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Wick action is the key factor in understanding the salt weathering of porous materials. In this study, concrete discs were partially exposed to Na2SO4 solution to simulate the wick action in concrete. We evaluated the effects of the relative humidity (RH), solution concentration, and pore structures (different water to cement ratios) on the solution transport mechanism based on the water evaporation rate. Interestingly, we found that lower RH and larger W/C ratio accelerated evaporation, but the higher concentration of the solution slowed it down. The micro-analyzer results of NMR and XRD confirmed that the formation of ettringite and gypsum due to chemical sulfate attack blocked the pores in the concrete, resulting in a decrease in water evaporation. Na2SO4 crystallization distress was not detected in the concrete. Therefore, the solution transport process in the concrete discs could not be described by wick action. [ABSTRACT FROM AUTHOR]

• The strength development and drying shrinkage of SBR-SAC compositeswith different ratios were studied. • The pore size distributions and microstructure change of the SBR-SAC composites were monitored. • The brittleness-ductility transition of the SAC-SBR composite was highlighted. The composite of sulphoaluminate cement (SAC) and styrene-butadiene rubber (SBR) latex is expected to possess rapid strength development and adjustable elastic modulus, mainly used in rush repair engineering. This paper investigates the mechanical strength and drying shrinkage of SBR-SAC composites with different proportions. The change of pore structure, phase composition, and microtopography behind the composites was further revealed. Results indicate that, when the SBR/SAC ratio increases from 0/10 to 3/10, the flexural strength of the composite is increased by 343% and its compressive strength is increased by 14.7%, the drying shrinkage is almost not considered, below 0.1%. Besides, at the SBR/SAC ratio of 5/10, the composite loses brittleness, with no obvious peak value of load–displacement curves, and the drying shrinkage of composite at 23 d is 1.496%. This is because dehydrated polymer occupies the location of SAC hydrates, and the polymer film gradually and continuously covers the surface of the cement and becomes thickened. With the increasing SBR/SAC ratio, the continuous phase of composite probably transforms from inorganic cement phase to organic polymer phase. [ABSTRACT FROM AUTHOR]

Abstract Biodegradable beta-tricalcium phosphate (β-TCP) particle reinforced magnesium metal matrix composites (Mg-MMC) have attracted increasing interest for application as implant materials. This investigation was conducted to study the effect of cooling rate on the microstructure and corrosion behavior of a biodegradable β-TCP/Mg-Zn-Ca composite. The composite was fabricated under a series of cooling rates using a wedge-shaped casting mold. The microstructure of the composite was examined by optical and scanning electron microscopy, and the corrosion behavior was investigated using an electrochemical workstation and immersion tests in a simulated body fluid (SBF). Faster cooling rates were shown to refine the secondary phase and grain size, and produce a more homogenous microstructure. The refined microstructure resulted in a more uniform distribution of β-TCP particles, which is believed to be beneficial in the formation of a stable and compact corrosion product layer, leading to improved corrosion resistance for the composite. Highlights • 1β-TCP/Mg-2Zn-0.5Ca composites prepared by a high shear solidification technology • The cooling rate had a strong impact on the grain size and secondary phase particles. • The composite solidified at faster cooling rates exhibited improved corrosion resistance. [ABSTRACT FROM AUTHOR]

In this paper, the effects of asphalt-to-cement ratio (A/C) and water-to-cement ratio (W/C) on the elastic modulus E c of cement asphalt (CA) binder were studied through measuring the stress-strain curves and phase volume fractions of various CA binder specimens. The results illustrate that the CA binder with high asphalt content (A/C ⩾ 0.6) is a two-phase composite with complicated microstructure formed by both cement hydrates and asphalt agglomerates. The elastic modulus of CA binder decreases with the increase of A/C and W/C, especially A/C. A composite model that describes the CA binder in terms of the properties of asphalt and volume fractions of cement phases is suggested, and E c of CA binder can be predicted by this model according to A/C, W/C and properties of asphalt. [ABSTRACT FROM AUTHOR]

