Alkali Activation Reaction Research Articles

Evaluating Alkali Activation in Magnesium Slag Carbonization and Its Mechanism

In recent years, magnesium slag has been used as a raw material for solid waste treatment using the carbonization method and has proven to be promising in reducing carbon emissions. In this study, the alkali activation reaction was introduced to promote the carbonization of magnesium slag. The resulting mechanical properties, microstructural attributes, and carbonization mechanism were studied by varying the sodium hydroxide content, temperature, and carbon dioxide concentration during the reaction process. The results showed that the amounts of calcium hydroxide, C-S-H, and calcium carbonate in the reaction products increased with the sodium hydroxide content, which enhanced the compressive strength of the composite. However, it does not influence the carbonization mechanism with the increasing reaction temperature, which only elevates the reaction rate. With the increase in the carbon dioxide concentration during alkali activation, the carbonization reaction is dominated by the amount of CO2 dissolved in the reaction medium, and the carbonization mechanism is changed. Thus, a significant decrease in the calcium hydroxide content and a sharp increase in the calcium carbonate content in the products occurred, which significantly improved the compressive strength of the resulting magnesium slag composite. Among them, the maximum compressive strength is 6.83 MPa.

Optimal development and performance evaluation of electrolytic graphene oxide synergistic all-solid waste cementitious grouting material

The low-carbon and friendly alkali-activated cementitious (AACM) grouting material has a broad application potential in the field of grouting engineering due to its excellent workability and higher early strength and is expected to replace cement grouting material in the future. In this study, an AACM grouting material using electrolytic graphene oxide (EGO) synergistic ground granulated blast-furnace slag (GGBS)-fly ash (FA)-rice husk ash (RHA) solid waste was proposed. The optimal ratio was 0.025 % EGO, 8.13 % FA, 26.6 % RHA, and 65.27 % GGBS, which determined by the Analytic Hierarchy Process (AHP), Entropy Weight Method (EWP), and Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) methods. A systematic evaluation of the mechanical properties and impermeability of the proposed AACM grouting material was conducted by macro experiments (compressive strength, flexural strength and permeability) and micro experiments (XRD, SEM-EDS, Fourier Transform Infrared Spectrometer (FTIR) and Thermogravimetry Analysis (TG)). The results show that the increment of compressive strength and flexural strength for AACM grouting material with 0.025 % EGO compared to the cement water-glass grouting material were 161.2 % and 2.9 %, respectively, at 7-day. While the permeability coefficient compared to AACM grouting material without EGO decreased by 43.9 %. The XRD results show that the EGO reduced the intensity of AACM grouting material diffraction peaks, and FTIR analysis reveals that EGO increased the visibility of O-C-O characteristic peaks. These confirmed that EGO could enhance the degree of alkali activation reaction. The TG results indicate that the addition of EGO promoted the formation of carbonates, which strengthen the mechanical properties of AACM grouting material. The SEM-EDS results demonstrate that EGO increased the Ca/Si ratio, promoted the formation of highly polymerized hydration products.

Influence of calcium oxide and hydroxide on non-ferrous metallurgical slag hydration in alkaline environments

The search for new supplementary cementitious materials (SCMs) to reduce CO2 emissions has become increasingly vital in cement and concrete research. Non-ferrous metallurgical slag (NFMS), often overlooked due to their low pozzolanic and hydraulic reactivity, present a promising alternative, particularly given their enhanced reactivity in the presence of alkalis. This study explores the hydration behaviour of NFMS under varying concentrations of CaO, Ca(OH)2, and NaOH, with a focus on dissolution kinetics and phase evolution. 1 M and 6 M NaOH solutions were selected to examine the effect of calcium additives on NFMS hydration, representing scenarios without (1 M NaOH) and with (6 M NaOH) alkali activation reactions. In 6 M NaOH, the addition of CaO/Ca(OH)2 had a minimal impact on dissolution rates but significantly influenced phase assemblage, with CaO promoting strätlingite formation and 10 % Ca(OH)2/CaO leading to katoite. At higher replacement levels (20 % CaO/Ca(OH)2), phase formation was hindered, although microstructure densification persisted, accompanied by reduced strength. In 1 M NaOH, low concentrations of CaO/Ca(OH)2 enhanced Al and Si dissolution but had limited impact on phase assemblage. Higher CaO content favoured katoite formation, while Ca(OH)2 exhibited traces of hydrocalumite. Both additives improved microstructure, but CaO addition, associated with katoite formation, predominantly enhanced strength. The findings confirm that NFMS has significant potential as a cement replacement in hybrid systems utilizing high ratios of slag, Portland cement, and alkalis. By promoting the formation of Ca-Al phases, NFMS improves microstructure and strength, making it a viable and environmentally friendly alternative in construction materials.

