Double Punch Test Research Articles

Tensile Strength Properties of Sand-bentonite Mixtures Enhanced with Cement

Measurement of tensile strength of soil by direct methods can be challenging due to difficulties in sample preparation and in fixing the specimen while applying uniaxial tension forces. However the tensile strength of soil samples can be measured by indirect tests, such as the Brazilian and double punch tests, assuming that tensile stress is distributed uniformly on the failure plane. In this study, the tensile strength of statically-compacted sand bentonite and cement-enhanced sand bentonite mixtures is measured in varying curing time periods using the “double punch” test. The compressive strengths of samples are also measured using the unconfined compression test, and the correlation between tensile and compressive strength is discussed in relation to curing time. A simple method is also applied to determine the undrained cohesion and internal friction angle of samples through the Mohr-Coulomb circle method, using the double punch tensile strength and unconfined compressive strength. The results show that cohesion increases in both sand bentonite and sand bentonite-cement samples along with curing time.

Correlation of Tensile Strength of Split Cylinder Test and Double Punch Test of a Rubberized Asphalt Concrete Used in Flexible Pavement Design

Correlation of Tensile Strength of Split Cylinder Test and Double Punch Test of a Rubberized Asphalt Concrete Used in Flexible Pavement Design

Assessing Tensile and Shear Properties of Recycled Sustainable Asphalt Pavement

Hot mix recycling of asphalt pavements is increasingly being used as one of the major rehabilitation methods by various highway agencies. Besides general savings in costs and energy expended, it also saves our natural resources and environment. Recycling process presents a sustainable pavement by using the old materials that could be reclaimed from the pavement; these materials could be mixed with recycling agents to produce recycled mixtures. The important expected benefits of recycling process are the conservation of natural resources and reduction of environmental impact. The primary objectives of this work are evaluating the Tensile and Shear Properties of recycled asphalt concrete mixtures, In addition to the resistance to moisture damage. The impact of implementing three types of recycling agents on asphalt concrete properties was also investigated. For this purpose, old materials reclaimed from field, (100% RAP), virgin filler at 3 percent content by weight of mixture and three types of recycling agents ( soft asphalt cement of penetration grade 200-300, soft asphalt cement of penetration grade 200-300 blended with 4% silica fumes and soft asphalt cement of penetration grade 200-300 blended with 6% fly ash ) at 1.5% content by weight of mixture have been implemented and used to prepare recycled mixtures. Mixtures were subjected to the following tests: Marshall Test (12 specimens), indirect tensile strength test at 20ºC, 25ºC, 40ºC, and 60ºC (48 specimens), indirect tensile ratio ( 12 specimens), double punch shear test (12 specimens).
 It was found that using (soft asphalt cement blended with silica fumes) as a recycling agent revealed better performance results than the other type of recycling agent. The percentages of variation for recycled mixtures with recycling agent of (soft asphalt cement blended with silica fume) when compared to aged mixture were ( -13.8%, -25.05%, 229.5%, -47.67%, ) for properties of ( Marshall stability, indirect tensile strength at 60ºC, tensile strength ratio, double punch test,), respectively.
 

Double-Punch Test of Fiber-Reinforced Concrete: Effect of Specimen Origin and Size

One of the main advantages of the Barcelona test is that the properties of fiber-reinforced concrete (FRC) can be determined by using cylindrical specimens, thereby permitting the use of cores to control the quality of concrete used in construction.; Using the results of an extensive experimental campaign, this paper establishes the relationship between the unitary load of cracking, residual strength and toughness of molded specimens, and cores of concretes reinforced with different types of fibers but with the same aspect ratio. The fiber diameter is observed to signifidantly influence the properties of molded specimens, whereas in the cores, the number of fibers that lose anchoring due to drilling determines the response of the FRC.

Evaluation of mechanical properties of steel-fibre-reinforced concrete exposed to high temperatures by double-punch test

The aim of this investigation was to study the factors influencing the mechanical tensile properties of steel-fibre-reinforced concrete exposed to high temperatures. The properties were estimated by the double-punch test having a high accuracy. Specimens reinforced with fibres of two types (twisted or hooked), two aspect ratios (l/d=60 or 80), and three fibre contents (volume fractions of 0.25%, 0.5%, or 1%) were tested after exposure to four different maximum temperatures (room temperature, 300°C, 500°C, and 700°C). Test results show that the residual compressive strength, DPT tensile strength and rupture energy of the specimens decreased with their increased heating. After the SFRC was exposed to the high temperatures, the relative loss in tensile strength was higher than that in compressive strength, but the relative loss of rupture energy was comparatively lower. After exposure to high temperature, the behaviour of the samples was more sensitive to the volume fraction and aspect ratio of the fibre than to its type. The coefficients of variation (COVs) of the rupture energy for SFRC specimens heated to higher temperatures is similar to those of the tensile strength, although the results are considerably more scattered than the compressive strength. A model predicting the residual tensile strength of heated SFRC measured by the DPT was proposed based on the test results.

