Study on Periodic Pulsation Characteristics of Corn Grain in a Grain Cylinder during the Unloading Stage

The fluctuation effect of corn grain often occurs during the unloading stage. To accurately explore the periodic pulsation characteristics of corn grain during the unloading stage, a discrete model of corn grain was established, and the effectiveness of the discrete element method in simulating the corn grain unloading stage was verified by a 3D laser scanner and the “spherical particle filling method”. The grain cylinder was divided into six areas, and the periodic pulsation characteristics at different heights were explored through simulation tests. The results showed that the faster the average speed of corn grain changes in unit time, the more significant the periodic pulsation characteristics were as the height of grain unloading increased. The corn grain pulsateon in the grain cylinder exhibited gradual upward transmission and gradual amplification in the process of transmission. The average velocity decreased with increasing height. The direct cause of pulsation was the variation in the average stress between grain layers. Simulation analysis of grain unloading for different half cone angles of the grain cylinder was carried out. The change in corn grain average velocity over time in the area below 20 mm of the upper free surface was extracted. The results showed that the speed of the top corn grain increased with increasing the half cone angle, and the periodic pulsation phenomenon became more obvious with increasing the half cone angle at half cone angles of 30–65°. A half cone angle of 65–70° marked the critical state of corn grain flow changing from funnel flow to overall flow in the grain cylinder. This study provides a method for studying the periodic pulsation characteristics of different crops during the grain unloading stage and provides a technical reference for the safe design of grain unloading equipment.

Influence of Polypropylene Fibre Factor on Flowability and Mechanical Properties of Self-Compacting Geopolymer

The possibility of using geopolymer instead of Portland cement could effectively reduce carbon dioxide emissions from cement manufacturing. Fibre-reinforced self-compacting geopolymers have great potential in civil engineering applications, such as chord member grouting for concrete-filled steel tubular truss beams. However, to the best of the authors’ knowledge, the quantitative relationship between FF and the properties of the fibre-reinforced geopolymer has been rarely reported. In this research, 26 groups of mixtures were used to study the influence of the polypropylene fibre factor (FF) on the flowability and mechanical properties and also the compactness of the fibre-reinforced self-compacting geopolymer. At the same volume fraction, geopolymers with long fibres present worse flowability than those having short fibres due to the easier contacting of long fibres. By growing the FF the influence of fibre addition on the V-funnel flow rate is more significant than the slump spread. This can be ascribed to the consequence of fibre addition and friction by the V-funnel which estimates the restrained deformability. For FF lesser than critical factor Fc = 100, influence of fibres is negligible and fibres are far apart from each other and, thus, they cannot restrict cracking under load and transfer the load to improve the mechanical properties. For FF between the Fc = 100 and density factor Fd = 350, a noteworthy enhancement of mechanical properties was obtained and the geopolymer was still adequately workable to flow by weight of self, without any symbols of instability and fibre clumping. Under this condition, better fibre dispersal and reinforcing productivity can lead to better hardened properties. For FF higher than Fd = 350, fibres tend to come to be entwined together and form clumping resulting from the fibre balling, resulting in worse hardened properties. This research offers a sensible basis for the application of the workability regulator of the fresh properties of fibre-reinforced geopolymer as an operative way to basically obtain ideal mechanical properties.

Short-Term Study on Mechanical and Fresh properties of Micro-silica based Self Consolidating Concrete in Nigeria

The ever increasing environmental challenge arising from improper waste management has been a great concern to researchers and the society. One of such industrial waste is micro silica; a bye-product of the Carbothermic reduction of high purity quartz at temperature of about 2000oC in the presence of coke. The finess of this material and its pozollanic nature makes it suitable for use in the production of self-compacting concrete. In this research micro silica was introduced in percentages of, 5, 10 and 15% as partial replacement of cement in the production of self-compacting concrete. The fresh properties were examined using slump flow, T50cm, slump flow, V-funnel and blockage ratio using L-Box. As the Micro silica were introduced, T50cm time increased, Slump flow reduced, V-funnel flow time increased and L-Box value reduced, due to increase in viscosity. Comparing the experimental results with European Federation of National Associations of Representing for Concrete EFNARC 2002, blockage ratio for 15% was below 0.8. The compressive stresses at 28days were higher than the control at 28days compressive stress with 8.6%, 19.04% and 11.9% for 5%, 10% and 15% respectively. Thus, cement can be partially substituted with micro silica up to 15% with improvement in compressive strength in self-compacting concrete.

