Ash Blends Research Articles

Mechanical properties and reaction mechanism of one-part geopolymer mortars

The use of traditional two-part geopolymers is limited to small scale engineering applications, due to difficulties with the transportation, storage and prefabrication of alkaline activator solutions. In this study, “just adding water” or one-part geopolymers were developed using solid activators. Flow tests, flexural and compressive strength tests were carried out on a number of one-part and two-part geopolymer mortar specimens to evaluate the effect of concentration, modulus and type of activators on the workability and mechanical properties of geopolymer mortar. The reaction heat during the first 7 curing days and the degree of reaction of one-part and its two-part geopolymer counterparts were measured to compare their reaction mechanism. The test results showed that the flexural and compressive strengths of one-part geopolymer mortar specimens were 88%-94% and 65%-95% respectively, of the corresponding strengths of the two-part counterparts. The results also revealed that anhydrous sodium silicate (Na2SiO3) is a more effective solid activator than the combination of hydrous Na2SiO3 and sodium hydroxide (NaOH) for metakaolin and fly ash blending precursor. Due to a higher degree of geopolymerization reaction, the highest compressive strength of one-part geopolymer mortar using anhydrous Na2SiO3 with modulus of 1.4, reached 49.2 MPa after 7-day ambient temperature curing. When using a combination of solid hydrous Na2SiO3 and NaOH as an activator, the strength difference between one-part and its corresponding two-part geopolymer mortar specimens decreased with an increase in the modulus of the activator.

Optimization of Liquid Nitrogen Dosage to Cool Concrete Made with Hybrid Blends of Nanosilica and Fly Ash Using Response Surface Method

Optimization of Liquid Nitrogen Dosage to Cool Concrete Made with Hybrid Blends of Nanosilica and Fly Ash Using Response Surface Method

Investigation on Co-Combustion of Coal Gasification Fine Ash and Raw Coal Blends: Thermal Conversion, Gas Pollutant Emission, and Kinetic Analyses

Investigation on Co-Combustion of Coal Gasification Fine Ash and Raw Coal Blends: Thermal Conversion, Gas Pollutant Emission, and Kinetic Analyses

Effect of curing on mechanical strength and microstructure of fly ash blend GGBS geopolymer, Portland cement mortar and its behavior at elevated temperature

The experimental work reported here lay emphasis on mechanical strength, thermal resistance and microstructural characteristics of geopolymer cement to traditional Portland cement prepared under different curing conditions. Portland cement mortars prepared under conventional water curing and air curing aided with 0.5,1, 1.5 and 2.0% dosage (O-1,2,3,4) of poly ethylene glycol (PEG) under different ages. An optimal combination of the PEG has been determined as 1–1.5% with the enhanced the C-S-H gel with better permeability. The strength development of alkali mediated Ground granulated blast furnace slag(GGBS) partially blended with 0, 25, 50, 75% fly ash(FA) (M−1,2,3,4) geopolymer mortars (GPM) prepared under air, water curing and with optimal dose of 1% of PEG . The compressive strength cured under open air and water are compatible that are found to be increased with increase in % GGBS. More than 80% of 28 days(d) strength attained at early ages of 7d in all the GPM samples irrespective of type of curing, suggest that these binders have potential to save time, energy and water that lead to cost economic construction practice. The results on GPM after exposure to elevated temperature 200–600 °C show almost retaining the compressive strength while the control of Ordinary Portland Cement(OPC) mortar significantly loses the strength with the development of wider crack width. The microstructural characterization using Scanning Electron Microscope(SEM) analysis indicate that densification of microstructure depends upon curing regime that effect the thermo mechanical strength significantly.

