A. Papo

Flow behavior of fresh cement pastes. A comparison of different rheological instruments and techniques

Abstract An investigation on the rheological behavior of fresh cement pastes is reported. In particular, the results obtained by the application of various experimental procedures and measurement devices with different geometric characteristics are compared and discussed. The coaxial cylinder viscometers Rotovisko-Haake RV3 and RV11 were employed. The cement pastes were prepared from a Portland cement 324. The water/cement ratio was within the range 0.30 + 0.40.

The phenomenological description of the thixotropic behaviour of fresh cement pastes

AbstractThe present work reports an investigation on the rheological behaviour of fresh cement pastes. Three types of Portland cement were used. The water/cement ratio was varied in the range 0.35 ÷ 0.40. The rheological tests were performed using the coaxial-cylinder viscometer Rotovisko-Haake RV 11. The material to be tested was subjected immediately after mixing to a constant shear rate until a steady value of shear stress (equilibrium value) was attained. All the pastes tested exhibited a flow behaviour of the partially thixotropic type. A rheological model consisting of a sole constitutive equation

Phenomenological description of the thixotropic behaviour of gypsum plaster pastes

\tau = \tau (\dot \gamma ,t)

Flow Behavior of Fresh Very High Strength Portland Cement Pastes

was defined according to the Cheng and Evans approach. The parameters of the constitutive equation were correlated with the cement specific surface and the water/cement ratio.

Effect of various superplasticizers on the rheological properties of Portland cement pastes

The influence of the addition of very effective superplasticizers, that are commercially available, employed for maximising the solid loading of very high-strength Portland cement pastes, has been investigated. Cement pastes were prepared from deionized water and a commercially manufactured Portland cement (Ultracem 52.5 R). Cement and water were mixed with a vane stirrer according to ASTM Standard C305. The 0.38 to 0.44 water/cement ratio range was investigated. Three commercial superplasticizing agents produced by Ruredil S.p.a. were used. They are based on a melamine resin (Fluiment 33 M), on a modified lignosulphonate (Concretan 200 L), and on a modified polyacrylate (Ergomix 1000). Rheological tests were performed at 25°C by using the rate controlled coaxial cylinder viscometer Rotovisko-Haake 20, system M5-osc., measuring device MV2P with serrated surfaces. The tests were carried out under continuous flow conditions. The results of this study were compared with those obtained in a previous article for an ordinary Portland cement paste.

Optimization of portland cement pastes

Gypsum plaster pastes are concentrated suspensions of calcium sulfate hemihydrate in water. The knowledge of their rheological behaviour plays an important role in the manufacture of gypsum products. In the present work, the approach suggested by Cheng and Evans has been taken into consideration in order to derive a constitutive equation suitable for characterizing completely the flow behaviour of these materials in the first stages after preparation. To this end, gypsum plaster pastes were produced with solid volume fractions in a range of practical interest. The rheological tests were performed using a coaxial-cylinder viscometer.

Sodium phosphates as dispersing agents for calcium carbonate industrial slurries: Rheological characterization

Rheological behaviour of recycled sludge from a secondary clarifier of a municipal wastewater treatment plant was studied by using the rate controlled coaxial cylinder viscometer Rotovisko-Haake 20, system M5-osc., measuring device NV. The tests (hysteresis cycles) were performed under continuous flow conditions and following an ad hoc measurement protocol. Sludge shear stress versus shear rate curves were fitted very satisfactorily by rheological models. An experimental equation correlating the solid concentration of sludge to relative viscosity and fitting satisfactorily flow curves at different Total Suspended Solids (TTS%) was obtained. Application of the empirical correlation should allow the monitoring of the proper functioning of a wastewater treatment plant measuring viscosity of sludge.

Effect of Various Superplasticizers on the Rheological Properties of Very High Strength Portland Cement Pastes

Flow behavior of fresh very high strength portland cement pastes prepared at various water/cement ratios was studied by using a rate-controlled coaxial cylinder viscometer (Rotovisko-Haake 20, system M5-osc., measuring device MV2P with serrated surfaces). The tests were performed under continuous flow conditions. Experimental shear stress and shear rate data were fitted very satisfactorily with various models, one of which has already been proposed by the authors. Excellent results were achieved also by applying the Quemada equation. In addition, the influence of two different commercial superplasticizing agents (Concretan RX and Ergomix 1000, the former based on polycyclic copolymers with modified structures, carrying hydroxylated side chains, and the latter on a modified polyacrylic resin) was studied with the aim of determining their optimum dosage and verifying the effectiveness by comparing rheological results with those obtained in a previous work on an ordinary portland cement. The use of superplasticizers modified rheological behavior of the pastes; however, no value of optimum dosage was found for any additive, but only a superplasticizer concentration range within which pastes presented very low values of viscosity. Moreover, both superplasticizers showed a greater effectiveness when added to HSPC pastes rather then the OPC ones formulated with the same water/cement ratio.