Reducing the carbon footprint of the cement industry has become one of the main concerns of researchers in the field. This study explores different strategies to reduce the setting retardation effect ...of high-SO3 fly ash (HSFA) on cement paste. The SO3 phase was found to correspond to hannebachite (CaSO3·0.5H2O). Chemical (calcium chloride), physical (fine limestone powder), and pre-washing strategies were investigated as means to reduce or eliminate the retardation. Each of these strategies showed some potential to decrease the retardation effect. A combination of fine limestone powder and HSFA pre-washing showed almost the same accelerating power as the calcium chloride, offering a good alternative when chloride incorporation is restricted. The retardation effect can be associated with a combined extension of the induction period and a depression of the initial silicate reactions of the clinker phases. A methodology to assess the hannebachite content based on a thermogravimetric analysis (TGA) technique is proposed, allowing a good alternative control approach for field conditions or for where X-ray (XRD or XRF) equipment is not readily available.
•Microcapsules slow down the reaction of both geopolymer and Portland cement pastes.•Increasing the temperature accelerates the setting times of geopolymer and Portland cement pastes.•Addition of ...microcapsules reduces the compressive strength.•Enhanced porosity at higher temperatures for both geopolymer and Portland cement.
To reduce pollution and global warming, the energy consumption needs to be decreased. Incorporation of Phase Change Materials (PCMs) into building materials can help lower the energy needed to cool and warm buildings, while keeping the indoor temperature at a comfortable level. However, incorporation of PCMs into construction materials alter their performance. In this study, the effect of temperature and addition of two different Micro-encapsulated Phase Change Materials (MPCM) to geopolymer concrete (GPC) and Portland cement concrete (PCC) and pastes was investigated. The samples were examined both below (20 °C) and above (40 °C) the melting points of the PCMs. While the MPCM is not damaged by the alkaline solution, a few microcapsules are broken during the mixing process. Isothermal calorimetry shows that MPCM addition slows down the reaction rate of both geopolymer and Portland cement paste. The setting times were faster when the temperature was increased. The mechanical properties are reduced when MPCM is added to GPC and PCC, although the compressive strength is adequate for building applications. Microstructural studies show more uniform and undamaged edges in the shell-concrete matrix transition zone of GPC than PCC. The samples cured at 40 °C exhibits more air voids in both GPC and PCC than at 20 °C.
•Temperature-dependent reaction kinetics of activated fly ash, slag, and their blends examined.•Kinetics of moist-cured blends with large amounts of fly ash studied.•Differences in the calorimetric ...response between slag and fly ash rich blends explored.•Kinetic models to extract the relevant parameters of the activation reaction.
Alkali silicate activated Class F fly ash–slag blends containing fly ash as the major constituent (up to 70% by mass) are proportioned to develop sufficient mechanical properties under moist curing conditions. Isothermal calorimetric studies are carried out on OPC, activated slag and fly ash, and selected fly ash–slag blends at 25°C, 35°C, and 40°C to explore their reaction kinetics. OPC and activated slag pastes exhibit similar heat release response, especially at higher temperatures (40°C). For the fly ash–slag blends, the calorimetric responses at ambient and elevated temperatures are markedly different from those of OPC and activated pure slag pastes. Two simple kinetic models are used to extract the relevant parameters of the activation reaction. Increase in temperature within the studied range influences the total heat released by the fly ash rich pastes more than those of slag pastes. For the fly ash rich blends, it is shown using the Knudsen rate constant that higher reaction temperatures are required to extract realistic model-based kinetic parameters.
•Presence of 0.9% sassolite in boron carbide retards cement initial setting time.•Filler effect of boron carbide powder enhances the cement hydration reaction.•Boron carbide radically increases ...concrete thermal neutrons absorption capability.•Boron carbide has an insignificant effect on concrete γ-rays attenuation properties.•Boron carbide in concrete slightly enhances fast neutrons shielding properties.•50% boron carbide in concrete benefit setting time and neutron shielding properties.
