The Decarbonization of Construction—How Can Alkali-Activated Materials Contribute?

1.Introduction and context Enormous emphasis is currently being paid to the decarbonization of the global built environment as a leading priority for the engineering community and related industrial sectors[1].One of the main contributors to the overall emissions footprint of the built environment-and thus a cornerstone of efforts to achieve decarbonization-is the emissions profile of construction materials during their production and utilization.The cement and concrete sector is the largest-volume contributor to the emissions incurred in meeting the world’s construction material needs and is therefore targeted in the discussion of the deep,rapid decarbonization that must be achieved in order to minimize irreversible damage to the Earth and its ecosystems.

Enhanced dealkalization of bauxite residue through calcium-activated desulfurization gypsum

A novel integrated approach to remove the free alkalis and stabilize solid-phase alkalinity by controlling the release of Ca from desulfurization gypsum was developed.The combination of recycled FeCl_(3)solution and EDTA activated desulfurization gypsum lowered the bauxite residue pH to 7.20.Moreover,it also improved the residual Ca state,with its contribution to the total exchangeable cations increased(68%-92%).Notably,the slow release of exchangeable Ca introduced through modified desulfurization gypsum induced a phase transition of the alkaline minerals.This treatment stabilized the dealkalization effect of bauxite residue via reducing its overall acid neutralization capacity in abating pH rebound.Hence,this approach can provide guidance for effectively utilizing desulfurization gypsum to achieve stable regulation of alkalinity in bauxite residue.

Effect of the Retarder on Initial Hydration and Mechanical Properties of the"one-step"Alkaliactivated Composite Cementitious Materials

This paper studied the effects of different retarders on the performance of the"one-step"alkali-activated composite cementitious material(ACCM)which is composed of ground granulated blast slag(GGBS)and fly ash(FA),and analyzed its mechanical properties,hydration mechanism,and retardation mechanism.The effects of retarders on the hydration products,mechanical properties,and hydration kinetics of ACCM were investigated using XRD,SEM,FTIR,EDS,and thermoactive microcalorimetry.The results showed that Na_(2)B_(4)O_(7)·10H_(2)O(B)delayed the exotherm during the alkali activation process and could effectively delay the setting time of ACCM,but the mechanical properties were slightly decreased.The setting time of ACCM increased with the increase in SG content,but the mechanical properties of ACCM decreased with the increase in SG content.C1_(2)H_(22)O_(11)(CHO)could effectively delay the hydration reaction of ACCM and weakly enhanced the compressive strength.H_(3)PO_(4)(HP)at a concentration of 0.05 mol/L had a certain effect on ACCM retardation,but HP at a concentration of 0.07 and 0.09 mol/L had an effect of promoting the setting and hardening time of ACCM.

Fundamental Study on Alkali-Activated Slag System with Sodium Carbonate or Calcium Hydroxide

Cement as a building material, has high fluidity, compressive strength, and durability, but carbon dioxide emissions during cement production are a major problem. As one of the countermeasures, alkali-activated cement using blast furnace slag powder with alkaline stimulants is considered to be a very promising solution for reducing carbon dioxide emissions, but there is a lack of information about the fundamental properties of alkali-activated materials. This study presents an experimental investigation of the fundamental properties of an alkali-activated slag system with sodium carbonate (NC) and calcium hydroxide (CH). The effects of calcium sulfo-aluminate (CSA) and shrinkage reducing agent (SRA) on the properties of blast furnace slag (BFS) based alkali-activated mixture were also investigated. In the experiments, fundamental characteristics including compressive strength, drying shrinkage, and water penetration tests of mortar were evaluated. Porosity, pH, and ignition loss were measured to verify the effectiveness of the materials. The experimental investigation revealed that the compressive strength was increased with the increasing replacement rates of NC in the BFS mortar, and in the case of water to BFS ratio of 0.45 with sodium carbonation addition contents 10 wt.%, the compressive strength for 28 days of curing reaches more than 50 MPa. Low water to BFS ratio and higher addition ratio of NC had a positive effect on the compressive strength development of mortar. Incorporating NC into BFS would affect the decrease in porosity and increase in ignition loss, leading to higher compressive strength. There was a negligible change to the compressive strength, porosity, pH, and ignition loss of BFS samples made with CH, thus, the addition rates of CH to BFS have no or little significant effect on the fundamental properties of alkali-activated cement. From the results of drying shrinkage and water penetration tests, the addition of NC and CH only to BFS exhibited poor drying shrinkage and water penetration characteristics. However, these problems may be overcome due to the use of CSA or SRA in the alkali-activated system made with NC or CH.

