Pozzolanic Activity Of Fly Ash Research Articles

Microstructural Assessment of Pozzolanic Activity of Ilmenite Mud Waste Compared to Fly Ash in Cement Composites.

This paper presents the influence of adding rinsed ilmenite mud waste (R-MUD) on the microstructure of Portland cement composites, compared to similar composites containing fly ash (FA). The aim of the study is the assessment of the pozzolanic activity of ilmenite mud waste by its impact on the microstructure of the cement matrix in comparison to the undoubted pozzolanic activity of fly ash. The presented test results include pore size distribution, phase composition, pozzolanic activity using thermal analysis, R3 bound water test, and microstructural analysis using scanning electron microscopy (SEM). Tests were performed on mortars cured for up to 360 days. The results presented in this paper have shown that R-MUD has a pozzolanic activity level similar to FA or better, which influences pore size distribution in the composite and its microstructure. During the curing process, the microstructure of composites containing R-MUD became more compact and sealed than those with FA, which might also increase their durability. The results of the R3 tests have proven the pozzolanic activity of R-MUD but its level was lower than FA. R-MUD might be a useful substitute for fly ash, especially given the lack of good-quality fly ash on the market.

Enhancing pozzolanic activity of fly ash via dry and wet milling: A comparative study for sustainable construction material enhancement

This investigation delineates the enhancement of fly ash (FA) properties through mechanical treatments for sustainable construction applications and reducing carbon dioxide (CO2) emissions. FA, a byproduct of coal combustion in power generation, inherently exhibits limited pozzolanic activity. This research evaluates the impact of particle size reduction via dry and wet milling treatments on FA's pozzolanic behavior. The study's comparative analysis involves three FA variants: untreated raw material, dry-milled, and wet-milled FA. Extensive characterization encompassed chemical composition, physical properties, and microstructural features. Results demonstrate a marked improvement in pozzolanic activity in milled FAs, with wet milling yielding superior outcomes in particle size reduction (98% diminution compared to raw FA) and pozzolanic reactivity. The comparative assessment underscores wet milling's efficacy over dry milling and untreated FA in enhancing FA's performance as a sustainable construction material. In light of these findings, the study advocates for continued exploration of FA treatments, aiming to optimize their utility in eco-friendly construction practices.

Effect of alkali sulfates in clinker on hydration and hardening properties of cement incorporating SCMs

Fly ash and slag are widely used in cement production. The effect of alkali sulfates in clinker on hydration and hardening of cement blended with fly ash and slag is studied. The results of hydration heat evolution, hydrates analysis and mechanical properties indicate arcanite (K2SO4), thenardite (Na2SO4), aphthitalite (3K2SO4·Na2SO4, K3NS4) and Ca-langbeinite (K2SO4·2CaSO4, KC2S3) in clinker could activate the pozzolanic activity of fly ash and slag, facilitating the appearance of the second hydration peak in the initial hydration period, and promote the hydration and hardening properties of blended cement. The adverse effects of alkali sulfates in clinker are alleviated with the addition of fly ash and slag; this can be attributed to the dilution and filler effects of supplementary cementitious materials (SCMs), as well as the effect of the alkali sulfates activating fly ash and slag. Arcanite, thenardite and aphthitalite (K3NS4) provide a better activating effect on mortar with slag than fly ash mortar to increase compressive strength and reduce drying shrinkage when the content of alkali sulfates is less than 0.6% sodium oxide equivalent (Na2Oeq).

