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To enhance the application of alkali-activated materials in mine filling, cemented tailings backfill was prepared using slag, fly ash, sodium silicate, and NaOH as primary constituents. The effects of the raw material type and dosage on the backfill were examined through a single-factor experiment. Additionally, response surface methodology (RSM) was utilized to optimize the mixing ratios of the backfill, with a focus on fluidity and compressive strength as key objectives. The evolution of backfill quality and compressive strength under the combined effects of dry–wet and freeze–thaw (DW-FT) cycles was analyzed. The hydration products, microstructure, and pore characteristics of the specimens were analyzed using X-ray diffraction (XRD), scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS), and nitrogen adsorption tests (NATs) across varying cycles. The results demonstrate that the optimal backfill composition includes 47.8% fly ash, 6.10% alkali equivalent, and a 1.44 sodium silicate modulus. The macroscopic behavior of the backfill under DW-FT coupling followed this progression: pore initiation → pore expansion → crack formation → crack propagation → structural damage. After a minor initial increase, the backfill strength steadily decreased. Microscopic analysis revealed that the decline in internal cementation products and the deterioration of pore structure were the primary causes of this strength reduction. Thus, the DW-FT coupling can cause significant erosion of the backfill. The technical solutions presented in this paper offer a reference for solid waste utilization and provide valuable insights into the durability of backfill under DW-FT coupling. [ABSTRACT FROM AUTHOR]

Abstract Alkali Activated Slag Concrete (AASC) has been a sustained research activity over the past two decades. Its promising characteristics and being environmentally friendly compared to Ordinary Portland Cement made AASC of exceptional interest. However, there is still no firm mix design, for the AASC, that can provide desirable fresh and hardened properties based on the composition of the binder and activator. This research specifically aims to investigate the affecting parameters on the slump and compressive strength of alkali-activated slag/lime-based concrete and provide a better understanding of the potential reasons for these characteristics. The experimental program consisted of two stages; the first stage studied the effect of different binder and activator compositions, and the second stage studied the water-to-binder ratio and binder content effects on the slump and compressive strength of alkali-activated slag/lime-based concrete. The binder and activator compositions were defined through two main parameters, the hybrid factor (HF = CaO/Si2O + Al2O3) and the solution modulus (Ms = SiO2/Na2O). The compressive strength, initial slump, and slump loss were measured to evaluate the different mixes and specify the optimum range of compositions. Based on the studied parameters, the effective range to achieve desirable slump and concrete compressive strength is from HF 0.6 up to 0.8 at Ms 1.5, this would achieve a compressive strength of more than 30 MPa and a slump of 100 mm after 90 min.

Asphalt modification with inorganic whiskers is a novel and green method to improve the performance of asphalt pavement, but it is still limited by the high costs and uneven dispersion of whiskers. In this study, an innovative asphalt modifier that can in-situ generate whiskers in hot mix asphalt (HMA) was developed by the alkali activation method using waste dolomite dust as raw material. The morphology and distribution of the alkali-activated waste dolomite dust (AWD) whiskers were examined by scanning electron microscopy and fluorescence microscopy, and the effects of AWD curing time, processing mode and dosage on the rheological and adhesion properties of the modified asphalt binder were evaluated. The results indicate that AWD can spontaneously form whiskers in the asphalt matrix under the flowing temperature of HMA, and the optimal performance enhancement effect on asphalt binder is achieved when the AWD curing time is 1 day, and its dosage is 5% of the asphalt binder mass. Compared with neat binder, the modified binder with AWD shows a 65% increase in rutting factor and a 2-level improvement in adhesion grade, while the costs of AWD are only 1/27 of those of commercial CaCO3 whiskers. These findings demonstrate that AWD is a cost-effective, eco-friendly and high-performance asphalt modifier, which has great potential for application in asphalt pavement engineering. [ABSTRACT FROM AUTHOR]

The strength development (up to 28 days) and drying shrinkage of alkali-activated metakaolin-Portland cement mortars at room temperature curing using an Na₂SiO₃ to NaOH ratio of 1.5 were investigated. The effects of different Portland cement (0-30%) and metakaolin (70-100%) mixes are reported on. The setting time and drying shrinkage were found to be reduced with increasing Portland cement contents when both materials were used. The early strength at 3 days was higher for the 100MK mix, but higher strength developments between 3 and 7 days were found in PC-MK mixes. At 28 days, the highest compressive strength was found in the mixes with a metakaolin content between 80-85%. The TGA analysis results showed that the N-A-S-H/(N, C)-A-S-H phases were detected as a geopolymer product.

