Water Film Thickness Research Articles

Effects of Pretreated Phosphogypsum and Granulated Blast-Furnace Slag on the Rheological Properties of the Paste Excited by NaOH

The main component of phosphogypsum (PG) is CaSO4·2H2O. PG contains a few impurities, heavy metals, and radioisotopes, which limit the use of PG and pose a danger to the environment. In this study, under the excitation of a sodium hydroxide solution, the rheological properties of a paste with granulated blast-furnace slag (GGBS) and PG treated with ultrasonic water washing were investigated. Experimental results showed that the ratio of GGBS to PG and the amount of sodium hydroxide solution significantly affect the density and viscosity of the paste, but the effect patterns of both are different. The maximum viscosity was 498 mPa·s when the ratio of GGBS to PG was 4:1. When the ratio changed from 3:2 to 1:4, the viscosity of the paste gradually decreased by 15.5%, 32.1%, 36.1%, and 46.8%, respectively. In contrast, the ratio of GGBS to PG had a greater effect on the viscosity than the amount of sodium hydroxide solution in terms of the standard consistency water consumption, viscosity, and water release ratio. The larger the PG ratio, the smaller the density, viscosity, and water release ratio of the paste. The variation in the ratio of GGBS to PG had a significant effect on the water film thickness of the paste, demonstrating that the larger the PG mixture, the larger the water film thickness of the paste, which reached 1.122 μm, 2.31 times the minimum water film thickness of the paste. At the same time, the water film thickness of the paste was negatively correlated with the water consumption of the standard consistency, viscosity, and water release ratio, and was positively correlated with the fluidity.

Experimental Study and Modelling of Fresh Behaviours of Basalt Fibre-Reinforced Mortar Based on Average Water Film Thickness and Fibre Factor

Though previous studies have indicated that the fresh behaviours of plain mortar/concrete are mainly governed by the average water film thickness (AWFT), whether the concept of AWFT is also applicable to fibrous mortar/concrete still needs to be explored. Furthermore, for fibrous mortar/concrete, it is obvious that the fibres added also have certain effects on the fresh behaviours. In two previous studies on basalt fibre-reinforced mortar (BFRM), the integral effects of the AWFT and fibre dosage as well as the integral effects of the AWFT and fibre length were individually investigated. In this study, a fibre factor (FF) defined as the fibre volume multiplied by the fibre aspect ratio was employed and 24 extra mortar groups were tested. A total of 68 mortar groups were applied in numerical analysis. The results of the regression analysis yielded good correlations of the workability, fluidity, cohesiveness, and adhesiveness of BFRM with the AWFT and FF, suggesting that the AWFT and FF are together the governing parameters controlling the fresh behaviours of BFRM. Hence, the AWFT and FF may be used to develop a model for the fresh properties of BFRM.

Effect of Hydrophobicity of Fluorescent Carbon Nanoparticles on Transport in Porous Media: Column Experiments and Modeling

AbstractEngineered carbon‐based nanoparticles are increasingly used for environmental, industrial, and medical purposes. Thus, understanding their interaction with and transport through materials is important. We examine the impact of nanoparticle hydrophobicity and porous medium surface area on the transport of carbon nanoparticles through sand‐packed columns under saturated and unsaturated conditions. The fluorescent carbon nanoparticles (FCNs) used in this study, synthesized from citric acid and ethanolamine, exhibit synthesis‐temperature‐dependent hydrophobicity. To quantify the impact of hydrophobicity on retention, we use FCNs synthesized at four temperatures: 190°C (FCN190), 210°C (FCN210), 230°C (FCN230), and 250°C (FCN250). Several observations are noted. First, the more hydrophobic particles (FCN230 and FCN250) attain lower outlet concentrations and mass recovery than more hydrophilic particles (FCN190 and FCN210). For instance, while 77% of the FCN190 was recovered after passing through a fine‐sand‐packed column, only 23% of the FCN250 was recovered. Second, sand surface area significantly impacts FCN recovery. A 17‐fold increase in sand surface area yields a 30% decrease in the recovery of FCN210. Third, no significant difference in the mass recovery of the FCNs was observed between the unsaturated and saturated conditions, which is attributed to the small size of the FCNs relative to the water film thickness surrounding sand grains. Fourth, the particle transport model in HYDRUS‐1D successfully simulated FCN transport, showing approximately a tenfold increase in the attachment coefficient for hydrophobic FCNs. In summary, through experiments and modeling, we show that hydrophobicity is a major factor impacting FCN transport.

