Ultrasonic Pulse Velocity Test Research Articles

Experimental Investigation of Crack Initiation and Growth in Concrete Slabs Placed Directly on Clayey Soil

The main objective of this study is to examine the impact of moisture concrete of clayey soil on the concrete slabs placed directly over it. This experimental study presents the mechanical properties of the concrete slab when placed on different clayey soil moisture content ranging from 0% to the optimum moisture content of 35%. The tests were performed on soil concrete specimens of 25*30*50 mm exposed to sprayed water curing conditions for 28 days. Tests of compressive strength, ultrasonic pulse velocity, crack depth and crack width were investigated through this paper. An ejection relationship between compressive strength of concrete and water content in the soil was observed, with a 26% increase with water increasing from 0% to 35%. The opposite was observed in the ultrasonic pulse velocity test, with a decrease of 58% from 0% to the highest water content ratio. As for crack depth and width, it recorded the highest depth and lowest width at 0% water content due to the increased susceptibility of the soil to the absorption of water from the concrete when it’s totally dry. The experiment has shown that the soil moisture content is considered as a critical factor in controlling concrete cracking, and its variation has considerable implications for concrete crack growth.

Mechanical Properties of Blast Furnace Slag and Rice Husk Ash with Coconut Shell as Partial Replacement of Aggregates

This research showed the application of concrete material in construction industry were highly demand which growing rapidly demonstrate the need for various types and properties of concrete to meet the diverse needs of the user. Normally, the quality of concrete with high durability properties can be generated by consideration of the composition of the materials used such as cement, sand, aggregates or water. Besides that, mix design and the way of production like mixing, transporting and pouring concrete is also the factors to get a better quality of concrete. Recently, the sustainability in construction is one of the efforts that have been practiced by developed countries to create healthier environment and to reduce the environmental impact of a building over its entire lifetime, while optimizing its economic viability and the comfort and safety of its occupants. One of the steps that can be practice is to use materials that are categorized as agricultural waste material such as palm oil fuel ash, rice husk, fly ash slag, sludge, coconut shell and etc. in concrete manufacturing. Hence, the objective of this paper is to evaluate the performance of blast furnace slag, rice husk ash and coconut shell as partial replacement of aggregates in cement. A series of test were conducted to investigate the performance of blast furnace slag, rice husk ash and coconut shell as partial replacement of aggregates in cement. The tests that are being conducted are compressive strength test, flexural strength test, rebound hammer test, ultrasonic pulse velocity test, water permeability test, sieve analysis test, water absorption test, carbonation test, alkali-silica reaction test, SEM test and shrinkage test.

A Unified Equation for Prediction of Concrete Strength at Various Ages Using the Ultrasonic Pulse Velocity

Using ultrasonic pulse velocity (UPV) testing has long been regarded as an effective approach for evaluating concrete strength; however, because of the influence of numerous factors (e.g., mixture proportion, type of coarse aggregate, pozzolanic admixture, and age of the concrete), the relationship between UPV and concrete strength cannot be conclusively determined, thus hindering the application of this approach. The objective of this paper is to develop a unified equation for prediction of concrete strength at various ages using the ultrasonic pulse velocity. Firstly, this study investigated the relationship between the UPV evolution index and the strength evolution index of normal concrete with various mixture proportions, coarse aggregate types, and ages. Subsequently, the influence of adding pozzolanic materials on this relationship was considered. The experimental results showed that excellent correlation between the UPV evolution index and the strength evolution index was found and a unified equation was established in this study through regression analysis to represent the relationship between the UPV and the strength evolution index. Finally, the applicability of the unified equation was verified by data obtained from different studies. The results indicated that for all concrete specimens more than 3 days old, the error of the strength estimation decreased to within ±15%, demonstrating that this unified equation has substantial value for application in decision-making processes for major construction procedures (e.g., applying post tensioning or removing formwork supports).

