Prismatic Specimens Research Articles

Dispersion of graphene nanoplatelets reinforcing type II cement paste

One of the most recent, affordable and at the same time cutting-edge class of carbon nanostructures are the graphene nanoplatelets (GnPs). They depict multifunctional capabilities such as improved mechanical properties in conjunction with high electrical and thermal conductivity making them suitable for the development of multifunctional materials. One of the most essential parameters, to successfully exploit the GnPs characteristics, is their homogeneous distribution inside the matrix. In this direction, the applicability of a method, similar to the one applied for the preparation of carbon nanofiber and carbon nanotube reinforced Type I cement nanocomposites, is here investigated. Ultrasonic processing and treatment with a 3rd generation superplasticizer was used to uniformly disperse the GnPs (of lateral size equal to 8 μm) in the mixing water. This admixture was exploited as a GnPs dispersing agent, as it is commonly used, to improve the workability of cementitious materials and is fully compatible with the matrix. The nanocomposites were prepared using Type II cement. The electrical resistivity of the nanocomposites developed was evaluated. Three-point bending tests were performed at prismatic beam specimens with an artificial notch at the age of 28 days. Both the effects of dispersing agent (superplasticizer) concentration and ultrasonication energy application were investigated. It was concluded that both the admixture concentration and ultrasonic energy application strongly affect the GnPs dispersion and reinforcing efficiency.

On Selection of the Model of Limiting State of Heat-Resistant Materials Under Uniaxial Asymmetric Loading

The limiting state of specimens made of heat-resistant nickel alloys under the combined action of static and cyclic loading in a wide range of temperatures is studied. The solution is constructed using the model of limiting state that relates the ultimate stresses in the form of exponential transcendent function. Computational results are validated experimentally for solid prismatic specimens.

Crack initiation of selected geopolymer mortars with hemp fibers

The aim of this paper is to quantify particularly fracture properties of selected types of mortars prepared with an alkali activated binder and hemp fibers. The main attention is focused on evaluation of three-point bending fracture tests of prismatic specimens with an initial central edge notch made of alkali activated fly ash mortars. The load versus crack mouth opening displacement (F–CMOD) diagrams were recorded during the fracture tests and subsequently evaluated using the Double-K fracture model. This model allows the quantification of two different levels of crack propagation: initiation, which corresponds to the beginning of stable crack growth, and the level of unstable crack propagation. The course of fracture tests was also monitored by acoustic emission method.

Investigating the fracture behavior of Portland limestone: an experimental study

An experimental investigation of the mechanical and fracture characteristics of the ‘Grove Whitbed’ Portland limestone is undertaken aiming to enhance understanding of the structural behavior of this natural building stone, commonly used in both new and restoration projects in Edinburgh, Scotland. A series of prismatic specimens, bearing a machined notch at their mid-span and comprising combinations of three different geometries (span/depth ratios) and three different sizes (span lengths) were subjected to three-point bending testing. The effect of specimen shape and size on flexural strength, deflection at mid-span, crack mouth opening displacement (CMOD) and fracture energy was studied. Despite the scattering of results which is significant but common in studies of the mechanical behavior of similar geomaterials, trends observed comprise (a) the negative correlation between the flexural strength of Portland limestone test specimens and their span lengths for all three shapes and (b) the positive correlation between fracture energy and specimen size. Conclusions drawn are in good agreement with similar ones for other quasibrittle materials and contribute to the assessment of the fracture behavior of full size structural members that are often beyond the range of possible failure testing.

Stress‐Strain Relation of Steel‐Polypropylene‐Blended Fiber‐Reinforced Concrete under Uniaxial Cyclic Compression

This paper investigates the cyclic stress‐strain behavior of steel‐polypropylene‐blended fiber‐reinforced concrete (BFRC) under uniaxial cyclic compression. A total of 48 prism specimens were tested for different fiber volume fractions and aspect ratios. The results show that the introduction of blended fibers has synergetic effects on improving the cyclic behavior of concrete in terms of peak strength, postpeak ductility, hysteretic energy dissipation, and stiffness degradation. Moreover, the increase in the volume fractions of both steel and polypropylene fibers can lead to a remarkable decrease in plastic strain accumulation. Furthermore, the stiffness degradation ratio as well as the stress deterioration ratio of BFRC can be significantly alleviated in comparison with those of plain concrete, notwithstanding that the degradation amount is insensitive to the variations of fiber parameters. Subsequently, based on the test results, a constitutive model is developed to generalize the cyclic stress‐strain responses of BFRC, with the contributions of blended fibers taken into account. The developed model is then verified by independent experimental results and other test data reported in the literature. It is observed that the prediction yields a close estimation of the cyclic compressive behavior of BFRC with varying fiber parameters.

