Static Compressive Strength Research Articles

Experimental Study on Mechanical Performance and Microstructure of Polypropylene Fiber Recycled Concrete

Recycled concrete reinforced by polypropylene fibers boosts an alternative sustainable solution to address the need of reusing waste concrete. This paper reports experimental and analytical studies of static and dynamic comprehensive behavior on recycled concrete specimens reinforced with different contents of polypropylene fiber (PPF). Electro-hydraulic pressure testing was used to obtain static compressive strength, whereas 74 mm diameter Split Hopkinson Pressure Bar (SHPB) was applied for dynamic impact compression tests at four strain rates. In addition, the reinforcing mechanism of polypropylene fiber on recycled concrete was analyzed of the micro-structure through Scanning Electron Microscope (SEM). Finally, ANSYS/LS-DYNA was applied for the simulation of the SHPB test, which was validated by good agreements of the stress waveform and failure modes of the fiber-reinforced recycled concrete specimen during the impact test. It appears that polypropylene fiber can optimize the microscopic pore structure inside the concrete, thus effectively improving the mechanical properties of recycled concrete which were originally defected by recycled aggregate. Also, higher strain rates significantly increase dynamic compressive strength as well as impact toughness. This study shows that the optimal content of polypropylene fiber in recycled concrete is 0.1% – 0.2%. The numerical simulation by ANSYS/LS-DYNA further proved that the HOLMQUIST-JOHNSON-COOK (HJC) constitutive model can better reflect the dynamic performance of concrete.

Ultra-high-performance fiber-reinforced sustainable concrete modified with silica fume and wheat straw ash

Developing ultra-high fiber-reinforced concrete (UHPFRC) demands an immense quantity of ordinary Portland cement (OPC). Using a high percentage of cement in UHPFRC leads to uneconomic concrete and significant release of CO2 into the atmosphere. Therefore, it is critical to address this issue by substituting the part of cement with a sustainable material. The current research has tried to tackle this issue by assessing the impact of adding wheat straw ash (WSA) and silica fume (SF) as a partial substitute of cement on the properties of UHPFRC on the static and dynamic compressive strength test, among other strength and durability characteristics. Two different batches of mixes were developed. The OPC was substituted for up to 40% in the first batch, with combined WSA plus SF at 10% intervals. In the second batch, OPC was replaced up to 40% with only WSA at an interval of 10%. Polypropylene fibers (PPFs) at 2% (by vol.) were added to modified samples to improve the ductility of concrete. The dynamic compression strength was evaluated utilizing a Split Hopkinson pressure bar, and quasi-static compression strength was determined using the compression machine. Moreover, splitting and flexural strength were also assessed, and water permeability and sorptivity tests were carried out for durability. The test outcome showed that the sample with 15% WSA plus 15% SF had higher compressive strength (174.8 MPa at 90 days) and improved durability than the sample with only 30% WSA (170.2 MPa at 90 days) and the control sample. The assessed properties tend to decline at 40% of WSA and 20% WSA with 20% SF. In dynamic compression strength, it was observed that the WSA and SF, and fibers samples performed similarly to the control sample, and these modified samples were not sensitive to strain rates. Adding 15% plus 15% SF had an optimal effect in improving the durability properties of UHPFRC. Also, the thermogravimetric analysis (TGA) confirms the role of WSA and SF in densifying the matrix of UHPFRC, decreasing the porous pores and amount of calcium-hydroxide and developing additional gels of calcium-silicate-hydrate, which enhances the strength and durability of UHPFRC. The current study revealed that the modified samples (with WSA and SF) had a low embedded CO2 for the sustainability features compared to the control sample.

Influence of water saturation on the compressive strength of concrete under high strain rates

AbstractIn this study, the influence of different water saturation achieved by different storage conditions on the static and dynamic compressive strength of three different concretes were investigated. The specimens were first dried then water‐saturated and tested both under static and impact loading. The impact tests were carried out in a split Hopkinson bar. Depending on the concrete strength class, increases in the compressive strength of 200%–300% at strain rates in the range of 90–160 1/s were observed. Compared to storage under ambient conditions, the compressive strength decreases as a result of drying due to microcrack formation. Furthermore, the concretes compressive strengths of water‐saturated specimens decrease compared to dry specimens. This decrease was observed under both static and impact loading and is independent of the strain rate. The failure of the dry specimens was more explosive with an increased number of cracks compared to water‐saturated specimens.