Experimental study on the high-speed frictional behavior between the tire and asphalt pavement

Driving speed, pavement type, surface characteristics, intermediate media, and tire properties are the key factors influencing the frictional behavior between tire and pavement. Although there are many kinds of equipment for friction coefficient tests based on the rubber-pavement contact mechanism, there is still a lack of equipment that can simulate the skid resistance behavior of high-speed vehicles based on real tire in the laboratory. Therefore, High-speed Friction Testing (HSFT) equipment was developed based on real tire loading, which well solves the deficiency of the current test methods. Based on this test platform, multi-factor coupling skid resistance tests were carried out on the asphalt concrete (AC-10/13/16) and the Open-Graded Friction Coarse (OGFC-10/13/16) samples. Statistical comparison and nonlinear fitting analysis were conducted on the results under various loading conditions The results show that driving speed, water film thickness, and tire load are all negatively correlated with skid resistance, and their influence extent can be ranked as water film thickness > tire load > driving speed. The established μHSFT skid resistance model based on multi-factor coupling shows high reliability, which can be used as the basis for pavement construction and is an important reference for future unmanned driving technology.

Numerical simulation on hydrodynamic lubrication performance of bionic multi-scale composite textures inspired by surface patterns of subcrenata and clam shells

Inspired by the surface of shells in natural world, six bionic multi-scale composite surface textures were designed. Numerical simulation was carried out to investigate the mechanism for influences of the texture geometric parameters and service conditions on lubrication characteristics. The results revealed that the bionic surface enhanced the load-carrying capacity and reduced the friction coefficient. Groove combinations offered a better lubrication performance than wavy combinations. The texture geometric parameters showed significant influence on the frictional characteristics. For all texture shapes, the load-carrying capacity increased approximately linearly with the rotational speed and decreased with the water film thickness. The results would help guide effective texture design to improve the lubrication performance of axial piston pump friction pairs under marine environments.

Numerical Simulation of Microscale Oblique Droplet Impact on Liquid Film

The oblique impact of microscale water droplets on liquid film is numerically investigated. Two-phase flow problems are simulated using three-dimensional incompressible Navier-Stokes equations, and the level-set method is employed for capturing the gas-liquid interface. The numerical model is verified using experimental results from a normal and oblique impact via the qualitative comparison of crown profile features and quantitative contrast of the crown height and radius varying with time. The article discusses the influence of tangential impact velocity, water film thickness, Reynolds number, and Weber number on the shape characteristics, tangential momentum, and kinetic energy of the annular crown. The results show that the decreasing momentum in the tangential direction can be divided into three clear stages: rapid decrease, slight increase, and continuous decrease. In addition, film thickness and Weber number have significant effects on the momentum decay rate.

Effect of Salinity and Polycarboxylate Superplasticizer on Fresh Property of Seawater-Blended Cement.

