scholarly journals Experimental Study on Mechanical Properties and Pore Structure Deterioration of Concrete under Freeze–Thaw Cycles

Materials ◽  
2021 ◽  
Vol 14 (21) ◽  
pp. 6568
Author(s):  
Kai Zhang ◽  
Jing Zhou ◽  
Zhigang Yin
Keyword(s):  
Mechanical Properties ◽  
Compressive Strength ◽  
Pore Structure ◽  
Design Theory ◽  
Damage Model ◽  
Concrete Structures ◽  
Frost Damage ◽  
Dynamic Increase Factor ◽  
Freeze Thaw ◽  
Dynamic Compressive Strength

Understanding the evolution of mechanical properties and microscopic pore structure of concrete after freeze–thaw cycles is essential to assess the durability and safety of concrete structures. In this work, the degradation law of mechanical properties and damage characteristic of micro-structure of concrete with two water-cement ratios (w/c = 0.45 and 0.55) is investigated under the condition of freezing–thawing cycles. The influence of loading strain rate on dynamic compressive strength is studied. The microscopic pore structure after frost damage is measured by low-field nuclear magnetic resonance (LF-NMR) technique. Then, a damage model based on the porosity variation is established to quantitatively describe the degradation law of macroscopic mechanical properties. The test results show that the relative dynamic modulus of elasticity (RDME), dynamic compressive strength, flexural strength, and splitting tensile strength of concrete decrease with the increase of freeze–thaw cycles. Empirical relations of concrete dynamic increase factor (DIF) under the action of freeze–thaw cycles are proposed. Moreover, the experimental results of NMR indicate that the porosity as well as the proportion of meso-pores and macro-pores of concrete gradually increased with the increasing of freeze–thaw cycles. The research results can provide reference and experimental support for the anti-frost design theory and durability life prediction of hydraulic concrete structures in cold regions.

scholarly journals Effects of Cyclic Freeze–Thaw on the Steel Bar Reinforced New-To-Old Concrete Interface

Molecules ◽  
2020 ◽  
Vol 25 (5) ◽  
pp. 1251
Author(s):  
Tao Luo ◽  
Chi Zhang ◽  
Xiangtian Xu ◽  
Yanjun Shen ◽  
Hailiang Jia ◽  
...  
Keyword(s):  
Compressive Strength ◽  
Shear Strength ◽  
Concrete Structures ◽  
Freezing Temperature ◽  
Frost Damage ◽  
Freezing And Thawing ◽  
Shear Properties ◽  
Freeze Thaw ◽  
Steel Bar ◽  
Concrete Interface

Frost damage of concrete has significant effects on the safety and durability of concrete structures in cold regions, and the concrete structures after repair and reinforcement are still threatened by cyclic freezing and thawing. In this study, the new-to-old concrete interface was reinforced by steel bar. The shear strength of the new-to-old concrete interface was tested after the new-to-old combination was subjected to cyclic freeze–thaw. The effects of the diameter of the steel bar, the compressive strength of new concrete, the number of freeze–thaw cycles and the freezing temperatures on the shear properties of new-to-old concrete interface were studied. The results showed that, in a certain range, the shear strength of the interface was proportional to the diameter of the steel bar and the strength of the new concrete. Meanwhile, the shear strength of the reinforced interface decreased with the decreasing of the freezing temperature and the increasing of the number of freeze–thaw cycles.

scholarly journals Study on Long-Term Dynamic Mechanical Properties and Degradation Law of Sandstone under Freeze-Thaw Cycle

2020 ◽  
Vol 2020 ◽  
pp. 1-10
Author(s):  
Qingsong Pu ◽  
Junhong Huang ◽  
Fuling Zeng ◽  
Yi Luo ◽  
Xinping Li ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Compressive Strength ◽  
Elastic Modulus ◽  
Strain Rate ◽  
Air Pressure ◽  
Freeze Thaw ◽  
Dynamic Mechanical ◽  
Thaw Cycle ◽  
Freeze Thaw Cycle ◽  
Dynamic Compressive Strength

