•The effects of the NA and WG on the bond behavior between the MPCM and steel fiber after immersion in water were evaluated.•The change laws of cracks in the ITZ were revealed.•Some basic research ...data for the application of the MPC in civil engineering were provided.
In recent years, the magnesium phosphate cement (MPC)-based polymer is a potential type of material to quickly repair existing structures due to some distinguished advantages. In this paper, a series of experimental studies were conducted to evaluate the effects of the nano-Al2O3 (NA) substitution rate, water glass (WG) substitution rate and immersion time on the bond behavior between the magnesium phosphate cement mortar (MPCM) and steel fiber (SF). The main properties of the pull-out specimens were examined, including the bond strength, energy consumption of steel fiber pull-out, and water stability of the MPCM-SF interface evaluated by the bond strength retention rate and relative bond strength retention rate. In addition, the micro analysis of the fiber-matrix interface transition zone (ITZ) were conducted by using the Scanning Electron Microscope (SEM), and the compositions analysis of the MPC paste with NA and WG were conducted by using X-Ray Diffraction (XRD). The experimental results indicated that regardless of the immersion time, the NA substitution rate of 4% and 6% had a clearer improvement on the bond behavior between MPCM and SF than those of other types of the specimens; the WG substitution rate of 1% and 2% had a more significant improvement on the bond behavior between MPCM and SF than those of other types of the specimens; the distance between the larger width crack and the steel fiber for the specimen with a NA substitution rate of 6% was larger than than those of other types of the specimens, which showed that the ITZ between MPCM and SF with NA substitution rate of 6% exhibited a denser micro-structure and better micro-mechanical properties; the micro-structure of the ITZ between MPCM and SF gradually deteriorated as the immersion time increased, which showed that the water stability of the MPCM-SF interface gradually decreased.
Display omitted
•Si3N4 powders were successfully synthesized.•The optimization of synthesized conditions is investigated.•The reduction rate of silica increases with increasing temperature.•The ...finding of this work has a potential application in ceramic fabrication.
Herein, Si3N4 powders were successfully synthesized via carbothermal reduction nitridation of glucose and water glass as starting materials. The effects of synthesis temperature, glucose-to-water glass molar ratio, and Si3N4 seeding on the production were investigated. The results show that the reduction rate of silica increases with increasing temperature. The highest Si3N4 yield of 98.5 % was observed at 1450 °C after 400 min. The conversion of amorphous silica to Si3N4 was increased when the molar ratio of glucose/water glass was from 3.6 to 9.0 and is slightly affected when this ratio is greater than 9.0. Moreover, the maximum nitrogen content (N wt%) was 39.1 % when Si3N4/water glass molar ratio was 0.05. In the early stage of the reduction process, SiO2 is mainly reduced to SiC which is then converted to Si3N4.
Highly crystalline, high-purity β-SiC whiskers were successfully synthesised from a mixed sol of coal fly ash (CFA) and water glass (a silicon resource), and activated carbon (a carbon source) in a ...carbothermic reduction. The efficiency of the process is over 70%. The alkali activation effects of the water glass on CFA were characterised by FTIR and MAS-NMR. In the activation reaction, silicate frameworks of water glass and CFA became connected to form a large network, producing a stable, uniform sol system. Experiments and thermodynamic analyses were used to study the effects of Na2O, Al2O3, and Fe2O3 on the synthesis of β-SiC whiskers, revealing that Na2O does not affect the synthesis process while Al2O3 and Fe2O3 promote the elongation of the SiC whiskers. The results of this study may not only help to reduce the production cost of SiC whiskers but also allow value to be extracted from waste.
Display omitted
•β-SiC whiskers were synthesised from fly ash, water glass, and activated carbon.•The fly ash underwent an alkali-activation pretreatment by the water glass.•Silicate frameworks of water glass and CFA became connected in alkali-activation.•The effects of Na2O, Al2O3 and Fe2O3 have been amply studied.
Although silica aerogel is an excellent thermal insulation material, the poor mechanical property limits its application. The glass fiber reinforced silica aerogel with excellent mechanical property ...through facile sol-gel process is reported. Innovatively, during the experiments, ethanol was introduced as the main solvent in the water glass based silica sol through ion concentration adjustion to get rid of the conventional solvent exchange. To improve the mechanical property of the product, glass fiber was introduced during the gelation process. Catalyzed by hydrogen chloride, hexamethyldisiloxane was utilized as the modificaton agent. The glass fiber reinforced silica aerogel with low thermal conductivity (0.024 W/m·K) was obtained after ambient pressure drying. Three-point loading tests indicated excellent anti-flexure ability of the as-prepared glass fiber reinforced silica aerogel. Moreover, the entire preparation period can be reduced to ~20 h.
•EtOH is introduced to the water glass based sol via ion concentration adjustion.•HCl/HMDSO system was conducted to modified the composite in a fast way.•Glass fiber/silica aerogel composite was obtained within 20 h.
