Fly ash and slag Giergiczny, Zbigniew
Cement and concrete research,
October 2019, 2019-10-00, Letnik:
124
Journal Article
Recenzirano
Low-calcium (FA) and high-calcium (HCFA) fly ash and granulated blast furnace slag (GBFS) are the most widely known, standardized and used SCMs in the composition of cement and concrete. In the last ...4 years, scientific work has focused on improving binder properties (e.g. long setting time, low early strength etc.) containing large quantities of FA, HCFA and GBFS. The main directions of activity are the introduction of high-level additives to concrete composition, such as nano-materials, chemical and mechanical activation. Due to the limited access to FA and GBFS, a large amount of studies is devoted to seeking synergies between FA, HCFA, GBFS and limestone. The research works focused on durability characteristics of composites cement containing FA, HCFA and GBFS. Moreover, attention was given to prospects of future application of other types of fly ashes and slags in cement and concrete.
•Slag/fly ash ratio and activator modulus show synergetic effects on reaction.•Activator modulus has a more significant influence on early age reaction.•Gel structures remain stable regardless of ...activator modulus and slag/fly ash ratio.•Slag content shows a dominating effect on compressive strength.
Room temperature cured alkali activated slag/fly ash blends have shown their advantages in field applications. Given that alkali activated materials are extraordinarily sensitive to the composition of the starting materials, identifying their influences is essential for their application. This paper focuses on the effects of two compositional factors: activator modulus (SiO2/Na2O from 1.0 to 1.8) and slag/fly ash mass ratios (between 90/10 and 50/50) on reaction kinetics, gel characters and compressive strength. The results show that when lowering the activator modulus, the early age reaction is significantly accelerated with a higher reaction intensity, and increasing the slag content also leads to an increased reaction rate, especially at low activator modulus. Regardless of the two influential factors, the main reaction products are chain structured C-A-S-H gels with similar water contents and thermal properties, and no typical N-A-S-H type gels are formed in the system. Slight differences in terminal SiO bonds and crystallization temperature are caused by the activator modulus and slag/fly ash mass ratios, respectively. The compressive strength results show that the optimum activator modulus changes with the slag/fly ash mass ratio, and higher slag/fly ash mass ratios prefer higher activator moduli in general, while either too high or too low activator modulus has detrimental effect on strength. Understanding the reaction, gel structure and strength changes are fundamental for determining key manufacturing parameters and tailoring the properties.
•The fly ash source has a significant effect on fly ash-based geopolymer concrete compressive strength.•The particle size distribution (PSD) has a direct effect on the compressive strength.•The fly ...ash source has a significant effect on fly ash-based geopolymer concrete microstructure.•The finer the fly ash particle size distribution, the more significantly permeable void ratio was reduced.•Fewer microcracks were observed when finer fly ash was used.
Geopolymer concrete has demonstrated promising mechanical and microstructural properties in comparison with conventional concrete; however, the variability found in fly ash sources and properties may be an obstacle to implementation. To better understand this variability, this study investigates the effects of particle size distribution and fly ash source on the mechanical and microstructural properties of fly ash-based geopolymer concrete. Two fly ash sources were studied including ordinary McMeekin and Wateree Station fly ash. McMeekin fly ash has three different fly ash particle grades, including the ordinary McMeekin fly ash (38.8 µm), Spherix 50 (17.9 µm), and Spherix 15 (4.78 µm). The Wateree Station is a thermally beneficiated fly ash, while McMeekin is a STAR Processed fly ash. A mixture of silica fume, sodium hydroxide, and water was used as an activating solution. The microstructure of fly ash-based geopolymer paste was observed using SEM. The density, absorption and permeable void ratios were estimated based on ASTM C642. Test results indicate that the resulting compressive strength is linearly affected by the average particle size distribution. The compressive strength of geopolymer concrete was decreased when McMeekin fly ash was used. In addition, the permeable void ratio and absorption after immersion ratio were decreased as a smaller particle size of fly ash such as Spherix 15 (4.78 µm) was used. The fly ash source influences the permeable voids, apparent density, bulk density, and absorption after immersion ratio.