Investigation of the use of ground raw vermiculite as a supplementary cement materials in self-compacting mortars: Comparison with class C fly ash

A significant part of the global CO2 emission comes from the production of Ordinary Portland Cement (OPC). Supplementary cement materials (fly ash, silica fume, blast furnace slag, natural pozzolans, etc.) have been used in concrete and mortar production for decades. Due to the limited resources of these supplementary cementitious materials, there was no significant reduction in CO2 emissions. Therefore, the search for new materials and methods continues. In recent years, the use of clay types such as kaolin, metakaolin and bentonite in mortar has become widespread. However, no information has been found in the literature regarding the use of finely ground raw vermiculite as a supplementary cement material. In this study, the effects of ground raw vermiculite (RV) replaced for cement on self-compacting mortar (SCM) were investigated. In this context, 5%, 10%, 15% and 20% ground RV was used in SCM mixtures. SCM mixes was tested for fresh concrete such as slump-flowing and V-funnel times. The pozzolanic activity of fly ash and ground raw vermiculite have been using the strength activity index test. Prism specimens of 40 × 40 × 160 mm3 were produced in order to determine their mechanical properties. These samples were subjected to the flexural strength test at the end of 7, 28 and 90 days and the compressive strength test was performed on the parts obtained from the flexural test. In addition, the durability properties of SCM mixes such as capillary water absorption, sorptivity and porosity were determined. The fresh concrete, mechanical and durability results of RV replacement mortars were compared with Class C fly ash (FA), which is commonly used in SCM mixtures. The results showed that the presence of 5% RV gives the highest compressive strength value at all ages. The presence of 5% and 10% RV improved the 90 days compressive strength value by 3.68% and 2.91%, respectively, compared to the FA substituted series at the same rate. The lowest sorptivity coefficient of 90 days was calculated in the RV5 series with 0.037 mm/min1/2. The results showed that the presence of ground RV in the range of 10–15% in SCM mixtures did not adversely affect the mechanical and durability properties of the mixtures. However, 20% RV use negatively affected the properties of SCM.

Comparing Permeability and Drying Shrinkage of the Concrete Containing Mineral Admixtures under the Equal Strength Grade

Fly ash (FA) and ground granulated blast-furnace slag (GGBS) are the most widely used mineral admixtures in engineering. However, their roles in concrete under the equal strength grade, a common comparison method in engineering, were seldom reported. This study investigated the chloride ion permeability and drying shrinkage of concrete samples containing FA or GGBS under an equal strength grade. The samples’ strengths and slumps maintained the same levels by adjusting the water-to-binder ratios and superplasticizer dosages. The results show that both FA and GGBS can promote the resistance to chloride ion penetration and decrease the chloride diffusion coefficients, especially at late ages, due to the hydraulicity of GGBS and pozzolanic activity of FA. Compared with FA, GGBS presents a greater reduction in the concrete permeability due to its higher reactivity. Forty percent replacement levels of FA and GGBS can decrease the penetration level from “high” of plain cement concrete to “moderate” and “low”, respectively. In addition, FA and GGBS can decrease the drying shrinkage of concrete at high replacement levels (30% and 40%). This decrease is more significant in the FA-containing concrete, with the shrinkage decreasing from approximately 400 με to 350 με at a 40% replacement level. The findings can provide scientific guidance for applying FA and GGBS in practical engineering.

Improvement of Mechanical Properties and Microstructure of Cementitious Materials in a Hot-Dry Environment

The hot-dry environment in high geothermal tunnels negatively affects the development of properties of cementitious materials. In order to improve the mechanical properties of cementitious materials in such environments, a proper curing system was developed, the material compositions were taken into account, and the related mechanism was analyzed by microscopic tests. The results showed that the mechanical properties and microstructure of cementitious materials can be improved effectively by adopting film curing and an adequate dosage of fly ash in a hot-dry environment. Compared with standard curing, a hot-dry environment accelerates the evaporation of water in fresh cementitious materials and the early hydration rate of cementitious materials, resulting in lots of unhydrated cement particles and an uneven distribution of hydration products, seriously decreasing the properties of the cementitious materials. Film curing keeps the water from evaporating and ensures enough water is available for hydration at an early age. The addition of FA reduces the amount of cement clinker and decreases hydration reaction rate in high temperature environments at an early stage, avoiding the unevenness of hydration products. High temperatures stimulate the pozzolanic activity of fly ash and promote the degree of secondary hydration reaction, producing more hydration products, as well as contributing to the improvement of the mechanical properties and microstructure of cementitious materials. In this study, in a hot-dry environment, the mechanical properties of mortar with 25% fly ash and 2–3 d film curing are better than those of other experimental groups, including those of standard curing.

