Alkali Sulfate Research Articles

Insight into catalytic effects of alkali metal salts addition on bamboo and cellulose pyrolysis

Alkali metal compounds have vital influence on biomass pyrolysis conversion. In this study, cellulose, and bamboo catalytic pyrolysis with different alkali metal salts catalysts (KCl, K2SO4, K2CO3, NaCl, Na2SO4, and Na2CO3) were investigated in the fixed-bed reaction system. The effects of cations (K+ and Na+) and anions (Cl-, SO42−, and CO32-) on the evolution properties of biochar, bio-oil, and gas products were explored under both in-situ and ex-situ catalytic pyrolysis. Results showed that alkali metal salts facilitated the yields of biochar and gases at the expense of that of bio-oil. Alkali metal chloride and sulfate showed a weaker catalytic effect, while alkali metal carbonate greatly promoted the generation of gas products and increased the condensation degree of biochar. With the addition of K2CO3 and Na2CO3, cyclopentanones content was over 50% from cellulose catalytic pyrolysis, and phenols content (mainly alkylphenols) reached over 80% from bamboo catalytic pyrolysis. Moreover, solid-solid catalytic reactions with K2CO3 and Na2CO3 catalysts had an important role in strikingly promoting conversion of pyrolysis products, and the solid-solid and gas-solid catalytic reactions with alkali metal carbonate catalysts were stronger than those with alkali metal chloride and sulfate catalysts. Furthermore, the possible catalytic pyrolysis mechanism of alkali metal salts on biomass pyrolysis was proposed, which is important to the high-value utilization of biomass.

Pozzolanic metakaolin reactivity: Time-dependent influence of calcium hydroxide, alkali hydroxides, and sulfates

In the quest for environmentally sustainable binders within the construction industry, metakaolin (MK) has emerged as a highly promising material. Its reactivity and hardening performance encompass a wide range of applications, spanning from lime to cement-based materials. This performance is primarily underpinned by the pozzolanic reaction with calcium hydroxide (CH), leading to the formation of various calcium aluminate silicate hydrates. The intricacies of the hydration kinetics and resultant reaction products hinge on several factors woven into the specifics of the binder type. This study investigates the influence of CH availability, explored through initially mixed MK/CH weight ratios of 0.33 and 1.0. Furthermore, the study examines the impact of introducing alkali hydroxides (KOH and NaOH) and/or sulfates (K2SO4 and Na2SO4) on the pozzolanic reactions. Short-term analysis employed inductively coupled plasma optical emission spectrometry (ICP-OES), and pH measurements for pore solution as well as isothermal calorimetry, and in-situ X-ray diffraction (XRD) on paste samples. Long-term investigations extended to 245 days at 40 °C, incorporating XRD, thermogravimetric (TGA) and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM/EDX). Results provide insights into the kinetics of phase assemblage and compositions of C-A-S-H gels, highlighting the transformation of metastable C2ASH8 and C4AH13 to stable Si-rich hydrogarnet phases, incorporating sulfate, under excess CH conditions. Higher MK/CH enriches Si/Ca, Al/Ca, enhancing C-A-S-H gels, while KOH addition further boosts Al/Ca ratios.

Melt Inclusions in an Aplite Vein in Granodiorite of the Lusatian Massif: Extreme Alkali Sulfate Enrichment

Melt Inclusions in an Aplite Vein in Granodiorite of the Lusatian Massif: Extreme Alkali Sulfate Enrichment

Measurement of Electric Double Layer Charging Dynamics on Platinum Electrodes in Aqueous Solutions of Alkali Sulfates and Nitrates

Measurement of Electric Double Layer Charging Dynamics on Platinum Electrodes in Aqueous Solutions of Alkali Sulfates and Nitrates

Effect of mineral admixtures on the calcium leaching resistance of porous cement stabilized macadam

