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Ferroaluminate cement is widely used in marine engineering applications owing to the remarkable durability and strength of its main hydrate, Al(Fe)–ettringite. The structure and performance of Al(Fe)–ettringite still require extensive exploration. An Al(Fe)–ettringite molecular model containing different Fe contents (0%, 25%, 50%, and 75%) was developed via Materials Studio. Radial distribution functions, time-correlated functions, and mean square displacement were used to analyze the structure of Al(Fe)–ettringite, after which Al(Fe)– ettringite was prepared using a coprecipitation method. The hydration of Al(Fe)–ye'elimite, the nanoindentation testing, and compressive strength of four ettringite types were assessed to facilitate a comparison with the simulation results. Increasing the Fe content resulted in increased lattice size and density. Fe atoms mainly reacted with Ohs atoms to form Fe–Ohs bonds, resulting in an increased Fe–Ohs bond length, with the Fe atom density resulting in volume expansion and increased density in Al(Fe)–ettringite. At 25% Fe content, the number of Hw–Ow hydrogen bonds in Al(Fe)–ettringite was 1166.14, the MSD value was 1.53 Å2, and the water molecules diffused the fastest. The improved macromechanical properties obtained by adding Fe atoms demonstrate that Fe atom substitution can enhance the ettringite structure. The experimental results validated the simulation results. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The wide application of surfactants in cement-based materials requires the understanding of the influence of surfactants on the structure and properties of C–S–H gel. In this study, cation surfactants (CTAB) and anion surfactants (SDS) in ionized type are successfully intercalated into C–S–H gel, generating different molecular models through molecular dynamics simulation. Systematic analysis and quantitative description were performed on the molecular structures, bonding properties together with deformation and fracture mechanisms. It was found that the majority of Br– ionized from CTAB could interact with Ca_interl, forming Br-−Ca_interl bonds. Smaller Na+ ionized from SDS could bond with both O_bri and O_nbri atoms, while O– and O atoms in SDS anions could interact with Ca_interl atoms as well. It is noteworthy that the intercalation of CTAB into C–S–H gel promotes the diffusion of water molecules, whereas the intercalation of SDS into C–S–H gel inhibits the diffusion of water molecules. Uniaxial tensile simulation results reveal that the breakage of both H_water–O_water hydrogen bonds and Ca_interl–O_water bonds dominates the failure process of CTAB/C–S–H gel, while the breakage of H_water–O_water hydrogen bonds governs the fracture of SDS/C–S–H gel. [ABSTRACT FROM AUTHOR]

The purpose of this study was to investigate how the addition of shrinkage-reducing polycarboxylate superplasticiser (SRPC) affected the shrinkage of cement-based materials (CBMs). SRPCs can significantly reduce the surface tension of cement solutions. In this work, a new molecular structure of SRPC was synthesised; its surface tension was reduced to 34·1 mN/m, which is lower than that of ordinary polycarboxylate superplasticisers (PCEs). Compared with mortars without additives, the shrinkage-reducing ratios of mortars containing SRPC at 7 and 49 d were about 33 and 22%, respectively, for an SRPC dosage of 0·2% by mass of cement. The results showed that the SRPC reduced the shrinkage of CBMs more effectively than an ordinary PCE. Furthermore, the shrinkage mechanism of CBMs containing SRPC was assessed regarding three aspects: the change in the pore size distribution of the cement pastes with pore size below 50 nm, the reduction of the capillary pore pressure in the hardened cement pastes after the addition of a low-surface-tension SRPC and the reduction in the evaporation rate of moisture through SRPC aggregation on the gas–liquid interface in cement pastes. [ABSTRACT FROM AUTHOR]

