Ash Size Distribution Research Articles

Measurement of Fly Ash Particle Size Distribution Using Lensless Digital In-Line Holography

Abstract We propose the use of a lensless digital in-line holography setup for the measurement of particle size distribution (PSD) of fly ash obtained from wet electrostatic precipitators of different power plants. The fly ash samples were prepared by spreading the ash nonuniformly over a glass slide. A number of holograms corresponding to distinct regions of the glass slide were recorded and reconstructed. The particle sizes in each reconstructed image were estimated using a circular Hough transform–based edge detection algorithm. PSDs in the range of 10 to 90 μm were obtained. A numerical scheme to extend the measurement range below 10 μm is discussed. The performance of the proposed method is compared with the laser particle-size analyzer and conventional hydrometer. The experimental results indicate that the performance of the proposed method is similar to the hydrometer, with lower experimental and time complexity.

Characterization, risk assessment, and potential utilization of fly ash from PLTSa Merah Putih at Bantargebang, Bekasi, Indonesia

Municipal solid waste incineration (MSWI) has been adopted in Indonesia to reduce the volume and mass of municipal solid waste. However, as a by-product of waste combustion, fly ash generation cannot be avoided. It can cause an environmental problem if not managed properly. Hence, this study aims to investigate the characteristics of fly ash generated from Indonesia’s first waste-to-energy incineration pilot plant and its potential utilization. Fly ash was characterized using X-Ray fluorescence (XRF), BET surface area measurement, pore size distribution (PSD), scanning electron microscopy with energy-dispersive spectrometry (SEM-EDS), and X-ray diffraction (XRD). The characterization results showed that calcium was predominant, around 28%, followed by titanium, silica, iron, and aluminum, with values of 7.10%, 5.70%, 4.40%, and 4.30%, respectively. These results demonstrated that MSW incineration fly ash was classified as a very active high-calcium fly ash. The surface structure of fly ash was flaky and complex, with some irregular material. The particle size distribution of fly ash shows that the diameters of most particles were nearly 12 μm. The specific surface area of fly ash was 3.06 m2/g, the total-pore volume was 0.01 cm3/g, and the average pore size was 11.82 nm. In addition, the environmental risk assessment was evaluated using the toxicity characteristic leaching procedure (TCLP). TCLP concentrations of heavy metals, including arsenic, barium, beryllium, cadmium, chromium hexavalent, copper, lead, mercury, nickel, selenium, and zinc, were lower than the regulatory level, indicating a low environmental risk. Therefore, it has great potential for utilization as a paving block mixture material.

Improving the properties of metakaolin/fly ash composite geopolymers with ultrafine fly ash ground by steam-jet mill

The particle size distribution and shape of fly ash (FA) are important factors affecting the properties of geopolymers. In this study, a steam-jet mill was used to optimize the fineness and properties of FA as a replacement for metakaolin (MK) in the production of geopolymers. The structural changes of FA by different grinding processes were observed by particle size analysis and SEM. As the treatment frequency increased, the particle size of FA decreased and the particles changed from spherical to irregular shape. XRD, FT-IR, SEM, EDS and LF-NMR were used to reveal the hydration mechanism of geopolymers with different treatment processes and FA substitution ratios and to investigate their mechanical properties. The results showed that the small particle size and irregular shape of the FA had high activity and excellent filling effect. After 28 days, the compressive strength of B-F30 (20% substitution MK and 30 Hz treatment) was 67.80 MPa, which was similar to that of A (0% substitution MK) at 66.36 MPa. FA crushed by the steam-jet mill allows optimization of the pore structure and further increases the compressive strength of geopolymers. This provides an effective way to prepare high-performance geopolymers using solid waste.