Porous cement stabilized macadam has a good drainage property, but the loss of strength due to calcium leaching can significantly reduce its road performance. The effect of the dosage of fly ash, silica fume, and slag powder on the calcium leaching resistance of porous cement stabilized macadam base material was investigated using the accelerated leaching method with 4 mol/L ammonium chloride. The results show that calcium leaching occurs simultaneously at multiple contact points between the internal cement paste and the leaching solution, and the leaching depth has exceeded the average thickness of the layered cemented paste within 3d. The dissolution of CH crystals and the decalcification of C-S-H gel increase the porosity of cement and reduce the strength of the base material. Volcanic ash reaction of silica fume and fly ash as well as slag powder by alkali excitation and sulfate excitation will consume CH and generate low alkalinity C-S-H gel with better dissolution resistance, which can reduce calcium leaching and delay the loss of strength. The optimum dosages of fly ash, silica fume, and slag powder are 20%, 15%, and 30%, respectively, and their optimum dosages can be estimated on the assumption that the mineral admixtures completely consume CH.

Gaseous alkali interactions with ilmenite, manganese oxide and calcium manganite under chemical looping combustion conditions

Alkali species present in biomass pose significant challenges in chemical looping combustion (CLC) processes and other thermal conversion applications. The interactions between different alkali species and three common oxygen carrier (OC) materials that are considered to be state of the art in CLC applications have been investigated. A dedicated fluidized bed laboratory reactor was used to study interactions of KCl, NaCl, KOH, NaOH, K2SO4 and Na2SO4 with manganese oxide, calcium manganite and ilmenite. Alkali vapor was generated by injecting alkali salts under reducing, oxidizing and inert conditions at 900 °C. Gaseous species were measured online downstream of the reactor, and the efficiency of alkali uptake was determined under different conditions. The result show significant alkali uptake by all OCs under the studied conditions. Ilmenite shows near complete alkali uptake in reducing conditions, while manganese oxide and calcium manganite exhibited less effective alkali uptake, but have advantages in terms of fuel conversion and oxidizing efficiency. Alkali chlorides, sulfates and hydroxides show distinctly different behavior, with alkali hydroxides being efficiently captured all three investigate OC materials. The findings contribute to a deeper understanding of alkali behavior and offer valuable guidance for the design and optimization of CLC with biomass.

Synergistic preparation of high-performance composite blast furnace slag powder from multiple industrial solid wastes: Performance regulation and optimization

Blast furnace slag (BFS) is commonly used as a substitute for cement clinker due to its hydration properties. However, the demand for BFS is outpacing the supply, and its price is rising steadily. Moreover, the significant accumulation of industrial waste with potential hydration properties poses a severe environmental threat. To address these challenges, this paper aimed to prepare high-performance composite blast furnace slag powder (CBFS) by incorporating red mud (RM), fly ash (FA), desulfurization gypsum (DG) and BFS, guided by the synergistic effects and the theory of medium-calcium systems. This paper reveals that the primary activation methods of the amorphous silicon-aluminum mineral phases in CBFS are alkali activation and sulfate activation. The optimal results demonstrate that the compressive strength of CBFS-cementitious material (50% CBFS + 50% cement) can reach 52.8 MPa, meeting the standards of Portland Cement PO 42.5. Additionally, RM, FA and DG account for 66% of CBFS and the hydration activity of CBFS is better than that of S95-grade BFS. Furthermore, the CBFS-cementitious material effectively immobilizes hazardous elements of the raw materials, and the leachate meets drinking water standards. The application of CBFS facilitates the recycling of industrial solid wastes, improves the quality of construction materials and reduces the construction industry's dependence on BFS.