Mechanical properties of SFRC using blended manufactured and recycled tyre steel fibres

This paper investigates the mechanical properties of 10 steel fibre reinforced concrete (SFRC) mixes at fibre dosages of 30, 35 and 45 kg/m3. Manufactured Steel Fibres (MSF) are used on their own, or blended with sorted steel fibres recycled from end-of-life tyres (RTSF). To characterise the flexural behaviour of the mixes, two flexural test methods, BS EN 14651:2005 3-point notched prism tests and ASTM C1550-05 centrally loaded round panel tests are employed. A strong correlation is found in the flexural behaviour of the SFRC prism and round panel specimens, with corresponding conversion equations proposed. The mechanical properties of hybrid mixes using RTSF vary depending on dosages, but are comparable with those of MSF-only mixes at the same fibre dosage. A positive synergetic effect is derived from hybrid mixes containing 10 kg/m3 of RTSF.

Thermo-physical and mechanical characteristics of sand-based lightweight composite mortars with recycled high-density polyethylene (HDPE)

Today, a large number of research projects are concerned with the recycling of plastic waste to be reused in the field of construction. This work, which is part of a research programme, focuses on the valorization of plastic waste from high density polyethylene (HDPE) pipes, to be used as aggregates. The HDPE aggregates were used as partial replacements of natural sand at 0, 15, 30, 45 and 60%, for the same volume. Only one particle size of the HDPE aggregates was used in each composition of the lightweight composite mortars (LWCM). Prismatic specimens 4 × 4 × 16 cm3 were prepared with a ratio W/C = 0.5. The density of the composite mortars was measured in the fresh and cured states. The compressive and flexural strengths, the thermo-physical characteristics as well as the ultrasonic pulse velocity (UPV) and the dynamic modulus of elasticity (Ed) were also investigated. In addition, composite mortars were analysed using a Scanning Electronic Microscope (SEM). Laboratory tests revealed encouraging results. Compared to the normal composite mortar (NMC), outcomes showed that composite mortar with 60% HDPE aggregates (LWCM60) increased ductility and reduced by 73% the dynamic modulus of elasticity. Analyses using SEM indicated that HDPE aggregates exhibited low adhesion to the cementitious matrix and mortars with higher HDPE rates improved the energy performance of composite mortars (LWCM).

Behaviour and strength assessment of masonry prisms

This is a case study presenting the cracking behavior and assessment of the compressive strength of masonry prisms. The compressive strength of masonry was determined by performing laboratory tests on 192 masonry prism specimens corresponding to 3 specimens each in 64 groups. The variables considered in the experimental program are type of brick, strength of masonry and height-to-thickness (h/t) ratio of the prism specimen. Pressed earth bricks and burnt clay bricks were used for the preparation of masonry prisms. A mathematical model is also proposed for the estimation of compressive strength of masonry prisms by performing a statistical multiple regression analysis on 232 data sets, which includes 64 test data from the present study and 168 test data published in the literature. The model was developed based on the regression analysis of test data of prisms made of a variety of masonry units namely clay bricks, pressed earth bricks, concrete blocks, calcium silicate bricks, stone blocks, perforated bricks and soft mud bricks. The proposed model not only accounts for the wide ranges of compressive strengths of masonry unit and mortar, but also accounts for the influence of volume fractions of masonry unit and mortar in addition to the height-to-thickness ratio. The predicted compressive strength of prisms using the proposed model is compared with 14 models available in published literature. The predicted strength was found to be in good agreement with the corresponding experimental data.