Selective oxidation of glycerol to lactic acid over activated carbon supported Pt catalyst in alkaline solution

Pt/activated carbon （Pt/AC） catalyst combined with base works efficiently for lactic acid production from glycerol under mild conditions. Base type （LiOH, NaOH, KOH, or Ba（OH）2） and base/glycerol molar ratio significantly affected the catalytic performance. The corresponding lactic acid selectivity was in the order of LiOH〉NaOH〉KOH〉Ba（OH）2. An increase in LiOH/glycerol molar ratio ele‐vated the glycerol conversion and lactic acid selectivity to some degree, but excess LiOH inhibited the transformation of glycerol to lactic acid. In the presence of Pt/AC catalyst, the maximum selec‐tivity of lactic acid was 69.3% at a glycerol conversion of 100% after 6 h at 90 °C, with a Li‐OH/glycerol molar ratio of 1.5. The Pt/AC catalyst was recycled five times and was found to exhibit slightly decreased glycerol conversion and stable lactic acid selectivity. In addition, the experimental results indicated that reaction intermediate dihydroxyacetone was more favorable as the starting reagent for lactic acid formation than glyceraldehyde. However, the Pt/AC catalyst had adverse effects on the intermediate transformation to lactic acid, because it favored the catalytic oxidation of them to glyceric acid.

Achieving high-efficient photocatalytic persulfate-activated degradation of tetracycline via carbon dots modified MIL-101(Fe)octahedrons

The synergistic reaction of photocatalysis and advanced oxidation is a valid strategy for the degradation of harmful antibiotic wastewater.Herein,carbon dots(CDs)modified MIL-101(Fe)octahedrons to form CDs/MIL-101(Fe)composite photocatalyst was synthesized for visible light-driven photocatalytic/persulfate(PS)-activated tetracycline(TC)degradation.The electron spin resonance(ESR)spectra,scavenging experiment and electrochemical analysis were carried out to reveal that the high visible light-driven photocatalytic degradation activity of TC over CDs/MIL-101(Fe)photocatalysts is not only ascribed to the production of free active radicals in the CDs/MIL-101(Fe)/PS system(·OH,·SO_(4-),^(1)O_(2),h^(+)and·O_(2)^(-))but also attributed to the consumption of electrons caused by the PS,which can suppress the recombination of photo-generated carriers as well as strong light scattering and electron trapping effects of CDs.Finally,the possible degradation pathways were proposed by analyzing intermediates via liquid chromatography-mass spectrometry technique.This research presents a rational design conception to construct a CDs/PS-based photocatalysis/advanced oxidation technology with high-efficient degradation activity for the remediation of organic antibiotic pollutant wastewater and for the improvement of carrier transport kinetics of photocatalysts.

Solidification/Stabilization of Zinc-lead Tailings by Alkali Activated Slag Cement

An appropriate proportion of alkali activated slag cement, abbreviated as AASC later, was determined based on strength test of paste specimens. Results showed that AASC prepared from 14% low modulus water glass and blast furnace slag presented its compressive strength of hardened cement paste of 69.6, 84.0 and 91.8 MPa at 3, 7, and 28 d curing ages respectively. Flowability of the fresh railings-cement pastes and the strength development of hardened tailings-cement paste were also tested both in the cases with addition of AASC and Portland cement. The fresh tailings-cemant paste added with AASC presented much better flowability and the corresponding hardened paste presented higher compressive strength, especially the long term strength, than those added with Portland cement. Therefore, tallings paste added with AASC allowed lager solid content than that of Portland cement in order to keep the similar flowability. SEM observation on the microstructure of the hardened tailings-AASC mixture pastes showed obvious cementation effect. MIP measurements also showed that the total porosity of the hardened tailings-cement pastes decreased, and the portion of larger pore also decreased when the dosage of AASC increased. It is believed that AASC is more suitable to be used as a binder for the stabilization of zinc-lead railings and for its backfilling operation than Portland cement.