Study on Mechanical and Microscopic Properties of Fly Ash Cement-Based Materials in High Geothermal Environment

Through simulating a hot and humid environment of high-ground-temperature tunnel and taking advantage of mechanics performance testing, differential thermal analysis (DTA) technology, and scanning electron microscope (SEM) observation technology, the macroscopic and microscopic properties of cement-based materials and their performance improvement measures can be investigated. Also, the mechanism of improvement can be revealed from the perspective of the hydration degree and microstructure. The experimental results indicate that under the hot and humid environment of high ground temperature, adding fly ash could efficiently weaken the early high-temperature curing effect of cement-based materials, improving their physical properties. But the mechanical strengths of cement-based materials go through a transformation from increase to decline with the rise of fly ash, appearing a maximum value in the process. Meanwhile, the differential thermal analysis and the microstructure analysis show that a hot and humid environment enhances the pozzolanic activity of fly ash and an appropriate ratio of fly ash could improve the microstructure of cement slurry, but when fly ash covers more than 30% of the mix of cement-based materials, the quantity of the alkaline exciting agent, calcium hydroxide, is not enough to meet the needs of the active effect of fly ash and the hydration degree of fly ash becomes extremely low. Last, under a hot and humid environment of high ground temperature, fly ash saturation in cementing material should range from 20% to 30% in mass of total binder, which makes for long-term performance of cement-based materials.

High industrial solid waste road base course binder: Performance regulation, hydration characteristics and practical application

The recycling ratio of industrial solid waste, e.g., steel slag (SS), phosphogypsum (PG) is still comparatively low in developing countries. This work aims to utilize industrial solid waste in a sustainable slow-setting slight-expansive road base course binder (RBCB) production involving the performance regulation, hydration characteristics and practical application. The results indicates that RBCB obtained the ideal retarding effect without additional retarder and avoided the strength loss which caused by the fast hardening during the rolling compaction process. The relatively high content of PG preferably stimulated the pozzolanic activity of fly ash (FA), and more effectively compensated the shrinkage through inhibiting the conversion of AFt to AFm in the later hydration stage. In addition, SS adjusted the setting time, improved the strength and regulated the expansion ratio of RBCB. Each kilometer of road base course absorbed 688.8 t solid wastes and saved 6.53% cost of materials compared with P·S 32.5 (Portland slag cement, strength grade is 32.5) in practical application. Excellent pavement performance, obvious environmental and economic benefits were achieved in the field experiment of RBCB containing high solid wastes. This investigation provides a promising and value-added way for the utilization of various original solid waste.

Production of sustainable green mortar by ultrahigh utilization of fly ash: Technical, economic and environmental assessment

Fly ash (FA) utilization in mortar/concrete as partial replacement of cement is commonly around 30 wt% and globally most of the FA is disposed of in landfills which possess environmental burden. The aim of this experimental work is to present a cost effective and practical solution for potential ultra-high-volume utilization of FA for synthesis of three types of mortar as specified in ASTM C1329. At first, the pozzolanic activity of FA was evaluated through modified Chapelle test, thermogravimetric analysis and strength activity index. Then mortar was prepared by replacing cement with FA up to 100% and the targeted compressive strengths were obtained through cementing and by alkali activation (geopolymerization). Different parameters such as; molarity of alkaline activators, liquid to solid ratio and sodium silicate to sodium hydroxide ratio, that influence the properties of geopolymer mortar were also studied. Tensile strength test and interfacial split tensile strength test was also conducted to evaluate its compatibility with conventional concrete. Characterization of all types of mortar was carried out by the Fourier-transform infrared spectroscopy analysis and verified the geopolymerization as well as their mechanical performance. Finally, comparative analysis was carried out in terms of sustainability, evaluation of technical-economic-environmental indicators. It was concluded that formulation of green geopolymer mortar is the sustainable solution, having better mechanical strength, least CO2 footprints and economical. Results revealed that 60% FA replacement is possible through cementing while for higher replacement levels, alkaline activation was needed to reach the targeted strength.

