Performance Of Alkali-activated Slag Research Articles

Effect of wastewater generated from fluoroacid etching of cenospheres on the performance of alkali-activated slag

The fluoroacid etching process to produce perforated cenospheres generates a considerable volume of waste etching water, yet no effective strategy has been proposed for the treatment or reutilization of this environmentally harmful wastewater. In light of this, the present study explores the feasibility of utilizing lime-treated etching wastewater (LTEW) as a potential source of mixing water for alkali-activated slag (AAS). LTEW exhibits a high concentration of Ca2+ and possesses strong alkalinity, making it potentially suitable for activating slag. The experimental findings revealed that the addition of LTEW enables a reduction in the concentration of the activator, NaOH solution, due to the presence of Ca2+ and NH4+ within LTEW. Consequently, the setting and hydration processes of AAS were retarded in correlation with the incorporation of LTEW. However, the reaction between Ca2+ in LTEW and NaOH resulted in the formation of Ca(OH)2, which could act as an auxiliary activator for AAS. Furthermore, the presence of expansive Ca(OH)2 crystals, possessing a higher elastic modulus compared to C-S-H gel, refined the pore structure of the mortars. The addition of increasing amounts of LTEW exhibited a gradual improvement in the compressive strengths of the mortars at all ages, ranging from 2.2% to 23.5% at 3 days, 2.4% to 21.6% at 7 days, and 6.0% to 24.6% at 28 days. The utilization of LTEW in AAS preparation offers significant economic and environmental benefits.

Mechanical and durability properties of alkali-activated slag/waste basalt powder mixtures

There are several studies investigating the feasibility of basalt powder as a precursor in alkali-activated cement production. The originality of this research lies in investigating the mechanical and durability features of alkali-activated mortars manufactured by partially substituting granulated blast furnace slag (GBFS) with waste basalt powder (WBP). In this study, 20% of GBFS was replaced with WBP, and high temperature (300 °C, 600 °C, and 900 °C) and magnesium sulfate (5% concentration) resistance of the manufactured mortars were investigated. The deteriorations of the mortars subjected to high temperature and magnesium sulfate were examined by compressive strength test, ultrasonic pulse velocity test, scanning electron microscopy analysis, and Fourier transform infrared spectroscopy analysis. The compressive strength of the mortar produced with 20% WBP substitution was 9.9% lower compared to the mortar containing 100% GBFS as the precursor. However, the performance of alkali-activated slag (AAS), known for its good resistance to high temperatures, did not decrease with the WBP substitution. The reduction in strength of both mortars after 900 °C was approximately 86%. No excessive changes were observed in the visual appearance and the compressive strength of the mortars after 3 months of exposure to magnesium sulfate. Microstructure analyses also revealed that WBP substitution had a limited effect on the high temperature and sulfate resistance of AAS.

Synergetic impacts of mesoporous α-Fe2O3 nanoparticles on the performance of alkali-activated slag against fire, gamma rays, and some microorganisms

This study describes the fabrication of green composite pastes with multifunctional properties that can be utilized in special applications. Low-cost mesoporous hematite nanoparticles (HNPs) were prepared using a sol-gel technique. Different doses of HNPs (0.25, 0.5, and 1%) were added to alkali-activated slag (AAS) using an aqueous solution of NaOH (5 wt % of slag) as an activator. All composite pastes, AAS and AAS-HNPs, were kept under high humidity at normal temperature for 90 days. After 28 days of curing, a group of specimens was fired at elevated temperatures in a range of 200–900 °C, and another group was exposed to 1000- 3000 KGy gamma radiation. The formed phases and morphological features of some selected composites were characterized using X-ray diffraction (XRD), thermal analyses (TGA/DTG), Fourier transformation infrared (FTIR), and scanning electron microscope with energy dispersive X-ray (SEM/EDX). The outcomes of the compressive strength test emphasized that AAS-0.25 HNPs composite paste has a superior thermal resistivity at all firing temperatures and the best impedance to radiation till 3000 KGy. Agar diffusion test (ASTM D4300-1) revealed that AAS containing 1% HNPs composite possessed an excellent antimicrobial activity with various microorganisms; two bacterial strains (Escherichia Coli ATCC 8739 and Staphylococcus aureus ATCC 6538) and two fungal strains (Aspergillus flavus and Mucor circinelloide).

