is advanced in the province, which formed a key Technology construction method was named the 2010 level in Anhui Province construction method.


References:
[1] asphalt pavement construction specifications (JTG F40-2004. People's Communications Press, 2004.

[2] road asphalt pavement construction specifications (JTJ 036-98. People's Communications Press, 1998.

[3] Tianjin Municipal Engineering Bureau, Tianjin waste tire rubber modified asphalt pavement technology procedures (J10732-2006. Links to free download http://www.hi138.com