The current paper explores the possibility of producing alkali-activated fly ash-based lightweight blocks with adequate properties at lower curing temperatures to use in various construction applications. Sodium-based alkaline activators are utilized to activate the fly ash. Two different curing temperatures are employed, 60 °C and 85 °C. The properties of the block, such as strength, density, and thermal conductivity, are evaluated. Aeration experiments reveal that the addition of Al powder to the paste leads to the collapse of the bubble structure. However, the addition of nano clay aids in stabilizing the formed bubbles, thereby preventing their collapse and maintaining the integrity of the aerated structure over time. The amount of nano clay depends on the quantity of Al powder added to the paste. Across all samples, strength is found to be inversely proportional to density and thermal conductivity. At 0.3% and 0.4% Al powder dosages, samples attained similar ultimate strength regardless of curing temperature, while density and thermal conductivity varied. The block achieved a strength of approximately 10.60 MPa and a thermal conductivity of 0.090 W/mK at a corresponding density of 450 kg/m³, which is higher than the IS standard codal provisions. The blocks were characterized using various analytical techniques such as XRD, FTIR, and SEM. The strength of the block depends on the reaction product formed during the activation process, with all techniques indicating the formation of stable sodium aluminosilicate gel. For samples cured at 60 °C, two new crystalline phases, trona and sillimanite, were observed. Trona is formed at the age of 28 days, while sillimanite forms at an early age, with its quantity decreasing over time. In conclusion, the study offers crucial insights into producing alkaline-activated fly ash-based lightweight blocks with satisfactory performance at lower curing temperatures.

A critical evaluation of the effects of mixture proportioning (binder paste content and coarse aggregate:fine aggregate ratio) on the workability, compressive strength and tensile strength of concrete made with alkali-activated fly ash (AAF) binder was undertaken. Tensile cracking in the fly-ash-based geopolymer concrete (FGC), as influenced by its fracture properties, was studied to understand the failure of the material. Microstructural analyses were conducted using scanning electron microscopy and energy-dispersive X-ray spectroscopy to ascertain product formation. The FGC mixtures demonstrated significantly higher slump and compressive strength than concrete made with Portland cement. The slump or flow of the FGC mixtures was determined by the binder paste and alkaline solution content, and the values increased with the fine aggregate content. An increasing relationship between the coarse aggregate content in the concrete mixture and its compressive strength was identified. A similar trend was observed for the splitting tensile strength, which reached 7% of the FGC compressive strength. The high strength of the FGC was attributed to the formation of sodium aluminosilicate gel and a denser interfacial transition zone (ITZ) near the aggregate interface. The dense ITZ around the aggregate contributed to an enhanced bond between the aggregate and AAF paste, resulting in aggregate fracture. The decrease in strength with binder content was attributed to the maximum paste thickness per unit volume, which contributed to a larger number of voids per unit volume of concrete.

The increasing importance of biomass-based energy production as a critical component of sustainable energy resources and effective waste management necessitates a comprehensive understanding of the fundamental properties of biomass feedstocks. This review critically evaluates the physicochemical and fuel characteristics of seven widely available biomass sources in India (sugarcane bagasse, sugarcane tops, rice husk, rice straw, maize stalks, maize cobs, and empty palm oil fruit bunches), with a particular focus on the impact of torrefaction. Despite the well-documented benefits of torrefaction in improving biomass properties, limited studies have compared the specific effects of this thermal pretreatment process across diverse biomass sources. This review addresses this gap by critically analyzing the impact of torrefaction on key biomass properties, including hemicellulose, cellulose, lignin, elemental composition (carbon, hydrogen, nitrogen, and sulphur), moisture content, volatile matter, and high heating value, providing a comparative analysis to determine the optimal biomass for energy applications. Moreover, the review critically analyzes the impact of torrefaction on key biomass properties, including hemicellulose, cellulose, lignin, elemental composition (carbon, hydrogen, nitrogen, and sulphur), moisture content, volatile matter, and high heating value. Furthermore, the review synthesizes recent findings to identify optimum torrefaction conditions that enhances the properties of each corresponding biomass. By providing a comprehensive analysis of the complex relationships between biomass characteristics and their practical applications, this review contributes to the advancement of sustainable energy production by optimising biomass-based energy systems and promoting waste-to-energy strategies.

