Research On Preparation And Flame-Retardant Mechanism Of Fire-Retardant Asphalt

With the rapid development of expressways in China, the number and size of highway tunnels have been growing dramatically. As cement pavement has a lot of weaknesses, it has become increasingly unsuitable for modern tunnels and gradually replaced by bitumen pavement in tunnel construction. However, the inflammability of bitumen poses great danger for tunnel operation. Although many extensive researches have been conducted on bitumen flame retardant (BFR), further in-depth studies are still necessary.This Paper starts with a literature review on the background of researches on flame retardant and flame-retarding technology in terms of high polymer and latest developments of BFR technology, which shows that it is possible to develop a new effective BFR through surface modification of halogen-free environmental-friendly flame retardant to improve the compatibility between retardant and bitumen. The Paper then presents a study on the development of new BFR and flame retardant bitumen by using coupling agent to modify the surface of flame retardant. Based on the findings, the Paper studies the flame retarding mechanism and analyzes and tests the performance of flame retardant bitumen mixture. The study mainly covers the following contents:1. Based on interface theory and compatibility principle, two new bitumen flame retardants with high activity, good compatibility with bitumen, and excellent flame retarding performance, are developed by respectively using Titanate coupling agent and Silane coupling agent to conduct surface modification (these two retardants are called BFR-Ti and BFR-Si throughout the Paper). Then FTIR, TGA and SEM are used to test, describe and represent the structure and property of said retardants. Results show that appropriate ratio of Titanate coupling agent to BFR is around 1.6% and that of Silane coupling agent to BFR is around 0.9%. After surface modification, new chemical bonds have been formed on bitumen surface, effectively improving its thermal stability and largely eliminating the occurrence of agglomeration.2. Two flame retardant bitumens are made by mixing bitumen with BFR-Ti and BFR-Si respectively. ZB is then added to test its synergy with the two bitumens and determine the appropriate ratio. FTIR, TGA and SEM are used to test, describe and represent the structure and property of said bitumens. Results show that appropriate granularity range of both bitumens is 2,000-2,500 and ratio of ZB to bitumen is both 9.0%. Results also show that ZB does not produce significant synergy with BRF-Si flame retardant bitumen as a result of chemical reaction between ZB and Silane coupling agent, but the amount of BFR has some relation to the rheological property of flame retardant bitumen.3. Inflammation of several flame retardant bitumens is studied to analyze the flame retarding mechanism, identify the correlation between the results of TGA and CCT, and analyze ZB's synergy with BFR-Ti flame retardant bitumen. Results show that in terms of inflammation property, compared to SBS modified bitumen, flame retardant bitumens have demonstrated significant changes regarding HRR, MLR, EHC and TIG and proved to be very flame retardant. Results also show that the breakdown temperature in TGA and corresponding TIG has sound correlation, high temperature carbon layer in TGA and residual carbon & HRR in CCT also have good correlation, and BFR-Ti-ZB flame retardant bitumen has shown significant synergy in the course of inflammation. In the course of inflammation, endothermic decomposition and carbonization occur to all flame retardant bitumen, indicating the flame retarding mechanisms is not single. As a result, the main flame retarding mechanisms is condensed phase flame retarding mechanisms, characterized by synergy and endothermic flame retarding mechanisms. The other flame retardant bitumens are the result of combination of condensed phase and endothermic flame retarding mechanisms.4. Tests are conducted to compare the properties of SMA13, AC 13 and GA10 respectively corresponding to SBS modified bitumen, BRF-Si flame retardant bitumen, BFR-Ti-ZB flame retardant bitumen. Real projects are studied to testify the road performance of flame retardant bitumen and its actual applications. Results show that compared to SBS modified bitumen, besides having bigger oil stones and improved moisture stability, flame retardant bitumen mixture boasts similar properties and therefore can meet pavement regulations. In addition, flame retardant bitumen can have satisfactory effect in actual application.