Rheological behaviour of fresh cement paste as measured by squeeze flow

A method is proposed for measuring the rheology of cement paste under conditions that suppress shear flow, i.e. squeezing. This method is based on squeezing samples in a servohydraulic compression-tension testing machine, and is different from the commonly used shear flow experiments. Possible artefacts such as the buoyancy of the piston that penetrates the paste, sedimentation of cement paste, geometry of the container, and friction at the interface between the top plate (or piston) and sample are investigated. Plots of stress versus apparent strain were obtained and compared with results from standard shear flow experiments. Because cement paste has both viscoelastic and viscoplastic characteristics, results are analysed in terms of both solid-like deformation and liquid-like flow behaviour. A first-approximation theoretical analysis is developed, based on the assumption that cement paste behaves as a non-Newtonian liquid, and results are compared with the experimental results.Nomenclature Shear strain rate in power law fluid model - _zr Shear strain converted from _zr - Shear strain rate - Normal strain rate - _zr Component of shear strain - _zr Component of shear strain rate - _zz Component of normal strain - Viscosity - Density of cement paste (3.2 g cm^–3) - _Cav Calculated average normal stress of cement paste - _Nav Calculated average normal stress of power law fluid - _m Measured normal stress of cement paste - _zz Normal stress in z direction - _eq Equivalent shear stress converted from normal stress - _rz Shear stress in momentum equation - a _i Coefficients in polynomial function of geometric factor for cement paste - B Buoyancy force - CGF Geometric factor for cement paste - d _o Amplitude of squeeze motion - F _N Load in normal direction - g Gravitational constant - h Sample height - h _o Initial sample height - Velocity of platen - k Order of polynomial function of geometric factor for cement paste - m Consistency in power-law fluid model - n Power index in power-law fluid model - P Pressure - P _a Atmospheric pressure - PGF Geometric factor for power-law fluid model - r Radial direction in cylindrical coordinates - R Radius of sample - s 1/n - V Volume of the top platen submerged into cement paste - v _r Velocity inr direction - v _z Velocity in z direction - z Vertical direction in cylindrical coordinates