Effect of TiO2, Al2O3 and CaCO3 nano-additives in singular, binary and ternary forms on the mechanical, thermal and microstructural propertites of fly ash supplemented cement matrix

In this paper, we focus on how nanoadditives such as nano-Al2O3, nano-TiO2 and nano-CaCO3 modify the mechanical and capillary permeability of fly ash cement mortars (5:1). When nanoadditives are added in proportions of 2%, 4% and 6% of the binder volume, hydration products are generated, and thermal conductivity and microstructure of cement mortars undergo a change. Mechanical property measured at 7, 28 and 90 days are measured to understand the underlying pozzolanic reaction and filling effect. The experimental findings reveal that the form and quantity of refractory chemicals in mortar production had an impact hardened matrix at the early age between 7 and 28 days, but thereafter, there is only a marginal strength gain. Nano-Al2O3 and nano-CaCO3 (at 2% of binder volume) additives were able to increase the mortar strength to the extent of 27% of the 28-day compressive strength at 7 days. The addition of 2% nano-TiO2 did not produce this effect. The addition of 6% nano-Al2O3 + nano-CaCO3 in binary and 6% nano-TiO2 + nano-Al2O3 + nano-CaCO3 blend in ternary combinations produced a phenomenally positive effect on the compressive strength with the reduction of capillary permeability at 90 days of setting. The X-ray diffraction patterns of these matrices compared with control showed a clear evidence of reduction of CH growth. Formation of a compact binding gel can be observed in scanning electron microscopic (SEM) pictures. A dense microstructure of binary and ternary nano additive mixes is establish to be favourable in decreasing the thermal conductivity of fly ash blend cement mortar measured at 30 °C. The combination of non-siliceous nano-size materials such as nano-Al2O3, nano-TiO2 and nano-CaCO3 in small quantities have an impact on the pozzolanic reaction with continual strength gain and are effective in counteracting the shortcomings of fly ash blended with cement mortars.

Performance of cementless binders produced from industrial waste products in strong acid

There is a growing demand for alternative low carbon binders. For these relatively new binder systems to be well received in industry it is important that detailed understanding of their durability performance is available. This paper investigates the hydrochloric acid resistance of geopolymer binders containing 100% fly ash and various blends of fly ash and blast furnace slag. Both physical and microstructural properties changes were examined to assess acid resistance and the leaching behaviour was also monitored. As the slag content of geopolymer binders increased, the resistance to hydrochloric acid also increased, evidenced by the reduced mass and strength loss observed. Findings also illustrate that geopolymer binders have hydrochloric acid resistance which exceeds that of traditional Portland cement binders in terms of the mass losses observed. The process of hydrochloric acid attack for each binder is also studied. • Fly ash/slag geopolymers had improved resistance to HCl than Portland cement. • As the slag content increased the resistance of geopolymers also increased. • Neat fly ash mixes had high apparent acid penetration but low surface deterioration. • Fly ash/slag geopolymers underwent decalcification of C-A-S-H type gel. • Neat fly ash mixes experienced dealumination of N-A-S-H gel.

Eco-friendly utilization of rice husk ash and bagasse ash blend as partial sand replacement in self-compacting concrete

Self-compacting concrete (SCC) is largely used construction material worldwide, uplifting the demand for river sand along with all of its constituents due to the recent construction boom. Rice husk ash (RHA) and Bagasse ash (BA) are the biomass waste of the abundantly produced crops in Pakistan, which causes several cardiovascular diseases to humans and poses threats to degrade air quality as well.Characterization of both RHA and BA was performed at the macro and microstructural level to study their suitability as fine aggregate in SCC. This research aims to study the effect of environment-friendly substitution of river sand with blended waste ashes of RHA and BA on microstructural, fresh, physicomechanical and sulfate resistant properties of SCC.The results of microstructural characterization revealed the pozzolanic nature of ashes is evident in Chapelle activity test and the adsorptive natured siliceous micro-sized ash particles contribute toward higher water demand in SCC. The scanning electron microscopy (SEM) analysis of SCC mixes containing blended ashes of RHA and BA revealed that the formation of secondary calcium silicate hydrate (CSH) gel occurred at a calcium to silica (Ca/Si) ratio of 1.41 as evident in Energy Dispersive X-ray Spectroscopy (EDX) analysis. The results of rheological properties revealed that the fluidity of SCC mixes reduced due to the porous nature of incorporated ashes, whereas the viscosity of the mixes improved upon the incorporation of blended ashes. The physicomechanical properties include water absorption, hardened density, compressive strength, and split tensile strength. The physicomechanical properties depicted that the 20% collective incorporation of waste ashes produced structural lightweight concrete confirming ACI 213R with the compressive strength and hardened density values of 20 MPa and 1816 Kg/m3, respectively. Conclusively, the eco-friendly utilization of blended ashes of RHA and BA improved the microstructure, viscosity, physicomechanical properties, and sulfate resistance of SCC.