Heavy metal ions and antibiotics were simultaneously detected in authentic water systems. This research, for the first time, employed synthesized sophorolipid-modified fly ash(SFA) to eliminate ...tetracycline(TC) and lead(Pb2+) from wastewater. Various characterization techniques, including SEM-EDS, FTIR, XPS, BET, and Zeta, were employed to investigate the properties of the SFA. The results showed that the sophorolipid modification significantly improved the fly ash's adsorption capacities for the target pollutants. The static adsorption experiments elucidated the adsorption behaviors of SFA towards TC and Pb2+ in single and binary systems, highlighting the effects of different Environmental factors on the adsorption behavior in both types of systems. In single systems, SFA exhibited a maximum adsorption capacity of 128.96 mg/g for Pb2+ and 55.57 mg/g for TC. The adsorption of Pb2+ and TC followed pseudo-second-order kinetics and Freundlich isotherm models. The adsorption reactions are endothermic and occur spontaneously. SFA demonstrates varying adsorption mechanisms for two different types of pollutants. In the case of Pb2+, the primary mechanisms include ion exchange, electrostatic interaction, cation-π interaction, and complexation, while TC primarily engages in hydrogen bonding, π-π interaction, and complexion. The interaction between Pb2+ and TC has been shown to improve adsorption efficiency at low concentrations. Additionally, adsorption-desorption experiments confirm the reliable cycling performance of modified fly ash, highlighting its potential as a cost-effective and efficient adsorbent for antibiotics and heavy metals.
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•This work develops a new fly ash based adsorbent for TC and Pb2+ and realize the resource utilization of solid waste.•SFA showed excellent adsorption capacity for both Pb2+ and tetracycline.•The closer the concentration of tetracycline is to that of lead, the stronger the mutual inhibition effect becomes.
•The effects of CRCA replacement level under the combined F–T and sulfate attack are analyzed.•The effects of LVFA and HVFA under the combined F–T and sulfate attack are analyzed.•The durability was ...more affected by the FA content than by the CRCA replacement level.•Interaction between F–T and sulfate attack to concrete with RCA and FA is discussed.•NMR and XRD analysis of concrete subjected to F–T cycles in sulfate solutions are conducted.
The present study investigated the effect of the combined action of freeze–thaw (F–T) cycles and sulfate attack on the resistance of concrete containing low-volume fly ash (LVFA) and high-volume fly ash (HVFA) made with coarse recycled concrete aggregates (CRCAs). Concretes with a water–binder ratio of 0.50 containing fly ash (FA; LVFA and HVFA) and CRCA (i.e., 0%, 20%, 50% and 100% also by weight) as a replacement for coarse natural aggregates (CNAs) were exposed to water, 5% sodium sulfate solution and 5% magnesium sulfate solution under F–T cycles. The performance, including residual compressive strength, relative dynamic modulus of elasticity and concrete microstructure, was evaluated after being subjected to certain F–T cycles in sulfate solutions. Results indicated that the resistance of the concrete mixtures to the combined F–T cycles and sulfate attack increased with the increase in CRCA content as CNA replacement. Compared with the concrete without FA, the LVFA-based concrete showed excellent improvement in the resistance to the combined action of F–T cycles and sulfate attack; however, the HVFA-based concrete had an adverse effect on the resistance. Concrete deterioration was attributed to the interaction between F–T and sulfate attack. Moreover, the resistance of LVFA- and HVFA-based concretes against the combined F–T and sulfate attack increased during the entire test when the concretes were subjected to F–T cycles in 5% sodium sulfate solution. The sulfate attack exerted more positive effects than negative on the F–T cycles. However, the resistance of LVFA- and HVFA-based concretes against the combined F–T and sulfate attack increased during the initial F–T cycles and then decreased in the 5% magnesium sulfate solution. The 5% sodium sulfate solution produced similar improvements in the F–T resistance of the LVFA- and HVFA-based concretes, whereas the 5% magnesium sulfate solution evidently reduced the F–T resistance of the concrete with HVFA than that with LVFA.