Micromechanical and chemical characteristics of interfacial transition zone in alkali-activated slag concrete containing lightweight iron-rich aggregates

This study explored the time-varying alkali-activation effects of the lightweight aggregates (LWA) on the interfacial transition zone (ITZ) of the alkali-activated slag concrete with different curing ages, molar ratios, and alkali concentrations from 28 to 300 d. The improved micromechanical performance of the ITZ at 28 d stemmed from the early-age internal curing effect of the porous LWA. However, the post-28 d internal curing effect diminished, with the alkali-activation dominating the performance of the ITZ from 28 to 300 d. Although alkali-activated cement possessed early strength characteristics, the deconvolved phase results illustrated that alkali activation persisted in the ITZ between the LWA and cement from 28 to 300 d, leading to a high proportion of calcium silica aluminate hydrate. As a marker, Fe from the lightweight iron-rich aggregates mitigated into the alkali-activated cement, demonstrating the alkali-activated reaction between the LWA and alkali-activated slag matrix. Molecular dynamics simulations further characterized that the low content of Fe did not decrease the overall strength of the ITZ. The interfacial interaction energy revealed the alkali-activation between the LWA and cement compensated for the weakening of mechanical properties caused by Fe ions on the ITZ.

Effect of synthesis parameters on the alkali activation reaction degree and the relationship between reaction degree and microstructure of fly ash-based geopolymers

This study systematically explored the impact of various parameters on the alkali activation reaction degree of fly ash-based geopolymers (FABGs) using the acid solubility test method. Key parameters such as the alkali activator modulus (AAM), alkali dosage (AD), and water-to-fly ash ratio (W/FA) were considered. The micromorphology, phase composition, and pore characteristics of FABGs were also examined, and the relationship between the alkali activation reaction degree and these microstructural characteristics was analyzed. The alkali activation reaction was relatively rapid during the early curing stage but slowed down in the later stage. The influence of synthesis parameters on the alkali activation reaction degree ranked from highest to lowest as AAM, W/FA, and AD. According to Spearman correlation analysis, the alkali activation reaction degree of FABGs is positively correlated with AAM and AD, and negatively correlated with W/FA. As the alkali activation reaction degree increases, the number of pores, cracks, and partially reacted FA particles decreases, and the bonding between FA particles and the matrix becomes denser. FABGs with higher alkali activation reaction degrees exhibit greater mass loss at 100–700 °C, indicating higher production of gel phases. Additionally, the pores in FABGs are predominantly gel pores and transition pores. Notably, there is a negative correlation between porosity and the alkali activation reaction degree of FABGs.

Insights into microstructural alterations in alkali-activated materials incorporating municipal solid waste incineration fly ash

