The subject of the experimental research is concrete with cold-bonded fly ash aggregate from fly ash of Novosibirskaya GRES Thermal Power Plant (Novosibirsk, Russia). Cold-bonded fly ash aggregate ...has the true specific gravity of 2.50 g/cm3, an average density of 1.53 g/cm3, water absorption by weight of 18.4 %, and an opened porosity of 28.15 %. Concrete with cold-bonded fly ash aggregate has a compressive strength after 28 days of 37.8 МPa, a flexural strength of 4.9 MPa, a coefficient of linear expansion of 14.8*10-6 K-1 and modulus of elasticity of 18*109 Pa. The water presoaking of lightweight aggregate did not affect the kinetics of heat emission and, consequently, the kinetics of hydration of cement. The shrinkage of concrete with dry aggregate was higher than concrete with presoaking lightweight aggregate. Moreover, the evaporation loss was also less for concrete with dry aggregate. The shrinkage of concrete with presoaking aggregates is much less than the shrinkage of concrete with dry aggregates with the same evaporation loss. The usefulness of presoaking aggregates in working conditions, as “internal curing”, has been confirmed. This will reduce the likelihood of shrinkage cracks during concrete drying.
The influences of fly ash and metakaolin added as substitutions (by up to 50 wt%) of magnesium potassium phosphate cement (MKPC) on the microstructures and compressive strengths of the MKPC pastes ...were investigated. The results indicate that the aluminosilicate fractions of both fly ash and metakaolin are involved in the acid-base reaction of MKPC system, leading to a preferential formation of irregular crystalline struvite-K incorporated with Al and Si elements and/or amorphous aluminosilicate phosphate products. Metakaolin is more reactive than fly ash in the MKPC system. For the same addition dosage, the MKPC pastes containing metakaolin exhibit higher compressive strengths than the pastes containing fly ash. This is attributed to the formation of more highly reinforced microstructures and denser interfaces between the metakaolin particle and hydration products (e.g. struvite-K) in the MKPC paste containing metakaolin. Addition of 30 wt% metakaolin increases the compressive strengths of MKPC pastes at all test ages.
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•FA-GGBS-MKwere activated using an alkaline solution to develop a binder system.•FA- GGBS -MK ternary powders have produced highly workable paste.•FA- GGBS -MK binders have developed ...high strength paste when cured at ambient conditions.•FA- GGBS -MK pastes produce CSH, CASH-NASH as the products of the reactions.•FA- GGBS -MK pastes compositions have been studied using FESEM, EDS, XRD, and FTIR.
The study reports properties of a stable and high strength ternary binder matrix using Fly Ash (FA), Ground Granulated Blast Furnace Slag (GGBS), and Metakaolin (MK). The bulk of the binder system is composed of Fly Ash and Ground Granulated Blast Furnace Slag (GGBS), while Metakaolin is added in three levels of 20%, 10%, 5% by weight, as suggested by the design of experiments. Alkali solution consisting of sodium hydroxide flakes and sodium silicate solution was used as the alkali activator. Fresh properties of all the Alkali Activated binder Pastes were studied to understand the Setting time and Mini-Slump. Mechanical properties of the hardened fly ash based ternary binder mortar were tested for compressive strength and ultrasonic pulse velocity (UPV) after 3, 7,28, and 56 days of curing. X-Ray Diffraction (XRD), Field-Emission-Scanning-Electron-Microscope (FESEM), Energy-Dispersive-Spectroscopy (EDS), and Fourier transform infrared spectroscopy (FTIR) were conducted in order to study the microstructural properties fly ash based ternary paste cured for 7 days. The compressive strength of hardened fly ash based ternary samples varied between 57.14 and 102.04 MPa. Ternary mixtures were observed to have a homogeneous and denser microstructure, with the development of various gels like CSH, CASH, NASH, and (N, C)-ASH.
•A synergistic utilization of bauxite tailings for flue-gas desulfurization and geopolymer preparation was investigated.•The bauxite tailings had significant alkalinity and desulfurization ...capacity.•The benefit of bauxite tailings after desulfurization is significant for geopolymer with class C fly ash.
As an industrial waste characterized by huge volume and high alkalinity, red mud has become a serious environmental problem. The reuse of red mud has been explored in previous studies, including as building materials and for soil and waste water treatment. In this study, an innovation was made for the reuse of red mud to create a synergistic effect. Red mud was first used in flue gas desulfurization (FGD), and then the desulfurized red mud was again reused to make a geopolymer material. By using one type of original red mud and three types of fly ash, this study revealed that with high alkalinity and desulfurization capacity, the red mud could serve as an excellent FGD sorbent. After FGD, the sodium sulfate in the desulfurized red mud acted as a chemical activator for geopolymer made with class C fly ash. A 25% increase in strength was observed between the geopolymers with the red mud after FGD and with the original one. There are no significant benefits of FGD on the class F fly ash-based geopolymers and further study is required.
The fly ashes derived from three giant coal-hosted Ge deposits, Lincang (Yunnan of southwestern China), Wulantuga (Inner Mongolia of northern China), and Spetzugli (Primorye, Russian Far East), are ...unique because they are highly enriched in elements, including up to (on an organic-free basis): 4.66% Ge, 2.12% As, 1.56% F, 1.22% Sb, 0.56% W, 0.56% Zn, 0.55% Pb, 0.13% Sn, 0.12% Ga, 0.056% Bi, 0.04% Be, 0.028% Cs, 0.017% Tl, and 0.016% Hg. These high element concentrations in the fly ashes are due both to their high levels in the raw coals from which they were derived and their high volatility during the coal combustion process.
