Unreinforced Samples Research Articles

Shear strength evaluation of composite pavement with geotextile as reinforcement at the interface

This research was conducted to investigate the shear strength at the interface between polymer concrete and asphalt concrete with geotextile as reinforcement at the interface of these two types of concrete. The samples were tested for the parameters of different surface conditions [rough and smooth], curing types [room and thermal curing], temperature effect and the impact of geotextile as reinforcement. To investigate the correlation between these parameters, four different testing conditions were implemented. The results showed a significant improvement of shear strength for rough surface sample as compared to smooth surface sample. Moreover, samples cured in oven had lower shear strength as compared to samples cured in room condition. Besides that, high temperature has an adverse impact on the shear strength at the interface between polymer concrete and asphalt concrete due to the weakening of asphalt concrete at high temperature. As for samples reinforced with geotextile, the shear strength resistance was better as compared to unreinforced samples. Through visual observation, the types of failure under all testing conditions were mixed failure mode.

Creep study of carcass composites reinforced with steel fiber of the Dramix type

The results of a creep study of disperse-reinforced building composites made by carcass technology are presented. In the experiment, steel fiber «Dramix» type fiber was used as dispersed reinforcement, the content of which was 1…3 % by volume of the composite. The impregnation matrix was made on the basis of portlandcement and a superplasticizing additive of the brand Melflux 1641 F. In the creep test, the samples-beams were loaded according to a 4-point scheme. The level of load applied to the samples was 30, 50 and 70 % of the maximum values. An unreinforced carcass composite was taken as a control composition. The tests continued until the moment when the value of the deflection became constant. Based on the data obtained, graphical dependencies «relative deflection – exposure time» were constructed. On the obtained creep curves of carcass composites in the general case, four sections of the kinetics of deflection change can be distinguished: the initial section, in which an intense, almost linear, increase in deflections occurs; the curved section where the attenuation of the process of growth of deflections is observed; a linear section in which the increase in deflections is insignificant and has a quasi-permanent character; the final section, when the stabilization of the deflections occurs, and their values become constant. The minimum deflection values were obtained for an unreinforced carcass composite, and the maximum for composite reinforced with 1 % «Dramix» fiber. When the composition of the carcass composites contains 2–3 % fiber, a significant decrease in the deflections was observed, but their values were higher than that of the control composition. This is explained by the different load applied to the reinforced and unreinforced samples of carcass composites, as well as the positive effect of increasing the content fiber to 2–3 % on their bending strength and stiffness. The studied dispersion-reinforced carcass composites can be used for the manufacture of monolithic industrial floors, foundations and pavements, working under the influence of increased mechanical influences.

Experimental Investigation of Root Tensile Strength for Slope Stabilization

Bioengineering approaches provide cost-effective ways to protect slopes against surface erosion and shallow mass movements. Indeed, vegetation is an excellent way to control slope erosion and instability of slopes. Plants play an active role both on the surface, protecting and holding soil particles, and at deeper layers, reducing pore pressure and increasing soil shear strength. The use of vegetation is particularly appropriate where soil conservation measures are needed. In the paper, a series of laboratory tests are described, together with the equipment used, to better understand plant root effects on soil shear strength and slope stability. Two species of Mediterranean plants, such as Asparagus acutifolius and Spartium junceum, were tested in the laboratory. More than 170 tensile tests have been performed on dry and saturated samples. In order to evaluate the effect of soil moisture, most several roots were also tested at different saturation ratios. Laboratory tests also included direct shear tests on root-reinforced and unreinforced samples. Comparison between reinforced and non-reinforced samples confirms the contribution of roots to improve the soil strength.