Analysis of the synergistic effect of particle size of compound mineral admixtures on the hydration properties and porosity of Portland cement under low-temperature conditions

The mechanical properties of cement matrix composites can be severely affected at low temperatures, limiting the environment in which they can be used. To ameliorate this problem, the addition of silica fume and fly ash to the matrix is an effective method. This study used silica fume and flew ash as composite admixtures mixed with Portland cement to characterize the heat of hydration, mechanical properties, and microstructure of the composite cementitious materials. The test results show that the particle size distribution of fly ash and silica fume can influence the hydration reaction rate and the whole hydration process. By adjusting the particle size of the admixtures, the structural loosening and strength attenuation of the concrete caused by low temperatures can be improved. At low temperatures, when cement hydration is low, the coarser the particle size, the better the gradation between silica fume and fly ash and the better the filling of the pores. In addition, the specific surface area of silica fume was fixed at 19.1m 2 /g, and the correlation between fly ash particle size intervals in mineral admixtures was strongest in (30~40μm), (40~50μm) on the total porosity. Silica fume in the (>0.4μm) and (0.25~0.4μm) particle size intervals had the strongest correlation with porosity. Finally, a prediction model between the particle size interval of the mineral admixture and the total porosity of the concrete under standard and low temperature curing conditions was established. • The admixture effectively fills micro-pores • Methods for improving the strength of cementitious materials at low temperatures • The particle size distribution affects the rate of hydration and the hydration process • The hydration rate can be increased by improving the particle size of the admixture.

Retrieval of refractive indices of ten volcanic ash samples in the infrared, visible and ultraviolet spectral region

Volcanic eruptions can emit large amounts of ash into the atmosphere, which can have significant impacts on infrastructure, human health, agriculture and air traffic. Remote sensing instruments can efficiently detect airborne ash plumes, and the measured spectra can be exploited to obtain information on the physical characteristics of ash (grain size distribution, concentration, optical depth). The key parameter on which all such satellite retrievals depend is the complex refractive index (CRI) which remains one of the largest sources of uncertainty in the retrieval process. Here we present a complementary dataset of refractive indices of volcanic ash to that published by Deguine et al. (2020), to cover a part of the major explosive eruptions occurred during the past 50 years. These CRIs were obtained using an innovative experimental methodology which consists in measuring simultaneously the extinction spectra in the IR and UV/visible domain and the size distribution of ash in suspension in a nitrogen flow. These experimental data are the main input to the retrieval process of CRI. The numerical routine uses Mie theory coupled with Kramers–Kronig relationship to retrieve the imaginary and the real part of the complex refractive index. This methodology has been successfully applied on samples collected from various eruptions and deposits in Indonesia (Kelud), Chile (Chaitén), Italy (Stromboli), Russia (Karymsky), Tanzania (Rungwe, Mount Meru), Ethiopia (Corbetti), Philippines (Taal, Pinatubo) and USA (Mount St. Helens). Significant variations of the real and imaginary part of the CRI are observed according to the chemical composition of the samples. Moreover, the sensitivity of the CRI to chemical composition and mineralogical structure (amorphous/crystalline fraction) has been investigated and shows a strong dependence of the CRI on these parameters.

Impact of PM10 Particles on the Measurement Error of SO2 Electrochemical Gas Sensor

To address the problems of poor measurement accuracy and long service life of SO2 electrochemical gas sensors when used in thermal power plant areas, fly ash emitted from a thermal power plant in China was used as the research object. Based on the analysis of the morphological characteristics of fly ash particles, theoretical calculations were used to obtain the settling speed of fly ash particles and the amount of fly ash deposited at different times, and then the impact of fly ash on the measurement error of a SO2 electrochemical gas sensor was investigated by experimental tests. The research results show that the particle size distribution of fly ash is 2–11 μm, the average settling speed of fly ash particles is 1.34 × 10−3 m/s, and the deposition amount of fly ash on the surface of the sensor inlet film is 0.95 mg per day. The deposition time of fly ash affects the sensor measurement error, and the longer the deposition time, the larger the sensor measurement error, which is due to the reduction of gas diffusion area S and diffusion coefficient K in the sensor caused by fly ash deposition. Fly ash deposition has a greater impact on the sensor when measuring low concentration gases. The higher the gas concentration, the lower the measurement error, because the higher the gas concentration, the faster the gas reaches the working electrode area and the higher the effective SO2 concentration detected in the limited response time. When using SO2 electrochemical sensors in environments with high concentrations of fly ash or dust, it is recommended to install dust-proof devices (such as air-permeable filter membranes with a pore size of less than 4 μm) and regularly clean the deposited fly ash, which can improve the accuracy of the sensor measurement and extend the service life.

