Tensile Strain Capacity Prediction of Engineered Cementitious Composites (ECC) Using Soft Computing Techniques

Plain concrete is strong in compression but brittle in tension,having a low tensile strain capacity that can significantly degrade the long-term performance of concrete structures,even when steel reinforcing is present.In order to address these challenges,short polymer fibers are randomly dispersed in a cement-based matrix to forma highly ductile engineered cementitious composite(ECC).Thismaterial exhibits high ductility under tensile forces,with its tensile strain being several hundred times greater than conventional concrete.Since concrete is inherently weak in tension,the tensile strain capacity(TSC)has become one of the most extensively researched properties.As a result,developing a model to predict the TSC of the ECC and to optimize the mixture proportions becomes challenging.Meanwhile,the effort required for laboratory trial batches to determine the TSC is reduced.To achieve the research objectives,five distinct models,artificial neural network(ANN),nonlinear model(NLR),linear relationship model(LR),multi-logistic model(MLR),and M5P-tree model(M5P),are investigated and employed to predict the TSCof ECCmixtures containing fly ash.Data from115 mixtures are gathered and analyzed to develop a new model.The input variables include mixture proportions,fiber length and diameter,and the time required for curing the various mixtures.The model’s effectiveness is evaluated and verified based on statistical parameters such as R2,mean absolute error(MAE),scatter index(SI),root mean squared error(RMSE),and objective function(OBJ)value.Consequently,the ANN model outperforms the others in predicting the TSC of the ECC,with RMSE,MAE,OBJ,SI,and R2 values of 0.42%,0.3%,0.33%,0.135%,and 0.98,respectively.

Influence of ultra-fine fly ash on hydration shrinkage of cement paste

Hydration shrinkage generated by cement hydration is the cause of autogenous shrinkage of high strength concrete. It may result in the volume change and even cracking of mortar and concrete. According to the data analysis in a series of experimental studies, the influence of ultra-fine fly ash on the hydration shrinkage of composite cementitious materials was investigated. It is found that ultra-fine fly ash can reduce the hydration shrinkage of cement paste effectively, and the more the ultra-fine fly ash, the less the hydration shrinkage. Compared with cement paste without the ultra-fine fly ash, the shrinkage ratio of cement paste reduces from 23.4% to 39.7% when the ultra-fine fly ash replaces cement from 20% to 50%. Moreover, the microscopic mechanism of the ultra-fine fly ash restraining the hydration shrinkage was also studied by scanning electron microscopy, X-ray diffraction and hydrated equations. The results show that the hydration shrinkage can be restrained to a certain degree because the ultra-fine fly ash does not participate in the hydration at the early stage and the secondary hydration products are different at the later stage.

Effects of synthesis temperature and raw materials composition on preparation of β-Sialon based composites from fly ash

β-Sialon based composites were successfully prepared from fly ash and carbon black under nitrogen atmosphere by carbothermal reduction-nitridation process. Effects of heating temperature and raw materials composition on synthesis process were investigated, and the formation process of the composites was also discussed. The phase composition and microstructure of the composites were characterized by X-ray diffraction and scanning electronic microscopy. The results show that increasing heating temperature or mass ratio of carbon black to fly ash can promote the formation of β-Sialon. The β-Sialon based composites can be synthesized at 1723 K for 6 h while heating the sample with mass ratio of carbon black to fly ash of 0.56. The as-received β-Sialon in the composites exists as granular with an average particle size of 2-3 μm. The preparation process of β-Sialon based composites includes the formation of O′-Sialon, X-Sialon and β-Sialon as well as the conversion processes of O′-Sialon and X-Sialon to β-Sialon.

Impact Properties of Engineered Cementitious Composites with High Volume Fly Ash Using SHPB Test

The split Hopkinson pressure bar （SHPB） testing with diameter 40 mm was used to investigate the dynamic mechanical properties of engineered cementitious composites （ECCs） with different fly ash content. The basic properties including deformation, energy absorption capacity, strain-stress relationship and failure patterns were discussed. The ECCs showed strain-rate dependency and kept better plastic flow during impact process compared with reactive powder concrete （RPC） and concrete, but the critical compressive strength was lower than that of RPC and concrete. The bridging effect of PVA fiber and addition of fly ash can significantly improve the deformation and energy absorption capacities of ECCs. With the increase of fly ash content in ECCs, the static and dynamic compressive strength lowered and the dynamic increase factor enhanced. Therefore, to meet different engineering needs, the content of fly ash can be an important index to control the static and dynamic mechanical properties of ECCs.

