Hexavalent chromium (Cr(VI)) is a highly toxic and mobile contaminant that requires effective stabilization in cement-based waste treatment systems. This study comparatively evaluates the Cr(VI) immobilization behavior of cement pastes incorporating four metallurgical slags: copper slag (CS), steel slag (SS), ground granulated blast-furnace slag (GGBFS), and ferronickel slag (FNS), with focus on chemistry-controlled mechanisms. Cr(VI) was introduced in the form of K2CrO4, and immobilization characteristics were examined through phase analysis, spectroscopic techniques, and leaching tests. The results indicate that CaO-rich slags promote the formation of Cr-bearing phases, including CaCrO4, CrO4-substituted AFt/AFm phases, and calcium (alumino)silicate hydrates, which contribute to chromate retention and partial reduction to Cr(III). In contrast, MgO-rich FNS limits the development of key hydrate phases and shows lower stabilization performance despite comparable strength. Phase quantification and chromium valence analysis show consistent agreement with leaching behavior, suggesting that hydrate assemblage and calcium availability play a more decisive role than mechanical performance in governing immobilization efficiency. Toxicity characteristic leaching procedure (TCLP) results confirm higher Cr(VI) retention in CaO-rich slag (SS and GGBFS) systems compared with CaO-deficient slags (CS and FNS), as well as 100% cement paste. These findings provide mechanistic insight into chromium stabilization in cementitious matrices and support the use of selected industrial slags as alternative low-carbon binders for hazardous waste immobilization.

This study evaluates the feasibility of recycling dehydrated cement paste (DCP) as a reactive calcium silicate source in fly ash-based alkali-activated materials (AAMs) and elucidates temperature-dependent phase evolution and gel chemistry. The performance of DCP was compared with that of hydrated cement paste and ordinary Portland cement under curing conditions of 25 degrees C and 60 degrees C. At 25 degrees C, the incorporation of DCP, containing residual C-S-H, promoted the early formation of C-(N)-S-H gel and improved initial strength via exothermic reactions. At 60 degrees C, the dissolution of both DCP and FA was significantly accelerated, leading to rapid phase evolution and substantially increased strength. Under these hydrothermal conditions, cancrinite was formed and subsequently transformed into C-(A)-S-H-type gel through ionexchange and structural reorganization processes. These transformations were confirmed by Xray diffraction, solid-state Si and Al nuclear magnetic resonance, and FE-SEM/EDS analyses. The results demonstrate that DCP acts not only as a reactive calcium source but also as a kinetic modifier that enhances both the reactivity and strength development of FA-based AAMs. This study provides new insight into the temperature-dependent behavior of recycled cementitious fines and demonstrates their potential as sustainable binder components.

This study examined the synergistic effect of alkanolamines (i.e., Triethanolamine (TEA), Triisopropanolamine (TIPA)) and nano-SiO2 on the hydration kinetics and mechanical properties of Portland limestone cement (PLC). Due to distinct hydroxyl groups linked to TEA and TIPA, their combined use with nano-SiO2 resulted in different hydration kinetics and physicochemical properties of the PLC pastes. The combined use of nano-SiO2 and TEA selectively accelerated the aluminate reaction before the onset of the silicate reaction in PLC, whereas incorporation of nanoSiO2 and TIPA highly promoted both the silicate and aluminate reactions. Although TEA alone contributed to strength reduction, the co-incorporation of nano-SiO2 successfully mitigated this effect. The highest compressive strength was attained via combined use of nano-SiO2 and TIPA, which also induced a greater formation of carboaluminate phases and led a significant pore size refinement effect. While use of TEA and nano-SiO2 both refined pores, the effect was less pronounced compared to that with nano-SiO2 and TIPA. These findings demonstrate that the combined use of nano-SiO2 and TIPA offers a superior route for enhancing the early-age mechanical performance of PLC.