Municipal solid waste incineration fly ash (MSWI FA) is categorized as a hazardous waste with significant implications on environmental safety and human health. This study tailored three types of alkali-activated materials (AAMs) by using ground granulated blast-furnace slag (GGBS) and metakaolin (MK) for the low-carbon stabilization/solidification (S/S) of MSWI FA. The intricate interactions between MSWI FA and AAMs synthesized from Al-rich precursors and Ca-rich precursors were investigated to elucidate the microstructural alterations of AAM-MSWI FA systems. Comprehensive characterization techniques were conducted, including isothermal calorimeter, thermal gravimetric analysis, Fourier-transform infrared (FTIR), X-ray diffraction (XRD), and 27Al and 29Si nuclear magnetic resonance (NMR). The results revealed that the incorporation of MSWI FA significantly delayed alkali activation reactions, hindering the formation of aluminosilicate gel due to high contents of Cl and potentially toxic elements (PTEs) in the MSWI FA. High volume of dissolved Cl from MSWI FA would react with available Ca from MSWI FA and GGBS as well as Al from GGBS and MK to form Friedel’s salt, and this reaction was found to be more dominant in the Al-rich environment. Meanwhile, the C-(N-)A-S-H gel exhibited longer chain length in the Al-rich environment than in the Ca-rich environment. Overall, this study delivers microstructural insights into AAM-MSWI FA systems utilizing GGBS and MK as precursors. The results provide scientific groundwork for diverse practical applications of AAM-MSWI FA materials, thereby supporting the development of resource-efficient and low-carbon hazardous waste treatment strategies.

Addition of ceramic waste for the preparation of VA-based alkali-activated material with high temperature resistance

This study prepares volcanic ash (VA)-blast furnace slag (S) based alkali-activated materials (AAM) with the addition of ceramic waste for exposure to high temperatures (1000 °C). The temperature resistance of alkali-activated materials were described by measuring their surface morphology, gel structure and thermal damage degree, through NMR and UPV tests. At calcination temperature of 800 °C, the VA-based alkali-activated materials with ceramic waste shows ultrasonic velocity of 1962 m/s and a porosity of 17.30 %, indicating the prevention from gel structural collapse. As low calcination temperatures (≤600 °C), ceramic waste only functions as filler materials and reduces compressive strength of the alkali-activated materials. While at calcination temperature of 800 °C, there is an activity generated by the transformation of crystalline phases into amorphous phases in the ceramic waste, thus participates the alkali-activated reaction and increases compressive strength of the alkali-activated materials. At 1000 °C, the collapse of skeleton of the alkali-activated material is induced by thermal incompatibility of the matrix and thermal compression.

The design of ternary all-solid-waste binder for solidified soil and the mechanical properties, mechanism and environmental benefits of CGF solidified soil

Utilization of industrial solid waste to develop binder and solidified waste soil, which can achieve ‘waste control by waste’. Based on the alkali-activated mechanism and interaction mechanism of the binder-soil particles-water, the component distribution ratio design method of ternary all-solid-waste binder for solidified soil was constructed. The CGF all-solid-waste alkali-activated binders (CGF binders) are composed of general industrial solid waste, with which calcium carbide slag (CCR) as alkali activator, ground granulated blast furnace slag (GGBS) and fly ash (FA) as high and low-activity pozzolanic material respectively. Macro and microscopic tests were performed to reveal the mechanical properties and solidification mechanism as well as quantitatively evaluate the environmental and economic benefits of CGF solidified pure clay, pure silt, and pure sand (CGF solidified soils). The results revealed that the strength of CGF solidified soils was significantly affected by the alkali activator content and the activity of pozzolanic materials, and the strength of partially CGF solidified soils were higher than cement solidified soils under the same conditions. The relationship between binder-soil particles-water, viz., the alkali-activated reaction between binder and water, along with the pozzolanic reaction between the alkali activator and the clay particles jointly determined the strength and strength growth rate of the solidified soil. The strength of the optimal CGF solidified soils were 1.38–2.30 times higher than cement solidified soils, however, the carbon emission per unit strength and cost per unit strength of the cement solidified soil were 71.43–125.02 times and 3.53–5.88 times higher than the optimal CGF solidified soils, respectively. The findings can provide a reference for the design and development of solid waste-based binders suitable for solidified soils.