Modelling Particle Size Distribution of Residual Fly Ash from Pulverized Biomass Combustion

The present work aims to develop a simple model for describing the particle size distribution (PSD) of residual fly ash from pulverized biomass combustion. The residual ash formation was modelled considering the mechanism of fragmentation and coalescence. The influences of particle shape and stochastic fragmentation on model description of the PSD of the fly ash were investigated. The results showed that biomass particle shape has a great influence on the model prediction, and a larger fragmentation number is required for cylindrical particles than that for spherical particles to get the same PSD of fly ash, and the fragment number of the particles increases with the shape factor increasing. For pulverized biomass with a wide size distribution, the model predicted ash PSD considering the stochastic fragmentation is very similar to that assuming uniform fragmentation. It implies that the simple model assuming uniform fragmentation is applicable for predicting fly ash size distribution in practical processes where biomass particles have a wide range of sizes. For the fuel with a narrower initial PSD, the stochastic fragmentation model generally predicts a coarser PSD of the residual ash than assuming uniform fragmentation. It means the stochastic fragmentation is of great influence to be considered for accurate description of ash formation from the fuel with a narrow PSD.

Influence of Particle Morphology of Ground Fly Ash on the Fluidity and Strength of Cement Paste.

The grinding process has become widely used to improve the fineness and performance of fly ash. However, most studies focus on the particle size distribution of ground fly ash, while the particle morphology is also an important factor to affect the performance of cement paste. This article aims at three different kinds of ground fly ash from the ball mill and vertical mill, and the particle morphology is observed by scanning electron microscopy (SEM) to calculate the spherical destruction (the ratio of spherical particles broken into irregular particles in the grinding process of fly ash), which provides a quantification of the morphology change in the grinding process. The fluidity of cement paste and the strength of cement mortar are tested to study the relation of spherical destruction and fluidity and strength. The results show that the spherical destruction of ground fly ash in a ball mill is more than 80% and that in a vertical mill with a separation system is only 11.9%. Spherical destruction shows a significant relation with the fluidity. To different addition of ground fly ash, the fluidity of cement paste decreases with the increase of spherical destruction. To the strength of cement paste, particle size distribution and spherical destruction are both the key factors. Therefore, spherical destruction is an important measurement index to evaluate the grinding effect of the fly ash mill.

Effect of Fly Ash with Different Particle Size Distributions on the Properties and Microstructure of Concrete

Fly ash has become an important component of concrete as a supplementary cementitious material. Fly ash, as an admixture in concrete, has a great impact on the improvement of concrete properties and utilization of resources. In this work, fly ashes with different particle size distributions (S. Tsivilis, Andersen, normal and F distributions) were selected to prepare concrete. The relationships among the particle size distribution of the fly ash, compressive strength, hydration, pore structure and microstructure of the concrete were studied. The results showed that the compressive strength of the concrete increased at 28 d with fly ashes with the S. Tsivilis and F distributions. Moreover, the porosity of the concrete at 28 d was reduced, and the pore structure of the concrete was improved. The early compressive strength of the concrete increased with the fly ash with a normal distribution. The second hydration heat release rate of the concrete with fly ashes with a normal distribution and an F distribution was obviously faster. In addition to the Andersen distribution, other distributions of fly ash had obvious improvement effects on the pore structure of the concretes. High-performance concrete can be made from fly ash with different particle sizes, which avoids the need for ultrafine grinding with a high energy consumption and high-cost chemical excitation processes.