Influence of processing route on microstructure and wear resistance of fly ash reinforced AZ31 magnesium matrix composites

Utilizing fly ash(FA)as reinforcement for magnesium matrix composites(MMCs)brings down the production cost and the land pollution.Magnesium alloy AZ31 was reinforced with FA particles(10 vol.%)successfully by two different processing methods namely conventional stir casting and friction stir processing(FSP).The microstructural features were observed using optical microscope,scanning electron microscope and electron backscatter diffraction.The sliding wear behavior was tested using a pin-on-disc wear apparatus.The stir cast composite showed inhomogeneous particle dispersion and coarse grain structure.Some of the FA particles decomposed and reacted with the matrix alloy to produce undesirable compounds.Conversely,FSP composite showed superior particle dispersion and fine,equiaxed grains by dynamic recrystallization.FA particles encountered disintegration but there was no interfacial reaction.FSP composite demonstrated higher strengthening and wear resistance to that of stir cast composite.The morphology of the worn surface and the wear debris were studied in detail.

Effect of fly ash content and grit size on mechanical and tribological properties of PVC composites

The polyvinyl chloride (PVC) composites containing fly ash of various grit sizes and contents were prepared by hot pressing. The hardness, impact strength of the composites were measured, and their friction and wear properties under dry and water lubrication sliding against quenched AISI-1045 steel were evaluated on an MM-200 tester. The fractograph of impact specimens, worn surfaces of the composites and their transfer films on the counterpart steel surfaces were observed with a scanning electron microscope and an optical microscope. Experimental results show that the composites containing 50% 74147μm fly ash have the highest hardness, highest impact strength and smallest wear rate. The wear rate of the composite is reduced by over two orders of magnitude. However, the composite containing over 50% fly ash has decreased wear-resistance, which is attributed to the weakened interaction between the filler and the polymer matrix in the presence of inadequate polymer matrix. The improved wear-resistance of the composite under dry sliding against the steel is attributed to the formation of the composite transfer film thereon.

MANUFACTURING OF ALUMINUM/FLY ASH COMPOSITE WITH LIQUID REACTIVE SINTERING TECHNOLOGY

The Al/fly ash composites are fabricated by liquid reactive sintering P/M process with fly ash particles as intensifying phases. The reactivity and newly formed phases during liquid sintering process have been analyzed by combing Thermochemicdl data base calculation and XRD characterization. The results show that some of constituents in fly ash have reacted with liquid aluminum so that the elemental Si, Fe, Ti as well as some amount of intermetallic compounds occur. The properties of aluminum/fly ash composites have been improved. With the fraction of fly ash increase, the composite density decreases; the hardness and the modulus of the composite increases, and the composite wear resistance are significantly increased. The fly ash reinforced composites represent a sort of low cost product with possible widespread applications in the automotive, small engine, and electromechanical machinery sectors.

Damping properties of fly ash/epoxy composites

An inexpensive fly ash （FA）, which is from a waste product, was employed to prepare fly ash/epoxy composites. The purpose of this study is to characterize the contributions of matrix viscoelasticity, hollow structure characteristic （porosity）, and filler/matrix interface friction to the high vibration damping capacity of such composites. The damping properties of the composites were investigated in the temperature range of-40 to 150℃ and in the frequency range of 10 to 800 Hz by using a tension-compression mode. The results indicate that the peak value of damping loss factor （tan3） for the fly ash/epoxy composites can reach 0.70-0.90 in test specification, and the attenuation of damping loss factor is inconspicuous with increasing frequency. In addition, scanning electron microscope （SEM） was used to observe the morphology of the fly ash as well as its distribution in the matrix, which will help to analyze the effect of fly ash on the damping properties of the fly ash/epoxy composites.

Nickel composite plating with fly ash as inert particle

The Ni/FA composite plating was realized by electrodeposition with fly ash （FA） as inert particles. The main compositions of FA are 72% SiO2 and 25% A1203 in the size of 3-7 Ixm. Electrodeposition was performed in Watts bath containing FA with concentrations of 5, 20, 50 g/L, current densities of 2 and 4 A/dm2, temperature of 50 ~C and magnetic stirring of 250 r/min. Scanning electron microscope （SEM＋EDX）, electrochemical and mechanical technique were used to study morphology, composition and properties of coating. FA content in deposit is dependent on the FA concentration in solution, as well as the plating parameters. Since FA particles were incorporated in the coating, the mechanical and electrochemical properties of the coating were increased. The microhardness of Ni/FA composite plating reaches HV 430 in comparison with HV 198 of pure Ni coating. It was confirmed by electrochemical measurement that the corrosion resistance of Ni/FA composite coating was higher than that of pure Ni.

