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    Advances in Materials Science for Environmental and Energy Technologies III
    Advances in Materials Science for Environmental and Energy Technologies III
    Advances in Materials Science for Environmental and Energy Technologies III
    Ebook614 pages5 hours

    Advances in Materials Science for Environmental and Energy Technologies III

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    This proceedings contains a collection of 26 papers from the following six 2013 Materials Science and Technology (MS&T'13) symposia:

    • Green Technologies for Materials Manufacturing and Processing V
    • Materials Development and Degradation Management in Nuclear Applications
    • Materials Issues in Nuclear Waste Management in the 21st Century
    • Energy Storage III: Materials, Systems and Applications
    • Nanotechnology for Energy, Healthcare and Industry
    • Hybrid Organic – Inorganic Materials for Alternative Energy
    LanguageEnglish
    PublisherWiley
    Release dateOct 10, 2014
    ISBN9781118996706
    Advances in Materials Science for Environmental and Energy Technologies III

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      Advances in Materials Science for Environmental and Energy Technologies III - Tatsuki Ohji

      COMPARISON OF THE NANOSECOND PULSE AND DIRECT CURRENT CHARGING TO DEVELOP THE STRONGLY CHARGED ELECTRET

      Keishi Awaya, Masaya Mitsuhashi, Tsubasa Sakashita, Hong Byungjin, Tadachika Nakayama, Weihua Jiang, Akira Tokuchi, Tsuneo Suzuki, Hisayuki Suematsu and Koichi Niihara

      Extreme Energy-Density Research Institute, Nagaoka University of Technology, Nagaoka, Japan

      ABSTRACT

      Recently, micro power generation using electrets has attracted much attention due to its large power output at a low frequency range. Since the theoretical power output is proportional to the square of the surface charge density of the electret, the development of a high-performance electret is required. Conventionally, electrets have been mainly manufactured by corona discharge generated using a direct current (DC) source. However, dielectric breakdown usually occurs when high voltage is applied to a material due to the increased surface charge density of the electret. Here, we focus on the nanosecond pulse (70 ns pulse width) that has ability to apply higher voltages to materials than when DC is used. A series of measurements of surface potential and thermally stimulated discharge current (TSDC) spectra is made for various polytetrafluoroethylene (PTFE) electrets, which were manufactured by DC and nanosecond pulses. It is found that the surface charge density and thermal resistibility of electric charges are improved by using nanosecond pulses. A surface charge density using a nanosecond pulse of 0.59 mC/m² is larger than that of using DC by 59%. In addition, the thermal stability of the electret manufactured by nanosecond pulses is superior to that of by DC. Moreover, discharge energy of nanosecond pulse generator is greater than that of DC power source. Therefore, we conclude that nanosecond pulse will be more useful for manufacturing electrets than DC.

      INTRODUCTION

      In recent years, energy harvesting attracts much attention all over the world¹. Especially, micro power generator using electret is studied actively², ³ Since the theoretical power output of generator is proportional to the square of the surface charge density of the electret⁴, the development of a high-performance electret is required. Conventionally, electrets are manufactured by corona discharge using DC power source. However, dielectric breakdown usually occurs when a high voltage is applied to materials due to the increased surface charge density of electrets. Here, we focus on the nanosecond pulse (70 ns pulse width) that has ability to apply higher voltages to materials without inducing dielectric breakdown. Nanosecond pulse has a potential to produce more strongly charged electret than DC, because it can apply higher voltage than DC to materials.

      The objective of the present study is to develop a fabrication method for a new electret using nanosecond pulse for higher surface charge density and thermal stability.

      EXPERIMENTAL

      Nanosecond pulse power source

      Figure 1 shows output wave pattern of a nanosecond pulse generator. Nanosecond pulse discharge generates an extremely short pulse width and because the voltage falls before the generation of insulation breakdown, which is induced by the application of a high voltage, it is possible to apply the higher voltages than when DC is used.

      Figure 1. Output wave pattern of nanosecond pulses

      Electret manufacture

      Electrets were manufactured by applying a high voltage to a needle and injecting ions using a corona discharge under condition given in Table I. Polytetrafluoroethylene (PTFE or Teflon) was used as an electret material because PTFE is highly insulating and is a typical electret material. A 6 × 6 cm² of 50-μm-thick PTFE was installed on an earth electrode, and electrification was performed using a corona discharge by applying a high voltage to a needle electrode at a fixed distance from the earth electrode. Fabrication conditions are shown in Table II. −6 kV DC is the maximum voltage that can be applied to the sample without being damaged.

