scholarly journals INFLUENCE OF FIBER REINFORCEMENT ON CONCRETE SHRINKAGE FOR RIGID ROAD AND AIRFIELD PAVEMENT REPAIR

2021 ◽  
pp. 78-86
Author(s):  
S.O. Kroviakov ◽  
◽  
V.O. Kryzhanovskyi ◽  
Keyword(s):  
Cement Content ◽  
Fiber Reinforcement ◽  
Moisture Loss ◽  
General Nature ◽  
Internal Stresses ◽  
Noticeable Effect ◽  
Concrete Shrinkage ◽  
Shrinkage Process ◽  
Dry Conditions ◽  
Composition Factors

Abstract. The influence of fiber reinforcement with steel anchor fiber on the shrinkage of modified concrete for rigid airfield pavements repair has been determined. A 2-factor experiment was carried out, in which the following composition factors were varied: the amount of hardening accelerator Sika Rapid 3 from 0 to 2.4% of the cement content (0-9.6 kg/m3); the amount of steel anchor fiber with 1 mm diameter and 50 mm length, from 0 to 100 kg/m3. For the concrete batching were used: Portland cement CEM II / AS 42.5 in the amount of 400 kg/m3, granite crushed stone 5-20 mm, quartz sand, plasticizer admixture BASF MasterGlenium SKY 608 in the amount of 1.2% by cement content. The workability of the mixtures was S2 (6-8 cm); W/C ratio depended on the concrete composition. Due to the use of superplasticizers, the W/C of all investigated mixtures was in the range of 0.309-0.343. The shrinkage of the prism specimens was recorded after 3 hours, 6 hours, 1, 2, 3 and 7 days of being in air-dry conditions. The shrinkage process does not end after 7 days of concrete hardening, however, the general nature of the influence of variable factors on its value remains. It has been established that fiber-reinforced concretes, with a fiber amount of 50 kg/m3 and with a fiber amount of 100 kg/m3, have 10-15% less shrinkage compared to unreinforced concretes. Compositions with a fiber amount of 50 kg/m3 and 100 kg/m3 have practically the same shrinkage, which is explained by an increase in W/C ratio with an increase in the amount of fiber reinforcement. The amount of hardening accelerator has a less noticeable effect on the amount of concrete shrinkage. By adding Sika Rapid 3, concrete shrinkage at the age of 7 days is reduced by 2-9%. This effect can be explained by the fact that internal stresses arising in the process of structure formation and moisture loss in concrete are contained in a more durable cement-sand matrix. The concrete shrinkage without fiber and accelerator was also measured up to the age of 98 days. It was found that the limiting shrinkage for such concrete is 2.5×10-4. The analysis of the drawn experimental-statistical model showed that with the amount of metal fiber from 60 to 90 kg/m3 and the amount of the hardening accelerator from 0.9 to 2.4%, the shrinkage of the investigated concretes is minimal (7 = 1.3×10-4). Thus, the use of fiber reinforcement with anchor steel fiber and a hardening accelerator can significantly reduce the concrete shrinkage for the rigid airfield pavements repair is important for this material.

scholarly journals Refined Finite Element Analysis of Crack Causes in SRC Arch Rib Bridges considering Multiple Factors

2018 ◽  
Vol 2018 ◽  
pp. 1-9
Author(s):  
Mengsheng Yu ◽  
Nianchun Deng ◽  
Qifeng Chen ◽  
Tianzhi Hao
Keyword(s):  
Steel Frame ◽  
Element Analysis ◽  
Shrinkage Temperature ◽  
Arch Bridge ◽  
Temperature Changes ◽  
Concrete Shrinkage ◽  
Shrinkage Process ◽  
Crack Problems ◽  
Arch Bridges ◽  
Bearing Structure

The SRC (steel-frame reinforced concrete) arch bridge is an important part of the development of arch bridges. Scholars worldwide have studied it from various aspects because of its stronger stiffness and stability than other types of bridges especially when crossing the canyon. The steel frame is a stress bracket during construction. Concrete becomes the main axial-pressure bearing structure when it fills the inner pipe and the encased frame. This article mainly focuses on the crack problems of SRC arch bridging during the postconstruction operation, local model of the midspan arch rib, and the equivalent relationship between the coefficient of expansion and the temperature of concrete. This study uses a cooling method to simulate the shrinkage process with detailed analysis of three properties including concrete shrinkage, temperature gradients, and concentrated hanger rod force. It is concluded that the SRC arch bridge will have large tensile stress on both inner and outer surfaces of slab and web when the temperature changes, and it is the main cause of cracks. The results agree well with measured data. At last, we come up with some reference suggestions in the design and construction of similar bridges in the future.