Static and dynamic compressive behaviour of 3D printed auxetic lattice reinforced ultra-high performance concrete

This paper presents a systematic experimental study on static and dynamic compressive behaviour of 3D octet, re-entrant honeycomb and triangular lattice reinforced ultra-high performance concrete, i.e., O-UHPC, H-UHPC and T-UHPC as well as steel fibre reinforced UHPC (S-UHPC). Mechanical tests were conducted to investigate the static and dynamic compressive behaviour of UHPC composites including failure pattern, stress-strain curve, dynamic increase factor (DIF), dynamic compressive strain and energy dissipation under various strain rates (i.e., 0, 34.8, 59.7, 86.7, 108.5 and 134.7 s−1). The plain UHPC and S-UHPC were used as references for comparison. Results indicate that H-UHPC has a 14.6–19.4% higher static compressive strength than O-UHPC and T-UHPC. S-UHPC exhibits higher dynamic compressive strength at lower strain rates, while the dynamic strengths of H-UHPC and T-UHPC at higher strain rates reach the highest, i.e., 262.7 MPa and 222.2 MPa, respectively. The highest total energy and post-crack energy at high strain rates take place on H-UHPC. Overall, H-UHPC has comparable static compressive behaviour but better dynamic compressive behaviour at high strain rates in terms of strength, ductility, energy dissipation and DIF, compared with other UHPC specimens, suggesting that re-entrant honeycomb is a better choice for manufacturing UHPC with optimal auxetic 3D lattices.

Effect of sludge ceramsite particle grade on static and dynamic mechanical properties of alkali-activated slag lightweight concrete at early age

Sewage sludge (SS) produced in water supply and drainage plants is a kind of solid waste with pollution and high water content. SS mixed with fly ash and other materials to make sludge ceramide (SC) can be used as light environmental protection building materials. Alkali-activated lightweight concrete (ASLC) is prepared by mixing SC with alkali-activated slag mortar with low carbon emission, which has lightweight and early strength characteristics. Using the split Hopkinson pressure bar test system, the dynamic and static uniaxial compressive tests of ASLC at an early age were carried out. The influence of aggregate particle gradation on the mechanical properties of ASLC was comprehensively evaluated from static compressive strength and dynamic peak stress. Experiments show that small-size SC has better mechanical properties and lower air content. SEM test shows that the paste has closely meshed with SC, which proves that SC has good compatibility with alkali-activated slag material. The air content of ASLC was quantified by mesopore characterization. The results show that the increase in SC size will increase the air content of the specimen and weaken the compressive performance of ASLC.

Effect of Aggregate Mix Proportion on Static and Dynamic Mechanical Properties and Pore Structure of Alkali-Activated Slag Mortar with Sludge Pottery Sand

The overexploitation of river sand will reduce the stability of the river. Using sludge pottery sand (SPS) as a substitute for fine aggregate in mortar can reduce the weight of building mortar and achieve pollution control and resource regeneration. Based on the consideration of energy-saving and carbon reduction, the combination of alkali-activated slag cementitious material and SPS with potential pozzolanic activity to prepare sludge pottery sand alkali-activated slag mortar (PSAM) can replace the traditional silicate river sand mortar. The static and dynamic peak stress of PSAM was tested, and the energy dissipation characteristics of PSAM specimens under the dynamic load were analyzed by using the wave acquisition system of a split Hopkinson pressure bar. The results show that the SPS with 0.15~2.36 mm has better mechanical properties. The increase in the mixing ratio with the SPS with 2.36~4.75 mm will gradually reduce the static and dynamic compressive strength of the specimen, and also reduce the density of the specimen. SEM images and binary pore morphology images showed that the increase in SPS size will lead to a large number of coherent pores inside the specimen, which will increase the air content of the specimen, but at the same time reduce the absorption capacity of the specimen to the wave, so the dynamic energy absorption peak of PSAM appears to decrease significantly. The image of ultra-high-speed photography revealed the mechanism of crack propagation of the PSAM specimen. The development of the crack is positively correlated with the dynamic energy absorption performance when the specimen is completely broken.

