A TG-FTIR investigation into smoke suppression mechanism of magnesium hydroxide in asphalt combustion process

In this study, the combined thermogravimetry-Fourier transform infrared spectroscopy (TG-FTIR) technique was employed to analyze the influence of magnesium hydroxide (MH) on the volatile release in asphalt combustion process. The experimental results indicate that the combustion processes of asphalt and asphalt/MH composite are both multistage, and the volatiles are different in each temperature interval. After adding MH into asphalt, the temperature rise of asphalt matrix is inhibited due to MH thermal decomposition. Firstly, the water vapor dilutes or absorbs some carbon particles to hinder the soot nucleation and aggregation, and then smoke density is decreased. Secondly, the active magnesium oxide (MgO) promotes the tight charring layer generation on the asphalt surface. The layer hinders carbon particles and flammable volatiles from releasing out of asphalt, and the starting release time of volatiles is also deferred. The incomplete combustion residue of asphalt is absorbed by MgO to prevent droplet generation at high temperature. Also, the smoke nuclear and soot particles are reduced by the sorption of MgO. Finally, because MgO is alkaline, the acid combustion products are neutralized quickly to generate some compounds in asphalt. Because of the above effects of cooling, dilution, absorption and neutralization from MH, the purpose of smoke suppression is achieved, and the release amount of harmful volatiles is reduced, without any generation of harmful substances during asphalt combustion process. It is concluded that MH may be used as a new kind of environment-friendly and efficient smoke suppressant for asphalt.