The salinity of seawater can affect the properties of mixtures of polycarboxylate superplasticizer (PCE) and seawater. The purpose of this research is to study the effect of different salinities of water on the property of seawater-mixed cement slurry. Two PCE types with different side chain lengths and acid-ether ratios were used. Their physicochemical properties were explained by nuclear magnetic resonance (NMR), size exclusion chromatography (SEC), Fourier transform infrared spectroscopy (FTIR), turbidimetry, and dynamic light scattering (DLS) analysis. The performance of the PCEs was measured using slump, rheological energy, and solidification time. Finally, by measuring the adsorption volume, adsorption layer thickness, and water film thickness (WFT), the mechanisms involved in performance modification were studied. The results show that the workability and rheological performances of seawater-mixed cement paste are decreased by increasing salinity. With the increase in salinity, the minislump of the seawater-blended cement pastes with two PCEs decreased from 285 mm to 120 mm and from 280 mm to 78 mm, respectively, and the thixotropic areas were increased from less than 2000 Pa/s to above 10,000 Pa/s. Moreover, the adsorption amount of the two PCEs in the cement mixed with high-salinity seawater decreased by 55.99% and 71.56%, respectively, and the thickness of the adsorption layer and water film was decreased with increasing salinity. Compared with the two PCEs, PCE with long side chains and a high acid-ether ratio provided better salt resistance.

Effect of a water film on the material removal behavior of Invar during chemical mechanical polishing

Understanding polishing mechanisms in water-lubricated environments has an important guiding value for surface engineering of precision devices. This work reveals the chemical mechanical polishing (CMP) mechanism of the Invar alloy under water lubrication by use of molecular dynamics simulation. The results show that the appropriate thickness of the water film and polishing speed can significantly reduce the surface roughness of the work piece and eliminate subsurface defects. With the increasing rolling speed, the variation of the surface roughness and subsurface damage thickness exhibits a trend of slowly decreasing and then reaching stability. In addition, with an increase in water film thickness, more defects were formed in the subsurface region due to greater surface stresses, although the roughness could be reduced due to an increase of passivated atoms on the work piece surface. These results would be helpful for understanding the CMP mechanism under water-lubricated conditions and for promoting the development of surface engineering for micro/nano components.

Quasi-Steady Simulation of Glaze Ice Accretion and Heat Transfer in the Supercooled Large Droplet Regime in Atmospheric Turbulent Air Flow

Abstract To avoid the use of a computationally intensive full unsteady simulation while providing an accurate solution, a quasi-steady simulation has been performed to study glaze and mixed ice accretion in the supercooled large droplet (SLD) regime in turbulent flow of atmospheric air. We have attempted to find the minimum time-step necessary to adequately simulate the icing process on an airfoil surface. Based on node displacement, a mesh morphing scheme has been adopted in the computations to account for the moving boundaries that are caused by the continuous ice buildup. We have modeled ice accretion on an airfoil surface for a time period of 232 s using several time steps. At each time-step we solved the steady-state conservation equations for the air and droplet phases and then used the results as initial conditions for the next time position. The magnitude of the time-step ranged from a least accurate two-shot simulation (where the time-step is 116 s) to a most accurate 2320-shot simulation (where the time-step is 0.1 s). In-between these two extreme time steps, we have performed a three-shot simulation (where the time-step is 77.33 s), a four-shot simulation (where the time-step is 58 s), a six-shot simulation (where the time-step is 38.67 s), a 46-shot simulation (where the time-step is 5 s), and a 232-shot simulation (where the time-step is 1 s). We have done so to find out the degree of accuracy (or inaccuracy) of the multishot simulation approach and to find out the appropriate time-step needed for a successful and valid quasi-steady simulation. A valid quasi-steady simulation needs to use a time-step that is small enough to reproduce the full time-dependent solution within a very small error band. We have found that both the 1 s and the 0.1 s time steps produce virtually identical results. This is the primary litmus test that proves the validity of the quasi-steady-state assumption. The results adopted in this paper are thus all based on the more conservative 0.1 s time-step. In the process of performing the simulations, remeshing was required in order to maintain the grid density in zones of high curvature to be able to capture the full physics in those zones. After successfully modeling glaze ice accretion over the airfoil surface using the 0.1 s quasi-steady simulation approach, the effects of supercooled large droplets (SLDs) impacting the surface have been examined and presented in terms of the variation of the local collection efficiency, the water film thickness, and the heat transfer rate. Examination of the variation of the angle that the ice horn makes with the airfoil chord line demonstrated a 20% improvement in angle prediction when the time-step is reduced from 116 s to 0.1 s. The analysis also reveals a 12% or 8.5% increase in the maximum collection efficiency, βmax, depending on whether the value of the liquid water content (LWC) has been doubled from 0.5 g/m3 to 1 g/m3, or the value of the freestream velocity has been doubled from 75 m/s to 150 m/s, respectively. Because of the need to monitor the local collection efficiency and convective heat fluxes at each shot (regardless of the number of shots employed), the approach adopted here was found to be effective in successively and successfully reproducing the curvature of the glaze ice horn.

