Micro- and macroscale coefficients of friction of cementitious materials

• Microscale (interparticle) coefficient of friction (COF) was determined with AFM.
• Macroscale (bulk) COF was measured under direct shear.
• Fly ash had the highest microscale COF and the lowest macroscale COF.
• Portland cement against GGBFS had the lowest microscale COF.
• Portland cement against Portland cement had the highest macroscale COF.

Millions of metric tons of cementitious materials are produced, transported and used in construction each year. The ease or difficulty of handling cementitious materials is greatly influenced by the material friction properties. In the present study, the coefficients of friction of cementitious materials were measured at the microscale and macroscale. The materials tested were commercially-available Portland cement, Class C fly ash, and ground granulated blast furnace slag. At the microscale, the coefficient of friction was determined from the interaction forces between cementitious particles using an Atomic Force Microscope. At the macroscale, the coefficient of friction was determined from stresses on bulk cementitious materials under direct shear. The study indicated that the microscale coefficient of friction ranged from 0.020 to 0.059, and the macroscale coefficient of friction ranged from 0.56 to 0.75. The fly ash studied had the highest microscale coefficient of friction and the lowest macroscale coefficient of friction.