Experimental 3D printed re-entrant auxetic and honeycomb spinal cages based on Ti-6Al-4 V: Computer-Aided design concept and mechanical characterization

This paper presents a method for modeling a biomedical device by adaptation a commercially available interbody cage for an auxetic metamaterial and honeycomb structure using standard operations in Computer-Aided design software. The mechanical properties of experimental prototypes of Ti-6Al-4 V cages made by selective laser melting using computer modeling (finite element analysis), static and low-cycle fatigue compression tests (up to 3500 cycles) are characterized. 3D printed cells with structures with an angle of inclination between cell edges of less than 90˚ (auxetic metamaterial) are shown to exhibit higher static compressive strength and fatigue resistance than cells based on structures with an angle of inclination greater than 90˚ (honeycomb structure). The changes in the inclination angle differently affect to the porosity and consequently to mechanical behavior of auxetic metamaterial and honeycomb structure. The Young modulus of the auxetic-based interbody cage is 6.68 ± 0.28GPa and comparable to the elastic modulus of human cortical bone. The honeycomb-based cage exhibits lower values of Young modulus (1.19 ± 0.03GPa) close to that of trabecular bone and vertebrae. Importantly, the auxetic-based cage is not destroyed after 3500 cycles under 14kN load with residual deformations ≤ 1 % (0.21 ± 0.10 mm displacements).

Dynamic compressive impact tests of building sandstone with a large split hopkinson pressure bar

The uniaxial compression behavior of building sandstone at high strain rates is not well understood. In this study, standard and flattened cylinders were fabricated for dynamic and static compression tests. A split Hopkinson pressure bar was employed to perform the impact tests at strain rates up to 93.2 s−1. The static compression strength of the flattened cylinders was 112.7 MPa, which was 50% higher than that of the standard cylinder. The fracture damage of the cylinder was closely correlated to the strain rate. Incomplete fragmentation appeared at low strain rates, whereas complete fragmentation appeared at a higher strain rate. Representative diagrams were developed using the characteristic points of the Type I and Type II diagrams, which were characterized by the rebounding and dropdown portions due to the strain rate level. The correlations between the dynamic strength, strain rate, and dynamic modulus were analyzed based on the experimental results. The dynamic increase factor (DIF) was overestimated when the static compressive strength of the standard cylinder was used. A two-portion expression for DIF was developed in accordance with the experimental data. The energy absorption density was proportional to the strain rate and dynamic strength. Two mathematical expressions were obtained based on the experimental energy absorption density, characterized by the experimental peak stresses. The present study is valuable for evaluating the dynamic behavior of sandstone under extreme loads.

Durability and mechanical properties of rubber concrete incorporating basalt and polypropylene fibers: Experimental evaluation at elevated temperatures

Waste tires cause serious environmental problems, such as pollution, which can be reduced by mechanically grinding rubber tires into powder to obtain rubber particles. These components are then used in equal mass (20%) to replace fine aggregate to manufacture rubber concrete (RC), a new type of environmentally friendly building material. This study explored the performance of RC and different volume fractions (0.5%, 1.0% and 1.5%) basalt-polypropylene fiber-reinforced rubber concrete (BPRC) under elevated temperatures through a series of experiments on mass, relative dynamic elastic modulus, static compressive strength, and dynamic compressive strength. The experimental results showed that with increasing temperature, mass loss in RC and BPRC gradually increased, their relative dynamic elastic moduli slowly decreased. Their static compressive and dynamic compressive strengths reflected different degrees of loss, the strength loss temperature node of pure rubber concrete is earlier and the loss degree is more. The best performance was shown by the BPRC with 1% and 1.5% volume ratios of basalt and polypropylene fibers, respectively. Mixing basalt and polypropylene fibers into RC is beneficial to improvements in its performance after an increase in temperature.

Dynamic compressive characteristics and damage constitutive model of coral reef limestone with different cementation degrees

Reef limestone has a heterogeneous, anisotropic, porous structure. According to apparent pore characteristics, shallow reef limestone can be divided into four types: weakly-cemented porous (WP), strongly-cemented porous (P), weakly-cemented dense (WD), and strongly-cemented dense (D) types. On this basis, physical properties including the density porosity, and longitudinal wave velocity of each type of reef limestone and their intrinsic correlations were measured and discussed. The quasi-static and dynamic compression tests were conducted on the four types of reef limestone samples to estimate the correlations of physical properties of reef limestone and its dynamic and static parameters. Results show that reef limestone is different from most terrestrial rocks; its compressive strength is weakly correlated with the strain rate and its static tension–compression ratio is slightly larger than that of terrestrial rocks (about one fifth). The static tensile and compressive strengths as well as the dynamic compressive strength of dense reef limestone all linearly increase with the density; the static compressive strength of porous reef limestone is weakly related to the density while the dynamic compressive strength increases with the elastic longitudinal wave velocity as a quadratic function. The dynamic fracture mode of dense reef limestone is dominated by block failure while strip-shaped fragments are mainly formed along the coral growth line in porous reef limestone. The energy-dissipation density of the two major types of reef limestone is roughly linearly correlated with the dynamic compressive strength. Finally, a constitutive model for dynamic damage of reef limestone under impact load was established based on statistical damage theory and its effectiveness was verified experimentally.

