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.

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.

Although carbon nanotubes (CNT) and nanosilica (NS) have shown substantial potential for enhancing the thermal resistance and post-fire mechanical recovery of cementitious composites, their combined synergistic effects remain unclear. This study aimed to elucidate the influence of CNT and NS double-hybrids on the physicochemical properties of cementitious composites under different heating temperatures (200, 500, and 800 C-degrees) and re-curing conditions (25 degrees C/65 % RH and water immersion). We assessed the changes in the compressive and tensile strengths, bulk density, surface morphology, hydration products, and pore characteristics using focused ion beam scanning electron microscopy to visualize the evolving nanoscale pore structures. Our findings reveal a remarkable synergistic effect on the thermal resistance and strength recovery properties of the CNT/NS hybrid samples, owing to the stable matrix observed after heating to 800(degrees)C. Following exposure to 800 C-degrees, the tensile strength exhibited a remarkable 69.6 % increase compared to its pre-heating state, without any indication of crack formation. The CNT served as nucleation sites, expediting the pozzolanic reaction of NS during heating and resulting in a homogenized pore structure with interconnected hydrates. The CNT/NS hybrid samples exhibited uniform shrinkage of hydrates without creating nanoscale rod-like pores typical in ordinary cement paste, while the increase in pore volume was predominantly attributed to the expansion of existing pores and the formation of nearby new pores.

Low-lime calcium silicate cement (CSC) is a CO2-reactive cement that utilizes the carbonation products of low- or non-hydraulic C2S, C3S2, and CS phases under H2O- and CO2-rich conditions. However, the reactivity and compressive strength of the CSC require further improvement. Therefore, this study aims to investigate the effects of blending ordinary Portland cement (OPC) as a reactive source into CSC on the initial reaction kinetics, phase evolution, and compressive strength development during carbonation curing. To assess the effects of blending CSC and OPC, CSC was substituted by OPC with the incremental ratio of 20 wt.%. Notably, the CSC sample with 20 wt.% OPC incorporation exhibited the highest compressive strength, which increased by up to 2.5 times compared to the pure CSC paste. Analysis of the microstructural phase evolution revealed that this significant increase in compressive strength was attributed to the strong mechanical interlocks between the rhombic CaCO3 crystals, which were reinforced by a substantial amount of vaterite.

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.

The thermal stability of geopolymer pastes with different Si/Al ratios (1.5 - 3.0) and sodium activators (Na 2 SiO 3 and/or NaOH) were evaluated in this study. The inclusion of Na 2 SiO 3 induced an active geopolymer reaction, enhancing pre-heating compressive strength, but gradually reduced from 300 degrees C due to vapor pressure and microstructural deterioration caused by entrapped physically bound water. Conversely, the strength of geopolymers containing only NaOH remained stable or increased up to 600 degrees C, owing to additional geopolymerization from unreacted raw materials and compact matrix induced by thermal shrinkage. The aluminosilicate networks of all geopolymers remained relatively stable until crystalline nepheline formed above 800 degrees C; larger crystalline particles were formed in geopolymers with Na 2 SiO 3 owing to its denser geopolymer matrix, whereas smaller crystalline particles were formed in geopolymers with smaller Si/Al and only with NaOH, resulting in fewer voids and stable mechanical strength. Swelling of silica was notable in Na 2 SiO 3 -acti- vated geopolymer, resulting in greater strength loss upon heating, indicating that Na 2 SiO 3 hinders the thermal stability of geopolymers at extreme temperatures.

