scholarly journals Impact Dynamic Properties and Energy Evolution of Damaged Sandstone Based on Cyclic Loading Threshold

2020 ◽  
Vol 2020 ◽  
pp. 1-12
Author(s):  
Qiangqiang Zheng ◽  
Hao Hu ◽  
Anying Yuan ◽  
Mengyao Li ◽  
Haibo Wang ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Compressive Strength ◽  
Cyclic Load ◽  
Split Hopkinson Pressure Bar ◽  
Dynamic Properties ◽  
Quadratic Function ◽  
Strength Increase ◽  
Impact Loads ◽  
Energy Evolution ◽  
Rock Bursts

Rocks in deep coal mines are usually in varying degrees of damage state before they are destabilized by impact loads such as rock bursts. For the problem of the mechanical properties and energy evolution of damaged rocks under impact loads, the authors use static loads with different cyclic load thresholds to act on sandstone specimens to make them in distinct degrees of damage. Then, the rock mechanics system (MTS-816) and the Split Hopkinson pressure bar (SHPB) are employed to perform uniaxial compression and impact dynamics tests on sandstones with different degrees of damage. The results show that, from the perspective of mechanical properties, the uniaxial compressive strength and dynamic compressive strength of the damaged sandstone gradually decrease with the increase of the upper limit of the cycle threshold and both obey the growth law of the quadratic function, and the dynamic strength increase factor (DIF) also decreases with the increase of the cyclic load threshold. In terms of energy, with the increment of the cyclic load threshold, the number of cracks in the damaged sandstone is large and the scale is enormous. Due to the effect of cracks, when the incident energy is a fixed value, the transmission energy decreases with the increase of the damage degree and the change law of the reflection energy is the opposite. The systematic study of the dynamic mechanical properties and energy evolution law of the damaged sandstone provides some reference for the prevention and mechanism research of rock bursts.

scholarly journals Effect of Heating Rate on the Dynamic Compressive Properties of Granite

Geofluids ◽  
2019 ◽  
Vol 2019 ◽  
pp. 1-12 ◽  
Author(s):  
Ronghua Shu ◽  
Tubing Yin ◽  
Xibing Li
Keyword(s):  
Compressive Strength ◽  
Elastic Modulus ◽  
Heating Rate ◽  
High Speed ◽  
Split Hopkinson Pressure Bar ◽  
Quadratic Function ◽  
Peak Strain ◽  
Hopkinson Pressure Bar ◽  
Compressive Properties ◽  
Dynamic Compressive Strength

Variation in the heating rate due to different geothermal gradients is a cause of much concern in underground rock engineering such as deep sea and underground tunnels, nuclear waste disposal, and deep mining. By using a split Hopkinson pressure bar (SHPB) and variable-speed heating furnace, the dynamic compressive properties of granite were obtained after treatments at different heating rates and temperatures; these properties mainly included the dynamic compressive strength, peak strain, and dynamic elastic modulus. The mechanism of heating rate action on the granite was simultaneously analyzed, and the macroscopic physical properties were discussed. The microscopic morphological features were obtained by scanning electron microscopy (SEM), and the crack propagation was determined by high-speed video camera. The experimental results show that the dynamic compressive strength and elastic modulus both show an obvious trend of a decrease with the increasing heating rate and temperature; the opposite phenomenon is observed for the peak strain. The relationships among the dynamic compressive properties and temperature could be described by the quadratic function. The ductility of granite is enhanced, and the number and size of cracks increase gradually when the heating rate and temperature increase. The microstructure of rock is weakened by the increased thermal stress, which finally affects the dynamic compressive properties of rock.