Gypsum has been known to regulate cement setting since more than 100 years, whereas the understanding of the physio-chemical mechanism remains incomplete. Here, we investigated the influence of gypsum on elasticity evolution of fresh tricalcium silicate (C 3 S) paste through small amplitude oscillation shear method. Isothermal calorimetry, X-ray diffraction, 1H nuclear magnetic resonance, and zeta potential measurements were performed to explore the corresponding changes in hydration, microstructure, and colloidal interaction. It was found that incorporating gypsum is beneficial for inter-particle agglomeration by significantly weakening electrostatic repulsion force between particles, which accelerates elasticity development in the early period of setting. Although the retardation effect of gypsum on C 3 S hydration hinders the further development of elasticity in the later period, the more divergent needle-like calcium silicate hydrate (C-S-H) and the stronger cohesion of the C 3 S particle network in presence of gypsum lead to a higher elasticity at the same hydration degree. [ABSTRACT FROM AUTHOR]

• The variation of internal temperature field of shotcrete in high ground thermal tunnel. • The phase distribution of shotcrete in high ground thermal tunnel. • Hydration and morphology of hydration products of shotcretein high ground thermal tunnel. • The mechanical properties and pore structure of shotcrete in high ground thermal tunnel. Geothermal tunnel creates one-dimensional heat conduction field which may have an uneven effect on the hydration, microstructures, and mechanical properties of shotcrete for the first lining layer. In this study, the evolution of the internal temperature gradient of shotcrete specimens subjected to the simulated geothermal environment was measured, and its effects on the heterogeneous distribution of internal microstructures, hydration products, and mechanical properties were characterized. Results showed that there was an obvious temperature gradient in the shotcrete exposed to the geothermal environment, which dramatically changes within 24 h of contact and then remains stable afterward. For the properties of shotcrete at an early age (within 24 h), the compressive and flexural strength of specimens exposed to a geothermal environment is significantly higher than that of specimens cured in standard conditions, due to the accelerating effect on hydration by the elevated temperature. The phase assemblage, hydration degree, and mechanical property in the specimens at an early age show a gradient distribution, and more hydration degree and lower porosity were formed in the internal regions with a higher temperature, resulting in a higher compressive and flexural strength. [ABSTRACT FROM AUTHOR]

Thermally activated healing of a cured epoxy/amine network using di-glycidyl ether of bis-phenol A (DGEBA) and triethylene-tetramine (TETA) was explored using a modified thermoplastic poly(ethylene- co-methacrylic acid) (EMAA) healing agent. Epoxy resins of differing molecular weight were blended and pre-reacted with EMAA to heal via covalent and non-covalent bonding. Healing depended strongly on compatibility and reactivity between the epoxy additive and EMAA. Reduced compatibility and preferential miscibility produced the greatest healing, while increased compatibility and epoxide chemical reaction reduced healing. More healing was achieved when the availability of reactive epoxide groups from the healing agent and amino groups from the amine rich DGEBA/TETA polymer networks both increased. [ABSTRACT FROM AUTHOR]

This article explores the use of two β nucleants to improve the fracture behavior of filled and unfilled homo-polypropylene (PP). The first was based upon an organic quinacridone, whereas the second was based upon the inorganic calcium pimelate. Formulations containing various concentrations of nucleant were prepared using single screw extrusion and then characterized by X-ray diffraction, differential scanning calorimetry (DSC), Izod impact strength, and tensile testing. The quinacridone nucleating agent produced higher levels of β crystallinity and better improvement in strain to failure, whereas the calcium pimelate imparted greater improvement in impact strength regardless of whether the PP was filled or unfilled. No direct relationship between β crystallinity and fracture properties was observed though synergistic enhancement in impact strength was evident. By varying the concentration of calcium carbonate in the calcium pimelate from 10 : 1, 5 : 1, 2 : 1, and 1 : 1 weight composition of calcium carbonate to pimelic acid, similar property enhancements were achieved regardless of composition although the 10 : 1 sample did produce superior elongation to break. The importance of cooling rate on microstructure within each sample was explored via a through the thickness study using DSC and nano-indenting methods. Variations in the β content through the thickness were related to cooling and found to be independent of sample composition and processing. Elastic properties varied inversely with β content. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013 [ABSTRACT FROM AUTHOR]

