Build-up Thickness Research Articles

Development of geopolymer and cement-based shotcrete mortar: Impact of mix design parameters and spraying process

Shotcrete mortar is used in various construction works, including repair, tunneling, mining, and slope stabilization, among others. Traditionally, cement is used to produce shotcrete mortars with high viscosity, flowability, and early strength. Geopolymers (GP) have the potential to replace cement in shotcrete mortars, owing to their ability to reduce the material’s environmental footprint without compromising performance. This investigation assesses the feasibility of utilizing fly ash and blast furnace slag-based GP mortars produced with dune sand in shotcrete applications while comparing them to cement-based mixtures. The GP and cement-based shotcrete mortars were designed to have similar yield stress values. The evaluated properties included the initial flow, thickness layer, rebound material, rheological properties, setting time, compressive strength, ultrasonic pulse velocity, and pull-off bonding strength. Test results showed direct relationships between the yield stress and initial flow values, as well as between the buildup thickness and plastic viscosity, revealing that GP mortars were suitable for shotcrete applications, specifically those produced with flow values of 18.5 cm or less. GP mixtures produced with higher slag content than fly ash, higher sand content compared to binder, higher SH molarity, and lower solution content achieved higher buildup thickness owing to their higher viscosity. In the second phase, the performance of four mixes with different initial flows was assessed at various pumping flow rates and distances between the wall and machine pipe nozzle. The findings confirmed that these spraying parameters are crucial to improve the shotcrete performance of GP mortar with varying fresh behaviors.

Development of Negative-Temperature Cement Emulsified Asphalt Spraying Materials Based on Spraying Performance and Rheological Parameters.

To develop a cement emulsified asphalt composite (CEAC) that can be sprayed under a plateau negative temperature environment, the effects of the water-solid ratio, calcium aluminate cement substitution rate, emulsified asphalt content, sand-binder ratio, and polyvinyl alcohol (PVA) fiber content on the spraying performance and rheological parameters of CEAC were explored through the controlled variable method. Additionally, the correlation between the spraying performance and rheological parameters of CEAC was established, and the optimal proportion of CEAC was determined. Then, the difference in frost resistance and pore structure between the cement slurry (CS) without emulsified asphalt and CEAC at the optimum proportion was analyzed. The results showed that the optimum proportions for sprayed CEAC were 0.14 water-solid ratio, 0.5 sand-binder ratio, 25% substitution of calcium aluminate cement, 5% emulsified asphalt content, and 1.5% PVA fiber volume mixing. The yield stress and plastic viscosity of CEAC were positively correlated with the build-up thickness, whereas the rebound rate and the latter showed a negative correlation. The spraying performance may be described by the rheological parameters; the ranges of yield stress and plastic viscosity of 2.37-3.95 Pa·s and 77.42-108.58 Pa, respectively, produced the best spray ability. After undergoing an equivalent number of freeze-thaw cycles, CEAC exhibited lower mass and strength loss rates compared to CS, thereby demonstrating superior frost resistance. In addition, the pore structure analysis showed that the difference in capillary and macropore contents was the main reason for the variability in frost resistance between CS and CEAC.

Rheological properties and shootability of sprayable geopolymer mortar

Geopolymer presents a promising alternative to Portland cement for shotcrete, offering reduced environmental impacts, favorable mechanical performance, and improved durability. At present, small-scale applications have been implemented, but the fresh performances of spayed geopolymer are still rarely studied, restricting its further large application. This research investigates the rheological properties and shootability of sprayable fly ash/slag/silica fume based geopolymers considering the effects of different mix parameters. The water to binder (W/B) ratio has the greatest effect on the yield stress, and the dynamic yield stress is increased from 64.47 Pa to 388.64 Pa as the W/B ratio is reduced from 0.32 to 0.28. The change in dynamic yield stress is mainly related to either the formation of hydration products or the solid volume fraction. Mixtures with the highest thixotropic indexes are ideal for achieving both pumpability and shootability, while also exhibiting relatively low characteristic time. A modified equation for pumpability assessment is presented, which is more reasonable and consistent with the experimental results. The static yield stress is recommended for evaluating the build-up thickness of the designed fresh mixture, as there is a recognized strong correlation between them. In addition, the build-up thickness decreases with the increase of flowability, which could be used as a potential indicator. With the increasing sand to binder ratio, the mechanical strength exhibits a valley, which could be linked to the critical volume fraction of aggregate that corresponds to an effective interacting network, below which the sand-induced defects cause damage to strength and above which the interacting skeleton could contribute to strengthening. The strong environment savings of the current material are demonstrated, with the reduction in carbon emissions more than 50%. This study provides valuable information towards regulating and controlling the shootability of sprayable geopolymer and expands its broader application.