      Table I. Capacity of nanosecond pulse generator

      Table II. Electret fabrication conditions

      Figure 2. Electret fabrication by corona discharge

      Measurement of surface potential and thermally stimulated discharge current

      In order to evaluate the performance of nanosecond pulses as a new fabrication method for electret, the temporal change of the surface potential was examined. The samples were stored at 23°C with 75% of humidity. The surface potential was measured with a surface voltmeter (Statiron DS3H, Shishido Electrostatic, Lid).

      Thermally stimulated discharge current (TSDC) was measured while applying heat to the electret, as shown in Figure 3 (a). By measuring the TSDC, it is possible to estimate parameters such as the trapped charge concentration, the depth of charge injection, and the electret lifetime. Conditions for temperature increase is shown in Figure 3 (b).

      Figure 3. Measurement of TSDC

      Measurement of discharge energy

      The discharge energy was measured by observing the voltage and current waveforms. Figure 4 (a) & (b) show the measurement systems used for DC and nanosecond pulses.

      Figure 4. Schematics of measurement system of discharge energy

      Discharge energy of DC power source was calculated as described below.

      equation

      Discharge energy of a nanosecond pulse generator was calculated as described below.

      equation

      RESULTS AND DISCUSSION

      Comparison of surface potential

      Figure 5 shows the surface potential as a function of discharging time under application of electrets −6 kV DC and −20 kV nanosecond pulses (repetition frequency: 200 Hz). It shows that surface potential of −2500 V (equal to surface charge density of 0.59 mC/m²) by nanosecond pulses is higher than that of DC by 59 % after discharge for 200h. This is mainly considered to be because the high voltage nanosecond pulses inject more charge into the electret.

      Figure 5. Surface potential of electret

      Figure 6 shows the surface potential measured after 150 h since they have been charged for 5 and 30 minutes. Comparison of the results for the DC and the nanosecond pulses reveals that by increasing the discharge times from 5 to 30 minutes for nanosecond pulses, the sample was charged at least 500 V higher. This is thought to occur due to the voltage application time being intermittent in the case of nanosecond pulse discharge so that it takes time to inject sufficient ions into the electret.

      Figure 6. Surface potential of electret (after 150 h)

      Comparison of thermal stability of electret

      Figure 7 shows the results of TSDC measurement of PTFE made into an electret by applying −6 kV DC and −20 kV nanosecond pulses (repetition frequency: 200 Hz). It shows that a peak appears at near 175°C after application of DC and at around 210°C after application of nanosecond pulses. It is conjectured that when the current peak occurs at a high temperature, the thermal stability goes high, ions are injected deeply, and which results in the longer lifetime of the electret. With application of nanosecond pulses, it is believed that because a high voltage was used, ions were deeply injected and the thermal stability was high.

      Figure 7. TSDC spectra of electret

      Figure 8 shows the TSDC of electrets charged at various output voltages using nanosecond pulses. It has been previously reported that, in the case of DC, the TSDC increased with increasing output voltage. The same trend, in which current peaks increase and the amount of injected charge increases, was also observed during application of nanosecond pulses. Since nanosecond pulse generator has ability to apply the higher voltage than DC without generating dielectric breakdown to applied materials, it can be expected that the electrets, manufactured by nanosecond pulse would be more strongly charged according to the increased voltage by nanosecond pulse power generator.

      Figure 8. TSDC spectra of electret

      Comparison of discharge energy

      Figure 9 shows the discharge energy per second for DC and the discharge energy per pulse for nanosecond pulses. The product of the discharge energy per pulse and the pulse repetition frequency equals the discharge energy per second. The discharge energy using nanosecond pulses at −20 kV was higher than the discharge energy at −8 kV, which is near the limit for DC (when the repetition frequency was 50 Hz or greater). It suggests that nanosecond pulse generator has ability to produce larger amount of ions than the DC power source.