Comparative interpretation of results after application of different non-destructive and portable techniques on historic concrete in the Centennial Hall in Wrocław

Many concrete buildings erected during the 20th century are assuming a cultural and historical value, and their conservation against the climate changes and the urban impact represent a major challenge for the heritage science for the future. A key aspect for their preservation is the development/application of innovative testing approaches based on non-destructive and portable techniques (NDPT) for diagnostics and monitoring the state of conservation. This research activity has been conducted on the case study of the Centennial Hall exhibition centre in Wroclaw (Poland), where the physical and mechanical characteristics of cementitious materials were estimated through indirect methods and therefore compared to prove their efficiency and usefulness in the limitation of invasive inspections. These methods were focused to control the hardness and compactness of the material (by ultrasonic pulse velocity and rebound tests), the surface permeability (by sponge test method), the water and salts content of the material (by Evanescent Field Dielectrometry - EFD), and the change of colour (by colorimetric measurements). In order to test the strength of the proposed approach, all these techniques (except the EFD) were made in duplicate by two different teams, using different instruments but following a similar protocol. The data were compared in between, and the environmental conditions were also considered. The results showed a good repeatability, furnishing useful information about the quality of concrete and its state of conservation, as well as possible forethoughts for a proper interpretation. This multi-technique approach could support the conservation decisions making process for the management of historic concrete building.

Compressive strength assessment of high strength concrete after fire using ultrasonic test method

This paper aims to evaluate the non-destructive ultrasonic pulse velocity (UPV) test method for determining the compressive strength of high strength of concrete (HSC) after fire. The compressive strength was determined through destructive cylinder test and by measuring ultrasonic pulse velocity. A total of 10 equations that relate compressive strength of concrete to UPV were evaluated in a total of 20 concrete samples. None of the equations were well suited for the case of HSC. The paper proposed a new equation and the UPV test showed suitable to assessment post-fire damaged HSC.

An Emerging Solution for Medical Waste: Reuse of COVID-19 Protective Suit in Concrete

With the continuous spread of COVID-19 (coronavirus disease 2019), a large number of medical protective suits (PS) have been used and discarded, causing great damage to the ecological environment. The main component of PS is polypropylene plastic, which will enter the oceans, rivers, and animals with groundwater and will not decompose for hundreds of years. Therefore, this global health crisis not only affects the health and economy of the world’s population now but will also continue to disrupt our daily lives after the pandemic ends. The main objective of this study is to explore an effective method to reduce the biological and environmental hazards of medical waste by combining PS with concrete. Due to the excessive size of the PS, protective suit fibers (PSF) were obtained from PS by cutting. To investigate the possibility of using PS in concrete, a series of experiments were conducted, including a physical parameter test, compression test, split tensile test, ultrasonic pulse velocity test, scanning electron microscope (SEM), and finite element simulation. The results indicated that the introduction of PSF significantly enhanced the mechanical properties of concrete, and the maximum compressive strength and splitting tensile strength increased by 7.3% and 43.6%, respectively. The ultrasonic pulse velocity and density of concrete containing PSF decreased compared with the control group. The images of SEM show that PSF binds tightly to the cement matrix and hinders the propagation of micro-cracks. The introduction of PS into the concrete material leads to the improvement of the mechanical properties of concrete and the improvement of the overall quality of the concrete, which is of great significance for reducing the damage of medical waste to the environment. The originality of this work is that polypropylene fibers acquired from PS were put into concrete for the first time for performance testing.

