1. 1 The cement used as the test material is ordinary silicon 325# (conch brand) produced by Anhui Wuhu Conch Group. The aggregate is limestone macadam produced by Wuhu Jingshan Stone Factory, which is actually used in Wuxuan Expressway. * * * is divided into four grades (square hole screen): 0~4.75, 4.75~9.5, 9.5~ 19 and19 ~ 37.5 mm.
1.2 See table 1 for the gradation of mixture ratio test. The modulus and strength test are compared with three kinds of gradation in mix design. In the shrinkage performance test, in order to understand the shrinkage characteristics of cement macadam under the condition of small cement dosage, the recommended gradation 2 and three different cement contents (4%, 5% and 6%) were used for analysis and comparison.
Manufacture and maintenance 1.3 specimen was formed by static pressure method, and the specimen size was divided into two specifications [1], one was φ 15× 15 cm cylindrical specimen, and the compressive modulus, splitting modulus, compressive strength and splitting strength were tested. The other is 10cm× 10cm×40cm middle beam specimen, and the dry shrinkage and temperature shrinkage tests are carried out. The forming parameters of the sample are shown in Table 2. After molding, the specimen was sealed with plastic bags and placed in a standard curing room (temperature 20 3℃, relative humidity above 90%) for moisture conservation.
2. Resilience modulus (static and dynamic) test Semi-rigid base modulus is an important parameter in pavement design and analysis, which reflects the deformation characteristics of semi-rigid materials under load.
The determination of modulus of pavement materials in China is mostly based on static tests. The stress state of the specimen in this method is quite different from the real stress state of the pavement structure, which can not truly reflect the actual mechanical properties of the pavement material. In this experiment, MTS8 10 material testing system is used to test the compressive resilience modulus (static and dynamic) and splitting modulus (static and dynamic) of semi-rigid base.
MTS test system has perfect dynamic test function, and can set dynamic loading program (waveform, frequency, loading sequence, loading interval, etc. ) according to the test needs. The loading of the system is controlled by hydraulic servo system, and the loading frequency does not exceed 30Hz. Foreign research shows that the actual stress frequency of pavement materials is generally around 10Hz, which is suitable for the requirements of MTS test system.
The maximum load of the test is 30% of the compressive strength of the specimen, and appropriate adjustments are made in the test to ensure sufficient elastic deformation during the test, which can also be compared with the research results of similar tests. According to specifications for design of highway asphalt pavement (JTJ0 14-97), cement stabilized macadam tends to be stable gradually after 3 months, and the determination of design parameters should be based on the age of 3 months. In this experiment, the modulus of 3 months old was measured, and the test results are shown in Table 3.
The same gradation and different cement content have little effect on modulus. In addition, it is known that the dynamic modulus of compression test is 5.3~6 times of the rebound modulus under static load. The dynamic modulus of splitting test is about 3 times of the static modulus. Obviously, there are obvious differences between dynamic modulus and static modulus. What modulus parameters are used in pavement structure analysis has great influence on fatigue life [2]. Therefore, in pavement design, the performance parameters of the materials actually used in the proposed road should be systematically tested to reflect the parameter values in line with the actual situation.
3. Strength test and growth law This test tested the compressive strength and splitting strength of three gradations for comparison. For the recommended gradation 2, the unconfined compressive strength and splitting strength of six ages (7d, 14d, 28d, 60d, 90d, 180d) were tested respectively, and the growth law of strength with age was analyzed by using three parallel specimens.
For gradation 2, from different ages, the compressive strength and splitting strength increase with the increase of cement content in the range of 4~6% in this test. There is a good relationship between compressive strength and splitting strength, and the ratio of compressive strength to splitting strength varies from 7.833 to 9.830.
