Influence Of Confining Pressure Research Articles

Experimental of the confinement effect on the compression strength of concrete

In this paper, the impact of confinement pressure on the compressive strength of concrete was carried out various levels of confinement on two concrete types, B20 and B25. As a result, the influence of confinement pressure on the compressive strength of concrete is quantified for the specific research problem at hand. The research findings provide recommendations for the application of the confinement effect concept in the design of reinforced concrete structures in Vietnam.

Performance of microcapsule-based self-healing concrete under multiaxial compression with large axial strain: Mechanical properties failure mode, and pore structure

• Triaxial behavior of microcapsule-based concrete was investigated. • The effect of microcapsules on triaxial strength declined with confinement pressure. • Microcapsules improved the plastic capacity and post-peak bulk modulus of concrete. • Concrete behavior under large axial strain was controlled by granular skeletons. To promote the application of microcapsule-based self-healing concrete in engineering structures, it is important to study the mechanical behaviour under complex stress conditions. Accordingly, this study aims to investigate the mechanical behaviour of microcapsule-based self-healing concrete under the triaxial compression state with large axial strain. The self-healing concrete was prepared by mixing different dosages of UF/Epoxy microcapsules, and the influence of confinement pressure, large axial strain, and microcapsule dosage on the mechanical behaviour of concrete was investigated through uniaxial compression, conventional triaxial compression, and mercury intrusion porosimetry (MIP) test. The results show that incorporating microcapsules reduced the cohesive strength and internal friction angle of the concrete. In contrast, the influence of microcapsule dosage on triaxial strength was rapidly weakened with increasing confinement pressure. Both the incorporation of microcapsules and the application of confinement pressure can improve the plastic deformation capacity and reduce the brittleness of the specimens. In addition, microcapsules may increase the bulk modulus of the specimens in the hardening stage. It should be noted that under the action of triaxial loading with large axial strain, the ultimate strengths of specimens with different microcapsule dosages are similar, and concrete behaviour is mainly controlled by the granular skeleton.

Influence of Confinement Pressure on the Mechanical Response of Emulsified Cold-Recycled Mixtures

Cold recycling of asphalt pavement is an effective rehabilitation technique in terms of saving natural resources and cost of construction. The current study focuses on cold-recycled asphalt mixture designated as emulsified cold-recycled mixture (ECRM) that contains 100% reclaimed asphalt pavement material and slow-setting asphalt emulsion. Here, a repeated haversine compression test is conducted with and without confinement pressure at six temperatures (0°C, 10°C, 20°C, 30°C, 40°C, and 50°C) and 10 frequencies (25, 20, 10, 5, 2, 1, 0.5, 0.2, 0.1, and 0.01 Hz). The stress–strain–time response of ECRM is investigated, and it is observed that the influence of confinement pressure is negligible in the temperature range of 0°C–10°C, whereas it is significant at temperature 30°C and higher, irrespective of the frequency of loading. However, at 20°C, the influence of confinement pressure is negligible at higher frequencies (25–10 Hz), and it is significant at lower frequencies (less than 10 Hz). The viscoelastic response of ECRM is seen at all temperature, frequency, and confinement conditions of loading from the analyzed Lissajous plots. The dynamic modulus and phase angle are computed using the regression and the fast Fourier-transform (FFT) methods. The dynamic modulus and phase angle master curve is then generated using a free-shifting approach and a model-based approach. The model-based approach involves the numerical solution of the exact Kramers–Kronig relations combined with the generalized logistic sigmoidal model. The FFT-based dynamic modulus is used to construct a master curve with the generalized logistic sigmoidal model. Such a model-based master curve resulted in excellent predictive capabilities for dynamic modulus, and hence it is suggested for ECRM.

Influence of Confinement Pressure and Rest Periods on Measurement of Dynamic Modulus of Bituminous Mixtures

AbstractIn the AASHTO T-378 protocol for computing dynamic modulus and phase angle, the bituminous mixture sample is subjected to a continuous loading from high frequency to low frequency. The post...