Evaluation of mechanical, physical and chemical properties of ecological modular soil-alkali activated bricks without Portland cement

With the growth of civil construction materials to mitigate environmental impacts and meet technical demands, modular soil-cement bricks have emerged as an alternative construction material in Brazil due to economic, social, and environmental reasons. However, the composition of Portland cement still generates environmental impacts due to CO2 emissions. Thus, this study aimed to produce modular bricks through alkali activation in real scale using a mixture of clay soil and sand, metakaolin (M) or blast furnace slag (BFS) as precursors, NaOH solution as a simple activator, or compound with hydrated lime. Thermal curing effects were analyzed. Water absorption, compressive strength, XRF, XRD, SEM and EDS analysis were performed, as well as Life Cycle Analysis (LCA). All bricks presented suitable water absorption values according to Brazilian standards. Groups with metakaolin and simple activator presented the lowest compressive strength since an incomplete geopolymerization was verified; however, when a compound activator was used, the compressive strength was highly increased. The BFS group presented the best overall performance under water absorption and compressive strength with mean values of 3.6 MPa and 13.4%, respectively. Microstructural analyses confirmed the development of microstructures such as Zeolite, Calcite and Hydrated Calcium Silicate from the alkali activation reactions. Alkali activated bricks presented at least 35% less CO2 emissions compared to ceramic bricks in LCA. Modular bricks made with MK or BFS and compound activator met all the requirements for their use, showing that these mixtures can be an alternative for sustainable brick production, with the reuse of industrial waste instead of Portland cement incorporation.

Ophthalmic glass lens waste as an alternative soluble silica source for alkali-activation reactions

This research study was aimed at assessing the potential use of glass powder (GW), from the production of optical lenses, as a substitute of commercial sodium silicate (SS), to produce fly ash-based alkaline cements. The dissolution of the GW and the subsequent activation were achieved either with a cleaning solution (CS) from the aluminium casting industry, and a commercial sodium hydroxide solution (SH) so as to. Firstly, GW dissolution with CS and SH was evaluated at different time and temperatures, i.e.,16 h, 3, 7 and 28 days at 20 °C and 16 h at 20, 40, 60 and 80 °C, to find the best dissolution rate, which an optimum point was observed when CS was the dissolving agent. Then, several pastes were synthesized and cured for 7 days at 50 °C to assess their mechanical behaviour and alkaline-activated gel formation by compressive strength test. Furthermore, reaction products were characterized by X-ray diffraction (XRD) and electron microscopy (SEM/EDX). The observations reveal that although SH solution acted well to dissolve GW, so that the compressive strength was close to that of SS, CS also showed reasonable potential to be used as a dissolving agent for GW, rendering a cheap and environmentally friendly alternative activator. Microstructural analysis also illustrated the rise in the crystallinity of the reaction products obtained from industrial by-products, i.e., GW and CS.

Effects of Waste Glass Powder on Rheological and Mechanical Properties of Calcium Carbide Residue Alkali-Activated Composite Cementitious Materials System.

As a municipal solid waste, waste glass undergoes pozzolanic activity when ground to a certain fineness. In this paper, calcium carbide residue (CCR) and Na2CO3 were used as composite alkali activators for a glass powder-based composite cementitious system. A total of 60% fly ash (FA) and 40% ground granulated blast furnace slag (GGBS) were used as the reference group of the composite cementitious material system, and the effects of 5%, 10%, 15%, and 20% glass powder (GP) replacing FA on the rheological behavior, mechanical properties, and microstructure of alkali-activated composite cementitious systems were investigated. The results showed that with the increase in GP replacing FA, the fluidity of the alkali-activated materials gradually decreased, the shear stress and the equivalent plastic viscosity both showed an increasing trend, and the paste gradually changed from shear thinning to shear thickening. Compared with the reference sample, the fluidity of the alkali-activated material paste with a 20% GP replacement of FA was reduced by 15.3%, the yield shear stress was increased by 49.6%, and the equivalent plastic viscosity was elevated by 32.1%. For the 28d alkali-activated material pastes, the compressive strength and flexural strength were increased by 13% and 20.3%, respectively. The microstructure analysis showed the substitution of FA by GP promoted the alkali-activated reaction to a certain extent, and more C-A-S-H gel was formed.