SOME ASPECTS OF MOISTURE ABSORPTION AND LOSS IN EGGS OF MELANOPLUS BIVITTATUS (SAY)

1952 ◽  
Vol 30 (1) ◽  
pp. 55-82 ◽  
Author(s):  
R. W. Salt
Keyword(s):  
Moisture Content ◽  
Moisture Absorption ◽  
Age Groups ◽  
Posterior Pole ◽  
Moisture Loss ◽  
Vitelline Membrane ◽  
Desiccation Rate ◽  
Gradual Onset ◽  
Dry Conditions ◽  
Moisture Conditions

The penetration of moisture into or out of eggs of Melanoplus bivittatus (Say) is assisted or retarded by a variety of envelopes. Proceeding inwardly these are, in the newly laid egg, the chorion, the primary lipoid layer (probably waxy), and the vitelline membrane; later, to these are added the secondary lipoid layer (probably oily), the yellow cuticle, a bonding material, the white cuticle, and the serosa, which secretes all the others of this group. The primary lipoid layer waterproofs the egg in its earliest stages, but its function is soon taken over by the secondary lipoid layer. A specialized moisture-permeable area, the hydropyle, is formed at the posterior pole. Moisture is absorbed from the environment chiefly through the hydropyle, reaching a peak of absorption on the eighth or ninth day at 25 °C. and then decreasing because of the limited expansion of the cuticular layers. The original moisture content of the egg is approximately doubled. Moisture loss in young eggs, up to seven days of age, is restricted at first by the primary lipoid layer and later by the secondary lipoid layer. From the eighth day to the end of anatrepsis, on the 14th day, the desiccation rate is greatly increased. Most of the loss occurs through the hydropyle, which at this time is normally absorbing water; however, the relationship between loss and gain through the hydropyle is not close. After blastokinesis, or after the 14th day of incubation at 25 °C., the desiccation rate is extremely variable. Some of the moisture loss takes place through the hydropyle, and when the rate is low all of it does so; however, in many eggs the general cuticular surface becomes permeable (to desiccation but not to absorption), and the losses are erratic and unpredictable. With the gradual onset of diapause after the 21st day, the desiccation rate declines. Changing the moisture conditions during incubation of the eggs results in changes in the desiccation rates. The variability of the rates in older eggs was not caused by retardation of development, irregular moisture absorption, intermittent drying, or laboratory techniques, but was probably the result of variable cuticular permeability. Most M. bivittatus eggs, regardless of age, survived losses up to one-third of their moisture content, but few survived more than a two-thirds loss. After more than a one-third loss, the collapsing action of the egg frequently produced distorted or abnormal embryos. Though these often lived for some time, they never hatched. Those individuals and those age groups with the lowest desiccation rates naturally survived dry conditions longest.

scholarly journals Antioxidant and Phenolic Changes Across One Harvest Season and Two Storage Conditions in Primocane Raspberries (Rubus idaeus L.) Grown in a Hot, Dry Climate

HortScience ◽  
2011 ◽  
Vol 46 (2) ◽  
pp. 236-239 ◽  
Author(s):  
Brenner L. Freeman ◽  
Janet C. Stocks ◽  
Dennis L. Eggett ◽  
Tory L. Parker
Keyword(s):  
Antioxidant Capacity ◽  
Total Phenolic Content ◽  
Phenolic Content ◽  
Total Phenolics ◽  
Storage Conditions ◽  
Oxygen Radical ◽  
Rubus Idaeus ◽  
Moisture Loss ◽  
Total Phenolic ◽  
Dry Conditions

Antioxidant phytochemical differences among cultivars and changes after storage have not been explored in primocane raspberries grown in a hot, dry climate. It was hypothesized that significant differences would be detected in total phenolics and antioxidant capacity [oxygen radical absorbance capacity (ORAC)] between cultivars and over time. ‘Autumn Bliss’ had the highest ORAC and phenolic content, whereas ‘Caroline’ had the lowest ORAC and phenolic content when fresh. Averaging all cultivars and pickings, refrigerated berries had a significantly higher total phenolic content than fresh or frozen berries, although some moisture loss occurred during standard refrigeration. Antioxidant capacity and total phenolic content of primocane raspberries grown in hot, dry conditions vary between cultivars, on average do not change significantly after storage, are higher later in the season, and are higher than supermarket cultivars.