Investigation on Roles of Packing Density and Water Film Thickness in Synergistic Effects of Slag and Silica Fume.

The ternary blended cement with finer slag and silica fume (SF) could improve the packing density (PD) through the filling effect. The excess water (water more than needed for filling into voids between the cement particles) can be released to improve the fresh properties and densify the microstructure which is beneficial for improving the hardened properties. To verify the hypothesis and reveal how and why (cement + slag + SF) the ternary blends could bring such advantages, the binder pastes incorporating slag and SF with various water-to-binder ratios were produced to determine the PD experimentally. To evaluate the optimum water demand (OWD) for maximum wet density, the influence of the dispersion state of the binder on PD was investigated using the wet packing density approach. The effect of PD of various binary and ternary binder systems on water film thickness (WFT), fluidity, setting time, and compressive strength development of cement paste was also investigated. The results show that the ternary blends could improve the PD and decrease the water film thickness (WFT). The enhanced PD and altered WFT are able to increase fluidity and compressive strength. The ternary blends could improve the compressive strengths by increasing PD and exerting nucleation and pozzolanic effects.

Rheological Properties and Structural Build-Up of Cement Based Materials with Addition of Nanoparticles: A Review

Nanoparticles improve the mechanical properties and durability of cement-based materials. However, owing to the high surface energy and specific surface areas of nanoparticles, the packing characteristic of cementitious particles will be affected. With the action of the electrostatic attraction and Van der Waals force, the cementitious particles are agglomerated into flocculation structures, and the free water is entrapped. Furthermore, as the water consumption of cement-based materials increases, the flowability gets worse, which is thought to be one of the reasons limiting its application in practical engineering. In addition, nanoparticles increase the viscosity and thixotropy of fresh cement-based materials and provide more nucleation sites in cement paste, accelerating the cement hydration process in early hydration. In this paper, the research progress on the rheological properties and structural build-up of cement-based materials with the addition of nanoparticles was reviewed. The applicability of rheological test methods and rheological models was summarized. The variation of rheological parameters of fresh cement-based materials affected by nanoparticles species, contents, dispersion method, superplasticizer, etc., were discussed. Based on the packing density, water film thickness, and flocculation structures, the action mechanism of nanoparticles on the rheological properties of cement-based materials was analyzed. Further research topics on the rheology and structural build-up of nano-modified cement-based materials are suggested as well.

Model Construction and Numerical Simulation for Hydroplaning of Complex Tread Tires

Euler-Lagrange coupling method is used to establish the fluid-structure interaction model for tires with different tread patterns by obtaining the grounding mark and normal contact force between tire and the road surface during tire rolling. The altering of load force, tire pressure, and water film thickness in relation to the effect on tire-road force during both constant speed and critical hydroplaning speed was analyzed. Results show that the critical hydroplaning speed and normal contact force between tire and the road surface are positively correlated with vehicle load and tire pressure and negatively correlated with water film thickness. Python language is used to develop the pre-processing plug-ins to achieve parametric modeling and rapid creation of Finite Element Analysis (FEA) model to reduce time costs, and the effectiveness of the plug-ins is verified through comparative tests.

