Cement Dispersion Research Articles

Research Progress of Adsorption Characteristics of Polycarboxylate Superplasticizers and Effect on Cement Dispersion, Hydration

Polycarboxylate superplasticizers(PCs) were important admixtures in modern concrete preparation, and working mechanism research was paid close attention since its invention. The international research progress of adsorption characteristics of Polycarboxylate superplasticizers and effect on cement paste dispersion, hydration was introduced, appropriate analysis and discussion were made focusing on existing problems in relational researches in purpose of providing ideas for further research of cement- PCs interactions.

Microcapsules prepared from a polycondensate‐based cement dispersant via layer‐by‐layer self‐assembly on melamine‐formaldehyde core templates

AbstractNovel microcapsules were prepared from colloidal core–shell particles by acid dissolution of the organic core. Weakly crosslinked, monodisperse and spherical melamine‐formaldehyde polycondensate particles (diameter ∼ 1 μm) were synthesized as core template and coated with multilayers of an anionic polyelectrolyte via layer‐by‐layer deposition technique. As polyelectrolytes, an anionic naphthalenesulfonate formaldehyde polycondensate that is a common concrete superplasticizer and thus industrially available, and cationic poly(allylamine hydrochloride) were used. Core removal was achieved by soaking the core–shell particles in aqueous hydrochloric acid at pH 1.6, resulting in hollow microcapsules consisting of the polyelectrolytes. Characterization of the template, the core–shell particles, and the microcapsules plus tracking of the layer‐by‐layer polyelectrolyte deposition was performed by means of zeta potential measurement and scanning electron microscopy. The microcapsules might be useful as microcontainers for cement additives. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Design and Performance Evaluation of a Unique Deepwater Cement Slurry

Summary The exploration and development of deepwater hydrocarbon resources necessitate the fast evolution of drilling and completion technologies for deepwater wells. To drill and complete deepwater wells successfully, sophisticated technologies need to be developed to solve various problems arising from low temperature, weak formations, shallow water/gas flow, environmental protection, and high deepwater rig rate. It is a challenge to develop a good cement slurry that can be used successfully for deepwater wells under low-temperature environment. Such cement slurry should have several distinct properties, such as a short thickening time, a fast transition from liquid to solid, a rapid development of compressive strength, and environmental friendliness. It usually takes a long time for conventional cement slurry to set and only limited compressive strength can be achieved at low temperatures. In addition, most additives used for the conventional cement have adverse effects on the environment. Therefore, it is of upmost importance to design an environmentally friendly and low-density cement slurry that is appropriate for deepwater wells. In this paper, a new deepwater cement [sulfur polymer cement (SP-C)] was designed and tested for the first time. This new deepwater cement combines the advantages of the sulfoaluminate cement and Class G oilwell cement. Green cement additives including cement dispersant, fluid-loss-control agent, and accelerator were also developed. Consequently, a unique low-density cement slurry was obtained for deepwater-well applications. Laboratory tests showed that the low-density slurry exhibited favorable properties including the nonexistence of free fluid, an excellent fluid-loss-control capability, a short waiting-on-cement time at low temperatures, and a shortened transition time of critical gel strength. This new cement slurry can be easily prepared and applied in deepwater wells without adverse impacts on the marine environment.

Cement-Dispersant Incompatibility due to Ettringite Bridging

Sulfonated naphthalene formaldehyde, a common dispersant for portland cement, was found to be incompatible with some cements, the incompatible combinations producing gelation rather than dispersion of cement–water mixtures. The gelation was found to be prevented by the addition of alkali hydroxide or alkali sulfate. The objective of this study was to explore the mechanism behind these incompatibilities. Three hypotheses were tested: ettringite bridging, superplasticizer consumption, and polymer bridging. Results showed that the ettringite formation was responsible for the gelation and that alkali addition inhibited the ettringite formation.