The objective of this study was to identify the optimal geopolymer binder compositions produced from local industrial by-products and compare them with commercially available materials. The first part investigated the optimal binder composition by studying 27 mixtures. In this part of the research, three series of binders were created: the first series of 18 mixtures was Na-based fly ash-slag, the second series consisted of 8 mixtures of K-based fly ash-slag, and the third series were a mixture of metakaolin-slag based geopolymer. The compressive strengths of the mixtures at the age of seven days ranged from 2.18 to 96.23 MPa. The strength development is clearly defined by the components and proportions of the blends. Geopolymers reach about 80% of their 28-day strength in seven days. The 25% water content was optimal for slag-fly ash geopolymers. The strength of the material increased from 68.08 to 96.23 MPa when the Blaine surface area of the slag increased from 3500 to 4500 cm2/g. The optimal proportions of the alkali solution were the intermediate ratios: SiO2/Na2O = 2.0 and SiO2/K2O = 1.5. In the case where Visonta fly ash is prepared for blending, the fly ash content can be maximized by 30%–50% in addition to the blast-furnace slag. In the second part of the research, mortars were prepared from the selected binders: 4 mixtures were prepared with two different binders. In one of these mortars, the solid part of the binder consisted of local raw materials originating from Hungary. This mixture was prepared with 43 m% fine aggregates. The optimal composition of the tested 27 binders tested was selected as the geopolymer matrix for the production of three further mortar mixtures. In these geopolymer mortars, 55, 65, and 75 m% of aggregate applied. The flowtable values of fresh mortars decreased when the proportion of sand increased. The lower the additive content was, the higher the strength of the geopolymer mortar. The 28-day compressive strengths of filtered fly ash-slag mortar sample with 55%, 65%, and 75% of fine aggregate (F–S-a55, F–S-a65, and F–S-a75) made with the selected optimised filtered fly ash-slag geopolymer binder of group A-I.3 (F–S-A-I.3) varied between 11.39 and 40.15 MPa, whereas the Visont fly ash-slag mortar sample with 43% of fine aggregate (V–S-a43) has been 25.05 MPa. For 28 days, the density ranged between 1870 and 2204 kg/m3. The V–S-a43 is found to be the lowest-density blend. The chloride migration test revealed that geopolymer mortars with higher slag content have higher resistance to Cl− ions.

This is an article in the field of ceramics and composites. With the growth of lithium smelting scale in China, the production of lithium slag increases year by year, the need for its resource utilization is becoming more and more obvious. To explore the physical and chemical properties of lithium slag and its potential as a cementitious material to prepare artificial aggregate, the composition and properties of lithium mica lithium slag in Yichun, China and lithium slag from spodumene in Australia were characterized, and their effects on alkali excitation performance were analyzed. Secondly, two kinds of lithium slag artificial aggregates were prepared by disk cold granulation method with sodium hydroxide as alkali activator, and their compressive strength was tested. Finally, the environmental risks of artificial aggregates were demonstrated by glass electrode method, inductively coupled plasma mass spectrometry, ion chromatography and spectrophotometry. The results show that the physical and chemical properties of lithium mica lithium slag are more suitable for the preparation of artificial aggregates by alkali excitation than lithium pyroxene lithium slag, and the resulting artificial aggregates are stronger and the liquid leachate is not environmentally hazardous.

To enhance the application of alkali-activated materials in mine filling, cemented tailings backfill was prepared using slag, fly ash, sodium silicate, and NaOH as primary constituents. The effects of the raw material type and dosage on the backfill were examined through a single-factor experiment. Additionally, response surface methodology (RSM) was utilized to optimize the mixing ratios of the backfill, with a focus on fluidity and compressive strength as key objectives. The evolution of backfill quality and compressive strength under the combined effects of dry–wet and freeze–thaw (DW-FT) cycles was analyzed. The hydration products, microstructure, and pore characteristics of the specimens were analyzed using X-ray diffraction (XRD), scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS), and nitrogen adsorption tests (NATs) across varying cycles. The results demonstrate that the optimal backfill composition includes 47.8% fly ash, 6.10% alkali equivalent, and a 1.44 sodium silicate modulus. The macroscopic behavior of the backfill under DW-FT coupling followed this progression: pore initiation → pore expansion → crack formation → crack propagation → structural damage. After a minor initial increase, the backfill strength steadily decreased. Microscopic analysis revealed that the decline in internal cementation products and the deterioration of pore structure were the primary causes of this strength reduction. Thus, the DW-FT coupling can cause significant erosion of the backfill. The technical solutions presented in this paper offer a reference for solid waste utilization and provide valuable insights into the durability of backfill under DW-FT coupling.

Copyright of Multipurpose Utilization of Mineral Resources / Kuangchan Zonghe Liyong is the property of Multipurpose Utilization of Mineral Resources Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Chemical stabilization is an effective approach to address various engineering problems related to saline soil, including salt heaving, frost heaving, dissolution, and corrosion. Through unconfined compression strength (UCS) test, x-ray diffraction (XRD) test, scanning electron microscope (SEM) tests and mercury intrusion porosimetry (MIP), this research investigates the macroscopic strength characteristics, microscopic mineral composition, and pore structure variation of quicklime, fly ash and sodium silicate joint solidifying sulfate saline soil under various freeze-thaw cycles, and discusses its solidification mechanism. The results indicate that when the contents of fly ash and sodium silicate are held constant, the unconfined compressive strength of the solidified soil increases first and then decreases with the increase of quicklime content. Additionally, the peak strength occurred at a quicklime content of 3 %; The strength of all the solidified soils decreased with the increase of the freeze-thaw cycles and the solidified soils with the optimum quicklime content has a relatively strong ability to resist freezing and thawing; The influence of quicklime content on solidification is reflected in the formation of hydrate gels and the variation of pore structure; The influence of freeze-thaw cycle on solidification is reflected in the destruction of solidified pore structure.