The environmental impact of Portland cement production has intensified the search for alternative low-carbon cement. Reactive magnesium oxide cement has emerged as a promising option. The current study investigates the hydration behavior, strength development, and phase evolution of MgO and MgO-RHA blends cured under sealed and carbonation conditions. Two RHA sources with differing amorphous content and particle size were used. A detailed investigation was conducted using various techniques, including calorimetry, TGA, FTIR, XRD, Raman spectroscopy, and SEM. Results showed that higher glassy content and finer particles in RHA enhanced cumulative heat release, hydration product formation, and compressive strength. Carbonation curing further improved strength consistently by promoting the formation of nesquehonite and magnesium silicate hydrate. Quantitative XRD revealed that M-S-H formation was influenced by the consumption of periclase and unreacted glassy phase. Raman and FTIR analyses confirmed significant chemical and structural transformations, including the formation of brucite, nesquehonite, and carbonate phases. The D and G-band features in MgO-RHA samples suggested variations in carbonated products, influenced by processing conditions. Finally, SEM analysis revealed various carbonated products, M-S-H, and a dense microstructure. Overall, the study emphasizes the critical role of RHA properties and curing strategies in optimizing the performance of MgO-RHA systems for sustainable binder applications.

The utilization of Linz-Donawitz (LD) slag in cementitious applications has gained traction due to its widespread availability, offering a potential solution to reduce global warming. This study evaluates the impact of particle size fractions on the chemical, mineralogical, and dissolution characteristics of LD slag. Nine particle size fractions were analyzed, revealing significant variations in oxide content based on particle size. While CaO, Fe2O3, and SiO2 contents remain similar in higher (þ500 μm and þ1,000 μm) and lower (þ3 μm) size fractions, particles between þ3 μm to þ75 μm exhibit a 1.5% free lime content. Quantification using XRD-based Rietveld refinement indicates LD slag primarily consists of crystalline phases (quartz, calcite, portlandite, brownmillerite, wustite, and belite) alongside an amorphous phase, with amorphous content ranging from 40% to 60% across all sizes. The þ3 μm size fraction exhibits the highest belite, brownmillerite, and wustite content, with comparatively lower free lime content than other size fractions. Dissolution analysis in an alkaline environment shows a slightly improved dissolution behavior with decreasing particle size from þ150 μm to þ3 μm. Calcium exhibits higher initial dissolution rates than iron and silicon within the first three hours, with silicon becoming more prominent after twelve hours. Overall, this study offers a comprehensive analysis of the correlation between particle size and chemical/mineralogical composition, highlighting the potential for converting industrial waste into ecofriendly products.

Concrete production is energy-intensive and has an adverse impact on the environment due to the raw materials involved. Currently, India has abundant reserves of fly ash and ground granulated blast furnace slag (GGBS). Despite various applications, fly ash often ends up in landfills. Given its abundance, there is a growing interest in utilising substantial quantities of fly ash in concrete production. In the current study, M30-grade concrete is designed with very high levels of fly ash and GGBS. Additionally, quick lime (QL) is incorporated as a supplementary agent to augment lime content. A total of twenty concrete mixes have been developed with different combinations of fly ash, GGBS, and QL. Results illustrate that the addition of QL does not show overall strength improvement to the GGBS-based mixes, but it impacts on fly ash-based mixes. The targeted design strength is achieved with 70% cement replacement with fly ash and QL. The strength development depends on the pozzolanic reaction initiated and the formation of hydration products in the system. The environmental impact of concrete is assessed by analysing its life cycle assessment using a cradle-to-gate approach. The energy requirement and kg-CO2 eq. emissions depend on the level of cement replacement. The fly ash-based concrete emits less kg-CO2 eq. and requires less energy than the GGBS-based mixes. Overall, the designed strength is achieved with 65% fly ash, requiring 59% less energy, reducing 54% CO2 footprint, 56% GWP100, 80% HTPinf, 46% ODPinf, and cost by 34% compared to OPC-based concrete.

