Adsorption characteristics of superplasticizers on cement component minerals

Adsorption characteristics of various superplasticizers on portland cement component minerals were investigated. Adsorption isotherms of various types of superplasticizers and ζ-potentials of cement component minerals at the maximum adsorption of the superplasticizers were measured. The value of the adsorption isotherm was calculated from the amount of the superplasticizer adsorbed on a cement component mineral in an equilibrated solution. The maximum amounts of adsorption and the adsorption isotherms varied with types of component mineral and superplasticizer. For all types of superplasticizers, a larger amount of superplasticizer was adsorbed on C₃A and C₄AF than C₃S and C₂S. However, the equilibrated concentration of each superplasticizer at the maximum adsorption was not influenced by types of superplasticizer. Without superplasticizer, C₃S and C₂S had negative ζ-potential. On the contrary, C₃A and C₄AF had positive ζ-potential. Therefore, accelerated coagulation of cement particles might occur due to their electrostatic potentials that are opposite each other. However, all component minerals of cement had negative ζ-potential when they were mixed with any superplasticizer. Fluidity of fresh cement paste is improved due to electrostatic repulsion acting between particles.     

Influence of PCE kind and dosage on ettringite crystallization performed under terrestrial and microgravity conditions

Early ettringite crystallization in the presence of 2 chemically different polycarboxylate superplasticizers was studied by hydrating a commercial portland cement (CEM I 52.5 N) for 10 seconds. It was found that the presence of polycarboxylate superplasticizers leads to ettringite crystals which are longer, yet slimmer (higher aspect ratio), compared with the crystals obtained from neat cement paste. This finding suggests that the polycarboxylate (PCE) polymers predominantly adsorb on the lateral faces of the hexagonal‐prismatic crystals of ettringite. For the methacrylate‐based PCE, this effect increases with increasing superplasticizer dosage, whereas for the IPEG‐PCE, the effect achieved at a very low dosage (0.05%) is not altered when dosage increases. The behaviors of both PCE polymers can be explained by their different adsorption behavior, whereby the IPEG‐PCE reached the saturated adsorbed amount at much lower dosage than the MPEG‐PCE. Microgravity only has a minor effect on the growth of ettringite. There, generally smaller crystals are observed.     

Ettringite formation: A crucial step in cement superplasticizer compatibility

The rheology of cementitious system containing superplasticizer is the consequence of a physical process due to the electrostatic repulsion between particles, but also of a chemical process linked to the nature of the phases that are formed. Ettringite crystallization play as a key role in this matter and the nature of the sulfate phase added to control cement setting is as important as its dosage. Alkali sulfates, which provide only SO₄²⁻ ions, do not promote the formation of ettringite for which the presence of large amounts of Ca²⁺ is necessary. The adsorption of superplasticizer molecules on hydrated cement grains slows down the dissolution rates of the constituents and modifies the nature of the compounds formed. It could result in a modification of the ettringite morphology.     

蒸养条件下两性聚羧酸减水剂对胶砂及混凝土强度的影响

合成了阴离子型和两性型聚羧酸减水剂,研究了两类聚羧酸减水剂对水泥水化热、蒸养胶砂和蒸养混凝土强度的影响.结果表明:在蒸养条件下,与阴离子型聚羧酸减水剂相比,掺两性型聚羧酸减水剂的水泥水化温峰更高;在相同水灰比时,掺两性聚羧酸减水剂的蒸养胶砂和蒸养混凝土的强度也更高.XRD分析可知,掺入两性聚羧酸减水剂在蒸养条件下生成更多的AFm和氢氧化钙,促进了C3S和C2S的水化.     

Basics of analytical methods used for the investigation of interaction mechanism between cements and superplasticizers

In order to better understand the interactions between cements and superplasticizers (high-range water reducers), various analytical methods have traditionally been applied, but some of these methods can introduce significant errors. In this paper the fundamental interaction mechanisms are reviewed and appropriate methods and sample preparation conditions are explained in detail. For superplasticizer adsorption measurements, analysis by size exclusion chromatography is useful in order to avoid the effect of other organic compounds released from cement by the action of the superplasticizer. For BET specific surface area measurements it is important to avoid pre-drying at over 60 °C, as otherwise ettringite can decompose and strongly increase the surface area. In order to evaluate pore solution chemistry correctly the aqueous phase must be extracted without dilution. In addition, the fluidity performance of many cements in superplasticized concretes can be changed simply by passage through a storage silo, for reasons which are not yet understood.     