The fireproof design of geopolymers through adjusting multi-component metallurgical solid wastes has attracted increasing attention, due to their potential low carbon emission, cost effectiveness, and role in environmental conservation. Herein, the effects of silica fume (SF) on the microstructure and mechanical properties of alkali-activated slag/FA (fly ash) pastes subjected to elevated temperatures (150, 500, 850, and 1200 °C) are investigated to clarify whether or not SF has a positive role in the mechanical strength of the slag/FA (slag/FA = 30:70, wt.%) geopolymer during building fires. The results show that the replacement of FA with 10 wt.% SF (silica fume) promotes the increasing pore volume with a diameter of 0.2~3 μm, leading to an increase in the compressive or flexural strength below 850 °C, "right shifts" of the endothermic peak, and uniform and compact fracture surfaces. Meanwhile, gehlenite and labradorite are generated after exposure above 850 °C. The bloating effect of the SF-containing sample occurs at 1200 °C, leading to a greater deformation due to the further restructuring of the amorphous geopolymer chain N–A–S–H or N–(Ca)–A–S–H composed of [SiO4]4− and [AlO4]5−. This paper explores an effective approach to improving geopolymers' fireproof performance by adjusting the formulation of solid waste. [ABSTRACT FROM AUTHOR]

The advantage of a prefabricated building is its ease of construction. Concrete is one of the essential components of prefabricated buildings. A large amount of waste concrete from prefabricated buildings will be produced during the demolition of construction waste. In this paper, foamed lightweight soil is primarily made of concrete waste, a chemical activator, a foaming agent, and a foam stabilizer. The effect of the foam admixture on the wet bulk density, fluidity, dry density, water absorption, and unconfined compressive strength of the material was investigated. Microstructure and composition were measured by SEM and FTIR. The results demonstrated that the wet bulk density is 912.87 kg/m3, the fluidity is 174 mm, the water absorption is 23.16%, and the strength is 1.53 MPa, which can meet the requirements of light soil for highway embankment. When the foam content ranges from 55% to 70%, the foam proportion is increased and the material's wet bulk density is decreased. Excessive foaming also increases the number of open pores, which reduces water absorption. At a higher foam content, there are fewer slurry components and lower strength. This demonstrates that recycled concrete powder did not participate in the reaction while acting as a skeleton in the cementitious material with a micro-aggregate effect. Slag and fly ash reacted with alkali activators and formed C-N-S(A)-H gels to provide strength. The obtained material is a construction material that can be constructed quickly and reduce post-construction settlement. [ABSTRACT FROM AUTHOR]

Composites that use fly ash and slag as alkali-activated materials instead of cement can overcome the defects and negative effects of alkali-activated cementitious materials prepared with the use of an alkali-activated material. In this study, fly ash and slag were used as raw materials to prepare alkali-activated composite cementitious materials. Experimental studies were carried out on the effects of the slag content, activator concentration and curing age on the compressive strength of the composite cementitious materials. The microstructure was characterized using hydration heat, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM), and its intrinsic influence mechanism was revealed. The results show that increasing the curing age improves the degree of polymerization reaction and the composite reaches 77~86% of its 7-day compressive strength after 3 days. Except for the composites with 10% and 30% slag content, which reach 33% and 64%, respectively, of their 28-day compressive strength at 7 days, the remaining composites reach more than 95%. This result indicates that the alkali-activated fly ash–slag composite cementitious material has a rapid hydration reaction in the early stage and a slow hydration reaction in the later stage. The amount of slag is the main influencing factor of the compressive strength of alkali-activated cementitious materials. The compressive strength shows a trend of continuous increase when increasing slag content from 10% to 90%, and the maximum compressive strength reaches 80.26 MPa. The increase in the slag content introduces more Ca2+ into the system, which increases the hydration reaction rate, promotes the formation of more hydration products, refines the pore size distribution of the structure, reduces the porosity, and forms a denser microstructure. Therefore, it improves the mechanical properties of the cementitious material. The compressive strength shows a trend of first increasing and then decreasing when the activator concentration increases from 0.20 to 0.40, and the maximum compressive strength is 61.68 MPa (obtained at 0.30). The increase in the activator concentration improves the alkaline environment of the solution, optimizes the level of the hydration reaction, promotes the formation of more hydration products, and makes the microstructure denser. However, an activator concentration that is too large or too small hinders the hydration reaction and affects the strength development of the cementitious material. [ABSTRACT FROM AUTHOR]