The current paper explores the performance, microstructure and environmental consequences of low-calcium fly ash-based geopolymer concrete compared to OPC-based concrete. The performance of the concrete is assessed based on strength, permeability, sulfate resistance, and acid attack. Two geopolymer mixes were designed by adjusting the binder dosage. The geopolymer concrete mixes achieved 11–16% higher strength than OPC-based concrete. However, increasing the binder dosage from 30 to 40% led to 5% reduction in strength at later ages. Geopolymer concrete demonstrated superior resistance to sulfate and acid attacks, as well as lower penetration depth and permeability coefficient compared to OPC-based concrete. Microstructural analysis was conducted using XRD and SEM techniques, identifying sodium aluminosilicate gel as the product formed during the polymerization process. The environmental impact was evaluated through a life cycle assessment using a cradle-to-gate approach. Geopolymer concrete requires 25–33% less energy and emits 14–28% less kg-CO2 eq. than OPC-based concrete. The production of OPC-based concrete had the greatest negative environmental impact, except in the categories of metal depletion (MDP) and ionizing radiation (IRP_HE). In geopolymer concrete, the use of alkaline activators accounted for higher energy consumption and accounted for 73–75% kg-CO2 eq. emissions. Overall, fly ash-based geopolymer concrete showed higher strength and excellent resistance to acid and sulfate attacks, along with a lower carbon footprint and energy consumption.

This study investigates the microstructure, phase formation, and mechanical properties of LC3-50 based autoclaved aerated blocks. The microstructure and phase formation is studied using SEM-EDS and X-ray diffraction techniques. The fresh and hardened properties are determined using different methodologies. Three different densities (i.e.500,600,700 kg/m3) are designed by varying the aluminum powder dosage. The compressive strength and thermal conductivity depend on the density of the block. The primary hydration product formed during the autoclave process is katoite, and it is responsible for the strength development in LC3-50 based blocks to a certain extent. The autoclave process will help the carbonation of the block altogether, and portlandite is converted to calcite during the autoclave process. Secondary phases like ettringite, monosulfoaluminate and hemicarboaluminate were converted to anhydrite during the autoclave process. Excess lime changes the mechanism of the phase formation, and it initiates the formation of two significant phases: tobermorite and katoite. Significant clinker is present in the unhydrated form.

This study investigated the strength and microstructural development of MgO and MgO-microsilica (MS) systems under sealed and carbonated conditions. The influence of hydromagnesite seeds on the performance of each system was also evaluated. The hydration mechanisms were studied via isothermal calorimetry. A correlation between the strength development and formation of different phases was established. XRD, TG/DTG, FTIR and SEM were used for the identification and quantification of different hydrate and carbonate phases. MgO systems relied on the conversion of brucite into carbonate phases for their strength development, whereas M-S-H was the main source of strength in MgO-MS systems. The effect of seeding was evident in MgO-MS systems, where the extra space provided by the seeds increased the rate and degree of hydration. The formation of M-S-H was responsible for strength development and denser microstructures, which could be further improved via the increased utilization of unreacted MgO and MS.

Current study explores the understanding of various parameters such as the role of aluminum powder dosage, water-to-binder ratio, and initial curing temperature on the production of lightweight blocks. Three different cementitious systems were used: limestone calcined clay cement (LC3), Portland pozzolana cement, and ordinary Portland cement. The aluminum powder dosage and the water-to-binder ratio clearly influence the hardened properties of blocks, whereas the initial curing temperature does not show much improvement to overall properties. Hardened properties such as dry density, compressive strength, and water absorption of blocks were evaluated. The required aluminum powder dosage varies from system to system, and it depends on the required density. To maintain lower density, OPC system required higher dosage of Al powder, and it showed lower strength compared to other systems. LC3-based lightweight blocks are produced with 3 MPa strength, and it showed good performance compared to other systems.