Tertiary alkanolamines play an essential role in the hydration of cement-based materials as one of the main components of cement grinding aids and concrete admixtures. Although the field has been well-studied, the significant effects of slight variations in alkanolamine type and dosage make it imperative for researchers to fully understand alkanolamines before using them. Therefore, it is necessary to understand in detail the mechanism of different alkanolamines affecting the hydration of cement-based materials and their effects on setting and hardening. Based on the synthesis and chemical characteristics of alkanolamines, the complexation between alkanolamine and metal ions is discussed in this paper. The influence of alkanolamines on hydration of cement-based materials and the role of complexation in hydration are studied. Various properties of cement-based materials in the presence of alkanolamines are rigorously reviewed. The synergistic effects of alkanolamine and other admixtures are also considered in this review. The research findings prove that the complexation of alkanolamines plays an essential role in hydration and further interferes the microstructure and properties of the cement-based materials. Variations in the molecular structure and dosage of alkanolamines can lead to significant differences in hydration. The modification of alkanolamines at the molecular level and their use in combination with other admixtures are the future research directions. The working mechanism of alkanolamines in the hydration process of cement-based materials still needs to be further explored. • Complexation of alkanolamines significantly affects cement hydration. • Different alkanolamines have different effects on mineral phase hydration. • Alkanolamines significantly affect the morphology of C-S-H gels and Ca(OH) 2. • The right dosage of alkanolamine could improve compressive strength. • TEA has a significant effect on setting time. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel PCE (ISC-PCE) with ionic side chains was elaborately designed and synthesized. • Good plasticizing and retention capacities were shown for wide potential applications. • Larger R h and more adsorption sites led to a gentle and continuous adsorption mode. • Introducing ionic groups into PCE side chains can greatly thicken the adsorbed layer. • Particularly designed "brush" conformation helped to improve the dispersion stability. A novel dispersant with ionic side chains (ISC-PCE) for cement slurries was elaborately designed and prepared by a simple two-step method and its molecular structure was proved. The performance test results showed that the cement paste containing ISC-PCE exhibited stronger fluidity retention (about 79.6 % after 3 h), longer free settling time (more than 3 h) and fewer flocculating structures, which presented significant dispersing stability. Furthermore, the working mechanism of ISC-PCE to cement particles was also probed via molecular conformation, adsorption, complexation ability, zeta potential and adsorbed layer measurements. It is interesting that the introduction of ionic side chains into conventional dispersant-polycarboxylate superplasticizer (PCE) molecules can achieve gentle and continuous adsorption and increase the adsorbed layer thickness (increased by 103.1 % compared to conventional PCE). The aim of this study is to offer a promising pathway to synthesize a novel PCE endowing outstanding workability stability and great rheological improvements to cement pastes by innovative molecular design. This PCE with ionic side chains has enormous promises as an effective substitute to conventional PCE with nonionic side chains, particularly in the cement paste systems with strict requirements on slump retention. [ABSTRACT FROM AUTHOR]

To solve the problem of high viscosity for fresh concrete especially high-grade concrete, a novel viscosity-reducing type of polycarboxylate superplasticizer (PCE) was synthesized based on innovative design of molecular structure, and also was characterized to confirm the designed molecular structure. The rheological performances of cement paste and fresh concrete containing synthesized PCE were probed, which were analyzed by means of surface tension, adsorption behavior and zeta potential. The plastic viscosity showed a good correlation with T50 and V-funnel time according to mesomechanics process model. Moreover, the investigation of working mechanism interestingly showed that lowering molecular weight and side chain length and introducing hydrophobic groups can achieve improved dispersion capacity and viscosity-reduction effectiveness. The aim of this study is to provide a promising avenue to synthesize PCE with superior workability and viscosity-reducing performance in fresh concrete. This new type of PCE can be used as a viscosity-reducing agent in concrete engineering. [ABSTRACT FROM AUTHOR]

