Investigation on mechanical properties of geopolymer cementing reclaimed asphalt pavement
The continuous improvement of expressway network is of great practical significance in promoting the economic and social development of our country.However, the main material for paving expressway pavement is asphalt mixture.Asphalt cementing material and aggregate are non-renewable materials.With the gradual consumption of petroleum asphalt resources, the price of asphalt remains high.In order to achieve green development of highways and protect the ecological environment, the cost of aggregates is also increasing.The increase of asphalt and aggregate prices has seriously affected the development pattern of expressways.In addition, a large amount of asphalt pavement maintenance will produce a huge amount of reclaimed asphalt pavement (RAP) , which is currently applied to the new asphalt mixture by recycling, but the utilization rate of recycled RAP materials is low.In order to alleviate the shortage of petroleum asphalt resources and realize efficient utilization of RAP resources, a new type of Geopolymer (S-F Geopolymer) for cementing RAP is developed by selecting fly ash, slag powder, alkali activator and other auxiliars.The basic mechanical properties and strength formation mechanism of S-F Geopolymer are studied through compressive and flexographic tests.The results show that:1) Fly ash, slag powder, alkali activator and other auxiliaries are selected to develop a new type of Geopolymer cementing RAP (S-F Geopolymer).The effects of different slag powder content and alkali concentration on compressive and bending test results are investigation, and the best formula is obtained that fly ash:slag powder (mass fraction) =2:1, alkali concentration, modulus and water-binder ratio is 0.05, 1.2 and 0.3, respectively.2) The content of slag has a significant effect on the compressive strength of S-F Geopolymer, and the higher the content of slag, the higher the early strength.However, excessive slag content will cause microcracks in S-F Geopolymer material, which will have a negative impact on the flexion strength.Reasonable maintenance measures should be taken to inhibit the occurrence of microcracks, such as film covering.3) The effect of alkali concentration on compressive and flexion strength of S-F Geopolymer lies in the dissolution rate of active Si and Al elements in gelling materials, and has a great influence on the early strength of slag powder.However, when alkali concentration exceeds a certain value, the dissolution of fly ash and slag will be weakened.On the other hand, the phenomenon of"caustic expansion"will occur during the maintenance of S-F Geopolymer, which will adversely affect the mechanical properties of S-F Geopolymer.The influence of modulus on the strength of S-F Geopolymer mainly comes from the concentration of active silicon provided by the alkaline activator, which will make the structure of S-F Geopolymer denser and stronger.However, above a certain value, the dissolution of slag will be reduced and the active silicon elements will accumulate, thus weakening the mechanical properties of S-F Geopolymer.The research results lay a foundation and provide guidance for the theoretical research and field engineering application of geopolymer in cementing RAP.
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