Investigation of austenitic stainless steel corrosion resistance against ash deposits from co-combustion coal and biomass waste

A high chromium concentration in the boiler material is believed to increase corrosion resistance, especially at high temperatures. It is related to the formation of a protective layer on the surface of the metal, called a chromium oxide (Cr2O3) layer. However, the impact of alkali and chlorine from co-combustion coal with biomass in power plants can harm this protective layer, reducing its effectiveness and potentially leading to increased corrosion. Therefore, it is important to evaluate the impact of these factors on the corrosion resistance of high-chromium materials. This research investigates coal co-combustion with empty fruit bunch (EFB) and plastic waste on the corrosion resistance of austenitic stainless-steel material on a laboratory scale using drop tube furnaces. The investigation steps included probe observation, SEM-EDS on ash and probe material, and XRD. The analysis indicates that the ash from the coal sample did not affect the probe, unlike the coal with EFB or EPL (mixture of EFB and plastic crackles), which caused up to 14% oxide layer degradation. The existence of alkali chloride, sulfate, and silicate in the ash that is still adhered to the surface of the probe can reduce the corrosion resistance of the metal.

Mineral Assemblage of Olivine-Hosted Melt Inclusions in a Mantle Xenolith from the V. Grib Kimberlite Pipe: Direct Evidence for the Presence of an Alkali-Rich Carbonate Melt in the Mantle Beneath the Baltic Super-Craton

This report deals with the first mineralogical examination of secondary crystallized melt inclusions (CMIs) in healed cracks within olivine in a mantle peridotite xenolith from the V. Grib kimberlite pipe (Arkhangelsk diamondiferous province). In contrast to micro/nano-inclusions in diamonds, the studied CMIs are quite large (up to 50 µm), so that the mineral composition of the CMIs can be determined via conventional analytical approaches, e.g., Raman spectroscopy and scanning electron microscopy. Garnet peridotite is a coarse-grained mantle rock that equilibrates at 3.3 GPa and 750 °C (corresponding to a depth of ~100 km). The CMIs are therefore tiny snapshots of melt that existed in the shallow lithospheric mantle and were entrapped in olivine. In total, nineteen mineral species were identified among the daughter magmatic minerals of the CMIs. Various Na-K-Ca-, Na-Ca-, Na-Mg-, Ca-Mg-, Mg- and Ca-carbonates; Na-Mg-carbonates with the additional anions Cl−, SO42− and PO43−; alkali sulfates; chlorides; phosphates; sulfides; oxides; and silicates were established. Within the mineral assemblage, carbonates were predominant, with their abundance being more than 62 vol.%. The CMIs contained twelve alkali-rich minerals; nine of them were Na-bearing and showed bulk molar (Na + K)/Ca ≥ 1. The CMIs’ parental melt was an alkali-rich carbonate liquid that contained low amounts of SiO2 (≤9.6 wt%) and H2O (≤2.6 wt%). According to our estimates, the time of complete equilibration between olivine within the healed cracks and host olivine in the mantle at the calculated P-T parameters for the studied xenolith should be no more than several years. Based on this geologically short time span, a genetic link between the studied CMIs and the magmatism that formed the V. Grib kimberlite pipe is suggested.

Process compatible desulfurization of NSP cement production: A novel strategy for efficient capture of trace SO2 and the industrial trial

Cement industry contributes to more and more SO2 emission due to utilization of alternative raw materials and fuels, whereas the available calcium-based dry flue gas desulfurization (FGD) technologies present low efficiency due to slow reversible de-SO2 reactions and short gas-solid contact time in the preheater. In the present study, the SO2 capture potentials of CaCO3, CaO, and Ca(OH)2 in the preheater environment were maximized by introducing V2O5-based catalyst and selecting optimal reaction temperature, and the de-SO2 mechanism was extensively discussed. The results showed that the de-SO2 efficiency of calcium-based adsorbents increased by 10–57 times as SO2 was effectively oxidized to SO3 in the presence of V2O5-based catalyst, then maximum de-SO2 efficiency of 75.5% was achieved using Ca(OH)2 and V2O5-CeO2 at 600 °C. Furthermore, CaCO3 assisted by V2O5-CeO2 also had a de-SO2 efficiency of 65.6%. Subsequently, a novel process compatible FGD technology was designed to maximize the de-SO2 ability of raw meal in the preheater by adding V2O5-based catalyst and humidification, the SO2 concentration of flue gas reduced from 1000 mg/Nm3 to less than 100 mg/Nm3 in the industrial-scale trial, as more sulfur was solidified into clinker in the form of alkali sulfate without reducing its properties. This novel process compatible de-SO2 strategy is of real significance for reducing SO2 emission of cement industry at low economic cost.

