Adsorption Of Superplasticizers Research Articles

Enhanced adsorption and properties of TPEG-type superplasticizers modified by maleic anhydride: a perspective from molecular architecture and conformation

Enhanced adsorption and properties of TPEG-type superplasticizers modified by maleic anhydride: a perspective from molecular architecture and conformation

Spatially resolved in situ analyses of the adsorption behavior of different admixtures on binders

AbstractAdmixtures play a key role in improving the performance of the cement paste matrix. A more efficient matrix can allow a reduction the binder content while maintaining the same properties. There is currently a lack of knowledge about the spatial distribution of admixtures in situ on binder surfaces which would facilitate the use of admixtures in general in inorganic binder systems. Imaging techniques such as confocal laser scanning microscopy (CLSM) and fluorescence microscopy can be used to study the spatiotemporal adsorption of superplasticizers and plasticizers on binder particles. However, in order to make the admixtures visible using these methods, they must first be coupled to a fluorescent molecule (staining). Different types of superplasticizers and plasticizers, including polycarboxylate ethers (PCE) and lignosulfonate (LS) were stained and tested. It was shown that not only adsorption but also desorption can be observed and that desorption cannot play a relevant role in a binder system. The absence of desorption could be used to observe a real system in permanent preparations, so that the adsorption on individual cement grains could be followed in a time‐dependent manner. The newly developed method provides unprecedented insight into the adsorption of additives.

Thixotropy of superplasticized cement pastes – Underlying mechanisms considering the polycarboxylate molecular structure, interparticle interactions and hydration kinetics

This paper deals with the decisive mechanisms of thixotropic structural build-up in superplasticized cement-based suspensions related to the PCE molecular structure. We investigate the effect of the side chain length and anionic charge ratio of tailored PCE superplasticizers on thixotropic structural build-up under quantitative consideration of colloidal and contact interactions as well as very early hydration kinetics. The thixotropic structural build-up of superplasticized cement pastes with systematically varying the PCE molecular structure was investigated at constant workability, i.e. dynamic yield stress, by adjusting the individual PCE dosage. Thixotropy was quantified using plate-plate rheometry, while at the same time superplasticizer adsorption, specific surface area, granulometric measurements and quantitative XRD analysis provided an experimental basis for the identification of the respective contribution to the structural build-up.Our results show that the thixotropic structural build-up increases with decreasing PCE side chain length and increasing anionic charge ratio. This is due to accelerated very early hydration kinetics, causing an increase in the specific surface area. The latter is primarily attributed to ettringite, modifying the particle size distribution of the hydrated cement paste. Our approach of separating the colloidal and contact interactions indicates that the PCE-induced change in particle size distribution due to accelerated ettringite formation as well as the change in the average effective layer thickness are the dominant mechanisms for the thixotropic structural build-up in this context.

Study on the Effect of Main Chain Molecular Structure on Adsorption, Dispersion, and Hydration of Polycarboxylate Superplasticizers.

Polycarboxylate ether (PCE) with different main chain structures was prepared by aqueous solution free radical polymerization using unsaturated acids containing sulfonic acid groups, acrylamide groups, and carboxyl groups and isoprenyl polyoxyethylene ether (IPEG). The molecular structure was characterized by infrared spectroscopy and gel chromatography, while adsorption, dispersion, and hydration properties were studied using a total organic carbon analyzer, rheometer, and isothermal microcalorimeter, respectively. The results show that the adsorption process of PCE on cement particles is spontaneous physical adsorption. The adsorption forces are mainly electrostatic interaction, and hydrogen bonding. The introduction of sulfonic acid groups and polycarboxylic acid groups reduces the initial adsorption amount of PCE but can accelerate the adsorption rate of PCE on cement and increase the adsorption amount at the adsorption equilibrium. The introduction of acrylamide groups in the PCE main chain is beneficial to the initial dispersion of PCE and can reduce the plastic viscosity of cement slurry. PCE can delay the hydration of cement. The introduction of acrylamide groups and dicarboxylic acid groups in the PCE main chain helps prolong the induction period of cement hydration, while the introduction of sulfonic acid groups is not conducive to its retarding effect.