Effect of Solid Sodium Silicate on Workability, Hydration and Strength of Alkali-Activated GGBS/Fly Ash Paste

Based on economic and environmental considerations, the recycling economy of mineral waste has been found to have great potential and economic benefits worldwide, in which alkali-activated cementitious materials are one of the main developing directions. The alkali activators commonly used in alkali-activated cementitious materials are the composite activators of sodium silicate solution and solid sodium hydroxide, which not only need to deal with high viscosity and corrosive chemicals, but also need to be prepared in advance and properly stored. In this paper, ground granulated blast furnace slag (GGBS) and fly ash were used as precursors, while solid sodium silicate powder was applied as the alkali activator. In addition, the precursors were mixed with the activator in advance and activated by adding water to prepare alkali-activated GGBS/fly ash cement. The influence of precursor components, the dosage of the alkali activator and the liquid–solid ratio on the working performance, mechanical strength and hydration process of alkali-activated cement was studied. The results showed that the further incorporation of GGBS accelerated the alkali activation reaction rate and improved the strength of the specimen. However, in the specimen with GGBS as the main component of the precursor, the main hydration product was C-A-S-H gel, which was different in the structural order and quantity. The compressive strength indicated that there was the best amount of activator to match it in terms of the precursor with certain components. A too high or too low amount of activator will hinder the alkali activation reaction. This study can provide some significant reference material for the use of solid alkali activators in alkali-activated cementitious materials.

Effects of phosphogypsum substitution on the performance of ground granulated blast furnace slag/fly ash-based alkali-activated binders

Phosphogypsum (PG) is a byproduct of the phosphate fertilizer industry. Using PG waste to produce environmentally friendly building materials is becoming a desirable waste recovery method. However, unprocessed PG contains impurities, which often impedes its application in the construction industry. Considering that PG can provide Ca2+ and SO42− to a reaction system, this study develops an economic and environmental approach for optimizing the performance of PG-based alkali-activated binders (PGAABs) based on the combined use of PG, ground granulated blast furnace slag (GGBFS) and fly ash as precursors. An experimental investigation was carried out to understand the effects of PG content, Na2O content (M+) and alkali modulus (AM) on the properties of fresh and hardened PGAABs. The X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, mercury intrusion porosimetry (MIP), and scanning electron microscopy (SEM)/energy-dispersive X-ray spectroscopy (EDX) results showed that using PG as a partial substitute for GGBFS in the precursors facilitated the alkali-activated reaction. The compressive strength of PGAABs cured at room temperature increased with increasing PG content, while the setting time decreased with increasing PG content. Compared with the specimen without PG, the PGAABs required lower activator doses to obtain high compressive strengths. Leaching results also confirmed that using PGAAB with 10% PG content can result in cost-related and environmental benefits.

Effect of waste oyster shell powder on the properties of alkali-activated slag–waste ceramic geopolymers

The ceramic and oyster farming industries produce large amounts of waste ceramics and oyster shells. Meanwhile, alkali-activated materials are less environmentally impacted materials with the potential to replace Portland cement. Adding ceramic powder (CP) and waste oyster shell powder (WOS) to alkali-activated materials can relieve the pressure on landfills and protect the environment, thereby having important implications. This study aims to add WOS to alkali-activated adhesives and investigate their effects on the properties of the samples. The blast furnace slag and ceramic powder were partially replaced by 0–20 wt% WOS. The specimens for control, 10% WOS, and 20% WOS are named as WOS-0, WOS-10, and WOS-20, respectively. Experimental studies on the compressive strength testing, heat of hydration, ultrasonic pulse velocity (UPV), thermogravimetric (TG) analysis, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and electrical resistance rate were performed. The experimental results are as follows: (1) An increase in the WOS substitution rate increased the hydration heat release rate and decreased the compressive strength. At 3 days of age, the compressive strength of the WOS-20 sample decreased by 4.3 MPa compared with the WOS-0 sample. (2) UPV and resistivity decreased with increasing WOS substitution. At 3 days of age, the UPV of the WOS-20 sample decreased by 0.11 km/s compared with the WOS-0 sample. (3) The TG results showed that WOS participated in the alkali-activated reaction. For the WOS-20 sample, the amount of calcium carbonate decreased by 2.9% as the age increased from 3 days to 28 days. (4) XRD and FT-IR spectra showed the intensified carbonate peak with the increase in the WOS content. These findings suggest that CP and WOS can be used as complementary gelling agents for alkali-activated materials.