Characterization and utilization of coal fly ash: a review

Fly ash is a by-product, obtained mainly from thermal power plants, composed of silicon dioxide (SiO2) and aluminum oxide (Al2O3). Other oxides present in fly ash include iron (III) oxide (Fe2O3), calcium oxide (CaO), magnesium oxide (MgO) and so on. It may also contain some trace elements such as arsenic (As), zinc (Zn), lead (Pb), selenium (Se), gallium (Ga) and germanium (Ge) and some lesser amount of rare-earth elements. The particle size of fly ash normally ranges from 0.01 to 200 μm. Such variability in the particle size distribution of fly ash could influence the modification of fly ash into many useful products such as zeolites, geopolymers and other composite materials. The physical, chemical and mineralogical characteristics of fly ash combined with its easy availability make this an attractive raw material for various applications. In order to explore the potential use of fly ash, it is essential to look deeply into its characteristic properties. This review meticulously studies the characterization of fly ash by different modern techniques, including X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, thermogravimetric test, energy-dispersive X-ray spectroscopy, differential scanning calorimetry, secondary ion mass spectroscopy and Raman spectroscopy and attempts to correlate the same with its potential applications.

Characteristics of fly ash from waste-to-energy plants adopting grate-type or circulating fluidized bed incinerators: a comparative study

ABSTRACT Although the pressure of waste siege was reduced by the development of waste-to-energy (WTE) plants, every year million tons of toxic municipal solid waste incineration (MSWI) fly ash is produced which is regarded as a hazardous waste. In this paper, ten MSWI fly ash samples were collected to analyze the composition, physical properties, leachability of heavy metals, and toxicity of dioxins to obtain a comprehensive evaluation, which has not been discussed in the previous studies. The analysis and comparison of fly ash is based on the main type of incinerators applied nowadays. Due to differences in the incinerator types, there were significant differences observed in the size distribution, microstructure, element content, and crystalline structure of fly ash, which are related to the heavy metal leachability and dioxin toxicity. The heavy metal leaching toxicity of nine fly ash samples failed to meet the requirements of the landfill regulations. The main heavy metals above an unacceptable level are Pb (4.271 mg/L) in the grate-type fly ash and Cd (1.035 mg/L) in the circulating fluidized bed (CFB) fly ash. Furthermore, the I-TEQ concentrations of dioxins of two CFB fly ash (3.207 and 3.212 ng I-TEQ/g) exceeded the limit value. The main contribution to the dioxin concentrations of the fly ash is from OCDD (18.7–64.3%), and the main contributor to the I-TEQ (international toxicity equivalent quantity) value is 23478-PeCDF (range 33.0 to 43.2%). In addition, correlation between compositional analysis and toxicity indexes was discussed carefully. The findings in this work can provide directions for the disposal and utilization of the fly ash from different incinerators, which can be beneficial for MSWI fly ash management.

Sensitivity of Volcanic Ash Dispersion Modelling to Input Grain Size Distribution Based on Hydromagmatic and Magmatic Deposits

The size distribution of volcanic ash is rarely measured in real time and Volcanic Ash Advisory Centres (VAACs) often rely on a default particle size distribution (PSD) to initialise their dispersion models when forecasting the movement of ash clouds. We conducted a sensitivity study to investigate the impact of PSD on model output and consider how best to apply default PSDs in operational dispersion modelling. Compiled grain size data confirm that, when considering particles likely to be in the distal ash cloud (< 125 µm diameter), magma composition and eruption size are the dominant controls on grain size distribution. Constraining the PSD is challenging but we find that the grain size of deposits from large hydromagmatic eruptions remains relatively constant with distance, suggesting that total (whole-deposit) grain size distributions (TGSDs) for these eruptions could be estimated from a few samples. We investigated the sensitivity of modelled ash mass loadings (in the air and on the ground) to input PSDs based on coarse to fine TGSDs from our dataset. We found clear differences between modelled mass loadings and the extent of the plume. Comparing TGSDs based on ground-only and ground-plus-satellite data for the Eyjafjallajökull 2010 eruption, we found that basing input PSDs on TGSDs from deposits alone (likely missing the finest particles) led to lower modelled peak ash concentrations and a smaller plume.

