Sieve Residue Research Articles

The physical–chemical characterization of mechanically-treated CFBC fly ash

Abstract The physical–chemical characteristics of mechanically-treated circulating fluidized bed combustion (CFBC) fly ash, such as 45 μm sieve residue, granulometric distribution, water requirement, specific gravity, pH value, and mineralogical phases, were investigated. It was found that the grinding process can be divided into three stages. The increase in fineness of ground CFBC fly ash is very sharp in the first stage, then slows down in the second stage, and in the last stage it becomes almost invary. The water requirement decreases with prolonged grinding time, and slightly increases during the last stage of grinding. Ground CFBC fly ash shows a higher specific gravity due to the crushing of coarse particles and carbon particles. The pH of ground CFBC fly ash is greater than that of the original CFBC fly ash, indicating that ground samples react more rapidly with water. The mineralogical compositions remain unchanged with grinding, although the intensity of the crystalline phases decreases and the half peak width increases.

Self-cementitious properties of fly ashes from CFBC boilers co-firing coal and high-sulphur petroleum coke

Self-cementitious properties of fly ash from circulating fluidized bed combustion boiler co-firing coal and high-sulphur petroleum coke (CPFA) were investigated. CPFA was self-cementitious which was affected by its fineness and chemical compositions, especially the contents of SO3 and free lime (f-CaO). Higher contents of SO3 and f-CaO were beneficial to self-cementitious strength; the self-cementitious strength increases with a decrease of its 45 μm sieve residue. The expansive ratio of CPFA hardened paste was high because of generation of ettringite (AFt), which was influenced by its water to binder ratio (W/A), curing style and grinding of the ash. The paste cured in water had the highest expansive ratio, and grinding of CPFA was beneficial to its volume stability. The hydration products of CPFA detected by X-ray diffraction (XRD) and scanning electron microscopy (SEM) were portlandite, gypsum, AFt and hydrated calcium silicate (C–S–H).

Development of a multipurpose tile body: Phase and microstructural development

In this study, an attempt was made in order to develop a multipurpose tile body using a single formulation. In order to achieve this, several body recipes were prepared using mainly local raw materials with clearly defined physical and chemical properties at different sieve residues and single fast fired under industrial conditions in the first part of the study. In the second part, the most suitable formulations with the corresponding sieve residues were determined and further fired at different peak temperatures under laboratory conditions in order to establish their vitrification ranges and optimum firing temperatures. The tested peak firing temperatures were varied at 20 °C intervals from 1120 to 1200 °C for multipurpose wall tile body and from 1140 to 1220 °C for multipurpose floor tile body. The physical and thermal properties of the fired bodies such as water absorption, linear firing shrinkage, bulk density and linear thermal expansion coefficient were measured. The vitrification behaviour of the multipurpose bodies was also evaluated using a double-beam optical non-contact dilatometer. Furthermore, the fired bodies were subjected to colour measurements. Particular consideration was given to the phase and microstructural evolution of the developed tile bodies. X-ray diffraction (XRD) was used to analyse the phases formed before and after firing. Scanning electron microscopy (SEM) in combination with energy dispersive X-ray spectroscopy (EDS) was further employed in order to observe the microstructural and microchemical characteristics of the fired bodies with respect to peak firing temperature. The preliminary experimental results showed that it was possible to obtain a multipurpose body with the properties in accordance with ISO-EN 10545.

Grinding characteristics of multi-component cement-based material

The grinding characteristics of two or multi-component material of clinker with limestone, blast furnace slag and fly ash were studied. Investigation was carried out on the particle size distribution, the Blaine fineness and the sieve residue of the separate and interground products. The relative contents of clinker and lime-stone in different size fractions of the interground product were examined, and the interaction of two components, which have different grindabilities, was analyzed. The results show there exists a selective grinding effect during intergrinding, one component can help or hinder the grinding of the other. Making good use of this interaction appropriately not only enhances the grindabilities of two or multi-component mixtures, which can promote the grinding process of clinker with industrial wastes, but also improves their particle size distribution and properties.