НИЗКОТЕМПЕРАТУРНЫЕ ФАЗОВЫЕ РАВНОВЕСИЯ В БИНАРНЫХ СИСТЕМАХ И ПОЛУЧЕНИЕ ФУНКЦИОНАЛЬНЫХ МАТЕРИАЛОВ

The problems of studying low-temperature phase formation in systems, which are the basis for obtaining functional materials, are selected. The use of salt fluxes (alkali metal nitrates and sulfates) is an effective method of accelerating the achievement of equilibrium in fluoride and oxide systems. Extrapolation of phase equilibria to absolute zero temperature, taking into account the requirements of the third law of thermodynamics, is a powerful method for obtaining relevant information. Summary phase diagrams of the ZrO2-Sc2O3 and albite — anorthite systems are proposed.

Hydrothermal sulfate surges promote rare earth element transport and mineralization

Abstract The generation of sulfate-rich hydrothermal fluids is of great significance to investigate because it is closely associated with the formation of many important ore deposits, such as hydrothermal rare earth element (REE) deposits. However, the transport of REEs in sulfate-rich hydrothermal fluids is complicated by the retrograde solubility of common sulfate minerals depicted in current thermodynamic models. We present in situ and ex situ hydrothermal experimental evidence suggesting that the solubility of alkali sulfate changes from retrograde at low pressures to prograde at elevated pressures. Accordingly, we propose a sulfate surge temperature and pressure (T-P) window (250 °C, 90 MPa), above which the solubility of alkali sulfate increases significantly with increasing P and T. Although REE sulfates are weakly soluble in water, sulfate-rich hydrothermal fluids can transport high contents of REEs under the T-P conditions above the sulfate-surge window. Our results indicate that depressurization, cooling, and alkali loss are key factors controlling REE mineralization, which agrees well with geological observations.

Compositions of Kimberlite Melts: A Review of Melt Inclusions in Kimberlite Minerals

This work is a comprehensive review of existing data on melt inclusions entrapped in minerals of kimberlite rocks emplaced in different cratonic settings at different times. The crystallized melt inclusions represent snapshots of kimberlite melts at different stages of their evolution. All inclusions are composed of daughter minerals and shrinkage bubbles, but no aqueous fluids and quenched silicate glasses have been so far found. More than 60 mineral species were identified among the daughter phases in the inclusions, however, such diverse phase assemblages are typical of all kimberlites studied to date. Daughter minerals are represented by various Na-K-Ca-, Na-Ca-, Na-Mg-, K-Ca-, Ca-Mg-, Ca-, Mg-, Na-carbonates, Na-Mg- and Na-carbonates with additional anions Сl–, \({\text{SO}}_{4}^{{2 - }},\) \({\text{PO}}_{4}^{{3 - }},\) alkali- sulfates, chlorides, phosphates, sulfides, oxides and silicates. Alkali carbonates, sulfates, and chlorides are usually absent among groundmass minerals the majority of kimberlites in the world, except the Udachnaya-East kimberlite in Siberia. On the other hand, this paragenesis in association with traditional kimberlite minerals, such as olivine, micas, monticellite, spinel group minerals, perovskite, rutile, ilmenite, calcite, and dolomite, is common in the crystallized melt inclusions in all studied kimberlites. Carbonates (~30 to 85 vol. %) always dominate over silicates (only up to 18 vol. %) within inclusions. All inclusions also contain variable (2 to 55 vol. %.) amounts of chlorides (halite and sylvite). When relatively low abundances of carbonate minerals (30–50 vol. %) are observed in the inclusions, chlorides (18–55 vol. %) appear to take over other minerals, including silicates that are traditionally considered as main components of “ultramafic” kimberlite parental melts. The published results on melt inclusions in the kimberlite minerals strongly imply that parental kimberlite melts were generated and further evolved within the Na2O-K2O-CaO-MgO-CO2-Cl system, that is, they were alkali-rich carbonatite/carbonatite-chloride liquids. According to various estimates, the SiO2 content in kimberlite melts at different stages of their evolution could have varied from the first to 19 wt. %. Obviously, during and after of а kimberlite bodies formation, interaction with external waters leads to serpentinization of kimberlite olivine and dissolution of a significant part of kimberlite igneous minerals, such as alkaline carbonates, sulfates, and chlorides. In the traditional approach to studying kimberlites, the role of components such as Na2O, CO2, Cl, and to a lesser extent K2O and S, F in the petrogenesis of kimberlite magmas and rocks have been largely underestimated, while olivine- and serpentine-forming components, such as of SiO2, MgO and H2O are still overestimated in contemporaneous literature.