Effect of nano-sized particles on grain structure and mechanical behavior of friction stir welded Al-nanocomposites

Weldability of heat-treatable 6061-T6 aluminum alloy results in deterioration of mechanical properties due to dissolution of strengthening precipitates in the nugget zone of friction stir welded joints. These properties were improved by addition of reinforcement particles in the weld joint line. In the present work, attempts were made to produce 6061-T6 Al-based nanocomposites using the friction stir welding process by incorporating titanium oxide nanoparticles into the aluminum matrix for microstructure refining of the nugget zone and prevent the grain growth in the heat-affected zone. The effect of addition of nanoparticles on the evolution of grains structure and mechanical behavior of friction stir welded samples based on different combinations of rotational and travel speed was studied and discussed. Results revealed that the unreinforced samples were successfully welded at both low and high heat inputs, whereas the reinforced samples are not feasible at tool rotational speed (ω) < 2000 r/min and transverse speed (v) > 70 mm/min, respectively. The significant refining of grains in the nugget zone is possible with addition of nanoparticles via the Zener-pinning effect. A more pronounced increment in tensile strength, microhardness, and wear properties was observed compared to sample without nanoparticles under the same processing parameters due to embedment of nano-sized particles in the weld nugget zone.

Abrasive Wear of a Steel Counterbody in Frictional Contact with Pressed Modified Wood

The article presents results of studying how an abrasive affects the wear of pressed modified wood and steel samples—counterbodies without hardening and with hardening by annealing and application of a diamond-like coating of titanium nitride. It is shown that the (linear and mass) wear rate of unreinforced steel samples is more than 20 times higher than for hardened samples; surface hardening via vacuum coating deposition is ineffective due to its intense peeling in the presence of an abrasive.

Dynamic behavior of clay modified with polypropylene fiber under freeze-thaw cycles

Abstract In order to explore the behavior of clay reinforced by polypropylene (PP) fiber, a series of dynamic triaxial tests were conducted on samples with multi-stage dynamic loading process under different confining pressures of 0.3 MPa, 0.4 MPa and 0.5 MPa. The soil physical properties were significantly affected by the seasonal freezing of the active layer. To simulate this effect, all samples were subjected to the freeze-thaw process of up to 15 cycles. Samples reinforced with 0.75% PP fiber showed the greatest dynamic strength, and a similar regularity was found for samples after 15 freeze-thaw cycles. The dynamic shear modulus decreased with the increase of confining pressure, but decreases with the increasing strain and number of freeze-thaw cycle. The dynamic shear modulus of samples with PP fiber is relatively larger than that of unreinforced samples. After 15 freeze-thaw cycles, the dynamic shear muduli of samples with 0.25%, 0.5% and 0.75% fiber increased by 27.3%, 50.1% and 63.6%, respectively, compared with the one of unreinforced samples at γ = 0.3% and σc = 0.3 MPa. The dynamic shear moduli of unreinforced sample and samples with 0.25%, 0.5% and 0.75% fiber content after 15 freeze-thaw cycles decreased by 7.9%, 7.6%, 5.4% and 6.3%, respectively, compared with the one before freeze-thaw cycle at γ = 0.05%. The damping ratio shows an increasing tendency with the increases of shear strain and fiber content. The damping ratio of samples reinforced with 0.25%, 0.5% and 0.75% fiber increased by 11.11%, 8.89% and 15.56%, respectively, compared with the one of unreinforced sample at γ = 0.005%. The Davidenkov model was adopted to describe the dynamic behavior of reinforced soil after freeze-thaw cycles at various confining pressures. The dependences of the normalized shear modulus on the shear strain amplitude are described. The behavior of the fiber after exposure to freeze-thaw cycles was analyzed by using Scanning Electron Microscope (SEM) method.

Preparation and Characterization of AA6061 Aluminum Alloy Composite Reinforced With Different Contents of Blast-Furnace Slag by Powder Metalurgy