Explosive boiling of water films based on molecular dynamics simulations: Effects of film thickness and substrate temperature

This paper deals with investigations of mechanisms governing explosive boiling of water films on hot copper substrate with plain surface. The investigations are based on results of molecular dynamics (MD) simulations in which film thickness (7.5 nm, 17 nm and 25.5 nm) and substrate temperature (800 K, 700 K and 600 K) are set as parameters. Analyses of heating transients, which lead to explosive boiling event, are done comparing the following quantities for considered MD configurations: time instant of explosive boiling onset, dynamics of vapour generation, increase of water film thickness due to thermal expansion and vapour generation, evolution of water temperature as well as heat transfer from the copper substrate to the water film. These analyses have shown that explosive boiling onset is related neither to the value of substrate temperature nor to the film thickness in a straightforward way. The investigations of temperature and per atom energy in the water region near the heating substrate surface have revealed that beside thermal also mechanical mechanisms can play significant role in triggering of explosive boiling. The mechanical mechanisms, related to pressure wave propagation in liquid film, comprise occurrence of tensile stresses which induce / intensify generation of vapour phase in the near wall region. The obtained results show that thermal effects are dominant in cases with high substrate temperature and thick liquid films as in these configurations the water temperature reaches spinodal value and explosive boiling is triggered before expansion wave reaches the near wall region. In cases when water in the near wall region is strongly overheated (but well below spinodal temperature), tensile stresses induced by expansive wave propagation cause intensive vapour generation and contribute dominantly to occurrence of explosive boiling. Finally, in cases with lower substrate temperature and thin liquid films, an interplay of thermal and mechanical mechanisms leads to explosive boiling. Beside these, the disjoining pressure seems to play a role in cases with thin liquid films.

Evolution of tire-pavement friction with the regular surface macro-texture characteristics and environmental factors using three-dimensional (3D) printing technology

Conventional gradation-based pavement design makes the constructed pavement surface too complex to quantify the contribution of texture on the tire-pavement friction accurately. This study aims to investigate the influence of regular macro-texture characteristics and environmental factors on friction using three-dimensional (3D) printing technology. The variation of friction with different texture shapes, heights, and gaps was investigated under dry and wet conditions. The evolutions of friction under different water film thicknesses and temperatures were also quantitatively analyzed. The results show that all specimens with different texture shapes, heights, and gaps can contribute to large friction under dry conditions, where the British pendulum number (BPN) is larger than 90. The friction sharply decreases under wet conditions, especially for the semi-circular texture specimens. The specimens with positive textures are much better than those with negative textures. The impact of texture shapes is more significant than texture height and gaps under wet conditions, where the texture gaps are relatively insignificant. The friction is slightly linearly increased with the water film thickness while slightly decreasing with the temperature. This study provides a friction-oriented pavement texture design method and manufacturing techonology.

Study on Strength Characteristics and Microstructure of Completely Decomposed Migmatitic Granite

Migmatitic granite is the product of mixed lithification and granitization, and completely decomposed migmatitic granite (CDMG) was formed after weathering. The engineering properties of CDMG are complex, and its engineering properties are complex after weathering, and water content has a great influence on the properties of (CDMG). Due to its loose structure and strong heterogeneity, it is difficult to determine its strength characteristics by conventional test methods. In the paper triaxial and micro-CT test were conducted to study the relationship between shear strength and microstructure of CDMG under different water content. The results show that with the increase of water content from 6% to 14%, the internal friction angle decreases from 31.8° to 27.3°, and the cohesion first increases from 76.5 kPa to 94.3 kPa and then decreases to 77.7 kPa. This is because the sliding friction coefficient between coarse particles decreases with the increase of water film thickness on the surface of particles, and the occlusal effect between coarse particles weakens and the displacement adjustment is easier during the triaxial loading process. Under different water content, the shear strength of CDMG is not sensitive to particle structure parameters including particle size, particle morphology and particle arrangement. The particle analysis results of post-test sample show that the crushing proportion of coarse particles increases with the increase of the internal friction angle. The clay minerals produce differential expansion potential with the increase of water content, and the porosity and pore connectivity first decrease and then increase. Cohesion has a linear relationship with porosity and pore connectivity. With the increase of porosity from 23.95% to 26.95%, cohesion decreases linearly by 17%. These results indicate that the internal friction angle of CDMG can be inferred by water content, and the cohesion can be inferred by porosity and pore connectivity obtained by microstructure analysis.