Investigating the effect of biological material on the property of concrete

Biomineralization is an innovative technology adopted in the area of construction field. Biomineralization method involves use of biological material to improve the property of the concrete structure. The present study investigated the effect of prepared biological material of Bacillus sparecisus strain introduced into fly ash concrete as a new approach on its durability and mechanical property. Mechanical and durability property of bacterial blended fly ash concrete were studied at cell concentration of 105 cells/ml with varying concentration of bacterial solution to water. Test results revealed that, in comparison with conventional samples, those containing alkaliphilic endospore-forming bacteria material cured in tap water, recorded increase in compressive strength up to 30 % and decrease of durability property to 30 %. The ratio of bacteria solution to water played important role in improving the properties of concrete. At higher ratio, calcite precipitation by bacteria resulted in improvement of properties of concrete. Scanning electron microscope and XRD tests were performed to confirm the formation of calcite in the opening spaces of concrete.

Mechanical properties of alkali-activated mortar in organic acid environment

Ingression of acid into the concrete results in early degradation by microstructural alteration of phases leading to mass changes, weakening of mechanical properties and increase in porosity due to calcium leaching. This paper discusses the resistance of geopolymer composites (GP) and conventional concrete system (OPC) in 0.125M and 0.25M concentrations of acetic acid medium by investigating the changes in the mechanical properties of mortar. The results of the study reveal that the GP samples display increased resistance to acetic acid attack not only in terms of mass and strength loss but also with reference to the variation in ultrasonic pulse velocity and relative dynamic modulus of elasticity. The results also manifest that blends of ground granulated blast furnace slag (GGBS) and fly ash (class F) (FA) with red mud (RM) offer increased acid resistance due to the nature of the main binder gel produced in GP systems.

Degradation kinetics of alkali-activated pastes in acetic acid

Growing urban and industrial activities globally are found to be the sources of rising acidic environment. These acidic environments ensue early degradation of concrete in terms of microstructural alteration of phases formulating to mass changes, weakening of mechanical properties, and increase in porosity due to calcium leaching. This paper probes into the acetic acid resistance of geopolymer composites (GP) and its comparison with conventional concrete system (OPC) in 0.125M and 0.25M concentrations of acetic acid medium. The GP samples displayed increased resistance to acetic acid attack in terms of mass and thickness loss. It was also found that blends of ground granulated blast furnace slag (GGBS) and fly ash (class F) (FA) with red mud (RM) offered increased acid resistance due to the nature of the main binder gel produced in GP systems.

Evaluation of developed alkali-activated bricks for energy-efficient building construction

Gradually, the temperature of the earth is increasing due to global warming, which has increased the operational energy demand in buildings. This energy usage can substantially be reduced using energy-efficient measures such as developing a thermally resistant building envelope. The building envelope mainly consists of walls, roof and floor, where walls play an important role in heat transfer that is a major contributor to operational energy demand. In this study, a walling material (alkali-activated bricks) was developed, where locally available industrial wastes (co-fired blended ash and stone dust (CBA-SD)) were activated by a sodium-based alkali activator and cured at an ambient temperature of around 37°C. The alkali-activated bricks were evaluated for mechanical-, physical-, thermal- and durability-related properties that are in accordance with Indian standards. The results showed that the developed alkali-activated bricks are lighter in weight and have lower thermal conductivity (0.35–0.4 W/(m K)) as compared to conventional fly-ash (FA) bricks (1.05 W/(m K)). A case of a residential building with varying building envelope and number of floors was simulated for analysing building performance using a computational approach. As compared to FA bricks, the CBA-SD brick model resulted in peak cooling load reduction by 49–51, 46–48 and 44–46% for single-, two- and three-storeyed buildings, respectively.