Display omitted
•Seawater influence testing of PU/WG grouting material was first conducted.•The fatigue resistance of PU/WG grouting material was confirmed through cyclic loading tests.•The ...adaptability of PU/WG grouting material to subsea tunnels was first addressed.
Polyurethane/water glass (PU/WG) is an organic–inorganic hybrid grouting material used in underground engineering. However, its adaptability to subsea tunnels remains poorly investigated. In this study, curing time, hardening time, seawater influence, strength growth, and cyclic loading tests of PU/WG as well as scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, and Fourier transform infrared spectroscopy characterizations were performed. The typical curing and hardening times of PU/WG were 2.02 and 2.49 min, respectively. The strength of the material developed fully when the sample was aged for 2 h. The peak strength and strain were respectively reduced up to 10.9% and 19.6% at the most owing to seawater corrosion. The minimum strength and minimum strain were of 37.7 MPa and 26.9%, respectively. The cyclic loading test results confirmed the high fatigue resistance of the PU/WG material. PU/WG is an ideal reinforcement grouting material for subsea tunnels.
•Thermal behaviour of alkali activated slag binder exposed to temperatures up to 1200°C was studied.•Superior mechanical performance at temperatures above 800°C was observed.•High temperature XRD ...revealed the crystallization of akermanite at 710°C.•Changes on molecular level during heating are described based on results of IR and MAS NMR measurements.
The paper covers the results of a study of microstructural changes in alkali activated granulated blast furnace slag exposed to high temperatures. Paste prepared from slag activated with solid sodium silicate glass was subjected to temperatures in the range of 200–1200°C for a period of 1h. The microstructural changes caused by the heat were investigated by means of SEM, HT-XRD analysis and FTIR and MAS NMR spectroscopy. Based on the latter two methods, only partial dehydration and decomposition of C–A–S–H phase can be observed up to 600°C. The principle changes in the microstructure of alkali activated slag occur between 600 and 800°C, when the dehydration of C–A–S–H phase is complete and new phases start to crystallize, among which akermanite is dominant. This significant phase transformation is reflected in the morphology, pore distribution, and mechanical properties of the AAS paste.
•A new cementitious anti-washout grouting material (CIS) was prepared which consist of ordinary Portland cement, water glass and xanthan gum.•The CIS grout has the advantages of short setting time, ...high early mechanical strength, high slurry viscosity, high slurry retention rate and non-toxic.•The contrast application of CIS grout with cement-water glass grout was carried out, and the water rushing was treated more effectively by CIS grout.
The inrush water disaster seriously affects the construction of tunnel and underground engineering. In order to improve the efficiency of dynamic groundwater sealing in karst area, a new cementitious anti-washout grouting material (CIS) was prepared which consist of matrix material ordinary Portland cement, coagulant accelerator water glass and flocculating agent xanthan gum. The results show that CIS grout has the advantages of short setting time, high early mechanical strength, high slurry viscosity, high slurry retention rate and non-toxic, and it has the advantages over the cement-water glass slurry which is most widely used in the dynamic groundwater sealing engineering. The mechanism effect of water glass and xanthan gum on the workability of CIS grout was discussed by hardening process, X-Ray Diffraction (XRD), Mercury Intrusion Porosimetry (MIP), Infrared spectrum (IR) and Scanning Electron Microscope (SEM). A design method of grouting parameters was proposed based on the setting time and viscosity evolution, and the contrast application of CIS grout with cement-water glass grout was carried out in water inrush control project of limestone mine in Karst Area, and the water rushing was treated more effectively by CIS grout.
Display omitted
In this study, silica aerogel was synthesized from rice husk ash-derived water glass through ion-exchange, sol-gel, solvent exchange and ambient pressure drying. The physical and ...chemical properties of silica aerogel were fully characterized by the Brunauer–Emmett–Teller theory (BET), Field emission scanning electron microscopy (FESEM), Thermogravimetric analysis-differential thermal analysis (TGA-DTA), Fourier transform infrared spectroscopy (FTIR). The effects of processing parameters, especially, the modulus of water glass on the characteristics of the products are deeply investigated. It is found that the modulus of water glass can significantly influence the specific area and pore volume of the aerogel through changing the polymerization degree of SiO group in the water glass solution. As well as, the pH value of sol-gel process and solvent concentration during modification are of importance for the physical properties of silica aerogel. When water glass modulus was 4.26, the gelation pH was 5.0 and the volumetric ratio of Trimethylchlorosilane (TMCS) to n-hexane was 7/50, silica aerogel was obtained with optimal performances of extremely high specific surface area (945.8 m2/g), pore volume (0.889 cm3/g), low density (0.071 g/cm3) uniform pore size distribution, high heat resistance temperature as 400 °C. The presented method is promising to synthesize high specific surface area silica aerogel from rice husk ash.