This study investigates the effect of wet-grinding on limestone and slag for improving compressive strength of ternary Portland limestone cement (PLC) binder. To evaluate the effect of wet-ground slag, two laboratory-prepared ternary PLC mixture systems consisting of cement clinker, gypsum, and either limestone or wet-ground limestone were investigated. The first group contained 15 wt.% of limestone, while the second contained 15 wt.% wet-ground limestone. The wet-ground slag accelerated silicate and aluminate reaction and significantly increased cumulative heat and compressive strength of the PLC binder added with limestone. The wet-ground slag enhanced the carboaluminate phases at early ages and formed more polymerized C-(A-)S-H, resulting in densified microstructure for its filler effect and increased reactivity. Although wet-ground slag decreased early strength of the ternary PLC binder added with wet-ground limestone, comparable strength could be achieved after 7 days which would offset the dilution effect. Likewise, wet-ground slag induced more hydrate growths (i.e., carboaluminate phases and C-(A-)S-H) and reduced porosity and average pore size. The improvement in mechanical performance and the generation of hydrates was attributed to the respective roles of wet-ground limestone and wet-ground slag during hydration, increasing effective water availability and accelerating hydration, respectively.

This study aimed to identify the optimum gypsum content and elucidate its effects on the physicochemical properties of Portland limestone cement (PLC) incorporating ground-granulated blast-furnace slag (GGBFS). As the gypsum content increased, the C3A reaction was retarded during the first 72 h, producing a clear separation of C3S hydration peaks. Partial replacement with limestone at 15 wt% and GGBFS at 20, 40 wt% reduced the clinker fraction of the binder, and consequently, the cumulative heat release. Higher compressive strengths were observed for OPC and PLC pastes with 5 wt% gypsum, which reflected these early-age hydration differences, whereas slag-bearing pastes with 20% and 40% GGBFS (S20, S40) peaked at 3 wt%. Therefore, gypsum dosage acts as an important control variable for hydration reactions and the resultant physicochemical properties of PLC-slag cement systems.

To investigate the role of trace alkaline earth group elements on the formation of cement clinker phases, cement clinkers doped with magnesium oxide (MgO) and strontium oxide (SrO) were synthesized at temperatures between 1200 and 1450 degrees C. The synthesized clinkers were characterized using X-ray powder diffraction (XRD) with Rietveld refinement, field-emission electron probe microanalysis (FE-EPMA), and compressive strength tests. The findings of this study demonstrate that the MgO content in the clinker phase leads to an increase in C3S-M3 and a decrease in C2S. Periclase appeared in the clinker with an increase in the MgO doping ratio. In contrast, SrO in the clinker phases promoted the transformation of C2S-alpha' and C3S-M1 at elevated temperatures. As the SrO content increased, free CaO emerged and increased instead of SrO and Sr(OH)2 in the cement clinker system. FEEPMA analysis revealed distinct distribution trends, with MgO preferentially concentrated in the order of C4AFC3A-C3S-C2S, while SrO was concentrated in the order of C2S-C4AF-C3A-C3S. The grain size of C3S increased with increasing SrO doping ratio, in contrast, that of C3S with MgO doping decreased slightly. The elemental compositions of the cement clinker in calcium silicate indicated that Mg ions were predominantly incorporated into C3S, whereas Sr ions were preferentially substituted into C2S, replacing Ca ions and significantly influencing the polymorphism of clinker phases. The results for mechanical properties show that the compressive strength of undoped cement (PC) can be improved via appropriate SrO doping.

This study investigated the impact of copper slag on the physicochemical properties of Portland limestone cement (PLC), focusing on the substitution of Fe for Al ions in hydrate phases like AFm and AFt. Addition of copper slag delayed induction period, slowed silicate and aluminate reactions, and reduced total heat release during hydration owing to its low reactivity and small surface area. In PLC paste added with 13.0 wt% copper slag, comparable or higher strength was achieved at all curing days compared to plain PLC paste. X-ray diffraction (XRD), thermogravimetric analysis (TGA), and Fourier transform infrared (FT-IR) spectroscopy showed similar formation of Fe-AFt and Fe-AFm at 28 days. Fe K-edge X-ray near-edge structure (XANES), transmission X-ray microscopy (TXM), and scanning electron microscopy (SEM) confirmed the replacement of Al with Fe ions in the AFt and AFm phases. By conducting mercury intrusion porosimetry (MIP), incorporation of copper slag induced a reduction in large pores (0.06-0.08 mu m diameters) and an increase in smaller pores (0.04-0.06 mu m diameters) of the PLC paste.