Experimental determination of the thermodynamic parameters affecting the adsorption behaviour and dispersion effectiveness of PCE superplasticizers

For adsorption of three different allylether-based PCE superplasticizers on CaCO 3 surface, the thermodynamic parameters Δ H, Δ S and Δ G were determined experimentally. The GIBBS standard free energy of adsorption Δ G 0ads, the standard enthalpy of adsorption Δ H 0ads and the standard entropy of adsorption Δ S 0ads applying to an unoccupied CaCO 3 surface were obtained via a linear regression of ln K (equilibrium constant) versus 1 / T (VAN'T HOFF plot). Additionally, the thermodynamic parameters characteristic for a CaCO 3 surface loaded already with polymer (isosteric conditions) were determined using a modified CLAUSIUS–CLAPEYRON equation. For all PCE molecules, negative Δ G values were found, indicating that adsorption of these polymers is energetically favourable and a spontaneous process. Adsorption of PCEs possessing short side chains is mainly instigated by electrostatic attraction and a release of enthalpy. Contrary to this, adsorption of PCEs with long side chains occurs because of a huge gain in entropy. The gain in entropy results from the release of counter ions attached to the carboxylate groups of the polymer backbone and of water molecules and ions adsorbed on the CaCO 3 surface. With increased surface loading, however, Δ G isosteric decreases and adsorption ceases when Δ G becomes 0. The presence of Ca 2+ ions in the pore solution strongly impacts PCE adsorption, due to complexation of carboxylate groups and a reduced anionic charge amount of the molecule. In the presence of Ca 2+, adsorption of allylether-based PCEs is almost exclusively driven by a gain in entropy. Consequently, PCEs should produce a strong entropic effect upon adsorption to be effective cement dispersants. Molecular architecture, anionic charge density and molecular weight as well as the type of anchor groups present in a superplasticizer determine whether enthalpy or entropy is the dominant force for superplasticizer adsorption.

Experimental testing of the new flow equation of cement dispersion

The new flow equation of cement dispersion included factor of the friction between cement grains is presented in the paper. The analysis of the calculation’s results confirms the property of new equation. In the main part of the paper the results of experimental research were presented. The first part of research applies to cement flow through annular pipe, which exactly matches the theoretical model assumptions. The second part of flow tests was carried out in aggregate pile, which is typical to many practical applications of cement injection. Calculation and experimental test’s results are compatible and proof the correctness of new flow equations.

Modification of the molar anionic charge density of acetone–formaldehyde–sulfite dispersant to improve adsorption behavior and effectiveness in the presence of CaAMPS®‐co‐NNDMA cement fluid loss polymer

AbstractSulfonated aldol polycondensates were synthesized from acetone, formaldehyde, and different amounts of sodium sulfite, resulting in polymers with varying degrees of sulfonation (DS). The anionic charge amount of these macromolecules measured by polyelectrolyte titration decreased with lower DS. The effectiveness of the acetone–formaldehyde–sulfite (AFS) polycondensates as cement dispersant was found to depend on the amount of polymer adsorbed on cement. AFS adsorption decreases with lower DS. Interaction and compatibility between AFS and CaAMPS®‐co‐NNDMA fluid loss additive was studied by formulating binary additive systems composed of one of the modified AFS polymers and CaAMPS‐co‐NNDMA. At high DS, AFS adsorbs strongly and prevents CaAMPS‐co‐NNDMA from adsorbing in sufficient amounts on the cement surface. The result is poor fluid loss control of the cement slurry. AFS polymers with lower DS, however, allow simultaneous adsorption of both polymers in sufficient quantities to provide good fluid loss control and low rheology at the same time. Thus, effectiveness of both additives was retained. Obviously, effectiveness of such multi‐admixture systems depends on the adjustment of the adsorption behavior of the individual components relative to each other. Molar anionic charge density of the polymers was found to be a major parameter influencing their relative adsorption behavior. The AFS polymer with DS = 0.2 possesses a molar anionic charge density comparable to CaAMPS‐co‐NNDMA. Thus, when admixtures with similar molar anionic charge densities are used, the performance of one component is not negatively influenced by the other. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Influence of the friction factor on the range of cement dispersion flow

Dispersial nature of cement grout makes many difficulties in practical applications of the injection process. It is also difficult to describe by theoretical equations. The rheological models treat cement paste as continuous material. In this paper the new flow equation was derived, which contains the factor of the friction between cement grains introduced to the Bingham model. The possibilities of the calculation of this new factor was presented. The analysis of the calculation’s results of the classical and new equations shows significant differences. The new equation allows to better predict the effects of the real injection applications.