Effects of biochar-amended alkali-activated slag on the stabilization of coral sand in coastal areas

Coral sand is widely encountered in coastal areas of tropical and subtropical regions.Compared with silica sand,it usually exhibits weaker performance from the perspective of engineering geology.To improve the geomechanical performance of coral sand and meet the requirement of foundation construction in coastal areas,a novel alkali activation-based sustainable binder was developed.The alkaliactivated slag(AAS)binder material was composed of ground granulated blast-furnace slag(GGBS)and hydrated lime with the amendment of biochar,an agricultural waste-derived material.The biocharamended AAS stabilized coral sand was subjected to a series of laboratory tests to determine its mechanical,physicochemical,and microstructural characteristics.Results show that adding a moderate amount of biochar in AAS could improve soil strength,elastic modulus,and water holding capacity by up to 20%,70%,and 30%,respectively.Moreover,the addition of biochar in AAS had a marginal effect on the sulfate resistance of the stabilized sand,especially at high biochar content.However,the resistance of the AAS stabilized sand to wet-dry cycles slightly deteriorated with the addition of biochar.Based on these observations,a conceptual model showing biochar-AAS-sand interactions was proposed,in which biochar served as an internal curing agent,micro-reinforcer,and mechanically weak point.

Morphology Difference between the Alkali Activated Cement and Portland Cement Paste on Multi-scale

The features of alkali activated slag（AAS） and portland cement （PC） were observed on multi-scale,the crack and fracture sections were observed with naked eyes,and SEM and AFM were used to study the structure morphology differences between PC and AAS on micrometer to nano meter scale.The experimental results indicated that the AAS paste had soil like fracture texture and it was composed of mainly C-S-H gel but lacks of crystals,and it had a very strong tendency to shrink and crack.AAS paste is much denser and more homogeneous than PC,and on the nano scale C-S-H nano particle in the AAS paste is much smaller and packs much denser than PC paste.

Setting and Strength Characteristics of Alkali-activated Carbonatite Cementitious Materials with Ground Slag Replacement

The effect of the ground granulated blast-furnace slag （ GGBFS ） addition, the modulus n （ mole rutio of SiO2 to Na2O ） and the concentrution of sodium silicate solution on the compressive strength of the material, i e alkuli-activated carbonatite cemeutitious material （ AACCM for short ） was investiguted. In addition, it is found that barium chloride has a sutisfiwtory retarding effect on the setting of AACCM in which more than 20% （ by mass ） ground carbonatite was replaced by GGBFS. As a result, a cementitious material, in which ground carbonatite rock served as dominative starting material, with 3-day and 28-day compressive strength greuter them 30 MPa and 60 MPa and with continuous strength gain beyond 90 days was obtained.

High adsorption selectivity of activated carbon and carbon molecular sieve boosting CO_(2)/N_(2) and CH_(4)/N_(2) separation

Flue gas and coal bed methane are two important sources of greenhouse gases.Pressure swing adsorption process has a wide range of application in the field of gas separation,and the selection of adsorbent is crucial.In this regard,in order to assess the better adsorbent for separating CO_(2) from flue gas and CH_(4) from coal bed methane,adsorption isotherms of CO_(2),CH_(4) and N_(2) on activated carbon and carbon molecular sieve are measured at 303.15,318.15 and 333.15 K,and up to 250 kPa.The experimental data fit better with Langmuir 2 compared to Langmuir 3 and Langmuir-Freundlich models,and Clausius-Clapeyron equation was used to calculate the isosteric heat.Both the order of the adsorbed amount and the adsorption heat on the two adsorbents are CO_(2)>CH_(4)>N_(2).The adsorption kinetics are calculated by the pseudo-first kinetic model,and the order of adsorption rates on activated carbon is N_(2)-CH_(4)>CO_(2),while on carbon molecular sieve,it is CO_(2)-N_(2)>CH_(4).It is shown that relative molecular mass and adsorption heat are the primary effect on kinetics for activated carbon,while kinetic diameter is the main resistance factor for carbon molecular sieve.Moreover,the adsorption selectivity of CH_(4)/N_(2) and CO_(2)/N_(2) were estimated with the ideal adsorption solution theory,and carbon molecular sieve performed best at 318.15 K for both CO_(2) and CH_(4) separation.The study suggested that activated carbon is a better choice for separating flue gas and carbon molecular sieve can be a strong candidate for separating coal bed methane.

