Анализ методик испытаний гидротехнических бетонов на прочность

Polypropylene fiber reinforcement is an effective method to enhance the durability of concrete structures. With the increasing public interest in the widespread use of polypropylene fiber reinforced concrete (PFRC), the necessity of evaluating the mechanism of polypropylene fiber (PF) on the permeability of concrete has become prominent. This paper describes the influence of PF on the concrete permeability exposed to freeze-thaw cycles under compressive and tensile stress. The permeability of PFRC under compressive and tensile loads is accurately measured by a specialized permeability setup. The permeability of PFRC under compressive and tensile loads, the volume change of PFRC under compressive load, and the relationship between compressive stress levels at minimum permeability and minimum volume points of PFRC are discussed. The results indicate that the addition of PF adversely affects the permeability of concrete without freeze-thaw damage and cracks. However, it decreases the permeability of concrete specimens exposed to freeze-thaw cycles and cracking. Under compressive load, the permeability of PFRC initially decreases slowly and follows by a significant increase as the compressive stress level increases. This phenomenon correlates with the volume change of the specimen. The compressive stress level of the minimum permeability point and compressive stress level of the minimum volume point of PFRC exhibit a linear correlation, with a fitted proportional function parameter γ ≈ 0.98872. Under tensile load, the permeability of PFRC increases gradually with radial deformation and follows by a significant increase. The strain-permeability curves of PFRC under loading are studied and consist of two stages. In stage I, the permeability of PFRC gradually decreases with the increase of strain under compressive load, while the permeability increases with the increase of strain under tensile load. In stage II, under compressive load, the permeability of PFRC increases with the increase of freeze-thaw cycles, whereas under tensile load, the permeability gradually decreases with the increase of freeze-thaw cycles. The reduction of PF on the permeability of PFRC under tensile load is greater than that under compressive load. In future research, the relationship between strain and permeability of PFRC can be integrated with its constitutive relationship between stress and strain to provide a reference for the application of PF in the waterproofing of concrete structures.

To investigate different responses of direct and indirect tensile strengths to loading rate, direct and indirect tension tests were performed on sandstone, rust stone, and granite specimens. Typical load curves indicate that a peak tensile stress frequently appears before the second peak stress, used to calculate the tensile strength in indirect tension tests. As expected, increase in the loading rate increases the tensile strength. In addition, the calculated tensile strengths of the indirect tension tests are frequently higher. Interestingly, the increase ratio of the tensile strength with the increase in the loading rate in indirect tension tests is higher. To verify the above results, crack propagation and stress evolution in direct and indirect tension tests were dynamically monitored using PFC 3D. For direct tension tests, specimens fail at the peak tension point, corresponding to the tensile strength. However, for indirect tension tests, minor cracks, composing of continuous microcracks, form before the peak stress and accompany with the decreased slope of the compression curve. At the peak point, tensile stresses significantly concentrate at the crack tips and further cause large‐scale crack propagation. In addition, the initiation stress instead of the peak tensile stress is closer to the tensile strength, obtained from the direct tests for the same loading rate.

In order to investigate mechanical behavior of red sandstone under cyclical compressive and tensile loads, a series of short-term uniaxial constant cyclical compressive and tensile loading tests and uniaxial constant cyclical compressive and tensile loading creep tests were conducted. First, based on the results of short-term uniaxial constant cyclical compressive and tensile loading experimental, the permanent residual strain, strains at peak stress were analyzed. Results show that the specimen shows permanent residual strain after suffering short-term cyclic loads; the residual strains and strains at peak stress show the “decay increase” and “steady-state increase” stages with the cyclic number N; the relationship between the strain at peak stress (tensile or compressive stress) and cyclic number can be well described by a modified Burger model. And then, in accordance with the creep experimental results, the creep behavior of the red sandstone was analyzed. Results show that there is obvious instantaneous strain, decay creep, and steady creep under each stress level of tensile or compressive stress stages; the specimen appears accelerated creep stage under the 5th tensile stress of 1.19 MPa. It was also found that power function can better express the relationship between steady strains and cycle number under tensile or compressive stress levels. In the end, a viscoelastic-plastic creep model was proposed; comparison of the test results with the proposed viscoelastic-plastic creep model predictions indicates that the proposed model is capable of describing the creep behavior of red sandstone subjected to cyclic tensile and compressive stress loading.