Sulfation of Gaseous KCl by H2SO4

The sulfation of gaseous KCl by H2SO4 in the presence of O2 and H2O was investigated in a laboratory laminar flow reactor at atmospheric pressure and temperatures ranging from 873 to 1523 K. The degree of sulfation was characterized by analysis of the elemental composition (Cl, S, and K) of the submicrometer particles captured on a filter downstream of the reactor. Furthermore, concentrations of HCl and SO2 in the outlet were measured. The experimental results were interpreted in terms of a detailed chemical kinetic model for the K/S/Cl chemistry. The degree of KCl sulfation depends on the reaction temperature and the reactant concentrations. The results show that H2SO4 is effective in sulfating KCl to K2SO4 at temperatures in the range 1073–1273 K, in particular at high H2SO4/KCl ratios. At temperatures of 1373 K and above, the sulfation efficiency decreases rapidly because alkali sulfate formation is no longer thermodynamically favored. The kinetic analysis shows that reaction is initiated by decomposition of sulfuric acid: H2SO4 + H2O ⇄ SO3 + H2O + H2O. Then KCl reacts directly with SO3 to form the intermediate KSO3Cl, which is further converted via KHSO4 to gaseous K2SO4. As the gas is cooled downstream of the isothermal zone, potassium sulfate nucleates homogeneously to form an aerosol, promoting further sulfation in the gas phase. The simulations are in satisfactory agreement with the experimental results, predicting correctly the temperature window for the process. However, the model overpredicts the SO2 yield at high temperature, indicating that the K/S interactions under these conditions are not fully understood. The results are important, both for validation of models of K/Cl/S interactions in combustion and for characterization of the sulfation of KCl by sulfuric acid to evaluate the potential of the sulfur recirculation process and identify the optimum process conditions.

ALKALI-CONTAINING MINERALS WITHIN MELT INCLUSIONS IN OLIVINE OF MANTLE XENOLITHS FROM BULTFONTEIN KIMBERLITE PIPE (KAAPVAAL CRATON): EVIDENCE ON HIGH CONCENTRATIONS OF ALKALIS IN KIMBERLITE MELTS