ABSTRACTThe constant search for the improvement of the performance of materials of industrial application, evaluated under aspects of weight reduction, greater resistance, greater resistance to wear and better thermal stability, among others, associated with the search for the development of ecologically viable products, that convert the context of environmental degradation in preservation and sustainability, reflects the need to conduct research that results in new materials. The objective of this work is to obtain composites of the AA6061 aluminum alloy reinforced with different contents of coke coal blast-furnace slag by powder metallurgy. The processing of these materials was done by sieving, mixing and compacting powders of reinforced aluminum alloy with 5, 10 and 15% of blast-furnace slag. The cold uniaxial compaction was realized at a pressure of 500MPa. The obtained materials were sintered at 580°C for 3h under inert atmosphere. Unreinforced aluminum alloy samples were also produced. The characterization of the materials was realized by density and hardness measurements and three-point bending tests. The analysis of its microstructure was realized by scanning electron microscopy. As results, the composites presented a homogeneous distribution of the reinforcing particles and also a progressive improvement of the hardness and the bending strength with the increase of the slag content, producing an increase of 79% in hardness and 128% in flexural strength, when compared to the material without reinforcement obtained by the same process. Such results give the coke coal blast-furnace slag a new possibility of exploitation in the metal-mechanical sector, besides contributing with the environmental issue.

Diagnostics of Fibre-Reinforced Concrete by the Nondestructive Method Based on Mechanoelectric Transformations Phenomenon

This article presents the results of a study of the effect of crack formation in concrete that occurs during uniaxial compression on the parameters of the electrical response under periodic impulse shock action. Researches were conducted on fibre-reinforced concrete samples and samples without reinforcement. It is shown that the method based on mechanoelectric transformations phenomenon can be equally applied to both unreinforced and fibre-reinforced concrete samples.

Microstructure characterization and evaluation of mechanical properties of stir rheocast AA2024/TiB2 composite

In this research, microstructure and mechanical properties of stir rheocast AA2024/TiB2 metal matrix composite have been investigated. The working temperature was 640℃, which was the selected semisolid temperature that corresponds to 40% of the solid fraction. Two weight percentage, 4 wt%, and 6 wt% of the TiB2 reinforcements were added to the matrix. The field emission scanning electron microscope micrographs of the developed composites showed a uniform distribution of the particles in the case of the 2 wt% and 4 wt% of the reinforcements. However, the particles agglomerated as the weight percentages of the reinforcement increases to 6%. The optical microscope of the liquid cast sample showed the dendritic structure, whereas the rheocast samples showed a globular structure. The X-ray diffraction analysis confirmed the distribution of the reinforcements in the matrix and the formation of some intermetallic compounds. Mechanical properties significantly improved by the addition of the reinforcements in the matrix. An increase in tensile strength of 13.3%, 40%, 28%, and 5% was achieved for the unreinforced rheocast sample, 2 wt%, 4 wt%, and 6 wt% reinforced rheocast samples respectively, compared to the liquid cast sample. An increase in 20% of hardness was attained for the composite with 2 wt% TiB2 compared to the liquid cast sample. According to the fractography analysis, small dimples were observed on the fractured surface of the unreinforced rheocast sample, whereas small and large voids were dominant on the fractured surface of the 2 wt% composite, which shows the ductile fracture mode.

Effect of Boron Carbide on Tribological properties of Zinc Aluminium Metal matrix composites

Metal-Matrix Composites (MMCs) are novel composite materials in which nano/micro-phase such as particles or rods like structured materials are reinforced with metals or alloys to improve the physical, mechanical, wear and other properties. The results of previous works have shown that the addition of B4C reinforcement to aluminium alloys has improved the hardness, tensile strength and Young’s modulus. Hence, the present work is focused on development and characterization of B4C reinforced MMCs. evaluating the outcome of the reinforcement on the physical properties such as wear property studies were carried out. The wear results exhibited reduction in wear volume compared to the unreinforced alloy samples and the coefficient of friction is beneath at lofty loads.

Fiber type effect on strength, toughness and microstructure of early age cemented tailings backfill