      Figure 9. Discharge energy of power source

      Varying the distance between the needle and earth electrodes for DC and nanosecond pulses and measuring the discharge energy revealed that, whereas the discharge energy varied greatly with the distance between the electrodes for DC, the variation was small for nanosecond pulses. This demonstrates that nanosecond pulses enable stabilizing the discharge without being affected by the distance variation between the electrodes.

      CONCLUSION

      In order to evaluate the performance of nanosecond pulses as a new fabrication method of electret, the surface potential and thermal stability of electrets charged by nanosecond pulse and DC, discharge energies of nanosecond pulse generator and DC were examined and compared. As for the surface potential, we have found that surface potential of −2500 V(equal to surface charge density of 0.59 mC/m²) by nanosecond pulses is higher than that of by DC after 200h from discharge by 59 %. This is mainly considered to be because the high voltage nanosecond pulses inject more charge into the electret. For the thermal stability, we have found that a peak of TSDC appears near at 175°C in the case of DC and at around 210°C in the case of nanosecond pulses. It would imply that in the case of nanosecond pulses, ions were deeply injected and the thermal stability of electret was high, because a high voltage was used. In terms of the discharge energy, we have found that the discharge energy using nanosecond pulses at −20 kV was higher than that using DC at −8 kV (when the repetition frequency was 50 Hz or greater). Moreover, variation of discharge energy depending on the distance between the electrodes of nanosecond pulse generator was smaller than that of DC. These demonstrate that nanosecond pulse generator produce more ions than DC and stable discharge is possible by using nanosecond pulses without being greatly affected by the distance between the electrodes.

      Therefore, we conclude that nanosecond pulse will be more useful for manufacturing electrets than DC.

      REFERENCES

      ¹R.J.M. Vullers, R.van Schaijk, I.Doms, C.Van Hoof, R.Mertens: Micropower energy harvesting, Solid-State Electronics, 53, 684–693 (2009)

      ²Hua-Bin Fanga, Jing-Quan Liua, Zheng-Yi Xub, Lu Donga, Li Wangb, Di Chena, Bing-Chu Caia, Yue Liub: Fabrication and performance of MEMS-based piezoelectric powergenerator for vibration energy harvesting, Microelectronics Journal, 37, 1280–1284 (2006)

      ³M. Nifuku, Y. Zhou, A. Kisiel, T. Kobayashi, H. Katoh: Charging characteristics for electret filter Materials, Journal of Electrostatics, 51–52, 200–205 (2001)

      ⁴Boland J, Chao C-H, Suzuki Y and Tai Y-C: Micro electret power generator, 16th IEEE Int. Conf. MEMS(Kyoto) 538–41 (2003)

      PROPORTIONING CONTROLLED LOW STRENGTH MATERIALS USING FLY ASH AND GROUND GRANULATED BLAST FURNACE SLAG

      Dr. Udayashankar B C

      Professor & Head, R.V.College of Engineering Bangalore, Karnataka, India.

      And

      Raghavendra T

      Assistant Professor, R.V.College of Engineering Bangalore, Karnataka, India.

      ABSTRACT

      As the construction industry continues to recognize the importance of sustainable development, technologies such as controlled low-strength material (CLSM) have come to the forefront as viable means of safely & efficiently using by-product & waste materials in infrastructure applications. CLSM is defined by ACI (American Concrete Institute) Committee-229 as a self-compacting, cementitious material used primarily as a backfill in-lieu of compacted fill. In this paper two industrial by-products, namely fly ash & ground granulated blast furnace slag, are used as constituent materials in CLSM. Mixture proportions developed for CLSM containing these waste materials were tested in the laboratory for properties such as flow & un-confined compressive strength. The cardinal aim is to analyze the experimental data generated to formulate a phenomenological model to arrive at the combinations of the ingredients to produce CLSM to meet the strength development desired at the specified age irrespective of the age & proportion of the mix.

      INTRODUCTION

      CLSM is defined by ACI Committee-229 [1] as a material that results in a compressive strength of 8.3MPa or less. Currently CLSM applications require unconfined compressive strengths in the range of 2 MPa or less, so as to allow future excavation of previously laid surfaces for alterations as the need arises. The upper limit of 8.3MPa allows using this material for structural fill under buildings where future excavation is unlikely. Besides CLSM should not be confused with compacted soil - cement, because CLSM requires no compaction (consolidation) or curing to achieve the desired strength unlike soil cement. These class of materials offer a direct means to utilize wide spectrum of waste materials which otherwise pose a problem in their safe disposal.

