Investigation of dilatancy mechanism of Portland cement paste

The increase in cement paste volume during the flowing has been determined by specially developed equipment and the investigation methodology was proposed. Pressure (kPa), under which the cement paste starts flowing, the average cement paste flow rate (cm/s), elastic deformation (%) and the increase in cement paste volume due to redistribution of solid phase particles (%) were established in experimental tests of Portland cement pastes with different W/C ratio, Portland cement pastes with SiO2 microparticle suspension and quartz sand additive. With the increase of W/C ratio or liquid phase in cement pastes the elastic deformation drops from 0.83% to 0.27%, while the volume of dispersion when the paste starts flowing increases from 0.63% to 1.31% due to cement particle redistribution under shear stress. When elastic rebound occurs, the volume of pastes with SiO2 microparticle suspension does not increase when solid phase particles redistribute during the flow; dilatancy is not observed in the pastes with this additive either or it is insignificant. When quartz sand particles of irregular size and large than cement particles redistribute during the flow, the volume of the paste increases more (1.24-1.64%) and dilatancy is observed in pastes with this additive. The test results confirm the earlier statements of researchers stating that disperse systems are subject to dilatancy because of the increase of the system's volume under shear stress (during the flow), i.e. because of redistribution of the solid phase in the system subjected to shear stress.