Raymond E. Davis and his associates appear to have coined the term “fly ash” in 1937. Following the pioneering studies by the U.S. Bureau of Reclamation for the Hungry Horse Dam, the use of fly ash for massive hydroelectric structures increased rapidly in the U.S., with ASTM issuing the first standard in 1954. In 1982, Canada issued a National Standard, CAN 3-A23.5-M82, entitled “Supplementary Cementing Materials and Their Use in Concrete Construction.” Because of the increasing interest in fly ash utilization, Canada Centre for Mineral and Energy Technology (CANMET) initiated research in the area of supplementary cementing materials in the early 1970's and has since published several comprehensive reports on the subject [1,2]. At the University of Calgary, we are studying Canadian fly ashes and their use in concrete, through an investigation of the physical, chemical, mineralogical and pozzolanic properties of fly ashes from fourteen sources across the country. We report here preliminary results from this study.

The course of the initial set reactions of Portland cement-PFA blends is markedly influenced by the presence of fly ash. Data are presented on the effect of two Class F PFA materials blended with cement in 30:70 ratio. Selected analyses of the aqueous phase compositions at lh to 336h are presented. During the first 6h a nearly steady state aqueous phase composition is achieved with respect to Na, K and Ca concentrations. Following a renewed burst of hydration activity, Ca decreases rapidly in the interval 6–24 h while Na and K contents rise more gradually.

A silico-aluminous (Class F) French fly ash has been studied during the last ten years. While over this period the fly ash was produced from different bituminous coals, it has demonstrated high constancy in terms of its chemical and physical composition as well as cementitious properties. The first part of this paper gives a complete physico-chemical characterization of this fly ash, including chemical composition, mineralogical composition of its crystallized fraction, chemical composition of its glass, grain-size distribution, specific surface area, and bulk density. The second part deals with physico-chemical experiments performed to determine the cementitious components of this fly ash through its dissolution in pure water and in lime water. The lime water experiment was also carried out on a washed sample containing few residual sulfates. This series of experiments demonstrates the importance of sulfates in this particular fly ash, especially during the early stages of hydration. Their action results in the formation of ettringite. The cementitious role of these sulfates has been confirmed by comparing the compressive strength of mortar cubes containing washed and nonwashed fly ash. After 7 days, mortar cubes made with this fly ash showed a slight compressive strength increase when compared to a reference mix containing the same amount of quartz. This compressive strength increase can be related to the formation of C-S-H due to the pozzolanic reaction. After 8 months, the pozzolanic reaction had consumed most of the lime generated by the hydration of C2S and C3S, so that practically no portlandite remained in the mortar.

Concrete with different strengths was produced using four types of cements, one ordinary Portland cement (OPC) and three blended cements with 10% pulverized fuel ash (pfa), 25% pfa, and 15% slag respectively. The pfa was added to the cement clinker during the end of the grinding process. The the slag was preground. Carbonation was tested using the phenolphtalein method. The concretes were exposed to four different climates: (1) 50% RH, 20 C and normal CO2 content (0.03%) of air; (2) 50% RH, 20 C and 0.1% CO2; (3) outside in the natural environment unsheltered from rain; (4) outside in the natural environment sheltered from rain. Curing time before exposure was varied. The preliminary results showed that concrete with blended cements carbonated somewhat faster than concrete with OPC. The influence of curing time before exposure and exposure condition was found to be evident but independent of the blend.

Carbonation in hardened pastes of fly ash cements, stored in a CO2 atmosphere and exposed to different relative humidities, has been investigated in order to study its effects upon different properties of cement pastes. Thermogravimetry (TG), x-ray diffractometry, SEM, and mercury porosimetry (MIP) have been used to characterize the carbonation phenomenon. The results indicate that different relative humidities in the storage chambers lead to carbonation of different solid phases in the hydrated pastes. This effect is discussed in terms of TG- and x-ray analysis. Changes in pore size distribution due to carbonation have been analyzed by MIP and SEM.

Reaction products of high lime fly ash (FA), mixed with distilled water and hydrated in contact with Portland cement (PC), and in hardened PC/FA pastes of various mix proportions, were examined by SEM and EDX. Structures contributing to early strength originated mainly through solution depositions of ettringite, and portlandite. Some evidence of ettringite instability suggested gypsum deficiency in PC/FA mixtures.