The study reports the mineral assemblage of the crystallized secondary melt inclusions in the olivine of sheared peridotites xenoliths from Bultfontein kimberlite pipe (Kaapvaal Craton, South Africa). In this type of xenoliths, the inclusions may correspond in composition to primitive kimberlite melts related to the magmatism that formed the Bultfontein pipe. Among 32 daughter phases within the inclusions, there are both ordinary rock-forming and minor minerals for kimberlites (silicates, carbonates, oxides) and "exotic" (alkali carbonates, sulfates, and chlorides) for these rocks. In the inclusions, 20 alkali-containing minerals are present, 12 of which are Na-bearing and – 4 Na-K-bearing. For instance, the inclusions contain nyerereite, K-nyerereite, shortite, gregoryite, eitelite, bradleyite, northupite, tychite, burkeite, aphthitalite, arcanite, thenardite, sylvine, and halite. On the basis of these results, the kimberlite melt of the Bultfontein pipe had Na-specification rather than Ca or K ones. The carbonates, sulfates, and chlorides significantly prevail over silicates, which content (serpentine + micas) does not exceed 16 vol. %, in the inclusions.The obtained results pose fundamental questions regarding the petrogenesis of kimberlites: (i) initial sodium concentrations in kimberlite melts and rocks, which are "traditionally" considered as very low; (ii) composition and ratio of volatile components in kimberlite magmas, namely, the initial contents of both CO2 and the components such as Cl, SO3 and H2O; (iii) primary magmatic mineral association of kimberlite rocks, which loses diverse alkali-containing minerals, but mica, due to serpentinization process.

Physico-chemical profile and corrosion mechanism of the failure grate bar from iron ore sintering process

The grate bars are a critical and easily consumable component of the sintering machine, and the control of their corrosion is of great importance to reduce their consumption. This investigation focused on revealing the physicochemical profile of the failure sintering grate bar and the potential corrosion mechanism. The results showed that the superficial area of the failure grate bar consisted of the adhesive layer, corrosion layer, and metal layer from outside to inside. The adhesion layer is characterised by a loose structure, consisting of higher contents of alkali chloride salts and sulphate, which were the typical corrosive substances. The main components of the corrosion layer were Fe2O3 and Cr2O3; the metal layer structure was dense, which remained the original composition of the grate bar. Based on the characteristics of sintering flue gas, the potential corrosion mechanism was summarised into three main types: (a) high-temperature oxidation, due to the periodic exposure of the grate bars to the high-temperature sintering flue; (b) chlorine corrosion, due to the existence of HCl, alkali (heavy) metal chloride salts (KCl, NaCl, PbCl2) in sintering flue gas, which formed the adhesive layer of grate bars; (c) sulphate corrosion, due to the existence of high SO2 contents and sulphate in the flue gas. The research findings are important to guide the development of grate bar corrosion control technologies.

Exploring new belousovite-related zinc and cadmium alkali sulfate halides: synthesis and structural variability.

Fourteen new belousovite-related compounds, AZn(TO4)X (A = K, Rb, Cs, Tl, NH4; T = S, Se; X = Cl, Br, I) have been prepared via melt and evaporation techniques by reacting AX and ZnTO4 either at high temperatures or in hot aqueous solutions. They adopt the layered structure of the belousovite archetype, and constitute a morphotropic series. The apophyllite-type layers in these structures undergo different corrugations, most pronounced in the case of CsZn(SO4)I. In addition, during the study two species unrelated to belousovite, namely Na4Zn(SO4)2Cl2 and Cs2Cd3(SO4)4, were found with framework crystal structures having different topology and belonging to new structure types.

Effect of leaching pretreatment on the inhibition of slagging/sintering of aquatic biomass: Ash transformation behavior based on experimental and equilibrium evaluation