Enhancement on mechanical and durability performances of binary cementitious systems by optimizing particle size distribution of fly ash

Fly ash is a well-known supplementary cementitious material that is the by-product of coal-fired thermal power plants. The contribution of fly ash to the enhancement of the mechanical and durability properties of cementitious materials has been documented in concrete technology for many years. In this study, to allow superior mechanical and durability properties, fly ash-based mixtures have been produced after optimization of particle size distribution (PSD) of Class F and Class C fly ash according to the formula of Fuller–Thompson. Different distribution modulus values ranging from 0.3 to 0.6 were used to achieve ideal PSD in accordance with the Fuller–Thompson equation. 30% of F- and C-class fly ash by weight of cement were used to replace with cement in cementitious composites by optimizing PSD with help of air jet sieve. The recommended optimization technique improved the 7-, 28- and 90-day compressive and flexural strength results of mortars. Compressive and flexural strength tests and rapid chloride permeability test of cement-based systems incorporating fly ash up to 15% replacement ratio with optimized PSD at 90-days exhibited better results than those of plain samples owing to the filler effect.

Combustion characteristics of sewage sludge solid fuels produced by drying and hydrothermal carbonization in a fluidized bed

The current study presents the experimental results investigating combustion characteristics of sewage sludge fuels (SS) reference to coal and wood pellet as the two typical base fuels. Two types of SS were produced by drying and hydrothermal carbonization technology. The composition analysis and the thermogravimetric analysis (TGA) showed that SS were highly volatile with low ignition temperature than coal and wood pellet. In the lab-scale bubbling fluidized bed experiments, the combustion gas composition and bed temperature were measured for the cases of single fuel and blended fuel. The morphology and the composition of fly ash collected at the cyclone were analyzed using particle size analyzer, ICP-OES, and SEM-EDS. In the single fuel cases, NOx and SO2 emission of SS were several times higher than the base fuels, but those could be reduced in the blend fuel cases while maintaining overall thermal input and bed temperature. The different size distribution and overall composition of fly ash for the single fuel cases became similar in the blend fuel cases. The change in the characteristics of fly ash was considered to be related to the distribution of mineral matters, such as Ca, K, and P in particular.

Rice Husk Ash Pozzolan as Valuable Supplement in Concrete for Industrial and Domestic Applications

Controlled burning of rice husks at<700°C produced rice husk ash (RHA) which is predominantly amorphous silica (SiO2). RHA was used as a substitute for laterite and cement in proportions of 5%, 10%, 15%, 20%, 25% and 30% of concrete. The concrete was cured for 7 days, 14 days, 21 days, and 28 days respectively. It was observed that 20% of RHA provides the optimum strength. The effects of different particle sizes of 75, 150, 212, 300, 425 and 600 microns (µm) were tested using a compression test machine. A graph of average strength against particle size indicates 2.9 Nm-2 as the optimum strength at 75 µm and 1.2 Nm-2 as the minimum at 150 µm. From the ash size distribution, the presence of grains of several different sizes was observed. The grains were weighed using a weighing machine and a graph of particle size against percentage plotted to determine the particle size distribution. This showed that rice husk ash (RHA) is coarse grain material.