Chloride ions, when present at sufficient concentration in the concrete pore fluid, may be associated with corrosion of the reinforcing steel even in normally passivative environments. The effectiveness of fly ash containing pastes in trapping chloride ions was studied. A paste was prepared containing 30% low-calcium fly ash and 70% type I cement, with mixing water (50% by weight) containing 0.4% C1− with respect to the solid. Samples were cured at 25°C and 38°lC at 95% R.H. At designated times extending over a six-month period, the pore fluids were expressed from the hardened pastes using a squeezing cell designed for this purpose. Special precautions were taken to avoid carbonation of the fluids; contact with the atmosphere was minimized. The expressed fluids were analyzed by DC plasma emission spectrometry for cations and by automated selective ion exchange chromatography for anions. Other studies (XRD, thermal analysis) were carried out to identify the compounds formed and determine their mechanisms of formation. Investigations indicated that the mechanism of trapping chloride ion is partly chemical and partly physical through adsorption on the surface of fly ash particles (initially physical and subsequently chemical).

Effective coefficients for the diffusion of Cs+ and Cl− ions accross hardened plates of Portland cement and Portland cement-fly ash blend pastes were measured at 27°, 38° and 60° for samples cured up to 28 d. The porosity and pore size distributions of the same hardened plates were also determined. The fly ash blends show lower anion and cation diffusion rates at higher temperatures, although the porosity is not significantly different from the neat paste. The finer pore size is considered responsible for the slower diffusion in the blends. The electronegative nature of the pore surfaces also contributes to the slower cation diffusion.

This paper describes preliminary a model for the strength of concretes containing industrial by-products such as fly ash, blast-furnace slag, and silica fume. A formula that describes the various strength production mechanisms of these by-products is developed. These materials produce strength by pozzolanic reaction, by latently hydraulic reactions and by self-cementing reactions similar to Portland cement. A method of separating the effect of each mechanism is proposed. A parameter for each of these strength producing mechanisms can be determined from concrete strength data.

A Factor Analysis Model was applied to existing literature data on fly ash and cement properties to relate them to the strength and durability of the cured pozzolanic concrete products. A normal curve was fitted to each independent fly ash and cement property and to each dependent strength property. Functions of the moments, such as indicators of skewness and kurtosis of each property, were calculated and the significance of their departures from the expected values of a normal population was examined. About one-half of the properties were log-normally distributed; the remainder were normally distributed as given. A predictive model was proposed for compressive strength, using the percent sulfate as representative of Factor I, the cement quantity as representative of Factor II, and the percent Fe2O3 as representative of Factor III.

Combinations of two types of commercially available Fly Ash (FA) and Portland cement (PC) were tested for compressive strength and permeance to gas flow. The cementitious components were combined in the concrete mixture in proportions PC/FA = 100/0, 75/25, 60/40 and 45/55 for a range of water/cement ratio, and equal workability. Strength and maturity efficiency factors were satisfactory for 75/25 and 60/40 blends. Gas tightness was improved at all levels of Fly Ash substitution.

Disposal of fly ash in landfills and surface impoundments continues to be the most cost-effective and common practice in the electric utility industry. Fly ash, like most solid residues from industrial processes, contains water soluble constituents. The composition of fly ash however varies from plant to plant with the type of fuel being used, the method of firing, and the way in which the ash is collected. Even though data on the bulk chemical composition of fly ash are now generally available, it is not known how this information can be used to predict the dissolution and migration of ash constituents in natural waters. Concerns for groundwater protection have raised issues which may alter the practice of land disposal for fly ash and make it more costly than necessary. Regulatory actions to date indicate that stricter engineering requirements may be placed on disposal practices in order to protect groundwater from contamination. Natural and artificial liners seem to be the most commonly required engineering solutions - an apparent over-reaction.