Nanostructure of semiconductor quantum dots in a borosilicate glass matrix by complementary use of HREM and AEM

1990 ◽  
Vol 48 (4) ◽  
pp. 728-729
Author(s):  
M.J. Kim ◽  
L.C. Liu ◽  
S.H. Risbud ◽  
R.W. Carpenter
Keyword(s):  
Quantum Dots ◽  
Borosilicate Glass ◽  
Glass Matrix ◽  
Optical Switching ◽  
Response Times ◽  
Fast Response ◽  
Processing Technique ◽  
Internal Stresses ◽  
Electron Hole ◽  
Spatial Dimensions

When the size of a semiconductor is reduced by an appropriate materials processing technique to a dimension less than about twice the radius of an exciton in the bulk crystal, the band like structure of the semiconductor gives way to discrete molecular orbital electronic states. Clusters of semiconductors in a size regime lower than 2R {where R is the exciton Bohr radius; e.g. 3 nm for CdS and 7.3 nm for CdTe) are called Quantum Dots (QD) because they confine optically excited electron- hole pairs (excitons) in all three spatial dimensions. Structures based on QD are of great interest because of fast response times and non-linearity in optical switching applications.In this paper we report the first HREM analysis of the size and structure of CdTe and CdS QD formed by precipitation from a modified borosilicate glass matrix. The glass melts were quenched by pouring on brass plates, and then annealed to relieve internal stresses. QD precipitate particles were formed during subsequent "striking" heat treatments above the glass crystallization temperature, which was determined by differential thermal analysis.

The Shikani HME: A New Tracheostomy Heat and Moisture Exchanger

2020 ◽  
Vol 63 (9) ◽  
pp. 2921-2929
Author(s):  
Alan H. Shikani ◽  
Elamin M. Elamin ◽  
Andrew C. Miller
Keyword(s):  
Ex Vivo ◽  
Moisture Loss ◽  
Speaking Valve ◽  
Time Zero ◽  
In Series ◽  
Turbulent Airflow ◽  
The Difference ◽  
Loss Efficiency ◽  
Heat And Moisture ◽  
Lung Simulation

Purpose Tracheostomy patients face many adversities including loss of phonation and essential airway functions including air filtering, warming, and humidification. Heat and moisture exchangers (HMEs) facilitate humidification and filtering of inspired air. The Shikani HME (S-HME) is a novel turbulent airflow HME that may be used in-line with the Shikani Speaking Valve (SSV), allowing for uniquely preserved phonation during humidification. The aims of this study were to (a) compare the airflow resistance ( R airflow ) and humidification efficiency of the S-HME and the Mallinckrodt Tracheolife II tracheostomy HME (M-HME) when dry (time zero) and wet (after 24 hr) and (b) determine if in-line application of the S-HME with a tracheostomy speaking valve significantly increases R airflow over a tracheostomy speaking valve alone (whether SSV or Passy Muir Valve [PMV]). Method A prospective observational ex vivo study was conducted using a pneumotachometer lung simulation unit to measure airflow ( Q ) amplitude and R airflow , as indicated by a pressure drop ( P Drop ) across the device (S-HME, M-HME, SSV + S-HME, and PMV). Additionally, P Drop was studied for the S-HME and M-HME when dry at time zero (T 0 ) and after 24 hr of moisture testing (T 24 ) at Q of 0.5, 1, and 1.5 L/s. Results R airflow was significantly less for the S-HME than M-HME (T 0 and T 24 ). R airflow of the SSV + S-HME in series did not significant increase R airflow over the SSV or PMV alone. Moisture loss efficiency trended toward greater efficiency for the S-HME; however, the difference was not statistically significant. Conclusions The turbulent flow S-HME provides heat and moisture exchange with similar or greater efficacy than the widely used laminar airflow M-HME, but with significantly lower resistance. The S-HME also allows the innovative advantage of in-line use with the SSV, hence allowing concurrent humidification and phonation during application, without having to manipulate either device.

