摘要 ：

The polycarboxylate superplasticizer/calcium silicate hydrate (PCE/C-S-H) nanocomposites have been used as an enhancing agent for the early strength development of cementitious materials by providing nucleation site for cement hydrates. This study aims to investigate the mechanism and the effect of PCE on the microstructure and properties of C-S-H. PCE/C-S-H with varying calcium-to-silicon ratio (C/S) are prepared via the co-precipitation method in PCE solution using methyl ally polyethylene glycol (MAPEG) as macromonomer and characterized by means of XRD, FTIR, TG, DSC, TEM, DLS, zeta potential and TOC. The mortar strength containing PCE/C-S-H with different C/S ratio is investigated at early curing age. The results from XRD show that the basal spacing of C-S-H interlayer is increased, indicating that the PCE can intercalate into the interlayer of C-S-H, which is consistent with the results from TG and DSC. Besides, the synthesized C-S-H can be well protected from carbonation in the presence of PCE. Combining the results of XRD, FTIR and TOC, it can be revealed that PCE only can graft in the vacant sites in silicate chain of C-S-H with C/S ratio of 1.7. Zeta potential results show that PCE can adsorb the surface of C-S-H. The results from mortar compressive strength show that the PCE/C-S-H with low C/S has a more acceleration performance than high C/S for low calcium content of PCE/C-S-H that contains more loose foil-like flasks than higher content of calcium, which can provide more nucleation sites for hydration products.

关键词 ：

Carbonation Mechanism Nanocomposite Calcium-to-silicon ratio C-S-H

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As an ancient architectural restoration material, hydraulic lime has good early properties, which is necessary to ensure its successful application. Metakaolin-air lime (MK-AL) composite material as a kind of hydraulic lime, the initial fluidity, macroscopic rheological properties, viscoelasticity and dissolution-early hydration are systematically investigated by setting different water to binder (w/b) ratios, polycarboxylate superplasticizer (SP) and metakaolin dosages. The results showed that the initial fluidity of MK-AL pastes has a more obvious improvement by adding SP. The rheological behavior of MK-AL paste was well characterized by both the Bingham model and H-B model. The reduction of yield stress and plastic viscosity on account of the better dispersion of particles in MK-AL paste. The rheological behavior expresses shear thickening without SP and shear thinning with SP in MK-AL paste are revealed. The viscoelastic transformation is illustrated by the macroscopic viscosity index, elastic index, storage modulus, loss modulus, solid-liquid balance and fluidity index parameters, these parameters have a reduction to a large degree with increasing w/b ratios and SP dosage, while the variation of metakaolin dosage has relatively little impact. The increase in w/b ratio and SP dosage promote the dispersion and dissolution of the particles in the aqueous solution, and the strong dispersive capacity delays the process that particles heap up rapidly and network structure formation in MK-AL pastes. Furthermore, the exothermic rate of the two hydration stages is reduced significantly, as well as the appearance of the exothermic peak of hydration is delayed.

关键词 ：

Network structure Metakaolin-air lime Rheological behavior Dissolution Superplasticizer Viscoelastic transformation

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Reducing or eliminating cracks caused by shrinkage of cementitious materials remains a daunting challenge for construction engineers. Drying shrinkage and autogenous shrinkage are the main shrinkage types in the service process of cement-based materials, which have a great impact on engineering applications. If cracks in concrete generate by drying or autogenous shrinkage, the mechanical properties, water resistance and durability of concrete will be also affected. It is an effective method to use chemical admixtures to inhibit the shrinkage of cement-based materials. Polycarboxylate plasticizer (PCE) is an important chemical admixture in cement-based materials and is widely used in practical engineering. It can bring great value by reducing the shrinkage effect through molecular design. Through our innovative design, a series of shrinkage-reducing polycarboxylate superplasticizers (SRPs) were synthesized, their molecular structures were confirmed by Fourier transform infrared spectroscopy (FTIR) and their molecular properties were determined by gel permeation chromatography (GPC). Furthermore, the shrinkage performances at different ages of the mortars containing the synthesized SRPs with different structures were systematically evaluated. The results showed that compared with the blank sample, the dry shrinkage rate and free shrinkage rate of the mortars containing SRP decreased by over 20% and 15%, respectively. Additionally, the shrinkage rates of the mortars containing SRP were significantly lower than that of the mortar containing conventional PCE, and moreover, the water-reducing performance was improved compared to conventional PCE. Based on the experimental results of surface tension and evaporation rate of different SRP solutions, the mechanism of the shrinkage-reducing effect was probed, as expected to provide guidance for the design and development of new shrinkage-reducing admixtures.