Preferential adsorption of superplasticizer on cement/silica fume and its effect on rheological properties of UHPC

The adsorption behavior of two comb-shaped superplasticizers (PCEs) containing only carboxyl groups and both carboxyl and phosphate groups on cement/silica fume, and their influence mechanism on rheological properties of pastes with low w/b of 0.2 were investigated. The preferential adsorption of PCEs on the surface of different powders (e.g. cement and silica fume) was observed. The PCE containing only carboxyl groups adsorbed more on the surface of cement, while phosphate-containing PCE adsorbed more on the surface of silica fume at low dosage and exhibited stronger adsorption capacity both on cement and silica fume at high dosage. For cement paste, PCE containing only carboxyl groups was suggested to improve flow spread. However, as silica fume was introduced, the blends of the two PCEs could achieve higher packing density of particles in paste due to the excellent dispersion of phosphate containing-PCE to silica fume, resulting in higher flow spread (lower yield stress) and lower viscosity.

Synthesis of sodium alginate-polycarboxylate superplasticizer and its tolerance mechanism on montmorillonite

Sodium montmorillonite (MMT) is a major mineral component of clay in manufactured sand which is an economical aggregate in concrete. Its lamellar structure has a negative effect on an important concrete admixtures polycarboxylate superplasticizer (PCE). In this study, sodium alginate (SA), a polysaccharide, was grafted with an unsaturated amide, having a double bond structure, to synthesize the acrylamide modified sodium alginate (Ugi-SA) through the Ugi reaction. Then, Ugi-SA, acrylic acid (AA), and isopentenol polyoxyethylene ether (TPEG) were used to synthesize sodium alginate-polycarboxylate superplasticizer (SPCE) by free radical copolymerization. The structures of Ugi-SA and SPCE were determined by gel permeation chromatography (GPC) and Fourier transform infrared (FT-IR). The fluidity of the montmorillonite (MMT) cement paste with SPCE and the traditional polycarboxylate superplasticizer (TPCE) was investigated. Furthermore, the adsorption behavior of SPCE on MMT was measured by X-ray diffraction (XRD), thermogravimetric analysis (TGA), total organic carbon analyzer (TOC) and the tolerance mechanism of SPCE on MMT was discussed. The FT-IR and GPC results showed that Ugi-SA and SPCE were synthesized successfully. The initial fluidity test results indicated that SPCE had a better dispersion effect and MMT tolerance than TPCE. TGA, TOC and XRD tests showed that the adsorption of SPCE on MMT was much lower than that of TPCE. This study demonstrated that the SA structure of SPCE appears to exhibit a large steric hindrance, which prevents the intercalation of SPCE into MMT.

Atypical adsorption of polycarboxylate superplasticizers on calcium silicate hydrate surface: Converting interaction by solvent effects

Although PCE adsorption occurrence is widely perceived to correlate to the anchoring of the carboxyl group on the PCE backbone, the understanding of the details is still insufficient. Here, we investigate the microstructural behavior of PCE adsorption with and without aqueous environments by molecular dynamics simulation and semi-empirical quantum chemistry calculation. We found that the introduction of an aqueous environment can change the mode of adsorption from strictly anchoring to atypical that the chains of PCE can sweep around the C-S-H surface. Two kinds of segments on the C-S-H surface have anchored the PCE, including Ca ions and hydroxyl. The aqueous environment alters the domination segments from Ca ions to hydroxyl. Further electronic analysis proves the weakening of bonding strength between PCE and C-S-H by solvation effects. This weakened interaction promotes the potential well of free energy away from the C-S-H surface and finally caused the atypical adsorption of PCE.

Effect of healing agents on the rheological properties of cement paste and compatibility with superplasticizer

Self-healing concrete is considered as a new generation of concrete with the ability to heal cracks without human intervention. The healing agents are incorporated into the concrete to activate the healing mechanism and to improve the healing efficiency. While both lab- and large-scale projects have shown that the addition of healing agents can have a possible positive effect on the hardened concrete properties (e.g. compressive strength), unfortunately, the evaluation of fresh properties of self-healing concrete mixes is often neglected. In the current study, the effect of healing agents is clearly identified starting from the paste level. Different techniques were used to study the effect of healing agents on the consistency, viscosity and adsorption behaviour of PCE-based superplasticizer in cement paste. A crystalline admixture and bacteria were used as healing agents, and CEM III/A was used as the binder component of the paste. The results showed that the inclusion of bacteria did not influence the rheological properties of the cement paste and no incompatibility issues were found with the superplasticizer. On the other hand, the presence of the crystalline admixture in the paste interfered with the rheological properties of the cement paste as a reduction of workability, an increase of paste viscosity, and an increased adsorption of superplasticizer.