Boron-containing compounds have an excellent radiation shielding capability against slow neutrons. Moreover, sassolite in boron-containing compounds adversely affects cement hydration by retarding cement setting times. Accordingly, experimental and analytical investigations were carried out to examine the filler effect of commercial boron carbide (B4C) fine powder with a mean particle diameter of 2.64 μm on Portland cement hydration reaction, and concrete mechanical and radiation shielding properties. Isothermal calorimetry method was used to study the heat evolution and the cement degree of hydration of mixes containing 0, 25, 50 and 75% of B4C to cement by weight. Effects of adding B4C on concrete compressive strength were then investigated. Analytical investigations, specifically mass attenuation coefficient using WinXcom program and effective atomic number using Auto-Zeff, were carried out to evaluate the radiation shielding of corresponding concrete mixes for photon energies ranging from 10 keV to 10 MeV. Moreover, macroscopic effective removal cross-sections for fast neutrons and thermal neutron macroscopic absorption cross-sections were calculated using MRCsC program and JANIS-4 software, respectively. The results confirm that the presence of sassolite in the studied B4C powder retards the hydration reaction for the first 24 h and reveal significant improvements in concrete strength thereafter with the increase of boron carbide due to the filler effect. Furthermore, the addition of boron carbide yielded measurable improvement in neutron shielding capabilities of concrete mixes.
Cement-based materials prepared with manufactured sand can exhibit quick loss of fluidity. However, the estimation of the flow loss remains difficult given the variable contents and physiochemical ...properties of the microfines in various sands. This paper studies the fluidity loss of mortar mixtures made with different manufactured sands varying in mineral composition and content of microfines. The effect of microfines on accelerating the early-age hydration of cement before the deceleration period was evaluated by quantifying the generation of early hydration products. Test results show that the growth of yield stress corresponding to the loss of mini-slump flow of mortar mixtures were mainly determined by the formation of early hydration products, in addition to the volume fraction and packing density of aggregate grains and powder particles. An approach was then proposed that can assess the loss of mini-slump flow of mortar mixtures prepared with manufactured sand, regardless of the type and content of the microfine materials in the sand.
•Manufactured sand with a relatively high content of microfines does not necessarily cause low fluidity of mortar.•Manufactured sand with a high fine content and MB would cause fast growth of rheological properties.•Flow loss of mortar with manufactured sand can be assessed by evaluating the generation of early hydrates.
•The exothermic performance of cement/starch-based admixture mixes are systemically compared.•Starch-based admixtures affect both the appearance time and maximum heat flow of the main hydration ...peak.•The effect is determined mainly by the action time of molecule in the cement paste.•Inhibiting the initial precipitation of C-S-H is proposed as the possible mechanism.
The effect of three types of starch-based admixtures, namely glucose and its derivatives, soluble dextrin with various degree of polymerization and a novel starch-based temperature rise inhibitor (TRI) with various degree of starch acidification on the exothermic process of cement hydration has been investigated through the calorimetry measurements. Except delaying the appearance of the main hydration peak as the retarding effect, starch-based admixtures can also reduce the heat flow during the acceleration period and induce a lower maximum heat flow as the depressing effect. Together with the dissolution and adsorption results, it can be concluded that the relationship between these two effects is determined by the action time of molecule in the cement paste. The soluble admixtures with fairly short action time focus mainly on disturbing the cement hydration during the induction period but have minor effect on depressing the main hydration peak. TRI with limited dissolution can persistently inhibit the cement hydration over a longer period of action time, inducing negligible retarding effect but apparent depressing effect.
All living systems function out of equilibrium and exchange energy in the form of heat with their environment. Thus, heat flow can inform on the energetic costs of cellular processes, which are ...largely unknown. Here, we have repurposed an isothermal calorimeter to measure heat flow between developing zebrafish embryos and the surrounding medium. Heat flow increased over time with cell number. Unexpectedly, a prominent oscillatory component of the heat flow, with periods matching the synchronous early reductive cleavage divisions, persisted even when DNA synthesis and mitosis were blocked by inhibitors. Instead, the heat flow oscillations were driven by the phosphorylation and dephosphorylation reactions catalyzed by the cell-cycle oscillator, the biochemical network controlling mitotic entry and exit. We propose that the high energetic cost of cell-cycle signaling reflects the significant thermodynamic burden of imposing accurate and robust timing on cell proliferation during development.
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•Real-time, non-invasive measurement of the energetics of embryonic development by isothermal calorimetry•Heat flow during cleavage stage development oscillates in phase with the cell cycle•The Cdk1-cyclin B1 phosphorylation-dephosphorylation cycle drives oscillatory heat flow•Substantial energetic costs are incurred by cellular encoding of cell-cycle timing
Rodenfels et al. measure the energetic costs of early zebrafish development using isothermal calorimetry and uncover prominent heat flow oscillations during reductive cleavage divisions that are independent of DNA replication, mitosis, and cytokinesis. Instead, oscillatory heat is driven by cell-cycle signaling, indicating that cell-cycle timing regulation is energetically costly.