In this study, aquatic biomasses of Ulva lactuca and Hydrilla verticillata were pretreated by water and acid washing. A comprehensive assessment strategy, including systematic experiments and equilibrium calculations, was used to study the migration of elements and transformation characteristics of minerals in aquatic biomass ash before and after leaching pre-treatment. The effect of leaching pre-treatment on slagging inhibition was analyzed. Owing to the different mineral compositions and characteristics of the two types of aquatic biomass, the serious slagging caused by Ulva lactuca was related to the presence of alkali (Na and K) sulfate. In contrast, the presence of silicate/aluminosilicates in Hydrilla verticillata had a greater effect on slagging. The removal of alkali metals (especially Na and K) and Cl from aquatic biomass by leaching pretreatment was conducive to alleviating aquatic biomass slagging. Following leaching pretreatment, the alkali index of the aquatic biomass was reduced to <0.17, and the Cl content was reduced to <0.3%. Furthermore, the abundant alkaline earth metals (Ca and Mg) in aquatic biomass can inhibit slagging by generating high-melting-point alkaline earth metal silicates or phosphates. The removal rate of alkaline earth metal oxides by acid washing was >96% and >78% in Ulva lactuca and Hydrilla verticillata, respectively, while water washing was less effective. Although water and acid washing can alleviate slagging, a comparative investigation showed that water washing of aquatic biomass had better outcomes than acid washing. Therefore, water washing is a better way to comprehensively pre-treat aquatic biomass. The results obtained can help promote the thermochemical utilization of aquatic biomass on an industrial scale.

Concrete seawalls: A review of load considerations, ecological performance, durability, and recent innovations

Increasing frequency of extreme weather events, driven by climate change, coupled with growing population densities, have contributed to an increasing demand for coastal structures to protect and stabilize shorelines. Concrete seawalls are a common category of coastal protection structures, designed with the primary objectives of absorbing wave action, preventing coastline erosion, and alleviating flooding. Much research has been carried out on improving concrete seawall performance. This work is a review of the current state-of-the-art in concrete seawalls focusing on design aspects including wave loading and innovative seawall designs, ecological considerations, and durability performance. Different conventional seawalls and their advantages and disadvantages are reviewed. Wave loads on seawalls have received significant attention; and multiple approaches for the quantification for the different types of loads are presented. However, wave load quantification remains a challenging task, especially for novel designs, and performance under load for such designs must be quantified through testing in wave tanks. Drawing inspiration from natural shorelines, modification of surface complexity at a multitude of scales can improve the otherwise poor ecological performance of seawalls. Ecological performance can also be improved by the incorporation of natural materials or structures in seawalls although the exact influence of concrete and other material chemistry on benthic diversity is unclear. The corrosion of the steel is a major durability concern, and the use of non-corrosive reinforcement can increase seawall durability toward corrosion. Other durability concerns include alkali silica reaction and sulfate attack, which can be mitigated through proper mixture design, including through the use of supplementary cementitious materials. Examples of innovative seawall designs and systems which have the capability to outperform conventional seawalls are discussed. Advances in structural design, ecological engineering, and infrastructure materials science will drive the development of multi-functional seawalls which are sustainable, durable, and resilient.

Self-Healing Products of Cement Pastes with Supplementary Cementitious Materials, Calcium Sulfoaluminate and Crystalline Admixtures

The phase composition of self-healing products generated in cracks affects self-healing performance. This study investigated the self-healing products of cementitious materials using supplementary cementitious materials (SCMs), a calcium sulfoaluminate (CSA) expansion agent, and crystalline additives (CAs). Ground-granulated blast-furnace slag (GGBFS), fly ash (FA), and silica fume (SF) were used as SCMs, and anhydrite, Na2SO4, Na2CO3, and MgCO3 were used as crystalline additives (CAs). An artificial crack method was used to collect the self-healing products in the crack of the paste. The phase composition of the self-healing products was analyzed through X-ray diffraction (XRD)/Rietveld refinements and thermogravimetry/differential thermogravimetry (TG/DTG) analysis, and their morphology and ion concentration were examined through scanning electron microscopy with energy dispersive spectroscopy (SEM–EDS). From the results, the main compound of self-healing products was found to be calcite. GGBFS and FA decreased the content of portlandite, and the use of CAs led to the formation of alkali sulfate and alkali carbonate. The SEM–EDS analysis results showed that when GGBFS and FA were used, a large proportion of the self-healing products contained C-S-H and C-A-H, and the use of CSA led to the formation of monosulfate and ettringite.