A huge amount of carbon dioxide is released in the Portland cement production process. A large quantity of greenhouse gases is produced because of the significant amount of energy consumption via making bricks through firing. Using the pozzolanic sources containing the aluminosilicate and alkaline reagents, a new type of green materials called geopolymeric materials is produced with quite lower environmental hazards. The use of laterite as an iron-rich aluminosilicate material has a high potential for the building materials. In this study, the effect of the curing temperature and characteristics of the alkaline reagent including the concentration of sodium hydroxide solution and the water-glass to sodium hydroxide mass mixing ratio on the mechanical strength of the lateritebased, oven-cured geopolymer samples was investigated. The results showed that the curing temperature had a significant effect on the compressive strength of the laterite-based geopolymer samples, so that with a 15°C change at the curing temperature, the compressive strength of the samples could be multiplied, and a sharp increase in the mechanical strength could occur. Also, according to the results of this study, the 6 M sodium hydroxide is recommended for the construction of the laterite-based geopolymer materials with low cost and relatively high strength, and for the construction of higher-strength building materials, the 14 M sodium hydroxide is recommended. [ABSTRACT FROM AUTHOR]

In this study, natural volcanic tuff-based foamed geopolymer was synthesized, characterized, and evaluated for its efficiency to remove heavy metals (zinc and lead) from wastewater. Sodium hydroxide was used as an alkaline activator to dissolve the constituents and form geopolymeric binders. Hydrogen peroxide (H2O2) was used as a foaming agent at different levels (0%, 1%, and 2%). The effect of curing temperature (60, 80, and 100 °C) on the physical properties and the removal efficiency was evaluated with a pH ranging from 3 to 7 for lead removal and 5 to 7 for zinc removal. The physical properties include compressive strength, density, and microstructural characteristics. The results indicated that higher curing temperatures increase the compressive strength and removal efficiency of the geopolymer foam. Geopolymers that are prepared at a curing temperature of 100 °C exhibited the highest removal efficiency for both Pb2+ and Zn2+ ions. The addition of H2O2 refined the microstructural characteristics of the foamed geopolymer and increased the efficiency of the zinc removal process. Results revealed that as the pH increases, the removal efficiency also increases. This can be due to the competition between H+ and Pb2+ and Zn2+ ions on the available adsorption sites at low pH values. As the acidity of the solution decreases, this competition decreases and led to higher removal efficiency.Article Highlights: Foam-based volcanic tuff geopolymer was synthesized and characterized. The geopolymer efficiency for heavy metal removal was evaluated. Increasing geopolymer curing temperature led to enhancing the removal efficiency. Increasing the foaming agent dosage has enhanced the removal efficiency. [ABSTRACT FROM AUTHOR]

The fireproof design of geopolymers through adjusting multi-component metallurgical solid wastes has attracted increasing attention, due to their potential low carbon emission, cost effectiveness, and role in environmental conservation. Herein, the effects of silica fume (SF) on the microstructure and mechanical properties of alkali-activated slag/FA (fly ash) pastes subjected to elevated temperatures (150, 500, 850, and 1200 °C) are investigated to clarify whether or not SF has a positive role in the mechanical strength of the slag/FA (slag/FA = 30:70, wt.%) geopolymer during building fires. The results show that the replacement of FA with 10 wt.% SF (silica fume) promotes the increasing pore volume with a diameter of 0.2~3 μm, leading to an increase in the compressive or flexural strength below 850 °C, “right shifts” of the endothermic peak, and uniform and compact fracture surfaces. Meanwhile, gehlenite and labradorite are generated after exposure above 850 °C. The bloating effect of the SF-containing sample occurs at 1200 °C, leading to a greater deformation due to the further restructuring of the amorphous geopolymer chain N–A–S–H or N–(Ca)–A–S–H composed of [SiO4]4− and [AlO4]5−. This paper explores an effective approach to improving geopolymers’ fireproof performance by adjusting the formulation of solid waste.

The advantage of a prefabricated building is its ease of construction. Concrete is one of the essential components of prefabricated buildings. A large amount of waste concrete from prefabricated buildings will be produced during the demolition of construction waste. In this paper, foamed lightweight soil is primarily made of concrete waste, a chemical activator, a foaming agent, and a foam stabilizer. The effect of the foam admixture on the wet bulk density, fluidity, dry density, water absorption, and unconfined compressive strength of the material was investigated. Microstructure and composition were measured by SEM and FTIR. The results demonstrated that the wet bulk density is 912.87 kg/m3, the fluidity is 174 mm, the water absorption is 23.16%, and the strength is 1.53 MPa, which can meet the requirements of light soil for highway embankment. When the foam content ranges from 55% to 70%, the foam proportion is increased and the material’s wet bulk density is decreased. Excessive foaming also increases the number of open pores, which reduces water absorption. At a higher foam content, there are fewer slurry components and lower strength. This demonstrates that recycled concrete powder did not participate in the reaction while acting as a skeleton in the cementitious material with a micro-aggregate effect. Slag and fly ash reacted with alkali activators and formed C-N-S(A)-H gels to provide strength. The obtained material is a construction material that can be constructed quickly and reduce post-construction settlement.