In this paper, an experimental investigation was carried out to study strength, toughness and microstructural properties of early age cemented tailings backfill (CTB) reinforced with three different types of fiber. Polypropylene, polyacrylonitrile and glass fibers were used in CTB to better understand the effect of fiber addition on the backfill’s strength and toughness properties. Different fiber contents (0 wt%, 0.3 wt%, 0.6 wt% and 0.9 wt%) and curing times (3 and 7 days) were designed for the preparation of CTB samples with two cement-to-tailings ratios (c/t = 1:4 and 1:6). The results indicated that the addition of different type and content of fibers caused a significant change in CTB’s toughness. The fiber content influenced the backfill’s strength performance. The strength gain of fiber-reinforced CTB samples showed an increasing trend as the fiber content rises. Linear relationships could be used to express relations between strength gain and fiber content. The peak strain factor K was defined during the toughness tests. K showed a monotonous increasing trend by the increase of fiber content. The polypropylene fiber was larger than polyacrylonitrile, but less than glass fiber when fiber content was 0.3 wt%. The unreinforced CTB samples were mainly parallel to the axial tensile cracks and a small amount of shear cracks, while the deformation of fiber-reinforced CTB was relatively large, it did not break into small pieces. The crack resistance of fiber-reinforced specimens was notably better than that of unreinforced ones. Failure mechanism and modes of fiber addition in CTB samples were also studied. As a result, this study could provide a theoretical/application basis for mines to reduce cement usage within the CTB matrix, achieve safe mine production, increase ore extraction and reduce ore losses and dilution.

Laboratory research on functioning of bridge structures reinforced with induction brazing

Welded metal bridge spans are one of the most wide-spread types of bridge spans, several thousand of them being in operation along motorways and in city areas in Russia. Similar to other welded structures they are prone to fatigue cracking which is usually repaired using metal plates fixed with high-strength bolts. The Siberian Research Institution of Bridges located in Siberian Transport University has developed the structure and technology of welded bridge span reinforcement using round metal plates fixed by induction brazing. To prove the efficiency of the technology a laboratory research and testing of girders reinforced with round metal plates fixed by induction brazing has been conducted. The research shows that after the induction brazing enforcement the bridge structures that have fatigue cracks obtain strength parameters 25 per cent higher compared to those of completely new unreinforced samples without fatigue cracks. The article is part of the dissertation research Usoltseva A.M.

Mechanical properties and behaviour of high-strength plain and hybrid-fiber reinforced geopolymer composites under dynamic splitting tension

Geopolymer materials have been of particular interest to the construction industry due to their environmental benefits. However, their behaviour has rarely been investigated under dynamic loadings, although it is of fundamental concern to assess their vulnerability against higher loading rates. In this study, the dynamic tensile properties of a newly fabricated high-strength ambient cured geopolymer material and fiber reinforced geopolymer composites (FRGC) are presented. Since geopolymers are intrinsically brittle, novel equal-part blend of hooked-end and spiral-shaped steel fibers at two different fiber volume fractions and hybrid steel-polyethylene combination were used to reinforce the geopolymer matrix. The quasi-static splitting tensile tests were performed using a 300 KN displacement controlled Shimadzu test machine, while a modified Ø100-mm split Hopkinson pressure bar (SHPB) apparatus was used to conduct the dynamic splitting-tensile tests. A high-speed camera was used to capture the fracture development processes and crack-opening of different types of FRGC. The test results show that under quasi-static splitting tension, the unreinforced geopolymer exhibited minimal tensile strain capacity. With the addition of steel fibers and hybrid steel-polyethylene fiber reinforcement, the energy absorption capability of FRGC samples was significantly improved. The dynamic tests reveal the strong strain rate dependency and prominent tensile strength enhancements for all composites, although unreinforced geopolymer samples were more sensitive to the strain rate effect within the considered test range. A comparison between the test data and modified CEB guidelines reflect the non-suitability of code formulae to establish the dynamic increase factor (DIFft) relation for geopolymers. Based on the test data, empirical DIFft relationships are proposed for unreinforced and different types of FRGC samples. It is also indicated by image analyses that the excellent bonding of spiral steel fibers with the geopolymer matrix is befittingly complemented by polyethylene fibers to maintain the material integrity.

