Interfacial Water Stability between Modified Phosphogypsum Asphalt Mortar and Aggregate Based on Molecular Dynamics

Area of Science:

• Materials Science
• Chemical Engineering
• Civil Engineering

Background:

• Phosphogypsum is a byproduct of fertilizer production.
• Phosphogypsum asphalt mortar is susceptible to water damage.
• Coupling agents can potentially improve material properties.

Purpose of the Study:

• To investigate the mechanism by which coupling agents modify the water sensitivity of phosphogypsum asphalt mortar.
• To evaluate the effectiveness of three coupling agents (KH-550, KH-570, CS-101) in improving the interfacial properties and reducing water sensitivity.

Main Methods:

• Molecular dynamics simulations using Materials Studio 2020.
• Simulation of adhesion between modified phosphogypsum asphalt mastic and aggregate minerals.
• Inclusion of a water film layer in simulations.
• Analysis of interfacial adhesion work and molecular dynamics of water molecules.

Main Results:

• Interfacial adhesion work increased with coupling agent dosage.
• The mean square displacement of water molecules decreased in the order: unmodified phosphogypsum > KH-550 > KH-570 > CS-101.
• The diffusion coefficient of water molecules significantly decreased with increased CS-101 modified phosphogypsum content (>5% by mass).

Conclusions:

• Coupling agents significantly improve interfacial adhesion work and limit water molecule diffusion in phosphogypsum asphalt mortar.
• CS-101 demonstrated the most effective performance, followed by KH-570 and KH-550.
• Coupling agent modification is a viable strategy to enhance the durability of phosphogypsum asphalt mortar.