Rheology of lime paste—a comparison with cement paste

Abstract

The rheological properties of a suspension of lime in water (lime putty) are studied with the help of creep tests in a wide range of deformations including very small values. The results are compared with those obtained with a cement paste and several similarities between the two systems are observed. It is shown that the apparent yield stress of a lime suspension is the sum of two components: one due to standard reversible colloidal interactions and one due to the formation of a brittle structure associated with the formation of links due to dissolution-precipitation mechanisms. This second component increases with the time of rest as the square root of time, and the corresponding structure irreversibly breaks as soon as some significant deformation has been imposed. We show that similar structures are formed at concentrations between 25 and 34 % (solid volume fraction) and evolve in a similar way when the time is scaled by a factor decreasing with the solid fraction.

NMR observation of water transfer between a cement paste and a porous medium

“…The rheological behaviour of lime pastes is complex, they were shown to be thixotropic yield stress fluids with a yield stress equal to the sum of two components, one due to reversible standard colloidal interactions and one due to a brittle structure whose strength increases in time and which breaks for very small deformations [29]. For the present lime paste the (almost constant) yield stress associated with the first structure was approximately 225 Pa.…”

“…This range corresponded to materials which did not exhibit significant sedimentation when left at rest for half an hour, and can be mixed by hand without breaking in independent parts. A cement paste is a yield stress fluid [28][29], which means that it can flow if a sufficient stress is applied on it, and acts as a solid otherwise. A yield stress can thus be defined in simple shear, which corresponds to the shear stress needed to induce the transition from the solid to the liquid regime (i.e.…”

“…Since in addition cement pastes are thixotropic [28][29][30], their rheological behaviour, and in particular their yield stress, depends on the history of the flow. This for example implies that the static yield stress, which corresponds to the stress needed for flow starting from rest, will differ from the dynamic yield stress, which corresponds to the stress at flow stoppage [28][29]. Typically the static yield stress will be larger than the dynamic yield stress, since during the flow the structure somehow breaks down [31].…”

“…Moreover these two yield stress values will depend on the exact procedure (stress history) followed in each case. Here rheology measurements of these two yield stresses for our cement pastes in a wide range of W/C were obtained from a sweep test (increasing-decreasing stress ramp) (see [29]), but without applying any preshear to avoid sedimentation (the sample was placed in the rheometer just after its preparation). Both yield stresses appear to decrease strongly with increasing W/C (see Figure 1): their variations as a function of W/C may be represented by a negative exponential function of W/C (see Figure 6) We also used cement pastes with Cellulose ethers (CE).…”

“…As a consequence, in the absence or air or water penetration inside the paste, we expect a shrinkage of the cement paste. In fact at the beginning of the hydration process, the yield stress of the material is in general still sufficiently low [29] for the paste to be able to shrink (so-called plastic shrinkage), so that no water is extracted from the bead packing.…”