Recent progress in understanding setting and hardening of alkali-activated slag (AAS) materials

Alkali-activated slag (AAS with type of slag being blast-furnace slag) binders possesses substantially different hydration mechanisms from Portland cement (PC) binders, leading to distinct setting and hardening behavior. Due to the highly amorphous nature of both of raw materials and hydration products, the characterization of hydrate assemblages and microstructural development of AAS materials is challenging. In the past decades, there has been increasing investigation interests in disclosing the nature of aluminum and sodium containing calcium silicate hydrate gel with undefined stoichiometry (C-(N-)A-S-H) along with the existence of intimately intermixed secondary phases. This paper provides an overview on the recent research progress and understanding of the complex alkali-activation reaction process from the perspectives of hydration kinetics, products and microstructure development. This is critical to the interpretation and control of setting and hardening of AAS materials at the early age. In addition, based on available information, hydration mechanisms of different AAS binders are proposed. For such a complex system, thermodynamic modelling and molecular dynamic modelling have shown their power to correlate the microstructure development and the macroscale behavior of AAS materials, which are discussed in this paper.

Engineering and micro-properties of alkali-activated slag pastes with Bayer red mud

• Red mud alleviates the flash setting phenomenon of AASR pastes. • Red mud exerted a positive effect on the compressive strengths of AASR pastes. • A proper amount of red mud enabled promoting alkali-activation of slag. • RM-donated alkali promoted the gel products formation of AASR pastes. In this study, we produced alkali-activated slag/red mud (AASR) pastes using sodium silicate as the alkali activator. The effects of Bayer red mud (RM) on the engineering and micro-properties of alkali-activated slag pastes were investigated. It was found that the decreased fluidity and the increased setting time of the fresh AASR pastes were achieved through the delayed gel coagulation of RM. The maximum compressive strength of the hardened AASR paste arrived at 89.93 MPa with an optimal proportion (i.e., R40S60). Furthermore, the increases in hydration heat peaks of AASR pastes were observed in some mixes (e.g., R20S80 and R40S60), which verified the appropriate amounts of RM enabled promoting the alkali-activated reaction of slag. Besides, the polymerization and hydration products (C-(N)-A-S-H gels and ettringite) of AASR pastes were elaborated through spectroscopic and micro-morphologic analyses.

Optimized formulation of waterproof coating based on polymer and sodium silicate-activated GGBS using Box Behnken design - Selection of additives

Waterproof coating based on polymer and sodium silicate-activated ground granulated blast-furnace slag (PSS-GGBS waterproof coating) is a kind of new two-component waterproof coating, which is expected to have a promising application in building field because of simple construction, high strength, and good durability. Additives plays a vital role in determining the properties of PSS-GGBS waterproof coatings. Thus, the optimum proportion of various additives for the preparation of waterproof coatings was designed via the response surface methodology (RSM) to enhance mechanical properties. Results show that the optimal dosage of the defoamer, silicone leveling agent, and dispersant is accounted for 0.86 wt%, 0.56 wt%, and 0.56 wt% of the liquid phase, respectively. In this case, the tensile strength and breaking elongation of the waterproof coating reach 2.40 MPa and 108.84%, respectively. The experiment results are in full agreement with the corresponding predicted data, and the waterproof coating fulfills the criteria of type Ⅱ in standard GB/T 23445–2009. The crosslinking between polymer latex and sodium silicate activated GGBS was more sufficient after adding additives. The dense C–S–H gels and CaCO3 crystals with a strong mechanical bond, which is due to improvement of the degree of alkali-activated reaction induced by the addition of additives, contribute a high mechanical property to coatings.