Autogenous shrinkage of slag-fly ash blends activated with hybrid sodium silicate and sodium sulfate at different curing temperatures

This study investigates the effect of sodium sulfate concentration and curing temperature (20 °C and 40 °C) on the autogenous shrinkage of hybrid sodium silicate and sodium sulfate activated slag/fly ash systems (AASF). Regardless of the curing temperature, the main reaction products formed are C-A-S-H gels, and no formation of N-A-S-H type gels is observed in the studied AASF systems. Due to increase in rate of reaction and refinement of the pore structure, the autogenous shrinkage increased with increasing sodium sulfate concentration. At a high curing temperature (40 °C), the decrease in rate of autogenous shrinkage with time is primarily attributed to the suppression of the self-desiccation process due to decrease in reaction rate, and formation of a matrix with high elastic modulus or restrain effect at early ages. Furthermore, the increase in crystallinity of C-A-S-H gels is also responsible for a lower autogenous shrinkage in samples cured at 40 °C. Ettringite does not form to compensate the autogenous shrinkage at early hours.

Evaluation of Mechanical and Durability Performance of Coir Pith Ash Blended Cement Concrete

India is one of the prominent producers of coconuts in the world. Along with the desired products, many undesirable by-products are also generated from the coconut and coir industry. Among the various by-products, coir pith and short coir fibres are the major ones and are obtained during the extraction of long coconut fibres. Raw coir pith was heated in a metallic vessel at 450 ℃ to obtain coir pith ash. In this study, the impact of the presence of CPA as a supplementary cementitious material, on the various mechanical and durability parameters are taken into consideration. The various parameters considered for assessing the mechanical performance include compressive strength, split tensile strength, flexural strength and Ultrasonic pulse velocity. Water absorption and resistance to sulphuric acid environments were considered to evaluate the durability of CPA blended concrete. The resistance of CPA blended concrete against sulphuric acid environment was evaluated by considering the variation in weight, water absorption and percentage loss in compressive strength. Five concrete mixes were used for the study with CPA content ranging from 0% to 20%. Indian standard method of concrete mix design with water-cement ratio 0.45 was adopted. To understand the effect of change in water-cement ratio on the durability parameters of concrete, the study also considered other water-cement ratios like 0.40 and 0.50. Results indicated that the mechanical and durability performance improves when CPA is used as supplementary cementitious material. Also, the specimens with water-cement ratio 0.40 performed better than other ratios.

Low carbon cementitious materials: Sodium sulfate activated ultra-fine slag/fly ash blends at ambient temperature

Na2SO4 (NS)-activated slag as a kind of alkali-activated slag (AAS) had great development potential in low carbon cementitious materials field, because NS could be obtained from natural resources with much lower CO2 emissions than NaOH and water glass. However, the main issue was its slower strength development at both early and later ages. With intention to mitigate this problem, ultra-fine slag was used, and the increased CO2 emissions caused by ultra-fine slag expected to be balanced by the use of fly ash (FA). In the present study, NS-activated ultra-fine slag/FA was designed. Effects of NS dosage and FA content on the compressive strength were researched, and the activated process was assessed by chemical shrinkage, XRD, TGA, pH value, ion concentration, NMR, and SEM. Finally, CO2 emissions were evaluated. Results showed that compressive strength of slag with D50 = 3.1 μm activated by 4% Na2O-E of NS reached 36.2 MPa and 77.3 MPa at 28 d and 90 d age. The main hydrates of NS-activated slag were ettringite and C-(N)–S–H. Moreover, in the NS-activated ultra-fine slag/FA mortars, 20% FA significantly reduced the 3 d compressive strength, but slightly increased the 28 d compressive strength. CO2 emissions of this blend seemed much lower than that of NaOH or water glass-activated slag. These results suggested one alkali-activated binder with low carbon emissions.