Interlaminar Fracture Toughness of Epoxy Glass Fiber Fly Ash Laminate Composite

Epoxy glass fiber laminate composite (PMCs) are finding ever increasing applications in aerospace and automobile industries due to its high strength to weight ratio and resistance to aqueous environment. Additions of particulate reinforcements in the polymer matrix are reported to improve the Interlaminar Shear Strength and Interlaminar Fracture Toughness of the composites. In the present investigation, epoxy glass fiber laminate composites were processed using hand layup and vacuum bagging technique. The particulate reinforcement precipitator fly ash (25 - 45 μm) was added in the epoxy matrix by mechanical mixing up to 10 wt%. The effects of fly ash reinforcement on the mechanical properties and Interlaminar Fracture Toughness were studied before and after exposure to aqueous fog in a salt fog chamber at 45°C. In unexposed condition Mode I interlaminar fracture toughness of epoxy glass fiber laminate composite improved by the addition of fly ash reinforcement 10% (By weight) by 49.43% and when it was subjected to aqueous fog for 10 days the interlaminar fracture toughness improved 58.42%. Exposure to aqueous fog for 10 days causes plasticization of resin matrix and weakening of fiber/matrix interface results in improvement in interlaminar fracture toughness. The fracture surfaces were analyzed using scanning electron microscopy.

Growth of Carbon Nanotubes by Pyrolysis of Composite Film of Poly (Vinyl Alcohol) and Modified Fly Ash

We found carbon nanotube (CNT) materials by the pyrolysis of the composite film of poly (vinyl alcohol) (PVA) reinforced with modified fly ash (FA) at 500°C for 10 min under 2 L/min flow of nitrogen. Fly ash was treated with 2M sodium hydroxide and used with PVA to fabricate the composite film by aqua casting. CNT materials were analyzed using XPS, Raman, SEM and TEM. The admixtures of CNT materials and FA are a potential filler material for fabricating composites with polymer and metal. The process is an eco-friendly recycling paradigm for using value-added advanced products for the proper management of sustainable waste materials, plastic and FA.

A Review on Utilization of Light Weight Fly Ash Cenosphere as Filler in both Polymer and Alloy-Based Composites

Fly Ash Cenospheres(FACs)are obtained from the coal power plants in the form of hollow spherical particles by burning the coal.FAC was started to use in early 1980-1985 as lightweight filler material in producing composites of cementitious and at present many researchers are focusing on use of FAC as filler in polymer and metals.In this paper,the systematic review on research activities and application of FAC in manufacturing light weight products are done.The influence of FAC on the physical and mechanical properties of incorporated polymer and alloy-based composites were summarized.Prospects of future for its use were also suggested and summarized in this paper.

MECHANICAL PROPERTIES AND MICROSTRUCTURE OF COMPOSITE BINDERS CONTAINING SHALE ASH AND FLY ASH

The microstructure and the mechanical properties of hardened mortars made of superplasticized composite binder containing shale ash and fly ash are investigated. The pozzolanic reaction consumes the oriented Ca (OH)//2 crystals, thus making the transition zone dense. Appropriately proportioning of shale ash and fly ash decreases the water requirement and increases the packing density of composite binder mortars, therefore increases their strength. Superplasticizer promotes the carbonation of calcium hydrates and the formation of ettringite that is transformed gradually into mono-sulfoaluminate hydrate in composite binder mortars. The joint action of fine complex mineral admixture and superplasticizer has a synergistic effect to improve the mechanical properties of composite binder. (Author abstract) 7 Refs.

Photocatalytic activity of TiO_2 supported SiO_2-Al_2O_3 aerogels prepared from industrial fly ash

A ternary composite of TiO2 and a SiO2-Al2O3 aerogel with good photocatalytic activity was prepared by a simple sol-gel method with TiO2 nanoparticles and SiO2-Al2O3 aerogels derived from industrial fly ash.The structural features of the TiO2/SiO2-Al2O3 aerogel composite were investigated by X-ray powder diffraction,Fourier transform infrared spectroscopy,transmission electron microscopy,gas adsorption measurements and diffuse reflectance UV-visible spectroscopy.The optimal conditions for photocatalytic degradation of 2-sec-butyl-4,6-dinitrophenol（DNBP],included an initial DNBP concentration of 0.167 mmol/L at pH = 4.86 with a catalyst concentration of 6 g/L,under visible light irradiation for 5 h.A plausible mechanism is proposed for the photocatalytic degradation of DNBP.Our composite showed higher photocatalytic activity for DNBP degradation than that of pure TiO2.This indicates that this material can serve as an efficient photocatalyst for degradation of hazardous organic pollutants in wastewater.

Preparation of Reactive Powder Concrete Using Fly Ash and Steel Slag Powder

To decrease the cement and SF content of RPC by using ultra-fine fly ash （UFFA） and steel slag powder （SS）, the effect of these mineral admixtures on compressive strength of RPC were investigated. The experimental results indicate that the utilization of UFFA and SS in RPC is feasible and has prominent mechanical performance. The microstructure analysis （SEM and TG-DTG-DSC） demonstrated that the excellent mechanical properties of RPC containing SS and UFFA were mainly attributed to the sequential hydration filling effect of the compound system.