AC impedance spectroscopy (ACIS) is a promising technique for monitoring the microstructure evolution of fresh cement paste in real-time. This paper compared the change of bulk electric resistivity (ρ bulk) obtained from ACIS with the developments of storage modulus (G′) and the mean transverse relaxation times (T 2) of fresh Portland cement pastes within 5 h. It was found that the three different phases (Phase I, II, and III) on the microstructural build-up process of fresh paste can be accurately distinguished by analyzing ρ bulk , as well as G′ and T 2. The use of ρ bulk fails to characterize the microstructural changes in Phase I due to the great sensitivity on the electrical conductivity of the interstitial solution. However, it can successfully reflect the developing features of microstructure in Phases II and III, and reliably evaluate the impacts of water to cement ratio, superplasticizer, and supplementary cementitious materials on the microstructural development. [ABSTRACT FROM AUTHOR]

• The rheological properties of LHC pastes with MEA and SRA were studied. • The variations of dynamic yield stress and plastic viscosity were estimated by response surface methodology. • The roles of MEA and SRA on the static yield stress development of LHC pastes were investigated. The combined use of low heat Portland cement (LHC), MgO-based expansive agent (MEA) and shrinkage reducing admixture (SRA) is beneficial to reduce the cracking risk of concrete. In this study, the effects of MEA and SRA on the rheological behaviour of LHC paste were investigated using dynamic and static shearing tests. The response surface methodology was used to estimate the effects of MEA, SRA, and superplasticizer on dynamic rheological parameters, while the zeta potential, calorimetric, and solid phases tests were conducted to explore the mechanisms of time-dependent rheological behaviour. Results indicate that MEA contributes to higher dynamic yield stress and plastic viscosity, while the effect of SRA is dependent on its dosage. MEA promotes the static yield stress development for accelerating the hydration of blends and the formation of Mg(OH) 2. SRA retards the hydration of LHC and blended paste and reduces the number of main hydration products. However, the static yield stress is further increased by SRA, showing a consistent changing trend with the surface area of hydrated particles. [ABSTRACT FROM AUTHOR]

This study systematically investigated the influence of varying carbon dioxide (CO 2) dosages and steel slag (SS) replacement rates on the fresh and hardened properties of concrete through the injection of CO 2 gas during the mixing process. The composition of hydration products, degree of hydration, and the evolution of microstructural characteristics within the CO 2 -SS-cement system were analyzed. The results showed that CO 2 addition during the mixing process enhanced early strength in SS concrete. For concrete with a 10 wt% SS replacement rate, the incorporation of CO 2 ranging from 0.4 wt% to 1.2 wt% of the total mass of cementitious materials resulted in notable compressive strength increases of 1.26%–12.47%, 0.64%–6.14%, and 11.79%–18.24% at ages of 1 d, 3 d, and 7 d, respectively. CO 2 rapidly reacted with SS to form calcite-type CaCO 3 and promoted the generation of C-S-H through synergistic hydration with cement. However, a high CO 2 dosage (1.2 wt%) led to issues such as microcrack propagation and interface loosening due to CaCO 3 deposition, which could be mitigated to some extent by appropriately increasing the SS content. • CO 2 -mixing and steel slag synergistically improve early strength of concrete. • Increasing steel slag content alleviates adverse effects of high CO 2 dosage. • CO 2 -mixing enhanced the early cement hydration. [ABSTRACT FROM AUTHOR]