FRCM strengthening systems efficiency on the shear behavior of pre-damaged masonry panels: an experimental study

Existing masonry constructions are highly vulnerable to seismic actions, as demonstrated by the severe earthquakes which stroke the Italian territory in recent years, causing great damages, especially in old masonry buildings. Therefore, restoring damaged buildings, with the aim to recover or improve their structural capacity, is a key aspect in the post-seismic interventions. Fiber reinforced composite materials could be effectively used to this purpose. One aspect which is worth to investigate is the application of these reinforcement typologies on damaged structural elements. Even though many experimental campaigns are available concerning the mechanical improvement given by composite materials applied on undamaged structural elements, only few can be found considering strengthening of already damaged masonry walls. The objective of the work here presented is to evaluate the shear response of damaged masonry panels strengthened using fiber reinforced cementitious matrix (FRCM). Two unreinforced brick masonry walls were subjected to diagonal compression tests, producing an extended state of damage. Afterwards, the same walls were strengthened with FRCM and diagonal compression tests were again performed. Comparisons were done between the results of the unreinforced samples and the pre-damaged strengthened ones, in terms of shear strength and post-peak behavior. The FRCM retrofitting system was also used to strengthen an undamaged masonry panel, which was tested in order to analyze similarities and differences with respect to results obtained for pre-damaged samples. The experimental campaign allowed to study the sole contribution of the reinforcement to the shear capacity of the wall panels. Results showed that the presence of FRCM reinforcements on damaged masonry panels influenced the shear behavior of the samples, which experienced a more ductile failure.

Experimental Investigation on Rockbolt Performance Under the Tension Load

Rockbolt performance may vary differently under complex geological and stress conditions, especially dynamic disturbance at deep underground mining. Therefore, reinforcement mechanism needs to be further explored to improve the support effect of rockbolt. In this study, static and dynamic Brazilian splitting tests of steel bar reinforced red sandstones were carried out to investigate the rockbolt performance under tension load. The deformation changes on the specimen’s surface and the rockbolt were recorded during the test. The strengths and failure modes of unreinforced and reinforced Brazilian disc samples were investigated. The results show that the stress of bolt increases steadily during elastic deformation process, indicating that the bolt shares the tension loading, and increases sharply when the bear capacity of specimen descends caused by crack propagation, indicating that the load is transferred from sandstone specimen. Furthermore, most of the damaged reinforced samples were still bonded by rockbolt, when the test finished. Therefore, the reinforcement mechanism can be divided into two phases. The first phase is the intact rock stage, during which the bolt shares stress reinforcing the strength. The second phase is crack propagation stage, in which the bolt restricts the crack propagation and almost bears the load. Compared with the results of unreinforced samples, it can be seen that the bolt can reduce failure of rock and the strength of the reinforced samples is enhanced. The results may provide a reference for analysis of reinforced mechanism and design of rockbolts.

Effect of crosslinker molecular structure on mechanical and thermal properties of resorcinol formaldehyde aerogel

In this paper, three different crosslinking processes were performed on resorcinol formaldehyde (RF) aerogel using methylene diphenyl diisocyanate (MDI) (type 1), MDI and mono ethylene glycol (EG) (type 2), and MDI and glycerol (GL) (type 3) crosslinking agents. The crosslinking processes were done on the final dried gels, not the wet gels. The creation of cross linkage was proved using Fourier Transform Infrared Spectroscopy (FTIR). The changes of mechanical properties and thermal conductivity were attributed to the necks thickness. Atomic Force Microscopic (AFM) confirmed the thickening of the necks by quantitative and qualitative investigations. Compared to the unreinforced sample, the strength of type 3 crosslinked sample ascends by factors of 17.28 and 15.3, in compression and bending tests, respectively. The strain at break for type 2 crosslinked sample was increased 2.05 and 6 times, in compression and bending tests, respectively. Also, type 2 and 3 crosslinked aerogels showed the highest impact energies. The reduced compressive strength data verified that the mechanical strength improvement corresponded to the presence of urethane linkage, not the higher density. The thermal conductivity data revealed that the enhancement of neck size increases the thermal conductivity due to the increase of interparticle connections.

