The technical requirements and conditions for the recycling of old asphalt pavement are comprehensively affected by the original asphalt pavement situation, the design requirements of new or maintained pavement, traffic load, climatic conditions and other factors, so the asphalt pavement recycling technology needs to be adapted to local conditions. In this paper, the effect of rap content on the properties of asphalt mixture was studied. By analyzing the volume index, water sensitivity and rutting resistance of recycled asphalt mixture with different RAP dosages, it was found that the RAP content had a significant effect on the above properties. Further analysis of the performance of the prepared asphalt mixture believes that the asphalt mixture of this project can be used for recycled asphalt mixture.
Keywords:
Asphalt mixture | rap |Water Sensitivity |Resistance to rutting.
At present, the use of recycling technology and related equipment, and the use of old asphalt and related materials to re-pave and cover roads, has become the preferred solution for road management departments for the following reasons:
1) Reduce the impact on the environment, due to the abandonment of crushed stone and the distillation and refining of asphalt, the energy consumption and pollution will be greatly reduced;
2) The cost of mining stone is getting higher and higher, and stone resources are decreasing;
3) Asphalt, aggregate and other related old asphalt pavement paving materials can be recycled asphalt, reducing a lot of costs;
4) If recycling equipment and technology are adopted, the asphalt pavement can be recycled and renovated and opened to traffic at the same time, which can effectively reduce traffic congestion
5) With the development of scientific and technological means, the old asphalt paving material after the use of the first can be prepared to produce a recycled asphalt mixture with better performance;
6) The state attaches more and more importance to asphalt recycling, and puts forward certain preferential policies in asphalt recycling.
The technical requirements and conditions related to the recycling and utilization of old asphalt pavement will be affected by comprehensive factors such as the condition of the old asphalt pavement, the design requirements of maintenance or new pavement, traffic load and climatic conditions, so the asphalt pavement recycling technology needs to be combined with local conditions and local conditions, and the best solution and best effect of asphalt pavement regeneration. In this paper, the effect of RAP content on the performance of plant-mixed hot recycled asphalt mixture was studied in combination with a project, in order to further improve the construction quality of the project and ensure the service level of pavement.
Experimental materials
Bitumen properties. The performance index of asphalt is tested according to the "Test Regulations for Highway Engineering Asphalt and Asphalt Mixture (JTGE20-2011)". The test results are shown in Table 1 and Table 2.
Aggregate performance. The performance index of aggregate is tested according to the "Highway Engineering Aggregate Test Regulations (JTGE42-2005)". The specific test results are shown in Table 3 and Table 5.
According to the grading characteristics of the on-site stone and the screening results of the RAP material, the gradation of the recycled asphalt mixture aggregate is shown in Figure 1.
Test results and analysis
Effect of rap content on volume index.
In this part, the Marshall test will be used to study the influence of RAP content on the volume index of asphalt mixture, and the test results are as follows.
The above results can be found that the RAP content has a significant effect on the volume index of asphalt mixture. On the whole, when the amount of new asphalt is the same, with the increase of RAP content, the saturation and gross bulk density of asphalt increase, and the stability and porosity decrease. Further analysis of the above results can find that the volume index requirements of recycled asphalt mixture under almost all working conditions can meet the required values of the specification.
In order to better analyze the performance of the recycled asphalt mixture under the condition of each dosage, the optimal asphalt dosage (oil-stone ratio) of each asphalt mixture was determined according to the above-mentioned volume index change law and the results of the previous production experience in the nearby area, as shown in Table 6.
In a follow-up study, the asphalt mixture will be formed at the optimal amount of asphalt and its various road properties will be analyzed.
Effect of RAP content on water stability of asphalt mixture.
In this section, an indirect tensile test is used to study the water stability of a recycled asphalt mixture. The analysis of the figure below shows that with the increase of RAP content, the indirect tensile strength of asphalt mixture gradually decreases, and on the whole, its decline is about 10%.
The test results of the splitting strength ratio of each asphalt mixture are shown in the figure below, and the residual splitting strength ratio of all asphalt mixtures is greater than 80%. Similar to the results of the indirect tensile test, the residual splitting strength ratio of each asphalt mixture decreases with the increase of RAP content. This indicates that when the RAP content is too high, it may cause early water damage to the road surface.
Effect of RAP content on rutting resistance of asphalt mixture.
In order to analyze the influence of different RAP dosages on the rutting resistance of asphalt mixtures, the hamburg rutting test was used to analyze the deformation of each asphalt mixture under repeated loads. The results are shown in the figure below.
The analysis of the above results shows that the depth of each asphalt mixture is increasing rapidly in the initial loading stage, which is caused by the secondary compaction of the asphalt mixture. Further analysis shows that with the increase of RAP content, the initial degree of compaction gradually decreases. When the number of load action is further increased, the rutting depth of each asphalt mixture also increases gradually, but on the whole, the higher the RAP content, the less the rutting depth increases. When the load is applied to 8000 times, it can be found that the rutting depth with 35% RAP content is the smallest, followed by the asphalt mixture with 25% RAP content and 15% RAP content, respectively. The asphalt mixture with a maximum rutting depth of 0% rap content was the largest.
Conclusion
1) Through the performance test of recycled materials in physical engineering, it was found that the RAP content had a significant effect on the volume index of asphalt mixture.
2) With the increase of RAP content, the water stability of asphalt mixture is worse, which means that when using recycled asphalt mixture in rainy or wet road sections, the upper limit of RAP content should be controlled, so that the recycled asphalt pavement has better water damage resistance.
3) Increase the RAP content, the better the rutting resistance of the asphalt mixture. For this characteristic, higher levels of RAP material can be considered for heavy loads, long longitudinal slopes, or other rut-prone road sections. However, at the same time, the properties of recycled asphalt mixture such as water damage resistance and fatigue resistance should be considered.
The full text was first published in the 6th issue of the technical application technology edition of "Highway Transportation Technology" in 2019.
One of the most common rutting instruments on the market, each test wheel is equipped with an independent servo motor drive, which can terminate the operation of one of the test wheels at any time, ensuring that each test piece can be analyzed individually. Now you can run wet or dry tests on two test wheels, or run them separately in dry and wet conditions at the same time.
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