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The fly ash–based geopolymer (FABG) containing slag has distinct advantages in field applications. In this work, given that the activator modulus is a significant parameter affecting the properties of FABG, the influence mechanism of activator modulus (SiO2/Na2O from 1.1 to 1.5) on the macro-mechanical properties and micro-structure composition of FABG containing slag is explored. According to the experimental results, the early product of FABG containing slag is mainly C-A-S–H gel, and N-(C)-A-S–H gel with high cross-linking degree is formed at a later stage. Both C-A-S–H and N-A-S–H gels are distinguished in reaction products by using 29Si NMR. The Si/Al ratio of N-A-S–H gel and C-A-S–H gel decreases with the increase of modulus, resulting in an increase of MCL in C-A-S–H. Appropriate activator modulus can effectively activate slag and fly ash to yield more gels and form a more uniform and dense micro-structure, resulting in a lower threshold pore size and macroporosity, and an associated increase of the material strength. Meanwhile, the gel amount has a positive effect on the strength development in the FABG. [ABSTRACT FROM AUTHOR]

Ferroaluminate cement (FAC), a low-carbon binder with high corrosion resistance, is not commonly utilized because of its high cost. It is more affordable to partially replace FAC with supplementary cementitious material (SCM) such as granulated blast furnace slag (GBFS). However, there have been few studies on the properties of GBFS-FAC binary binder systems, in order to make a good understanding of the properties of FAC blended with GBFS, the effect of GBFS on the hydration and hardened properties of FAC was investigated from hydration heat, compressive strength, chloride penetration resistance, hydration products, pore structure, etc., and the simulated pore solutions of FAC and OPC were prepared and characterized to explore the hydration mechanism of GBFS in FAC environment. The results indicated that GBFS incorporation slowed down the hydration rate and significantly altered the hydration process of FAC such as delaying the formation of ettringite. When the GBFS content was more than 20%, the amount of hydration exotherm peaks of FAC blended with GBFS decreased due to the disappearance of the third exothermic peak. Adding GBFS did not affect the phase assemblage, but reduced the amount of hydration products and increased the porosity of the samples, resulting in the deterioration of the compressive strength and chloride penetration resistance (with the GBFS content increasing from 0% to 30%, the 28d compressive strength decreased from 44.25 MPa to 31.86 MPa). The hydration activity of GBFS in FAC pore solution was lower compared to that in OPC pore solution, due to the lower Ca and S concentrations, lower pH, and lower conductivity of FAC pore solutions. [Display omitted] • GBFS content strongly influences the hydration process of the GBFS-FAC binary system. • Low hydration activity of GBFS in FAC leads to a decrease in hardened properties. • Reason for the low hydration reactivity of GBFS in FAC environment is revealed. [ABSTRACT FROM AUTHOR]

To reduce the reliance on cement clinker, employing ultrafine powders as supplementary cementitious materials (SCMs) is gradually gaining importance. This study investigated the effect of an ultrafine composite powder (UCP) having a specific surface area of approximately 730 m²/kg, produced by industrial ball milling ordinary blast furnace slag and fly ash at a 1:1 ratio, on cement hydration and its durability. The ultrafine composite powder was characterized by X-ray fluorescence spectrometer (XRF), X-Ray diffraction (XRD), particle size analyzer, and scanning electron microscope (SEM). The effects of ultrafine composite powder on the macroscopic properties of cement-based materials were assessed through flowability tests, setting time tests, and mechanical properties tests. Then, the hydration heat release, hydration products and microstructures of the pastes were characterized using isothermal calorimetry, XRD, thermogravimetric (TG), SEM and mercury intrusion porosimetry (MIP). Finally, the effects of ultrafine composite powder on the durability of cement-based materials were evaluated by electrical flux, chloride diffusion coefficient, and mechanical properties tests. The results showed that ultrafine composite powder enhanced the flowability of cement paste under the synergistic effect of superplasticizer. However, the setting time was prolonged due to the dilution of cement by ultrafine composite powder. The ultrafine composite powder significantly improved the early mechanical properties of the mortar, and the mechanical properties after 28-days was equivalent to that of the control. The ultrafine composite powder could significantly decrease the cumulative heat release of cement paste. Due to the high SO 3 content, an additional exothermic peak representing ettringite formation was observed. As the hydration time extends, the hydration products in the paste changed, especially the transformation from ettringite to kuzite, and the formation of hemicarbonate and monocarbonate. As the ultrafine composite powder content increases, the proportion of gel micro-pores increased, whereas the proportion of middle and large capillary pores decreased. Consequently, the total pores in the paste also decreased. The addition of ultrafine composite powder enhanced the durability of the cement-based materials, making it an ideal choice for use in coastal engineering projects. ● UCP was beneficial for enhancing the flowability of cement mortar. ● UCP could enhance the early mechanical properties of cement mortar. ● UCP could make the microstructure of cement paste more compact. ● UCP improved the durability of cement mortar. [ABSTRACT FROM AUTHOR]