Silk fabric protection obtained via chemical conjugation of transglutaminase and silk fibroin reinforcement

Historic silk fabric is an important part of Chinese precious cultural heritage and its protection has always been a major challenge. This paper proposes a bio-safety method by the chemical conjugation of transglutaminase (TGase or TG) and sodium caseinate (SC), which produced a macromolecular polymer between protein molecules and enhanced silk fabrics. The changes of the mechanical properties of the reinforced silk fabric after washing by 10 cycles were not obvious, indicating good washing durability. After TGase and SC reinforcement, the silk fibroin (SF) solution was sprayed on the surface of silk fabric to improve the mechanical properties, where the secondary structure were formed by the self-assembly of SF to improve the mechanical properties. Therefore, the breaking stress attained the maximum value when the SF solution concentration was 1.0%. Meanwhile, the breaking stress increased by about 20.89% compared with untreated silk fabric. When the artificially alkali aged silk fabric is reinforced, the breaking stress and strain of the reinforced sample increased by 37.77% relative to the alkali aged fabric. The surface morphology and secondary structure transformation of the samples were also analyzed by scanning electron microscopy and Fourier transform infrared spectroscopy, respectively. The results indicated that a significant SF layer was introduced on the surface of the silk fabric and the β-sheet structure increased due to the synergetic role of the macromolecular polymer and SF. Moreover, it is concluded that an increase in temperature and humidity will result in a decrease in the preservation index, which caused the degradation of silk fabric and proved that the preservation time of the reinforced silk fabric in the same environment was longer than that of the unreinforced sample. The biological enzyme chemical conjugation with silk fabric and physical combination of the pure SF solution is expected to be applied to the protection and enhancement of silk cultural relics.

Thermo-mechanical and swelling properties of three-dimensional-printed poly (ethylene glycol) diacrylate/silica nanocomposites

Abstract

Drained volumetric behaviour and static liquefaction of very loose sand reinforced with synthetic fibres

Synthetic fibres may be used to reinforce soils. Fibre reinforcement may, for example, improve the mechanical behaviour of very loose sand which is usually susceptible to static liquefaction. In this study, two types of polypropylene fibres are mixed into sand to explore the effect of fibre reinforcement on drained volumetric behaviour and undrained static liquefaction. Drained and undrained stress-controlled triaxial compression tests are conducted on both unreinforced and fibre reinforced samples which are in very loose states. It is observed that, under drained compression, both unreinforced and fibre reinforced samples show volumetric contraction. In undrained compression the excess pore water pressure eventually becomes almost equal to the initial confining stress in all samples. This represents a state of liquefaction in unreinforced samples, and they become fluidised indicating the effective stress has become zero. However, in reinforced samples, the fluidised condition is absent, indicating that a conventional type of liquefaction has not occurred. It is concluded that static liquefaction in very loose sand can be prevented by fibre reinforcement, as the induced tensile stress in fibres makes the effective stress (that is the stress carried by the soil skeleton) remain above zero even when the excess pore water pressure is equal to the confining stress.

Experimental Research on Mechanical and Energy Characteristics of Reinforced Rock under Dynamic Loading

The properties of anchored surrounding rock may vary considerably under complex geological and stress conditions, especially dynamic loading in deep mining. Therefore, comprehensive study of the reinforced mechanism is required to prevent failures associated with deep mining. In this paper, with sandstone as matrix and steel bar as bolt, the dynamic compression test of reinforced rock was carried out by using a 50 mm rod diameter split Hopkinson pressure bar (SHPB) test device. The mechanical and energy characteristics of reinforced rock under dynamic loading were analyzed. The results show that the dynamic strength of reinforced sample is greater than that of unreinforced sample and increases with the increase of the strain rate. The reflected energy and absorbed energy increase with the increase of incident energy, while the transmitted energy increases slightly. The higher the strain rate, the larger the energy dissipation rate and the higher the degree of fragmentation. It shows that the energy dissipation characteristic reflects the internal damage process to some extent. Compared with the results of unreinforced samples, the reflected energy of reinforced samples significantly increases and the absorbed energy will significantly decrease. It can be seen that the bolt can reduce absorbed energy of surrounding rock, thereby improving the stability of roadway surrounding rock. The results may provide reference for the stability of deep roadway and support design.