In order to study the effect of water cement ratio on the damage degree of concrete at different stress levels, the acoustic and acousto-ultrasonic characteristics of concrete with different water cement ratio under multi-stage loading were analyzed. It was concluded that with the increase of the damage degree of concrete, the damage variable and the third harmonic ratio increased, while the acousto-ultrasonic velocity and acousto-ultrasonic energy decreased. Among them, the third harmonic ratio was the most sensitive parameter affecting the damage degree. The compressive strength of concrete decreased with the increase of water cement ratio, and they were linearly related. Furthermore, with the increase of the stress level or the increase of the water cement ratio, the damage of concrete occurred during the holding period increased.

To find out the ideal radiation shielding material from civil engineering and radiation aspect especially in the medical sector, in this research made sand iron mortar was made with mix proportion of 1:4 with addition variation of lead oxide Pb3O4 that are 0% (M1), 20% (M2), 30% (M3), and 40% (M4) of loose volume of sand iron and also Viscocrete-10 addition 0.6% of cement weight. Water cement ratio used for M1, M2, M3, and M4 are 0.4, 0.41, 0.44, and 0.48 respectively. Sand iron and lead oxide Pb3O4 as fine aggregate are tested to obtain its density and unit weight as a basis to calculate the mix design. The specimens of each variable of mortar are tested on its physical and mechanical properties, namely weight per m3, compressive strength, tensile strength, and water absorption with the number of specimens are 3 (three) of each variable of mortar. After that, the specimens are tested with Gamma radiation with energy 1170 keV, 1330 keV (Cobalt 60), 662 keV (Cesium 137), and 323 keV (Cr 51) and X Ray radiation with energy 70 kV and 90. The specimens are block shaped size 10 cm x 10 cm with thickness variation of 1 cm up to 12 cm. The result shows that the density of sand iron and lead oxide Pb3O4 are 3,8259 and 8,4693 respectively and the unit weights are 1,965 gr/cm3 and 2,535 gr/cm3 respectively. Weight per m3 of mortar was increased caused by the increasing of lead oxide Pb3O4 on mortar. The compressive strength significantly increased starting on M2 (37,328 MPa) from M1 (7,594 MPa) and a bit decreased on M3 and M4, i.e. 32,188 Mpa and 30,144 Mpa respectively caused by the increase of water cement ratio. The value of water absorption was decreased as an effect of lead oxide Pb3O4 addition. From the result of Gamma radiation test, it shows that the higher the density, the higher the attenuation coefficient of the material and if the energy increases, the attenuation coefficient of the material decreases except at the energy above 1200 keV where the attenuation coefficient increases back as a result of a pair production phenomenon. The attenuation coefficient values of M1, M2, M3, and M4 are 0.102 cm-1, 0.145 cm-1, 0.152 cm-1, and 0.184 cm-1 respectively for energy 1330 keV; 0.060 cm-1, 0.104 cm-1, 0.120 cm-1, and 0.155 cm-1 respectively for energy 1170 keV; 0.157 cm-1, 0.212 cm-1, 0.242 cm-1, and 0.284 cm-1, respectively for energy 662 keV, and 0.202 cm-1, 0.309 cm-1, 0.330 cm-1, and 0.426 cm-1 respectively for energy 323 keV. The different result shows rom X ray radiation test whereas occurred inaccurate data as a result of scattering caused by wide beam owned by X ray so that the result cannot be compared with the result of Gamma radiation test. So, the results of X ray radiation test which can be used are the X ray photo of mortars that shows the homogeneity of each variable of mortar. From the effectiveness aspect as a radiation shielding, mortar M4 is the most effective because it has the biggest attenuation coefficient value.