Influence of solution chemistry on the hydration of polished clinker surfaces—a study of different types of polycarboxylic acid-based admixtures

The influence of two different types of polycarboxylic acid-based superplasticizers (homo- [HP] and copolymer [CP]) on the early hydration of Portland cement clinker is investigated. Polished clinker surfaces are hydrated in aqueous phase extracted from cement paste with and without superplasticizers as well as in saturated Ca(OH)₂/CaSO₄ solution and in deionized water. Scanning electron microscopy (SEM) is used to characterize the early hydration products after 30 min and after 24 h of hydration. Contrary to the hydration reaction with deionized water, in the presence of ionic solutions, the texture and morphology of the clinker surface are significantly altered, and amorphous and crystalline hydration products, mainly ettringite, are formed. The amount and type of ettringite formed are strongly related to solution chemistry and type of superplasticizer. In the presence of superplasticizers, the formation of hydration products and ettringite is reduced and the hydration of the surface is suppressed. Furthermore, the rate of hydration in mortar is studied in the presence of the two admixtures by measuring the temperature evolution as a function of time. The concentration-dependent delay in temperature evolution correlates well with the microscopic observations of different amounts of ettringite formation.     

抗泥型聚羧酸减水剂的制备及性能

以甲基丙烯酸（MAA）、甲基丙烯酸羟乙酯（HEMA）为单体,过氧化氢（H₂O₂）/抗坏血酸（Vc）为引发剂,甲基烯丙基磺酸钠（SMAS）为链转移剂,合成了一种抗泥型聚羧酸减水剂,通过红外光谱（FTIR）、凝胶渗透色谱（GPC）对聚合物进行结构表征,通过水泥净浆流动度、蒙脱土层间官能团、X射线衍射和吸附量测试,对其分散性能及抑制蒙脱土机理进行了探究。结果显示：合成的抗泥型聚羧酸减水剂在摩尔比为2.5：1时分散性能最佳,当减水剂折固掺量为0.25%时,水泥初始净浆流动度为268mm;与普通聚羧酸减水剂相比,合成的抗泥型减水剂对蒙脱土敏感性较低,与蒙脱土作用后的层间未出现抗泥型减水剂的特征官能团,层间距为1.40nm,抗泥型减水剂在蒙脱土上的吸附量远小于普通减水剂的吸附量。     

Design and function of novel superplasticizers for more durable high performance concrete (superplast project)

In this article we shall describe our quest and ultimate success in furthering our understanding of the action of superplasticizers on the rheology of cement and concrete. By specifically producing superplasticizers with varied architectures, we have been able to show the important structural features of the macromolecules that lead to a successful superplasticizer or water reducing agent. Both polycarboxylate and lignosulfonate polymers have been investigated. Using both non-reactive model MgO powders, three different types of cement blends, the adsorption behaviour and the effect on the rheological properties of these two important superplasticizer families have been used to further develop a conceptual model for superplasticizer — cement behaviour. This paper will deal mainly with the conceptual model, the materials and methods used to asses the polymer adsorption behaviour and rheological properties of the systems studied. We shall briefly describe the adsorption of the polymers onto the different surfaces and their influence on surface charge and rheology and the influence of the various ionic species found in cement pore solutions that may influence polymer-cement affinity. The key factors are shown to be the effective adsorbed polymer thickness and the induced surface charge which can be influenced by the polymer architecture, the pore solution composition and the initial particle surface charge.     