Micro‐ and Nanoforaminifera from Abyssal Northeast Atlantic Sediments: A Preliminary Report

AbstractRose Bengal stained benthic foraminifera which pass through a 63 μm mesh (microforaminifera and nanoforaminifera) have been extracted by handsorting the fine sieve residues (> 45 μm, 31 μm, 28 μm, 20 μm, 15 μm) of abyssal sediment samples. The samples were collected using a multiple corer in four areas of the northeast Atlantic between 31° N and 59° N. The abundance of these minute foraminifera varied from 2 specimens per 1 cm2 (Madeira Abyssal Plain) to > 110 per 1 cm2 (BIOTRANS area). They include a variety of taxa, the most common being certain rotaliid species, hormosinaceans and other multilocular agglutinated forms, the unilocular agglutinated genus Lagenammina, soft‐bodied agglutinated sphaeres and flasks (saccamminids and psammosphaerids) and allogromiids. Some specimens are < 63 μm in maximum dimension but others belonging to elongate taxa are longer.Two samples taken 10 cm apart on the Porcupine Abyssal Plain suggest that minute foraminifera may be patchily distributed on a small scale. One sample, which was overlain by substantial amounts of phytodetritus, contained > 100 stained specimens (> 30 per 1 cm2) while the other, in which much less phytodetritus was present, yielded only 10 specimens (2.9 per 1 cm2). This observation suggests that some micro‐ and nanoforaminifera may flourish in the presence of decaying organic matter, perhaps consuming the associated bacteria. The presence of phytodetritus may also explain why two of our samples from the Madeira Abyssal Plain (MAP) contained an order of magnitude more stained tiny foraminifera than two other MAP samples in which phytodetritus was absent.

Particle Size Distribution and Rate of Strength Development of Portland Cement

The fineness of a portland cement is a key factor in determining its strength development characteristics. A simple one‐parameter fineness characterization such as a Blaine value or a sieve residue is often inadequate for a precise evaluation of the influence of fineness on the strength development of cement, especially when comparing cements ground with different grinding equipment. Information on the whole particle size distribution (PSD) of the cement must be used. A mathematical model relating PSD to strength, based on comparison of cements made from the same basic materials (clinker and gypsum) but ground to different PSD, is presented. The model assumes that at a given time of hydration all particles have reacted to the same depth from the original surface. Integrating over the total PSD will give the degree of hydration for a specific size distribution. From a correlation between strength and degree of hydration, differences in degree of hydration can be converted into relative strengths. The applicability of the model is demonstrated by two examples. The first example compares two cements which are ground to different finenesses in the same mill. The second example compares two cements which are ground to the same specific surface area in two different mill systems, bringing about cements with PSDs of different shape. The depth of reaction values found to give the best description seems to be proportional to the square root of time of reaction, indicating a diffusion‐controlled hydration reaction.

Contribution of PFA to concrete workability and strength development

An assessment of the nature of the components of pulverized-fuel ash (pfa) has shown a dominance of hollow, glassy spheres with a composite shell. Total of partial coating by magnetite can be present. The form, size and physical nature of the particles are shown to be the main influences affecting the workability and water demand of fresh pfa concretes. The relationship between progressive pfa particle reaction and strength gain with time has been observed for standard cured concretes up to two years old. The early pfa contribution to strength development is largely a beneficial interaction with the normal hydration of Portland cement while the pozzolanic reaction becomes significant after 28 days. The potential performance of pfa can be predicted from a consideration of its fineness, as measured by 45 μm sieve residue.

Fine grinding and states of equilibrium

During grinding, temporary and permanent dynamic equilibria may occur due to the interaction of particles. These equilibria are represented by the constancy of the sieve residue and the zero value of the grinding rate. The temporary dynamic equilibrium occurring during the initial stage of grinding does not imply the end of increasing fineness but is accompanied in every case by increased power consumption. The state of permanent dynamic equilibrium occurs during grinding for a longer period and indicates the end of increasing fineness for the given particle size. The so-called curve of state of grinding equilibrium combines the states of equilibrium occurring at the individual particle sizes and separates the stages of increasing and decreasing fineness.

Some Questions Concerning ASTM Standards and Methods of Testing Fly Ash for Use with Portland Cement

Abstract Although the potential for substantial energy conservation by the use of fly ash in blended cements is well recognized, present test methods and standard specifications do not appear to be adequate to insure predictable performance. A review of the literature led to an analysis of the scientific bases for existing tests for water requirement for pozzolanic activity. Questions are raised concerning the use of fixed proportions in both tests. It is suggested that proportions be adjusted in the mortar flow test to take into account the 45-μm (No. 325) sieve residue of the fly ash. It is also suggested that variable proportions of fly ash and cement be used in the pozzolanic activity tests to facilitate optimization of concrete properties.