Silurian barrier reef in Lithuania: Reservoir properties and low enthalpy geothermal heat potential

The Silurian barrier reef zone in Lithuania extends for hundreds of kilometres in the narrow zone in Middle Lithuania continuing from the Saukenai reef in the north to the Vilkupiai reef in the south. After prolific Cambrian sandstone reservoirs, they are considered a secondary oil target in Lithuania. However, drilling data showed that the detected reefogenic bodies are either “dry" or saturated with water and/or viscous oil thus practically no valuable oil supply has been obtained. This study illustrates a review of the existing geological and geophysical data, acquired during oil and gas explorations since the 1960s, specifically re-analysed for geothermal purposes.The heat production rates of well doublets within the Silurian reefs range from 0.000044 to 0.24 MWh. Within the area of the Kudirka structure, 6 well doublets could be arranged from the existing 16 exploration wells, at the average distance between the producing-injecting wells of around 700 m. Kudirka has the largest reservoir volume and hence the largest reservoir heat potential (250 GWh). At the smallest distance between the doublet wells of 486 m, the thermal breakthrough would be reached after around 30 years of production-injection. Pavasaris reef shows the best geothermal capacity of a well doublet (0.241 MWh). Reservoir properties are especially good in the partially open fracture zone interval. Pavasaris reef has got 2 wells penetrating the reef, thus one doublet could be arranged within the structure. However, the available thermal energy is limited due to hydrogeological closure and small reservoir size (11.2 × 103 MWh). Other reefs (Saukenai, Vilkupiai, North Bliudziai and a reef in the north of the Vadzgirys reef belt) are small isolated structures, thus their heat potential is low. Moreover, they show low flow rates and hence thermal energy that can be extracted at their wellheads in 30 years is well below 1 × 103 MWh. The study indicates that even though the thickness of the reefal build-ups may reach up to c.90 m, the effective thickness of the reservoirs rarely reaches 20 m. Analysis of the well logs and the core sections show a high heterogeneity of the structures, and hence low recovery factors of the doublets. The distribution of effective layers is usually associated with processes such as stylolitisation and secondary fracturing with enhanced dissolution. For measured low flow rates (<9 m3/h), reusing the existing wells shows low economic viability due to the narrow diameters of the boreholes. Therefore, Silurian reefs show low potential for the application of geothermal energy in Middle Lithuania, although small geothermal projects could be achieved in the Kudirka and Pavasaris sites.

Influence of materials and nozzle geometry on spray and placement behavior of wet-mix shotcrete

Shotcrete finds extensive applications in civil engineering, from repair and rehabilitation to new constructions. Nevertheless, shotcrete construction frequently suffers from placement issues, such as rebound and overshooting. These challenges can result in reduced operational efficiency, increased material wastage, diminished construction quality, and potential workplace hazards. It is worth noting that these placement issues are intrinsically linked to the spray characteristics of shotcrete. These characteristics are contingent upon various factors, including the material's flowability and viscosity, as well as the nozzle geometry. This research experimentally characterized the spray behavior of wet-mix shotcrete. High-speed cameras and image analysis techniques were utilized to capture and characterize wet-mix shotcrete on a full-scale spraying setup. The study experimentally determined the key placement performance parameters such as placement, rebound, and final build-up thickness and correlates the placement performance of shotcrete with the spray characteristics. The findings reveal that wider spray opening angles, smaller droplet sizes, and higher velocities contribute to improved material deposition, reduced rebound, and increased build-up thickness. The study also assesses the impact of nozzle geometry and rheology of the shotcrete mixture. Increased flowability led to slightly better spray behavior and placement. Higher material viscosity produced a more consistent spray which enhanced shotcrete performance. Multi-air jet guns, where compressed air directly contacts droplets, can enhance shotcrete spray efficiency.