A novel star-shaped polycarboxylate superplasticizer (SPCE) was synthesized through a simple two-step method. 1 H Nuclear Magnetic Resonance ( 1 H NMR) and Infrared Spectroscopy (IR) measurements were used for structural characterization. SPCE and comb-shaped polycarboxylate superplasticizer (CPCE) with same molecular weights were designed and synthesized. The cement paste containing SPCE exhibited better fluidity, fluidity retention, water reduction, 25% lower saturated dosage of PCE, 10% longer setting time, lower hydration heat, more delayed hydration heat evolution and lower amount of hydration products at early ages. Furthermore, the adsorption behavior of SPCE and CPCE in cement pastes and the zeta potential were investigated, and then the working mechanism of SPCE was theoretically explained. It is interesting that changing topological structure from comb-shape to star-shape can achieve the optimization of dispersion effect, and further improve the working effectiveness. The aims of this study are to provide a new avenue to synthesize superplasticizer with novel structure achieving the chemical diversity of superplasticizer structure, and to verify the contribution of optimizing molecular shape. This new type of superplasticizer can be used as a rheology modifying agent in fresh cement-based materials. [ABSTRACT FROM AUTHOR]

Chemical admixtures are indispensable functional ingredients in modern construction, and their raw materials for synthesis are mainly sourced from petrochemical products, leading to petrochemical resource consumption and environmental damage. Using biomass as a raw material for preparing chemical admixtures for concrete is an effective and environmentally friendly method that holds great promise for overcoming these environment problems and obtaining exceptional application properties. This work systematically addresses the recent research advances in chemical admixtures using polysaccharide, polyphenol biomass and biorefineries, including their preparation methods, application effects and environmental impact assessment. The results show that the molecular structures of polysaccharide and polyphenol biomass contain a large number of active functional groups, which help bio-based chemical admixtures to be prepared by acylation, sulfonation and/or graft copolymerization, significantly improving the dispersibility, water retention, retardation, anti-adhesion and durability of cement-based materials. Also, the use of biorefinery technology endows chemical admixtures with superior environmental performance. In addition, this review addresses the importance of the life cycle assessment (LCA) method in evaluating the environmental impacts of bio-based chemical admixtures and establishes that environmental pollution can be substantially minimized by optimizing the preparation process (e.g., use of renewable raw materials, adoption of biorefineries, etc.). This article gives an overview on bio-based chemical admixtures and their high-value utilization and ecological development that provide a theoretical basis for the design of energy-saving and low-cost bio-based chemical admixtures. [Display omitted] • Potential application of biomass in preparation of environment-friendly admixtures. • Preparation processes of conventional and new bio-based admixtures were compared. • Bio-based admixtures show better properties and lower environmental impact. • Application of LCA methodology in preparation of bio-based chemical admixtures. • Performance and environmental benefits of biomass into bio-based admixtures. [ABSTRACT FROM AUTHOR]

This work aims to investigate the solubilizing ability of alkanolamines on steel slag (SS) and the chelating ability of alkanolamines with metal ions. In this paper, the chelation effect of four alkanolamines, including triethanolamine (TEA), triisopropanolamine (TIPA), diethanol-isopropanolamine (DEIPA), and methyl diethanolamine (MDEA), and metal ions on the dissolution of SS was investigated. The conductivity meter, pH meter, X-ray powder diffraction (XRD), inductively coupled plasma atomic emission spectroscopy (ICP-AES), total organic carbon (TOC) and isothermal calorimetry were used to investigate the solubilizing ability of SS impacted by alkanolamines. Additionally, the conductivity meter and chemical precipitation method (CPM) were used to investigate and explore the chelating ability of alkanolamines interacting with the metal ions. Finally, the nuclear magnetic resonance hydrogen (1HNMR) spectroscopy was adopted to investigate the chelating mechanism between alkanolamines and metal ions. The results showed that the alkanolamines increased the elemental concentrations of [Ca], [Al], [Fe] and [Si] in the liquid phase of SS through chelating and promoted the dissolution of the mineral phase of C 3 S, C 2 S and C 4 AF in SS. Among the different alkanolamines, DEIPA was present in the liquid phase for the longest time and possessed a more sustained ability to chelating metal ions. The result also shows that alkanolamines can chelate the Ca2+, Al3+ and Fe3+ in solution. The chelating ability of tertiary alkanolamines were stronger than the secondary alkanolamine. And the alkanolamine with asymmetric molecular structure have stronger chelating ability than those with symmetric molecular structure. Tertiary alkanolamines form ternary five-ring structure with metal ion through nitrogen and oxygen atoms. • Alkanolamines promoted the dissolution of the mineral phase in steel slag. • DEIPA possessed a more sustained ability to chelating metal ions. • Alkanolamine with asymmetric molecular structure have stronger chelating ability. • Ternary five-ring structure formed between the ternary alkanolamine and metal ion. [ABSTRACT FROM AUTHOR]