4, indoor shrinkage test
4. 1 Dry Shrinkage Test Wuxuan Expressway line area belongs to the Yangtze River system, with developed surface water system, large annual rainfall and annual average humidity of 80%. Therefore, it is particularly important to study the drying shrinkage test of cement stabilized macadam base. At present, there is no uniform standard for measuring the drying shrinkage characteristics of semi-rigid base materials. In this experiment, hand-held strain gauge (accuracy 0.00 1mm) was used to measure the shrinkage deformation of trabecular bone at a certain water loss rate.
Three kinds of grade 2 cement with different cement contents (4%, 5% and 6%) were used to prepare indoor specimens, and the forming pressure of the specimens was 500-550 kN. After 7 days of heat preservation and moisture preservation, take out the specimen, install the probe on the top surface of the specimen with a standard distance of 20cm, and dry the specimen under natural humidity. The indoor temperature of this experiment is always kept at about 20℃. Observe the weight and deformation of the specimen at different times until the water content no longer decreases and the volume of the specimen remains basically unchanged.
; The shrinkage test * * * tests the deformation of 14d, and calculates the shrinkage coefficient α d according to the accumulated shrinkage strain: α d = ∑Δε di/∑Δε ω i (formula 1).
Where: σδεdi cumulative shrinkage strain (10-6); σδεωI lost water.
4.2 Temperature Shrinkage Test
1) this test adopts JNZS-200 1A pavement material expansion and contraction tester developed by the key laboratory of road and traffic engineering of Tongji university. Take out the cured 14d specimen, install the 20cm probe, and then put it into the pavement material temperature shrinkage tester.
2) Temperature Range According to the climatic and hydrological data of Wuxuan Expressway, the annual average temperature in this area is 16.6℃, the annual average maximum temperature in Leng Yue is 2.7℃~2.0℃, the extreme minimum temperature is -8.9℃, and the annual average maximum monthly temperature is 27℃~28.6℃. Therefore, the annual temperature control range is 25℃~-5℃.
3) The initial temperature of temperature shrinkage test is 25℃. After standing at the set temperature for 6 hours, take out the sample and quickly measure the deformation of the sample with a hand-held strain gauge. Then put the specimen back into the temperature shrinkage instrument, seal the temperature shrinkage instrument, and adjust it to the next set temperature for the next test.
4) Calculate the temperature shrinkage coefficient αT according to formula (2), where ∑ΔΔ ε t is the experimental deformation at the temperature interval Ti+ 1-TO, and the temperature shrinkage coefficient of the same specimen is the average of parallel tests.
α t = δ ε t/(Ti+ 1-t0) Formula (2)
Where: δ ε t cumulative temperature shrinkage strain (×10-6); Current temperature of Ti+ 1 (℃); T0 initial temperature (℃).
It can be seen from Table 7 and Figure 3 that the temperature shrinkage strain of cement stabilized graded macadam increases gradually with the decrease of temperature, and the change of cement content has no obvious effect on the temperature shrinkage characteristics of cement macadam between 25℃ and -5℃. Generally speaking, in the positive temperature range, the dry shrinkage strain of semi-rigid base material is much less than the warm shrinkage strain.
5. Conclusion
Based on the test of modulus, strength and shrinkage of cement stabilized macadam base mixture of Wuxuan Expressway, the growth law equation of compressive strength and splitting strength with age is established, which has good correlation and can provide reference for future engineering construction quality control. The elastic modulus of semi-rigid base materials measured by different test methods is quite different, and the static modulus and dynamic modulus are also obviously different. There are also some differences in strength indexes, and the actual working state of pavement structure (mechanical model, material properties) is far from the current static mechanical system, so it is particularly important to study the dynamic characteristics and dynamic parameters of pavement structure under dynamic load. Semi-rigid base material will shrink when the temperature or humidity changes, and it is easy to crack. When the asphalt pavement surface is thin, it is easy to form reflection cracks. The test of dry shrinkage and temperature shrinkage characteristics will provide important guidance for future construction and provide basis for further analysis of pavement cracks.
For more information about project/service/procurement bidding, and to improve the winning rate, please click on the bottom of official website Customer Service for free consultation:/#/? source=bdzd