•Summarizing the latest literature on CNTs and GO reinforced cement composites.•Cement fabrication focuses on separating and avoiding re-agglomeration of nanomaterials.•Preserving the workability of ...nanocomposites is accomplished by using admixtures.•The seeding of C–S–H gel occurs on the large surface area of nanomaterials.•Reinforcement and pore refinement by 1D and 2D nanomaterials strengthen cement.
Progress in the field of nanomaterials presents an invaluable opportunity to develop cementitious composites at the nanoscale. Engineered nanomaterials exist in three principal shapes, namely 0D nanoparticle, 1D nanofiber and 2D nanosheet. The application of 0D nanoparticle and 1D nanofiber, such as nanosilica and carbon nanotubes (CNTs), respectively, has been reported in literature. The discovery of 2D nanosheet known as graphene oxide (GO) provides an extra dimension to interact with cement and concrete matrix and has yet to gain widespread attention. In this paper, recent research studies in developing cement and concrete nanocomposites are comprehensively reviewed. Also highlighted herein are the effect of incorporating nanomaterials in low dosages to the fabrication, workability, hydration, microstructure, and mechanical properties of cement-based composites.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The strength and transient creep of geopolymer and ordinary Portland cement (OPC)-based material (paste and concrete) were compared at elevated temperatures up to 550°C. The strength properties were ...determined using an unstressed hot strength test and unstressed residual strength test for paste and concrete, respectively. At 550°C, compared with the original strength, the strength of geopolymer was increased by 192% while the strength of OPC paste showed little change. However, after exposure to 550°C, the residual strength percentage of both geopolymer and OPC concretes was similar. Transient creep data show that geopolymer had little change in transitional thermal creep (TTc) between 250 and 550°C while OPC paste developed significant TTc in this temperature range. In comparison with OPC concrete, a higher strength loss of geopolymer concrete is thus believed to be due to the absence of TTc to accommodate nonuniform deformation during thermal exposure.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
When fly ash-based geopolymer mortars were exposed to a temperature of 800 °C, it was found that the strength after the exposure sometimes decreased, but at other times increased. This paper shows ...that ductility of the mortars has a major correlation to this strength gain/loss behaviour. Specimens prepared with two different fly ashes, with strengths ranging from 5 to 60 MPa, were investigated. Results indicate that the strength losses decrease with increasing ductility, with even strength gains at high levels of ductility. This correlation is attributed to the fact that mortars with high ductility have high capacity to accommodate thermal incompatibilities. It is believed that the two opposing processes occur in mortars: (1) further geopolymerisation and/or sintering at elevated temperatures leading to strength gain; (2) the damage to the mortar because of thermal incompatibility arising from non-uniform temperature distribution. The strength gain or loss occurs depending on the dominant process.
Full text
Available for:
DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
► A study on the effect of aggregate size on spalling of concrete in fire. ► Geopolymer, high and normal strength concretes were investigated. ► Effect of aggregate size was same regardless of the ...type of concrete. ► The effect is independent of binders’ chemical compositions. ► The degree of spalling has a good correlation to the fracture process zone length.
This paper presents a study on the effect of aggregate size on spalling of concrete in fire. Three concretes with completely different chemical compositions and strengths were investigated, namely, geopolymer concrete and high strength and normal strength Portland cement concretes. The effect of aggregate size was found to be the same regardless of the type of concrete. The concretes containing 10mm aggregates spalled while the ones with 14mm did not spall. Since this effect is the same in geopolymer and Portland cement concretes, it is independent of binders’ chemical compositions. This paper shows that the degree of spalling has a good correlation to the fracture process zone length, which increases with increasing aggregate size; this in turn reduces the flux of kinetic energy from pore pressure and thermal stress that is released into the fracture front and thereby improves the spalling resistance.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
This paper reports stress versus strain curves of geopolymer tested while the specimens were kept at elevated temperatures, with the aim to study the fire resistance of geopolymer. Tests were ...performed at temperatures from 23 to 680
°C and after cooling. Hot strengths of geopolymer increased when the temperature increased from 290 to 520
°C, reaching the highest strength at 520
°C, which is almost double that of its initial strength at room temperature. However, glass transition behaviour was observed to occur between 520 and 575
°C, which was characterised by abrupt loss of stiffness and significant viscoelastic behaviour. The glass transition temperature is determined to be 560
°C. Further, the strength reductions occurred during cooling to room temperature. This is attributed to the damage due to brittle nature of the material making it difficult to accommodate thermal strain differentials during cooling phase.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
This paper presents the effects of cation type, silicate concentration, compositions of low-calcium fly ash and test load on softening temperature and hot-strength (loaded while at high temperature) ...of fly ash-based geopolymers. It was found that softening temperature (
T
s
) of sodium (Na) based-geopolymer remained the same (610
°C
±
20
°C) regardless of the silicate concentration, fly ash composition, and test load. However, when the cation was changed from sodium to potassium (K), the
T
s
increased to 800
°C. Further, when Na/K is mixed, the
T
s
dropped to 570
°C.