Determination of the most dangerous flight modes of aircraft in icing conditions

In this paper, the object of research is the icing of aircraft surfaces during flight in the atmosphere. On many light aircraft, as well as on unmanned aircraft weighing less than 30 kg, there are no on-board de-icing systems. Nevertheless, aviation events occur with these aircraft, which are a consequence of their icing. Therefore, determining the most dangerous flight modes of aircraft in icing conditions is an urgent task. In view of the high cost of conducting flight tests and the impossibility of covering all possible events due to their potential danger, the complexity of creating flight conditions for aircraft in icing conditions on the ground, the mathematical modeling method was used in this study. To solve this problem, the analysis of the airworthiness standards of civil light aircraft, transport category aircraft, rotorcraft of normal and transport category was carried out within the framework of the work, the influence of various parameters on the thickness of ice build-up was investigated using a computational experiment conducted on the software developed by the authors of the article. On the basis of the results of the computational experiment, the dependences of the ice thickness on various icing parameters were obtained, a method was developed for determining the combination of heights and flight speeds of an aircraft, at which ice of the greatest thickness is formed on the surface of aircraft, other things being equal. Possession of this information will allow the aircraft crew and air traffic control specialists to avoid the most dangerous flight modes in terms of icing.

Mechanical properties of sprayable ultra-high ductility magnesium phosphate cement -based composites

With the aim to investigate the mechanical properties of sprayable ultra-high ductility magnesium phosphate cement-based composites (UHDMC), the effects of starch ether content, water-solid ratio, quartz powder-binder ratio, borax content, fly ash (FA) content and volume content of polyvinyl alcohol (PVA) fibers on the build-up thickness, compressive strength and tensile properties were studied. The mechanism about the change of mechanical properties was explained by Mercury Intrusion Porosimetry (MIP) test. The results showed that the optimum mixture proportion suitable for sprayable UHDMC was as follows: M/P of 4, starch ether content of 0.15%, water-solid ratio of 0.14, quartz powder-binder of 0.3, borax content of 8%, FA content of 40% and PVA content of 2%, presenting the compressive strength of 35.9 MPa, the ultimate tensile strength of 3.7 MPa and the ultimate tensile strain of 4.1%. A linear relationship was established between pore structure parameters and mechanical properties. The macropores and capillary pores had great influence on the compressive strength, while transition pores mainly affected the ultimate tensile strength. Moreover, similar porosity and pore size distribution were presented between the sprayed and cast UHDMC under the optimum mixture proportion.

Development of sprayable ultra-high ductility magnesium phosphate cement-based composites based on the rheological properties

To develop a sprayable ultra-high ductility magnesium phosphate cement-based composite (UHDMC), this study explored the effects of starch ether content, water–solid ratio, powder-binder ratio, borax content (B/M), fly ash (FA) substitution and volume content of polyvinyl alcohol (PVA) fiber on the shootability and rheological properties of magnesium phosphate cement-based materials. The correlation between shootability factors (build-up thickness and rebound rate) and rheological parameters (yield stress and plastic viscosity) was established, and the optimum mixture proportion suitable for the sprayed UHDMC was selected and then analyzed by the mechanical properties and pore structure between the cast and sprayed specimens. The results showed that the optimum mixture proportion of the sprayed UHDMC was as follows: starch ether content of 0.15%, water–solid ratio of 0.14, powder-binder ratio of 0.3, borax content (B/M) of 8%, FA substitution of 40%, and the PVA fiber volume content of 2.0%. The yield stress and plastic viscosity were both positively correlated with the build-up thickness, and negatively correlated with rebound rate. To some extent, rheological parameters can be used to characterize the shootability factors, in which the best shootability was shown when the ranges of yield stress and plastic viscosity were 91.64–118.77 Pa and 4.85–7.17 Pa·s, respectively. The compressive strength and ultimate tensile stress of the sprayed UHDMC were lower than that of the cast UHDMC, while the ultimate tensile strain of the sprayed UHDMC could still reach above3.6%, presenting good performance to meet the requirement of above 3% strain of high ductility cement-based materials. Moreover, the analysis of pore structure verified that the capillary pores and macropores contents were mainly affected the strength and tensile strain, respectively.