How do discharge rate and pipeline length influence the rheological properties of self-consolidating concrete after pumping?

Pumping changes the rheological properties, workability and construction performance of fresh concrete. However, there were limited knowledges on influences of discharge rates and pumping distances on the fresh properties of concrete. In this paper, effects of various discharge rates and pipeline lengths on rheological properties of self-consolidating concrete (SCC) after pumping were studied. A total of 12 SCC mixtures with the slump flow of 650–745 mm were pumped in pipelines with measured lengths of 342 m, 545 m, and 1044 m by constant discharge rates ranging between 5.1 and 11.4 L/s. Rheological properties were measured before and after pumping. Physical conditions of SCC during pumping, including pressure, shear, and temperature were estimated theoretically and experimentally. Moreover, the total organic carbon in the pore solution of SCC mixtures was measured to evaluate the change of superplasticizer adsorptions after pumping. Test results indicated that, due to pumping, the yield stress increased; the initial tangential viscosity decreased and the shear-thickening phenomenon was eliminated. The changes of yield stresses and viscosity were encouraged by discharge rates. Besides, lower initial slump flow of SCC exhibited a larger slump flow loss after pumping due to a higher shear rate experienced during pumping. The yield stress and viscosity after pumping increased with the increase of pipeline length at similar discharge rates, but decreased with the pipeline length under similar pumping pressures. The adsorption of superplasticizer increased after pumped at relative low discharge rates (5.2–5.7 L/s), but decreased at discharge rates of 7.7–10.8 L/s.

Amphoteric polycarboxylate superplasticizers with enhanced clay tolerance: Preparation, performance and mechanism

From the point view of molecular structure design, three different kinds of amphoteric polycarboxylate superplasticizers (APC) by introducing a cationic monomer such as [2-(methacryloyloxy)ethyl]trimethylammonium chloride (DMC), 3-[2-(methacryloyloxy)ethyl]dimethylammonio-propane-1-sulfonate (DMAPS) and acrylamide (AM) were synthesized by free radical polymerization. The functional groups, molecular weights and molecular weight distributions of these superplasticziers were characterized by Fourier transform infrared spectra (FT-IR) and gel permeation chromatography (GPC). The dispersion performance of as-prepared APC were evaluated by the fluidity of cement paste and cement mortar. The results showed that the fluidities of samples mixed with APC were higher than that of the conventional polycarboxylate ether (PCE) superplasticizers, indicating excellent dispersion performance and dispersion retention. The strengths of concrete with APC or PCE were greatly improved compared with that of the standard concrete, and the strengths of samples with APC were superior to that with PCE. By substituting cement with 1 wt% sodium bentonite, the fluidity of the cement pastes with APC was higher than that with PCE1, which can be ascribed to the enhanced clay tolerance of APC. Total organic carbon (TOC), X-ray diffraction (XRD) and thermo gravimetric analysis (TGA) were conducted to study the adaptability of superplasticizers to cement and clay. Adsorption capacity measurement revealed that APC and PCE exhibit selective adsorption on cement and clay and APC exhibited better adaptability to clay than PCE. The interlayer spacing of sodium bentonite increased by 0.2 nm after the adsorption of superplasticizer, without significant difference between APC and PCE. A possible mechanism was proposed that the cationic groups can insert into the interlayer of clay by cation exchange, and the intercalation of PEO side chains was inhibited, which is different from that of PCE.

Fluorescence Microscopic Investigations of the Retarding Effect of Superplasticizers in Cementitious Systems of UHPC.

The adsorption of superplasticizer molecules to particle surfaces in cementitious systems is a very important aspect for the desired liquefaction of pastes and concretes. This way, the comb shaped polymers shield attractive forces between the particles and induce a well-dispersed, homogeneous suspension. These admixtures allow the usage of fine fillers even in combination with low amounts of mixing water, and thus, are the basis for modern high performance concretes. However, the adsorption does not cause beneficial effects only: The polymer covered particle surfaces, especially clinker, are hindered to interact with water, thus hydration is retarded. This is the reason for lower early strength and is very disadvantageous for certain applications. Today it is known that the molecular structure of the polymers, for instance the chain length and charge density, affects the retardation strongly. The complexity and diversity of cementitious systems is the main reason why research in this field is quite empiric and time as well as cost intensive. To investigate the adsorption of superplasticizers in various systems in-situ, a fluorescence microscopic approach was applied: By staining the polymers with fluorescent dye they become localizable and the adsorption quantifiable. This work shows the influence of molecular structure to adsorption characteristic of different polymers and the correlation to the retarding effect of superplasticizers, especially concerning the presence of silica fume, which is indispensable for ultra-high performance concrete (UHPC).