葡萄糖酸钠对萘系高效减水剂塑化水泥浆体流动性的影响(英文)

研究了掺萘系高效减水剂浆体中同时掺入葡萄糖酸钠时,对水泥浆体流动性和流动性损失的影响。适量的葡萄糖酸钠可显著提高浆体初始流动度,并降低流动度损失。采用紫外分光光度计、zeta电位仪、X衍射仪和扫描电子显微镜测试了浆体对萘系高效减水剂的吸附量、水泥颗粒表面电位、水化产物钙矾石X衍射峰值强度和微观形貌。结果表明:在同等萘系高效减水剂掺量下,葡萄糖酸钠延缓了钙矾石的生成,并与萘系减水剂在水泥颗粒表面形成竞争吸附,导致了水化过程中萘系高效减水剂消耗量的降低,增加了高效减水剂在水泥颗粒表面的有效吸附量。     

Interaction between ettringite and a polynaphthalene sulfonate superplasticizer in a cementitious paste

It has been recognized that the interaction between a superplasticizer and C3A is crucial when controlling the rheology of Portland cement grouts, mortars and concretes. In spite of the fact that a great deal of research has been done to understand the exact nature of this interaction using different experimental techniques, there is not yet a clear understanding of all the basic principles which command that interaction. In an attempt to cast some complementary light in the type of interactions developed between C3A, Portland cement and a polynaphthalene sulfonate superplasticizer in the presence of calcium sulfate, the rheological behavior of a particular cementitious system in which only calcium aluminates or calcium sulfoaluminates hydrated phases could be formed has been studied. This study has shown that superplasticizer molecules are not only adsorbed on unhydrated cement phases but also and perhaps more on some of their hydrates. This adsorption on the hydrates slows down drastically or even stops the growth of ettringite germs. However, when all the initial superplasticizer molecules have been consumed normal growth of ettringite resumes. This interaction between superplasticizer molecules and ettringite can be used to explain the important water consumption in the early stages of mixing as well as the never answered question: where are all the superplasticizer molecules in a hardened concrete.     

The effect of superplasticizers and air-entraining agents on the Zeta potential of cement particles

The effect of superplasticizers and air-entraining agents on the Zeta Potential (ZP) of a Portland cement was studied by microelectrophoresis. The purpose of the experiments was to investigate the adsorption mechanism of electronegative polymers and surface-active agents, and the interaction between these when added in combination. As a preliminary experiment the microelectrophoresis technique was investigated in order to obtain the most precise and reproducible method of measuring Zeta Potentials. The results show that the superplasticizer type with the longer polymer chain and thereby the largest amount of electronegative charges per chain gives the highest negative Zeta Potential. This is interpreted as indicating that this type of superplasticizer has a higher dispersing capability. Data from dosage of air-entraining agents show that a part of the air-entraining effect is due to the fact that the molecules are adsorbed on the cement surface, thereby making it hydrophobic. The results of combined use of superplasticizers and air-entraining agents show that only a slightly smaller ZP is obtained than when a superplasticizer is dosed alone, which however still indicates an interaction. Finally the ZP has been determined of cement alone.     

Effects of polycarboxylate-type superplasticizer on fluidity and hydration behavior of cement paste

Polycarboxylate (PC)-type superplasticizers were synthesized with different average molecular weight of polyethylene oxide (PEO) graft groups, the molar ratios of graft group to carboxylic group, and then the chemical structure, polymerization condition, and physical and chemical properties were analyzed. In order to evaluate the effects of PC-type superplasticizers in cement paste, the adsorption, the initial plasticity and slump retention characteristics and the degree of hydration reaction were investigated. As the average molecular weight of graft group decreased and molar ratio increased, the conversion rate to copolymers, the adsorption amount of PC-type superplasticizer on cement particles improved; on the other hand, the hydration reaction was delayed.     

Synthesis,working mechanism and effectiveness of a novel cycloaliphatic superplasticizer for concrete

In this study, the synthesis, performance and mode of action of a new type of superplasticizer is presented. From cyclohexanone, formaldehyde and sulfite, a high molecular weight polycondensate (M_w ≈ 220,000 g/mol) was synthesized. The resulting CFS superplasticizer was characterized by size exclusion chromatography and anionic charge density measurement. Performance of CFS in cement was probed by mini slump test and by determining the maximum water reduction achievable. The working mechanism was identified via adsorption and zeta potential measurements. The results show that CFS behaves like a typical polycondensate superplasticizer such as BNS. It enhances the fluidity of cement due to electrostatic repulsion. Advantages of this novel type of superplasticizer are simple preparation method, effectiveness at low water-to-cement ratio, huge water reducing capability and stable performance in the presence of clay.     