关键词 ：

molecular design polycarboxylate superplasticizer shrinkage-reduction mortar synthesis

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The reactivity ratio of monomer and the microstructure of copolymer as polycarboxylate ether (PCE) superplasticizer were investigated. Polycarboxylate ethers (PCEs) were synthesized from methyl allyl polyethylene glycol (MAPEG, M-w=2 400 g/mol) and methacrylic acid (MAA) via aqueous free radical copolymerization in low conversion (P<20%). Gel permeation chromatography (GPC) and high performance liquid chromatography (HPLC) were used to track the residual concentration of the reactants and the amount of copolymer formed during the copolymerization. The reactivity ratios of monomers, MAPEG and MAA, were determined as r(1(MAPEG)) =0.0489 and r(2(MAA)) =1.6173, respectively, by employing the K-T and YBR methods. According to the obtained monomer reactivity results, the sequence distribution of the copolymer, the number average length of MAA in the polymerisate were found to decline with the decrease of the mole fraction of MAA in the polymerization system. As a result, the distribution of chain segments becomes narrower and the copolymer structure becomes more uniform. Therefore, uniform polymers could be obtained by slowly adding MAA monomer during copolymerization process.

关键词 ：

copolymer K-T method polycarboxylate reactivity ratio sequence distribution

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A novel polycarboxylate superplasticizer (PCE) was synthesized by graft copolymerization between acrylic acid (AA) and end-functionalized poly (allyl sulfonate) (PALS) to produce comb polymer, i.e. PAA-g-PALS. The molecular structure was confirmed by Infrared Spectroscopy (IR) and H-1 Nuclear Magnetic Resonance (H-1 NMR), and the molecular properties were characterized by Gel Permeation Chromatography (GPC). The conventional PCE with comb structure using isobutenyl polyethylene glycol (IPEG) as side chains (i.e. PAA-g-IPEG) was also synthesized to explore the effect of the side chain on the PCE performances. The fluidity and its retention, rheological properties, hydrodynamic radii (R-h), adsorption behavior and zeta potential of the cement pastes containing PAA-g-PALS or PAA-g-IPEG were comparatively tested. It was found that this designed "sulfonate modified PCE" exhibited stronger dispersing stability and sulfate tolerance to cement paste and less sensitive to the sulfate competitive adsorption and the increase in ionic strength. Based on the above results, the evaluation method (the sulfate resistance index of PAA-g-PALS was increased by 24% as compared to that of PAA-g-IPEG) was innovatively established and the mechanism of sulfate resistance was clarified in detail. The purpose of this research is to offer an avenue with great potentials to synthesize a novel PCE with excellent workability retention and sulfate tolerance in fresh cement pastes. This sulfonate-modified polycarboxylate superplasticizer has great potentials as a viable alternative to conventional PCE, especially in some harsh cement systems. (C) 2020 Elsevier Ltd. All rights reserved.

关键词 ：

Sulfate tolerance Cement Dispersion Molecular design Polycarboxylate superplasticizer Sulfonation modification

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Polycarboxylate superplasticizer (PCE) is widely used in concrete, but the clay content in the aggregate is increasing at present, which seriously weakens the dispersing function of PCE. Therefore, in order to lower the sensitivity of PCE to the clay, beta-cyclodextrin (beta-CD) was used for synthesizing anti-clay polycarboxylate superplasticizers (AC-PCE). Firstly, the clay tolerance property of AC-PCE was explored by the fluidity and rheological test; then, the PCE was mixed with montmorillonite (MMT), and interaction mechanism was studied. The results showed that compared with the conventional polycarboxylate superplasticizer (CO-PCE), an increase of 19.5% and 14.9% was observed in the fluidity of cement paste and mortar for AC-PCE, indicating that the sensitivity of AC-PCE to the clay was lower than that of CO-PCE. Both CO-PCE and AC-PCE were adsorpted on MMT. XRD results showed that intercalation adsorption had occurred for both CO-PCE and AC-PCE. N-2 adsorption results showed that although AC-PCE was also inserted into the interlayer of MMT, its adsorption amount was lower than that of CO-PCE due to steric hindrance from beta-CD, which increased the sorption level of the AC-PCE on the cement clinkers particles. Therefore, the clay tolerance of PCE was enhanced significantly by beta-CD.