• Microwave heating reduces energy required for decarbonization of gasification ash. • Mineral species and enrichment in gasification ash increase after decarbonization. • Electron binding energy decreases on active mineral surfaces post-microwave exposure. • Microwave thermally activated fine ash exhibited excellent hydration activity. The presence of residual carbon in coal gasification fine ash (CGFA) significantly impacts its subsequent processing and utilization. This paper proposes and investigates the use of microwave field heating to decarburize CGFA, exploiting its favorable microwave absorbing characteristics attributed to its composite structure comprising carbon, iron, and water. The experimental results demonstrate an 81% reduction in the required time and a 74% decrease in energy consumption (based on preliminary calculations) to achieve a decarburization rate of 95% compared to conventional thermal electric furnace calcination methods. The treated CGFA exhibits optimized mineral species, reduced electron binding energy, enhanced solubility, and increased heat release intensity during hydration, leading to improved reactivity of mineral phases in alkaline environments. Furthermore, when used as supplementary cementitious material, the activity index of CGFA shows a remarkable 21% increase in macroscopic performance testing. [ABSTRACT FROM AUTHOR]

Highlights • The differences between natural and artificial hydraulic lime mortars were revealed. • NHL mortar have preferable fluidity compared to the artificial lime mortars. • The mechanical properties of artificial lime mortar have advantages over NHL mortar. • A part of artificial lime mortars is nearby to NHL mortar in environmental resistance. • Three kinds of lime mortars have big difference in hydration and carbonation reaction. Abstract To evaluate the differences of properties between natural and artificial hydraulic lime mortars, the macro and micro properties of natural hydraulic lime (NHL2 and NHL5) mortars, white Portland cement-aerial lime-based (CL15 and CL25) mortars and slag-aerial lime-based (SL20 and SL40) mortars were studied through the examination of their physical and mechanical properties, environmental resistance properties, hardening mechanism and microstructure of lime mortars or pastes. The results show that the NHL mortars have preferable fluidity compared to the artificial CL and SL mortars, while the mechanical properties of artificial CL and SL mortars are advantageous compared to those of NHL mortar. In terms of environmental resistance, the water resistance of SL mortar is best, closely followed by the CL mortar, and the NHL mortar is relatively weak; moreover, CL mortar shows the best sulphate resistance, and SL mortar has the best alkali resistance. The hydration reaction (or pozzolanic reaction) and carbonization reaction could occur in the three kinds of hydraulic lime pastes, and the hydration reaction of the NHL and CL pastes mainly occur in the early stage of paste hardening (before 28 days), while the pozzolanic reaction of the SL paste reach a high degree at early hardening stage (28 days) and still maintains a certain reaction rate in the later period. The carbonation reaction process of the three kinds of lime pastes continues to the later period of the hardening, and the carbonation rate of SL pastes in the later stage would be obviously enhanced; furthermore, the carbonation degree of NHL paste is obviously higher than that of the CL and SL pastes. The different hydration-hardening process and mechanism of the three lime pastes lead to differences in the morphology and pore structure among them. There are more large-size pores in NHL5 paste (the pore volume in the range of pore diameter greater than 200 nm reaches 63.13%), while the pore size of the SL paste is relatively small (the pore volume in the range of pore diameter less than 100 nm reaches 44.15%). The porosity during the 180 days curing period was as follows: SL40 (27.32%) < CL25 (29.65%) < NHL5 (33.09%). [ABSTRACT FROM AUTHOR]