An experimental investigation of fly ash activated with sodium-based alkali-silicate activating solutions is presented. As the first step a detailed characterization of the low-calcium fly ash is performed. The reactive SiO2 and Al2 O3 in fly ash are shown to be smaller proportions of the total SiO2 and Al2 O3 indicated by the oxide analysis. In the experimental program, the roles of reactive oxide ratios, and the molarity of sodium hydroxide in influencing the compressive strength of alkali-activated fly ash are evaluated. The reactive silica content in the alkali-activated fly ash is taken as the sum of the reactive silica contributed by the fly ash and the soluble silica from the activating solution. The reactive alumina in the fly ash and the total sodium in the activating solution are used in determining the reactive oxide ratios. The ratio of reactive Al2 O3 /Na2 O close to 2.5 produces the highest compressive strength. The maximum ultimate compressive strength is attained for a reactive SiO2 /Al2 O3 mass ratio equal to 2.0 in the activated system. The minimum required molarity of NaOH in the alkali-activated mixture is 3M. The results presented in this paper indicate that the composition of the activating solution for achieving the highest compressive strength would depend on the reactive oxide composition of the fly ash. Producing high strength geopolymers requires optimizing the activating solution for the specific reactive oxide ratios based on the reactive oxide content in the fly ash.

Current study explores the estimation of reactivity and dissolution mechanism in low glassy content siliceous fly ashes. Two different fly ashes directly collected from thermal power stations were used in this study. Dissolution experiments were carried out in different sodium hydroxide-based alkaline environments and at different curing temperatures. The dissolution of elements from fly ash is directly related to the glassy portion. During the dissolution process, the crystalline phases are not affected, and it remains the same in various alkaline environments. Higher molarity and temperature enhance the dissolution process.

Fly ash-based geopolymers are being developed as sustainable alternate binders for producing concrete. The consistent production of a stable geopolymeric binder suitable for use in structural applications from alkaline activation of low-calcium fly ash was explored in this paper. The role of working solution and total reactive oxide ratios in consistently achieving high compressive strength in fly ash-based geopolymers were evaluated using different source fly ashes. The primary source variability was identified with the reactive silica and alumina contents in the fly ash. The maximum strength achieved from the activated fly ash was determined by the reactive alumina content in the fly ash. Due to source variability of reactive species contributed by fly ash, maintaining a constant composition of the activating solution resulted in varying compressive strength from the activated fly ash. Keeping constant reactive oxide contents in the activated system produced consistent strength from the fly ash-based geopolymers. The composition of the aluminosilicate gel depended on the reactive oxide ratios, and it varied with the fly ash composition for identical solution ratios. Global reactive oxide ratios, which are calculated based on the reactive oxide contents of the fly ash and the alkaline solution, were established. The link between strength and product formation was established, and the global reactive oxide ratios resulted in a larger reaction product content.

The utilization of post-industrial waste materials is often challenging due to environmental regulations. Additionally, the scarcity of raw materials for producing cement is generating the demand for alternate sources of materials. The current study explores the production of cement and clinker on a large scale using post-industrial waste materials from different sources. Lime sludge generated by the paper mill industry and sponge iron produced during the processing of iron are used as primary source materials for producing clinker. A large-scale vertical kiln is used for clinkering. The unburnt carbon present in the sponge iron is used as an energy source for calcining the raw materials reducing the demand on external fuel. A Portland Composite Cement (PCC) is produced by inter-grinding the clinker with waste generated by the pharmaceutical industry, silico-manganese slag and fly ash. An evaluation of the clinker and the PCC is performed and compared with a commercially available Ordinary Portland Cement (OPC). Hydration studies and characterization of the materials are performed using different analytical techniques. This work provides the fundamental basis for an environmentally sustainable utilization of post-industrial waste in the production of clinker suitable for use in construction.