Magnesia Modification of Alkali-Activated Slag Fly Ash Cement

A new type of magnesia modification alkali-activated cement was prepared, the strength, setting time, shrinkage ratio and cracking behavior, as well as the composition and structure of the hydration product were investigated. The results indicate that the setting time of this cement is similar to that of the ordinary commercial cements; its strength reaches the standard of 42.5 degree cement, its cracking resistance has been remarkably improved because of the micro-aggregate effect of fly ash and shrinkage compensating of magnesia.

Mechanical Property and Microstructure of Alkali-activated Yellow River Sediment-Coal Slime Ash Composites

This work focuses on the production of a new composite material using Yellow River sediment and coal slime ash via alkali-activating method. XRD, FTIR and SEM/EDS were used to characterize the alkali-activated products and microstructure of the composite material. Compressive strength was tested to characterize the mechanical property of the composite material. It is found that the compressive strength of the Yellow River sediment-coal slime ash composites increases as the added Ca（OH）_2 content grows. The compressive strength increases fast in the early stage but slowly after 28 days. The strength of the composites can be significantly improved via the addition of small amount of Na OH and gypsum. The products（C-S-H, ettringite and CaCO_3）, especially C-S-H, make much contribution to the enhancement of strength. The highest strength of the composites can reach 14.4 MPa after 90 days curing with 5% Ca（OH）_2, 0.2% NaOH and 7.5% gypsum. The improved properties of the composites show great potential of utilizing Yellow River sediment for inexpensive construction materials.

Thermal pretreatment of willow branches impacts yield and pore development of activated carbon in subsequent activation with ZnCl_(2) via modifying cellulose structure

Development of pore structures of activated carbon(AC)from activation of biomass with ZnCl_(2) relies on content and structure of cellulose/hemicellulose in the feedstock.Thermal pretreatment of biomass could induce dehydration and/or aromatization to change the structure of cellulose/hemicellulose.This might interfere with evolution of structures of AC,which was investigated herein via thermal pretreatment of willow branch(WB)from 200 to 360℃and the subsequent activation with ZnCl_(2) at 550℃.The results showed that thermal pretreatment at 360℃(WB-360)could lead to substantial pyrolysis to form biochar,with a yield of 31.9%,accompanying with nearly complete destruction of cellulose crystals and remarkably enhanced aromatic degree.However,cellulose residual in WB-360 could still be activated to form AC-360 with specific surface area of 1837.9 m~2·g^(-1),which was lower than that in AC from activation of untreated WB(AC-blank,2077.8 m~2·g^(-1)).Nonetheless,the AC-200 from activation of WB-200 had more developed pores(2113.9 m~2·g^(-1))and superior capability for adsorption of phenol,due to increased permeability of ZnCl_(2) to the largely intact cellulose structure in WB-200.The thermal pretreatment did increase diameters of micropores of AC but reduced the overall yield of AC(26.8%for AC-blank versus 18.0%for AC-360),resulting from accelerated cracking but reduced intensity of condensation.In-situ infrared characterization of the activation showed that ZnCl_(2) mainly catalyzed dehydration,dehydrogenation,condensation,and aromatization but not cracking,suppressing the formation of derivatives of cellulose and lignin in bio-oil.The thermal pretreatment formed phenolic-OH and C=O with higher chemical innerness,which changed the reaction network in activation,shifting morphology of fibrous structures in AC-blank to“melting surface”in AC-200 or AC-280.

Waste Activated Sludge Alkaline Fermentation Liquid as Carbon Source for Biological Nutrients Removal in Anaerobic Followed by Alternating Aerobic-Anoxic Sequencing Batch Reactors