Landfill leachate concentrate (LLC) is a high-salinity organic wastewater produced in the process of membrane separation and has become an urgent problem because of its complex composition and high ...biological toxicity. Solidification/stabilization (S/S) technology using geopolymers provides a feasible and economical zero-discharge LLC treatment method. This study developed one-part fly ash-based geopolymers using LLC as the only solvent. The results showed that the solid alkali activator significantly increased the LLC treatment capacity with a high liquid−solid ratio of 0.55. The high-salinity LLC significantly promoted the substitution of Al for Si and improved the compressive strength of the geopolymers. Three leaching experiments showed that the prepared geopolymers had excellent stability, high S/S rates for organic matter (92.9%) and NH3-N (91.4%), and a high contaminant removal rate to reduce acute biological toxicity. Microscopy tests showed that sodium aluminosilicate hydrate (N-A-S-H) gel was the main component of the fly ash-based geopolymers after the addition of LLC. Cl− attached to the surface of the geopolymer gels through exchange with OH−, while SO42− was bound within the geopolymer structure in the form of Na2SO4 crystals. There was no evidence that organic matter and NH3-N were chemically combined with the geopolymer material, rather, they were physically encapsulated within the geopolymer structure. This study proposes a technical strategy for LLC S/S using fly ash-based geopolymer. The geopolymer can be used as a new building material, which provides a new perspective for the treatment of LLC and the utilization of fly ash resources.
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•Landfill leachate concentrate (LLC) can replace water to prepare one-part geopolymer.•High-salinity concentration of LLC accelerates the substitution of Al for Si.•Fly ash-based geopolymers can effectively immobilize organic matter and NH3-N.•The leaching toxicity of the immobilized LLC decreases from 72.5% to 13.8%.•Geopolymers save 20% in costs and reduce 2/3 of CO2 emissions compared to cement.
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•The maximum amount of water to successfully form zeolite from fly ash via alkaline fusion was determined.•Five metals were simultaneously adsorbed in a single step ...process.•Adsorption selectivity decreased in the order: Pb(II) > Cu(II) > Cd(II) > Zn(II) > Co(II).•Similar levels of each of the five metals were present on the zeolite after adsorption.
This study reports the potential for the simultaneous removal of Cd(II), Co(II), Cu(II), Pb(II), and Zn(II) ions from aqueous solutions by FAU-type zeolites prepared from coal fly ash. The zeolite synthesis route was via alkaline fusion followed by the addition of deionised water and hydrothermal treatment using fly ash to water mass ratios of 4, 10, 15, and 20. XRD, XRF, SEM and N2 adsorption measurements were used to characterize the prepared zeolites. Adsorption experiments were carried out for variations in concentration, time, and adsorbent loading. The adsorption process followed pseudo second-order kinetics and Langmuir adsorption isotherm; intra particle diffusion model fitting indicated that diffusion within the pores affected the rate controlling steps and mass transfer across boundary layers for the adsorbate – adsorbent system. The efficacy of FAU – type zeolite for the quinary-metal ions adsorption studied decreased in the order Pb(II) > Cu(II) > Cd(II) > Zn(II) > Co(II).
