Keywords: high temperature mixing and paving asphalt mixture; Pre-poured asphalt macadam; Small high temperature paver
The Akashi Strait Bridge is erected on the Akashi Strait between Wuzi in the vertical waters of Kobe City and Matsumi (Awaji Island) in Awaji-CHO, Jin Ming Prefecture. The main span is 1990.8m, and the structural system is a three-span double-hinged truss suspension bridge.
Highway connecting the four countries in Honshu: Kobe Awaji Mingmen Automobile Dedicated Road is accompanied by the completion and operation of Akashi Strait Bridge and related sections, thus connecting the national trunk highway network into a whole and contributing to the development of regional industry, economy and culture.
Akashi Strait Bridge is a steel deck. In order to improve the driving performance of vehicles, make up for the structural deficiencies and minimize the expansion devices, there is no precedent for multi-span continuous non-composite structures. The performance of high temperature mixing and paving silent mixing board was studied. The results show that the axial construction length of the bridge is limited, and the section direction is divided into five parts.
This paper summarizes the paving method of high-temperature mixed asphalt mixture and the overall construction of bridge deck pavement.
1 Overview of paving works
The construction area of the bridge deck pavement project of Akashi Strait Bridge in the Strait is about 92,000m2. The composition of pavement layer is subject to the pavement regulations of the four countries in this state.
According to the different types of highway bridge deck structure, steel bridge deck can be divided into upper and lower middle parts and shoulders with grids (stiffening truss beams are generally steel bridge decks. The construction area accounts for 88.5%, hereinafter referred to as the general stiffening part), and there is no grid (the full width of the stiffening truss beam is steel deck). The construction area accounts for .5%, hereinafter referred to as the full-width stiffening part) and the full width of the road truss beam above the anchor block is the steel bridge deck). The construction area accounts for 30%, hereinafter referred to as the road truss section, but the composition of the pavement is the same.
Asphalt mixture is mixed and spread at high temperature. In order to prevent foaming and enhance its flow resistance and slip resistance between surface layers, No.5 pre-poured macadam is selected, and the static pressure is 10kg/㎡.
2 surface treatment
For the steel bridge deck, in order to prevent it from rusting before paving, a thick film inorganic zinc-rich primer with a thickness of 50um is applied in the factory. However, the damaged parts of zinc-rich primer, the on-site welding parts and the parts where the pendant is disassembled shall be manually painted with organic zinc-rich primer on site. The reinforced truss surface material has been used for two years as the driving road to transport the automatic flat car to the site, and it has been exposed to the humid environment in the strait for a long time. Due to these factors, red rust, white rust and tire pollution can be observed.
Generally speaking, the surface treatment of steel bridge deck adopts one method of sand blasting or two or four methods of grinding wheel rust remover, brush and wire brush. However, in order to ensure its adhesion to the road surface, inhibit the foaming phenomenon of high-temperature mixture and improve the durability of the road surface, rust removal type is adopted.
Sand blasting is the most basic method to clean the steel deck of Akashi Strait Bridge, and the sand blasting density is determined according to the results of the test project.
The blasting density of the cleaning project varies from 50 to 300 kg/㎡, and it is divided into six sections. The rust removal effect of rhombic steel bridge deck in each section is observed by visual inspection. The change of spray density should be adjusted according to the cleaning speed, and the cleaning speed with a spray density of 300kg/㎡ should be 1.2m/min.
According to the results of the test project, according to different corrosion factors, four spray densities are formulated. According to the visual results of steel bridge deck, the construction scope of different spraying densities is formulated. When making the range, the vertical direction is 1m and the horizontal direction is the sweeping width of the sweeper. In this range, the highest spraying density is used. Immediately after cleaning, apply rubber asphalt glue (0.4L/㎡) twice as the adhesive layer.
3 high temperature mixing paving asphalt mixture pavement
3. Study on1Laying Method
The deck pavement of Akashi Strait Bridge is the pavement structure with the longest continuous span and the widest non-synthetic steel deck in Shikoku Bridge in Honshu. According to the experience of four-nation contact bridges in Honshu (such as Daming Gate Bridge and Seto Bridge), the thermal deformation of high-temperature mixing asphalt mixture pavement on non-synthetic steel bridge deck should be treated with caution. As far as the Akashi Strait Bridge is concerned, the laying scheme will be divided into three parts according to the single lane, which was originally a whole structure. Therefore, the performance of the assumed steel bridge deck is studied, and as a measure to eliminate the negative reaction, some bolts at the bearing are loosened.
However, some time before the paving work began, the steel bridge deck unexpectedly extended due to the increase of external temperature, the elongation of the expansion device was zero, and the paint on the expansion joint tooth plate peeled off. The reason is that the temperature between the stiffening truss and the steel bridge deck is as high as 25℃ when the bridge is erected (before laying high-temperature mixed asphalt mixture) due to the reduction of the spacing between the erection mechanical materials. During the construction of high-temperature mixing and paving asphalt mixture, the temperature difference is further increased, the structure is out of sync, and the construction efficiency is very low. Considering the actual laying conditions (basic data of construction width and construction speed), a detailed study is carried out.
During the research, the following points were considered:
(1) Try to avoid the construction joints in the cross-sectional direction and continue the construction as much as possible.
(2) No joint shall be set within the construction width range of longitudinal beam, longitudinal rib position and wheel load position.
(3) Avoid construction in summer, so as to avoid a large temperature difference between the stiffening truss and the steel bridge deck.