The success of ordinary Portland cement (OPC) comes at a risk to the environment because of the large carbon dioxide emissions associated with cement manufacturing. This has led the scientific community to look for alternative cementitious materials with lower environmental impact. Alkali activated cement (AAC) is an excellent alternative to this end. In this study, the effect of binder content, alkaline solid to binder ratio (AS/B), sodium silicate to sodium hydroxide solids ratio (SS/SH), and total water content to total solid binder ratio (TW/TB) on the strength, setting time and flowability of ambient cured AAC mixtures are studied using Taguchi method of experimental design. Binder content was varied from 550 to 750 kg/m3, AS/B ratio from 0.14 to 0.22, SS/SH ratio from 1.5 to 2.5, and TW/TB ratio from 0.29 to 0.39. The study results showed that within the investigated range, an increase in binder content has a minor effect on strength but resulted in a considerable increase in setting time and flowability. An increase in the AS/B ratio resulted in increased flowability and setting time and a decrease in strength. Moreover, the study also investigated the relationship between compressive strength and flexural strength. [ABSTRACT FROM AUTHOR]

For the constantly evolving alkali-activated materials (AAMs), expanding and optimising the raw materials base in accordance with increasing ecological and technical requirements is one of the determining factors for a promising future. Because of developments in inorganic material chemistry, the range of potentially suitable aluminosilicates has changed and expanded continuously throughout the history of AAMs. Recently, new efforts have been undertaken to find more types of adequate alternative aluminosilicate sources and alkali activators, in addition to conventional granulated blast furnace slag (GBFS), fly ash (FA), and metakaolin (MK). This search has led to extensive studies, which have substantially increased understanding of the suitability of various natural sources and wastes for the production of alkali-activated cements (AACs). Recent advances in the design and research of AACs based on several groups of aluminosilicates (non-ferrous slags, ash-form wastes, waste glasses, mining and ceramic wastes, natural rocks, and natural pozzolans) and alkali materials (ashes, waste glasses, chemicals, and alkaline wastes) are reviewed in this paper. By analogy with low-Portland clinker cements, alkali-activated low-GBFS, low-FA, and low-MK (up to 50%) cements incorporated with various alternative aluminosilicates have been found to represent very promising types of AACs in terms of availability of raw materials, engineering and economic performance, and commercialisation. [ABSTRACT FROM AUTHOR]

The variation of the raw materials is critical for the wide application of alkali-activated fly ash/slag (AAFS) in practice. In this study, four fly ashes sourced from different power plants were collected and analyzed. The calcium content in fly ash had insignificant impact on setting time, flowability and compressive strength of AAFS binders when the slag content was 50%. Low calcium content in fly ash promotes the formation of C-(N)A-S-H gel with high Al substitution and improves the compressive strength at later age. It seemed that the grinding process promoted the dissolution of reactive SiO2 in fly ash, resulting in reduced setting and flowability. The replacement of silica fume promotes the formation of Si-rich C-(N)A-S-H gel with reduced gel pore size. The replacement of metakaolin accelerated the initial reaction and increased the compressive strength of binders at early age due to the reduced gel pore size in C-(N)A-S-H gel. [ABSTRACT FROM AUTHOR]

Hybrid artificial geopolymer aggregates (GPA) and natural silica sand were used to strategically tailor the tensile strain-hardening behavior of high-strength engineered cementitious composites (HS-ECC). With such hybridization, the weaknesses of GPA (i.e., relatively low strength and stiffness) were utilized in the performance-based design of HS-ECC, while the advantages of GPA were retained (e.g., the utilization of industrial by-products/wastes through chemical activation and conservation of natural resources). In this study, a comprehensive experimental program was conducted at multiple scales on the HS-ECC. It was found that increasing the replacement ratio of silica sand by GPA improved the tensile ductility, crack control ability, and energy absorption of HS-ECC, although its compressive and tensile strengths were reduced. GPA with low alkalinity were observed to react with the cementitious matrix, and the pozzolanic reaction provided additional chemical bond and thus enhanced the GPA/matrix interface. In addition, GPA could be regarded as “additional flaws” in the HS-ECC system. According to the Weibull-based modeling, it was found that GPA could play a crack-inducing role in activating more inactive initial flaws. Therefore, GPA can tailor the active flaw size distributions in HS-ECC matrix. The findings of this study provide a new avenue for the utilization of GPA.