The compressive strength achieved in alkali-activated low-calcium fly ash depends on the total reactive oxide ratios in the activated system, the reactive alumina content in fly ash and the initial molarity of NaOH. The total reactive silica in the system is the reactive silica contributed by the fly ash and soluble silica from the alkaline solution. A minimum molarity of NaOH is required to ensure complete dissolution of the glassy phase present in fly ash. The maximum compressive strength depends on the amorphous reaction product content formed, which is determined by the reactive alumina content in the fly ash. The highest compressive strength is achieved for the ratio of the total reactive silica to sodium ratio in the activated system equal to 4.72 and lower. More Na is incorporated in the reaction product on increasing the Na 2 O content relative to the reactive oxides.

The roles of temperature and curing periods on product formation and strength gain in alkali activation of low-calcium siliceous fly ash are evaluated. Higher temperature favors the kinetics of amorphous reaction product formation and inclusion of Si in the reaction product, which accompanies the densification of the microstructure. Following initial curing at 60 °C, the reaction product continues to form in the activated system on decreasing the temperature to 25 °C. Initial curing at 25 °C does not lead to formation of reaction product. Reaction product forms in the system for initial curing temperature of 40 °C and higher. The rate of the solid-based reaction, after hardening, is increased by temperature. The total amorphous reaction product content formed in the system depends on the water to solids ratio of the activated mix. The amorphous product composition, however, varies with temperature. With time there is an increase in the Si/Al ratio in the reaction product formed 40 °C and higher. For initial curing at 60 °C, there is no increase in the Si/Al ratio in the reaction product when the temperature is decreased to 25 °C. Reaction product with a higher Si/Al atomic ratio achieves a higher ultimate compressive strength. On increasing the Si/Al ratio in the reaction product from 2.5 to 3.3, the ultimate compressive strength achieved increased from 60 MPa to 74 MPa. Early curing, immediately after mixing, at a higher temperature is critical in achieving a higher Si/Al atomic ratio in the reaction product. Optimum initial curing time at high temperature is based on achieving a high Si/Al atomic ratio in the reaction product.

An experimental investigation on the dissolution of low-calcium fly ashes in an alkaline solution is presented. Fly ashes collected directly from different sources are used in the study. Changes in the elemental concentrations in the solution are determined using optical emission spectroscopy and the residue is characterised using X-ray-based techniques. The increase in the concentration of ions in the alkaline solution is primarily associated with the dissolution of the glassy phase and the crystalline content of fly ash is largely unaffected by the alkaline exposure. The increase in the concentration of Si in the solution relative to the concentration of Al is not influenced by the solution molarity or the temperature. The glass that contains Ca is more reactive and dissolves earlier than the aluminosilicate glass present within the fly ash. The X-ray diffraction pattern of the fly ash glassy phase is adequately fit using a single pseudo-Voigt (PV) peak. The peak position of the PV fit is invariant of the dissolution of the glassy phase and an intensity-based measure of the X-ray diffraction analysis intensity pattern with the PV fit provides an accurate estimate of the undissolved glassy content present in the fly ash.

A large quantity of fly ash is being used in various civil Engineering applications all over the world. Proper characterization of fly ash is essential to utilize the fly ash to its full reactive potential. results from an experimental program using multiple characterization techniques on samples of fly ash collected from different sources located in the Southern part of India are presented. the composition of fly ash is determined using X-ray flouresence (XrF) spectroscopy and the total reactivity of fly ash is established using an X-ray diffraction (Xrd) spectorscopy. It is shown that the fly ash composition and reactivity varies with the source. the reactive silica and the reactive alumina contents of fly ash are determined using combined Xrd and XrF techniques. the reactive silica content determined using the combined X-ray based techniques compared favorably with the dissolution procedure given in IS 3812 (part-1). Significant proportions of the silica and alumina in the fly ash are present in the non-reactive crystalline forms associated with quartz and mullite. the total contents of silica and alumina obtained from the oxide composition do not provide any indication of the reactive silica and the reactive alumina contents present in the amorphous phase of fly ash. there is no clear relationship between the total silica and the reactive silica in the fly ash. Similarly, there is no correlation between the total alumina and the reactive alumina present in the amorphous form. An inverse linear relationship is established between the Mullite content in the fly ash and the iron content in its amorphous phase. there is a significant Fe content in the amorphous phase of the fly ash, which is identified with specific textured spherical particles in the size range from 5 to 8 microns. All the fly ashes have a very low calcium content, which is predominantly present in its amorphous glassy phase.