To investigate the synergistic effects of steel slag (SS) and granulated blast furnace slag (GBFS) on cementitious systems during carbon dioxide (CO 2) mineralization curing. Ternary paste specimens containing SS, GBFS, and Portland cement (PC) were prepared to analyze the influence of drying pre-treatment time and SS–GBFS mixing ratios on mechanical properties, CO 2 fixation rate, and microstructure evolution. Results emphasize the significance of appropriate drying pre-treatment in enhancing mineralization degree and compressive strength. At 60 °C drying pre-treatment temperature, extending drying pre-treatment time up to 12 h enhances both compressive strength and CO 2 fixation rate. However, beyond 12 h, a decline is observed in both parameters. Moreover, under the optimal drying pre-treatment time, the compressive strength of ternary paste specimens post-mineralization increases with higher SS content, with SS exerting a more pronounced positive effect on CO 2 fixation rate and compressive strength compared to GBFS. After 4 h of mineralization curing, specimens with 50% SS and 10% GBFS demonstrate a 13.16% increase in compressive strength and a 9.16% increase in CO 2 fixation rate compared to specimens with 10% SS and 50% GBFS. Microscopic test results reveal that the primary crystalline product in ternary paste specimens after mineralization is calcite, with traces of aragonite. The SS–GBFS mixing ratio has minimal effect on the type of reaction products but has a predominant influence on the total content and crystallinity of calcarea carbonica. • The increase of steel slag content can improve the degree of mineralization curing. • Increasing blast furnace slag reduces calcite crystallinity. • Steel slag boosts carbon fixation more than blast furnace slag. [ABSTRACT FROM AUTHOR]

• The effect of roughness on bonding performance between old OPC concrete and new MPC concrete was studied. • Fractal dimension was used to define the roughness of the bonding surface. • Roughness has significant influence on the bonding strength and microstructure of interface between new and old concretes. This paper investigated the bonding performance between magnesium phosphate cement concrete (MPC) and ordinary portland cement concrete (OPC) with different roughness. The bonding interface was characterized using fractal dimension, backscattered electronic microscopy, and microhardness. The optimal mixture proportion of MPC is selected with the mass ratio of MgO-KH 2 PO 4 (M/P) by 3:1 and Na 2 B 4 O 7 ·10H 2 O-MgO (B/M) by 40%, which has the compressive strength of 52.8 MPa and the initial setting time of 24 min 20 s. It is found that the roughness indicated by fractal dimension has a positive correlation to rough depth and the bonding performance. The bonding interface can be categorized into two forms that either MPC paste bonds to OPC paste or bonds to the aggregate. Micro-analysis shows that the former has denser hydration products and lower porosity, providing better chemical bonding and the latter contributes to the mechanical interlocking which is the major form of the bonding force. MPC is a potential material for the field application of wet joints of the floating slab tracks. [ABSTRACT FROM AUTHOR]

Workability and early-ages mechanical properties are important indicators of magnesium potassium phosphate cement (MKPC) as a repair material. The effect of metakaolin (MK) on the setting time, fluidity and early-ages strength of MKPC paste was studied, and its influence mechanism was analyzed through pore structure, microstructure and nanomechanical properties. The results show that 10% and 20% of MK prolong the setting time of MKPC paste, but excessive MK shortens the setting time of MKPC paste. Meanwhile, incorporating MK reduces the fluidity of MKPC paste, and the early-ages strength of MKPC specimens increases when the substitution ratio of MK is 10%. When 10% of MK is incorporated to the MKPC paste, the 30-d shrinkage of the sample is only 69% of the control group. Meanwhile, a proper amount of MK can improve the pore structure of the MKPC specimen and make its microstructure denser by generating amorphous aluminosilicate phosphate gel. It is observed from the nano-scale characteristics that incorporating 10% MK can reduce the content of pore phase and unreacted MgO phase, and increase the volume fraction of hydration products. [ABSTRACT FROM AUTHOR]