Rare earth elements and yttrium (REY) were fractionated during coal combustion. They are more enriched in fly ashes than in slag from the respective coals. Maximum REY enrichment may occur either in fine-grained fly ash from baghouse filters or in coarse-grained fly ash from electrostatic precipitators. Cerium and Eu are more enriched in the fly ashes than other REY, and yttrium is relatively depleted in the fly ashes in comparison with the slag.
Three types of unburnt carbon can be identified in the fly ashes: (1) carbon with well-preserved initial maceral structures (fusinite and secretinite), (2) isotropic and anisotropic carbon, and (3) secondary fine-grained carbon. The last type of unburnt carbon is characterized by embedded fine-grained Ge-bearing and other mineral phases.
Ge oxides (e.g., GeO2) are the major Ge carrier in the fly ashes. Other Ge-bearing mineral phases, however, were also identified, including glass, Ca ferrites, solid solutions of Ge in SiO2, and probably elemental Ge or Ge (Ge-W) carbide, as well as previously-unknown complex oxides including (Ge,As)Ox, (Ge,As,Sb)Ox, (Ge,As,W)Ox, and (Ge,W)Ox. Some portion of the Ge occurs as adsorbed species in different types of unburnt carbon (Types 1 and 2) in the ash particles.
•The Ge-rich fly ashes are highly enriched in Ge and toxic trace elements.•Three types of unburnt carbon can be identified in the fly ashes.•Rare earth elements and yttrium (REY) were fractionated during coal combustion.•Ge oxides (e.g., GeO2) are the major Ge carrier in the fly ashes.•Other Ge-bearing mineral phases in the fly ash were also identified.
The effects of ground granulated blast furnace slag/fly ash (GGBFS/FA) ratio, mass ratio of SiO2 to Na2O (Ms) of activator solution and sodium silicate dosage on structural build-up, flow properties ...and setting characteristics of alkali-activated cement (AAC) mixtures were investigated. The solid-like behavior becomes more dominant with increasing GGBFS/FA ratio. Ms value had significant effect on the structural build-up. Significantly higher initial storage modulus with a low increasing rate was observed for the Ms values lower than 0.8. However, for higher Ms values, a sudden increase in storage modulus was observed after negligible initial structuration. An increase in sodium silicate dosage caused a considerable delay in the abrupt increase in the structural formation. It was observed that flow curves of AAC fit the Herschel-Bulkley model with shear-thickening behavior. ICP-OES tests revealed the lower release of aluminum and calcium into the pore solution of GGBFS/FA mixtures with low Ms values.
•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.
This paper aims to study the effect of hydrogels on the self-healing processes in cementitious systems with a large dosage of supplementary cementitious materials including slag and fly ash. The ...material characterization was conducted using thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM/EDS). The healing products in the cement slag system consisted primarily of calcium carbonate and hydration products including calcium silicate hydrate (C-S-H) and ettringite. In the cement fly ash system, calcium carbonate and C-S-H/C-A-S-H comprise the main phases in the healing products. It was noticed that the ratio of calcium carbonate to the hydration products was larger in the cement fly ash systems compared to the cement slag systems. The addition of hydrogels resulted in a higher content of calcium carbonate in the healing products of both systems. Hydrogels enhanced the mechanical regain and crack filling in both cement slag and cement fly ash systems compared to the control system without hydrogels.
•Hydrogels enhanced mechanical regain and crack filling in cement/slag or fly ash.•Hydrogels increased calcium carbonate (CC) content in the healing products.•The ratio of CC/healing products was larger in cement/fly ash than cement/slag.
The pore solutions of a series of hardened alkali-activated slag/fly ash pastes were extracted by the steel-die method, and analyzed using ICP-OES analysis technique. According to the saturation ...index from thermodynamic calculations, the pore solutions of alkali-activated slag pastes kept oversaturated with respect to solid reaction products with time. In the pore solutions of alkali-activated fly ash pastes, an increase of temperature (from 40 °C to 60 °C) led to decreases of the concentrations of Si, Al, Ca, Na, OH−, K, Fe and Mg, while the soluble silicate in the alkaline activator resulted in increases of the concentrations of these elements. Compared to the alkali-activated slag paste with the same alkaline activator, 50% replacement of slag by fly ash did not result in a substantial change of the pore solution composition. Based on the experimental results, conceptual models were proposed to describe the elemental concentrations in the pore solutions.
•The pore solution composition of AAMs depends on the alkaline activator and curing temperature.•The pore solutions of alkali-activated slag keep oversaturated with respect to solid reaction products with time.•50 wt% replacement of slag by fly ash does not result in a substantial influence on the pore solution composition of alkali-activated slag blended with fly ash.•Conceptual models are proposed to describe the elemental concentrations in the pore solutions of AAMs.
The highly viscous property of alkali silicate-activated cements is one of the critical challenges that hinder their wide application. The present study focuses on ameliorating the rheological ...performance of sodium silicate-activated fly ash/slag pastes by using fly ash microsphere (FAM), which are highly spherical particles collected from fly ash with electrostatic adsorption classification technology. The FAM particles work as ‘ball-bearings’ in the pastes to reduce the internal friction between fly ash and slag grains, and meanwhile mitigate the agglomeration of flocs and fragmentation to release the locked water. The interrelationship between the FAM particle geometry and plastic viscosity of the paste is well described by the Krieger-Dougherty equation, which supports the proposed mechanisms of ‘ball-bearings’ effects. FAM can work as an inorganic dispersing agent to improve the workability of alkali-activated cement products for a variety of application aspects.
•Fly ash microsphere is collected from fly ash with electrostatic adsorption classification.•Fly ash microsphere acts as ‘ball-bearings’ in alkali-activated cements.•Fly ash microsphere works as inorganic dispersing agent to improve workability.•Fly ash microsphere exhibits a good compatibility in alkali-activated cements.
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