Rheology, fresh and hardened properties of self-consolidating concrete utilizing metal and PVA polymer fibers

Fiber reinforced self-consolidating concrete (FRSCC) has a tremendous potential to be used in construction industry as it combines the advantagees of both self-consolidating concrete (SCC) and fiber reinforced concrete (FRC). 18 concrete mixtures were developed by incorporating differenct volumes (0 to 0.3) of polyvinyl alchohol (PVA) and metallic fibers. Fresh, rheological, mechanical and durability (in terms of chloride penetration resistance) properties of all FRSCC mixtures were evaluated. The influences of fiber types/size/ dosages and fiber combination (used in hybrid mixes) on fresh (slump flow, L-box passing ability, V-funnel flow time and segregation index), rheological (plastic viscosity and yield stress) and hardened (fracture energy and compressive/flexural/splitting tensile strength) properties were critically analyzed to examine the relationships among various properties as well as to suggest suitable FRSCC mixtures. The fibers (especially metallic ones) wre more effective in increasing the fracture energy of FRSCC than compressive/splitting tensile/flexural strength. A fracture energy gain of about 730% was observed (which is substantial) compared to 10% of compressive strength, 39% of splitting tensil strength and 124% of flexural strength. The improved strength and fracture energy of FRSCC mixtures can significantly reduce the amount of tensile reinforcement and subsantially increase the energy absorbing capacity of concrete structures.

Rheology, fresh and hardened properties of self-consolidating concrete utilizing metal and PVA polymer fibers

Fiber reinforced self-consolidating concrete (FRSCC) has a tremendous potential to be used in construction industry as it combines the advantagees of both self-consolidating concrete (SCC) and fiber reinforced concrete (FRC). 18 concrete mixtures were developed by incorporating differenct volumes (0 to 0.3) of polyvinyl alchohol (PVA) and metallic fibers. Fresh, rheological, mechanical and durability (in terms of chloride penetration resistance) properties of all FRSCC mixtures were evaluated. The influences of fiber types/size/ dosages and fiber combination (used in hybrid mixes) on fresh (slump flow, L-box passing ability, V-funnel flow time and segregation index), rheological (plastic viscosity and yield stress) and hardened (fracture energy and compressive/flexural/splitting tensile strength) properties were critically analyzed to examine the relationships among various properties as well as to suggest suitable FRSCC mixtures. The fibers (especially metallic ones) wre more effective in increasing the fracture energy of FRSCC than compressive/splitting tensile/flexural strength. A fracture energy gain of about 730% was observed (which is substantial) compared to 10% of compressive strength, 39% of splitting tensil strength and 124% of flexural strength. The improved strength and fracture energy of FRSCC mixtures can significantly reduce the amount of tensile reinforcement and subsantially increase the energy absorbing capacity of concrete structures.

Silo discharge: influence of the particle shape on the velocity profiles

Experiments on the discharge of a silo with an inclined outlet are performed using flattened seeds in order to evaluate the validity of a previous theoretical formulation developed in our work group [1]. In that description, funnel flow regime is assumed to be based on a free fall parabolic arc. The shape of this arc is described with a parameter which is the only one involved in the flow rate formulation. An experimental analysis of the behavior of this parameter is carried out based on the geometry and shape of the grains within the silo. Also, video analysis of the silo discharge is performed in order to investigate the velocity profiles at the outlet of the hopper for these non-spherical particles. Experiments are contrasted with analytical predictions derived from the proposed formulation in order to assess and discuss its validity for the case of flattened particles.