Surface Dose and Skin Toxicity in Low-Magnetic Field MR-Linac

<h3>Purpose/Objective(s)</h3> Radiation induced skin toxicity is a common side effect that results in poor patient satisfaction and unplanned treatment breaks thus prolonging the overall treatment time with poor outcome. It is hypothesized that treatments on low-field MR-Linac will not produce higher surface dose which is investigated in this study. <h3>Materials/Methods</h3> Skin dose has always been an area of active clinical interest that is dependent on many parameters including beam energy, field size, material thickness and atomic number in the beam, material distance from surface, source to surface distance, beam angle (obliquity factor), concomitant chemotherapy etc. Along with these parameters, magnetic field is also a critical parameter that affect surface dose. With the development of the MRL system focus has shifted towards Lawrence force giving rise to electron return effect along with other treatment parameters affecting the skin dose. A Linac equipped with 6MV FFF photons with 90 cm source to axis distance is used. A Markus parallel plate ionization chamber is used in a solid water phantom with proper correction factor to investigate surface and buildup dose with six different gantry angles 15⁰ apart gantry (equivalent of standard Linac 0⁰, 15⁰, 30⁰, 45⁰, 60⁰, and 75⁰) for field sizes of 1.66 × 1.66 cm² (small), 9.96 × 9.9 cm² (reference) and 24.1 × 24.1 cm² (maximum). Measurements were made with increasing buildup thickness in steps of 1 mm to 20 mm of solid water in 0.35 T magnetic field. <h3>Results</h3> In traditional linear accelerators surface dose is 30-40% for a 6MV photon beam, without any modifier. This value increases significantly with beam angle. In MR-Linac, surface dose is relatively low, 12.6%, 14.9% and 16.7% for small, reference and maximum fields at zero-degree gantry angle, respectively. These values are 12% to 2% higher (at 0⁰ and 75⁰ respectively) for maximum field size compared to the reference field size. For lower field sizes minimum variation of 10% was observed at 75° for reference field size. The surface dose increases with increasing radiation field size but magnitude is still lower as the case with traditional lilacs. Table 1 shows the surface dose with field size and gantry angles. <h3>Conclusion</h3> Surface dose in low-field magnetic environment is relatively lower than traditional accelerators. It is concluded that low-field MR-Linac system may not add any additional skin toxicity compared to conventional Linac. However, the effect may be different for high-field MR-Linac system, and appropriate skin evaluation needs to be performed to differentiate between radiation induced toxicity specially for the oblique beams versus RF-thermal effect.

Influence of geometric dimensions on early failures of adhesively retained composite resin core build-ups.

To determine the influence of the geometric dimensions of core build-ups on early core build-up failure, that is, loss before definitive prosthesis cementation. Adhesive core build-ups of exclusively vital teeth in 114 participants were evaluated (n materials: 40 Rebilda DC, 38 Multicore Flow, 36 Clearfil DC Core; n teeth: 8 incisors, 54 premolars, 52 molars). Impressions of the abutment teeth were made (1) after removal of insufficient restorations/caries and (2) after core build-up and preparation for a fixed prosthesis. Digitized model surfaces of both situations were aligned (Geomagic Design X) and core build-up volume (VCBU ), remaining hard tissue volume (VAbut ), and size of the adhesive surface (Aadh ) were assessed. The derived measure dCBU =VCBU /Aadh can be interpreted as mean arithmetic core build-up thickness. Associations between participant or core build-up design characteristics and the occurrence of early failures were statistically evaluated (SPSS v27, α=0.05). A total of six (5.3%) core build-up failures were registered. Higher participant age, greater core build-up volume VCBU and greater arithmetic uniform thickness dCBU were associated with a greater incidence of failure in bivariate and univariate, however, not in multivariate statistics. Core build-up volume and thickness were associated with early success or failure. In the case of voluminous/thick core build-ups in relation to the adhesive surface, additional measures, such as the preparation of retentive elements to increase the bonding area, might be considered to reduce the risk of early core build-up failure.

