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Investigation on Smoke Suppression Mechanism of Hydrated Lime in Asphalt Combustion 时间:2018-10-02 23:21   来源:未知   作者:admin   点击: 次 Abstract:In this study, cone calorimeter and thermogravimetric analyses were used to simulate the asphalt combustion process under the conditions of fire radiation and programmed temperature increase. The gaseous compositions and release rules were analyzed by infrared spectroscopy to investigate the influence of hydrated lime on the smoke suppression mechanism in the asphalt combustion process. The experimental results show that hydrated lime can promote the asphalt mastic surface to form a barrier layer during the combustion process. This barrier layer can reduce the burning intensity of asphalt. Although the compositions of gaseous products do not change much, the rates of CO production and smoke release are decreased. In addition, hydrated lime is alkaline and can thus neutralize acidic gases such as SO2 and reduce the toxicity of gaseous products. With the addition of 40 wt.% hydrated lime, the total smoke release and the CO release rate both decrease by more than 20% relative to the addition of the same amount of limestone fillers and decrease by more than 10% relative to the addition of the same amount of magnesium hydroxide flame retardant.
1. Introduction
  Asphalt is a combustible mixture composed of hydrocarbons and relatively nonmetallic derivatives, which is wildly used in road pavement and waterproofing systems [1, 2]. The combustion of asphalt is typically accompanied with a quantity of toxic smoke [3, 4], seriously endangering any personnel within the affected areas. To solve this problem, applying flame retardant to asphalt has become a common way to reduce the hazards associated with pavement during tunnel fires [5–12].
   Due to their nontoxic characteristics and their capability for smoke suppression, metal hydroxides are prevalently used to modify the flame resistance of asphalt [7–12]. Among them, hydrated lime did not initially attract the attention of researchers since it decomposes at a relatively high temperature that exceeds the ignition point of asphalt [13]. However, some recent studies have shown different results. Hydrated lime has been proved to promote the formation of a dense inert layer on the asphalt surface by carbonation in the combustion process [7], thus inhibiting the continuous combustion of asphalt, serving as an excellent flame retardant [14]. However, the mechanism of how hydrated lime affects the smoke release of asphalt during combustion requires further study.
The smoke release characteristics of asphalt during combustion have been investigated by the combination of a simulated combustion test platform and smoke analyzer. Wu et al. [4] studied the smoke release law of asphalt and binder at a high rate of heating by combining a fixed bed combustion test and infrared spectroscopy. It was observed that the main gaseous products from asphalt combustion include CO2, CO, NO, NO2, and SO2, and that the volatile components of asphalt are the key factors influencing the smoke release rate (RSR) during combustion. Puente et al. [15] studied the combustion characteristics of an asphalt mixture at a radiation intensity of 50 kW·m−2 by the combination method of cone calorimeter-Fourier transform infrared spectroscopy (FTIR) and analyzed the release characteristics of CO2, CO, and SO2 in combustion. Additionally, Xu and Huang [11, 12] analyzed the combustion procedure of asphalt binder during the process of temperature rise by thermogravimetric analysis (TGA)- FTIR, revealing the mechanism of how Mg(OH)2 affects the release of gaseous products during the various reaction stages of asphalt. In addition, by TGA-MS (mass spectrometry) analysis, Zhao et al. [16] investigated the components and release characteristics of smoke produced from the combustion of four components of asphalt. These studies indicate that combustion test methods [4, 15], especially the fixed bed combustion test and cone calorimeter, can be used to simulate the actual burning environment with a high rate of temperature rise and strong radiation, but it is challenging to analyze the specific reaction process accurately. Temperature-programmed combustion test methods [11, 12, 16], such as TGA, are more effective in analyzing the different smoke release characteristics and mechanisms of asphalt combustion during each reaction temperature range, but the reaction condition is quite different from the real situation. A comparison between these two methods is still lacking in the research conducted to date.