The role of individual reactive components and process variables such as molarity and temperature on alkaline activation of different low-calcium fly ash is explored. The oxide ratios in the activated system, based on the total silica (total SiO2) in the system consisting of the reactive silica contributed by fly ash and the reactive alumina in fly ash are shown to provide consistent results for achieving the highest strength. For a given total SiO2 content in the system, an increase in the sodium content above a certain dosage does not influence the ultimate compressive strength. An optimum (total SiO2) to Na2O ratio, equal to 2.66 is established for achieving maximum strength. The role of temperature within the range of 60°C-85°C is not significant when the molarity of NaOH is high. A N-A-S-H type gel with Si/Al ratio ranging between 2.5 to 3.0 and the Al/Na ratio varying between 1.30 to 0.9 is formed on decreasing the (total SiO2)/Na2O ratio from 6.55 to 2.66

Activation of low calcium fly ash is investigated using activating solutions of sodium hydroxide (NaOH) and sodium silicate (Na2SiO3). The oxide ratio of Na2O relative to the total reactive silica in the activated mix provides consistent results in achieving the highest ultimate strength. The total reactive silica used for calculating the ratio consists of the reactive silica contributed by fly ash and the silica from the activating solution. There is an increase in the ultimate compressive strength on increasing the total sodium content relative to the total reactive silica content in the activated system. Increasing the sodium content beyond a certain limit does not provide additional gain in the ultimate compressive strength. The ratio of total reactive SiO2 to Na2O in the activated system equal to 4.72 is shown to provide the highest compressive strength and there is no further increase in the ultimate strength on increasing the sodium content. A N-A-S-H type gel with reaction products containing Si, Al and Na, is formed in the activated system. The ultimate strength achieved is directly related to the reaction product content in the system and is dependent on the extent of glassy phase dissolution from fly ash. The extent of glassy phase dissolution and the quantity of reaction product formed in the system increases with an increase in the molarity of NaOH, which also contributes to an increase in the sodium content in the activating solution. The decrease in the unreacted glassy phase content of fly ash is sensitive to temperature at a lower molarity of NaOH. The Al/Na ratio in the reaction product approaches a value of 0.9 on increasing the sodium content in the activated system. The Si/Al ratio in the reaction product varies within a range of 2.3–2.8.

A direct decomposition method of X-ray diffraction pattern associated with amorphous phases in a binary blend containing hydrated cement and siliceous fly ash is developed. The method relies on identifying patterns associated with individual components within the overall intensity pattern produced by the total amorphous phase. The intensity pattern associated with the total amorphous phase in a binary blend of siliceous fly ash and hydrated cement is obtained using the Pawley intensity refinement method. The features of the intensity patterns associated with the amorphous reaction products in hydrated cement and the glassy content of siliceous fly ash extracted by decomposition of the overall intensity pattern produced by the combined amorphous phase are shown to match the features obtained directly from the pure phases. The direct decomposition method allows for quantification of amorphous components, which can be applied to study the evolving phases in a hydrating binary system.

A method for quantitative X-ray diffraction analysis is developed for direct determination of the glassy phase content of fly ash in a hydrating binary blend of cement and low-calcium, siliceous fly ash. The intensity contributions of the unhydrated glassy phase of fly ash and the amorphous reaction products to the intensity pattern of the total amorphous phase in the hydrating binary blend are obtained by decomposition of the total intensity signature as a sum of component pseudo Voigt (PV) peaks. An experimental program involving binary blends with three different low calcium siliceous fly ashes and two different curing temperatures is reported. The centers of the component PV peaks of the fly ash glassy phase fitted to the overall intensity pattern are found to be invariant. The glassy phase content of hydrating binary blends determined from the XRD method were found to agree well with the values obtained from a selective dissolution method.