Rheological based interpretation of shotcrete pumpability and shootability

In this article, particle size distribution in shotcrete and the diverse effects of admixtures on gradation were discussed. Although admixtures can enhance concrete rheological behavior, they introduce uncertainty into mixture behavior and may lead to segregation, pumping line blockage, and low shootability. Moreover, the assessment of these factors using the Chapdelaine and Burns concepts showed divergence from practical pumpability. We introduced a method to analyze shotcrete behavior using a rheological method that was found more effective. As a result, a model for predicting the build-up thickness was proposed using a statistical method. In addition, a zonal effectiveness plot that could accurately characterize pumpability and shootability, overcoming the uncertainties associated with normal shotcrete analysis methods, was developed using confidence ellipses and prediction intervals that can be used in practical applications in the wet-mixed shotcrete field.

Rheological Behavior of High-Performance Shotcrete Mixtures Containing Colloidal Silica and Silica Fume Using the Bingham Model.

There have been numerous studies on shotcrete based on strength and durability. However, few studies have been conducted on rheological characteristics, which are very important parameters for evaluating the pumpability and shootability of shotcrete. In those studies, silica fume has been generally used as a mineral admixture to simultaneously enhance the strength, durability, pumpability, and shootability of shotcrete. Silica fume is well-known to significantly increase the viscosity of a mixture and to prevent material sliding at the receiving surface when used in shotcrete mixtures. However, the use of silica fume in shotcrete increases the possibility of plastic shrinkage cracking owing to its very high fineness, and further, silica fume increases the cost of manufacturing the shotcrete mixture because of its cost and handling. Colloidal silica is a new material in which nano-silica is dispersed in water, and it could solve the above-mentioned problems. The purpose of this research is to develop high-performance shotcrete with appropriate levels of strength and workability as well as use colloidal silica for normal structures without a tunnel structure. Thereafter, the workability of shotcrete with colloidal silica (2, 3, and 4%) was evaluated with a particle size of 10 nm and silica fume replacement (4 and 7%) of cement. In this study, an air-entraining agent for producing high-performance shotcrete was also used. The rheological properties of fresh shotcrete mixtures were estimated using an ICAR rheometer and the measured rheological parameters such as flow resistance and torque viscosity were correlated with the workability and shootability. More appropriate results will be focusing on the Bingham model properties such that the main focus here is to compare all data using the Bingham model and its performance. The pumpability, shootability, and build-up thickness characteristics were also evaluated for the performance of the shotcrete. This research mainly focuses on the Bingham model for absolute value because it creates an exact linear line in a graphical analysis, which provides more appropriate results for measuring the shotcrete performance rather than ICAR rheometer relative data.

Measurement of unwanted powder build-ups in manufacturing using high frequency ultrasonic bursts and standing waves reflectance method

This paper proposes a combination of high frequency ultrasonic techniques to characterize non-invasively the thickness of unwanted powder build-ups that occur in pipes and charge hoppers during industrial processes. Three compressed iron oxide powder cakes were reproduced in laboratory in different thicknesses varying from 5 mm to 15 mm. The density and hardness of the samples made in the laboratory were compared to samples that formed in-situ in a charge hopper using time of flight ultrasonic measurements, light optical microscopy, and pycnometer densitometry techniques. The powder build-ups were deposited on a metal plate instrumented with miniaturized ultrasonic sensors operating around the center frequency of 10 MHz. These sensors operated using both the reflection coefficient methodology and a new standing waves approach. The thickness of the powders was measured by correlating the standing wave resonant frequency change to the quantity of powder deposited on the surface. The powder build-ups were also compressed using a pressure up to 15 MPa and the reflection coefficient and the frequency change using the ultrasonic reflectance method were used to decouple the effect of load to the thickness measurement. Build-ups of 5, 10 and 15 mm of thickness were obtained, and the ultrasonic method measured the layer thickness with an accuracy of 10 %.

Surface dose and build-up region depth dose measurements in non-standard beams of Cyberknife and tomotherapy systems.