The histidine brace (His‐brace) is a copper‐binding motif that is associated with both oxidative enzymes and proteinaceous copper chaperones. Here, we used biochemical and structural methods to ...characterize mutants of a His‐brace‐containing copper chaperone from Pseudomonas fluorescens (PfCopC). A total of 15 amino acid variants in primary and second‐sphere residues were produced and characterized in terms of their copper binding and redox properties. PfCopC has a very high affinity for Cu(II) and also binds Cu(I). A high reorganization barrier likely prevents redox cycling and, thus, catalysis. In contrast, mutations in the conserved second‐sphere Glu27 enable slow oxidation of ascorbate. The crystal structure of the variant E27A confirmed copper binding at the His‐brace. Unexpectedly, Asp83 at the equatorial position was shown to be indispensable for Cu(II) binding in the His‐brace of PfCopC. A PfCopC mutant that was designed to mimic the His‐brace from lytic polysaccharide monooxygenase‐like family X325 did not bind Cu(II), but was still able to bind Cu(I). These results highlight the importance of the proteinaceous environment around the copper His‐brace for reactivity and, thus, the difference between enzyme and chaperone.
•Sulfate balance can be quantified via time derivatives of isothermal calorimetry.•Kernel regression method can accurately parametrize isothermal calorimetry curves.•Early hydration of LC3 can be ...modified considerably by the fineness of the mixture.•Metakaolin fraction mediates the sulfate balance of LC3 significantly.
Achieving the correct sulfate balance in limestone calcined clay cements (LC3) to control aluminate hydration is critical for early hydration and property development, but the role of the calcined kaolin (metakaolin) fraction relative to other compositional variables has not been previously well-explored. In addition, little published research has investigated the influence of water-to-solid ratio (w/s) and superplasticizers in this context. This study assesses the influence and quantifies the relative significance of compositional predictors on the sulfate balance and cumulative heat evolved by 24 h for LC3 through a stepwise regression model. Sulfate balance was defined as the time difference between the sulfate depletion point and the time of maximum of alite peak obtained from a time derivative of data obtained through isothermal calorimetry. A methodology based on Kernel smoothing was used to precisely identify these events. The first 24 h of hydration of some LC3 pastes was also monitored via in-situ X-ray diffraction to develop linkages between LC3 composition and hydrated phase assemblage. The statistical analysis identified the metakaolin fraction as particularly significant for the sulfate balance. The results suggest that the metakaolin fraction influences the sulfate balance of LC3 both directly and through its interactions with other constituent materials such as limestone.
Significance Events that occur between entry of the HIV-1 capsid into the cytoplasm of the target cell and the delivery of the viral genetic material into the nucleus constitute some of the less well ...understood processes in the viral life cycle. We demonstrated that PF74, a small-molecule inhibitor of HIV-1, and the host proteins CPSF6 and NUP153 bind to a preformed pocket within the CA protein hexamers that exist within the assembled capsid. Our results suggest that key features of the CA hexameric lattice remain intact upon docking at the nuclear pore. In addition, low molecular weight ligands that better mimic virus–host, protein–protein interactions at the intersubunit interfaces within the assembled viral capsid may offer novel avenues for therapeutic intervention.
Upon infection of susceptible cells by HIV-1, the conical capsid formed by ∼250 hexamers and 12 pentamers of the CA protein is delivered to the cytoplasm. The capsid shields the RNA genome and proteins required for reverse transcription. In addition, the surface of the capsid mediates numerous host–virus interactions, which either promote infection or enable viral restriction by innate immune responses. In the intact capsid, there is an intermolecular interface between the N-terminal domain (NTD) of one subunit and the C-terminal domain (CTD) of the adjacent subunit within the same hexameric ring. The NTD–CTD interface is critical for capsid assembly, both as an architectural element of the CA hexamer and pentamer and as a mechanistic element for generating lattice curvature. Here we report biochemical experiments showing that PF-3450074 (PF74), a drug that inhibits HIV-1 infection, as well as host proteins cleavage and polyadenylation specific factor 6 (CPSF6) and nucleoporin 153 kDa (NUP153), bind to the CA hexamer with at least 10-fold higher affinities compared with nonassembled CA or isolated CA domains. The crystal structure of PF74 in complex with the CA hexamer reveals that PF74 binds in a preformed pocket encompassing the NTD–CTD interface, suggesting that the principal inhibitory target of PF74 is the assembled capsid. Likewise, CPSF6 binds in the same pocket. Given that the NTD–CTD interface is a specific molecular signature of assembled hexamers in the capsid, binding of NUP153 at this site suggests that key features of capsid architecture remain intact upon delivery of the preintegration complex to the nucleus.
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