This study is based on the tunnel-face slope engineering of Dongfeng tunnel in Shanxi section of China’s Shuozhou-Huanghua Railway. The sandstone specimens in the perennial freeze-thaw zone of the slope were collected to carry out freeze-thaw cycle static physical mechanics test and split Hopkinson pressure bar (SHPB) dynamic mechanical test. Thus, the damage process of sandstone under freeze-thaw cycle and impact load is studied. Also, the dynamic compressive strength and dynamic elastic modulus of sandstone are analysed under different loading strain rates and freeze-thaw cycle based on LS-DYNA, a dynamic finite element program. The results showed that the dynamic compressive strength of sandstone subjected to multiple freeze-thaw cycles under 0.04 MPa air pressure has a greater damage ratio than that under 0.055 MPa and 0.07 MPa air pressure, which was more likely to cause damage to slope sandstone than in actual engineering; the dynamic compressive strength and elastic modulus of sandstone decrease greatly within a certain range of freeze-thaw cycles and loading strain rate, leading to significant deterioration. When the freeze-thaw cycle exceeded 200 times and the strain rate was greater than 200 s−1, the physical and mechanical properties of sandstone gradually tended to be stable.

scholarly journals Dynamic Mechanical Properties and Damage Mechanism of Freeze-Thaw Sandstone under Acid Corrosion

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-15
Author(s):  
Xiaoxiao Cao ◽  
Meimei Feng ◽  
Kangsheng Yuan
Keyword(s):  
Mechanical Properties ◽  
Compressive Strength ◽  
Elastic Modulus ◽  
Strain Rate ◽  
Coupling Effect ◽  
Acid Corrosion ◽  
Dynamic Mechanical Properties ◽  
Peak Strain ◽  
Freeze Thaw ◽  
Dynamic Compressive Strength

During the construction of geotechnical engineering in cold regions, the stability of rock is inevitably affected by freeze-thaw cycles and hydrochemical corrosion. In order to study the effect of hydrochemical corrosion on dynamic mechanical properties of freeze-thaw rocks, dynamic compression tests were carried out on sandstone samples corroded by four different concentrations of HCl solutions with the same number of freeze-thaw cycles using split-Hopkinson pressure bar (SHPB) test system. The coupling effects of freeze-thaw cycles with different concentrations of HCl solutions and strain rate on mechanical properties of sandstones were explored. The results showed that strain rate could enhance the dynamic compressive strength and peak strain but had no significant effect on the elastic modulus. The coupling effect of freeze-thaw cycles and acid corrosion weakened the dynamic compressive strength, and elastic modulus but enhanced the peak strain. In addition, X-ray diffractometer (XRD) and scanning electron microscope (SEM) were used to analyze the changes of mineral composition and microstructure damage of sandstone samples under the coupling effect of acid corrosion and freeze-thaw cycles. The analysis results were basically consistent with the damage characteristics of macro mechanical properties. The research results can provide reference for open pit coal mining in cold regions.

Physical Properties of Building Blocks from Hemp Shives Aggregate and Cementitious Binder, Manufactured in the Expanded Clay (Vibro Pressing) Production Line

2017 ◽  
Vol 908 ◽  
pp. 118-122 ◽  
Author(s):  
Giedrius Balčiūnas ◽  
Viktor Kizinievič ◽  
Justinas Gargasas
Keyword(s):  
Mechanical Properties ◽  
Thermal Conductivity ◽  
Compressive Strength ◽  
Physical Properties ◽  
Production Line ◽  
Scientific Literature ◽  
Building Blocks ◽  
Freeze Thaw ◽  
Cementitious Binder ◽  
Pressing Technology

Scientific literature mostly aims at investigation of composites with fibre hemp shives (FHS) aggregate and lime binder, although, such materials are characterised by pretty low mechanical properties. In order to obtain higher mechanical properties of a composite, it is appropriate to use cementitious binder. This work investigates physical properties of blocks from hemp shives aggregate and cementitious binder, manufactured in the expanded clay production line using vibro pressing technology. Following properties of the blocks are determined: freeze-thaw resistance, compressive strength, thermal conductivity and density. Thermal resistance according to EN ISO 6946 for the block with cavities is calculated as well. It is found that compressive strength of FHS-cement blocks may be up to 3.18 MPa when the density is of ~850 kg/m3 and thermal conductivity up to 0.135 W/(m∙K). It is found as well that the decrease of compressive strength is 8.7% after 25 freeze-thaw cycles.