Composites that use fly ash and slag as alkali-activated materials instead of cement can overcome the defects and negative effects of alkali-activated cementitious materials prepared with the use of an alkali-activated material. In this study, fly ash and slag were used as raw materials to prepare alkali-activated composite cementitious materials. Experimental studies were carried out on the effects of the slag content, activator concentration and curing age on the compressive strength of the composite cementitious materials. The microstructure was characterized using hydration heat, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM), and its intrinsic influence mechanism was revealed. The results show that increasing the curing age improves the degree of polymerization reaction and the composite reaches 77~86% of its 7-day compressive strength after 3 days. Except for the composites with 10% and 30% slag content, which reach 33% and 64%, respectively, of their 28-day compressive strength at 7 days, the remaining composites reach more than 95%. This result indicates that the alkali-activated fly ash–slag composite cementitious material has a rapid hydration reaction in the early stage and a slow hydration reaction in the later stage. The amount of slag is the main influencing factor of the compressive strength of alkali-activated cementitious materials. The compressive strength shows a trend of continuous increase when increasing slag content from 10% to 90%, and the maximum compressive strength reaches 80.26 MPa. The increase in the slag content introduces more Ca2+ into the system, which increases the hydration reaction rate, promotes the formation of more hydration products, refines the pore size distribution of the structure, reduces the porosity, and forms a denser microstructure. Therefore, it improves the mechanical properties of the cementitious material. The compressive strength shows a trend of first increasing and then decreasing when the activator concentration increases from 0.20 to 0.40, and the maximum compressive strength is 61.68 MPa (obtained at 0.30). The increase in the activator concentration improves the alkaline environment of the solution, optimizes the level of the hydration reaction, promotes the formation of more hydration products, and makes the microstructure denser. However, an activator concentration that is too large or too small hinders the hydration reaction and affects the strength development of the cementitious material.

Copyright of Bulletin of the Chinese Ceramic Society is the property of Bulletin of the Chinese Ceramic Society Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Alkali‐activated materials are increasingly being used in practical applications as potential alternatives to Portland cement. If alkali‐activated slag (AAS) is to be applied to prestressed engineering and large‐size structures, it is necessary to study the creep performance of AAS. Existing studies have found that the creep of AAS concrete is larger than that of ordinary Portland cement (OPC) concrete, and adding fiber is an effective way to overcome this defect. In this study, we investigated the creep of basalt fiber–reinforced AAS (FRAAS) concrete for fiber contents ranging from 0% to 0.9% (by volume) at a stress–strength ratio of 0–0.6. After analyzing the experimental results, it was found that the basalt FRAAS concrete had no obvious linear creep range. It was observed that with an increase in the fiber content, the inhibition effect of fiber on creep became stronger initially and then weaker. The inhibitory effect of fiber on creep was strengthened by the increase in the stress–strength ratio. The creep coefficient showed no obvious change when the fiber content was in the range of 0%–0.9%. Based on the existing OPC concrete creep models, a method for predicting the creep of basalt FRAAS concrete was proposed. [ABSTRACT FROM AUTHOR]

An experimental study was carried out to evaluate the effect of several fibers on the mechanical properties, drying shrinkage, and microstructural characteristics of alkali‐activated kaolin binders. Four different types of fibers were evaluated in this study: polypropylene (PP) fiber, discontinuous structural synthetic (DSS) fiber, brass‐coated steel (BCS) fiber, and hooked steel (HS) fiber. The fibers were added to the alkali‐activated kaolin at a volume fraction of 0%, 0.5%, 1%, and 1.5%. The experimental results revealed that the compressive strength of alkali‐activated binder increased by about 60% when 1% of PP fiber is added, whereas the addition of HS fiber substantially enhanced the flexural strength (more than 200% when 1.5% fiber volume content is added). BCS and HS fibers were found to more effective compared to PP and DSS fibers in maintaining the binder integrity prior to high temperatures exposure. All fiber‐reinforced alkali‐activated composites yielded lower drying shrinkage (≤450 microstrains), where HS fiber was found to effectively prevent the shrinkage of the binder (≤60 microstrains). The microstructural investigation revealed good interfacial bonding between the alkali‐activated binder and the fibers. [ABSTRACT FROM AUTHOR]

Abstract An alternative cement system created through geopolymerization of fly ash offers favorable properties such as able to resist acidic fluids and possess high compressive strength. However, the application of fly ash geopolymer as wellbore cement under carbon dioxide (CO2) environment at elevated temperature is not well recorded in the literature. This paper characterizes the fly ash-based geopolymer cement and experimentally investigates its mechanical and microstructure changes after exposed to CO2 under elevated temperature. Microstructure identification on the altered cement paste was conducted by the analysis of XRD and SEM. In this study, fly ash-based alkali-activated cement was made using 8 molal sodium hydroxide and sodium silicate as alkali activators. The results found that crystal-like shape identified as calcium carbonate was formed at the surface of spherical fly ash particle after carbonation formation. The strength of geopolymer cement was found not to be decreased although carbonation process was occurred. Microstructure analysis revealed that zeolite was formed during CO2 acid exposure for geopolymer cement which contributes to the strength development.