      CLSM is also regarded as flowable fills since they are liquid like materials that harden to the consistency of stiff clay. It is a combination of sand, fly ash and small percent of cement, water and admixtures. Sand is the major component of most of these flowable fills. Other benefits of processing flowable fills are limited labor component, accelerated construction, ready placement in inaccessible zones and the ability to manually re-excavate for relaying utilities if required.

      MATERIALS AND METHODS

      In our present experimental study, two industrial by-products, namely fly ash and ground granulated blast furnace slag, are used as constituent materials in CLSM. Mixture proportions were developed for CLSM containing these industrial by-products and tested in the laboratory for various properties, such as flowability and un-confined compressive strength (UCS). This project deals with the technology of proportioning CLSM with Low-Calcium (Class F) dry Fly ash procured from Raichur Thermal Power Plant, Karnataka and Ground granulated blast furnace slag procured from Jindal Steel Works, Karnataka, as the base materials.

      The present investigation aims to generalize the two basic principles namely Abrams law and Lyse’s rule for proportioning the cement based controlled low strength materials.

      Fly ash is the finely divided residue resulting from the combustion of pulverized coal, which is transported from the fire box through the boiler by flue gases. Since fly ash has pozzolanic properties like natural pozzolana, it is considered to have some self-cementitious properties. The term fly ash is also described as any fine particulate material which precipitated from the stack gases of industrial furnaces burning solid fuels. The solid and fine-grained materials were collected by mechanical or electrical separators. The specific gravity of the fly ash was found to be 2.4, the results of the chemical analysis are tabulated in Table I, Chemical analysis conducted on the ash indicated that the ash conforms to the requirements of IS: 3812 (Part-I)-2002. It can be seen that the content of SiO2+Al2O3 is 88.10% for the ash against minimum of 70% stipulated in IS: 3812(9) (Part-I)-1981.

      Table I. Chemical Composition of flyash

      Ground granulated blast furnace slag (GGBS) is a mineral admixture and could be used as cement replacing materials in concrete composites. As per ASTM C 989-99 blast–furnace slag is defined as the non metallic product, consisting essentially of silicates and alumino–silicates of calcium and other bases that are developed in a molten condition simultaneously with iron in a blast furnace. Unlike pozzolonic materials like silica fume, fly ash, high reactivity metakaolin, GGBS is a latent hydraulic material. It produces C-S-H gel after reacting with water. The reaction is accelerated in the presence of CaOH that is produced from the primary hydration of OPC. Table II, gives the physical and chemical properties of GGBS used for the experiment.

      Table II. Physical and Chemical properties of GGBS

      Flowability

      The workability of the mix is determined by spread flow test. The apparatus for this test consists of a mould in the form of a frustum of a cone, 60mm high with 70 mm top diameter and 100mm at the base. Since the mixes does not contain coarse aggregate this test is in order to assess workability. The cone placed on a base plate of about a meter in diameter is filled with the mix of combinations of solid constituents at different water content is filled without any air entrapment and lifted. Due to its own weight the mix spreads whose diameter in mutually perpendicular directions is measured and averaged.

      The relative flow area, RFA is calculated from the relation:

      equation

      Where D is the average diameter of the spread mix in mm

      It has been observed that the spread increases with increase in water content and the relative flow area is in the range of 5 to 15 which is of self flowing and self leveling consistency as needed for controlled low strength materials

      AIM AND SCOPE OF INVESTIGATION

      Our aim is use of industrial by-products namely flyash and ground granulated blast furnace slag, as constituent materials in CLSM, to generate a set of experimental data, analyze them and formulate a phenomenological model i.e. a kind of ready to use equation. The use of such an equation would be to proportion CLSM mixes for desired strength (at specified age and binder/water ratio) and flow (at specified water content). Du. L et al. [6] made efforts to develop predictive models for the compressive strength of CLSM, various models and statistical approaches were considered but no single model was found to work well for the entire range of materials and mixture proportions. The various combinations of materials involved in the generation of CLSM mixes would involve multiple iterations to achieve desired flow and strength. With the help of phenomenological model it is required to make a single trial and determine its flow and strength values respectively. Further this trial mix value would enable us to predict flow and strength of other mixes within no time and without much time consuming effort. TR & BCU [2] have formulated phenomenological model for CLSM mixes constituting cement, GGBS and sand. Their experimental values fairly matched with the predicted values and hence reinforcing confidence in the application of these phenomenological models, formulated for a specific set of constituent materials. However, if the constituents are changed, as in the case of our investigation to proportion CLSM mixes constituting cement, flyash, GGBS and Sand, then it becomes necessary to formulate a fresh phenomenological model out of newly generated set of experimental data.

