The technology of asphalt overlay on old cement concrete pavement is usually called “white plus black”, which is widely used at home and abroad because of its good road performance, low cost and short construction period
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In order to ensure the expected service life and good road performance of “white plus black” pavement, it is necessary to strictly control all kinds of raw materials and every link of construction according to the design requirements
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Combined with the quality control of the construction process of the Nanjian Beihai Road Reconstruction Project (Nanjian Qinzhou section) of Guangxi Coastal Expressway, this paper focuses on the control measures of some key links of the construction quality in the “white plus black” road reconstruction project, mainly including the bottom grouting of cement concrete slab, the leveling of the original road and the control of the thickness of asphalt layer
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1 project overview Nanning Beihai section of Guangxi Coastal Expressway is a section of G75 (Lanzhou Haikou)
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It was completed and opened to traffic on November 1, 1997
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The section from Nanjian to Qinzhou is a two-way six lane highway with a design speed of 120km / h and cement concrete pavement
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The pavement structure of the original carriageway is 24cm thick C30 cement concrete panel + 18cm thick cement stabilized gravel (lime fly ash stabilized gravel) base + 18cm thick graded gravel (gravel)
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The reconstruction design is as follows: 4cm modified asphalt stone SMA-13 + 8cm modified asphalt ac20c + 3cm modified asphalt SMA-10 stress absorbing layer (also used as leveling layer) + anti cracking coiled material + cement concrete slab after thorough treatment of disease, and layer sticking oil is sprayed between each asphalt layer
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Among them, the treatment of the cement concrete slab includes: replacing the slab with defects, and after the treatment of the diseases of the base and subbase, the grouting treatment is carried out on all plates, and then the sand blasting is carried out
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2 grouting quality control 2.1 void condition of the original road: according to the test results before reconstruction, the average void ratio of the original road is 46.3%, and the lane with the highest void ratio is 59.8%, as shown in Table 1
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Considering the influence of traffic organization changes on the pavement during construction and the expected service life, all cement concrete slabs are grouted, and the deflection of slab corners is detected by FWD plate by plate after grouting, so as to meet the technical requirements of “the intercept of deflection curve under different loads is less than 0.03mm, the single point deflection is less than 0.14mm, and the deflection difference of adjacent plates is less than 0.06mm”; No It should be treated again until it is qualified
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2.2 construction process control (1) in order to facilitate continuous detection and recording, and ensure that the four corners of each slab can be detected, the cement concrete slabs are numbered according to the following rules
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Route direction and lane information: there are 6 lanes on the left and right sides (3 on the left and 3 on the left, Z on the left and Y on the right); the lanes from the median to the hard shoulder are 1 Lane, 2 lane and 3 Lane respectively
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Therefore, the lane numbers are Z1-Z3 and y1-y3 respectively
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Measuring line: there are two measuring lines in each lane during the detection process, which are line a and line B along the median to the hard shoulder
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Front and rear plate angle: according to the normal driving direction, the front plate angle is the front plate angle, and the rear plate angle is the rear plate angle
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In order to ensure that each plate corner is not missed, the electronic form as shown in Table 2 is used for statistics
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The qualified points are marked as “1”, and the unqualified points are marked as “0”, so that the position of the unqualified plates can be clearly distinguished
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Table 1 test results of original pavement void Table 2 statistical results of void test (2) according to the test data in the process of construction monitoring, the effect of grouting in rainy days is poor, and the qualified rate of initial test is only about 60%, while the qualified rate of grouting in sunny days can basically reach about 90%
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Therefore, grouting should avoid rainy season as far as possible
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(3) the grouting test results during the implementation of the project are shown in Table 3
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It can be seen from table 3 that the grouting effect of the side close to the median and the side close to the hard shoulder is worse than that of other places
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Due to the transformation of the central divider, the side close to the central divider is not constrained, and the slurry is easy to flow out during grouting, which can not achieve the expected effect; therefore, the twice grouting method can be adopted, that is, when the slurry flows out at the side of the central divider during the first grouting, the grouting shall be stopped, and the pressure grouting shall be carried out after 24 hours
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The poor grouting effect on the side near the hard shoulder is due to the continuous passing of construction vehicles in the grouting process, and the slurry has not yet formed strength
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This problem can be solved by strengthening the traffic organization and management
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Table 3 initial test results after grouting of the whole line 3 leveling of the original pavement after slab replacement of the project, the level is used to measure a section every 10m, and two points are measured for each section, which are respectively 1.25m and 13.35m away from the central line (i.e
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the outer edge of the cement concrete slab), and then the vertical section and cross section are fitted to calculate the leveling layer thickness of each section
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On the premise of ensuring the smoothness and pavement drainage, in order to control the investment scale, the leveling is only for the “mutation” parts, and the uniform settlement parts are not treated separately
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It can be seen from the data in Table 4 that the cost can be saved about 90% when only leveling the “mutation” position
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Table 4 Comparison of right slope adjustment schemes of k2073 + 870 ～ k2074 + 070 (200m long): it should be pointed out that when applying the steel wire lofting method considering the influence of uneven paving layer thickness, the actual paving thickness of each section should be calculated according to the measured data
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Asphalt layer thickness control asphalt layer thickness as one of the key indicators of quality acceptance, it is particularly important to control in the construction process
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At present, the commonly used thickness control method is to measure the thickness by core drilling after the asphalt layer is paved
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This method can directly judge the paving thickness of asphalt layer, but the number of core drilling is limited, the position of core drilling is greatly affected by human factors, and the representativeness is not strong, and core drilling detection is a kind of destructive detection, which will cause a certain degree of damage to the road
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In the implementation process of this project, the international advanced pavement radar detection system is used to carry out non-destructive testing on asphalt pavement, which has the characteristics of accurate data, high sampling rate and good safety
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It can control the thickness in the construction process and play the role of “correcting deviation in advance”
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It can be seen from the data in Table 5 that after the middle surface course is paved, the average value of the representative thickness is 10.2cm, and the thinnest section is only 9.3cm, which can not meet the design requirement of 11cm
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If the upper layer is paved according to the average 4cm, the final thickness representative value and qualified rate can not meet the requirements of the specification, which directly affects the evaluation results of the road
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Table 5 thickness control of k2039 + 309 ~ k2047 + 000 therefore, during the construction of the upper layer, it can be controlled according to the test results of each section
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From the final test results, it can be seen that the thickness representative value and qualified rate can meet the design and specification requirements
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5 ﹣ conclusion ﹣ combined with the construction process quality control of Guangxi Coastal Expressway Nanjian Beihai pavement reconstruction project (Nanjian Qinzhou section), this paper puts forward the control measures for the original cement concrete slab bottom grouting, the original pavement leveling and the asphalt layer thickness
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Practice has proved that the corresponding control measures should be taken for each link of construction, so that the possible problems can be effectively controlled in the construction process, and the construction quality of “white plus black” pavement can be guaranteed..
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