Compression behavior and constitutive model establishment of fly ash cenosphere/polyurethane aluminum alloy syntactic foam

The aluminum matrix syntactic foam was fabricated by pressure infiltration technique,and the filling material is syntactic foam material with fly ash cenosphere as the main component and polyurethane foam as the binder.Split Hopkinson pressure bar(SHPB)dynamic compression and quasi-static tests were carried out to examine the compressive response of syntactic foam in this study.Then the dynamic constitutive model was established.Results show that the compressive stress-strain curve of syntactic aluminum foam is similar to that of other metallic foam materials:both kinds of aluminum matrix syntactic foams have strain rate effect,and the syntactic foam has higher compressive strength and energy absorption than the same density aluminum foams.However,due to the different sizes of cenospheres,the dynamic compression results of two kinds of syntactic foams are different,and the energy absorption effect of syntactic foam with small size under dynamic impact is the best.In the range of strain rate and density studied experimentally,the curves of constitutive model fit well with the curves of experimental data.

Preparation of ZrN(ZrON)-SiAION Composite Ceramics via a Pressureless Sintering Process

ZrN-SiAlON composite materials were synthesized at 1 550 ℃ for 6 h via a carbothermal reduction nitridation route using fly ash （≤74 μm）,zircon （≤ 44 μm） and active carbon as starting materials.The processed ZrN-SiAlON composite micropowders were mixed with polyvinyl alcohol as binder to prepare ZrN （ZrON）-SiAlON composite ceramics by carbon-embedded pressureless firing at 1 450,1 500 and 1 550 ℃ for 1 h,respectively.Influences of firing temperature on the phase compositions,microstructure and sintering properties of the ceramics were investigated.The results show that：（1） β-SiAlON based composite ceramics with different compositions can be prepared by controlling firing temperature,and the main crystalline phases of the specimen fired at 1 550 ℃ for 1 h involve ZrN,ZrON and β-SiAlON （z =2,Si4Al2O2N6）; （2） ZrN （ZrON）,β-SiAlON and a Fe-Si based compound can be observed in the microstructures of the specimens fired at different temperatures.ZrN （ZrON） particles distribute homogeneously in the β-SiAlON matrix; （3） raising firing temperature can increase the shrinkage ratio of the ceramics,and the volume shrinkage ratio increases from 19.4％ to 40.3％ when the firing temperature rises from 1 450 to 1 550 ℃.

Mineralogical and Active Mechanical Excitation Characteristics of Filled Fly Ash Cementitious Materials

To reveal the influence of mechanical activation on the performance of fly ash, the microanalysis（the energy spectroscopy, XRD and SEM）, the distribution size of particle of fly ash and cement paste intensity of various age for different grinding time were studied. The relationships of the activity and the composition of fly ash, microstructure and the distribution of particle size by mechanical activation of fly ash were obtained. The internal glass beads with activity were released by grinding fly ash for a certain time. The particle specific surface area was improved and the hydration reaction of the interface and the surface active center was increased by grinding. The granularity distributing of fly-ash trended towards optimization. The polar molecules or ions were easier to intrude into the internal cavity of the vitreous body. The active silica and alumina of fly ash were rapidly depolymerized. Each performance index of fly ash was increased before grinding for 20 min. Cement paste intensity of various age increased along with the grinding time, and the early strength increase range was big, but the later period intensity increase range hastened slightly. The internal part of vitreous of fly ash was destroyed if the fly ash continued to be ground and the activity of fly ash was reduced. It is suggested that Guozhuang＇s fly ash should be ground for 20 min.

Methods of Modifying the Brittle Behavior of Cementitious Composites

We put forward effective methods of increasing the tensile strain of cementitious composites with 2% PVA fiber and high fly ash content. The test results show that curing condition has a significantly effect on the tensile performance. It is approved that the specimens incorporated appropriate volume fraction rubber powder and lightweight aggregate greatly increase the tensile strain of composites at medium-term age, but indefinitely at long-term age. To a certain extent, EVA can limitedly enhance the tensile performance of comentitious composites owing to the formation of polymer membrane and the hindered hydration of cement.

Analysis of chemical composition of precipitation in a typical background site

background precipitation in Lijiang, China was investigated. Results showed that the chemical composition of atmospheric background precipitation mainly comes from fly ash and continental atmospheric transfer, and does not have any obvious correlation with oceanic aerosol, taking Amsterdam in the Pacific Ocean and St. Georges in the Atlantic Ocean and Katherine, Australia as examples for analysing.