Scalar Damage Modeling of Reinforced Concrete Beam Under Polarized Monotonic Stress Field Using Ultrasonic Pulses

The extensive use of concrete has increased the demand for reliable non-destructive evaluation (NDE) techniques to investigate aging structures thoroughly. Among these NDE techniques, the ultrasonic pulse velocity (UPV) test stands out because of its versatility in-field application and its relatively low cost. Unfortunately, despite the promising results of UPV and pulse attenuation, its dependency on the nature of the applied stress is continuously overlooked. This research pioneered an approach that focused on developing a scalar damage model that relates the damage variable to the nature and the intensity of the applied stresses, concrete strength, and steel ratio. The results showed that transducers placed at different locations exhibited different deterioration rates of which the higher the applied stress intensity, the higher the scalar damage's inclination angle. Transducers placed in concrete under compression stress deteriorate earlier as compared to concrete under tension. As the steel ratio and concrete strength increase, the inclination angle of the elastic data trend also decreases. It was established in this research that beams with ductile response to the applied load tend to have a larger inclination angle for the elastic data trend while its UPV readings at the data trend's transition are greater than 3000 m/s which is conventionally accepted as concrete within normal to good quality although the beam undergoes critical stress redistribution as it approaches plastic hinging. Ultimately, this study showed that the scalar damage model exhibited superiority in quantitatively monitoring early damage propagation, in contrast to UPV reading and pulse attenuation.

Biochar Produced from Saudi Agriculture Waste as a Cement Additive for Improved Mechanical and Durability Properties-SWOT Analysis and Techno-Economic Assessment.

The Kingdom of Saudi Arabia generates an enormous amount of date palm waste, causing severe environmental concerns. Green and strong concrete is increasingly demanded due to low carbon footprints and better performance. In this research work, biochar derived from locally available agriculture waste (date palm fronds) was used as an additive to produce high-strength and durable concrete. Mechanical properties such as compressive and flexural strength were evaluated at 7, 14, and 28 days for control and all other mixes containing biochar. In addition, the durability properties of the concrete samples for the mixes were investigated by performing electric resistivity and ultra-sonic pulse velocity testing. Finally, a SWOT (strengths, weaknesses, opportunities, and threats) analysis was carried out to make strategic decisions about biochar’s use in concrete. The results demonstrated that the compressive strength of concrete increased to 28–29% with the addition of 0.75–1.5 wt% of biochar. Biochar-concrete containing 0.75 wt% of biochar showed 16% higher flexural strength than the control specimen. The high ultrasonic pulse velocity (UPV) values (>7.79 km/s) and low electrical resistivity (<22.4 kΩ-cm) of biochar-based concrete confirm that the addition of biochar resulted in high-quality concrete free from internal flaws, cracks, and better structural integrity. SWOT analysis indicated that biochar-based concrete possessed improved performance than ordinary concrete, is suitable for extreme environments, and has opportunities for circular economy and applications in various construction designs. However, cost and technical shortcomings in biochar production and biochar-concrete mix design are still challenging.

Utilisation of crumb tire rubber in development of sustainable metakaolin based high strength concrete

Environmental protection necessitates induction of 3R (recycle, reuse, reduce) principle into the construction sector. The study investigated fresh, strength properties, and SEM/XRD analysis of high strength concrete containing 15% metakaolin and crumb rubber up to 30% as sand replacement upto 90 days. SonReb method was used to determine relationship of Ultrasonic Pulse Velocity and Rebound Hammer tests with compressive strength. Results indicate loss of workability, density, compressive strength, split tensile strength and modulus of elasticity but improved ductility at 20% crumb rubber replacement which depicted highest toughness index. Equation derived from SonReb method predicted compressive strength with reliable accuracy.

Mechanical and Durability Properties of Green Concrete

This research is designed to assess the durability characteristics of green concrete and its compressive and flexural behavior. It measures the possibility of using by product materials in the concrete mix as cement partial replacement. Thus, the experimental compressive stress-strain curves are measured for the cylinder specimens made with green concrete. Furthermore, the durability of green concrete is evaluated using the thaw-freeze test and ultrasonic pulse velocity test. The flexural behavior of green concrete is also investigated. Prismatic beams and cylinder specimens are cast from different types of green concrete made from different by product materials including fuel ash, silica fume, and iron filings using two different percentages 15% and 20% as cement partial replacement. The prismatic specimens are cured over 550 days and then exposed to 60 thaw-freeze cycles. Although concrete made with pulverized fuel ash has the highest compressive strength at 120 days, it has the worst durability characteristics when exposed to 60 iterative thaw/freeze cycles at 550 days. Concrete made with iron filings is more durable than other specimens are. It is recommended using iron filings, pulverized fuel ash and silica fume in the concrete mix. However, iron filings are highly recommended for durable concrete.

