•Assessment of calcite formation on steam flown concrete crack surfaces.•Combined evaluation of crack healing by mineralogical analysis and flow measurement.•Calcite layers increases along the steam ...exposure time up to a stable level.•Evidence of mass flow reduction in steam flown cement cracks by autogenous healing.
Under accidental conditions, concrete containments of nuclear power plants often remain as final barrier to the environment. To evaluate the contribution of self-healing processes of cracked concrete containments, small scale experiments were conducted for given accident scenarios to examine the mineralogical processes on cement crack surfaces in contact with hot steam-air mixes. The surface analyses with ESEM, µ-RFA and microscope showed a calcite formation, where layer thicknesses increased along the exposure times until reaching a stable level. The potential for crack healing was principally demonstrated through flow measurements, where the outflowing mass decreased during the experiments along with increasing calcite formation.
Geopolymers have the potential to function as an environmentally friendly substitute for ordinary Portland cement, with up to 80% less CO
2
emission during production. The effect is best utilized for ...geopolymers prepared with amorphous silica instead of waterglass (Na
2
x
Si
y
O
2
y
+
x
) to adjust the Si:Al ratio. The reactivity of the precursors with the alkaline activator affects the final mineralogical properties of the binder. The purpose of the present study was to investigate the amount of different phases formed during geopolymerization and to understand the quantitative evolution of carbonation during geopolymer synthesis by determining the solubility of metakaolinite and amorphous SiO
2
in NaOH at various concentrations. The solubility was studied by ICP-OES measurements. X-ray diffraction was used for qualitative and quantitative phase analysis of the geopolymers. The solubility of the precursors increased with calcination temperature of metakaolinite, reaction time for amorphous SiO
2
, and at higher NaOH concentrations. Partial dissolution resulted in free Na
+
, which is a source for the formation of carbonates in the geopolymers. Thermonatrite occurred prior to trona formation in all samples.
An open question in predicting the rheological properties of cement suspensions has been whether changes of rheology during hydration are merely a result of shifts in the electrostatic interaction ...patterns of the particles over time, or whether and to which extent steric bridging by hydration products occurs. The latter could explain phenomena such as thixotropy. In this context, parallel investigations using both rheological tests and isothermal calorimetry, 1H NMR relaxometry, conductance and small-angle X-ray scattering (SAXS) measurments were carried out. It could be shown that as early as approx. 2.5 h after water addition at approx. 30 °C, small amounts of Calcium Silicate Hydrate (C-S-H) form which may contribute to a bridging of the cement particles. This phase is followed by rapid C-S-H formation, leading to a non-linear increase in paste stiffness. This phase ends with percolation, i.e. the paste stiffness increases dramatically, simultaneously with the formation of gel pore like structures, which could be observed using NMR.
Geopolymers and supplementary cementitious materials (SCM) are potential substitutes for ordinary Portland cement (OPC). Calcined common clays appear to be well suited as raw materials for the ...production of geopolymers. Due to the multiphase composition of common clays, it is necessary to study geopolymers first, which are prepared of individual calcined clay minerals. Nanoindentation was used to investigate the mechanical properties of metakaolinite, metasmectite, and metaillite geopolymers. For geopolymer production Si:Al ratios between 1:1–3:1 and NaOH concentrations ranging from 4 to 10.79 mol/L were used. All geopolymers were prepared without the use of commercial waterglass. All three clay minerals could be constituents of a natural common clay. Additionally, mercury porosimetry was used to determine the porosity and average pore radius of the samples. The porosity of the studied geopolymers (20.3–31.6%) was in the range found for cement pastes. The average pore radius decreased with increasing concentration of NaOH or increasing Si:Al ratio. Hardness and average pore radius of the geopolymers with the same precursor showed a negative correlation. The highest hardness (1.09 GPa) of all geopolymers was reached by one produced with the metasmectite precursor. On average, the metakaolinite geopolymers reached a hardness of 0.19 GPa and a Young's modulus of 4.72 GPa, the metasmectite geopolymers reached values up to 0.60 GPa and 18.88 GPa. The metaillite geopolymers showed an average hardness of 0.26 GPa and an average Young's modulus of 8.43 GPa. A positive correlation of the Si:Al ratio and the hardness was determined. The hardness values found in this study were comparable to hardness values of cement pastes.
•Different calcined clay minerals are suitable to produce geopolymers.•Porosity of the produced geopolymers was comparable to cement paste porosity.•Average pore radius decreased with increasing concentration of NaOH or Si:Al ratio.•Hardness of up to 1.09 GPa was reached.•A positive correlation of the Si:Al ratio and the hardness was determined.