To improve the utilization efficiency and application property of smelting solid waste in blended cement, a ternary blended cement (Fuller-SS-S-C binder) containing high volume steel slag (SS) and granulated blast-furnace slag (GBFS or S) was designed and prepared based on Fuller distribution model. The results show that the cumulative distribution of Fuller-SS-S-C binder particles is close to Fuller distribution as a whole, but the particles of 0–15 μm, 15–30 μm, 30–45 μm and 45–80 μm fractions are SS-S-C (composite powder containing SS, S and cement), C (cement), SS-S (composite powder containing SS and S) and SS, respectively. The properties of Fuller-SS-S-C binder can be adjusted by changing compositions of SS-S-C in the range of 0–15 μm. Fuller-SS-S-C binders prepared have higher strength than reference blended cement, and their hydration heat contain three exothermic peaks and concentrate on after 15 hours. Compared with pure cement, the non-evaporable water content of Fuller-SS-S-C binder has great gap, but the pore size distribution of Fuller-SS-S-C binder is dominated by innocuous pores of less than 20 nm, moreover, the porosity, total pore volume and medium pore diameter of Fuller-SS-S-C binder are lower than those of reference blended cement and pure cement, indicating that Fuller-SS-S-C binder has dense microstructure. [ABSTRACT FROM AUTHOR]

• The hydration superposition effect of SSCP was clarified. • The microstructure of SSCP hydration products was analyzed. • The hydration mechanism of SSCP was revealed. Steel slag has great potential as a supplementary cementitious material, and often shows good effects when used in combination with granulated blast furnace slag (GBFS). In order to reveal the interaction law of steel slag and GBFS, the hydration superposition effect and mechanism were studied in this paper in terms of ion dissolution, hydration heat, hydration products, hydration degree, microstructure and mechanical properties. The results show that steel slag and GBFS have a significant hydration superposition effect, and the strength of the paste when the two are used in combination is much higher. The mechanical properties at the early and later ages are the best (16.5 MPa at 7 days and 31 MPa at 28 days) when the steel slag-to-GBFS ratio is 1:1 and 2:3, respectively. Steel slag-slag composite powder (SSCP) has three exothermic peaks, which are the dissolution peak, hydration peak of steel slag and pozzolanic ash reaction peak of GBFS (after 85 h), respectively. The fibrous and amorphous C-S-H gels and plate Ca(OH) 2 appear in the SSCP pastes at 3 days. Furthermore, the microstructure of hydration products consists of a number of fiber-like and particle-like C-S-H gels with widths ranging from 15 nm to 20 nm and lengths ranging from 50 nm to hundreds of nanometers. The C-S-H gels wrap the unhydrated mineral phase (UMP) to form a nucleus(UMP) - membrane (C-S-H) structure. The early hydration of steel slag would increase the pH and conductivity of the pore solution, promoting the dissolution of aluminosilicate glass in GBFS and pozzolanic ash reaction, at the same time, the consumption of Ca(OH) 2 by the pozzolanic ash reaction would promote the further hydration of steel slag. The synergistic hydration effect of SSCP would promote hydration and generate more hydration products to fill the pore structure, resulting in good hardening properties. [ABSTRACT FROM AUTHOR]

