# Investigation on the Factors Affecting the Exhaust Degradation Performance of Porous Pavement Mixtures with Nano-TiO2 Photocatalysts

## TL;DR

This study explores how porous pavement materials with nano-TiO2 photocatalysts can degrade exhaust pollutants, focusing on factors like void ratio and photocatalyst dosage.

## Contribution

The study introduces a new method to evaluate the exhaust degradation performance of porous pavement mixtures with nano-TiO2 under various conditions.

## Key findings

- Degradation rates of NO and CO followed a 'slow–fast–steady' pattern, while NO2 and HC followed a 'fast–slow–steady' pattern.
- Increasing void ratio and photocatalyst dosage improved degradation rates and reduced equilibrium time.
- Porous cement concrete showed faster initial degradation than porous asphalt mixtures.

## Abstract

The substantial voids of porous pavement materials permit light and exhaust pollutants to infiltrate to a considerable depth. Consequently, utilizing porous mixtures as carriers for photocatalytic materials enables greater exposure to an environment conducive to the exhaust degradation reaction. This study employed porous asphalt mixtures and porous cement concrete as carriers for photocatalytic pavements. Various amounts of TiO2 were incorporated as photocatalysts to produce eco-friendly pavement materials with exhaust degradation capability. Based on a self-developed apparatus and methodology, its exhaust degradation performance was evaluated under different preparation conditions and pavement structures. The influences of void ratio, photocatalyst dosage, pavement type, and pavement thickness on the exhaust degradation function were examined. The degradation rates of NO and CO among the four monitored pollutants were observed to follow a three-stage pattern of “slow–fast–steady”, while the degradation rates of NO2 and HC followed a “fast–slow–steady” pattern. Increasing the void ratio and the photocatalyst dosage yielded similar effects on exhaust degradation efficacy, enhancing the degradation rate and reducing the time required to reach equilibrium. The increase in the void ratio of porous asphalt mixtures and porous cement concrete reduced the time required to reach equilibrium by an average of 4.4 and 2.3 min for the four pollutants monitored, respectively. Increasing the dosage of photocatalytic material by 2 kg/m3 increased NO degradation by an average of 1.5% and reduced the time required to reach equilibrium by an average of 0.8 min. The degradation rate of porous cement concrete in the first reaction stage was faster than that of porous asphalt mixtures, and the time required to reach equilibrium state increased by 2 min compared to that of porous asphalt mixture. And the impact of specimen thickness on exhaust degradation performance was minimal.