Currently, a novel shrinkage‐reducing polycarboxylate superplasticizer (SR‐PCA) is used to control cementitious shrinkage. To clarify its mechanism when applied in cementitious materials, the ...influence of SR‐PCA on the composition, morphology, and structure of synthetic calcium–silicate–hydrate (C–S–H), together with the interaction between SR‐PCA and C–S–H at the atomic level, is investigated. For comparison, a commercial polycarboxylate superplasticizer (PCA) is also employed. The results show PCA and SR‐PCA can adsorb on the C–S–H surface rather than intercalate into the layers. Compared with PCA, SR‐PCA has a milder impact on C–S–H crystallinity. SR‐PCA refines the pore structure of C–S–H drastically, whereas PCA loosens the structure by increasing the mesopore volume. In addition, the adsorption effect of SR‐PCA on the C–S–H surface is less significant than that of PCA. At the atomic level, this less adsorption of SR‐PCA is attributed to the lower adhesion energy of the C–S–H/SR‐PCA interface due to the weaker Ca–O bond strength.
The impact of a calcined clay (CC) rich in meta kaolin (~50 wt%) present in composite cements at 0–40% substitution rate for the clinker was studied relative to the dispersing force of different PCE ...superplasticizers. It was found that CC increases the water demand of the blended cements considerably (+85% for the 60:40 blend vs. neat OPC). Furthermore, PCEs which fluidize OPC best also provide optimal performance in CC blended cements, but require much higher dosages (in OPC/CC 60:40, 4–6 times as compared to neat OPC). In all systems, HPEG-PCE produced superior dispersing performance over anionic MPEG-PCEs. A mechanistic study involving zeta potential measurements revealed that the initially negatively charged calcined clay surface adsorbs huge amounts of Ca2+ ions from the pore solution, thus facilitating adsorption of anionic PCE superplasticizers. The results signify that commercially available PCE products can effectively fluidize OPC/CC blended cements.
•Cements containing 0–40 wt% of a calcined clay rich in meta kaolin were studied.•The calcined clay decreases fluidity of the blended cements considerably.•In cement, the calcined clay adsorbs a large amount of Ca2+ ions.•A common HPEG polycarboxylate superplasticizer fluidizes OPC/CC blends best.•A zwitterionic PCE also fluidizes well and adsorbs in similar amounts as HPEG.
To improve the flowability of ultrafine-tailings cemented paste backfill (UTCPB) while keeping water content low, superplasticizers (SP) are usually used. The water film thickness (WFT) theory was ...introduced to investigate the flowability of UTCPB incorporating SP. The obtained results show that the packing density of particles increases significantly with the increase of SP dosage due to the improved particle size distribution of the flocs by de-agglomeration effect of SP. The flow spread of fresh UTCPB can be characterized by the unary exponential-type function of WFT to some extent due to the weakened direct effect of SP dosage by high water content. Flocs still exist in the fresh UTCPB incorporating SP and the WFT of flocs (FWFT) can be regarded as the only factor controlling the flow performance of fresh UTCPB. The results presented in this study will contribute to a better understanding of the flow behaviour of UTCPB with SP.
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•Effects of superplasticizer on flowability of UTCPB were investigated from WFT theory.•The flow behaviour of the UTCPB incorporating SP before and after the threshold WFT is quite different.•Superplasticizer influences UTCPB flowability through changing FWFT.