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.

scholarly journals Effect of the Alkalized Rice Straw Content on Strength Properties and Microstructure of Cemented Tailings Backfill

2021 ◽  
Vol 8 ◽  
Author(s):  
Shi Wang ◽  
Xuepeng Song ◽  
Meiliang Wei ◽  
Wu Liu ◽  
Xiaojun Wang ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Tensile Strength ◽  
Compressive Strength ◽  
Rice Straw ◽  
Low Cost ◽  
Strength Properties ◽  
Hydration Reaction ◽  
Strength Increase ◽  
Improvement Effect ◽  
Naoh Solution

The tailings and rice straw are waste by-products, and the storage of tailings on the ground and the burning of rice straws will seriously damage the ecological environment. In this study, the effect of different contents of alkalized rice straw (ARS; rice straw was alkalized with 4% NaOH solution) on the mechanical properties and microstructure of cemented tailings backfill (CTB; ARSCTB) was studied through uniaxial compressive strength (UCS), scanning electron microscopy (SEM), and X-ray diffraction (XRD) tests. The results indicated that 1) the UCS of ARSCTB could be improved by ARS. However, with the increase in the ARS content from 0.1 to 0.4 wt%, the UCS showed a monotonous decreasing trend. The UCS improvement effect was best when the ARS content was 0.1 wt%, and at 7, 14, and 28 days curing ages, the UCS increased rate was 6.0, 8.3, 14.7% respectively. 2) The tensile strength of ARSCTB was generally higher than that of CTB and positively correlated with the ARS content. The tensile strength increase rate was 24.1–34.2% at 28 days curing age. 3) The SEM test indicated that the ARS was wrapped by cement hydration products, which improves its connection with the ARSCTB matrix. ARS performed a bridging role, inhibited cracks propagation, and provided drag or pulling force for the block that is about to fall off. Therefore, the mechanical properties of ARSCTB were enhanced. However, under high ARS content, the inhibition of ARS on hydration reaction and the overlap between ARS were not conducive to the improvement of the UCS of ARSCTB. 4) The post-peak residual strength and integrity effect of ARSCTB were greater. It is recommended to add 0.1–0.2 wt% ARS to the backfill with high compressive strength requirements such as the empty field subsequent filling mining method and the artificial pillar. 0.3–0.4 wt% ARS is incorporated into backfill with high tensile strength requirements such as high-stage filling with lateral exposure and artificial roof. This study further makes up for the blank of the application of plant fiber in the field of mine filling and helps to improve the mechanical properties of backfill through low-cost materials.

scholarly journals Mechanical Properties of OPC - Geocement Concrete

2019 ◽  
Vol 8 (4) ◽  
pp. 3733-3736
Keyword(s):  
Mechanical Properties ◽  
Compressive Strength ◽  
Portland Cement ◽  
Ordinary Portland Cement ◽  
External Heat ◽  
Partial Replacement ◽  
Strength Development ◽  
Strength Increase ◽  
Heat Curing ◽  
Compressive Strength Development

Nowadays geopolymer concretes are subjected to heat curing. A large amount of highly corrosive and the hygroscopic alkaline activators are nowadays generally utilized in producing geopolymer concretes. In this paper, hybrid Ordinary Portland Cement (OPC) and geopolymer mixes are developed. The mainly used activator id the Solid potassium carbonate at different percentage is used as 5% & 10% of the weight of geopolymeric materials and OPC was blended with geopolymeric materials in different proportions. By adding cement, improves all the geopolymer properties except workability. By Applying external heat, it plays an important role in gaining strength. Strength gained by the absence of external heat is achieved by using Portland cement as a partial replacement of geocement. The influence of OPC content on the compressive strength development is investigated, and the optimized amount of solid activator to be used in the mix is also investigated. It is observed that percentage of strength increase decreases from52.24% to 14.77% as the OPC content increased from 20% to 60%.

Improve the thermal and mechanical properties of foam polystyrene by gebrile soil

2020 ◽  
Vol 27 (4) ◽  
pp. 8-12
Author(s):  
montajb Al-khodary ◽  
sabah AL-sibai ◽  
moaffaq Tellawi
Keyword(s):  
Mechanical Properties ◽  
Compressive Strength ◽  
Thermal Insulation ◽  
Permissible Limit ◽  
Strength Increase ◽  
Thermal And Mechanical Properties ◽  
Polystyrene Foam ◽  
Natural Materials ◽  
Foam Polystyrene ◽  
Insulation Materials

n this research we tried to improve the thermal insulation efficiency of polystyrene foam by adding some natural materials. The gebrile soil was selected for several reasons, including abundance and ease of processing before the addition - There are many previous researches for soil treatment -. We have found at ratio 20%(The proportion of the soil in the compound) the coefficient of conduction is low and then rises after this percentage As for the absorption of water it increases by increasing the soil, but at this ratio the absorption is within the permissible limit according to the specifications required for the insulation materials and also compressive strength increase with the increasing of the soil ratio because of increasing of mechanical links between the polycarbonate and polystyrene particles and composite-material’s density increasing in general.