Accuracy-enhanced constitutive parameter identification using virtual fields method and special stereo-digital image correlation

The virtual fields method (VFM) is generally used with two-dimensional digital image correlation (2D-DIC) or grid method (GM) for identifying constitutive parameters. However, when small out-of-plane translation/rotation occurs to the test specimen, 2D-DIC and GM are prone to yield inaccurate measurements, which further lessen the accuracy of the parameter identification using VFM. In this work, an easy-to-implement but effective “special” stereo-DIC (SS-DIC) method is proposed for accuracy-enhanced VFM identification. The SS-DIC can not only deliver accurate deformation measurement without being affected by unavoidable out-of-plane movement/rotation of a test specimen, but can also ensure evenly distributed calculation data in space, which leads to simple data processing. Based on the accurate kinematics fields with evenly distributed measured points determined by SS-DIC method, constitutive parameters can be identified by VFM with enhanced accuracy. Uniaxial tensile tests of a perforated aluminum plate and pure shear tests of a prismatic aluminum specimen verified the effectiveness and accuracy of the proposed method. Experimental results show that the constitutive parameters identified by VFM using SS-DIC are more accurate and stable than those identified by VFM using 2D-DIC. It is suggested that the proposed SS-DIC can be used as a standard measuring tool for mechanical identification using VFM.

Effectiveness of mineral additives in mitigating alkali-silica reaction in mortar

The effectiveness of mineral additives in suppressing alkali-silica reactivity has been studied in this work. Experimentation has been performed in accordance with the procedures prescribed in ASTM C 1567. In the scope of the investigation, a quarry aggregate which was reactive according to ASTM C 1260 was tested. In the experimental program, prismatic mortar specimens measuring 25x25x285 mm were produced. Ten sets of production, three specimens for each set, were made. Length changes were measured at the end of 3, 7, 14 and 28 days and then expansions in percentage have been calculated. Fly ash, silica fume, and metakaolin have been used as cement replacement in different ratios for the testing of the alkali-silicate reactivity of the aggregate. In the mixes performed, the replacement ratios were 20%, 40%, and 60% for the fly ash, and 5%, 10%, and 15% for the silica fume, and 5%, 10%, and 15% for the metakaolin. Mixes without mineral additives were also produced for comparison. The beneficial effect in suppressing alkali-silica reactivity is highly noticeable as the replacement ratios of the mineral additives increase regardless of the type of the mineral additive used. Being more concise, the optimum concentrations of using silica fume and metakaolin in mortar in suppressing ASR is 10%, respectively, while it is 20% for fly ash.

Specimen size effect on compressive and flexural strength of high-strength fibre-reinforced concrete containing coarse aggregate

Abstract It is a well-known fact that the size of the sample influences values of mechanical properties of concrete measured during the tests. However, the comparison of results of various researchers clearly shows that the importance of this effect varies for different types of concrete. The paper presents outcomes of extensive experimental study focused on determination of relations between the size of the specimen and results of mechanical tests of high-strength fibre-reinforced concrete (HSFRC) with coarse aggregate (maximum aggregate size 16 mm). The main observed parameter was compressive strength. Six different HSFRC mixes having the expected compressive strength between 100 and 175 MPa were investigated. Cube samples of four sizes – 40, 100, 150 and 200 mm – were examined. The results proved that the size dependence of compressive strength diminishes with increasing strength of concrete. For very high strength materials (more than 130 MPa), the results were almost size independent. Additionally, flexural strength of two high-strength concrete mixes was measured on prismatic specimens of two different sizes. The results indicated that flexural strength of HSFRC with coarse aggregate is size dependent without regard to expected compressive strength. Conversion factors for the tested type of material were proposed for both compressive and flexural strength measurements.

An Anisotropic Model for Granular Material Based on Experiments

Soil is a heterogeneous material and most natural soil deposits show a definite stratification. The mechanical behaviour of such material is generally different in different directions, especially in the direction parallel and perpendicular to the stratification. A series of isotropic compression tests were carried out to study the behavior of granular material produced under controlled stratification in the laboratory. These tests were conducted both on cylindrical and square prismatic tri-axial specimens. It was observed that for hydrostatic loading, the strain response was different in different directions, especially in directions parallel and perpendicular to the direction of soil deposition. A definite trend of anisotropy was observed in the deformation pattern. The observed anisotropy is modeled in this paper by treating soil-dilatancy as a variable quantity. The equation of the plastic potential surface of the model which obeys a non-associated flow rule, is assumed to be dependent on three main variables confining pressure ( $$\sigma_{3}$$ ), void ratio (e) and the angle of bedding plane orientation (δ) during deposition. The angle of bedding plane orientation (δ) was measured with respect to the direction of the major principal stress. The model has a cap yield surface in the isotropic stress direction, which is supplemented by a shear hardening Mohr–Coulomb surface in the deviator direction. This paper focuses on predicting the anisotropic strain response of stratified soil deposits subjected to isotropic compression. The proposed anisotropic model incorporates within an existing strain-hardening sand model, a modified cap yield surface and a modified plastic potential function related to the cap surface, to account for the anistropic response observed in isotropic compression tests. The two dimensional stress–strain model was extended to three dimensional Cartesian space. The strain anisotropy observed in the isotropic compression tests was predicted by the three dimensional anisotropic model proposed for granular materials.