Passive Earth Observations of Volcanic Clouds in the Atmosphere

Current Earth Observation (EO) satellites provide excellent spatial, temporal and spectral coverage for passive measurements of atmospheric volcanic emissions. Of particular value for ash detection and quantification are the geostationary satellites that now carry multispectral imagers. These instruments have multiple spectral channels spanning the visible to infrared (IR) wavelengths and provide 1 × 1 km2 to 4 × 4 km2 resolution data every 5–15 min, continuously. For ash detection, two channels situated near 11 and 12 μ m are needed; for ash quantification a third or fourth channel also in the infrared is useful for constraining the height of the ash cloud. This work describes passive EO infrared measurements and techniques to determine volcanic cloud properties and includes examples using current methods with an emphasis on the main difficulties and ways to overcome them. A challenging aspect of using satellite data is to design algorithms that make use of the spectral, temporal (especially for geostationary sensors) and spatial information. The hyperspectral sensor AIRS is used to identify specific molecules from their spectral signatures (e.g., for SO2) and retrievals are demonstrated as global, regional and hemispheric maps of AIRS column SO2. This kind of information is not available on all sensors, but by combining temporal, spatial and broadband multi-spectral information from polar and geo sensors (e.g., MODIS and SEVIRI) useful insights can be made. For example, repeat coverage of a particular area using geostationary data can reveal temporal behaviour of broadband channels indicative of eruptive activity. In many instances, identifying the nature of a pixel (clear, cloud, ash etc.) is the major challenge. Sophisticated cloud detection schemes have been developed that utilise statistical measures, physical models and temporal variation to classify pixels. The state of the art on cloud detection is good, but improvements are always needed. An IR-based multispectral cloud identification scheme is described and some examples shown. The scheme is physically based but has deficiencies that can be improved during the daytime by including information from the visible channels. Physical retrieval schemes applied to ash detected pixels suffer from a lack of knowledge of some basic microphysical and optical parameters needed to run the retrieval models. In particular, there is a lack of accurate spectral refractive index information for ash particles. The size distribution of fine ash (1–63 μ m, diameter) is poorly constrained and more measurements are needed, particularly for ash that is airborne. Height measurements are also lacking and a satellite-based stereoscopic height retrieval is used to illustrate the value of this information for aviation. The importance of water in volcanic clouds is discussed here and the separation of ice-rich and ash-rich portions of volcanic clouds is analysed for the first time. More work is required in trying to identify ice-coated ash particles, and it is suggested that a class of ice-rich volcanic cloud be recognized and termed a ‘volcanic ice’ cloud. Such clouds are frequently observed in tropical eruptions of great vertical extent (e.g., 8 km or higher) and are often not identified correctly by traditional IR methods (e.g., reverse absorption). Finally, the global, hemispheric and regional sampling of EO satellites is demonstrated for a few eruptions where the ash and SO 2 dispersed over large distances (1000s km).

Lightning Effects on the Grain Size Distribution of Volcanic Ash

AbstractNatural volcanic ashfall samples were examined, and high‐current (~100 kA) electrical impulse experiments were conducted to reveal the changes in grain size that can occur during lightning discharge. Experiments on pseudo ash samples manufactured from volcanic deposits of both rhyolitic and basaltic composition show that aggregates of very fine grained ash particles (<32 μm) melt and degas to form vesiculated pumice fragments >100 μm in size. In some cases, bubbles <5 μm in diameter expand and detach from the outer surface of the pumice to form hollow spheres of glass, one type of lightning‐induced volcanic spherule, while other bubbles fragment. Volcanic ashfall from the 2009 Redoubt eruption and the 2016 Pavlof eruption contains both pumiceous grains and individual spherules. Results of this study reveal that volcanic lightning will alter the grain size distribution of ash through melting, vesiculation, and fragmentation of individual particles or ash aggregates.