Paste fluidity of two-component cement dispersant formulation: Another additivity rule

Ultrafiltered lignosulfonate (UF-LS), PEO comb-shaped polycarboxylate (PC), and gluconic acid (GA) are formulated with varied ratio, and their dispersion ability is tested in cement paste. While PC and GA formulation follows an ordinary paste flow value additivity (dose–response additivity), UF-LS and PC formulation obeys the additivity in terms of its required dosage for a given paste flow (required dose additivity). The observed required dosage additivity rule may help us further understand cement and multiple-component dispersant interaction.

Application of a rotatable orthogonal central composite design to the optimization of the formulation and utilization of an useful plasticizer for cement

Black liquor (BL), a by-product of Alfa pulping industry, is mixed with small amounts of sulfonated naphthalene formaldehyde polymer (SNF) to give a useful cement dispersant having a durable action. In order to check the effect of three variables (the ratio water/cement, % black liquor, % SNF) on two properties of the cement grout (cement plasticity and cement plasticity loss), a rotatable orthogonal central composite design is set up. It is concluded from response surface and isorespon se curve studies that the level of plasticity is governed by the percentage of SNF while its durability is ensured by the percenta ge of the black liquor.

The role of steric repulsive force in the dispersion of cement particles in fresh paste prepared with organic admixture

The existence of the steric repulsive force has never yet been determined, though the improved dispersibility of solid particles in concrete by adding the organic admixture is considered to be primarily caused by the dispersion of solid particles by the electrostatic repulsive force based on the formation of an electric double layer made of the admixture adsorbing to the surface of solid particles and the increase of the surface potential, and by the steric repulsive force based on the interaction between the adsorption layers of admixture. The authors proved for the first time the existence of the steric repulsive force acting on the surface of cement particles adsorbing the organic admixture by measuring the interactive force between surface of cement clinker adsorbing the admixture with an atomic force microscope, and measuring the zeta potential of fresh cement paste under actual water-to-cement ratio by electrokinetic sonic amplitude method. It is also clarified that the rate of contribution of electrostatic and steric repulsive force to the dispersion of cement and hydrated cement particles differs by the kind of organic admixture.

Portland Cement Dispersion by Adsorption of Calcium Lignosulfonate.

THE RESULTS OF TURBIDITY TESTS ON PORTLAND CEMENTS SUSPENDED IN AN AQUEOUS MEDIUM, WITH AND WITHOUT ADDITION OF CALCIUM LIGNOSULFONATE, AS OBTAINED WITH THE WAGNER TURBIDIMETER, SHOW THAT THE ADDITION AGENT DISPERSES THE SUSPENDED CEMENT PARTICLES. IN THE TESTS REPORTED, THE DEGREE OF INCREASE IN TURBIDITY FOR TWO TYPES OF PORTLAND CEMENT IN AN AQUEOUS MEDIUM IS SHOWN TO BE A FUNCTION OF THE AMOUNT OF ADSORBED DISPERSING AGENT. IT MAY BE CONCLUDED THAT THE MECHANISM OF DISPERSION INVOLVES THE POSITIVE ADSORPTION OF LIGNOSULFONATE ANIONS BY THE CEMENT PARTICLES. THE DETERMINATION OF AN ADSORPTION ISOTHERM FOR CALCIUM LIGNOSULFONATE AND PORTLAND CEMENT SUSPENDED IN WATER IS DESCRIBED. DATA ARE GIVEN FOR A TYPICAL CEMENT. /AUTHOR/