The microstructural evolution of alkali-activated binders based on blast furnace slag, fly ash and their blends during the first six months of sealed curing is assessed. The nature of the main ...binding gels in these blends shows distinct characteristics with respect to binder composition. It is evident that the incorporation of fly ash as an additional source of alumina and silica, but not calcium, in activated slag binders affects the mechanism and rate of formation of the main binding gels. The rate of formation of the main binding gel phases depends strongly on fly ash content. Pastes based solely on silicate-activated slag show a structure dominated by a C–A–S–H type gel, while silicate-activated fly ash are dominated by N–A–S–H ‘geopolymer’ gel. Blended slag-fly ash binders can demonstrate the formation of co-existing C–A–S–H and geopolymer gels, which are clearly distinguishable at earlier age when the binder contains no more than 75 wt.% fly ash. The separation in chemistry between different regions of the gel becomes less distinct at longer age. With a slower overall reaction rate, a 1:1 slag:fly ash system shares more microstructural features with a slag-based binder than a fly ash-based binder, indicating the strong influence of calcium on the gel chemistry, particularly with regard to the bound water environments within the gel. However, in systems with similar or lower slag content, a hybrid type gel described as N–(C)–A–S–H is also identified, as part of the Ca released by slag dissolution is incorporated into the N–A–S–H type gel resulting from fly ash activation. Fly ash-based binders exhibit a slower reaction compared to activated-slag pastes, but extended times of curing promote the formation of more cross-linked binding products and a denser microstructure. This mechanism is slower for samples with lower slag content, emphasizing the correct selection of binder proportions in promoting a well-densified, durable solid microstructure.
•Properties of HVF-SCC predicted from VVF-SCC data by using SVM method.•Appropriate inputs was used and kernel coefficients calculated by grid search.•New models were compared by previous methods and ...validated by experimental results.
Support vector machines (SVMs) have recently been used to model the properties of low volume fly ash self-compacting concrete (LVF-SCC) by means of kernel functions to minimize the experimental work. Appropriate linear and non-linear SVM models with different kernels (linear, polynomial, radial basis and sigmoid) were proposed in this paper to predict the fresh properties and compressive strength of high volume fly ash SCC (HVF-SCC) from various volume fly ash SCC (VVF-SCC). Since most available data contain relative low volume fly ash, new SVM models were trained on VVF-SCC mixture proportions adapted from literature, and the prediction results were compared to those of previous models for HVF-SCC and LVF-SCC. Moreover, an experimental plan containing six different SCC mixtures was established and the proposed SVM models were validated by experimental results, including compressive strength, L-box, slump, U-box, and V-funnel. Results showed that new SVM models provide better outcomes if considering appropriate input vector and wide range data to obtain the proper kernel function coefficient to predict the various properties of HVF-SCC. Among the kernel functions, prediction results of the SVM – RBF model were more accurate compared to other kernels.
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•MSWIFA was used for manufacturing alkali-activated cementitious material.•Blending 10 % of MK significantly increased the compressive strength.•C-S-H was identified in AAFA, whereas ...C-(A)-S-H and ettringite was observed in AAFM.•Concentrations of heavy metal in AAFM were significantly reduced to the recommendation in Chinese standards.•AAFM reduced 64.8 % of total TEQ of PCDD/Fs in MSWIFA.
The proper treatment on hazardous municipal solid waste incineration fly ash (MSWIFA) is important. The application of alkali-activation technology to prepare alkali-activated MSWIFA (AAFA) material provides a potential not only to immobilise the heavy metals, but also to trigger its pozzolanic property in manufacturing building material. In this study, in addition to investigate the feasibility of alkaline activation technology in preparing AAFA with sodium silicate activator, the effect of metakaolin in AAFA (AAFM) was also explored to enhance its performance. The results showed that, compared to the AAFA, blending 10 % metakaolin in AAFA significantly improved both 28-day and 90-days compressive strengths, which was almost 200 % higher than that of AAFA. The compressive strength was increased with increasing the dosage of sodium silicate. The C-S-H gel was observed as the main hydration product of AAFA and AAFM. Moreover, the ettringite was observed in AAFM due to the reaction between the CaSO4 in MSWIFA and aluminate phase from metakaolin. Finally, the 28 and 210-day leaching behaviours of AAFM on Zn, Cu, Pb, Cd, Cr and Ni were successfully suppressed to less than 1 % of that originally from MSWIFA, which can meet the requirement from Chinese standards.
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