Study on the mechanical properties of desert sand concrete

In this paper, the manufactured sand was replaced by desert sand with contents to prepare desert sand concrete with different grades. Then the compressive strength, axial compressive strength, static compressive elastic modulus and axial tensile strength of desert sand concrete were tested to analyze the influence of desert sand replacement rate on the mechanical properties of concrete at different ages and different grades. It was shown that the negative influence of desert sand on the compressive strength of concrete would be increased with the increase of concrete grade, and the influence increased with the increase of age. The addition of sand would be resulted in the decrease of axial compressive strength and static elastic modulus of concrete, and with the increase of concrete grade, the strength would be decreased obviously. The addition of desert sand had no significant effect on the axial tensile strength of concrete in general.

Mechanical properties of concrete containing recycle concrete aggregates and multi-walled carbon nanotubes under static and dynamic stresses

The growing demand for natural aggregates in the construction industry has motivated researchers to utilize recycled concrete aggregates (RCA) to preserve the natural resources and provide sustainable structure. However, the use of RCA in concrete applications has revealed defects in performance with low strength and rapid collapse under static and dynamic loads, respectively. Thus, the objective of present research is to improve these properties by using multi-walled carbon nanotubes (MWCNT). This study involves evaluating the fresh and hardened properties of recycled aggregate concrete (RAC) modified with different levels of MWCNT. The study involves RCA (i.e., 0 %, 25 %, 50 %, 75 % and 100 %) as replacement for natural aggregates, and MWCNT (i.e., 0.05 %, 0.1 % and 0.25 %) as weight of cement. The experimental testing consists of 240 specimens prepared from different mixtures. Workability is assessed using slump tests. Mechanical properties including static compressive strength and dynamic impact resistance are evaluated at 7 and 28 days. Experimental results show that incorporating MWCNT at all levels significantly reduces the slump values for all specimens. On the other hand, the compressive strength is increased by adding MWCNT to the concrete samples. The compressive strength of the RAC increased by as much as 70 % when modified with MWCNT. Furthermore, the inclusion of MWCNT is found to significantly increase the impact resistance of RAC specimens with percentage developments reaching approximately 11–508 % and 110–679 % at 7 and 28 days, respectively, at both first crack and failure stages. The dosage of 0.1 % MWCNT is shown to exhibit the highest percentage enhancement in impact resistance among the other nano levels. The failure patterns and cracks propagation are presented as well.

Experimental study on the competing effects of strain rate and water weakening on compressive strength of saturated rocks

Measuring the rock compressive strength under combined effects of strain rate and water weakening is of great importance and at the same time a major issue for engineers. In this study, we explore the ability to detangle the contributions of strain rate and water-weakening effects on rock compressive strength within a wide static and dynamic strain rate range. To this end, we conduct a series of compression tests and acoustic emission (AE) tests on two types of rock with specific mineral compositions (i.e., limestone and granite). The correlations between rock compressive strength, including static compressive strength σcs and dynamic compressive strength σcd, and water-weakening factors fw with strain rate are derived. The experimental AE waveform data is analyzed using a new methodology named statistical analysis of dominant frequency, from which we infer the intrinsic rock progressive failure and evaluate the competing effects of water weakening and strain rate. Our results show that water saturation causes a drastic loss in the compressive strength of limestone and a small reduction in the compressive strength of granite. The strain rate effect governs the changes in the compressive strength of dry rocks, characterizing a reduction in low dominant frequencies of AE waveforms with increasing strain rates. Whether the strain rate effect or water-weakening effect plays a dominant role depends largely on the rock types and loading regimes. We proposed that the primary effects on σcs of saturated limestone are strain rate under relatively low static strain rate (lower than 8.33 × 10−5 s−1) and pore water pressure under relatively high static strain rate (beyond 8.33 × 10−5 s−1), respectively, and that on σcd of saturated limestone is strain rate. The variations of σcs and σcd of saturated granite are both determined by the strain rate effect within the strain rate range investigated. Additionally, the exertions of various water-weakening effects of limestone and granite at different strain rates, which are responsible for their fw variations, are evaluated in detail.