At present, due to the excellent properties of graphene, which can significantly enhance the performance of lubricants, researchers are conducting extensive studies on it. However, the poor ...dispersion of graphene limits its application in lubrication, which becomes an urgent problem for researchers to solve. Moreover, with the concept of green environmental protection becoming more and more popular, the research on water-based lubricants is of great significance. Therefore, we modify three-dimensional graphene (3DG) by polycarboxylate superplasticizer (PCE) to prepare a water-based lubrication nano-additive with long-term dispersion stability, named PCEG. PCEG nanomaterials can stably disperse in water for more than three months, which effectively solves this problem. Tests show that friction coefficient and wear volume of the lubricant with 0.5 wt% PCEG are reduced by 31.1 % and 23.1 %, respectively, compared to the base fluid at 20 N (2.7 GPa) heavy load conditions. The enhanced lubrication performance is attributed to the fact that PCEG, which has excellent dispersion stability, forms a strong adsorption and continuous dense lubrication film on the friction surface. In addition, it fills and polishes the grooves and pits, thus improving the friction-reduction and anti-wear properties. This study not only greatly solves the problem of poor dispersion stability of graphene and develops a nano-lubricant that is consistently effective under heavy load conditions, but also provides an important reference value for the subsequent development of high-performance and stable graphene-based lubricants.
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•PCEG with excellent dispersion stability was prepared.•PCEG as an additive improves by 31.1% and 23.1% in friction and wear.•The modification method used in this study is easy to operate and can be applied in large-scale production.•PCEG provides a reference solution the problem of poor dispersion of graphene in water-based lubricants.
At first, a critical overview of current polycarboxylate (PCE) technology including the chemistry of different kinds of PCEs, characteristic molecular properties, their interaction with cement and ...application aspects are discussed. In the following, the classification and chemistry of clays and clay minerals is presented. In addition, the interaction of PCE superplasticizers with clay minerals and in particular the very harmful chemical sorption of PCE by montmorillonite (MMT) clay which causes a substantial reduction or even complete loss of PCE dispersing effectiveness are introduced. Possible mitigation strategies from the open literature to remedy the negative effects of clay are outlined. Over the last years, calcined clays have gained substantial attention as supplementary cementitious material (SCM). This paper also covers their chemistry and properties as well as their different interaction mode with PCE superplasticizers. Finally, future concepts in PCE technology regarding enhanced clay tolerance and enhancement of the fluidity of Limestone-Calcined Clay Cement (LC3) are proposed.
•The workability of cemented tailings backfill (CTB) are greatly affected by solid content, superplasticizer type and dosage.•The best performance on fluidity behavior of fresh CTB mixtures are ...obtained from the naphthalene-based admixtures.•The mechanical strength performance of CPB samples can be increased significantly by the superplasticizer added to the backfill mix.
This paper presents the coupled effect of solid content and superplasticizer type and dosage on the fluidity and strength properties of cemented tailings backfills (CTB). A total of three different superplasticizers (namely, naphthalene, ether-based and ester-based polycarboxylate) were used at a ratio varying from 0% to 0.5% by mass of CTB. The CTB mixes were proportioned with a solid content of 65%, 66%, 68% and 70%. The unconfined compressive strength tests were performed on CTB samples after 3, 7 and 28 days of curing period. The obtained results show that the effect of superplasticizer on CTB performance depends on type and dosage of the superplasticizer used as well as solid content. The naphthalene-based polycarboxylate admixtures demonstrate the best improvement on fluidity behavior of fresh CTB mixture. For a given superplasticizer type, increases in the dosage of superplasticizer and decreases in the solid content lead to better workability of CTB samples. When increasing solid content, fresh CTB with high superplasticizer dosage performs a relatively low rate of decrease in the workability. A relatively high solid content and superplasticizer dosage have greatly contributed to improved mechanical strengths, especially at 28-day curing age, mainly due to a major reduction in water-to-cement ratio and porosity.
Novel polyphosphate superplasticizers were synthesized by copolymerization reaction between 2-(methacryloyl oxy) ethyl phosphate monomer and the macromonomer polyethylene glycol methacrylate ester at ...different molar ratios.
The synthesized phosphated comb polymers were characterized by size exclusion chromatography and elemental analysis and their dispersing performance in cement was assessed via mini slump tests in cement paste.
The phosphated comb polymers exhibited superior dispersing performance over conventional polycarboxylate comb polymers (PCEs), were less retarding on cement and showed comparable robustness against sulfate and clay impurities. These properties can be explained by the high calcium complexing capacity of the phosphate groups. Thus, phosphated comb polymers present a viable alternative to polycarboxylate superplasticizers.