Development of Quality Assessment Criteria for Burnt Clay Bricks of Different Ages Based on Ultrasonic Pulse Velocity Test

Burnt clay bricks are widely used as a construction material in Pakistan, and their testing for quality confirmation is frequently needed for new and old bricks used in existing structures. The destructive testing methods are time-consuming and not always feasible for testing the bricks used in existing structures. The current study investigated the feasibility of using the ultrasonic pulse velocity (UPV) test as a non-destructive technique to assess the quality of both new and old bricks in masonry structures. A relationship was developed after performing the UPV test followed by a compression test on burnt clay brick samples of five different ages acquired from different sources. The acquired brick samples ranged from new to a century old. Consequently, as a novel contribution, brick quality assessment criteria based on UPV were proposed according to which a UPV value greater than 3000 m/s represents an excellent first-class brick whereas a UPV value lower than 2000 m/s shows a second-class brick. Further, the effectiveness of the UPV test to assess the compressive strength of old bricks was demonstrated with a case study of a 100-year-old masonry structure. The research concluded with the remarks that the compressive strength of bricks can be assessed with reasonable accuracy using the UPV test. The developed quality assessment criteria can be used to quickly check the quality of new and old burnt clay bricks.

“Sustainable self-compacting concrete containing waste ceramic tile aggregates: Fresh, mechanical, durability, and microstructural properties”

In construction industry, the use of ceramic materials is rising continuously in the form of sanitary fittings, ceramic tiles, and electrical insulators etc. The ceramic manufacturing industry necessarily generates wastes, categorical of the newly introduced developments in manufacturing processes. During processing, fixing and transportation, the brittle nature of ceramic materials adds to the waste generation in large amounts. Use of all this waste in making of self-compacting concrete (SCC) can help with waste management along with improving the properties of SCC. Hence, in this study, fresh properties, mechanical strength, durability and microstructure of SCC containing waste ceramic tile (WCT) were examined. Six SCC mixes were prepared using crushed WCT as a substitution of natural river sand (NRS). The use of waste ceramic tile as a partial and full substitution (0%, 20%, 40%, 60%, 80% and 100%) of NRS of SCC was examined. The fresh SCC properties tests performed were Slump-flow, T500 time, V-funnel, U- box, J-ring and L-box test, while the mechanical and durability properties were assessed by compressive strength, flexural strength, split tensile strength, water absorption, water permeability and ultrasonic pulse velocity tests. The fresh properties of all mixes were found within limits prescribed by EFNARC. The integration of WCT in SCC mixtures found increase in the compressive, flexural and split tensile strength at 60% substitution and further substitution led to reduction in all strength of SCC. The superior ultrasonic pulse velocity values and higher impermeability characteristics of waste ceramic based SCC mixtures were found till 100% incorporation of WCT, when compared to the reference SCC mix. The microstructural study using Fourier transform infrared radiation (FTIR) technique, X-ray diffraction (XRD), Scanning Electron Microscope (SEM) was performed on hardened SCC to know in depth behavior of waste ceramic over control mix.