Effects of fibers and conventional reinforcement contents on fibers scaterring in prismatic bars

This paper presents results from a second stage of an experimental study of the dependence of steel fibers distribution along RFC prismatic specimens on the conventional reinforcement ratio and on the total amount of fibers in the concrete mix. The experimental program included two types of prismatic specimens with 30- and 60- kg/m3 of hooked-end steel fibers. Each specimen was sawed into equal segments and the numbers of fibers appearing at the cross-sections were counted and used for a further statistical analysis. This analysis comprised calculations of the average value and standard deviation of a non-dimensional variable, which represents the distribution of the total steel along the specimen. They were used to calibrate a theoretical model, which had been previously proposed by the authors. The test results showed reasonable to good agreement with the theoretical model. A comparison between the results of the 30- and 60-kg/m3 fibers shows that as the conventional reinforcement ratio increases, the standard deviations for the different mixtures approach each other.

Effect of NaOH concentration and curing regime on geopolymer

Abstract The effect of alkali concentration and curing temperature regime on fly ash-based geopolymer pastes was investigated in this study by using NaOH solutions. Prismatic specimens were molded, cured at 65 °C and 85 °C and submitted to flexural and compressive strength tests. Unreacted fly ash and geopolymers were characterized by X-ray diffraction and thermogravimetric analysis. In general, the mechanical strength was enhanced by increasing the molar concentration and the curing temperature. This trend was confirmed by thermogravimetric data. However, for a lower amount of NaOH there were no significant differences between the strength results. The mixture with the highest strength was obtained with the 16 M NaOH solution and curing temperature of 85 °C, which resulted in flexural strength of 4.20 MPa, compressive strength of 21.35 MPa and also the highest weight loss of 9.89%.

Fragmentation of Mansurov granite under quasi-static compression

The fragmentation statistics was studied in the quasi-static compression experiments conducted on prismatic specimens of Mansurov granite. The statistical analysis showed that the cumulative fragment mass distribution for granite specimens is well described by a power law function, but the fragment number-sieve size distribution deviates from the power law in the range of are equal to about 1 mm. In order to explain this fact, we investigated the structure of fractured material (Computed Tomography and microstructures study in thin sections). A sharp increase the number of grains in the range of size from to 0.5 mm to 1 mm and a change in the fragment shape (from splinter to oval) allow us to suppose that there is an addition fracture mechanism associated with disintegration of feldspar and amphiboles grains.

Interfacial Fracture Toughness of Adhesive Resin Cement-Lithium-Disilicate/Resin-Composite Blocks.

Resin composite blocks (RCB) are advocated as alternative to ceramic blocks (CB). Prior to use, adherence to these materials should characterized. This study aimed to test the null hypothesis (H0 ) that material and surface treatment combinations do not influence interfacial fracture toughness (KIC ) of a self-cured adhesive resin cement [RelyX Ultimate (RXU)] to RCB or CB, under nonaged and aged conditions. Two RCB, Lava Ultimate (LU) and Enamic (EN), and one CB, IPS e.max Press (EMP) were used. Half-size [(6 × 6 × 6 × 6 mm)] specimens were prepared for EMP (n = 30), EN (n = 30), and LU (n = 60). RCB specimens were prepared by wet cutting/grinding, while CB specimens were pressed. Surfaces of EMP and EN were preconditioned with hydrofluoric acid (5%); surfaces of LU were sandblasted with either 27 μm alumina (LUS) or 30 μm silica-modified alumina Rocatec soft (LUR). All specimens were bonded with Scotchbond Universal adhesive and RXU. Additionally, twenty (4 × 4 × 4 × 8 mm) RXU specimens were prepared. All specimens were stored in water at 37°C and tested after 1 and 60 days. Interfacial KIC was determined with the notchless triangular prism specimen KIC test. Results were analyzed with two-way ANOVA and Scheffé multiple means comparisons (α = 0.05). Preconditioned and selected fractured surfaces were characterized with scanning electron microscopy. At 24 hours, LUS-RXU and LUR-RXU had significantly higher interfacial KIC than EN-RXU and EMP-RXU and were not different from KIC of RXU. Aging lead to a significant decrease in KIC of RXU and interfacial KIC of LUS-RXU, LUR-RXU, and EMP-RXU; interfacial KIC of EN-RXU was not affected. Based on the results, H0 was rejected. Under the conditions of this study, at 24 hours, interfacial KIC of LUS-RXU and LUR-RXU was superior to EMP-RXU and EN-RXU. Aging in water at 37°C did not affect interfacial KIC of EN-RXU but adversely affected KIC of RXU and the other interfacial KIC . The results suggest that RXU and its adherence to LU and EMP deteriorates upon exposure to water at 37°C. In making clinical decisions related to material selection, practitioners should consider in vitro results.