Influence of Elevated Temperatures and Cooling Method on the Microstructure Development and Phase Evolution of Alkali-Activated Slag.

The performance of alkali-activated slag (AAS) under thermal treatment has received particular attention. In this study, the effect of five elevated temperatures (25, 200, 400, 600, and 800 °C) and two cooling methods (air cooling and water spraying) on the mechanical and durability properties, microstructure, and phase evolution of AAS was investigated. The results show that AAS mortars exhibit higher resistance to thermal attack than OPC in terms of strength and durability. AAS samples cooled in air show higher residual strength than those cooled by spraying water, which is mainly attributed to fewer cracks formed in the former. The resistance to carbonization of exposed AAS mortars depends on the pore size distribution, while that to chloride ion penetration depends on the porosity. Cooling methods show a minor effect on the phase evolution of reaction products, suggesting that the microstructure degradation is mainly responsible for the damage of AAS structures. This study provides fundamental knowledge for the thermally induced changes on AAS which contributes new ideas for the development of construction structures with higher fire resistance.

Influence of Basalt Fiber on the Performance of Alkali-Activated Slag with Different Activators

Influence of Basalt Fiber on the Performance of Alkali-Activated Slag with Different Activators

Understanding the effect of hydrozincite and witherite nanominerals on the performance and phase composition of alkali-activated slag

The individual effect of nano hydrozincite and witherite (nHZ and nW, respectively) with different contents (0, 0.5, 1.0, and 1.5% by weight of slag) on the performance of alkali-activated slag (AAS) at early (from 1 to 7-days) and later ages (from 28 to 365-days) of curing was evaluated. The results proved that incorporating nHZ caused a retardation impact on the early hydration rate of AAS; whereas nW demonstrated an acceleration effect. These opposite effects were ascribed to the formation of zinc and barium hydroxides through the alkali-dissolution of nHZ and nW at 1-day of curing. A remarkable change in Ca/Si ratio within calcium silicate hydrate has been identified at both AAS-nHZ and AAS-nW mixtures. The proposed approach succeeded in the production of the hardened materials with high mechanical performance (55–64 MPa) using low nanominerals (0.5 wt%) and NaOH (3 wt%) contents.

Internal Curing Effect of Pre-Soaked Zeolite Sand on the Performance of Alkali-Activated Slag.

This study clarifies the effects of pre-soaked zeolite sand as an internal curing material on the hydration, strength, autogenous shrinkage, and durability of alkali-activated slag (AAS) mortars. The liquid-to-binder ratio (L/b) of all of the AAS mortars was 0.55. Sodium hydroxide solution was used as an alkali activator and an internal curing liquid. Calcined zeolite and natural zeolite sand replaced the standard sand at 15% and 30%, respectively. The setting time, autogenous shrinkage, compressive strength, ultrasonic pulse velocity, and surface electrical resistivity were tested. The following conclusions were drawn: (1) The addition of zeolite significantly reduces the autogenous shrinkage of AAS mortar. Compared with the control group, 30% calcined zeolite reduced the autogenous shrinkage by 96.4%. Moreover, the autogenous shrinkage of the AAS mortars was noticed in two stages (a variable temperature stage and an ambient temperature stage), and the two stages split at one day of age. (2) The compressive strength of all of the specimens increased as the zeolite sand content increased, and the highest compressive strength was obtained for AAS combined with 30% natural zeolite sand. (3) Internal curing accelerated the formation of the second peak of heat flow and reduced the accumulated heat release. (4) Calcined zeolite sand delayed the setting time of the AAS mortars. (5) The addition of zeolite significantly reduced the surface electrical resistivity of the AAS mortars. In summary, zeolite sand is extremely useful as an internal curing agent to reduce autogenous shrinkage and to increase the compressive strength of AAS mortars.