Activated sludge process has been widely used to remove phosphorus and nitrogen from wastewater. However,the nitrogen and phosphorus removal is sometimes unsatisfactory due to the low influent COD.Another problem with the activated sludge process is that large amount of waste activated sludge is produced,which needs further treatment.In this study,the waste activated sludge alkaline fermentation liquid was used as the main carbon source for phosphorus and nitrogen removal under anaerobic followed by alternating aerobic-anoxic conditions,and the results were compared with those using acetic acid as the carbon source.The use of alkaline fermentation liquid not only affected the transformations of phosphorus,nitrogen,intracellular polyhydroxyalkanoates and glycogen, but also led to higher removal efficiencies for phosphorus and nitrogen compared with acetic acid.It was observed that ammonium was completely removed with either alkaline fermentation liquid or acetic acid as the carbon source. However,the former resulted in higher removal efficiencies for phosphorus(95%)and nitrogen(82%),while the latter showed lower ones(87%and 74%,respectively).The presence of a large amount of propionic acid in the alkaline fermentation liquid was one possible reason for its higher phosphorus removal efficiency.Exogenous instead of endogenous denitrification was the main pathway for nitrogen removal with the alkaline fermentation liquid as the carbon source,which was responsible for its higher nitrogen removal efficiency.It seems that the alkaline fermentation liquid can replace acetic acid as the carbon source for phosphorus and nitrogen removal in anaerobic fol- lowed by alternating aerobic-anoxic sequencing batch reactor.

Fate and Behavior of Tetracycline Resistance Genes in Activated Carbon Adsorption

The accessibility of tetracycline resistance gene (tetG) into the pores of activated carbon (AC), as well as the impact of the pore size distribution (PSD) of AC on the uptake capacity of tetG, were investigated using eight types of AC (four coal-based and four wood-based). AC showed the capability to admit tetG and the average reduction of tetG for coal-based and wood-based ACs at the AC dose of 1 g·L-1 was 3.12 log and 3.65 log, respectively. The uptake kinetic analysis showed that the uptake of the gene followed the pseudo-second-order kinetics reaction, and the uptake rate constant for the coal-based and wood-based ACs was in the range of 5.97 × 10-12 - 4.64 × 10-9 and 7.02 × 10-11 - 1.59 × 10-8 copies·mg-1·min-1, respectively. The uptake capacity analysis by fitting the obtained experiment data with the Freundlich isotherm model indicated that the uptake constant (KF) values were 1.71 × 103 - 8.00 × 109 (copies·g-1)1-1/n for coal-based ACs and 7.00 × 108 - 3.00 × 1010 (copies·g-1)1-1/n for wood-based ones. In addition, the correlation analysis between KF values and pore volume as well as pore surface at different pore size regions of ACs showed that relatively higher positive correlation was found for pores of 50 - 100 Å, suggesting ACs with more pores in this size region can uptake more tetG. The findings of this study are valuable as reference for optimizing the adsorption process regarding antibiotic resistance-related concerns in drinking water treatment.

Properties of Activated Carbons from Sugarcane Leaves and Rice Straw Derived Charcoals by Activation at Low Temperature via KMnO_(4)Pre-Oxidation-Hydrolysis

Activated carbon preparation from sugarcane leaves and rice straw by carbonization(250℃–400℃)and activation at 500℃were studied.The effects of pre-oxidation,hydrolysis of derived charcoals by boiled KMnO4 aqueous solution were evaluated.The derived charcoals products were pretreated using oxidation-hydrolysis with 1–5 wt.%KMnO4 at 100℃and then activated at 500℃.The derived charcoal and activated carbon products were characterized by FTIR,XRD,SEM-EDS and BET.Iodine number and methylene blue number of derived products were also used for the analysis of the products.It was found that fabricated charcoal materials made at 350℃–400℃possess good characteristics with low content of surface functional groups and high carbon content.After pre-oxidation-hydrolysis and activation at 500℃,the resulting derived activated carbon materials from charcoals with 400℃carbonization temperature have high content of oxygen containing surface functional groups such as Mn-O,Si-O,Si-O-Si,C-O,or O-H.In addition,MnO_(2) accumulated on the surface of the derived activated carbon products.The surface area and pore volume of the activated carbon products have also increased with increasing of KMnO_(4) concentration from 1 to 3 wt.%and then decreased with 5 wt.%used during activation.Therefore,activated carbon products made by pre-oxidation-hydrolysis with 3 wt.%KMnO_(4) were used for Fe(Ⅲ)adsorption experiments.It was found that Fe(Ⅲ)adsorption on the activated carbon materials can be fitted with both the Freundlich and the Langmuir models.The calculated maximum Fe(Ⅲ)adsorption capacities of sugarcane leaves derived activated carbon and rice straw derived activated carbon products were 50.00 and 39.37 mg/g,respectively.It was shown that the effect of pre-oxidation-hydrolysis by KMnO_(4) and activation at 500℃are beneficial for activated carbon preparation with environmentally friendly and low-cost simplified operation.