      Materials used

      The following materials and variable parameters are used.

      Binders:

      a. cement (C): 53 Grade; Specific gravity = 3.14

      b. Fly-ash (F): Source: Raichur thermal power plant; Specific gravity= 2.00

      c. Ground granulated blast furnace slag (G); Specific gravity = 2.8

      d. Sand; Specific gravity= 2.6

      Type of curing: Humidity chamber

      Tests conducted:

      a. Fresh state: Flow test for workability.

      b. Hardened state: Strain controlled unconfined compression test on cylindrical specimens. Size of specimen: Diameter = 40 mm; Height= 80 mm

      Variable parameters:

      a) Fly ash -cement Ratio (F/C) Mortar: 3.5, 2.8, 2.33, 2.0 and 1.75

      b) Fly ash + GGBS - cement Ratio {(F+G)/C} Mortar: 8, 4 and 2.66

      c) Water Content % Mortar: 20, 22, 24 and 26

      d) Strength tests at the age of 7 and 28 days

      For each series 40 specimens were casted i.e. 10 specimens were casted for each (Water Content / Binder) ratio and testing of five specimens in each set after age of 7 and 28 days was performed. Tables III & IV, gives the material calculations for different combinations at 1:1.5 Mortars.

      Table III. Material calculation for different combinations of cement and flyash 1:1.5 Mortars

      Table IV. Material calculation for different combinations of cement, flyash and GGBS 1:1.5 Mortars

      PHENOMENOLOGICAL MODEL FOR FLOW & STRENGTH DATA

      Generalized Abrams’ Law has been used for the purpose of development of phenomenological model. For this a reference value i.e. B/W ratio of 1.81 has been identified. It implies that a trial test done at this ratio would take care of synergy between all the ingredients. These strength values are normalized with respect to their respective reference value. In figures – 3, 4, 5 & 6, the linear fit of the data is done since according to Bolemey’s Law the consideration of inverse of W/B ratio is done to transform the data into linear form in all other investigations dealing with cement based composites. The linear relationships are obtained for the combinations given in Tables III & IV. The equation of the trend line itself is the phenomenological model generated. The left hand side of phenomenological model represents normalized values of strength.

      In the development of phenomenological model for flow assessment also, a reference value of RFA at water content of 24 percent (since no segregation and bleeding, also optimum RFA range from 5 to 15) for 1:1.5 mortar series has been identified. The flow lines of these data points are normalized with respect to their respective reference value. Thus normalized values of all the series are plotted to a scale along the ordinate against the water content values which are plotted along the abscissa, as shown in figures 1 & 2. To use this phenomenological model one set of data with a known combination of ingredients at reference value has to be generated. The tests conducted for any given set of ingredients at these reference values would take of material properties and associated synergy between interacting and non—interacting constituents with water. This is needed to use the phenomenological model as input parameter in the denominator of the left hand expression in the equations formulated.

      Figure 1: Generalization for flow of (C+F) mortar

      Figure 2: Generalization for flow of (C+F+G) mortar

      Figure 3: Generalization for 7-day strength of (C+F) mortar

      Figure 4: Generalization for 7-day strength of (C+F+G) mortar

      Figure 5: Generalization for 28-day strength of (C+F) mortar

      Figure 6: Generalization for 28-day strength of (C+F+G) mortar

      With this data the RFA at other water content can be assessed and vice versa. The validation of this model for an independent set of data is also examined.