Interfacial design of nano-TiO2 modified fly ash-cement based low carbon composites

An enhanced use of fly ash in cement composites can decrease energy consumption, reduce related CO2 emissions, and conserve natural resources. However, low activity fly ash reduces the degree of early-age hydration and early strength of cement composites. This paper presents a facile processing method to increase the reactivity of fly ash and improve the early strength of low-carbon composites. Fly ash is mixed with TiO2 nanoparticles through ball milling, and the resulting roughened particles are used as supplementary cementitious materials (20 wt%) in a cement matrix. The TiO2 nanoparticles coated on the surface of fly ash improve the interfacial interlocking between fly ash and cement, and increase the early-age pozzolanic activity of fly ash. At a nano-TiO2 composition of 1 wt% of the binder materials, the early flexural strength and compressive strength of the paste exhibit a dramatic increase (of 37.74% and 39.11%, respectively) over those of a paste without nano-TiO2. A hydration heat evaluation of the fly ash–cement pastes conducted by an isothermal calorimeter indicates that the TiO2 nanoparticles coated on the surface of fly ash increase the hydration rate and hydration extent of the early hydration reaction of fly ash–cement paste. The thermogravimetric analysis results indicate that the TiO2 nanoparticles coated on the surface of fly ash promote the reaction of fly ash with calcium hydroxide (hydration products). This study illustrates the effectiveness of the interfacial design by this facile ball-milling process in overcoming the low reactivity of class-F fly ash and improving the early strength of low-carbon composites. More importantly, the proposed strategy can be conveniently extended to other waste materials, which could potentially improve the waste recycling efficiency.

CONCRETOS AUTOADENSÁVEIS E CONVENCIONAIS: ANÁLISE DAS PROPRIEDADES EM ESTADO FRESCO E ENDURECIDO

RESUMO: Os concretos autoadensáveis destacam-se por suas características essenciais: capacidade de preenchimento de fôrmas, habilidade passante e resistência à segregação, permitindo assim o aumento da qualidade de peças estruturais de concreto, assim como a otimização de sua execução. Contudo, para obtenção de suas características essenciais, um fator é imprescindível trata da utilização de materiais finos, com o objetivo de controlar os efeitos negativos de segregação e exsudação à que o concreto fresco é suscetível a apresentar. Neste contexto, o presente trabalho tem por objetivo comparar as propriedades no estado fresco e endurecido de um concreto autoadensável, utilizando cinza volante como material fino, com um concreto convencional, produzidos com materiais disponíveis na região de Toledo-PR. Os resultados demonstraram que o concreto autoadensável apresentou melhor desempenho quanto às propriedades mecânicas em relação ao concreto convencional. As imagens obtidas por meio da microscopia eletrônica de varredura corroboraram para sustentar as afirmativas acerca da melhora nas propriedades mecânicas do concreto autoadensável, uma vez que foi evidenciada uma menor quantidade de vazios graças à atividade pozolânica da cinza volante. Neste sentido, este trabalho contribui para a difusão do concreto autoadensável e seu uso em construções usuais, resultando em estruturas de concreto duráveis e confiáveis, reduzindo a necessidade de manutenções.
 ABSTRACT: The self-consolidating concretes stand out for their essential characteristics: flowability, passing ability and segregation resistance, allowing the increase of the structural elements quality, as well as the optimization of their production. However, in order to obtain its essential characteristics, the main factor is the use of fines, in order to control the negative effects of segregation and bleeding to which fresh concrete is susceptible. In this context, the aim of this paper is to compare the properties, in the fresh and hardened states, of self-consolidating concretes, using fly ash as fine material with the properties of a conventional concrete, produced with materials available in the Toledo-PR, Brazil. The results showed that the self-consolidating concrete presented better performance in relation to the mechanical properties compared to conventional concrete. Using scanning electronic microscopy the affirmations about the improvement in the mechanical properties of self-consolidating concrete were proven, since a smaller amount of voids was evidenced due to the pozzolanic activity of fly ash. In this sense, this work contributes to the diffusion of self-consolidating concrete in the literature and its use in usual constructions, resulting in durable and reliable concrete structures, reducing the maintenance works.