Uniaxial step loading test setup for determination of creep curves of oxidation-sensitive high strength materials in vacuum under tensile and compressive load

Mechanically sensitive nociceptor afferents were studied in a preparation of isolated skin from rat leg. Each neuron was studied while the skin was subjected to tensile and compressive loading. The experiment was designed to create highly uniform states of stress in both tension and compression. Tensile loads were applied by pulling on the edges of the sample. Applied loads were used to determine the tensile stresses. Surface displacements were used to determine tensile strains. Compressive loads were applied by indenting the surface of the skin with flat indenter tips applied under force control. The skin was supported by a flat, hard substrate. Compressive stresses were determined from the applied loads and tip geometry. Compressive strains were determined from skin thickness and tip excursions. All nociceptors were activated by both tensile and compressive loading. There was no interaction between the responses to compressive and tensile stimuli (i.e., the responses were simply additive). Responses of nociceptors were better related to tensile and compressive stresses than to strains. Nociceptors responded better to tensile loading than to compressive loading. Response thresholds were lower and sensitivities were higher for tensile stress than for compressive stress. The response to compression was better related to compressive stress than to other stimulus parameters (i.e., load/circumference or simply load). Indentations of intact skin over a soft substrate such as muscle would be expected to cause widespread activation of nociceptors because of tensile stresses.

Flexible solar wings with high energy density, lightweight, small size and large deployment area are one of the first choices for next‐generation spacecraft. However, the flexible solar wings are subjected to irradiation in space and tensile mechanical stress, which produce the charge accumulation effect and result in electrostatic discharge. It is necessary to establish a test method for the conductivity and space charge behaviour of polyimide under tensile stress. The stress–strain characteristics of polyimide under different tensile stresses are studied by the authors. The longitudinal length‐strain characteristics and transverse thickness evolution characteristics under different stresses are also obtained. The results show that the variation of film thickness with tensile force is only about 1% before the yield point. The polyimide films from 50 to 200 μm thick have similar yield and tensile strengths. The ultimate stress of the specimen decreases from approximately 126 to 103 MPa with increasing thickness. The thickness model of polyimide under tensile stress were obtained, which could accurately calculate the voltage amplitude applied on the specimens for measuring the conductivity under different tensile stresses. A basis for investigating the stress–strain characteristics of polyimide films under different tensile stresses are provided, which will facilitate the formulation selection and performance improvement of polyimide for flexible solar wings of spacecraft.

In Vitro Assessment of Retention and Resistance Failure Loads of Teeth Restored with a Complete Coverage Restoration and Different Core Materials.

A water tank is used to store water to surge over the daily requirement. In the construction of concrete structure for the storage of water and other liquids the imperviousness of concrete is most essential. The permeability of any uniform and thoroughly compacted concrete of given mix proportions is mainly dependent on water cement ratio. The increase in water cement ratio results in increase in the permeability. The decrease in water cement ratio will therefore be desirable to decrease the permeability, but very much reduced water cement ratio may cause compact ion difficulties and prove to be harmful also. Design of liquid holding structure has to be based on the anticipation of cracking in the concrete having regard to its tensile strength. Cracks can be prevented by avoiding the use of thick timber shuttering which prevent the easy escape of heat of hydrate ion from the concrete mass the risk of cracking can also be minimized by reducing the restraints on free expansion or contraction of the structure.

Experimental study on expansion and cracking properties of static cracking agents in different assembly states

The effect of water-cement ratio on the microstructure of set Portland cement

Improving latent heat storage capacity of polyethylene glycol/cement composite prepared via solution blending method

Study on the performance of sealing slurry at the bottom of geomembrane composite vertical cut off walls

Wpływ systemów korzeniowych wybranych gatunków drzew na przyrost wytrzymałości gruntu na ścinanie