a b s t r a c t  ：Phosphate type single alkyl oxygen base titanates TM-P was used to modify the surface of phosphorus slag powder in this paper. The surface characteristics and modification mechanism of phosphorus slag particles were characterized by using Scanning Electronic Microscopy (SEM). The effects and mechanism of the surface modified phosphorus slag powder to the asphalt and asphalt mixtures were analyzed by Fourier Transform Infrared Spectroscopy (FTIR), dynamic shear rheological test (DSR), Marshall test, rut- ting test and freeze-thaw splitting test. The results show that phosphorus slag powder modified by TM-P (10% by weight of the powder) enhance the compatibility with asphalt, resulting in the increase of anti- aging, rutting resistance and water damage resistance of asphalt  mixture.

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1. Introduction

China is full of phosphate and the total storage is only after Morocco in in the world [1]. According to statistics, 8–10 tons of phosphate slag will be produced with the average production of 1 ton of yellow phosphorus. China produces nearly 900 million tons of phosphate slag every year, resulting in serious waste of land resources and groundwater pollution [2,3]. Hence, the application of phosphate slag into highway construction is not only conducive to environmental protection and resources conservation but also beneficial  to  economic development.

Due to the superior characteristics of powder material, inor- ganic micro powder has been selected as one of the optimal choice to improve the performance of asphalt and mixture [4]. As one of the inorganic micro powder, phosphorus slag powder has  great specific surface area and high surface energy because its particle size is too small to micron or even nanometer level. Under the Cou- lomb force and van der Waals force, the powder particles will be reunited, contributing to performance degradation   [5,6].

At present, phosphate slag is mainly used in the field of building materials. As a raw material or modifier for cement, phosphorus slag powder can significantly enhance the strength, workability and durability of cement and cement concrete [7–11]. Furthermore, it can also be used as the raw material to produce phosphorus slag Brick and self-leveling material [12]. In addition, due to full of Si, P, Ca and other necessary elements for the growth of crops, phosphate slag is commonly processed to produce agricultural fertilizer [13]. However, there are few studies on the phosphate slag powder selected as asphalt or asphalt mixture modifier. Paul T. Foxworthy et al. have shown that phosphate slag-based slag aggregates can be successfully applied to asphalt concrete [14]. Our research team have found that the addition of phosphorus slag powder can improve anti-aging,  rutting  resistance,  flame  retardant  of  asphalt mixture . Due to the nature characteristic of inorganic, polar and sur- face hydrophobic of phosphorus slag powder, the compatibility dif- ference between phosphorus slag powder and asphalt will exist, which will lead to separation between the two materials and phos- phorus slag powder disperse uneven and is easy to segregation, thereby decreasing some aspects of road performance.

Therefore, how to reduce the agglomeration of the ultrafine par- ticles of phosphorus slag and improve the interface compatibility between the slag powder and asphalt to improve  performance have become the key factor to affect the application of the slag powder in asphalt.

2. Materials and methods

2.1. Surface modification of phosphorus slag powder

Due to the nature characteristic of inorganic, polar and surface hydrophobic and oleophobic, phosphorus slag powder is incompatible with asphalt, which will lead phosphorus slag powder to uneven dispersion and easy segregation, so separation between the two materials will occur. Thus, it is necessary to modify the phospho- rus slag powder before adding to asphalt.