The interfacial transition zone (ITZ) is the most vulnerable and porous phase in concrete, corresponding to the interface between aggregates and the cement matrix. To densify the ITZ microstructure, this study proposes the incorporation of graphene oxide (GO) into silica fume-modified mortars with high and low water-to-binder (W/B) ratios of 0.4 and 0.2, respectively. GO enhanced the degree of hydration by providing nucleation sites and promoting the pozzolanic reaction of silica fume and Ca(OH)2, leading to the formation of secondary amorphous phases. In the mortars containing GO, the calcium-to-silicon ratio of the phase around the aggregate surface increases because the GO nanosheets absorbed Ca2+ ions and migrated with the mixing water. The comparative effects of GO on the mechanical properties of the ITZ in the mortars with high and low W/B ratios were assessed using nanoindentation tests. The results indicate that the GO nanosheets interlocking with the Ca2+ ions resulted in the formation of denser hydration products with high elastic modulus in the vicinity of the aggregates at a W/B ratio of 0.4 while reducing the amount of unhydrated cement grains at a W/B ratio of 0.2. Overall, this study highlights the comparative effects of GO on enhancing the performance of normal- and high-strength cement composites and mortars, with a particular focus on the improvement of ITZ.

This study evaluated the synergistic effects of nano-alumina and triisopropanolamine (TIPA) on the physicochemical properties of Portland limestone cement (PLC) with varying gypsum contents. The incorporation of nano-alumina and TIPA into PLC pastes with 3 and 9 wt % of gypsum resulted in increased heat release during the initial dissolution period and total heat release of cement hydration, and significantly enhanced the silicate and aluminate reactions. In addition, their combined use significantly improved the compressive strength of the PLC pastes, produced denser microstructures with lower porosities, and altered the pore shapes in the pastes. The synergistic advantages are likely related to the role of nano-alumina as a reactive filler and the use of TIPA that enhances the reactivity of the clinker phases.

This study explored the influence of alumina type and gypsum content on the hydration, mechanical properties, and chemical changes of Portland-limestone cement (PLC) using isothermal calorimetry, inductively coupled plasma-optical emission spectroscopy (ICP-OES), ionic chromatography (IC), compressive strength testing, X-ray diffraction (XRD), 27Al magic angle spinning nuclear magnetic resonance (27Al MAS NMR) spectroscopy, and mercury intrusion porosimetry (MIP) testing. The addition of alumina shortened the induction period, accelerated the acceleration period, and increased the mechanical strength of the PLC pastes with 3 and 7 wt% gypsum. The acceleration effect and strength enhancement were not distinct in the PLC pastes with less gypsum (0.1 wt %). The addition of gamma-alumina led to the greatest accelerating effect and strength improvement in the PLC pastes with 3 and 7 wt% gypsum, and the compressive strength achieved was comparable to those of pure Ordinary Portland cement (OPC) pastes without limestone. The addition of gamma-alumina induced the rapid dissolution of gypsum and consumption of sulfate ions. The chemical change affected by the addition of alumina varied greatly depending on the gypsum content, and trends in AFt and AFm formation in the PLC pastes with different gypsum contents were confirmed. Finally, pore size refinement was observed through the addition of alumina to PLC pastes with 3 and 7 wt% gypsum.

This study investigates the impact of nano-CaCO3 and nano-SiO2 on limestone calcined clay cement (LC3), focusing on its hydration kinetics and mechanical properties. Nano-CaCO3 incorporation accelerated early-stage hydration and induced extensive carboaluminate formation; however, it reduced the mechanical strength at later hydration stages due to its effect on calcium-(alumino)silicate-hydrate (C-(A-)S-H) characteristics and hydrate composition. A higher CaCO3 dissolution rate increased the Ca/Si ratio in the matrix, and a large amount of carboaluminate formation consumed the Ca(OH)2 and water required for the pozzolanic reaction of metakaolin. Conversely, nano-SiO2 incorporation improved the mechanical strength across all hydration stages through the filler effect, good dispersion quality, and pozzolanic reactivity. Nano-SiO2 accelerated the early-stage hydration and produced ample C-(A-)S-H, which effectively refined the pore structure and enhanced the mechanical strength. However, the combined use of nano-CaCO3 and nano-SiO2 adversely affected the mechanical strength and pore structure of the cement pastes owing to strong agglomeration, despite accelerated hydration in the early-stages.