• The hydration process of ferroaluminate cement is tested and analyzed. • Gas permeability and chloride diffusion coefficient of FAC is much lower than OPC. • Pores with size of 10–100 nm have dominant effect on permeability and diffusivity. This study investigated the hydration process and durability properties of ferroaluminate cement (FAC). Hydration heat, hydration products, compressive strength, gas permeability and chloride diffusion coefficient were investigated experimentally for FAC mortar samples with different water-to-cement ratio (0.5, 0.45 and 0.4) and were compared with OPC mortar samples with the same mixing proportion. The mechanism of the difference in the durability of two cements was revealed from the perspective of pore size distribution and hydration products. The results show that FAC has a relatively fast hydration rate and the compressive strength at early age is larger than OPC. The gas permeability and chloride diffusion coefficient of FAC mortar samples are approximately 3–4 times lower than that of OPC mortar samples. The permeability and diffusivity of both FAC and OPC decrease significantly when the w/c decreases from 0.5 to 0.4. The main hydration products of FAC are ettringite, ferric hydroxide and aluminum hydroxide gel, large amounts of ettringite make FAC to form a dense structure, the proportion of the pores with pore size of 10–100 nm in FAC sample decreases greatly with compare to the OPC sample, which endows FAC superior impermeability properties. [ABSTRACT FROM AUTHOR]

• The chloride binding properties of geopolymer and Portland cement were compared. • The physical adsorption and chemical binding mechanism of geopolymer were revealed. • The evaluation of resistance to chloride ion diffusion of geopolymer was discussed. In this work, the chloride binding capacities and chloride diffusion resistance of alkali-activated fly ash and slag powder geopolymer systems prepared with seawater and coral sand are investigated. Through the macro tests (e.g., chloride ion binding ratio, electric flux, etc.), stripping C-S-H, C/N-A-S-H from anhydrous particles and a variety of microscopic tests (e.g., MIP, XRD, SEM-EDS), the chloride binding mechanism of ordinary Portland cement (OPC) and geopolymer are analyzed and compared. The result shows that the chloride binding capacity of geopolymer samples under standard curing is better than that of OPC samples under the same condition (for instance, the 28-day chloride binding coefficient of geopolymer (FS1): 83.372%, OPC (R1): 73.223%). And the binding of chloride ion can be improved to a certain extent by increasing the initial chloride concentration. Geopolymer bounds the chloride ions through physical absorption or chemical reaction with cement compositions. The porous structure of C/N-(A)-S-H gel and high content of Al element promote the chloride binding capacity. The additional porous coral sand can reduce the chloride resistance capacity of specimens. But with slag proportion increasing, the geopolymer shows better chloride resistance capacity (for example the chloride diffusion coefficient decreases by 98% from 152.61 m2/s to 2.86 m2/s when slag proportion increased from 10% to 90%). The chloride diffusivity of geopolymers measured by the electric flux method has a large deviation, which is not suitable for direct evaluating of resistance to chloride penetration of geopolymer system. [ABSTRACT FROM AUTHOR]

• The size of f-MgO in LFS is reduced by an order of magnitude after air quenching. • f-MgO/f-CaO in air-quenched MLFS can be consumed gradually in early hydration stage. • Air quenching treatment has an obvious improvement on the volume stability of LFS. Ladle furnace slag (LFS) has great potential as a new type of cementitious material, but the important value has not been effectively used at present. One of the main reasons is that the over-burned free MgO (f-MgO) and free CaO (f-CaO) phases in LFS would cause the volume expansion of material. In this study, the f-MgO and f-CaO phases in LFS are optimized by air quenching treatment. It was found that the size of f-MgO is reduced from 30 to 45 μm to 2.5–3.5 μm, which is about an order of magnitude lower. The f-CaO is distributed in the leaf-like morphology with smaller size in the range of 15–20 μm. The f-MgO and f-CaO in air-quenched modified LFS (MLFS) can be dispelled in the early hydration stage. Compared with LFS, the volume expansion of blended cement with 20% MLFS is reduced by more than 10%, showing an obvious improvement effect on volume stability. [ABSTRACT FROM AUTHOR]