Application of machine learning in predicting the rate-dependent compressive strength of rocks

Accurate prediction of compressive strength of rocks relies on the rate-dependent behaviors of rocks, and correlation among the geometrical, physical, and mechanical properties of rocks. However, these properties may not be easy to control in laboratory experiments, particularly in dynamic compression experiments. By training three machine learning models based on the support vector machine (SVM), back-propagation neural network (BPNN), and random forest (RF) algorithms, we isolated different input parameters, such as static compressive strength, P-wave velocity, specimen dimension, grain size, bulk density, and strain rate, to identify their importance in the strength prediction. Our results demonstrated that the RF algorithm shows a better performance than the other two algorithms. The strain rate is a key input parameter influencing the performance of these models, while the others (e.g. static compressive strength and P-wave velocity) are less important as their roles can be compensated by alternative parameters. The results also revealed that the effect of specimen dimension on the rock strength can be overshadowed at high strain rates, while the effect on the dynamic increase factor (i.e. the ratio of dynamic to static compressive strength) becomes significant. The dynamic increase factors for different specimen dimensions bifurcate when the strain rate reaches a relatively high value, a clue to improve our understanding of the transitional behaviors of rocks from low to high strain rates.

Influence of Recycled Concrete Fines Content on the Dynamic Mechanical Properties of Coal Mine Roadway Support Mortar

This study investigated the dynamic properties of coal mine roadway support mortar with recycled concrete fines as supplementary cementitious materials to partially replace Portland cement. Mortars with different replacement levels (0%, 10%, 20%, and 30%) were prepared to investigate the effects of the replacement levels on the static compressive strength, pore size distribution, dynamic compressive strength, dynamic peak strain, dynamic growth factor, and dynamic ultimate toughness of the mortars. A split Hopkinson pressure bar was used to test the dynamic compressive strengths of the mortars at d 28. The results showed that the static compressive strength of the mortar with recycled concrete fines decreased with recycled concrete fine replacement level. With an increasing average strain rate, the dynamic compressive strength, dynamic peak strain, and the dynamic ultimate toughness of the mortar showed the strain rate effect. Compared with plain mortar, mortars with recycled concrete fines had higher strain rate sensitivity under impact loading. Moreover, mortars with 10% recycled concrete fines exhibited better impact resistance and ultimate toughness than the other groups, suggesting that a low replacement level of recycled concrete fines could increase the energy absorption of the mortars, which was beneficial for the deformation and stability of coal mine roadway support mortar under impact loading.

The mechanical properties of concrete in water environment: A review

The service performance of concrete structures in a water environment differs from that in a normal environment. An accurate evaluation of the mechanical properties and service status of wet concrete is related to the reliable design and safe operation of concrete structures, e.g., hydraulics, marine engineering, bridges, and tunnels. To promote the application of new and high-performance concrete to complex water environments and grasp the future development trend, the research progress on the service performance of concrete in water environments was reviewed worldwide. Starting from the internal water content of concrete, the existing research is combed, the influence of water content, water pressure, and loading rate on the static and dynamic characteristics of concrete in a water environment is summarized, and the influence mechanism is analyzed. The literature review demonstrates that the static compressive strength of wet concrete is lower than that of dry concrete; however, the elastic modulus improves. With an increase in the strain rate, the compressive strength of wet and dry concretes improves, and the rate sensitivity of the wet concrete is greater than that of the normal concrete. Pore structure characteristics mainly affect the static strength of the wet concrete. The improvement in the dynamic strength of the wet concrete is caused by the combined effect of the concrete rate sensitivity, “Stefan” effect, and water pressure.

Effect of fibre addition on the static and dynamic compressive properties of ambient-cured geopolymer concrete

This paper presents an experimental study on the static and dynamic compressive properties of ambient-cured fibre reinforced geopolymer concrete (FRGPC) containing mono steel, mono polypropylene (PP) or hybrid steel-PP fibres. A Split Hopkinson Pressure Bar (SHPB) was used to carry out dynamic compressive tests under different strain rates up to 130.5 s−1. The effects of fibre addition on static compressive strength, splitting tensile strength, dynamic failure process and damage mode, dynamic compressive strength, specific energy absorption and dynamic increase factor (DIF) were investigated and analysed. The results revealed mono steel fibre as the most effective in improving static compressive and splitting tensile strengths, which increased by 21.92% and 21.05% respectively, compared to plain geopolymer concrete (GPC). The dynamic compressive strength of both plain GPC and FRGPC increased with the increase of strain rate. There is a positive relationship between DIFs of compressive strengths and strain rates for all GPC and FRGPC samples. The samples containing mono PP fibres showed the most strain rate sensitivity with respect to compressive strengths and specific energy absorption within the tested strain rates. Furthermore, empirical formulae are proposed accordingly to predict the DIFs and specific energy absorption of ambient-cured GPC and FRGPC.