Recycled waste medical glass as a fine aggregate replacement in low environmental impact concrete: Effects on long-term strength and durability performance

Recycling and reusing solid wastes as construction materials is an issue that has received much attention from research scholars around the world in recent years. This research was developed to investigate the long-term mechanical and durable characteristics of concrete that was produced utilizing recycled waste medical glass aggregate (WGA) as a partial to full replacement of natural crushed sand (NCS). The mechanical properties of the different concrete mixtures were evaluated using compression and ultrasonic pulse velocity tests, and durability was assessed using water absorption, rapid chloride permeability, and sulfate resistance tests. The effects on the environmental impact of concrete production using WGA as an NCS replacement in terms of energy consumption and CO2 emissions were also assessed. The experimental results indicate that both the mechanical properties and durability of the concrete mixtures were improved as the level of WGA replacement increased from 0 to 60%, while the 80% and 100% WGA mixtures were inferior in terms of mechanical and durability to the standard concrete mixture (i.e., 0% WGA). The 60% WGA mixture exhibited the highest performance in terms of both mechanical properties and durability. This assessment was confirmed by the scanning electron microscope results, which indicated the 60% WGA mixture had the densest structure with more calcium silicate hydrate. Finally, the environmental assessment result supports using WGA as an environmental-friendly construction and building material in concrete for sustainable development.

Compressive Strength Assessment of Normal and Self-Compacting Concrete Made with Recycled Coarse Aggregate Using In-Situ Tests

There is an increasing trend in construction for using recycled coarse aggregate (RCA) concrete, which is a more sustainable approach for reducing natural resource consumption. One typical method for developing more environmentally friendly structures is to partially substitute natural aggregate. limited studies investigated the use of in-situ tests to assess the compressive strength of concrete made with RCAs. In this study, ultrasonic pulse velocity (UPV) and core sampling (CST) tests were used to evaluate the compressive strength of normal vibrated (NVC) and self-compacting (SCC) concretes made with recycled coarse aggregates (RCAs). Four different compressive strengths ranging from 25 to 55 MPa were adopted for each concrete type to consider the effect of replacing 0, 20%, 40%, 60%, 80%, and 100% of the required natural coarse aggregates (NCAs) with (RCAs). Exponential relationships were adopted to relate the UPV values with the compressive strength for both RCA-NVC and RCA-SCC. Also, suggested factors were adopted to correct equivalent core strengths for both RCA-NVC and RCA-SCC. The results of both test methods (UPV) and (CST) showed good correlations to estimate the compressive strength of RCA-NVC and RCA-SCC with confidence limits of 93%.

A Case Study on Condition Assessment of Fire-Damaged RC Members of Turbo-Generator

Many researchers across the globe have carried out fire safety risk analysis to gather evidence and pertinent data for different Reinforced Cement Concrete (RCC) members exposed to fire. Assessment of fire-damaged structures furnishes the minute details of the effect of fire on the properties of concrete.The study indicates the condition assessment of the turbo-generator (TG) unit, comprises of concrete bearing pedestals, deck and supporting columns. The research was conducted using Non-Destructive Testing (NDT) techniques using Rebound hammer test, Ultrasonic Pulse Velocity (UPV) test, Concrete Cover measurement, Carbonation and Crack depth measurements followed by microstructural studies using an X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), Optical Microscope (OM), and Mercury Intrusion Porosimetry (MIP). The samples were taken from a fire-damaged concrete bearing pedestal B2 and a non-fire-damaged concrete bearing pedestal B4 of the TG unit. The approach enabled us to find the extent of damage to the RCC members exposed to fire. The above mentioned test witnessed that the concrete bearing pedestal B2 was the moderately distressed member, expressed doubtful quality of concrete, higher porosity, reduced residual compressive strength and reduction in yield strength of steel. However minor distress in form of crushing at the top grout portion was observed in concrete bearing pedestal B4, and no apparent distress was observed in supporting columns of TG unit. Based on the distress identified, repair and remedial measures were proposed to concrete bearing pedestals in order to improve the performance of the TG unit.