Assuming that the single lane construction width is divided into three parts, four parts and five parts, the following analysis and research are carried out on the steel bridge deck with general stiffening part and full width stiffening part.
(1) Limit of horizontal reaction force of bearing caused by horizontal bending.
(2) the limit of negative reaction of the bearing.
(3) Guarantee of bearing spacing.
(4) Guarantee the spacing of expansion joint devices.
According to the research results, the following paving methods are adopted:
① The assumption is based on the five-part division. In order to reduce the total heat, in comparison, continuous construction can be carried out in the general stiffening parts (when laying, the spacing of expansion joints should be specially managed, and when the displacement of expansion joints is close to 20mm, continuous construction should be interrupted and moved to other parts for construction).
② In order to restrain horizontal bending, two lanes are constructed at the same time (the middle lane is constructed last).
(3) The construction shall be carried out in blocks within the range of full width 5, and discontinuous construction shall be carried out on one slab.
In order to verify the accuracy of the above analysis and research results, a test project was carried out in three slabs (node 25 1- node 248, length 42.6m) (construction time 60min, construction speed 70cm/min, construction width 2.65m, and simultaneous construction of two lanes 1.6m), and the measurement time/kloc-0 was carried out. The following items are measured as the pavement progresses.
(1) Temperature of steel bridge deck.
(2) Bearing floating amount.
(3) the horizontal movement of the bearing.
④ Plane bending of steel bridge deck.
⑤ The spacing between expansion joint tooth plates.
The internal surface temperature of steel bridge deck varies with time, showing a difference, with the highest temperature of120 C, and the temperature peak appears about 10min (about 7m in length) behind the high-temperature paver. At this time, the external air temperature and the initial temperature of the steel bridge deck are about 22℃ and 25℃ respectively.
Here, in order to avoid horizontal construction joints in the full width range, the construction is staggered 1.5m before and after the slab boundary (node).
In addition, for the negative reaction force (uplift force) at the supports of G3 and G4 beams, the vertical floating deformation of the beams is measured when the constraints at the supports are released. The floating amount of the bearing changes with time, and the maximum floating amount reaches 9.7mm (G4 beam at node 250). The peak value shown in the figure corresponds to 5 ~ 6 minutes after the peak temperature of steel bridge deck appears.
The measured results show that the calculated values are basically consistent with the measured values. However, because the floating amount of the bearing is larger than expected, in order to reduce the negative reaction force of the bearing, the measures of loosening the bearing bolts were taken during the implementation of this project.
3.2 High temperature mixing asphalt mixture pavement
Because the construction is divided into two lanes and five parts at the same time, the construction width of high-temperature asphalt mixture pavement is narrow, so a small high-temperature paver (construction width is 0.4 ~ 2.0m) is used for construction.
Manual paving of pre-poured asphalt macadam. As the Akashi Strait is an important international waterway, it is not allowed to drop objects during construction. In addition to using rubber mats at the grid structure for health preservation, in order to completely prevent the pre-poured asphalt macadam from flying away, a mobile protective net is specially used.
In order to prevent molten joint material from extruding from the surface of high-temperature asphalt mixture when static pressure pre-poured macadam is applied at the end of pavement, the size of molding joint filler with a width of 40mm (thickness of 10mm) is changed to a width of 35mm (thickness of 5mm).
Bridge deck pavement began from June+10 in 5438, in order to avoid the summer construction with large temperature difference between stiffening beam and steel bridge deck. Five copies of the two lanes are built at the same time, and the first one consists of three parts. Fortunately, with little rainfall, the pavement construction was completed within 2.5 months.
High temperature mixing asphalt mixture shall be supplied by two permanent asphalt mixing stations at the same time, and the mixture ratio of main materials shall be consistent. Asphalt consists of straight-run asphalt (20~40) and Trinidad Lake asphalt (hereinafter referred to as TLA) in a ratio of 75: 25. The mixing method of TLA is to crush it into 20mm particle size in advance and measure it. After bagging, manually put it into asphalt mixer for mixing according to the set amount.
4 modified asphalt mixture surface layer
When paving in general stiffening section, full-width stiffening section and road beam section, the construction shall be carried out by joint method. The asphalt mixture used in the surface course adopts the modified asphalt type I (the fourth modified asphalt type I) specified in the bridge deck pavement standard (discussion draft) of Shikoku Contact Bridge in this state, which has high stability and good durability. In addition, considering the stability of coarse aggregate quality and the stability when it is supplied in large quantities, according to the results of X-ray diffraction analysis, the hard sandstone without iron sulfide produced in Kitakyushu City is selected. Asphalt mixture is the same as high temperature mixing, and two permanent asphalt mixing stations are used for simultaneous production and supply. There are no restrictions on the loading hoppers of the two asphalt finishers, but the surface of the supplied surface is specified, and it is confirmed that there is no difference in the physical properties of the mixture. Therefore, it can be judged that there is no problem in feeding two asphalt mixing stations at the same time.
In order to drain the road surface, a water-collecting hole for drainage is set at the edge of the shoulder, and the hole is filled with water-permeable oxidized polyurethane foam, and heated joint material is injected from it. At the joint filling position of the shoulder, a groove with a width of 10mm is cut with a dry cutter after the pavement is completed. Clean it with a sweeper and apply a layer of adhesive. In places where grooving is difficult, set up two overlapping templates in advance, and uncover the film after paving.
In addition, what are the shoulder settings above the base of the full-width stiffening part and the road beam part? 0? 4 10mm drainage pipe, so that rainwater seeping into the surface can be discharged in time.