Microscopic production characteristics of tight oil in the nanopores of different CO2-affected areas from molecular dynamics simulations

Understanding the mechanisms of CO2 extraction or flooding are vital for enhancing oil recovery (EOR) in tight reservoirs. In this study, the CO2 EOR mechanism in the displacement-affected area (DPAA) and diffusion-affected area (DFAA) of quartz nanopores were thoroughly investigated using molecular dynamics simulation techniques. First, the following two contents were mainly simulated, namely CO2 flooding oil in the single/double nanopores of DPAA and CO2 extraction oil in dead-end nanopores of the DFAA with and without the water film. Then, tight oil potential energy, threshold capillary pressure, CO2 solubility, and oil swelling in nanopores were calculated to clarify the effects of CO2 on oil transport. Moreover, different CO2 injection/flowback rates and different water film thicknesses on dead-end nanopores on oil recovery were discussed. In the DPAA, the CO2 solubility and the oil swelling factor gradually decreased with distance from the CO2-oil interface (Y = 0 nm), where the higher the injection rate, the more easily the CO2 dissolved in the oil. However, the injection rate of CO2 was inversely proportional to oil recovery. In addition, it took longer for the displacement efficiency in the 6 nm pore of double pores to reach the same displacement efficiency as in the single 6 nm pore. In the DFAA, the effect of flowback rate on the displacement efficiency of oil was relatively low. However, the thickness of the water film was a key factor that affected the oil displacement efficiency in the DFAA.

Influence of thin water film on asphalt pavement skid resistance: from indoor to in-situ test

ABSTRACT Pavements skid resistance, especially in wet states, is an essential indicators of traffic safety. However, the existing testers cannot reflect actual road friction situations and oversimplify water’s effect on texture and skid resistance. Therefore, this study compared a traditional British pendulum tester (BPT) with actual vehicle braking. A simplified water coverage simulation programme was proposed, and the BPT characterised the influence of different thin water films on skid resistance in the laboratory. Besides, several freshly constructed road sections (AC-13, SMA-13, and PAC-13) were tested with both BPT and vehicle braking during rainfall. The results showed that water film, even thin, is unfavourable for pavement skid resistance. The BPT results were inconsistent with that of the vehicle braking. Because the tribological properties characterised by BPT are provided by micro-texture and partly macro-texture within the rubber-texture interaction depth (0.1 mm). Larger texture depth and more tortuous and connected pores will offer pavements larger water capacity and higher water permeability, which is beneficial for alleviating braking distance reduction during rainfall. In general, an ideal skid resistance tester should consider characteristics within the rubber-texture contact depth and should consider braking conditions such as speed, water film thickness, drainage method, and slip rate.