Research on Alkali-Activator and its Effects on Mechanical Properties of Slag-Based Geopolymer at early Age

2014 ◽  
Vol 556-562 ◽  
pp. 399-403 ◽  
Author(s):  
Li Shun Chen ◽  
Xiao Chen ◽  
Jian Tong Xu ◽  
Zhong Yang
Keyword(s):  
Mechanical Properties ◽  
Compressive Strength ◽  
Flexural Strength ◽  
Compression Strength ◽  
Downward Trend ◽  
Early Age ◽  
Strength Increase ◽  
Apparent Increase ◽  
Alkali Activator

This report studied the influence of effects such as type, modulus, dosage of the alkali-activator on mechanical properties of slag-based geopolymer. The analyzing results indicate that compare to the Na2SiO3, K2SiO3has significant activate effects on slag-based geopolymer. The modulus and dosage have obvious significance on early compression strength of slag-based geopolymer. With the increase of modulus, its early compression strength has apparent increase. With the increase of dosage, its early compression strength increase firstly and then decrease. When the dosage is 12%, the compression strength of the material is highest. The change of modulus and dosage of the alkali-activator has little influence on flexural strength of slag-based geopolymer. With the increase of dosage, its ratio of flexural to compressive strength has a downward trend. And the material brittleness addition.

Mechanical Properties of High Strength Concrete Filled Steel Tubular Columns

2012 ◽  
Vol 472-475 ◽  
pp. 1119-1125 ◽  
Author(s):  
Ke Feng Tan ◽  
Lai Bao Liu
Keyword(s):  
Mechanical Properties ◽  
Compressive Strength ◽  
High Strength Concrete ◽  
High Strength ◽  
Steel Tube ◽  
Strength Increase ◽  
Strength Concrete ◽  
Tubular Columns ◽  
Short Columns ◽  
Core Concrete

This study investigated the mechanical properties of High Strength Concrete filled steel tubular short columns (HSCFSTSC) with length to diameter ratio (L/D) of 3.5.The strength of concrete used to fill the steel tubular columns ranged from 54MPa to 116MPa. The test results showed that using a steel tube as confinement can significantly improve the ductility and compressive strength of core concrete. The magnitude of compressive strength increase of core concrete was directly proportional to the Confinement Index, , and the extent of improvement of the ductility increases as the  increases. For thoroughly improving the ductility of core concrete, the Confinement Index  should be equal or larger than 0.48. The formula used to calculate the load bearing capacity of HSCFSTSC was given out.

scholarly journals Influences of Curing Period and Sulfate Concentration on the Dynamic Properties and Energy Absorption Characteristics of Cement Soil

Crystals ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 1291
Author(s):  
Jing-Shuang Zhang ◽  
Xiang-Gang Xia ◽  
Bin Ren
Keyword(s):  
Compressive Strength ◽  
Split Hopkinson Pressure Bar ◽  
Dynamic Properties ◽  
Solution Concentration ◽  
Sulfate Concentration ◽  
Hopkinson Pressure Bar ◽  
Absorption Energy ◽  
Curing Period ◽  
Dynamic Compressive Strength ◽  
Cement Soil

To study the influences of curing period and sulfate concentration on the dynamic mechanical properties of cement soil, this study used a split Hopkinson pressure bar device. Impact tests were conducted on cement soil specimens with different curing periods and different sulfate concentrations. The relationships between the dynamic stress–strain, dynamic compressive strength, and absorption energy of these cement soil specimens were analyzed. The test results show that with continuous loading, cement soil specimens mainly experience an elastic stage, plastic stage, and failure stage; with increasing curing period and sulfate concentration, the dynamic compressive strength and absorption energy of cement soil specimens follow a trend of first increasing and then decreasing. The dynamic compressive strength and absorption energy of cement soil specimens reached maximum values at a curing period of 14 d and a Na2SO4 solution concentration of 9.0 g/L. Increasing the dynamic compressive strength and absorption energy can effectively improve the ability of cement soil specimens to resist damage. This paper provides a practical reference for the application of cement soil in dynamic environments.