Understanding the effects of oxyfuel combustion and furnace scale on biomass ash deposition

Recycled wood oxyfuel combustion is attractive for the advantages of reusing the waste bioenergy and reducing the carbon emissions. However, the changes in the fuel properties and combustion conditions can lead to uncertainties in the ash deposition. In addition, the understanding of the differences in the ash deposition between the pilot-scale and full-scale furnaces is very limited. We have performed ash deposition experiments on a 250 kW pilot-scale furnace for recycled wood air and oxyfuel combustion along with the EI Cerrejon coal combustion as a reference. A CFD-based ash deposition model, which uses the excess energy based particle sticking model, has been developed and the predictions are in qualitative agreement with the measurement data. The results suggest that, besides furnace temperature, the aerodynamics and ash physicochemical properties dictate the ash deposition. The recycled wood has a much higher deposition rate than the coal in the pilot-scale furnace; however, the biomass can numerically have a lower deposition rate under high velocities close to the full-scale boilers. This is mainly due to the biomass having a much lower sticking efficiency since it has high calcium and silicon concentrations and low potassium concentration. Although the effect of oxyfuel combustion is small and within the experimental uncertainties, it is found that oxyfuel combustion can affect the particle impaction and sticking behaviours depending on the fly ash properties and these effects occur in different ways in the pilot-scale and full-scale conditions. Great care should be taken to perform the transfer of the deposition observations from the pilot scale to the full scale and this is because the furnace scale has an effect on the selective deposition behaviour. In this paper a relationship between the fly ash properties (ash composition, size, etc.) and ash deposition for the woody biomass has been proposed. Additionally, the uncertainty analysis of the CFD modelling is undertaken, which indicates that the fly ash size distribution and the heterogeneity are responsible for the major source of errors along with the experimental uncertainties.

Influence of Nanosilica on Workability and Compressive Strength of Wood Ash Cement Concrete

Studies have revealed that wood ash cement concrete just like other pozzolanic cement concrete has lower early strength compared to plain cement concrete. Nanoparticles have been found to improve the early strength of concrete due to its small size and large surface area. This paper reports the influence of nanosilica on the workability and compressive strength of wood ash cement concrete. Wood ash was obtained as a waste product from Ladoke Akintola University of Technology (LAUTECH) bread bakery, Ogbomoso. Biological synthesis of nanosilica using kola Pod extract and silica precursor (1:5) was conducted at Nanotechnology research group laboratory at LAUTECH. The chemical composition, specific gravity and particle size distribution of wood ash, fine and coarse aggregate used were determined. Concrete with 10% wood ash replacement for cement was produced using1:2:4mix proportion and water to binder ratio of 0.5.Nanosilica was added at 0.5, 1.0, 1.5 and 2.0% levels. Concrete with no wood ash and nanosilica served as the control. Workability and compressive strength of the plain and composite concrete were determined. The results showed that concrete workability was enhanced with introduction of nanosilica. The compressive strength also increased with addition of nanosilica. Maximum compressive strength of 27.53MP was achieved at 90 days with 1.5% nanosilica addition. It was concluded that nanosilica enhanced workability and improved both early and later strength development in wood ash concrete with 1.5% as the optimum addition.

Shrinkage behavior of fly ash based geopolymer pastes with and without shrinkage reducing admixture

In this study, flowability, compressive strength, drying and restrained shrinkage, cracking potential, and pore size distribution of fly ash based geopolymer (FG) pastes were investigated. The FG pastes were made with two SiO2/Na2O mole ratios (Module), two solute mass concentrations (Concentration), with and without shrinkage reducing admixture (SRA), and their properties were compared with those of Portland cement (PC) pastes. A liquid-to-binder ratio (L/B) of 0.33 was used for both PC and FG pastes. The drying condition of 25 °C and 50% RH was used for both free and restrained drying shrinkage tests. The results indicated that the Module and Concentration of activators affected all properties of FG pastes investigated. All FG pastes had a lower cracking tendency than the PC pastes, the latter of which cracked first although its shrinkage was not the highest. The drying shrinkage of FG pastes increased with decreasing Module and increasing Concentration. There was a critical pore size, ds, computed from both the water loss and pore size distributions, which was strongly related with free drying shrinkage of all the pastes studied. The smaller the ds value, the larger the free drying shrinkage a paste will have. SRA substantially coarsened pore structure, significantly reduced free drying shrinkage, noticeably reduced restrained ring shrinkage, distinctly delayed crack initiation time, and considerably decreased crack width of all pastes studied.