关键词 ：

polycarboxylate mechanism analysis beta-cyclodextrin clay tolerance fluidity superplasticizer

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With the rapid development of the construction industry, it is necessary to synthesize environment-friendly functional polymers, especially when developing "green" construction industry types. Herein a novel solid-state polycarboxylate superplasticizer (PCE) with low energy-consumption was designed and synthesized. In industrial application, solid-state PCE has exhibited better cement paste fluidity and concrete slump compared to liquid-state PCE. A life cycle assessment (LCA) of the PCE synthesis, the packaging materials used, and the transportation of the PCE were conducted based on the ReCiPe method. The results indicated that liquid-state PCE has a far greater environmental impact at >60% than solid-state PCE, which is less significant at <40%. The inventory data that are associated with the production of the new polymer are disclosed for the first time to enrich the related database in this field. This study demonstrates the optimization of the state and synthesis technique of a functional polymer, improving the performance and lowering the environmental impacts involved in producing the polymer, while reducing the risks to human health and protecting the ecosystem at the same time.

关键词 ：

Concrete Technical optimization Environmental impacts LCA Solid-state Superplasticizer

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摘要 ：

A superplasticizer was synthesized by maleic anhydride and isoprenyl-PE-PPG according to molecular structure design principle. The molecular structure of superplasticizer was determined by Fourier transform infrared spectroscopy, 1H nuclear magnetic resonance and gel permeation chromatography, respectively. The surface tension, adsorption behavior, zeta potential, the flow behaviour of superplasticized cement paste, rheological behavior of cement pastes, and application performance in concrete have been measured. Results of evaluation on performance have showed that superplasticizer has good viscosity-reducing effect and the mechanism of superplasticizer has been analyzed. © 2021, Materials Review Magazine. All right reserved.

关键词 ：

Structural design Cements Fourier transform infrared spectroscopy Molecular structure Nuclear magnetic resonance spectroscopy Viscosity Gel permeation chromatography High performance concrete

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Conductive parameters (electrical resistivity and electrochemical impedance spectroscopy) and profound mechanism of fresh cement slurry with water to cement (w/c) ratios of 0.35, 0.4, and 0.45 and samples whose w/c ratio is 0.4 containing 90% cement and 10% silica fume (or 10% blast furnace slag) are studied in this paper. Furthermore, fresh cement slurry with various dosages of superplasticizer is prepared to explore different rheological properties of the fresh paste. Results indicate that the evaluation function for electrical resistance and slump flow or apparent viscosity fits well with one dimensional Gauss function equation. Silica fume can improve the conductivity of fresh cement slurry, while blast furnace slag shows a contrary effect. The conductivity of fresh cement slurry can be simplified as an equivalent circuit which consists of the contact resistance between embedded electrodes and fresh cement slurry and three following series-connected electrical components (three resistor elements and three capacitance elements). Both the rheological and electrical properties of fresh cement slurry are closely related to the content of free water which highlights the possibility of monitoring the rheological parameters of fresh cement slurry through electrical testing ways. (C) 2020 Elsevier Ltd. All rights reserved.

关键词 ：

Electrical resistivity Electrochemical impedance spectroscopy Fresh cement slurry Rheological properties Scanning electron microscopy

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摘要 ：

Shrinkage-reducing polycarboxylate superplasticizer (SRPC) has a good effect on reducing shrinkage of cement-based materials because of its low surface tension. However, the effect of SRPC on the properties of cement-based materials needs to be further explored. A comparative study of SRPC and polycarboxylate superplasticizer (PCE) was carried out with the aim of correlating the adsorption in fresh cement pastes with their dispersing capability and the impacts on cement hydration. The results indicate that the adsorption amounts of SRPC are less than PCE. Both of them exhibit a multilayer adsorption; the fluidity of cement pastes with SRPC and PCE are related to the first adsorbed layer, and the secondary adsorbed layer does not contribute to the enhancement of fluidity. The retarding cement hydration of SRPC is weaker than PCE because of weak adsorption capacity of SRPC.

关键词 ：

adsorption fluidity hydration shrinkage-reducing polycarboxylate superplasticizers

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