Experimental and mesoscopic investigation of self-compacting rubberized concrete under dynamic splitting tension

Self-compacting rubberized concrete (SCRC) has gained extensive investigations due to its good impact resistance and environmental friendliness, while the dynamic splitting tensile properties of SCRC are seldom studied. In this study, river sand in SCRC was replaced by three rubber volume fractions (5%, 10%, 15%). The experiments indicated that the static compressive strength, static tensile strength, elastic modulus and dynamic splitting tensile strength declined with the increase of rubber content. The dynamic splitting tensile strength, dynamic increase factor (DIF) and failure mode of SCRC were sensitive to strain rate. SCRC with a higher rubber volume had a greater DIF. The critical strain rate of different SCRC was obtained by piecewise fitting, which decreased with the enhancement of rubber content. Meanwhile, a three-dimensional mesoscopic model of SCRC was established. The rubber particles were generated by a random polyhedron algorithm and randomly thrown into the sample by the take and place algorithm. The numerical calculation suggested that the mesoscopic model could exhibit the fracture process of SCRC under high strain rates. The propagation of cracks bypassed the rubber particles and produced a mass of branch cracks under high strain rates, dissipating a large amount of energy and elevating the DIF, which is consistent with the macroscopic failure pattern. In addition, the effect of strain rate and rubber volume on DIF was discussed combined with the mesoscopic model.

Assessment of Machine Learning Models for the Prediction of Rate-Dependent Compressive Strength of Rocks

The prediction of rate-dependent compressive strength of rocks in dynamic compression experiments is still a notable challenge. Four machine learning models were introduced and employed on a dataset of 164 experiments to achieve an accurate prediction of the rate-dependent compressive strength of rocks. Then, the relative importance of the seven input features was analyzed. The results showed that compared with the extreme learning machine (ELM), random forest (RF), and the original support vector regression (SVR) models, the correlation coefficient R2 of prediction results with the hybrid model that combines the particle swarm optimization (PSO) algorithm and SVR was highest in both the training set and the test set, both exceeding 0.98. The PSO-SVR model obtained a higher prediction accuracy and a smaller prediction error than the other three models in terms of evaluation metrics, which showed the possibility of the model as a rate-dependent compressive strength prediction tool. Additionally, besides the static compressive strength, the stress rate is the most important influence factor on the rate-dependent compressive strength of the rock among the listed input parameters. Moreover, the strain rate has a positive effect on the rock strength.

Determination of some physical properties, angles of repose and frictional properties of a local variety of kernel and nut of oil palm

The study was to determine the moisture content, size, volume, sphericity, solid density, bulk density and porosity, angle of repose, coefficient of static friction and compressive strength of oil palm kernel and nut. The results show that the moisture contents were 7.94% and 25.31% for the kernel and nut respectively. The arithmetic and geometric mean diameters were 1.56 cm and 45.79 cm (kernel) and 0.87 cm and 1.27 cm (nut). The average volumes were, 1.75 cm3 (kernel) and 0.79 cm3 (nut). The average sphericities were 66.37 % (kernel) and 64.36 % (nut). The average solid densities, bulk densities and porosities of the samples were 1.63 g/cm3, 0.00053 g/cm3 and 61.32 % (kernel) and 2.13 g/cm3, 0.0008 g/cm3 and 46.91 % (nut). The average values for the angles of repose on wood were 20.8 0 (fresh), 22.81 0(boiled), 19.09 0 (kernel) and 60.71 0 (nut). On glass, the angles of repose were 17.53 0 (kernel) and 64.08 0 (nut). Those on metals were, 18.55 0 (kernel) and 62.3 0 (nut). The coefficients of static friction on wood were 0.35 (kernel) and 1.89 (nut). On glass, coefficient of static friction was 0.32 (kernel) and 2.18 (nut). Those on metals were 0.34 (kernel) and 2.0 (nut).