Sewage sludge ash: A comparative evaluation with fly ash for potential use as lime-pozzolan binders

The disposal of sewage sludge ash (SSA) has become an environmental issue due to the limited available landfill space. This study aims at applying the finely-ground sewage sludge ash (FSSA) with quicklime and hydrated lime to develop a new type of lime-pozzolan system and study the effects of different types of lime on the mechanical properties of the systems. A traditional pozzolanic material (i.e. coal fly ash (FA)) was also used to compare with the FSSA. Multiple techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA) were used to assess the hydration kinetics and microscopic characteristics of the lime-pozzolan systems. The results showed that the quicklime system exhibited lower strength than the hydrated lime system, which was due to its lower reaction degree with the FSSA and the higher porosity caused by the expansion during the vigorous hydration reaction of quicklime. Compared to FA, the FSSA attained higher strength for the whole curing period (up to 90 d) in the lime system due to the highly porous nature of FSSA leading to a lower effective water to binder ratio. However, in the hydrated lime system, due to the higher overall pozzolanic activity of FA, its long-term strength values gradually improved. Besides, calcium phosphate hydrate crystals were detected by XRD in the FSSA; while some clinotobermorite was found in the FA both from XRD and SEM, which might govern the strength gain in the lime-FA system. Overall, the application of FSSA as a pozzolan in the lime-pozzolan system could be a promising option to both relieve the waste disposal pressure and provide a potential sustainable construction material.

Evaluation of coal fly ash in cementitious matrices

Abstract The addition of ash, initially classified as waste in cement matrices, is essential to achieve the requirements of National Policy of Solid Waste. However, technologies that enable such applications should be sought, especially when the material has adequate pozzolanic activity. The aim of this study was to verify the pozzolanic activity of fly ash from coal burning, from the aluminum manufacturing process, such as mineral admixture in mortars and conventional concrete. For that, physicochemical characterization of the ash sample and the mechanical behavior of mix dosage of mortar and commercially used concrete tests were carried out. Results showed the ash in evaluation has pozzolanicity as relevant standards employed and when inserted in the studied cementitious matrices, showed the expected performance for this type of addition (higher mechanical strength at older ages).

Modifications of dolomite-based self-compacting concrete properties using mineral additives

This paper addresses fresh and hardening properties of self compacting concretes (SCC) made with dolomite filer and pozzolanic materials, fly ash and matekaolin as cement replacement in different amounts. For this study, seven mixtures were prepared with a constant water-to-powder ratio and powder content. Fresh SCC properties were assessed by means of slump flow, L-box and sieve segregation test, while hardened properties were evaluated by means of compressive strength and modulus of elasticity at ages of 2, 7, 14, 28 and 365 days. In addition, the activity of mineral additives was assessed by heat of hydration measurement. Obtained results showed that mixtures containing fly ash exhibited better performance concerning workability properties needed for SCC, while cement replacement with metakaolin enhanced the mechanical properties. Slower pozzolanic activity of fly ash reflected in slower strength development, but ultimate strength obtained at the age of 365 days was not reduced by the presence of fly ash.

Parametric Study for Replacement of Sand by Fly Ash for Better Packing and Internal Curing

The use of fly ash as replacement of sand is an economical solution for making green and denser concrete. The paper presents a concrete mix design procedure for partial replacement of sand with fly ash. Present method could produce additional compressive and flexural strength for concrete with partial replacement of sand with fly ash over control concrete, with higher slump. Addition of 0.5% super plasticizer could further improve compressive and flexural strength with higher slump over control concrete. Concrete with sand replaced by fly ash was also found to be economical without and with super plasticizer, when cost per N/mm2 was compared. The beneficial effect may be attributed to better packing, pozzolanic activity of fly ash and internal curing by fly ash as partial replacement of sand. Based on experimental results, correlations are developed to predict compressive strength, flexural strength and cost per N/mm2 for percentage sand replacement with fly ash.