Empirical studies were done to develop alkali activated Self-Compacting Geopolymer Concrete (SCGC) using Ground Granulated Blast furnace Slag (GGBS), incorporated with 2 % nano silica by weight, through evaluation of its fresh and hardening properties. Experimental investigation on 6 mix designs of varying molarity of 10M, 12M and 16M of alkaline solution and binder content of 450 Kg/m3 and 500 Kg/m3 were done and compared with GPC mix design composed of 16M alkaline solution concentration and 500 Kg/m3 binder content without nano silica. The Sodium Silicate to Sodium Hydroxide ratio (SS/SH), Alkaline Activator Liquid to Binder ratio (AAL/B) and Water to Binder Ratio (W/B), which significantly affect the performance and mechanical properties of GPC, were fixed at 2.5, 0.45 and 0.27 respectively. To catalyze the early stage geopolymerisation, oven curing was done maintaining the temperature at 60 ˚C. This paper also elucidates the test results for fresh Self-Compacting Concrete (SCC) done as per guidelines established in EFNARC. Mechanical tests conducted were compressive strength test after 7, 28, 56 and 90 days; split tensile strength test and flexure test after 28, 56 and 90 days; X-ray diffraction test to analyze the mechanical performance and sorptivity test for testing of permeability. The study revealed that the sample of 16M concentration of alkaline solution with 500 Kg/m3 binder content containing 2% nano silica produced the highest compressive, flexural and split tensile strength of 81.33 MPa, 7.875 MPa and 6.398 MPa respectively at 90 days.

Ordinary Portland cement (OPC) is known for its significant contribution to carbon dioxide emissions. Geopolymer has a lower footprint in terms of CO2 emissions and has been considered as an alternative for OPC. A well-developed understanding of the use of fly-ash-based and slag-based geopolymers as separate systems has been reached in the literature, specifically regarding their mechanical properties. However, the microstructural and durability of the combined system after slag addition introduces more interactive gels and complex microstructural formations. The microstructural changes of complex blended systems contribute to significant advances in the durability of fly ash/slag geopolymers. In the present review, the setting time, microstructural properties (gel phase development, permeability properties, shrinkage behavior), and durability (chloride resistance, sulfate attack, and carbonatation), as discussed literature, are studied and summarized to simplify and draw conclusions.

Featured Application: This work is a contribution to better knowledge of the behavior of a new family of materials obtained by alkali activation of a binder, which belongs to the geopolymers group. The possibility of its use in structures with finishes of different colors and textures is a feature that would be of great interest in some innovative architectural applications. Geopolymer materials are characterized by their high durability and low carbon dioxide emissions, when compared with more traditional materials, like concrete made from ordinary Portland cement. These are interesting advantages and might lead to a more sustainable construction industry. The aim of this study is the characterization of the mechanical behavior of the materials obtained by the activation of metakaolin. The activator is a mixture of sodium hydroxide with sodium silicate in different proportions. The influence of the composition of activator is studied. For the analysis of the mechanical properties of the different mixtures two different types of tests were performed, bending tensile strength tests and compressive strength tests. The results show that an activator with not less than 300 g of sodium hydroxide and not exceeding 600 g of sodium silicate per 750 g of metakaolin gives the best results, for both tensile strength and compressive strength. [ABSTRACT FROM AUTHOR]

One of the most widespread techniques in concrete pavement construction is roller-compacted concrete (RCC) in which Portland cement is used. Recently, an inclination has been seen toward alternative cementitious materials due to environmental concerns expressed over the production of Portland cement. Alkali-activated slag concrete (AASC) has been proposed as a solution to this problem. However, the application of this type of concrete in RCC has been rarely investigated. This study was to fill this gap in the existing literature experimentally. A solution of sodium hydroxide and sodium silicate helped to activate the slag content of AASC. The mechanical and rheological properties of roller-compacted alkali-activated slag concrete (RC-AASC) were assessed by measuring compressive and flexural strengths, optimum compaction moisture, setting time, and strength development of concrete samples. In mix design of RCC, determination of its optimum compaction moisture is a crucial step; therefore, the optimum moisture required for ultimate compaction was estimated, while the variation in combination of alkali activator affected this optimum moisture. The results indicated that the compressive and flexural strengths of RC-AASC with minimum cementitious content were comparable to those of conventional RCC which is mentioned in ACI 327R-14. [ABSTRACT FROM AUTHOR]

An alternative cement system created through geopolymerization of fly ash offers favorable properties such as able to resist acidic fluids and possess high compressive strength. However, the application of fly ash geopolymer as wellbore cement under carbon dioxide (CO2) environment at elevated temperature is not well recorded in the literature. This paper characterizes the fly ash-based geopolymer cement and experimentally investigates its mechanical and microstructure changes after exposed to CO2 under elevated temperature. Microstructure identification on the altered cement paste was conducted by the analysis of XRD and SEM. In this study, fly ash-based alkali-activated cement was made using 8 molal sodium hydroxide and sodium silicate as alkali activators. The results found that crystal-like shape identified as calcium carbonate was formed at the surface of spherical fly ash particle after carbonation formation. The strength of geopolymer cement was found not to be decreased although carbonation process was occurred. Microstructure analysis revealed that zeolite was formed during CO2 acid exposure for geopolymer cement which contributes to the strength development. [ABSTRACT FROM AUTHOR]