This study explores the influence of the interatomic structure of sodium aluminosilicate hydrate (N-A-S-H) with varying silica contents on the mechanical properties of metakaolin-based geopolymer. Geopolymer pastes comprising Si/Al ratios between 2.0 and 3.0 were synthesized. A larger number of Si-O-Si linkages compared to Si-O-Al linkages and a higher atomic number density were found in the geopolymers with higher silica contents, which enhanced the compressive strength of the geopolymer pastes up to the optimal Si/Al ratio of 2.5. The paste with a Si/Al = 2.5 exhibited a greater portion of Q4(1Al and 2Al) and denser morphology compared to the other geopolymer pastes. Furthermore, in-situ high-energy synchrotron X-ray scattering experiments were conducted to assess the elastic modulus of the aluminosilicate structure at a local atomic scale. The modulus value in real space decreases with increasing silica contents up to Si/Al = 2.5 and increases with the presence of excessive unreacted silica fume. The modulus value in reciprocal space for the axial and lateral directions both presented a positive value at the geopolymer comprising a Si/Al ratio higher than 2.5, indicating that the load-bearing property of N-A-S-H changed at higher Si/Al ratios. Moreover, the smallest difference between the strains along the axial and lateral directions was detected for the geopolymer with Si/Al = 2.5 in both the real and reciprocal space, owing to the most interconnected and flexible nanostructure, which led to the highest mechanical strength.

Although the mechanism of pore formation in cement paste owing to high temperatures is a critical characteristic directly linked to fire resistance, research regarding the 3D characteristics of nano-scale pores within a consistent volume is limited. This study uses synchrotron X-ray nanoimaging to investigate the impact of heating at various temperatures (400, 600, and 800 degrees C) on the morphology, distribution, and volume changes of nano-scale pores in a consistent volume of ordinary Portland cement paste. The mechanical and hydration properties were assessed via compressive strength tests, X-ray diffraction, and thermogravimetry. After heating to 400 degrees C, new highflatness pores formed, whereas heating to 600 and 800 degrees C resulted in pore coalescence and the formation blade-like pores developed around unhydrated cement particles. Elongated pores formed after heating to 600 degrees C, which resulted from the decomposition of Ca(OH)2, leading to the structure being prone to internal cracking.

The effects of various initial carbonation curing environments on the phase evolution and resulting mechanical characteristics of tricalcium silicate paste were studied. For the analyses of the reaction products and microstructure, synchrotron X-ray diffraction, thermogravimetry, Fourier transform-infrared spectroscopy, scanning electron microscopy with energy dispersive X-ray spectroscopy and high-resolution X-ray computed tomography were utilized. C3S cured under carbonation environment pressurized by 0.1 MPa showed excellent mechanical properties owing to the highest degree of reaction and homogeneous generation of CaCO3 with low-Ca/Si calcium silicate hydrates, resulting in a dense matrix with refined pore structure. C3S paste treated under other carbonation conditions underwent deteriorative microstructural phase transitions, including void evolution by decalcification of C-S-H and an inhomogeneous composition of crystalline phases, resulting in inferior properties.

본 논문에서는 시멘트 경화체를 보강하기 위한 그래핀 옥사이드(GO), 기능성 탄소 나노 튜브(f-CNT), 나노 실리카(NS)의 최적 비율을 조사하였다. 먼저 초음파 분산기로 분산시킨 나노 소재를 Ca(OH)₂ 포화 용액과 섞은 후 분산도를 측정하여 시멘트 교반 과정에서의 나노 물질들의 분산 특징을 알아보았다. 또한, 세 가지 나노 소재의 혼합비 중 어느 비율이 가장 시멘트 경화체를 성공적으로 보강하는지를 알아보기 위해 다양한 혼합비를 갖는 나노 소재 강화 시멘트 경화체의 수화물 조성 및 압축 강도를 평가하였다. 이후, 나노 소재의 분산도와 나노 소재 보강 시멘트 경화체의 압축강도 사이의 상관관계를 조사하였다. 0.04 g GO, 0.01 g f-CNT, 1 g NS의 최적 비율을 갖는 삼중 소재 보강 시멘트 경화체에서는 나노 소재 간의 뛰어난 분산도로 인하여 단일, 이중 나노 소재 보강 시멘트 경화체에 비해 높은 압축 강도가 발현되었다.