The purpose of this study was to measure the surface dose and build-up region depth dose characteristics of 6 MV photon beams in Cyberknife and helical tomotherapy (HT) systems for non-standard small fields using parallel plate chambers (Roos and Markus), Gafchromic EBT3 films, and nanoDot optically stimulated luminescence dosimeters (OSLDs), as well as to investigate the effect of oblique incidence on the surface dose of the beam. All measurements were conducted in a virtual water phantom under machine-specific reference conditions. The Roos and OSLDs overestimated the surface dose when compared with the Markus chamber and EBT3 films by 20%. We applied water equivalent thickness (WET) correction to account for the intrinsic build-up thickness of the detectors from their effective point of measurement (EPOM). With WET correction, a reasonably close surface dose estimate was obtained for all detectors, within 1.9% agreement for the 60mm collimator of Cyberknife and 3.1% agreement for the HT system, with a 5 × 10 cm2 field size. The surface dose increased from the normally incident Cyberknife and HT fields with increasing angle of incidence. The surface dose increased to twice its value at normal incidence for highly oblique angles of incidence above 55°. For the tested fields, a reasonable surface dose estimate could be measured with the detectors if the correction for intrinsic buildup thickness was applied. Nevertheless, the use of Roos chambers with large dimensions and nanoDot OSLDs is not recommended for estimating the surface dose for small fields.

Predicting the Depositional Environments of Mishrif Formation from Seismic Isopach Map in the Dujaila Oil Field, Southeast-Iraq

In this paper, we attempt to predict the depositional environments with associated lithofacies of the main reservoir of the late Cretaceous Mishrif carbonate Formation, depending on the analysis of the created seismic isopach map by integrating seismic and well data. The isopach map was created from a 3D-seismic reflection survey carried out at the Dujaila oil field in southeastern Iraq, which is of an area of 602.26 Km2, and integrated with the data of the two explored wells. Based on the interpretation of the seismic isopach map, the diagram of the 3D-depositional environment model of Mishrif Formation was constructed. It showed three distinguished depositional environments, which were graduated from a back reef lithofacies of a shallow open marine (shelf) environment in the west and NW, to a shoal environment of isolated Rudist reefal buildup in the middle, and a fore reef lithofacies of the deep open marine basin environment in the SE of the field. A 3D-instantaneous frequency model was generated to verify the capability of the seismic isopach map of predicting the depositional environments, which in turn showed that the low frequency was restricted in the region of the high thickness of Rudist reefal buildups (porous reservoir facies) in the vicinity of the productive well Dujaila-1.

Influence of Mix Proportions on Rheological Properties, Air Content of Wet Shotcrete—A Case Study

To study the influence of different mix proportions on the fresh properties of wet shotcrete, the rheological properties and air content of wet shotcrete with different admixtures before pumping were measured. In addition, the pressure drop along the pipeline and the build-up thickness were studied, and the relationship between the rheological properties and the pumpability and sprayability was discussed. This paper attempts to reveal the influence mechanism of admixtures on the fluidity of wet shotcrete by means of pictures. The results show that free paste effect and ball effect are two key factors that affect the performance of fresh wet shotcrete. Air-entraining agent and fly ash are commonly used admixtures, which improve the pumping performance and spraying performance. Finally, the mix proportions of wet shotcrete are put forward to meet the requirements of different types of shotcrete.

Sprayable engineered cementitious composites (ECC) using calcined clay limestone cement (LC3) and PP fiber

Sprayable engineered cementitious composites (ECC) has demonstrated in field applications as a promising repair material. However, the large cement dosage that leads to a high carbon footprint and potential restrained shrinkage cracking suggests needed improvements. In this study, a sprayable ECC was developed using calcined clay limestone cement (LC3), calcium sulfoaluminate (CSA) expansive additive and polypropylene (PP) fiber to increase the material greenness and durability. The sprayability and mechanical performance were examined by the flow table and uniaxial tension tests. The one-time build-up thickness achieved was 45 mm for vertical spraying and 35 mm for overhead spraying at 20–30 min rest-time, and up to 80 mm for vertical spraying at 50 min rest-time. The ECC had a comparable strength but higher tensile strain capacity (5.7%) and reduced crack width (30 μm at 1% tensile strain) when sprayed, in comparison to specimens prepared by casting. A spray-repaired layered ECC-concrete composite revealed multiple cracking and strain-hardening performance under flexural loading. The advantages of low carbon, low shrinkage, low cost, and ultra-high ductility of the developed sprayable ECC promote broader applications in infrastructure repair.