scholarly journals Research on the Dynamic Mechanical Properties and Energy Dissipation of Expansive Soil Stabilized by Fly Ash and Lime

2019 ◽  
Vol 2019 ◽  
pp. 1-13 ◽  
Author(s):  
Sheng-quan Zhou ◽  
Da-wei Zhou ◽  
Yong-fei Zhang ◽  
Wei-jian Wang ◽  
Dongwei Li
Keyword(s):  
Mechanical Properties ◽  
Compressive Strength ◽  
Fly Ash ◽  
Expansive Soil ◽  
Dynamic Mechanical Properties ◽  
Test Results ◽  
Absorbed Energy ◽  
Dynamic Mechanical ◽  
Stabilized Soil ◽  
Dynamic Compressive Strength

To probe into the dynamic mechanical properties of expansive soil stabilized by fly ash and lime under impact load, the split-Hopkinson pressure bar (SHPB) test was carried out in this study. An analysis was made on the dynamic mechanical property and final fracture morphology of stabilized soil, and the failure mechanism was also explored from the perspective of energy dissipation. According to the test results, under the impact pressure of 0.2 MPa, plain soil and pure fly ash-stabilized soil exhibit strong plasticity. After the addition of lime, the stabilized soil shows obvious brittle failure. The dynamic compressive strength and absorbed energy of stabilized soil first increase and then decrease with the change of mix proportions. Both the dynamic compressive strength and the absorbed energy reach the peak value at the content of 20% fly ash and 5% lime (20% F + 5% L). In the process of the test, most of the incident energy is reflected back to the incident bar. The absorbed energy of stabilized soil increases linearly with the rise of dynamic compressive strength, while the absorbed energy is negatively correlated with the fractal dimension. The fractal dimension of pore morphology of the plain soil is lower than that of the fly ash-lime combined stabilized soil when it comes to the two different magnification ratios. The test results indicate that the modifier content of 20% F + 5% L can significantly improve the dynamic mechanical properties of the expansive soil.

scholarly journals Preparation and properties of magnesite aggregate radiation - proof concrete

2018 ◽  
Vol 175 ◽  
pp. 01003
Author(s):  
Bingquan Sun ◽  
Jiajia Sun
Keyword(s):  
Mechanical Properties ◽  
Compressive Strength ◽  
Pore Structure ◽  
Water Content ◽  
Radiation Protection ◽  
Point Of View ◽  
Crystal Water ◽  
Ordinary Concrete ◽  
Mixing Water

This paper, from the point of view of improving compactness of density and crystal water content of radiation-proof concrete, using magnesite with high crystal water content as aggregate and alkaline potential water as mixing water, prepared ordinary density radiation-proof concrete and studied its mechanical properties, resistivity and pore structure. The results show that, compared to base ordinary concrete, the prepared concrete has better 28d compressive strength and resistivity, overall porosity decreases by 17%, and pore gradation at all ages improves significantly. It is indicated that the prepared magnesite aggregate radiation concrete has good density and durability, improves concrete radiation protection performance.

The Influence of Pore-Strucrure on the Campressive Strength of Hardened Cement Paste

1984 ◽  
Vol 42 ◽  
Author(s):  
Huang Yiun-Yuan ◽  
Ding Wei ◽  
Lu Ping
Keyword(s):  
Mechanical Properties ◽  
Compressive Strength ◽  
Pore Structure ◽  
Cement Paste ◽  
Total Porosity ◽  
Hardened Cement ◽  
Hardened Cement Paste ◽  
New Information ◽  
The Relationship ◽  
Empirical Constants

AbstractThe pore-structure strongly influences the carpressive strength of hardened cement paste (hcp) and other porous materials, as well as other mechanical properties. The simplest but most currently used expression representing the relationship between the pore-structure and compressive strength is fram Balshin: σ = σ0 (l-P)A, in which only the total porosity P is involved as a single parameter and σ0 and A are empirical constants. The influence of pore size distribution and pore shapes etc. are not considered.The authors introduce second parameter w - the factor of relative specific surface area of the pores other than the total porosity P into consideration and a new expression is proposed:σc=K11-p/1+2p(K2(1-p))K3w+K4 all the constants K1 - K4 can be determined experimentally. By using of this expression the new information relating the influence of pore-structure on the caopressive strength of hcp can be predicted.