The long-term failure mechanisms of alkali-activated slag mortar exposed to wet-dry cycles of sodium sulphate

This study investigates the long-term (570 days) performance of alkali-activated slag (AAS) mortar exposed to combined wet-dry cycles and sodium sulphate solutions (i.e. 5 wt% and 10 wt%). Physical and mechanical characteristics of AAS mortars (i.e. visual appearance, compressive/flexural strength, mass change, capillary porosity, water sorptivity) as well as mineralogical and chemical parameters were determined using XRD, FTIR, DSC and BSE. Findings were compared to Portland cement (PC) and high sulphate resistant (HSR) samples. Results indicate that AAS mortars perform better than PC and HSR samples with minimal changes to compressive strength at 570 days (1.7% increasement). The main failure mode for AAS mortar was external spalling, which could be due to the crystallisation/dissolving pressure of sodium sulphate. Moreover, the results indicate key differences in the deterioration mechanism of AAS. Unreacted slag, exposed during sodium sulphate attack under wet-dry cycles, can continue to react in sodium sulphate to form silicon-rich gels. The formation of highly siliceous gel regions has beneficial impacts, such as the increase in flexural strength. While no calcium sulphate phases were detected via XRD and FTIR after 570 days of exposure, it is evident that the molecular changes in the microstructure reveal depolymerisation and enhanced formation of Si–O phases after long-term sodium sulphate exposure. These results are important to understand the long-term degradation mechanisms of AAS materials exposed to sodium sulphate under wet-dry cycles.

Characterisation of temporal variations of alkali-activated slag cement property using microstructure features and electrical responses

Relatively few studies currently exist concerning temporal variation of the overall performance of alkali-activated slag (AAS) cement; a topic essential for quality control in practice. This study uses microstructural characteristics and electrical responses to reflect performance variation of AAS cement. To achieve this, four key performance parameters were assessed, pore formation factor, chloride transport coefficient, permeability coefficient and compressive strength. Classical theories used for PC-based materials were applied to estimate the performance of AAS paste. It is found that the formation factor of AAS can be assessed by combining bulk conductivity and pore solution conductivity and the permeation properties of AAS cement cannot be reliably assessed by the Katz-Thomoson (KT) model, while the Millington-Quirk (MQ) model works better. To assess the relationship between compressive strength and permeable porosity, the Balshin and Ryshkevitch equations performed best in terms of describing the relationship between these two parameters. Meanwhile, AAS cement is more sensitive to the mix proportions and additional care is needed to ensure its quality. It is the first time to use electrical response to predict the chloride transport coefficients of AAS cement, which would provide a powerful tool for its quality control and service life prediction.

Influence of Na2O Content and Ms (SiO2/Na2O) of Alkaline Activator on Workability and Setting of Alkali-Activated Slag Paste.

The performance of alkali-activated slag (AAS) paste using activators of strong alkali components is affected by the type, composition, and dosage of the alkaline activators. Promoting the reaction of ground granulated blast furnace slag (GGBFS) by alkaline activators can produce high-strength AAS concrete, but the workability might be drastically reduced. This study is aimed to experimentally investigate the heat release, workability, and setting time of AAS pastes and the compressive strength of AAS mortars considering the Na2O content and the ratio of Na2O to SiO2 (Ms) of binary alkaline activators blended with sodium hydroxide and sodium silicate. The test results indicated that the AAS mortars exhibited a high strength of 25 MPa at 24 h, even at ambient temperature, even though the pastes with an Na2O content of ≥6% and an Ms of ≥1.0 exhibited an abrupt decrease in flowability and rapid setting.

Behavior of alkali-activated slag in the presence of different aluminosilicate sources

This article presents an investigation into the performance of alkali-activated slag (AAS) in the presence of different aluminosilicate sources. AAS was individually replaced by 10, 20, and 30 wt. % Metakaolin (MK), Ground ceramic waste (GCW) and ground clay brick waste (GCBW). The results showed that the Na2O/Al2O3 and CaO/SiO2 molar ratio play a crucial role in the behavior of AAS. GCW and GCBW with different contents have positive impact on the compressive strength of AAS, especially at later ages of curing. AAS performed well in the presence of 10 wt. % MK. Meanwhile, 20 and 30 wt. % caused the AAS compressive strength regression. The water demand of AAS increased with an increase in aluminosilicate’s weight percentage. Also, AAS containing GCBW showed the shortest setting times as well as the highest mechanical properties as proved by XRD, FTIR, and SEM.