An algorithm for deducing an effective sieve residue from the rate of powder passage through a sieve

The effect of non-ideal aperture distribution of a sieving surface on the sieve residue has been the object of many experimental studies. Unfortunately, the sieving kinetics of many sieving techniques do not result in a simple probability relationship between the size distribution function of the powder and the sieve aperture distribution function. If one specifies a certain type of sieving kinetics, then one can apply probability theory to the rate of movement of powder through the sieve and the size aperture distribution function of the sieve. Under such specified sieving conditions it can be shown that it is possible to deduce a size characteristic parameter of the powder being sieved, which in this publication is described as the kinetic residue of the sieve. An algorithm for the automatic computation of the kinetic residue from the rate of powder sieving is described. The possible implementation of this algorithm to automate sieve analysis is explored.

The application of the BS 4550 test for pozzolanic cements to cements containing pulverized-fuel ashes

Synopsis A large number of pulverized-fuel ashes were tested, in proportions of 20 to 40%, with Portland cement, in accordance with the chemical test for pozzolanic cements incorporated in BS 4550: Part 2:1970. The ashes had a range of particle-size distributions and losses-on-ignition. The results of the test were unrelated to the loss-on-ignition of the ashes, but strongly related to the particle-size distribution measured in terms of the residue on a 45 pm sieve, although other unidentified characteristics of the ashes also infiuenced the results. A positive result is unlikely to be obtained for an 80:20 0PC:pfa mix unless the pfa has a 45 pm sieve residue of less than 20%. Most pulverized-fuel ashes will only give a positive result if present in a proportion exceeding about 25%.

Burnability of cement raw mixes at 1400°C II the effect of the fineness

The discussion of the burnability relationship presented in the first part has been continued. For a typical PC raw mix the sieve residues calcite > 125 μm (K) and quartz > 44 μm (Q) are shown to be adequate parameters for describing the influence of raw mix fineness upon content of free CaO (X) after 30 minutes at 1400°C. For a reference raw mix with typical composition and fineness, ∂X/∂K and ∂X/∂Q are calculated, and the values are in good agreement with those in the empirical burnability relationship. The calculations are based on the known burnability of the reference raw mix, and on assumptions concerning particle-size distributions and reaction mechanisms. Limitations and possibilities of improvements are discussed for the relationship and for the assumptions.

New equations for the kinetics of crushing and their use for calculating the output of ball mills

1. The author has derived new equations of crushing kinetics, expressing the variation of the sieve residue surface, relative to that of the grains of the control size, with the crushing time. 2. The use of these equations enables one to calculate the increase in mill output according to the degree of decrease in the initial ore size, its hardness, and the crushing size.

Filth in Fruit Paste

Abstract Development of a method for recovering all types of filth encountered in fruit paste has been initiated. A number of people were consulted about their experiences in examinations of fig paste by method 36.053 and their efforts to improve recovery of rodent hairs, fly eggs, and maggots by supplementary or substitute procedures. Their answers indicate that a method incorporating extensive digestion of the fruit tissue to liberate filth elements, followed by sieving on a No. 140 screen and washing forcibly with a spray of water to reduce the amount of fruit tissue, then examining the sieve residue microscopically for insects and hairs, appears feasible. Application of this procedure to a commercial straight Calimyrna fig paste resulted in improved filth recovery compared to the AOAC method but proved time-consuming due to the amount of residual fig tissue on the sieve. Kerosene-water flotation treatment of the washed residue on the screen expedited the counting of filth elements, giving recoveries intermediate to those obtained by the AOAC method and direct microscopic examination of digested and sieved residues. It is recommended that the study be continued.

INVESTIGATION INTO THE POSSIBILITIES OF DEVELOPING A RATE METHOD OF SIEVE ANALYSIS

At present it is difficult to assess the accuracy of a sieve analysis because it is necessary to decide arbitrarily when the sieving process is complete. The possibilities of the alternative approach of predicting the final sieve residue from a study of the rate of sieving, have been investigated. It is shown that for spherical particles on a wire-mesh sieve a “rate” method of analysis is possible which gives a value of the oversize percentage, independent of the operator and sieve loading. Experiments are described which indicate that the method may also be possible with irregular metal powders on wire-mesh sieves.

The application of methods of particle size and surface area measurement to whiting

The application to whiting (calcium carbonate) of various methods of determining particle size distributions and surface area is considered and results by various methods are compared. Techniques for determining sieve residues on fine sieves and particle size distribution by sedimentation are described. These methods, together with surface area measurements by air permeability are considered to give data on whitings adequate for most purposes.