scholarly journals Recycling of Oily Sludge as a Roadbed Material Utilizing Phosphogypsum-Based Cementitious Materials

2019 ◽  
Vol 2019 ◽  
pp. 1-10 ◽  
Author(s):  
Wei Xiao ◽  
Xiao Yao ◽  
Fuyang Zhang
Keyword(s):  
Heavy Metals ◽  
Compressive Strength ◽  
Pore Structure ◽  
Cementitious Materials ◽  
Solid Particles ◽  
Oily Sludge ◽  
Water Stability ◽  
Volume Stability ◽  
Freeze Thaw ◽  
Stability Performance

Oily sludge is a hazardous waste containing emulsified petroleum hydrocarbons, water, heavy metals, and solid particles. The objective of this work is to employ solidification/stabilization (S/S) techniques to utilize oily sludge as a roadbed material with ordinary Portland cement (OPC), fly ash (FA), and silica fume (SF) as binders and phosphogypsum (PG) as a stabilizer. The efficacy of the S/S process is assessed mainly through an unconfined compressive strength (UCS) test and a toxicity leaching test. Road performance, including water stability, freeze-thaw resistance, and volume stability, is also tested on the solidified samples. The mineralogical compositions, microstructures, and pore structure are characterized through X-ray diffractometry (XRD), scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP). The results show that the addition of 20% binders (OPC : FA : SF = 1 : 0.7 : 0.8) in combination with phosphogypsum to the oily sludge not only increases the 28-day compressive strength of the solidified samples and remarkably decreases the release of heavy metals but also refines the pore structure and compacts the microstructure. The solidified body had sufficient strength and good water stability performance, freeze-thaw resistance, and volumetric stability. This solidification/stabilization (S/S) process, which combines oily sludge treatment and phosphogypsum resource utilization, significantly enhances environmental protection and renders the solidified product economically profitable.

scholarly journals Experimental Study on Dynamic Mechanical Properties and Energy Evolution Characteristics of Limestone Specimens Subjected to High Temperature

2020 ◽  
Vol 2020 ◽  
pp. 1-12 ◽  
Author(s):  
Qi Ping ◽  
Chuanliang Zhang ◽  
Haipeng Su ◽  
Hao Zhang
Keyword(s):  
Mechanical Properties ◽  
Compressive Strength ◽  
Elastic Modulus ◽  
High Temperature ◽  
Incident Energy ◽  
Dynamic Mechanical Properties ◽  
Energy Evolution ◽  
Strain And Strain Rate ◽  
Evolution Characteristics ◽  
Dynamic Compressive Strength

To study the effect of high temperature on the dynamic mechanical properties and energy evolution characteristic of limestone specimens, the basic physical parameters of limestone specimens that cool naturally after experiencing high temperatures of room temperature (25°C), 200°C, 400°C, and 600°C were tested. In addition, compression tests with 6 impact loading conditions were conducted using SHPB device. The changes of basic physical properties of limestone before and after temperature were analyzed, and the relationship among dynamic characteristic parameters, energy evolution characteristics, and temperature was discussed. Test results indicated that, with the increase of temperature, the surface color of specimen changed from gray-black to gray-white, and its volume increased, while the mass, density, and P-wave velocity of specimen decreased. The dynamic compressive stress-strain curve of limestone specimens after different high-temperature effects could be divided into three stages: elasticity stage, yield stage, and failure stage. Failure mode of specimen was in the form of spalling axial splitting, and the degree of fragmentation increased with the increase of the temperature and incident energy. With the increase of the temperature, the reflection energy, the absorption energy, the dynamic compressive strength, and dynamic elastic modulus of rock decreased, while its transmission energy, the dynamic peak strain, and strain rate increased. The dynamic compressive strength, dynamic elastic modulus, dynamic strain, and strain rate of limestone specimens all increased with the increase of incident energy, showing a quadratic function relationship.

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