Impact of Slope Orientation on Inlet Spacing: Gutter Flow Analyses

A roadway’s capacity to drain itself is of utmost importance for the safety and comfort of its users. Standing water and any amount of channelized flow on roadways create nuisances to the users, and the extent of encroachment into the lanes and the water-film thickness over the lanes are crucial for motorists with relatively high speed. Guidelines cover a wide range of subjects from size and type of inlets, which capture the channelized flow for conveyance into enclosed drains, to the decision for slope orientation, but the guidelines seem to lack in checking the depth of channelized flow. HEC-22 (the urban drainage design manual of US Department of Transportation) endorses limiting the flow depths to curb height (as if the concern is no longer the roadway users) and fixes the criterion for the inlet spacing (restricted to 90 to 150 m) to maximum allowable flow spreads. This study analyzed the maximum allowable inlet spacing via setting three criteria: fixed maximums to flow depth, spread for the channel flow, and to over-lane water-film thickness. The impact of slope orientation on inlet spacing is tested along with some other factors for roadways of two types (local and highway). The results were graphed for various uniform slope orientations under a wide range of rainfall intensities for the determined inlet spacing values. This was performed by combining a kinematic wave equation solution to dismiss the conditions that lead to hydroplaning depths when using the Rational Method and Manning’s equation to obtain water depths and inlet spacings for an inlet of full capture capacity. It is found that the allowable spacing values do not constitute any major restrictions in highway setting (3 m shoulder) in terms of recommended spacing. In the local setting, however, with a maximum spread of 1.8 m, maximum allowable inlet spacing becomes a limitation in many orientations, and slope optimization under such conditions becomes crucial at times when providing the same spacing for two orientations.

Molecular simulation studies on the water/methane two-phase flow in a cylindrical silica nanopore: Formation mechanisms of water lock and implications for gas hydrate exploitation

The water/gas two-phase flow is a frequently encountered question in the percolation field, and is especially important for the exploitation of natural gas hydrates because their decomposition products are exactly liquid water and natural gas. We studied the water/methane two-phase flow in a hydrophilic cylindrical nanopore by performing molecular simulations, and obtained high-quality nanoflows under different water saturation (Sw) thanks to the newly established nano-manometer method to control pressure difference accurately. With increasing Sw, the methane flow decreases almost linearly until a sudden stop when Sw ≥ 0.52. The formation of the water lock accounting for this phenomenon is observed clearly, and the larger Sw, the earlier formation of the water lock as well as the longer water lock. Based on careful data analysis, a water lock model and its formation mechanism are newly proposed with two pieces of strong evidence — the continuous reduction of the surface area of the water/gas interface when the water lock forms and the existence of maximum thickness of water film for different Sw. Thus, the competition between the surface tension of the water/gas interface and the adsorption of the water/wall interface controls the development of the water lock. These findings are very helpful for understanding the two-phase percolation and optimizing the gas production and water removal schemes during hydrate exploitation. In addition, the nano-manometer can be widely used in other nanoflow simulations for measuring the local pressure accurately.

Effects and mechanism of superplasticizers and precursor proportions on the fresh properties of fly ash – slag powder based geopolymers

To promote the application of green geopolymer materials, the effects and mechanism of commercial superplasticizers on the fresh properties of one-part geopolymers prepared from fly ash (FA), slag powder (Slag) and anhydrous sodium silicate powder were studied, including flowability, rheological properties and particles packing properties. And the influence of precursor proportion (FA:Slag) i.e. the mass proportion of FA and Slag on the effectiveness of superplasticizers was also considered. The results show the fluidity of geopolymer with 2.4 % liquid naphthalene-based superplasticizer (N-L) increased by 19.20 % when FA:Slag = 85:15, and the 0.20 % one kind of solid polycarboxylate-based superplasticizer (PC-S2) increased the fluidity of geopolymer by 16.47 % when FA:Slag = 95:5. The addition of superplasticizers could improve fluidity, increase plastic viscosity, and decrease yield stress of the pastes. The particles packing properties, including excess water and water film thickness (WFT) of the geopolymer pastes with superplasticizers also increase. It is interesting to find that the effectiveness of superplasticizers varies from different types of superplasticizers. This could be understood by the mechanism of the two types of superplasticizers based on Zeta, FTIR results, and water film theory. Accordingly, naphthalene-based superplasticizers guided by the adsorption-dispersion effect, due to their stable molecular structures and short chains, could improve the workability, while the effectiveness of polycarboxylate-based superplasticizers guided by the steric hindrance effect of lateral chains may be judged by the combined effects of the interaction between particles and the effects induced by superplasticizers.