Tests to determine the reactivity of supplementary cementitious materials (SCMs) by using isothermal calorimetry and thermogravimetric analysis have been proposed. In one such test, the heat release ...and calcium hydroxide consumption of SCMs mixed with calcium hydroxide (3:1 ratio of calcium hydroxide and SCM) at 50 °C in a 0.5 M potassium hydroxide environment are measured. In this study, we show the results of such testing for a large variety of SCMs and fillers, ranging from conventional materials such as fly ash, slag, silica fume, quartz, and limestone, to alternative materials such as calcined clays, municipal solid waste incineration fly ash, basic oxygen furnace slag, ground lightweight aggregates, ground pumice, ground glass pozzolan, and basalt fines. A total of 54 SCMs are tested using this approach. Results show that even among SCMs of the same type, there is considerable difference in the heat release and calcium hydroxide consumption, likely due to differences in amorphous content, chemical composition, and fineness, leading to different reactivities. Based on the response in the test, SCMs are classified into inert, pozzolanic, and latent hydraulic; the pozzolanic and latent hydraulic materials are further classified into less reactive and more reactive. The relationship between heat release and calcium hydroxide consumption depends on the chemical composition of the SCMs, and SCMs with high calcium, high alumina, and high silica contents show different relationships (determined by the slope of the heat release vs. calcium hydroxide plot).
As concrete freezes and thaws cracks may develop. These cracks can provide a path for water and ionic species to penetrate the concrete. This may reduce the service-life of the concrete element. In ...this study, X-ray computed tomography (CT) was used as a non-destructive technique to characterize the microstructure of mortar samples that were exposed to different levels of freeze-thaw damage by varying degree of saturation in the samples (75, 90, 95, and 100% degrees of saturation). Acoustic emission (AE) experiments were performed during freezing and thawing to investigate sample cracking behavior. The volume of cracks present within the mortar samples after freezing and thawing were determined using X-ray CT and compared to passive acoustic emission data. The location/source of cracks was also determined using X-ray CT. The crack sources (i.e., void, aggregate, interfacial transition zone, or paste) were determined using X-ray CT and were related to AE activities during cracking. Crack volumes were found to increase with increased levels of saturation, and visual observations of cracking were found to correlate with AE signatures of various crack sources.
Bioorthogonal uncaging strategies have recently emerged as an experimental therapeutic approach to control drug release. Herein we report a novel masking strategy that enables to modulate the metal ...chelating properties of hydroxamic acid groups by bioorthogonal chemistry using Pd-functionalized resins. This novel approach allowed to devise an inactive precursor of the histone deacetylase inhibitor vorinostat that was efficiently uncaged by heterogeneous Pd catalysis in cell culture models of glioma and lung cancer.
Display omitted
•The influence of CNC on cement rheology was studied by measuring the changes in yield stress and viscosity.•At low CNC dosages, cement pastes reduced yield stress by up to 54%.•At ...high CNC dosages, cement pastes increased yield stress more than 10 times the original value.•The presence of C3A phase can significantly impact CNC rheological behavior.
The rheology of cement pastes containing cellulose nanocrystals (CNC) was assessed. Nine CNC obtained from various sources were added to cement pastes. Cement pastes were made using Type I/II and Type V cement with CNC addition rates from 0.023 vol% –3.311 vol%, relative to dry cement. Pastes were made using water to cement ratios of 0.30, 0.35, and 0.40. A Bingham model was used to evaluate changes in yield stress. The goal of these experiments was to identify the characteristics of the CNC which impact rheological behavior. The results showed the rheological behavior of cement pastes with CNC was not strongly related to Zeta potential, average CNC particle length, nor the average CNC particle respect ratio. However, it was found that maximum yield stress reduction occurred at higher CNC dosages as water to cement ratio increased. In addition, the rheological measurements suggested that at lower dosages (<0.2%), CNC behaved more like a water reducing admixture, reducing the yield stress up to 54%, while at higher dosage (more than 0.5%), CNC increased the paste yield stress, similar to certain viscosity modifying admixtures.
This paper examines the role of alkali content on the transport properties of cementitious materials. While cement with high alkali content may be a concern due to the potential for alkali silica ...reaction (ASR), the alkali content also influences the electrical properties of pore solution and the bulk cementitious system. Higher concentrations of alkalis decrease the resistivity of the pore solution. However, the alkalis may also impact the microstructure formed during hydration. This paper examines the role of alkali content on both the pore solution and on the microstructure that forms. Water vapor desorption measurements indicate that systems with a higher alkali content have a lower overall porosity. This dense microstructure is not caused simply by a higher degree of hydration (DOH) (i.e., an increase in reacted products), as suggested by loss on ignition (LOI), but rather possibly from the improved morphology and distribution of calcium hydroxide, as observed with scanning electron microscope (SEM).These improvements in the microstructure alter the electrical resistivity and the results of steady and non-steady state migration tests. This indicates that with higher alkali content, cement may have a beneficial influence on reducing chloride ion transport. Furthermore, alkali leaching during saturated curing is observed, quantified, and discussed as it relates to the interpretation of electrical measurements and microstructure formed.