The Effects of Marble Dust on the Rheological and Mechanical Properties of Shotcrete

Recycling industrial waste materials has become an environmental and economic necessity. The utilization of these materials to develop concrete contributes not only to their disposal, but also to the preservation of the environment. This study attempted to evaluate the properties of sprayed concrete with Marble Dust (MD) as partial replacement of concrete components. For this purpose two series of concrete mixtures were prepared: the first series included six mixtures containing MD as cement replacement with percentages of 5%, 10%, 15%, 20%, 25%, and 30% by weight, the second series included six mixtures containing 5%, 10%, 15%, 20%, 25%, and 30% of MD as replacement for sand. Also, conventional concrete mixture with 100% cement and 100% sand was produced as control mixture. Rheological and mechanical properties as pumpability, build-up thickness, rebound percentage, adhesion strength, and compressive and tensile strength were studied. In general, the results indicate that use of MD improves shotcreting as an application and shotcrete’s performance.

Determination of single cryoablation outcome within 30 to 60 seconds of freezing based on ice impedance.

BackgroundA direct indicator of effective pulmonary vein isolation (PVI) based on early ice formation is presently lacking.ObjectiveThe initial impedance rise within 30 to 60 seconds (sec) of single cryoablation relating to ice on the distal surface of the cryoballoon could; predict effective PVI with early termination, the need for prolonging the cryoablation, or failure to achieve effective ablation.MethodsImpedance measurements were taken between two ring electrodes, at the anterior balloon surface and at the shaft behind the balloon. Ice covering the anterior ring leads to impedance rise. Single cryoablation (eight animals, 37 veins) was applied for 90 to 180 sec. Cryoapplication was terminated if the impedance reached ≥500 Ω. Impedance levels at ≤60 sec of cryoablation were divided into three groups based on the characteristics of the impedance rise. PVI was confirmed acutely and at 45 ± 9 days recovery by electrophysiology mapping and histopathology.ResultsAt 60 sec of freezing, an impedance rise of 34.1 ± 15.2 Ω (13‐50 Ω) and slope of the impedance rise (measured during 15‐30 sec of cryoapplication) less than 1 Ω/sec resulted in failed PVI. An impedance rise of 104.4 ± 31.5 Ω (76‐159 Ω) and slope of 2 Ω/sec resulted in 100% PVIs. An impedance rise of 130.9 ± 137.8 Ω (40‐590 Ω) and slope of 10 Ω/sec resulted in 100% PVIs with early termination at 90 sec.ConclusionThe efficacy of single cryoablation can be defined within 30 to 60 sec based on ice impedance. Three unique impedance profiles described in this investigation are associated with the uniformity and thickness of the ice buildup on the anterior surface of the balloon. One cryoablation with an adequate impedance rise is needed for successful outcomes.

Investigation of AAA dose calculation algorithm accuracy in surface and buildup region for 6MV photon beam using markus parallel-plate ion chamber.

In radiotherapy, dose distributions are obtained by using dose calculation algorithms that are implanted in treatment planning systems (TPS). This study aims to compare the surface doses of separate field sizes calculated by different version of The Analytical Anisotropic Algorithm (AAA) and measured by the parallel-plate ion chamber that is admitted as the most reliable dosimetry system for the surface region dose measurements. In order to measure the near surface dose, water equivalent solid phantom was used and measurements were made for 6MV photon beam at 100 cm source-detector distance for 5×5, 10×10, and 20×20 cm2 field sizes. AAA 8.9 and AAA 15.1 versions of the Varian Eclipse TPS were used for surface dose calculations by generating beams with separate field sizes. The doses were read by considering the effective buildup thickness of Markus parallel-plate ion chamber. The surface doses using 6 MV photon beams for 10×10 cm2 field size at 0.07 mm were found to be 11.04%, 26.25%, and 19.69% for AAA v8.9, AAA v15.1 and Markus chamber, respectively. It was seen that for both of the AAA versions and Markus parallel-plate ion chamber, increasing field sizes also increase surface dose. For all field sizes, surface dose was lowest by using AAA v8.9 at 0.07 mm. The different versions of the same TPS algorithms may calculate the surface doses distinctively. After upgrading of TPS algorithms, surface doses should be calculated and compared by measurements with different dosimetry systems to better understand their calculation behaviors in the near surface region.