Microstructure and macro properties of sustainable alkali-activated fly ash mortar with various construction waste fines as binder replacement up to 100%

Utilizing construction waste fines as eco-friendly binder for sustainable alkali-activated materials provides new approach to recycling construction waste. This work investigated the characterization of alkali-activated fly ash mortar (AAM) incorporating construction waste fines at varied types and replacement levels. The results showed that incorporating waste paste powder containing abundant hydrated products refined the pore size of AAM, but mixing waste mortar powder and waste concrete powder that contained massive inert quartz and calcite adversely affected the alkali-activated reaction and pore structure of AAM. The incorporation of construction waste fines was found to reduce the fluidity but increased the drying shrinkage of AAM. At identical replacement level of construction waste fines, the waste paste powder incorporated AMM has lower fluidity and greater drying shrinkage than the waste mortar powder or waste concrete powder incorporated AAM. Substituting waste paste powder for fly ash improved the mechanical strength of AAM, but the strength decreased as waste mortar powder or waste concrete powder was incorporated. Particularly, the AAM blended with 100% construction waste fines still owned good strength. Mixing construction waste powder reduced the chloride diffusion coefficient and chloride ingress depth of AAM, and the waste paste powder mixed AAM had better chloride resistance than the waste mortar powder or waste concrete powder mixed AAM. Therefore, the hydrated products in construction waste fines was revealed to benefit the micro-characteristics of alkali-activated materials, and optimizing the type and replacement level of construction waste fines can achieve sustainable AAM with good mechanical strength and chloride ingress resistance.

The effect of sodium citrate on NaOH-activated BFS cement: Hydration, mechanical property, and micro/nanostructure

This paper presents a study on the effect of sodium citrate solution (0.25M, 0.5M, 0.75M) on the hydration process and microstructure evolution of NaOH-activated blast furnace slag (BFS) paste. The setting behavior, flowability, mechanical strength, hydration kinetics, and micro/nanostructure characteristics were investigated through multiple tests—such as Vicat test, mini-slump test, x-ray diffraction, spectroscopy analysis, nuclear magnetic resonance, and mercury intrusion porosimetry—to reveal the hydration mechanism of NaOH-activated BFS paste in presence of sodium citrate. The results indicate that the citrate ions retarded the hydration process and contributed significantly to slag dissolution and precipitation of hydration products during the alkali-activated reaction process. The microstructure build-up from the early stage (3 days) to the mature stage (28 days) underwent a different process, resulting in a more densified and less porous matrix with higher compressive strength. However, no significant changes were observed in the type of hydration products and their nanostructural characteristics.

Reaction kinetics, microstructure and phase evolution of alkali-activated Si-Mn slag during early age

Alkali-activated material with Si-Mn slag (SiMnS) as precursor is regarded as an efficient way of resource utilization in large-scale and green mode. This study aims to investigate the reaction kinetics, microstructure, and phase evolution of alkali-activated SiMnS during the early age. The reaction kinetics of SiMnS activated by water glass with different modulus was studied by isothermal calorimetry, the phase and the microstructure evolution of reaction products from alkali-activated SiMnS at typical alkali activation reaction (AAR) times (15 min, 30 min, 1 h, 3 h, 12 h, and 24 h) were studied by XRD, FTIR, SEM, BET, and thermogravimetric experiments. Reaction kinetics analysis showed that alkali-activated SiMnS exhibited two main exothermic processes attributing the generation of Si-rich gel (mainly C-S-H) and Al-rich gel (mainly C(N)-A-S-H) respectively. The alkalinity and existence form of polymeric silicate of alkaline activator (AA), which depend on the modulus of AA, determined the intensity of AAR and the characteristics of AAR process respectively. Characterization results of samples indicated that alkali-activated SiMnS could be divided into three steps: formation of Si-rich gel, formation of Al-rich gel, increase of gel polymerization degree, and maturation, respectively. SiMnS can be an alternative raw material in the alkali-activated application.