Significant increases in hot-strengths (at 530
°C and 730
°C) were found in all geopolymers. This increase in strength was observed to be in conjunction with heat release, indicating an exothermic reaction. Since the reaction between fly ash and activators is exothermic, this reaction is believed to be the reason for the strength gain at high temperatures.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The lockdown due to COVID-19 created a rare opportunity to examine the nonlinear responses of secondary aerosols, which are formed through atmospheric oxidation of gaseous precursors, to intensive ...precursor emission reductions. Based on unique observational data sets from six supersites in eastern China during 2019–2021, we found that the lockdown caused considerable decreases (32–61%) in different secondary aerosol components in the study region because of similar-degree precursor reductions. However, due to insufficient combustion-related volatile organic compound (VOC) reduction, odd oxygen (O x = O3 + NO2) concentration, an indicator of the extent of photochemical processing, showed little change and did not promote more decreases in secondary aerosols. We also found that the Chinese provinces and international cities that experienced reduced O x during the lockdown usually gained a greater simultaneous PM2.5 decrease than other provinces and cities with an increased O x . Therefore, we argue that strict VOC control in winter, which has been largely ignored so far, is critical in future policies to mitigate winter haze more efficiently by reducing O x simultaneously.
Full text
Available for:
IJS, KILJ, NUK, PNG, UL, UM
Organic aerosols (OAs), which consist of thousands of complex compounds emitted from various sources, constitute one of the major components of fine particulate matter. The traditional positive ...matrix factorization (PMF) method often apportions aerosol mass spectrometer (AMS) organic datasets into less meaningful or mixed factors, especially in complex urban cases. In this study, an improved source apportionment method using a bilinear model of the multilinear engine (ME-2) was applied to OAs collected during the heavily polluted season from two Chinese megacities located in the north and south with an Aerodyne high-resolution aerosol mass spectrometer (HR-ToF-AMS). We applied a rather novel procedure for utilization of prior information and selecting optimal solutions, which does not necessarily depend on other studies. Ultimately, six reasonable factors were clearly resolved and quantified for both sites by constraining one or more factors: hydrocarbon-like OA (HOA), cooking-related OA (COA), biomass burning OA (BBOA), coal combustion (CCOA), less-oxidized oxygenated OA (LO-OOA) and more-oxidized oxygenated OA (MO-OOA). In comparison, the traditional PMF method could not effectively resolve the appropriate factors, e.g., BBOA and CCOA, in the solutions. Moreover, coal combustion and traffic emissions were determined to be primarily responsible for the concentrations of PAHs and BC, respectively, through the regression analyses of the ME-2 results.
Full text
Available for:
IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Among children with the most severe presentation of Marfan syndrome (MFS), an inherited disorder of connective tissue caused by a deficiency of extracellular fibrillin-1, heart failure is the leading ...cause of death. Here, we show that, while MFS mice (Fbn1C1039G/+ mice) typically have normal cardiac function, pressure overload (PO) induces an acute and severe dilated cardiomyopathy in association with fibrosis and myocyte enlargement. Failing MFS hearts show high expression of TGF-β ligands, with increased TGF-β signaling in both nonmyocytes and myocytes; pathologic ERK activation is restricted to the nonmyocyte compartment. Informatively, TGF-β, angiotensin II type 1 receptor (AT1R), or ERK antagonism (with neutralizing antibody, losartan, or MEK inhibitor, respectively) prevents load-induced cardiac decompensation in MFS mice, despite persistent PO. In situ analyses revealed an unanticipated axis of activation in nonmyocytes, with AT1R-dependent ERK activation driving TGF-β ligand expression that culminates in both autocrine and paracrine overdrive of TGF-β signaling. The full compensation seen in wild-type mice exposed to mild PO correlates with enhanced deposition of extracellular fibrillin-1. Taken together, these data suggest that fibrillin-1 contributes to cardiac reserve in the face of hemodynamic stress, critically implicate nonmyocytes in disease pathogenesis, and validate ERK as a therapeutic target in MFS-related cardiac decompensation.
The fifth generation (5G) wireless communication networks are being deployed worldwide from 2020 and more capabilities are in the process of being standardized, such as mass connectivity, ...ultra-reliability, and guaranteed low latency. However, 5G will not meet all requirements of the future in 2030 and beyond, and sixth generation (6G) wireless communication networks are expected to provide global coverage, enhanced spectral/energy/cost efficiency, better intelligence level and security, etc. To meet these requirements, 6G networks will rely on new enabling technologies, i.e., air interface and transmission technologies and novel network architecture, such as waveform design, multiple access, channel coding schemes, multi-antenna technologies, network slicing, cell-free architecture, and cloud/fog/edge computing. Our vision on 6G is that it will have four new paradigm shifts. First, to satisfy the requirement of global coverage, 6G will not be limited to terrestrial communication networks, which will need to be complemented with non-terrestrial networks such as satellite and unmanned aerial vehicle (UAV) communication networks, thus achieving a space-air-ground-sea integrated communication network. Second, all spectra will be fully explored to further increase data rates and connection density, including the sub-6 GHz, millimeter wave (mmWave), terahertz (THz), and optical frequency bands. Third, facing the big datasets generated by the use of extremely heterogeneous networks, diverse communication scenarios, large numbers of antennas, wide bandwidths, and new service requirements, 6G networks will enable a new range of smart applications with the aid of artificial intelligence (AI) and big data technologies. Fourth, network security will have to be strengthened when developing 6G networks. This article provides a comprehensive survey of recent advances and future trends in these four aspects. Clearly, 6G with additional technical requirements beyond those of 5G will enable faster and further communications to the extent that the boundary between physical and cyber worlds disappears.
Full text
Available for:
EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
PDF