Ultrasonic Pulse Velocity Test on Hybrid Fiber Reinforced Concrete

Concrete is a material of high importance in infrastructure and development projects. Concrete is characterized as a brittle material. In order to minimise the brittle failure, it is beneficial to add the fibers to the concrete mix without compromising the quality of concrete. The length of polypropylene fibers (PPF) and steel fiber (SF) used in concrete mixtures are 50mmand 35mmrespectively. The aimof this paper is to learn the quality of concrete and dynamic modulus of elasticity by using Ultrasonic Pulse Velocity (UPV). The percentages of polypropylene fiber are 0%, 0.3%, 0.6%, 0.7%, 1% and steel fiber are 0%, 0.1%, 0.4%, 0.7%, 1%. Comparison of conventional and Hybrid fiber-reinforced concrete (HFRC) is studied further. Experimental investigation is carried out on 18 cubes of M40 grade concrete of size 150X150X150mm for Ultrasonic Pulse Velocity (UPV) and compression test. The results show that conventional as well as fiberreinforced concrete are of excellent and of good quality with 28-day strength of 60.74 MPa. Conventional concrete has the highest pulse velocity and dynamic modulus of elasticity of 5.1903 5Øß5Ø‘Ü and 62.43 GPa. Next to it C-3-5 has a pulse velocity of 4.886 5Øß5Ø‘Ü, dynamic modulus of elasticity as 48.61 GPa and compressive strength of 61.77 MPa. Among FRCs Polypropylene fiber-reinforced concrete with 1% fiber volume fraction showed appreciable value of pulse velocity and elasticmodulus. In hybrid fiber-reinforced concrete C-3-3with 0.7%SF and 0.3% PPF has proven to have better quality as compared with other HFRCs.

Destructive and Non-Destructive Testing of the Performance of Copper Slag Fiber-Reinforced Concrete.

Concrete technology is adopted worldwide in construction due to its effectiveness, performance, and price benefits. Subsequently, it needs to be an eco-friendly, sustainable, and energy-efficient material. This is achieved by replacing or adding energy-efficient concrete materials from industries, such as ground granulated blast furnace slag, steel slag, fly ash, bottom ash, rice husk ash, etc. Likewise, copper slag is a waste material produced as molten slag from the copper industry, which can be used in concrete production. Copper slag can perform roles similar to pozzolans in the hydration process. This paper extends the comparative study of copper slag concrete with polypropylene fiber (PPF) subjected to destructive and non-destructive testing. Under destructive testing, compressive strength of concrete cubes, compressive strength of mortar cubes, splitting tensile tests on cylindrical specimens, and flexural tests on plain cement concrete were conducted and analysed. Ultrasonic pulse velocity and rebound hammer tests were performed on the samples as per IS13311-Part 1-1992 for non-destructive testing. The 100% replacement of copper slag exhibited a very high workability of 105 mm, while the addition of 0.8% PPF decreased the flowability of the concrete. Hence, the workability of concrete decreases as the fiber content increases. The density of the concrete was found to be increased in the range of 5% to 10%. Furthermore, it was found that, for all volume fractions of fiber, there was no reduction in compressive strength of up to 80% of copper slag concrete compared to control concrete. The 40% copper slag concrete was the best mix proportion for increasing compressive strength. However, for cement mortar applications, 80% copper slag is recommended. The findings of non-destructive testing show that, except for 100% copper slag, all mixes were of good quality compared to other mixes. Linear relationships were developed to predict compressive strength from UPV and rebound hammer test values. This relationship shows better prediction among dependent and independent values. It is concluded that copper slag has a pozzolanic composition, and is compatible with PPF, resulting in good mechanical characteristics.