This study developed artificial lightweight aggregates (CNF aggregates) using a Ca(OH)2-Na2CO3-activated fly ash (CNF) binder system and boron compounds (H3BO3 and Na2B4O7) for thermal neutron shielding through cold-bonding pelletization. The study demonstrated that the CNF aggregates having 5 wt% H3BO3 and Na2B4O7 were lightweight and adequate for structural use, satisfying ASTM C 330, Korean CSD, and KS F2527. The CNF aggregates were safe from heavy metal toxicity and did not noticeably lose boron due to leaching. In addition, these aggregates had only a small amount of quartz and thus had considerably lower risks of neutron-induced volumetric aggregate expansion in PC concretes than crushed (or natural) aggregates. The use of the CNF aggregates in PC concrete production was excellent in increasing the thermal neutron shielding performance of PC concrete. The thermal neutron shielding efficiencies of the PC concretes with CNF aggregates having 5 wt% H3BO3 and Na2B4O7 were 96.6 % and 99.3 %, respectively. In addition, the compressive strengths of PC concrete with these CNF aggregates were high enough (29.2-30.2 MPa) to satisfy the structural lightweight aggregate concrete requirement (>17 MPa) according to ACI 213.

Graphene nanoribbons (GNRs) possess superior electrical properties due to their unique structures, making them increasingly valuable in composite materials. This study investigated the ability of GNRs to serve as nanoreinforcing agents that modify the electrical and self-sensing properties of cementitious composites compared to conventional nanomaterials such as carbon nanotubes (CNTs). Because they are highly dispersible in alkaline environments, GNRs can form effective conductive networks within a cement matrix. Incorporating 0.05 wt% GNRs into a cementitious composite significantly reduced the electrical resistivity of the sample after 28 d of curing by 64.61 % compared to the control sample. After drying, its electrical resistivity was still 42.82 % lower than that of the control sample. Furthermore, the GNRs-incorporated sample (dry state) exhibited a remarkable 63.65 % fractional change in resistivity when subjected to cyclic compressive stress. These results suggest that GNRs hold significant potential for enhancing the electrical and self-sensing properties of cementitious composites.

With the advent of rapid climate change and global warming, the cement industry has been actively striving to minimize its carbon footprint. An effective approach for reducing carbon emissions is to utilize supplementary cementitious materials (SCMs). Limestone calcined clay cement (LC3) has garnered significant attention because of its ability to reduce clinker use by approximately 45 wt%, compared to ordinary Portland cement. However, the raw materials involved in LC3 production, which are obtained through mining and heating of raw clay, also counts toward the carbon footprint. Therefore, the present study aims to explore the feasibility of using oyster shells as a replacement for limestone in LC3 systems. Various amorphousness of calcined clay were tested to investigate the hydration reaction and strength of the oyster shell calcined clay cement (OC3). Data collected using techniques such as X-ray diffraction, thermogravimetry, scanning electron microscopy, isothermal calorimetry, compressive strength testing, and 29Si nuclear magnetic resonance spectroscopy were analyzed to elucidate the hydration reaction mechanisms of OC3, considering the type of calcite (oyster shell or limestone) and the extent of the transformation of kaolinite clay to metakaolin. The findings of this study demonstrate that oyster shells can effectively replace limestone as a raw material for LC3. Furthermore, the irregular morphology of the shell particles enhanced the hydration reaction and development of the cement's microstructure.

This study demonstrated that the Ca(OH)2-Na2CO3 activation produced a near-white surface of hardened samples having a high lightness index using dark coal-fired bottom ash. In this study, the lightness index (L*) (index of black (0) to white (1 00)) of raw dark bottom ash was 36.73, but after the activation, the hardened sample showed a significantly increased L* (77.93) (i.e., 112.2% L* increase) with a near-white surface. The Ca(OH)2- Na2CO3-activation also decreased the values of a* (index of green to red) and b*(index of blue to yellow), implying the removal of chromatic colors. However, this whitening effect significantly depended on the particle size of raw bottom ash, controlled by the milling process, and the produced amounts of white reaction products (particularly, C-S-H (gel) and CaCO3), affected by the milling process and substituted ratios with fly ash and ground granulated blast furnace slag (GGBFS). The compressive strength of the 100 wt% bottom ash sample was only 5.3 MPa at three days, but it was enhanced to have enough strength over 7.4-10.3 MPa (adequate for structural bricks) without losing the surface brightness noticeably (L* > 70) by the milling process or by substituting bottom ash with fly ash or GGBFS.