Effect of coral powder on the properties of cement-based materials

In the construction of offshore engineering, a growing number of coral sand and coarse aggregate is used as concrete aggregates in the local construction. Thereupon, a lot of coral powder is left as a solid waste. This work is an attempt to study the potential of the coral powder replacing part of cement as supplementary cementitious materials. The flow properties of fresh cement paste with coral powder were studied, as well as the mechanical properties of hardened cement paste. Experimental results show that the fluidity of cement paste blended with coral powder decrease with the dosage of micro coral powder, due to its high water demand and high adsorption of polycarboxylate superplasticizer (PCE). Replacement of cement by coral powder have positive effects on the cement hydration and mechanical properties of cement paste at early ages. However, at the curing age of 7 days, the addition of coral powders deceases the strength of cement paste regardless of replacement levels.

In-situ investigation of superplasticizers: From fluorescence microscopy to concrete rheology

Concretes with advanced strength and durability necessitates organic polymers to receive a homogeneous concrete mixture due to a low amount of mixing water and a high content of fine fillers with large inner surface. The basic working mechanisms of those so-called superplasticizers are widely understood in theory, but still there are unclear phenomena like incompatibilities with certain additives. This study presents a novel method to investigate the interaction of superplasticizers with mineral particles. With the application of fluorescence microscopy, it is possible for the first time to localize and quantify the adsorption of superplasticizers to particles and to vary experimental parameters during the measurement. The presented results prove this method, which enables first time to investigate the superplasticizer interaction with mineral surfaces in situ. The important role of calcium ions for the necessary adsorption of those polymers to mineral particle surfaces is obvious in the shown fluorescence microscopic experiment. Furthermore, the detected amount of adsorbed polymers depending in the concentration of calcium ions present in the used suspension correlates with the development of the zeta potential of various minerals. Finally, a correlation between the microscopically measured adsorption of two different superplasticizers to rheological properties of a test mortar succeeded.

Thixotropy of SCC—A model describing the effect of particle packing and superplasticizer adsorption on thixotropic structural build-up of the mortar phase based on interparticle interactions

This article considers the thixotropy of SCC mortars and the responsible mechanisms. The objective is a model describing the thixotropic structural build-up based on interparticle interactions and hydration kinetics of the fresh binder paste. In the experimental studies, the formation of thixotropic structure in SCC mortars was varied by changing the composition of the binder paste and quantified rheologically. At the same time, the surface coverage of particles by superplasticizer polymers and the particle packing in the suspension were determined to characterize interparticle interactions. Based on the results, a qualitative model as well as a calculation method were developed to describe the thixotropic behaviour. It is shown that the contribution of colloidal surface interactions and hydration reactions to thixotropy both increase with decreasing surface coverage and therefore decreasing particle separation. In addition, thixotropy increases with increasing contact interactions resulting from a higher solid volume fraction or a lower maximum packing density.

Inverse gas chromatography as a method for determination of surface properties of binding materials

Inverse gas chromatography (IGC) is a promising measurement technique for investigating the surface properties of binding materials, which are the major influence element for the adsorption performance of superplasticizer. In this work, using the IGC method, blast furnace slag (BFS), sulphoaluminate cement (SAC) and portland cement (P·O) are employed to systematically evaluate the corresponding dispersive component (γsd), specific surface free energy (γsab), and acid-base properties. The obtained results show that γsd contributes to a major section of the surface free energy in the three binding materials, suggesting they are of a relatively low polarity. Compared to the two kinds of cements, the BFS possesses the highest dispersive and specific surface free energies (the values are 45.01 mJ/m2 and 11.68 mJ/m2, respectively), and also exhibits a wider distribution range of γsd, indicating their surfaces are heterogeneous. For acid-base properties, the results indicate the surfaces of three samples are basic in nature. In addition, the adsorption investigation shows that per unit surface of BFS adsorbs the most superplasticizer molecules, which indicates the higher surface free energies is beneficial to the superplasticizer adsorption.