Low-calcium fly ashes from eastern Pennsylvania power plants, stabilized with Portland cement, have a potential application as a pipeline bedding material. A typical fly ash, and a cement-stabilized material made with this fly ash, were subjected to extensive physical and chemical characterization. Two procedures were used to investigate whether leachates from the bedding materials were nonhazardous according to the criteria of the regulatory agencies. The first was the short-term EPA test, used to define a hazardous waste under the RCRA regulations, and the second was a long-term flow-through test developed at MRL/PSU. In the second test, driving pressure, flow rate and permeability were monitored during the experiment. Calculations showed that this flow-through technique simulates rain water percolation in a similar sized bed for about 25 years. The leaching fluids in both methods were deionized water (EPA procedure) and simulated rain water. Analyses for seventeen metals by DC plasma emission spectrometry and for seven anions by ion chromatography were performed. Concentrations of the leachates from the two procedures were well below the levels that define a hazardous waste. Considerable insight into the long term leaching mechanisms of various elements was obtained from the flow-through experiments.

three different fixed-bed gasifiers have been leached using: (1) the EPA-EP leaching test; (2) a similar test that starts with a synthetic North Dakota groundwater; (3) the ASTM D3987–81 method; (4) a long-term (120 day) leaching experiment. The gasification ashes were highly alkaline and produced pH's in the range 10–13 during tests 2 through 4. Compositions of major, minor and trace elements were determined by AAS and ICAP analyses of leachates. None of the EPA-EP test leachates from any of the ashes exceeded the EP Trigger values that define a hazardous waste according to the RCRA criteria. The long-term leaching experiments provided insights into the rates of extraction of elements from ash and could be useful in modeling selected failure scenarios in an ash disposal pit. At various times during the long-term leaching experiments, substantial fractions of the Na, K, Al, S, As, Mo, Se and V in the ash were extracted. Liquid to solid (l:s) ratios were important in determining the quantities of elements extracted and in controlling solution pH; during most of the 120 day experiments, pH's were near 13 in a 2:1 ratio experiment and just below 10 in a 20:1 ratio experiment. X-ray diffraction analysis of the leaching residue indicated that only a portion of the ash reacted with the leaching solutions. The reaction products were largely noncrystalline, but minor amounts of zeolites, calcite and gibbsite were identified. The formation of such secondary solid phases appears to be important in controlling leachant concentrations.

The technical hasis for codisposal of gasification ash from the Great Plains Gasification Associates plant, combined with cementitious “scrubber ash” and bottom ash from the adjoining Antelope Valley generating station, both located in Beulah, North Dakota, has been explored. Nine blends containing only the ashes and tap water were fabricated into cylinders and tested for compressive strength and other physical properties. A blend having the ash proportions of the two plants was tested for leachability with respect to several regulated and minor elements. Mineralogical characterization by XRD was performed on the individual waste solids and the cured mixes. Most of the blends had compressive strengths greater than 400 psi after 7-day/38 C and 28-day/21 C curing. The 7-day treatment led to better consolidated test cylinders. Leaching behavior, evaluated by the EPA-EP and ASTM tests, was determined for As, Se, B, V, Mo, Ba, Sr, and K. Average fixation factors (the ratio of leaching expected from a weighted average of its components to the actual leaching of the specimen) of 2 to 4 were observed for the 7-day cured specimens and 1 to 2 for the 28-day specimens. Not all elements had reduced leaching in the fabricated specimens; Se and V leaching increased in the fabricated specimens. In addition to ash proportions, curing conditions (T, pH2O, time) and water to solid ratio appear to key parameters in obtaining well-consolidated and lower leachability products. XRD indicated that ettringite and minor calcite were the only crystalline reaction products of the cementitious reactions in the cured codisposal mix.

Waste processing at the Savannah River Plant will involve reconstitution of the salts (NaNO3, NaNO2, Na2 SO4 and NaOH) into a concentrated solution followed by solidification in a cement-based waste form. Phase stability and mechanical durability of this material will depend to a considerable extent on the thermal properties of the waste form. Fly ash has been used to moderate the hydration and setting processes so as to avoid high temperatures which could cause thermal stresses. Both high-calcium (Class C) and low-calcium (Class F) fly ashes were studied. Other constituents of the mixes include granulated blast furnace slag and finely crushed lime-stone. The adiabatic temperature increases and thermal conductivities were measured and related to matrix mineralogy and microstructure as determined by x-ray diffraction and scanning electron microscopy, respectively.