Water-saturated cellulose microfibers (CMFs) incorporated into fresh cement composites can mitigate microcracking induced by self-desiccation during drying. This study utilized a nonlinear impact resonance acoustic spectroscopy (NIRAS) technique to elucidate the mechanism underlying the CMF-driven mitigation of selfdesiccation. The hysteresis nonlinearity parameter (& alpha;) from the NIRAS was used to quantify the microstructural changes in three different mixtures (0 0.3 and 1% dosages of CMFs). Computed tomography (CT) compression tests and periodic measurements of mass and resonance frequency were performed to obtain more insights into mitigating self-desiccation. Supported by the collected data the results show a remarkable reduction in & alpha; over time confirming high sensitivity of & alpha; to the microstructural change. Furthermore the trend of & alpha; was consistent with the pore size distribution estimated by the CT test which provides quantitative evidence to support the mitigation of self-desiccation promoted by CMFs. We envision that these findings can be used as guidelines for enhancing the durability of cement composites facilitated by CMFs.

This study investigates the effectiveness of ground-granulated blast furnace slag (GGBFS) and fly ash in improving the durability of concrete specimens subjected to thermal damage. Multiple techniques, including nonlinear impact resonance acoustic spectroscopy (NIRAS), compressive strength, X-ray diffraction, and thermogravimetry, are employed to capture the physical and chemical phenomena resulting from a temperature elevation of 200, 400, 600, and 800 degrees C. The experimental results demonstrated that replacing cement with fly ash (20 wt%) and GGBFS (40 wt%) yields significant mitigation of microcracking development, highlighting their potential as agents for enhancing concrete durability under high-temperature exposure. Notably, the hysteresis nonlinearity parameter (alpha) measured using NIRAS exhibits a high sensitivity for detecting the transition from micro to macroscale defects, and the trend of alpha sufficiently coincides with the results of the mineralogical analyses, confirming the evaporation of free water, dehydration of calcium silicate hydrate (C-S-H), and decomposition of calcium hydroxide (CH).

This study examined the influence of the crystallinity of added nano-alumina on the sulfate resistance of ordinary Portland cement (OPC) paste. Two crystalline types of nano-aluminas (α-and γ-phase) were incorporated in cement pastes, which were exposed to sulfate solution. In the results, both paste samples having α- and γ-phase aluminas had accelerated compressive strength loss and increased length expansion compared to the sample without alumina addition. In particular, the rapidly decreased dynamic elastic modulus of the nano-alumina added samples postulates the greatly increased internal stress likely by the increased formation of volume expansive reaction products, such as ettringite, which was supported by the XRD and TG results. The greater ettringite formation in the nano-alumina added samples was likely due to reactive AH 3 (=Al(OH) 3 ) gel formation as the higher consumption degree of portlandite in the alumina added samples indirectly indicates the active AH 3 gel formation, resulting in additional ettringite formation from the reaction of AH 3 with Na 2 SO 4 solution. A further degree of sulfate attack was observed in the γ-alumina added sample for the long-term Na 2 SO 4 exposure (180 days) mainly due to the greater degree of gypsum formation inducing more internal expansive stress compared to the α-alumina added sample.

This study investigates the impact of nano-CaCO3 and nano-SiO2 on limestone calcined clay cement (LC3), focusing on its hydration kinetics and mechanical properties. Nano-CaCO3 incorporation accelerated early-stage hydration and induced extensive carboaluminate formation; however, it reduced the mechanical strength at later hydration stages due to its effect on calcium-(alumino)silicate-hydrate (C-(A-)S-H) characteristics and hydrate composition. A higher CaCO3 dissolution rate increased the Ca/Si ratio in the matrix, and a large amount of carboaluminate formation consumed the Ca(OH)2 and water required for the pozzolanic reaction of metakaolin. Conversely, nano-SiO2 incorporation improved the mechanical strength across all hydration stages through the filler effect, good dispersion quality, and pozzolanic reactivity. Nano-SiO2 accelerated the early-stage hydration and produced ample C-(A-)S-H, which effectively refined the pore structure and enhanced the mechanical strength. However, the combined use of nano-CaCO3 and nano-SiO2 adversely affected the mechanical strength and pore structure of the cement pastes owing to strong agglomeration, despite accelerated hydration in the early-stages.