聚醚型聚羧酸减水剂的合成和表征及对水泥的微观作用机制

本文以聚醚、丙烯酸、丙烯酸羟乙酯为原料,通过自由基聚合法合成了聚羧酸减水剂JS-PCE和BT-PCE。通过正交优化所得的JS-PCE合成条件为:聚合温度25 ℃,抗坏血酸-巯基丙酸混液、丙烯酸滴加时间分别为3 h、2.5 h,酸醚物质的量比为4.25∶1,引发剂加量为聚醚质量的1.10%。添加JS-PCE的水泥净浆流动度达230 mm,表现出较好的流动性。采用界面化学及电化学等方法探究了减水剂对水泥的微观作用机制,结果表明聚羧酸减水剂在水泥颗粒表面存在饱和吸附量,其与水泥颗粒存在强吸附作用,因此产生分散和减水作用。流变行为分析得出JS-PCE和BT-PCE的最佳折固掺量分别为0.3%、0.4%。     

Influence of Ca2+ on the performance of poly(acrylic acid)-g-poly(ethylene glycol) comb-like copolymers in cement suspensions

Poly(acrylic acid)-g-poly(ethylene glycol) (PAA-g-PEG) comb-like copolymer (PCE) is one of the best kind of superplasticizers for cement suspensions. But PCE can be considered as polyelectrolyte which is easily affected by the ions in cement suspensions. In cement system, calcium ions are the most abundant cations which would have great influence on the performance of polymer superplasticizer. Here, the effects of calcium ion on the surface charge, adsorption and dispersion in cement system with PCE as dispersant are investigated in detail. And the changes in the conformation of PCE before and after adding calcium ions are studied by methods of dynamic light scattering and transmission electron microscopy. Calcium ions increase the zeta potential of cement particles and make the molecular chains of PCE curlier, which induces the changes in adsorption and dispersion behavior. The adding of calcium ions makes the ion bridging between calcium and PCE to take place and the ion bridging makes the PCE molecules shrink to smaller size. In this paper, it tells that the molecular structure of PCE polymer could be changed based on the conclusion to adapt the cement with different content of calcium. In cement suspensions, the effect of calcium ions on the performance of PCE polymer would be weakened by decreasing the content of carboxyl groups in the molecular chain.     

Adsorption of superplasticizer admixtures on alkali-activated slag pastes

Alkali-activated slag (AAS) binders are obtained by a manufacturing process less energy-intensive than ordinary Portland cement (OPC) and involves lower greenhouse gasses emission. These alkaline cements allow the production of high mechanical strength and durable concretes. In the present work, the adsorption of different superplasticizer admixtures (naphthalene-based, melamine-based and a vinyl copolymer) on the slag particles in AAS pastes using alkaline solutions with different pH values have been studied in detail. The effect of the superplasticizers on the yield stress and plastic viscosity of the AAS and OPC pastes have been also evaluated.The results obtained allowed us to conclude that the adsorption of the superplasticizers on AAS pastes is independent of the pH of the alkaline solutions used and lower than on OPC pastes. However, the effect of the admixtures on the rheological parameters depends directly on the type and dosage of the superplasticizer as well as of the binder used and, in the case of the AAS, on the pH of the alkaline activator solution. In 11.7-pH NaOH-AAS pastes the dosages of the superplasticizers required to attain similar reduction in the yield stress are ten-fold lower than for Portland cement. In this case the superplasticizers studied show a fluidizing effect considerably higher in 11.7-pH NaOH-AAS pastes than in OPC pastes. In 13.6-pH NaOH-AAS pastes, the only admixture observed to affect the rheological parameters is the naphthalene-based admixture due to its higher chemical stability in such extremely alkaline media.     