Synthesis of Fly Ash-Based Geopolymers: Effect of Calcite Addition and Mechanical Activation

Blends of fly ash and natural calcite, mechanically activated for 0–400 s in a planetary mill, were used to synthesize geopolymers at ambient temperature. The calcite content in the blends was 0–10 wt.%. Sodium hydroxide solution was used as an alkaline agent. Mechanical activation of the raw material considerably enhanced its reactivity with respect to the alkaline agent, as was observed using Fourier-transform infrared spectroscopy, isothermal conduction calorimetry, thermogravimetry coupled with mass spectrometry analysis of the evolved gas, and SEM/EDS. The addition of calcite to the fly ash improved the compressive strength of the geopolymers, especially during the early age of curing. For 7 d aged geopolymers based on the 90% fly ash + 10% calcite blend, the strength was 8.0-, 3.5- and 2.9-fold higher than that for the geopolymers based on the unblended fly ash for 30 s, 180 s and 400 s mechanical activation time, respectively. Using Mössbauer spectroscopy, it was revealed that iron present in the fly ash did not play a significant part in the geopolymerization process. The dominant reaction product was sodium containing aluminosilicate hydrogel (N-A-S-H gel). Calcite was found to transform, to a small extent, to vaterite and Ca(OH)2 in the course of the geopolymerization.

In-situ analysis of the effect of CaO/Fe2O3 addition on ash melting and sintering behavior for slagging-type applications

Slagging-type technologies, particularly entrained-flow gasification, have been quickly developed and industrialized due to their inherent advantages. The ashes of many feedstocks are rich in SiO2 and Al2O3. Therefore, a high operating temperature is required, making the process less efficient. The use of pure additives such as limestone does not meet the requirements. In consequence, binary additives of CaO/Fe2O3 are studied to improve the fusibility. The CaO/Fe2O3 ratio is varied in order to optimize cost efficiency and the operation and control of processes. Ash fusion temperatures (AFTs) and X-ray diffraction (XRD) combined with in-situ methods of thermomechanical analysis (TMA) and high-temperature scanning electron microscopy (HT-SEM) are used to explore the effect of CaO/Fe2O3 on ash fusibility. The CaO/Fe2O3 ratio affects the ash fusion behavior due to changes in the mineral phase composition. The AFTs reveal an optimum combination for the joint addition of CaO and Fe2O3 compared to blends with the same amount of one single additive, while sintering is less strongly affected. Based on the in-situ analyses, the blends of ash and additive are categorized into two or three regimes of sintering, swelling, and fusion in the high temperature range. Depending on the applied additive ratio, different regimes of ash fusion are detected, which affect the slag properties.

Effect of CO2 atmosphere on Ca-containing mineral transformation behaviors during a Ca dominated coal co-firing with a Si/Al dominated coal in oxy-fuel condition

Coal blending is an effective method to reduce the slagging tendency. The mineral transformation within blended coal ashes has an important influence on the slagging behaviors, which have been well studied under conventional air-fuel condition. Oxy-fuel combustion is recognized as one of the most promising CO2 reduction technologies. However, the mineral transformation within blended coal ashes in oxy-fuel condition has yet to be fully understood. This work is aimed to comprehensively study the influence of CO2 atmosphere on Ca-containing mineral transformation behaviors during a Ca dominated coal co-firing with a Si/Al dominated coal in O2/CO2 condition by TG-DSC, XRD and HSC simulation. These results show that the atmosphere significantly affects on the transformation of Ca-containing mineral and the final existing form of Ca in the blended coal ashes. When the high content Ca coal is blended with the high content Al/Si coal in the O2/CO2 atmosphere, the CO2 promotes the transformation of Ca into CaCO3 and Ca under low temperature mainly exists in the form of CaCO3 (little CaSO4) in the blended coal ashes. CaCO3 under high temperature is decomposed to produce highly active CaO, and CaO reacts with Al/Si to form the low melting point minerals, which may aggravate the slagging tendency. The present study can provide useful information to reduce the slagging behavior of the blended coals in the O2/CO2 atmosphere.

Studies on the Properties of Fly Ash–Rice Husk Ash-Based Geopolymer for Use in Black Cotton Soils