Fly ash-based geopolymer concrete (FABGC) is a type of environment-friendly building material that displays remarkable mechanical properties and durability. It has the potential for extensive application in the field of civil engineering. This paper considers the related research on the microstructure and durability of FABGC to systematically summarize the results on its alkali-activated reaction, pore structure, and interface characteristics. The degradation mechanisms of FABGC in various corrosive environments are analyzed, and the factors that affect its microstructure and durability are discussed. It is observed that aluminosilicate gel produced by the alkali-activated process of FABGC has an optimizing effect on the pore structure and interfacial transition zone. An effective development of the microstructure can improve the durability of FABGC to a certain extent. At present, there is no consensus on the research conclusions on the microstructure and durability of FABGC. Therefore, further research is required. [ABSTRACT FROM AUTHOR]

This review summarizes the interaction between cement and asphalt emulsion from two aspects: the adsorption of asphalt emulsion on cement grains and the destabilization of asphalt emulsion by cement hydration. [Display omitted] • The adsorption abilities of cement for two types of asphalt emulsion are analyzed. • Both of the physical and chemical interaction mechanisms are summarized. • Effect of interaction on various properties of CA paste are evaluated. • Future research is recommended to develop the high-performance CA composites. Cement asphalt emulsion (CA) composites which integrate the advantages of both rigidity and flexibility, have been widely used as the key materials in ballastless slab track, semi-flexible base, cold recycling of asphalt pavement. The critical properties of both fresh and hardened CA paste are greatly depended on the interaction between cement and asphalt emulsion, which is reviewed in this paper. The interaction mechanisms are summarized from two aspects: the adsorption of asphalt emulsion on cement grains and the destabilization of asphalt emulsion by cement hydration. The main influencing factors and evaluation methods for both the physical and chemical adsorption of asphalt emulsion, and interaction with Ca2+ are introduced. Meanwhile, the influencing mechanisms of interaction on asphalt emulsion demulsification, cement hydration and rheology of CA pastes are analyzed. Last, the prospective direction for research is also suggested. [ABSTRACT FROM AUTHOR]

Abstract: A novel Eu2+ activated Sr-SiAlON oxynitride phosphor, with the chemical composition of Sr14Si68−s Al6+s O s N106−s :Eu2+ (s ≈7), was synthesized by firing the powder mixture of SrO, SrSi2, α-Si3N4, AlN and Eu2O3 at 1900°C for 6h under 1MPa nitrogen atmosphere. The structure has a typical feature of SiAlON consisting of the host framework which is constructed by a three-dimensional MX4 tetrahedral (M: Si or Al; X: O or N) network, and Sr or Eu2+ ions as the guest ions. It has been shown that the Sr-SiAlON:Eu2+ phosphor has the excitation band covering the range of the ultraviolet light region to 500nm, and exhibits an intense blue-green color with the emission band centered at about 508nm. The temperature dependent emission intensity of the Sr-SiAlON:Eu2+ phosphor is better than that of a typical blue-green Ba2SiO4:Eu2+ phosphor. It is demonstrated that Sr-SiAlON:Eu2+ phosphor is very promising for use in white -LEDs. [Copyright &y& Elsevier]

Abstract: Eu-α-SiAlON (Eu m/2Si12−m−n Al m+n O n N16−n ) was synthesized with nominal compositions having small m and n values, by firing the powder mixture of Eu2Si5N8, α-Si3N4, AlN, and Al2O3 at 1900°C for 6h under 1MPa nitrogen atmosphere. The ratio of the oxidation state of Eu2+/Eu3+ was estimated from the X-ray absorption fine structure (XAFS) measurement. The observed X-ray absorption near edge spectrum (XANES) showed that the Eu ion in Eu-α-SiAlON was mainly in divalent state but also coexisted with a small amount of Eu in the trivalent state. The crystal structure of Eu-α-SiAlON was refined by the Rietveld analysis of the X-ray powder diffraction patterns. The lattice constants of the samples increased with increasing m and n values. The excitation band of Eu-α-SiAlON ranged from the ultraviolet to the visible light region and a broad emission band centered at about 590nm were observed. The emission intensity decreased significantly with increasing the ratio of trivalent Eu ion, suggesting that the trivalent Eu could be one of the luminescent killer centers. [ABSTRACT FROM AUTHOR]