A technique based on direct decomposition of the XRD signature of the amorphous phase in alkali activated siliceous fly ash for determining the unreacted glassy phase content in fly ash and the amorphous reaction product content is presented. For the purpose of evaluation, a low-calcium siliceous fly ash, alkaline working solutions with different oxide ratios and two different curing temperatures were used. The intensity profile for the amorphous phase obtained from a Pawley intensity refinement of the XRD signature is expressed using pseudo-Voigt peaks for the individual intensity profiles of the glassy phase of fly ash and the amorphous reaction products. The peak characteristics of the amorphous reaction products identified with the aluminosilicate gel are found to be constant for the different curing temperatures and alkaline solutions. The percentage of reaction product and unreacted glassy content in fly ash were determined using selective dissolution combined with Rietveld refinement. The reaction product content and unreacted glassy phase content of fly ash determined from the decomposition of the XRD signature compare favourably with values obtained from selective acid dissolution. The amorphous products of reaction identified from the XRD analysis are shown to correlate well with the compressive strength. XRD is shown to be a powerful technique which can be used to study the influence of process variables on changes in the glassy phase content of fly ash and the evolution of products of reaction in alkali activated siliceous fly ash.

The influence of temperature and added lime on the dissolution of the glassy phase in a binary blend of low-calcium siliceous fly ash and cement. An XRD-based technique is used for quantification of the glassy phase content and the amorphous reaction products in the binary blend. The experimental technique allows for tracking the formation of amorphous reaction products, the availability of lime and the unreacted glassy content. The rate limiting step in the pozzolanic reaction of low calcium fly ash is established to be the dissolution of its glassy phase. Results indicate that increasing the temperature from 25°C to 40°C produces a significant increase in the rate of dissolution of the glassy phase of fly ash and an increase in the rate of formation of reaction products. Addition of quicklime is very effective in producing reactive lime in the solution. The rate of dissolution of the glassy phase of fly ash and the rate of pozzolanic reaction are not significantly influenced by the lime content in the system. The proportion of fly ash which remains unreacted which is indicated by the undissolved glassy phase depends on the availability of lime in the system.

Quantitative analysis of the amorphous phase in binary blends of siliceous fly ash and hydrated cement is presented using the Partial Or No Known Crystal Structure (PONKCS) method. In binary blends, the total amorphous phase contains contributions from the glassy phase in fly ash and amorphous components of hydrated cement. A single pseudo-Voigt function is found to adequately fit the broad hump in the X-ray diffraction pattern resulting from diffuse scattering produced by the glassy phase in siliceous fly ash. The weight fractions of the amorphous component of hydrated cement and the glassy phase of siliceous fly ash in a binary blend are determined using the fitted profiles for the X-ray diffraction (XRD) patterns. For low lime content of less than 5%, the peak characteristics of the fitted function for the broad hump in the XRD pattern of fly ash are nominally identical for different oxide compositions of the glassy phase. The PONKCS method is shown to provide good accuracy in determining siliceous fly ash content in binary blends.

The role of lime activation on the strength development in concrete with very high fly ash replacement of cement is explored. Quicklime is shown to be very effective in providing increased quantity of lime in the mix, which provides significant enhancement in strength particularly at later ages. Concrete strengths of 30 MPa and higher were achieved with a cement content of 100 kg/m3. The efficacy of quicklime increases with increasing temperature. At 40oC, the rate of strength gain is significantly increased and 30 MPa is achieved within 15 days. It is known that strength gain in concrete is related to the depletion of lime in the system, which is directly influenced by silica provided by fly ash. An investigation of the underlying reactions reveals the potential for further strength enhancement through activation of all the reactive components of fly ash.