Preparation of amphoteric polycarboxylate superplasticizers and their performances in cementitious system

A series of amphoteric polycarboxylate (PC) polymers were synthesized by radical copolymerization of acrylic acid (AA), [3‐(methacryloylamino) propyl] trimethylammonium chloride (MAPTAC) and ω‐methoxypolyoxyethylene methacrylate ester (MPEGMA). Cationic groups were introduced in to PC molecules with expectation of less retardation effect on cement hydration compared to the traditional anionic PC superplasticizers. The content of cationic groups in polymer was varied by changing the monomer ratio of MAPTAC to AA in the synthesis recipes. The structure of the synthesized amphoteric PCs was verified by gel permeation chromatography (GPC) and Fourier transform infrared spectroscopy (FTIR). The performances of the amphoteric PCs were evaluated by measurement of flowability and zeta‐potential of cement pastes and adsorption amount of PC in cement pastes. Impacts of the PCs on cement hydration were studied by isothermal calorimetry. It is concluded that both anionic and cationic PC polymers can be effectively adsorbed onto the surface of cement particles and thus change the zeta potential of cement pastes. The adsorption amounts of the amphoteric PCs decrease with increasing content of cationic units. A proper incorporation of cationic units into PC polymers may lead to a higher fluidizing performance in fresh cement pastes. The amphoteric PC polymers with higher content of cationic units show less retardation effect on cement hydration and hence higher early strength of cementitious materials may be achieved by using amphoteric PCs with appropriated content of cationic units without losing their plasticizing efficiency. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41348.     

Tailoring the anionic function and the side chains of comb-like superplasticizers to improve their adsorption

Nowadays admixtures and especially superplasticizers are unavoidable components of the concrete formulation. The high fluidizing efficiency of the comb-like superplasticizers must not overshadow their high costs. This study aims to determine the PCE structure parameters which influence their adsorption in order to enhance their resistance to sulfate competitive adsorption and thus minimize their dosage. The PCE adsorption has been studied on calcite and ettringite which are both surfaces representative of early hydrating cement. The effect of the POE side chain length and density and also of the PCE anionic function i.e. carboxylate, dicarboxylate or phosphate on the adsorption has been analyzed. As main result, the modification of the anionic is a good technological way to improve the resistance to sulfate competition. At equivalent charge density, the dicarboxylate polymer is less sensitive to sulfate ion concentrations than the monocarboxylate one, while the phosphate PCE is quite insensitive for the concentrations studied.     

Synthesis and performance of methacrylic ester based polycarboxylate superplasticizers possessing hydroxy terminated poly(ethylene glycol) side chains

The synthesis and performance of new methacrylate ester based polycarboxylate superplasticizers is shown. These new superplasticizers possess hydroxy termination of the poly(ethylene glycol) side chains instead of conventional methoxy termination. Properties of the new superplasticizers in cement paste were compared to those of conventional ones. For this comparison, methacrylic acid-poly(ethylene glycol) methacrylate ester copolymers having three different side chain lengths and either hydroxyl or methoxy terminated graft chains were synthesized. For characterization of the superplasticizers, gel permeation chromatography (GPC) as well as anionic charge density determination was carried out. The performance of the polymers in cement was tested by measuring paste flow, adsorption as well as zeta potential. Additionally, retardation of the copolymers possessing side chains of 45 ethylene oxide units was investigated by heat calorimetry. According to the data, macromonomers based on hydroxy terminated poly(ethylene glycol) methacrylate ester chemistry allow to produce superplasticizers of high quality.     

Structure and Characterization of Sulfated Chitosan Superplasticizer

A new sulfated chitosan superplasticizer (SCS) was synthesized by sulfation chitosan. The chemical structure and molecular weight of SCS were characterized by FTIR and gel permeation chromatography (GPC). The application performances of SCS in cement paste and concrete were investigated in the views of fluidity, slump, setting time, porosity as well as compressive strength. The results indicated that the SCS has better applied performance compared with polycarboxylate superplasticizer (PCs). A notable feature is that SCS has better maintenance for cement paste fluidity and concrete slump. The action mechanism behind this behavior was further revealed by zeta‐potential and adsorption amount. Meanwhile, SCS comes from renewable source and has biodegradability. This research work provides not only a new superplasticizer but also a method for preparing superplasticizer from the renewable biopolymer.