On necessary precautions when measuring solid polymer linear viscoelasticity with dynamic analysis in torsion

Solid polymer linear viscoelasticity in shear is often characterized by applying torsion and using the Saint-Venant solution when rectangular prismatic specimens are considered. It is shown that experimental dynamic torsion tests can show a dependency of the storage modulus and damping factor on the dimensions of the rectangular prismatic specimen when linear temperature ramps are applied. While the discrepancy of damping factor is explained by temperature heterogeneities and can be corrected easily by applying temperature steps, the inconsistency of storage modulus is due to an invalid application of the Saint-Venant solution. Finite element simulations allowed definition of the sample dimensions for which the Saint-Venant solution provides a good approximation, and a coefficient is given to correct the results obtained with commercial instruments when other sample dimensions are used.

Stress-Strain Relationship of Plastic Fiber Reinforced Rubber Concrete

Abstract The uniaxial compression tests were carried out on the prism specimens of plastic fiber–reinforced rubber concrete with three water-binder ratios and six kinds of plastic fiber contents, and the stress-strain curves were monitored. According to the uniaxial compression test, the change rule of the rising and falling of the stress-strain curve and the change of the peak strain were analyzed. Based on the features of the stress-strain curves, the uniaxial compressive constitutive model for plastic fiber–reinforced rubber concrete is proposed containing constitutive parameters A and B. By using the regressive analysis with the least squares principle method for the experimental data, we propose the mathematical expression of the constitutive parameters “a” and “b” of the rubber concrete, which demonstrates the specific relationship between the constitutive parameters A and B. Thus, the constitutive equation for plastic fiber–reinforced rubber concrete was obtained.

Postcracking residual strengths of fiber‐reinforced high‐performance concrete after cyclic loading

The effect of fatigue loads on one of the main mechanical properties of fiber‐reinforced high strength concrete (FRHSC) is studied in this work. In particular, this paper analyzes the variations in the residual tensile strength of steel fiber‐reinforced concretes following cyclic flexural loading, which causes a predefined level of damage. To do so, a total of 40 prismatic specimens were tested. The specimens were not notched, but had previously been subjected to precracking. This has a similar effect to notching, but with a much smaller radius around the edge of the crack, which is therefore more vulnerable to fatigue. The results show that the damage provokes a progressive reduction in the residual traction strength. The study proposes two numerical expressions for the stress–crack width softening curves under tensile loads: an exponential formulation and a potential formulation. In both cases, the coefficients of both formulations depend on the damage that is induced. In addition, the proposal is to use fitted curves of the above‐mentioned potential type.

Compressive behavior of stirrup-confined concrete under dynamic loading

Systematic experiments were designed and performed to investigate the compressive behavior of cuboid stirrup confined concrete under dynamic loading. A total of 123 prismatic concrete specimens with four stirrup volume ratios were tested under three levels of strain rates with the help of an electro-hydraulic servo-controlled concrete testing system. Photos of the failed specimens and the complete stress–strain curves were obtained under the strain control loading scheme. The mean values and the standard deviations of stress–strain curves were also obtained and analyzed. The results show that the strength of concrete are enhanced by the stirrups as well as strain rates. The enhancement of stirrup confinement and the enhancement of strain rate are comparable to each other. The stochastic damage model is adopted to describe the nonlinear performance and the randomness of concrete. Based on the experimental data, the model is verified and the parameters are identified. This study provides a foundation for the dynamic analysis of concrete structure.