With the development of the coal gasification industry, the comprehensive utilization of coal gasification fine slag (CGFS) has become increasingly important. This study explored the potential of producing non-sintered ceramsite by combining CGFS with blast furnace slag (BFS). The impacts of the alkali activator modulus, dosage, and BFS-CGFS ratio on the ceramsite's cylinder compressive strength, bulk density, apparent density, water adsorption ratio, hydration products, microstructure, and adsorption capacity were investigated. Moreover, the leaching behavior of heavy metals in acidic environments and the production costs were evaluated. The results indicated that the modulus and dosage of the alkali activator, along with the BFS-CGFS ratio, significantly affected the properties of the ceramsite. The cylinder compressive strength, bulk density, and apparent density of the ceramsite increased with the increase in the alkali activator dosage and modulus, but decreased as the BFS-CGFS ratio decreased. The water absorption rate behaved oppositely. With increasing alkali activator modulus and dosage, the ceramsite's adsorption capacity for iodine, COD Cr , and methylene blue first increased and then decreased, peaking at a modulus of 1.4 and a dosage of 12%, respectively. A reduced BFS-CGFS ratio increased the adsorption capacity of the ceramsite for iodine and COD Cr. Considering both mechanical and adsorption properties, the optimal composition for the ceramsite was found to be an alkali activator modulus of 1.4, a dosage of 12%, and a CGFS content of 70%. With this ratio, the use of ceramsite would not result in secondary environmental pollution. This study not only provided a new approach to enhance the utilization of CGFS but also avoided the use of calcination processes in producing ceramsite, demonstrating its potential in reducing environmental impact. [Display omitted] • Non-sintered ceramsite was prepared using alkali-activated CGFS and BFS. • C-(N)-A-S-H was one of the main hydration products of ceramsites. • Macropores and mesopores determined the adsorption performance. • Non-sintered ceramsites met the leaching requirements for heavy metals. [ABSTRACT FROM AUTHOR]

Hydraulic lime is an ancient building repair material, and its good early performance is necessary to ensure a successful application. In this study, hydraulic lime (metakaolin (MK)-air lime (AL), MK-AL) were prepared by the amount of MK was used for different mixtures in AL, which provided the materials with both hydraulicity and the ability to air harden. The early-age (before 28 days) properties of natural hydraulic lime (NHL5), AL and MK-AL (MK20-AL and MK40-AL) pastes were studied through an examination of their physical and mechanical properties, hydration heat, thermal properties and microstructure. The strength growth trend of the MK-AL paste was similar to that of the NHL5 paste, and the compressive strength of the MK40-AL paste reached 21.06 MPa at 28 days. There was only a carbonation reaction in the AL paste, C-S-H formed mainly by the hydration reaction of C 2 S in the NHL5 paste, the pozzolanic reaction and carbonation reaction occurred in the MK-AL pastes, and the carbonation reaction in the MK-AL pastes was at a low level before 28 days. The MK-AL pastes had a longer hydration stage than the NHL5 paste, and there were two exothermic hydration peaks during the pozzolanic reaction for the MK-AL pastes. Laminar Ca(OH) 2 and amorphous C-S-H gel comprised the skeleton in the NHL5 paste, and the large laminar Ca(OH) 2 structures that formed the skeleton were converted into an interweaved structure of the pozzolanic reaction products and carbonated products in the MK-AL pastes. There were many large pores (>200 nm) in the AL, NHL and MK20-AL pastes, while the pore size of the MK40-AL paste was relatively small (<100 nm). The porosity of all lime pastes had the following trend: NHL (38.96%) < MK40-AL (42.89%) < MK20-AL (45.47%) < AL (51.22%). • The strength growth of MK-AL paste are fast before 7 days and are similar NHL5 paste. • MK-AL pastes have a longer hydration stages compared with NHL5 paste. • The carbonation reaction degree of MK-AL pastes locate a lower level before 7 days. • Pore structure have a high correlation with mechanical property in MK-AL pastes. [ABSTRACT FROM AUTHOR]