Alkali-activated materials have attracted increasing interest owing to their excellent properties and environmental protection. However, there have been few studies on their creep properties. The aim of this article is to investigate the effect of the stress–strength ratio on the creep property of sodium silicate–based alkali-activated slag (AAS) concrete. For this reason, five groups of AAS concrete with different stress–strength ratios (0.15, 0.3, 0.45, 0.6, and 0.75) were tested. The results indicate that the creep of AAS concrete has a convergent nonlinear stage and a non-convergent stage but not an obvious linear stage. The AAS concrete basically has a consistent creep coefficient and diverse specific creep under a stress–strength ratio of 0.15–0.6. The elasticity modulus of AAS is much smaller than that of ordinary Portland cement (OPC) concrete, which is the reason for the greater creep compared to that in OPC concrete, and the inaccuracy of the model prediction. By applying the actual elastic modulus, the models can predict the specific creep and stress-dependent strain of AAS concrete with a 0.3 stress–strength ratio, except for the B3 model. The secant modulus of AAS concrete decreases linearly with an increase in the stress–strength ratio. Finally, we propose an improved creep model for AAS concrete with a wide stress–strength ratio based on the GL2000 model. [ABSTRACT FROM AUTHOR]

Highlights • Fractional factorial design method was used to analyze the affecting factors. • Five factors each at three levels were considered. • Increase of sodium hydroxide molarity enhanced the mechanical properties. • Increase of sodium hydroxide to sodium silicate enhanced the mechanical properties. • Best results of curing time had been achieved when the curing period is 2 days. Abstract This research work aims to study the factors affecting the mechanical properties of alkali activated blast furnace slag concrete. The mechanical properties studied herein were, compressive strength, tensile strength and modulus of elasticity. Five factors each at three levels were considered throughout this research. The effect of sodium hydroxide molarity (10, 12 and 14 M), alkaline solution/slag content (0.40, 0.45 and 0.50), curing temperature (30 °C, 60 °C, 90 °C), curing time (1, 2 and 3 days) and sodium hydroxide: sodium silicate mass ratio (1:1.75, 1:2.50 and 1:3.25) were considered throughout the research program. The fractional factorial method of experimentation was used through the experimental program to reduce the number of mixes. The results generally showed that the increase in sodium hydroxide molarity and sodium hydroxide to sodium silicate enhanced all of the mechanical properties, while the increase in alkaline solution/slag, curing temperature has adversely affected the alkali activated slag concrete. The best results of curing time has been achieved when the curing period is 2 days. [ABSTRACT FROM AUTHOR]

Concrete is the most commonly used construction material because of its various advantages, such as versatility, familiarity, strength, and durability, and it will continue to be in demand far into the future. However, with today’s sensitivity to environmental protection, this material faces unprecedented challenges because of its high greenhouse gas emissions, mainly during cement production. This paper investigates one of the promising cement replacement materials, alkali-activated cement (AAC) concrete. Being produced mainly from byproduct materials and having a comparable structural performance to conventional concrete, AAC concrete can transform the construction industry. Mechanical properties such as compressive and flexural strength and the relationship between them are studied. Different source materials such as fly ash (FA), ground granulated blast furnace slag (GGBS), silica fume (SF), and Metakaolin (MK) are used. The effect of the source materials and the activator solutions on the concrete performance is studied. Furthermore, the freeze-thaw resistance of the concrete is studied. The study results showed that the behavior of AAC depends highly on the source material combinations and type used. The effect of the alkaline solution is also dependent on the source material used. Mixes with higher GGBS content showed the highest strength, while mixes with MK showed the highest flexural strength. The freeze-thaw test results showed that proper design of AAC concrete with lower water content is critical to achieving a good resistance.

Geopolymer materials are characterized by their high durability and low carbon dioxide emissions, when compared with more traditional materials, like concrete made from ordinary Portland cement. These are interesting advantages and might lead to a more sustainable construction industry. The aim of this study is the characterization of the mechanical behavior of the materials obtained by the activation of metakaolin. The activator is a mixture of sodium hydroxide with sodium silicate in different proportions. The influence of the composition of activator is studied. For the analysis of the mechanical properties of the different mixtures two different types of tests were performed, bending tensile strength tests and compressive strength tests. The results show that an activator with not less than 300 g of sodium hydroxide and not exceeding 600 g of sodium silicate per 750 g of metakaolin gives the best results, for both tensile strength and compressive strength.

The long-term effect of extreme conditions, such as high concentrations of CO2, a combination of chloride and air, and sulfuric acid, on the performance of steel fibre reinforced alkali-activated fly ash and slag (AAFS) mortars was investigated. The selected conditions simulated the long-term exposure to the marine environment and had an influence on both the matrix and the fibres. Four AAFS mixes were analysed alongside a control ordinary Portland cement (OPC) mix. Mechanical properties such as the compressive strength, elastic moduli and ductility indices, as well as microscopic analyses were carried out. It was found that the AAFS was stable in most of the conditions. The primary way for its reduction in strength was through the neutralisation of pore fluids and the leaching of sodium cations. The addition of the short fibres could reduce the ingress of deleterious materials by limiting the development of cracks and allowing for the efficient use of higher activator ratios. The fibres were susceptible to corrosion by chloride and acid attacks. The relatively chemically stable environment of the AAFS provided protection to the embedded fibres. Based on this study, in a very aggressive environment, a combination of 1%–2% fibre by volume, with a high activator content in the AAFS mortar, could be the most suitable.