Activated Protein C Resistance in Patients with Pre-Eclampsia in Lagos, Nigeria

Background: Preeclampsia is reported to complicate 2% - 8% of pregnancies globally and is an important cause of maternal and perinatal morbidity and mortality. The aetiology and pathogenesis are still poorly understood and substantial improvement has not been made in the prediction, prevention and treatment of the disease. Objective: To compare the frequency of activated protein C resistance (APC-R) in patients with pre-eclampsia to that of normotensive pregnant women and to determine the correlation between activated protein ratio (APC-ratio) and the severity of pre-eclampsia. Methodology: A cross-sectional study was carried out in 100 pre-eclamptic patients and 100 normotensive pregnant controls. The APC-ratio was determined using the modified activated partial thromboplastin time. Study participants with APC-ratio of less than 2.0 were defined as having APC-R. Data was analyzed using SPSS version 22.0. Results: Mean APC-ratio was significantly lower in pre-eclamptics (2.89 ± 1.70) compared to normotensive pregnant women (3.57 ± 1.06) (p = 0.0008) and the levels were also higher in mild (2.95 ± 1.15) compared to severe pre-eclamptics (2.62 ± 1.14). The frequency of APC-R was 26% among women with pre-eclampsia compared to 4% among normotensive controls (p = 0.000). Among 100 pre-eclamptic women 7 (21.2%) out of 33 with mild pre–eclampsia had APC-R, while 19 (28.4%) out of 67 with severe pre-eclampsia had APC-R. APC-ratio had a significant negative correlation with mean arterial blood pressure (r = −0.324;p = 0.000) and proteinuria (r = −0.379;p = 0.000) among study participants. Conclusion: The frequency of activated protein c resistance is significantly higher in pre-eclamptics compared to normotensive pregnant women and this is more pronounced in those with severe pre-eclampsia compared with those with mild disease. APC-R may therefore be used as a marker of severity in the disease.

Study of the reaction mechanism for preparing powdered activated coke with SO_(2)adsorption capability via one-step rapid activation method under flue gas atmosphere

In this study,the impact of different reaction times on the preparation of powdered activated carbon(PAC)using a one-step rapid activation method under flue gas atmosphere is investigated,and the underlying reaction mechanism is summarized.Results indicate that the reaction process of this method can be divided into three stages:stage I is the rapid release of volatiles and the rapid consumption of O_(2),primarily occurring within a reaction time range of 0-0.5 s;stage II is mainly the continuous release and diffusion of volatiles,which is the carbonization and activation coupling reaction stage,and the carbonization process is the main in this stage.This stage mainly occurs at the reaction time range of 0.5 -2.0 s when SL-coal is used as material,and that is 0.5-3.0 s when JJ-coal is used as material;stage III is mainly the activation stage,during which activated components diffuse to both the surface and interior of particles.This stage mainly involves the reaction stage of CO_(2)and H2O(g)activation,and it mainly occurs at the reaction time range of 2.0-4.0 s when SL-coal is used as material,and that is 3.0-4.0 s when JJ-coal is used as material.Besides,the main function of the first two stages is to provide more diffusion channels and contact surfaces/activation sites for the diffusion and activation of the activated components in the third stage.Mastering the reaction mechanism would serve as a crucial reference and foundation for designing the structure,size of the reactor,and optimal positioning of the activator nozzle in PAC preparation.

Effect of activator on rheological properties of alkali-activated slag-fly ash pastes

The time-dependent rheological behaviors of alkali-activated cement(AAC)are expected to be precisely controlled,in order to meet the requirements of modern engineering practices.In this paper,the effects of activator,including the Na_(2)O concentration and SiO_(2)/Na_(2)O(S/N)molar ratio,on the rheological behavior of alkali-activated slag fly ash pastes were investigated.The small amplitude oscillatory shear(SAOS)and shear test were used to evaluate the structural build-up and flowability of pastes.Besides,zeta potential measurement,calorimetric test and thermogravimetric analysis(TGA)were carried out to reveal the physico-chemical mechanisms behind the rheological evolution of fresh pastes.It was found that high Na_(2)O concentration and low S/N molar ratio improved the flowability and structural build-up rate of paste.Moreover,the structural build-up of alkali-activated slag-fly ash pastes consists of two stages,which is controlled by the dissolution of solid reactants and formation of C-(A)-S-H gels,respectively.