Abstract: In this work, aragonite CaCO3 with complex morphologies was synthesized through homogeneous precipitation, in which calcium acetate and urea precipitated at 90°C in the presence of PVP. The effect of the concentration of urea and PVP on the CaCO3 crystalline was investigated. The morphology and structure of the CaCO3 particles were characterized by SEM, XRD, and FT-IR. It was found that the concentrations of urea and PVP in the mixed aqueous solution were turned out to be important parameters for the morphology of CaCO3 particles. All CaCO3 particles were mainly aragonite with morphology from bundles of rods, bouquet-like and dumbbell-like. And there was no phase transition under the research conditions. Moreover, the possible process for the formation of the morphology of aragonite was discussed. [Copyright &y& Elsevier]

• Amine molecular structures play a key role on the aggregation behaviors in C–S–H gel. • Penetration depth and residence time reflect bonding property and molecular mobility. • High concentrated hydroxyl groups in TEAs form strong hydrogen bonds in a remarkable stability. • Breakage of hydrogen bonds in water leads to the failure of C–S–H gel and its nanocomposites. Determining the amine molecules behaviors in the nanochannels enables the interpretation of the microstructure and macroscopic properties of amines modified cement based materials. In this study, quantitative analysis were performed on the behaviors of amine molecules (TEPAs, PAMs and TEAs) by molecular dynamics (MD) simulation in the nanochannels of C–S–H gel. According to the interaction of amine molecules with C–S–H gel substrates or water molecules, research works revealed that amine molecules with special spatial structures illustrate different aggregation behaviors. TEPAs with linear structures tend to aggregate in a regular sequence at the center of the C–S–H gel nanochannels. Instead, PAMs and TEAs with branched structures prefer dispersing in the aqueous solution in the C–S–H gel nanochannels. Such different aggregation behaviors allow amine molecules to have various penetration depth and residence time in the interfacial regions. It was found that oxygen atoms and active hydrogen atoms in PAMs and TEAs can form stable interaction with calcium ions and oxygen atoms of C–S–H gel substrates, respectively. The oxygen involved bonds are stronger than nitrogen involved ones for all the molecules due to great electronegativity. There is no formation of hydrogen bonds in TEPAs, but polar atoms in PAMs and TEAs can interact through hydrogen bonding. Moreover, TEPAs cannot form strong hydrogen bonding with water molecules due to their aggregation behavior, whereas PAMs and TEAs formed strong hydrogen bonding with surrounding water molecules. In addition, formation of more hydrogen bonding with amine molecules leads to a lower diffusion coefficient of water molecules. Breakage of hydrogen bonds of water molecules causes the final failure of C–S–H/amine molecules nanocomposites subjected to tensile loads. [ABSTRACT FROM AUTHOR]

• A novel sulfonate-modified PCE was synthesized based on innovative molecular design. • Sulfonate modification on the side chains of PCE can enhance the sulfate tolerance. • Effects of competitive adsorption, ionic strength and conformation were studied. • Good performance retention and stability were shown for solving compatibility problem. • Many quantitative evaluation indexes for sulfate tolerance of PCE were established. 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 1H Nuclear Magnetic Resonance (1H 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. [ABSTRACT FROM AUTHOR]