Amplitude-Modulation Vibro-Acoustic Technique for Damage Evaluation

This study proposes an amplitude-modulation vibro-acoustic (AMVA) technique to track the evolution of thermal damage in pristine graphene mortar. In the proposed amplitude-modulation technique, the pump wave is amplitude-modulated using three different methods: (1) the pure amplitude-modulated (PAM) method, (2) the suppressive amplitude-modulated (SAM) method and (3) the transmitted amplitude-modulated (TAM) method. The nonlinear parameters , and corresponding to the PAM, SAM and TAM methods, respectively, are theoretically established and experimentally demonstrated that the nonlinear parameters associated with the material nonlinearity, and they can be used to quantitatively characterize different damage stages of thermal damage. Meanwhile, the resonant frequency (RF) and ultrasonic pulse velocity (UPV) tests are conducted. The linear measurements, dynamic elastic modulus obtained from RF test and ultrasonic pulse velocity collected by UPV test, are used to compare with the nonlinear parameters. The results show that the proposed AMVA technique is more sensitive and feasible to serve as the tool for thermal damage detection in cement-based material compared with the conventional RF and UPV techniques.

Investigating the Behavior of Waste Alumina Powder and Nylon Fibers for Eco-Friendly Production of Self-Compacting Concrete.

Self-compacting concrete (SCC) incorporating secondary raw materials has been extensively used around the globe due to its improved fresh, mechanical and durability properties. This study was planned to evaluate the suitability of locally available waste alumina powder (AP) and nylon textile fibers (NF) as a partial replacement for fine and coarse aggregates with the ultimate goal to locally produce SCC with desired properties. The used AP was acquired from a local market and NF was collected from a local textile factory. Various dosages of AP (10%, 20%, 30%, 40% and 50% by volume of fine aggregates) and NF (1% and 2% by volume of coarse aggregates) were studied. Tests including slump flow, V-funnel and J-ring tests were performed for examining the fresh properties of developed SCC. Results showed that the addition of AP has an insignificant effect on the superplasticizer dosage for maintaining a constant flow of 70 cm. However, a higher dosage of superplasticizer was required for a mixture with increasing dosages of NF to sustain a constant flow. Similarly, slump flow time (for a spread of 50 cm) and V-funnel time increased for mixtures with higher dosages of AP and NF. Tested SCC mixtures incorporating 40% and 50% of AP with 1% and 2% of NF showed an extreme blocking assessment due to their increased interparticle friction, the higher water absorption capacity of used AP and NF leading to increased flow resistance and hence, showed lower passing ability. The compressive strength was 16% higher for specimens incorporating 40% of AP due to the filling effect of AP which fills the micro-pores, leading to a more dense and compact internal micro-structure, confirmed through scanning electron microscopy analysis. An ultrasonic pulse velocity test conducted on hardened specimens verified the findings of the compressive strength results. Moreover, it was observed that NF has an insignificant effect on the compressive strength; however, flexural strength was increased due to the incorporation of NF, especially at higher dosages of AP.

Evaluation of Shear Strength Parameters in Unreinforced and Shotcrete Reinforced Coal through Experimental and Numerical Methods

The shear strength of coal mines forms the most significant aspect in the evaluation of mining disasters. A series of direct shear strength tests were conducted on intact coal specimens and coal-shotcrete specimens to evaluate the shear strength characteristics of the coal and coal-shotcrete interface. The tests were carried out under 1, 2 and 3 MPa of normal pressure respectively. The peak shear strength in intact coal specimen reaches its maximum value of 3.96 MPa under 3MPa of normally applied pressure while the shotcrete-coal interface has an estimated peak shear strength of 0.73, 0.80 and 0.86 MPa under the normal pressure of 1, 2 and 3 MPa respectively. Mohr-Coulomb model parameters such as adhesion strength and angle of adhesion were further determined that were used for the design and evaluation of shear strength of in situ coal mines. Numerical simulations of coal-shotcrete and intact coal specimens were performed using the Mohr-Coulomb model in Abaqus software and the numerical results obtained were found in good agreement with experimental results exhibiting peak variation of less than 15%. Further, ultrasonic pulse velocity test measurements were performed on coal specimens to evaluate the dynamic shear strength parameters and the parameters obtained were found to be enhanced compared to static strength parameters.