Influence of Confinement Pressure on the Development of Three Stage Curve for Bituminous Mixtures

As part of the mechanistic-empirical pavement design procedure, the flow number test is used to rank the bituminous mixtures for rutting. In the flow number test, a sample is subjected to 0.1 s of loading followed by 0.9 s rest period and a haversine load waveform is used. This test protocol has serious limitation and these are due to the loading conditions applied and the post-processing procedure followed for flow number determination. In this investigation, three changes were made in the existing flow number protocol. The first one was in the load waveform. A trapezoidal waveform was used instead of the haversine load waveform. The second change was related to loading conditions. Different combinations of confinement and deviatoric loading were applied and the final choice was made based on the resulting three stage creep curve. The third change was related to post-processing method and a Francken model to capture the complete three stages of deformation was used. A BC mix with mid-gradation following MoRTH (Specifications for roads and bridge works. Indian Roads Congress, New Delhi 2013) guidelines was used with VG30 and CRMB60 binder. PReSBOX shear compactor was used for making cylindrical samples of 94 mm diameter and 150 mm height. The samples were cast with a target air voids of 6 %. All the testing was carried out at 50 and 60 °C. Different confinement conditions ranging from 50 to 200 kPa were used with the deviatoric loading ranging from 200 to 600 kPa. The influence of modified binder was clearly seen in the development of three stage curve. The collected data was post-processed using Francken model and the flow number was determined. This flow number was bench marked with the existing flow number protocol and it was seen that there were gross discrepancies.

Elastoplastic cup model for cement-based materials

Based on experimental data obtained from triaxial tests and a hydrostatic test, a cup model was formulated. Two plastic mechanisms, respectively a deviatoric shearing and a pore collapse, are taken into account. This model also considers the influence of confining pressure. In this paper, the calibration of the model is detailed and numerical simulations of the main mechanical behavior of cement paste over a large range of stress are described, showing good agreement with experimental results. The case study shows that this cup model has extensive applicability for cement-based materials and other quasi-brittle and high-porosity materials in a complex stress state.

Scale and size effects in dynamic fracture of concretes and rocks

Structural-temporal approach based on the notion of incubation time is used for interpretation of strain-rate effects in the fracture process of concretes and rocks. It is established that temporal dependences of concretes and rocks are calculated by the incubation time criterion. Experimentally observed different relations between ultimate stresses of concrete and mortar in static and dynamic conditions are explained. It is obtained that compressive strength of mortar at a low strain rate is greater than that of concrete, but at a high strain rate the opposite is true. Influence of confinement pressure on the mechanism of dynamic strength for concretes and rocks is discussed. Both size effect and scale effect for concrete and rocks samples subjected to impact loading are analyzed. Statistical nature of a size effect contrasts to a scale effect that is related to the definition of a spatio-temporal representative volume determining the fracture event on the given scale level.

Influence of confinement pressure and air voids on the repeated creep and recovery of asphalt concrete mixtures

A laboratory investigation was conducted to capture the influence of confinement pressure and specimen air voids on the creep and recovery response of asphalt concrete (AC) mixtures. AC specimens were fabricated at 2% and 7% air voids and tested at three temperatures (20, 40 and 55°C) and at unconfined and confined conditions (100 and 200 kPa). A total of 20,000 repetitions of a repeated trapezoidal loading and recovery cycle were applied. The resulting creep curves showed four distinct patterns of the three-stage creep curve depending on the loading condition and specimen density. To quantify the mechanical response during the secondary stage where the response was found to be linear, linear viscoelastic modelling was carried out. Using creep time, energy stored and energy dissipated, which were determined from model parameters; the influence of air voids and confinement pressure was quantified.

Influence of Confining Pressure on the Kaiser Effect of Rocks

AE法を用いた初期地圧の推定において再載荷時の拘束圧の影響に関する実験を行い, 得られた実験結果よりカイザー効果のメカニズムを検討した. 原位置での応力状態を模した三軸圧縮の先行載荷を行った供試体に対し, 先行載荷とは異なる大きさの拘束圧で再載荷を行った. このときのAE発生傾向には二つの急増点が観察され, 先行載荷時の軸差応力と軸応力とに対応している. 軸差応力と軸応力をそれぞれ記憶したクラックの存在が考えられ, これらは拘束圧の大きさに影響されない. この結果をもとに軸差応力を記憶しているクラックモデルとして2次クラックが甫載荷時に成長する際にAEが発生するモデルが実験結果とよく対応することを示した.

Brittle-Ductile Transition Of Anisotropic Rocks During Three-Point Bending Test

Firstly Karman (1910, 1911), after Griggs (1936) later many other researchers (e.g. Handin and Hager 1957, Paterson 1958, Heard 1960, Byerlee 1968, Edmond and Paterson 1972, Rutter 1972, Gowd and Rummel 1980, Scott and Nielsen 1991, etc.) observed the influence of confining pressure on the behaviour of rocks which were brittle at zero and low confining pressure. At high confining pressure, however, the same rocks may be ductile. That means they may fault or otherwise deform without loss of compressive strength. The amount of ductile deformation and the strength increase progressively with increasing confining pressure until fully ductile deformation occurred with apparent work-hardening.