Cement Content of Durability Cement Stabilized Macadam Base Course in Seasonal Freezing Zone

CICTP 2020 ◽  
2020 ◽  
Author(s):  
Junchen Ma ◽  
Chunyu Liang ◽  
Ying Wang ◽  
Lidong Zhang ◽  
Weiwu Cui ◽  
...  
Keyword(s):  
Cement Content ◽  
Seasonal Freezing ◽  
Base Course

Enhancing the power generation of Rhodopseudomonas palustris-based MFC

2020 ◽  
Vol 64 (1-4) ◽  
pp. 1261-1268
Author(s):  
Shu Otani ◽  
Dang-Trang Nguyen ◽  
Kozo Taguchi
Keyword(s):  
Activated Carbon ◽  
Rhodopseudomonas Palustris ◽  
Ozone Treatment ◽  
Maximum Power Density ◽  
On Demand ◽  
Long Time ◽  
Dry Conditions ◽  
Carbon Sheet ◽  
Uv Ozone

In this study, a portable and disposable paper-based microbial fuel cell (MFC) was fabricated. The MFC was powered by Rhodopseudomonas palustris bacteria (R. palustris). An activated carbon sheet-based anode pre-loaded organic matter (starch) and R. palustris was used. By using starch in the anode, R. palustris-loaded on the anode could be preserved for a long time in dry conditions. The MFC could generate electricity on-demand activated by adding water to the anode. The activated carbon sheet anode was treated by UV-ozone treatment to remove impurities and to improve its hydrophilicity before being loaded with R. palustris. The developed MFC could generate the maximum power density of 0.9 μW/cm2 and could be preserved for long-term usage with little performance degradation (10% after four weeks).

Theoretical study of the prestressing strand's stress by computer modeling methods

2020 ◽  
Vol 76 (11) ◽  
pp. 1139-1148
Author(s):  
A. G. Korchunov ◽  
E. M. Medvedeva ◽  
E. M. Golubchik
Keyword(s):  
Residual Stresses ◽  
High Strength ◽  
Pearlitic Steel ◽  
Internal Stresses ◽  
Steel Microstructure ◽  
Compressive Stresses ◽  
Wide Range ◽  
Prestressing Strands ◽  
Increasing Temperature ◽  
Wire Strand

The modern construction industry widely uses reinforced concrete structures, where high-strength prestressing strands are used. Key parameters determining strength and relaxation resistance are a steel microstructure and internal stresses. The aim of the work was a computer research of a stage-by-stage formation of internal stresses during production of prestressing strands of structure 1х7(1+6), 12.5 mm diameter, 1770 MPa strength grade, made of pearlitic steel, as well as study of various modes of mechanical and thermal treatment (MTT) influence on their distribution. To study the effect of every strand manufacturing operation on internal stresses of its wires, the authors developed three models: stranding and reducing a 7-wire strand; straightening of a laid strand, stranding and MTT of a 7-wire strand. It was shown that absolute values of residual stresses and their distribution in a wire used for strands of a specified structure significantly influence performance properties of strands. The use of MTT makes it possible to control in a wide range a redistribution of residual stresses in steel resulting from drawing and strand laying processes. It was established that during drawing of up to 80% degree, compressive stresses of 1100-1200 MPa degree are generated in the central layers of wire. The residual stresses on the wire surface accounted for 450-500 MPa and were tension in nature. The tension within a range of 70 kN to 82 kN combined with a temperature range of 360-380°С contributes to a two-fold decrease in residual stresses both in the central and surface layers of wire. When increasing temperature up to 400°С and maintaining the tension, it is possible to achieve maximum balance of residual stresses. Stranding stresses, whose high values entail failure of lay length and geometry of the studied strand may be fully eliminated only at tension of 82 kN and temperature of 400°С. Otherwise, stranding stresses result in opening of strands.

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