Improvement of coal fly ash pozzolanic activity by different physical methods

This paper presents the results of laboratory investigations performed in order to determine the possibility of improving the pozzolanic activity of coal fly ash from two Serbian Thermal Power Plants. The initial samples of fly ash were treated by different physical processes (mechanical activation, grinding and classification). On the obtained samples, the pozzolanic activity was determined using standard methods (with lime and Portland cement). It was found that the above procedures can significantly improve the pozzolanic activity of fly ash, and the best results were achieved when the fly ash was treated by mechanical activation process in the laboratory ring mill.

Experimental study on strength gaining characteristics of concrete using Portland Composite Cement

This study deals with experimental investigation of strength gaining characteristics of concrete made with Portland Composite Cement (PCC) and Ordinary Portland Cement (OPC). Compressive strength of concrete is often considered as a measure to determine the rate of strength gain of concrete with age and different cement composition. Strength developments of five concrete types have been investigated in terms of cement content and curing duration. Experimental observations on 495 specimens reveal that the early age strength of PCC concrete is lower than that of OPC concrete. Based on the test results, lack of proper pozzolanic reaction in the presence of fly ash in PCC concrete strength is lower at early age. The pozzolanic activity of fly ash also contributes to the strength gain at later stages of continuous curing. This study also concludes that drying ambient conditions reduce the strength potential of PCC concrete as the secondary (pozzolanic) reaction fails to contribute to the development of strength.

The Effect of Curing Time on Compressive Strength of Composite Cement Concrete

The effect of curing condition of five different composition of Portland composite cement (PCC) and ordinary Portland cement (OPC) were investigated in this study. Compressive strength development of five different concrete types has been investigated in terms of cement content and curing duration. From the experimental observation, it is found that the early age strength of concrete made with PCC is lower than that of concrete made with OPC due to the presence of fly ash in PCC which is responsible for the pozzolanic reaction. The continued pozzolanic activity of fly ash contributes to increase strength gain at later ages at continued curing condition. It is also found that drying ambient conditions reduction of the strength potential of concrete made with PCC because the secondary (pozzolanic) reaction fails to contribute to the development of strength.

Effect of size fraction on composition and pozzolanic activity of high calcium fly ash

To improve the properties of fly ash-incorporating Portland cement and utilise fly ash more efficiently, a high calcium fly ash was classified into several fractions by an air classifier. The composition, morphology, water requirement and activity index of different fly ash fractions were examined in the present study. Pozzolanic activity of fly ash fractions in simulative pore solution of Portland cement paste was determined. The experimental results show that the chemical and mineral compositions of fly ash particles vary with particle size. Fine fly ash fractions present high amounts of alkali, un-burnt carbon, CaO, SO3 and glass phase, whereas coarse fly ash fractions have more crystalline phases. In addition, the fly ash fractions with mean size under 8 μm show significantly higher pozzolanic activity and higher compressive activity index than coarse fractions. Thus, these fractions are recommended to serve as supplementary cementitious material for Portland cement-based materials.

Corrosion resistance performance of high-volume fly-ash self-compacting concretes

The corrosion performance of self-compacting concretes with high-volume replacements of fly ash was evaluated by some electrochemical techniques. In this study, eight self-compacting fly-ash concretes of various strength grades were designed at desired fly ash percentages of 0, 10, 30, 50, 70 and 85%, and were compared with five different mixtures of normal vibrated concretes at equivalent strength grades. The corrosion characteristics of the developed concretes were studied through the measurement of resistivity, pH, carbonation depth, half-cell potential and corrosion rate. Results demonstrate that self-compacting concretes at all levels of fly ash replacement performed significantly better than the corresponding normal vibrated concretes. This can be mainly attributed to the pozzolanic activity of fly ash. The carbonation was, however, higher in low- and medium-strength self-compacting concretes compared to the normal concretes.