Bioorthogonal chemistry has become one of the main driving forces in current chemical biology, inspiring the search for novel biocompatible chemospecific reactions for the past decade. Alongside the ...well-established labeling strategies that originated the bioorthogonal paradigm, we have recently proposed the use of heterogeneous palladium chemistry and bioorthogonal Pd0-labile prodrugs to develop spatially targeted therapies. Herein, we report the generation of biologically inert precursors of cytotoxic gemcitabine by introducing Pd0-cleavable groups in positions that are mechanistically relevant for gemcitabine’s pharmacological activity. Cell viability studies in pancreatic cancer cells showed that carbamate functionalization of the 4-amino group of gemcitabine significantly reduced (>23-fold) the prodrugs’ cytotoxicity. The N-propargyloxycarbonyl (N-Poc) promoiety displayed the highest sensitivity to heterogeneous palladium catalysis under biocompatible conditions, with a reaction half-life of less than 6 h. Zebrafish studies with allyl, propargyl, and benzyl carbamate-protected rhodamines confirmed N-Poc as the most suitable masking group for implementing in vivo bioorthogonal organometallic chemistry.
► Water absorption tests are influenced considerably by the moisture content of the samples before starting the test. ► The conditioning procedure described in ASTM C1585-04 is not able to eliminate ...the “moisture history” of the samples. ► It is recommended that field samples be pre-saturated prior to being exposed to the conditioning regimen of ASTM C1585. ► Conditioning samples in an oven at 105
°C is not recommended, as it can adversely affect the microstructure of samples.
ASTM C1585 is commonly used to determine the absorption and rate of absorption of water in unsaturated hydraulic cement concretes. Unfortunately, a wide range of relative humidities can exist in the samples after this relatively short conditioning period and such variation may considerably influence the test results. Three main variables were studied in this program: the water to cement ratio, the paste volume fraction, and the effect of sample conditioning. The results confirm that water absorption testing is considerably influenced by sample preparation. Samples conditioned at 50% relative humidity can show up to six times greater total absorption than similar samples conditioned at 80% relative humidity. Samples that were conditioned in the oven at 105
°C do not appear to follow a similar trend when compared with specimens conditioned in chambers at lower temperatures for a longer duration. The absorption is also influenced by the volume of paste in the samples. The experiments show that a lack of control on moisture content or lack of consideration of the material composition may lead to a misunderstanding of the actual absorption behavior.
Different constituents of concrete can have cracking behavior that varies in terms of the acoustic waveform that is generated. Understanding the waveform may provide insight into the source and ...behavior of a crack that occurs in a cementitious composite. In this study, passive acoustic emission (AE) was used to investigate the waveform properties of the individual components of concrete (i.e., aggregate, paste, and interfacial transition zone (ITZ)). First, acoustic events produced by cracks generated using mechanical loading in a wedge splitting test were detected. It was observed that cracks that occurred through the aggregate have an AE frequency range between 300kHz and 400kHz, while cracks that propagated through the matrix (paste and ITZ) have a frequency range between 100kHz and 300kHz. Second, tests were performed using samples that were susceptible to alkali silica reaction; and AE and X-ray computed tomography were used to detect cracking. AE events with a frequency range between 300kHz and 400kHz were detected at early ages, suggesting the initiation of cracks within reactive aggregate. At later ages, AE events were detected with frequency ranges of 100–300kHz, indicating crack development and propagation in the matrix.
We report on the design and performance of the Keck Cosmic Web Imager (KCWI), a general purpose optical integral field spectrograph that has been installed at the Nasmyth port of the 10 m Keck II ...telescope on Maunakea, Hawaii. The novel design provides blue-optimized seeing-limited imaging from 350-560 nm with configurable spectral resolution from 1000-20,000 in a field of view up to 20″ × 33″. Selectable volume phase holographic (VPH) gratings and high-performance dielectric, multilayer silver, and enhanced-aluminum coatings provide end-to-end peak efficiency in excess of 45% while accommodating the future addition of a red channel that will extend wavelength coverage to 1 micron. KCWI takes full advantage of the excellent seeing and dark sky above Maunakea with an available nod-and-shuffle observing mode. The instrument is optimized for observations of faint, diffuse objects such as the intergalactic medium or cosmic web. In this paper, a detailed description of the instrument design is provided with measured performance results from the laboratory test program and 10 nights of on-sky commissioning during the spring of 2017. The KCWI team is lead by Caltech and JPL (project management, design, and implementation) in partnership with the University of California at Santa Cruz (camera optical and mechanical design) and the W. M. Keck Observatory (observatory interfaces).
As the number of potential supplementary cementitious materials (SCMs) increase, there is a need to determine their reactivity. Most recent methods to assess pozzolanic reactivity are based on ...measuring certain outputs such as heat release (Q), calcium hydroxide (CH) consumption, and nonevaporable water. This paper uses thermodynamic modeling to aid in the interpretation of these tests and the quantifcation of reactivity. It is shown that pozzolanic reactivity should be interpreted based on the SCM type. The presence of sulfates and carbonates during reactivity quantification alter the reaction of the Al.sub.2O.sub.3 phases, making the interpretation of the reactivity test results challenging. The reactivity of commercial SCMs should be interpreted specific to the type of SCM as described by ASTM International/AASHTO. A proposed interpretation for commercial SCMs is provided in this paper. Keywords: pozzolanic reactivity test (PRT); reactivity; supplementary cementitious materials (SCMs); thermodynamic modeling.
PDF