This study aimed to reveal the synergistic effects of graphene oxide (GO)/nanosilica (NS)/functionalized carbon nanotube (FCNT) hybrid nanomaterials on the thermal resistance and pore refinement of cementitious composites. The dispersion states and sizes of the nanomaterials in distilled water and Ca2+-rich solutions were assessed. In addition, the pore characteristics and thermal resistance of the nanomaterial-incorporated cementitious composites were analyzed. In the GO/NS/FCNT hybrid solution, a reinforcing effect of FCNT on the GO plate resulted in high resistance to wrinkling and agglomeration of GO; therefore, the stretched GO plate structure was advantageous for long-term dispersion maintenance, and well-dispersed NS enabled a more active pozzolanic reaction in cement paste. As a result, the triple-hybrid GO/NS/FCNT-reinforced cementitious composites demonstrated improved thermal resistance owing to their high residual strength after heating as well as homogenized pore structures with less elongated pore shapes and lower porosity than control specimens without nanomaterials.

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 proposes an ultrasonic treatment method for enhancing the decontamination efficiency of cement waste under the lower acid concentration. The phase transitions and decontamination efficiency of the hydrates and Co nuclides in the cement paste were respectively studied using various concentrations of sulfuric acid. The effect of pre-heating the acid-treated cement paste at 500 celcius on its phase transition and decontamination effi-ciency were also studied. The underlying mechanism of the enhanced decontamination efficiency was elucidated by inductively coupled plasma spectrometry, powder X-ray diffraction, thermogravimetry, laser diffractometry, and X-ray absorption spectroscopy. Ultrasound-assisted decontamination by 1.0 M H2SO4 was 1.5 times more efficient than non-sonication-assisted decontamination with double the acid concentration (2.0 M H2SO4), owing to the detachment of the outer-layer phases of CaSO4 that obstructed the contact between the acid and the nuclides. The thermally-treated samples showed similar decontamination efficiencies under treatment with high acid concentrations and ultrasonication, due to the vigorous acid reaction kinetics regardless of the thermal decomposition of the hydrates.

This study explored the effect of M-S-H formation on the local atomic arrangements and mechanical properties of C-S-H. The elastic moduli of the samples were calculated using shifted atomic distances (r) and d-spacings (d) acquired by applying an external load on the pastes during X-ray scattering experiments. The experimental results indicated that the crystal structure of C-S-H remained intact with MgCl2 addition. At the highest Mg/Si ratio (Ca/Si = 0.6, Mg/Si = 0.2), change in the dominant phase occurred from C-S-H to M-S-H because the low pH environment hindered the formation of C-S-H and facilitated the formation of M-S-H. The elastic modulus decreased with increasing Mg/Si ratio up to 0.1 owing to both C-S-H destabilization and low M-S-H content in the samples. Conversely, the elastic modulus increased in the paste synthesized with the highest Mg/Si ratio because considerable M-S-H had formed, which exhibited a higher elastic modulus than C-S-H.

This study investigates the synergistic strengthening mechanism of graphene oxide (GO), functionalized carbon nanotubes (f-CNT), and nano-silica (NS) triple hybrid-reinforced Portland cement composite. GO was selected as the variable owing to the synergistic effect of GO with both f-CNTs and NS upon dispersion by forming bonds with both nanomaterials. At a low GO dosage (similar to 0.03 wt% of cement), the bond between GO and NS deteriorated the dispersion in Ca2+-rich solution due to the overly attached NS on the GO surface. The highest GO fraction (0.05 wt%) also led to poor dispersion as the excess GO was agglomerated by Ca2+ ions. However, an optimal amount of GO (0.04 wt%) significantly improved the dispersion quality. The enhanced dispersion of the triple hybrid positively influenced the hydration degree and mechanical performance of the cement paste (133 % and 156 % for compressive and tensile splitting strength compared to OPC) and the pozzolanic reactivity of NS.