scholarly journals Some Mechanical Properties of Cement Treated Base (CTB) Incorporating Waste Portland Cement Concrete Under Different Corresponding Conditions

2018 ◽  
Vol 7 (4.37) ◽  
pp. 138
Author(s):  
Asst. Prof. Dr. Khawla H. H. Shubber ◽  
Eng. Sajjad Hashim Mohamed
Keyword(s):  
Mechanical Properties ◽  
Compressive Strength ◽  
Portland Cement ◽  
Granular Materials ◽  
Compression Strength ◽  
Cement Content ◽  
Strength Increase ◽  
Test Results ◽  
Portland Cement Concrete ◽  
Cement Concrete

This research represents a trial of understanding and improving mechanical properties of base or subbase granular materials, used in pavement construction, stabilized with Portland cement known as cement treated base (CTB) in terms of density, optimum water content (O.W.C), and compression Strength of three curing ages (3, 7, 28) days under different situations. Different Portland cement percent of (0, 5, 7, 10, 12, and 15) % by weight were added to selected base course granular materials (type B according to local standard specification in Iraq). Results showed that the density of mixture increase with increasing added cement percent, while O.W.C takes its maximum value around 7% cement content, and compression strength increase with increasing cement content and curing age. Then effect of replacing 50% of natural granular materials by waste Portland cement concrete (WPCC) was investigated on the results of (0, 7& 15)% cement content on density, O.W.C and compression strength in the three curing ages. Results reveled although density of mixture cooperating WPCC for 0% cement content was higher, CTB of natural granular material were denser. On the other hand compressive strength decrease in case of using WPCC for all percent cement added and curing ages. Finally, effect of soaking in water on CTB with (7 &15)% cement compressive strength of three curing ages was studied, under three period of soaking (1 week, 2 weeks, &one month). Test results exposed that, CTB Compressive strength increase with increasing soaking period but still less than that of un-soaked and for all curing ages. For each test stage mathematics relationships with acceptable correlation were presented proofing test results tendency.  

scholarly journals Effects of Cyclic Wetting-Drying Conditions on Elastic Modulus and Compressive Strength of Sandstone and Mudstone

Processes ◽  
2018 ◽  
Vol 6 (12) ◽  
pp. 234 ◽  
Author(s):  
Shiyuan Huang ◽  
Junjie Wang ◽  
Zhenfeng Qiu ◽  
Kai Kang
Keyword(s):  
Mechanical Properties ◽  
Compressive Strength ◽  
Elastic Modulus ◽  
Uniaxial Compressive Strength ◽  
Strength Increase ◽  
Compression Tests ◽  
Wetting And Drying ◽  
Rock Stability ◽  
Degradation Rates ◽  
Degradation Degree

The influence of water on the mechanical properties of rock is vital for determining the rock stability when subjected to changes of water conditions. In this paper, a series of uniaxial compression tests were conducted to investigate effects of cyclic wetting and drying on the mechanical properties of sandstone and mudstone collected from Chongqing city, China. The results showed that both elastic modulus and uniaxial compressive strength of sandstone and mudstone were reduced by wetting and drying cycles, and that the degradation rate of the two mechanic parameters of mudstone was always larger than sandstone. The parameters, including water adsorption, degradation degree of elastic modulus, degradation degree of uniaxial compressive strength, increase with the increase of the wetting-drying cycles (N). The relationship between these three parameters and the value of N + 1 could be well fitted by logarithmic curves. The average degradation degree was also used to describe the degradation of per time wetting-drying cycles. It is found that the average degradation degree of elastic modulus and uniaxial compressive strength decrease with the increase of wetting-drying cycles. Moreover, the relationships between the mechanical properties and the porosity are presented, which can be fitted by linear curves. In the cyclic wetting-drying process, the elastic modulus and the uniaxial compressive strength decreased with the porosity increasing, and the degradation rates of sandstone mechanic parameters were higher than those of mudstone.

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