•Underlying mechanism of SP dosage on viscosity of cement pastes is proposed.•A high concentration of un-adsorbed SP is found in interstitial solution of the paste.•Hydroclustering and SP ...entanglements could be induced in paste with low w/b.
In this paper, the influence and underlying mechanism of superplasticizers (SP) dosage on the viscosity of cement pastes with four water-binder ratio (w/b) were investigated. The results showed that apparent viscosity of the pastes with w/b of 0.24 and 0.32 decreased with SP dosage. Whereas, it is reverse for cement paste with w/b of 0.20 and 0.16. The addition of SP increased the packing density and the water film thickness of pastes with a w/b of 0.32 and 0.24. However, the increase of SP dosage had little effect on the packing density and the water film thickness of pastes with a very low w/b (0.16). For the cement pastes with a very low w/b (e.g., 0.16), the small spaces between the binder particles and the high concentration of the un-adsorbed SP in the interstitial solution may be the primary factors responsible for the increase in viscosity of the pastes.
•Amide-PCE was synthesized successfully and the optimal conditions were determined.•The structure of amide-PCE and its sufficient amidation reaction were confirmed.•Amide-PCE has better application ...performance than the conventional PCE in concrete.•The dispersion mechanism of amide-PCE in cement–water system was illustrated.•It can provide electrostatic repulsion, steric hindrance, complex and lubrication.
The amide-structural polycarboxylate superplasticizers (amide-PCEs) were synthesized by amidation reaction between polyacrylic acid (PAA) and amino-terminated methoxy polyethylene glycol (amino-PEG) under different conditions, and the effects of amide-PCE's synthesis on amidation rate and flow performance of cement paste were investigated. Fourier Transform Infrared Spectroscopy (FTIR), 1H Nuclear Magnetic Resonance (1H NMR), and molecular-weight measurements were used for structural characterization, and the results confirmed ideal amide structure and sufficient amidation reaction. Amide-PCE with the carboxyl–amino ratio of 4:1 exhibited the lowest surface tension, highest adsorption percentage, and the best paste fluidity results. Based on the above results, the dispersion and adsorption mechanisms of amide-PCE in cement–water system were discussed. The application performances in concrete showed that amide-PCE had similar slump to that of conventional PCE, but also had better air-entraining ability, bubble retention and concrete frost-resistance than those of conventional PCE. Depending on this amide structure and good performances, amide-PCE shows broad application prospects.
•Addition of AS in PCE system enhances bleeding and segregation resistance.•Competitive adsorption between AS and PCE occurs.•AS perturbs the adsorption ability of PCE.
Polycarboxylate ...superplasticizer (PCE) and aliphatic superplasticizer (AS) are widely used water-reducing agent in concrete. In actual practice, the addition of AS has been developed as a common way to alleviate the bleeding and segregation of concrete plasticized by PCE, while the main reason for this phenomenon is not clear. In this research, the effect of AS on dispersion of PCE was investigated. Adsorption behavior of AS and PCE and conformation of these polymers in liquid phase were analyzed with total organic carbon (TOC), conductivity, and dynamic light scattering (DLS). Finally, the experimental results were verified by molecular dynamics simulation, and the dispersion model was proposed to better understand the mechanism behind. The results showed that the effects of AS on the rheological performance of cement paste containing PCE was closely related to the added dosage, and it was observed that three stages were divided according to the dosage of AS. The main reason was due to competitive adsorption between AS and PCE. In addition, PCE molecules, which existed in the liquid phase due to competitive adsorption, would be crosslinked through calcium ions in pore solution, leading to the increase in plastic viscosity of cement paste despite with the decreased yield stress. These results explained why the addition of AS in PCE system could enhance the resistance to bleeding and segregation. These results would offer usefully experience for the application of multiple superplasticizer systems in practical engineering.