Expansive soils are found in many parts of the countries like India, Australia, Ethiopia, Sudan and USA in the form of black cotton soil (BCS). The distress induced by swelling and shrinkage behavior of black cotton soil results in millions of dollars of damage to the construction industry each year. In this study, experimental investigations are carried out for the stabilization of BCS using fly ash (FA) and rice husk ash (RHA)-based geopolymer. For this purpose, a mixture of sodium silicate (SS) and sodium hydroxide (SH) mixed in the ratio of 1.5 is used as the alkaline activator solution. A mixture of FA and RHA (mixed in weight percentage of 100:00, 75:25, 50:50, 25:75, 00:100) is used as the precursor and is referred as blended ash (termed as FARHA) in this paper. Stabilization potential of the geopolymer is determined by conducting unconfined compressive strength test, free swell ratio (FSR) test and shrinkage limit test on the stabilized specimens. Attempts are also made to establish the effects of varying the quantity of FARHA (5, 10, 15, and 20%) and curing period on strength properties of BCS. X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier Transformed Infrared Spectroscopy (FTIR) studies were conducted to analyze the micro-level changes due to geopolymerization. Results obtained from the experiments indicate that the geopolymerization significantly improves the strength of BCS and at the same time makes it less prone to swelling and shrinkage. Thus, BCS stabilized with blended ash geopolymer can be used as a sustainable alternative to conventional stabilizers.

Influence of biomass ash additive on fusion characteristics of high-silicon-aluminum coal ash

The influence of cow dung ash (CDA) additive on the ash fusion characteristics of high-silicon-aluminum coal ash (SHA) was investigated using ash fusion temperature analyzer (AFTA), X-ray diffraction (XRD), thermogravimetric analyzer (TG-DSC) and FactSage thermodynamics software. In order to clarify the shrinkage/expansion and flow behavior of ash, high-temperature heating stage coupled with optical microscope (HSOM) was used to record the morphological change of ash in the heating process. The results show that the ash fusion temperatures (AFTs) decreased firstly and then increased with the addition of CDA. There was a minimum value of AFTs when the addition amount of CDA was 60%. Due to the high content of silicon and aluminum in SHA, the mullite with skeleton structure became the main crystalline phase in molten ash, which led to the high AFTs of SHA. The addition of CDA resulted in the increase of calcium and phosphorus in coal ash. Consequently, low-melting-temperature minerals such as anorthite and chlorapatite, which were responsible for the decrease in AFTs of blended ash, would be formed. With the continuous addition of CDA, the decrease of amorphous content led to the increase of AFTs. According to the results of ash fusion characteristics, SHA melting process only underwent the sintering stage due to the high AFTs, and its ash fusion behavior followed “softening-melting” mechanism. For CDA and blended ash (60% CDA), the melting process went through the sintering and melting stages, and the ash fusion behavior followed the “melting-dissolution” mechanism.

The slagging propensity of Zn-rich scrap tyre ash in reducing environments consisting of CO and CO2 and its promotion of the slagging of Si-rich coal ash

This study includes a comprehensive investigation on the ash slagging characteristics of zinc (Zn)-rich tyre ash and its interaction with silica (Si)-rich coal ash blended at different ratios in a 5% CO in CO2 reducing environment. Such an environment is expected to occur near the burner in a combustor, as well as serves as a fundamental study on the slagging propensity upon the effect of CO, which is a principal reducing agent in a gasifier. An approach consisting of experimental studies using modified inclined plane (M-IP) methodology, advanced analytical techniques including the scanning electron microscopy (SEM) and x-ray photoelectron (XPS) spectroscopy, and thermodynamic equilibrium calculations were used to elaborate the slagging propensities of the single and blended ashes. Furthermore, the fate of Zn within tyre ash and its potential implications on the slagging properties were evaluated. Tyre ash easily melts to liquid slag upon increasing temperature compared to the silica-rich coal ash. Zinc does not evaporate but rather remains within tyre slag mostly as a hemimorphite (Zn4(Si2O7)(OH))-like coordination structure attributing to the characteristic blue colour of tyre slag. The low ionic potential value of 2.7 for Zn2+ is characteristic of basic ions that have a greater tendency to depolymerise the Si-rich ash slag matrix and acts as a fluxing agent in ash slag. Moreover, it was proven that Zn2+ plays a synergistic role with Ca2+ in enhancing the flowability of the Si-rich slag remarkably. Furthermore, for the pure tyre slag, Zn was found to preferentially deposit at the corundum (Al2O3) substrate interface and even penetrate/react with the porous corundum, causing a strong corrosion on the substrate. However, blending of tyre ash with coal ash alleviates this problem by a preferred scavenging of Zn into the entire Si matrix, which in turn protects the corundum plate.