      RESULTS AND DISCUSSIONS

      The strength and flow data has been synthesized in Table V. cement+flyash and cement+flyash+GGBS, for a particular ratio with corresponding sand mixed with specified water content forms one set. For such a set the strength does not vary beyond the range of experimental discrepancy as seen in figures – 3, 4, 5 & 6. This is in accordance with the Bolemy’s consideration of Abrams’ Law. As the F/C ratio changed to 3.5, 2.8, 2.0 and 1.75 and and (F+G)/C ratio changed to 8, 2.66 the strength changes since the set of cementing material changes & Pozzolanic nature of flyash, flyash+GGBS has a role to play. The increase in strength takes place as the ratio of F/C, (F+G)/C decreases due to cement playing the dominant role in strength development lessening the Pozzolanic nature of the flyash, flyash+GGBS. Water–cementitious ratio, W/(C+F) & W/(C+F+G), (0.50, 0.55, 0.60 & 0.65) is the main variable. The variation of F/C (3.5, 2.8, 2.0 and 1.75 for cement + flyash mortars) and (F+G)/C (8,4 and 2.66 for cement + flyash + GGBS mortars) forms six combinations of cementing materials. They have to be considered separately since they are equivalent to six types of cementing materials. The strength development with age (7 and 28 days) is also a variable.

      Table V. Average flow & strength results for cement+flyash & cement+flyash+GGBS Mortars

      The flow data has been converted to relative flow area of spread (RFA), calculated from the relation (D/100)²-1, and is tabulated in Table V. It is clear that the flow increases with increase in water content and increases with F/C and (F+G)/C ratios irrespective of W/(C+F) and W/(C+F+G) ratios. This is in conformity with Lyse’s rule. For a given set of materials, represented by its F/C ratios, as the water content increases the spread also increases. It is not possible to examine the generalization to arrive at generalized Lyse’s rule since at water content of 45% there appears to be sudden transition in the relative flow area, because of inevitable bleeding. To circumvent this it would be necessary to examine the flow behavior from altogether different consideration such as flow time through a flow cone akin to vee-bee time. This has not been done in this investigation due to the need of fabrication of such a facility. This forms proposed future investigation.

      Average flow and strength results

      It can be seen that in the above case (cement + flyash mortars and cement + flyash + GGBS mortars) the relative flow area increases with increase in water content. This is in accordance with Lyse rule. Likewise even the strength decreases with decrease in binder/fluid ratios in accordance with Abrams law. Since binder/fluid ratio is considered in figures it can be seen that trend in variation can be represented linearly with a high degree of correlation coefficient.

      Even with the age, the strength gain also follows the same pattern. It is interesting to note that when flow or strength data is superposed as water content or binder/fluid ratio increases, relative flow area lines plotted against varying water content and strength lines plotted against varying binder/fluid ratios are all converging lines towards decrease in the binder - fluid ratio i.e. corresponding increase in fluid/binder ratio. The range of RFA and Strength development is quite considerable implying that number of trials would be involved in arriving at suitable combinations. It is to be examined as to how the properties of a given set of materials and their combinations can be brought about into the fold of a functional relation.

      Figures 7 to 10 show the predicted path for strength & flow generated from phenomenological models. Combined series graphs are generated by using four series (F/C=3.5 + F/C=2.8 + F/C=2 + F/C=1.75) RFA and Strength values for cement + flyash 1:1.5 mortars and using two series ([F+G]/C=8 + [F+G]/C=2.66) RFA and Strength values for cement + flyash + GGBS 1:1.5 mortars.

      Figure 7: Predicted path for flow of F/C=2.33 mortar, from combined generalized equation

      Figure 8: Predicted path for flow of (F+G)/C=4 mortar, from combined generalized equation

      Figure 9: Predicted path for 28-day strength of F/C=2.33 mortar, from combined generalized equation

      Figure 10: Predicted path for 28-day strength of (F+G)/C=4 mortar, from combined generalized equation

      Examination of experimental values for an independent series {F/C=2.33; cement + flyash 1:1.5 mortar and (F+G)/C=4; cement + flyash + GGBS 1:1.5 mortar} and predicted values reveal that, in general the trend is followed and in few cases there is considerable discrepancy. There are two reasons for this. In the case of experimental RFA values for certain combinations due to bleeding taking place it is difficult to identify the exact water content responsible for flow. In the case of experimental strength values one factor was observed like in the cases where bleeding took place at higher water content, the cylindrical samples made showed some dewatering leaving some water standing on the top of samples before final setting takes

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