Biochemical indicators and in vitro models, if they mimic in vivo responses, offer potentially sensitive tools for inclusion in toxicity assessment programs. The purpose of this study was to ...determine whether the HepG2 cell line would mimic known in vivo or in vitro (or both) responses of mammalian systems when confronted with cadmium (Cd2+). Uptake and compartmentalization of Cd2+, metallothionein (MT) compartmentalization, and glutathione (GSH) depletion were examined. In addition, several cytotoxic and stress effects, e.g., viability (neutral red NR uptake, 3-4,5-dimethylthiozole-2-yl-2,5,-biphenyl tetrazolium bromide MTT dye conversion, and live/dead L/D), membrane damage (lactate dehydrogenase leakage), metabolic activity (adenosine triphosphate levels), and detoxification capabilities (GSH content, cytochrome P4501A1/2 EROD (ethoxyresorufin-o-deethylase) activity, and MT induction), were measured in both naive (no previous exposure) and Cd2+ preexposed cells. Cadmium uptake increased during a 24-h period. Metallothionein induction occurred in response to both Cd2+ and ZnCl2; however, Cd2+ was the more potent inducer. Both Cd2+ and MT were localized primarily in the cytoplasmic compartment. All biochemical responses, except EROD, showed concentration– response relationships, after 24-h exposure to Cd2+ (ranges 0–3 ppm 26.7 μM). Cadmium effects were reduced in preexposed cells, indicating adaptive tolerance or increased resistance had occurred. Twenty-four–hour LC50, dose causing death of 50% of the test subjects, values were 0.97, 0.69, and 0.80 ppm (8.7, 6.2, and 7.2 μM) for naive cells and 1.45, 1.21, and 1.39 ppm (12.9, 10.7, and 12.3 μM) for preexposed cells based on the NR, MTT, and L/D assays, respectively. These data indicate that this carcinoma cell line is a useful in vitro model for cadmium toxicity studies.
Background
In joint revision surgery, bone cement extraction remains a major challenge which even today has not seen a satisfactory solution yet. We studied in an experimental setting the impact of ...heat sources on the mechanical properties and microstructure of bone cement and determined the glass transition temperature (
T
G
) of bone cement. As a result, it would be possible to establish a thermomechanical method which makes use of the structural and material-specific property changes inherent in bone cement at elevated temperatures.
Methods
Prepared samples of polymerized bone cement were thermoanalyzed with a Netzsch STA 409 C thermal analyzer. Samples weighing approx. 55 mg were heated to 390 °C at a rate of 5 K/min. Both simultaneous differential thermal analysis and thermogravimetry were employed. The thermomechanically induced changes in the microstructure of the material were analyzed with a computed tomography scanner specifically developed for materials testing (3D-μXCT).
Results
The bone cement changed from a firm elastic state over entropy-plastic (air atmosphere 60–155 °C) to a plastic viscosity state (air atmosphere >155 °C). Between 290 and 390 °C, the molten mass disintegrated (decomposition temperature).
Conclusion
Our study was able to determine the glass transition temperature (
T
G
) of bone cement which was about 60 and 65 °C under air and nitrogen, respectively. Heating the dry bone cement up to at least 65 °C would be more than halve the strength needed to detach it. Bone cement extraction would then be easy and swift.
This study examined the effects of the organochlorine (OC) insecticides chlordane,
o,
p′-DDT, dieldrin, endosulfan, kepone, methoxychlor, and toxaphene on human HepG2 cytochrome P450 (1A-EROD and ...2B-PROD) activities and glutathione (GSH) levels. Cells were exposed for 24
h at high concentrations (1, 5 or 10
mM) and for 48
h at lower concentrations ranging from 0.01 to 1
mM to evaluate dose responses. Our results show that after 48
h all but dieldrin significantly induced both P4501A and 2B. P4502B responses were greater at all exposure concentrations and times. Mixed responses in GSH levels were observed. All OCs except dieldrin and MXC significantly depleted GSH after 24
h. At 48
h, chlordane, endosulfan and toxaphene significantly increased GSH at low levels and decreased GSH at high levels, while kepone and methoxychlor produced significant declines in GSH at all concentrations. These results support findings of OC insecticides inducing CYP1A, 2B in rats, with CYP2B responses more important. GSH levels declined when P4502B activity was significantly elevated and were significantly increased in the absence of significant P450 activity, suggesting that GSH levels influence the catalytic activity of the cytochrome P450s and the cytochrome P450s influence the cell’s ability to regulate GSH.
The interest in concretes based on alkali‐activated binders (AABs) is increasing significantly along with the continued research into and development of these novel construction materials from lab ...scale to practical application. The paper summarizes current knowledge about concretes based on AABs to address the following questions: What are structural concretes based on AABs? What are the specific characteristics with regard to the chemical binder reaction? What has to be considered for the mix designs of AACs? And which material performances can be expected?
In order to analyse the behaviour of concrete under fire exposure experimental investigations are used 1. This practice is expensive and very time-consuming. So, it is essential to get as most ...suitable information out of such experiments as possible. At the present, most standard experiments are only capable of comparing a condition of concrete before and after the experiments 1. Unfortunately, information of the time-dependent development of the damaging process cannot be resolved. In order to fully understand the mechanism of dynamic concrete damage under fire exposure, this information is crucial. Therefore, it is necessary to develop measurement systems which are able to monitor and detect the entire exposure process and its consequences. These systems should be applied additionally to the temperature monitoring, the visual inspection and a weighting of the specimen before and after the experiments. For this purpose volume-oriented non-destructive testing methods are considered. It is possible to use ultrasonic systems or impact-echo methods, but the most suitable are acoustic emission techniques. With this method it is possible to monitor damage processes of the complete specimen volume and during the whole time of the experiments. The paper will present results of experimental investigations where such systems have been successfully applied to test the feasibility, practicability and the usefulness of different measurement systems to verify the time-dependant development of concrete spalling under fire exposure.
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