Interactions between fluoride ions and cement paste containing superplasticizer

Fluoride compounds are used as fluxes in the low-temperature calcination of cement. Elution of fluoride ions after calcination decreases the fluidity of cement paste containing superplasticizers, but the mechanism of fluidity decrease is unclear. Authors investigated the effects of fluoride on cement pastes containing superplasticizers and the fluidity decrease mechanism. KF addition to cement paste containing a polycarboxylate- or naphthalenesulfonate-based superplasticizer increased the yield stress, the amount of adsorbed superplasticizer, and the solid-phase specific surface area. KF addition increased the amount of adsorbed superplasticizer for alite paste but not for Ca3Al2O6-CaSO4 paste. Transmission electron microscopy found SiO2 fine particles after KF addition. In the absence of water, the increase in specific surface area with fluoride was larger in hydrated than in unhydrated cement. It is supposed that the fluidity decrease results from the preferential adsorption of superplasticizer on SiO2 particles generated by reactions between hydrated calcium silicate and fluoride ions.

Effect of Zinc oxide and Al-Zinc oxide nanoparticles on the rheological properties of cement paste

Abstract This study aims to evaluate the effect of aluminum doped zinc oxide (AZO) and undoped Zinc oxide (ZnO) nanoparticles addition on the superplasticizer adsorption isotherm and rheological properties of cement paste composites. The adsorption isotherm and zeta potential of pastes containing different proportions of ZnO and AZO nanoparticles were also analyzed. The mechanism of superplasticizer adsorption by nanoparticles was found to be a dominant factor which governs the rheological properties. It was found that the amount of superplasticizer adsorbed increases significantly by incorporating nanoparticles which implies that nanoparticles compete with cement particles to adsorb the polymer. Consequently, the addition of both nanoparticles resulted in a considerable increase in saturation point, yield stress and viscosity values relative to plain cement paste. All mixtures containing 0.4 wt % nanoparticles or lower showed excellent workability retention as compared to the reference mix while, the poor workability retention was observed a higher dosage.

Study on the Effect of Condensate-Type and Copolymer-Type Combined Superplasticizers on Hydration of Cement

For the limitation of single-component superplasticizer, condensate-type and copolymer-type combined superplasticizers were prepared. The adsorption of compound superplasticizers on cement paste was tested by Total Organic Carbon (TOC) measurement. Influences of superplasticizers on early hydration process of cement and Organo-mineral phase formation were studied by X-Ray Diffraction Analysis (XRD), Scanning Electron Microscope analysis (SEM) and so on. The results show that owing to the electrostatic repulsion and steric effect cooperative mechanism, condensate-type and copolymer-type combined superplasticizers reduce the superplasticizers adsorption in cement minerals and its hydration products surface, delay the process of hydration of C3A, form Organic-Layered double hydroxides (LDH), increase the early chemical shrinkage and promote the growth of cement early hydration and Ettringite

Effects of clay on properties of polycarboxylate superplasticizer and solutions

The influence law of clay on mortar fluidity mixed with polycarboxylate superplasticizer was studied. Several methods of inhibiting clay adsorption of polycarboxylate superplasticizer were discussed. The experimental results show that clay has significant effect on the dispersion of polycarboxylate superplasticizer and montmorillonite clay has more significant impact on mortar fluidity than other clays. The pH value and the salts of the solution can affect the adsorption of clay to polycarboxylate superplasticizer. The incorporation of a small amount of sodium hydroxide solution, sodium silicate or cationic surfactants can improve the effect of the clay on the dispersion of polycarboxylate superplasticizer.

Effect of macro-mesoporous rice husk ash on rheological properties of mortar formulated from self-compacting high performance concrete

In the present study, effect of macro-mesoporous rice husk ash (RHA) on rheological behavior and flowability of mortar formulated from self-compacting high performance concrete (SCHPC) was investigated. For comparison, the investigation was also conducted on samples containing silica fume (SF). The results reveal that the incorporation of RHA/SF decreased mini-slump flow, and increased superplasticizer adsorption, superplasticizer saturation dosage, yield stress and plastic viscosity of mortar. The effect of RHA on yield stress and plastic viscosity is significantly stronger than that of SF, especially when the coarser RHA or the higher content of RHA is used. Interestingly, the increase in particle size or content of RHA predominantly increased plastic viscosity and yield stress rather than decreased mini-slump flow of mortar, especially 60min after water addition. Fresh mortar in this study is a shear-thickening material. The shear-thickening degree decreased over time. The incorporation of RHA/SF decreased the shear-thickening degree where the effect of SF is much stronger than that of RHA. It is suggested that the rheological behavior of mortar is attributable to the capacity and progress of the water adsorption of RHA.