Effect of the moisture suction to thermal gradient of the porous asphalt concrete

Abstract

The global temperature increase and extreme climate have significantly influenced human life in the past decade This phenomenon is especially severe in the urban area since the heat island effect due to densely populated buildings and impermeable road pavements are more prominent Numerous studies have been conducted in the past on the effect of pavement types concerning the urban heat island and one promising solution is using the permeable pavement The benefit of using permeable pavement includes reducing noise managing rainwater runoff volume improving water quality and reducing the impact of heat islands effect Porous asphalt concrete (PAC) is a commonly used surface material for permeable pavement Studies in the past have shown that PAC can cool the pavement temperature as a result of increased air voids Some studies further incorporated moisture content in the previous concrete and numerically model the micro evaporation process of water and its effect to alleviate the pavement temperature However few studies that focused on experimentally quantifying the coupling effect of temperature and moisture content variation in the porous asphalt concrete This study was aimed to investigate the effect of the micro-evaporation and thermal properties to the temperature of porous asphalt concrete A laboratory-simulated thermal-hydro experiment was performed in this study with four types samples were used different mixtures two different proportions of oxidated slag incorporated PAC (80% and 50% slag) PAC with natural aggregate and dense grade asphalt concrete with natural aggregate Solar energy was simulated using infrared light and scenarios including 0% moisture and suction-water saturate conditions were designed to simulate different moisture conditions of PAC and time-series thermal and moisture properties of PAC were measured The water evaporation rate heat flux the gradient of temperature in the PAC slab were measured The results show that the surface temperature of PAC is higher than DGAC in dry conditions This is because the low thermal conductivity of PAC is difficult to transfer heat energy to the deep layer causing heat to accumulate on the surface But PAC is cool down faster than DGAC which can be imagined at night PAC can quickly cooling to the ambient temperature and making the night air temperature more comfortable while in a wet conditions PAC can absorb more water and facilitate evaporative cooling effectively reducing the pavement temperature moreover PAC-80OS has the best cooling performance cause using the oxidated slag which has a larger thermal conductivity than general natural aggregates so the heat conduction process is faster and this material can be used in PAC pavement

Date of Award	2020
Original language	English
Supervisor	Shih-Hsien Yang (Supervisor)