Influence of Sample Thickness and Capping on Characterization of Bedding Mortars from Historic Masonries by Double Punch Test (DPT)

For determination of compressive strength of bedding mortar used in historic masonries, a promising moderately-destructive technique is double punch test (DPT). DPT consists of loading prismatic samples of mortar (about 4×4×1 cm3) by means of two circular steel platens (typically 2 cm diameter) and then calculating mortar compressive strength as the ratio of the failure load to the cross section of the circular platens. In this study, the influence of mortar sample thickness and mortar sample capping on the reliability of results obtained by DPT was systematically investigated. The influence of sample thickness was assessed by comparing DPT results obtained for samples with 5, 10, 15 and 20 mm thickness with compressive strength determined by testing reference 4 cm-side cubes. Different mortars were considered (cement, lime-cement, natural hydraulic lime), in order to investigate a wide range of mortar mechanical characteristics. The influence of surface capping was evaluated on a lime-cement mortar by comparing compressive strength determined on reference cubes with strength obtained by DPT on proper samples, without capping and after capping with rubber, gypsum and cement. The results of the study indicate that sample thickness substantially influences mortar compressive strength determined by DPT, which may vary by up to three times depending on sample thickness. A good estimation of the actual mortar compressive strength was obtained when samples with thickness similar to the loading platens diameter were tested, which suggests that choosing the size of the loading platens for DPT based on the thickness of mortar joints under investigation may be an effective way for obtaining reliable estimations. As for the influence of surface capping, in those cases where no mortar sample regularization is possible, because of the poor quality of the mortar, the results of the study indicate that sample capping actually seems necessary in order to avoid significant underestimations of mortar compressive strength. Considering the higher practicality offered by gypsum with respect to rapid-setting cement for surface capping, the use of gypsum seems preferable.

Assessing Tensile and Shear Properties of Aged and Recycled Sustainable Pavement

The effect of two types of recycling agents on aging after recycling properties of asphalt concrete , and the effect of accelerated aging (Short and Long -Term) on physical properties for aged and recycled asphalt concrete were investigated. The preparation of asphaltic mixtures involves the use of penetration grade (40-50) asphalt cement, mineral aggregate with 12.5 mm nominal maximum size, ordinary Portland cement as mineral filler. Specimens were prepared at optimum asphalt content and at asphalt contents of 0.5 percent above, and below optimum using Marshal Method. Mixtures have been subjected to indirect tensile test at 25oC, 40oC, and 60oC and double punch test. Aged specimens were prepared by subjecting the loose asphalt concrete mix to (short-term aging); the mixture was then compacted and subjected to long-term aging process. Recycled mixture was prepared from short and long-term aged asphalt concrete using two different recycling agents at (1.5%) by weight of mixture. The recycled asphalt concrete was subjected to accelerate short and long-term aging. It was found that using (soft asphalt cement blended with silica fume) as a recycling agent revealed better performance than the other type of recycling agent. Short and long-term aging after recycling shows that Indirect tensile strength at 25˚C, was less than that of recycled mix by 43%, while it increases by 16.5% and 78% when tested at 40 and 60 ˚C respectively; Punching shear strength was higher than that of recycled mixed by 34% at optimum asphalt content.

Fibre distribution in macro-plastic fibre reinforced concrete slab-panels

This paper focuses on the study of the influence of flowability and wall-effects of the formwork in the orientation pattern of macro-plastic fibres. In order to identify the preferential orientation of fibres caused by the geometry of slabs, pairs of specimens drilled from PFRC slabs with different width/length – ratio are tested using the multidirectional double punch test (MDPT). The results show that plastic fibres tend to be oriented parallel to the walls or surfaces of the formwork and perpendicular to the flow direction for a free surface flow. The side walls slightly redistribute the fibre orientation, as the transverse dimension of the slabs is reduced. Additionally, a computed tomography (CT-scans) was, for the first time, successfully applied to assess the amount of macro-plastic fibres as well as its distribution and orientation in a prismatic core.

Multidirectional double punch test to assess the post-cracking behaviour and fibre orientation of FRC

The wide variety of tests currently used for the characterization of fibre reinforced concrete (FRC) only allow a unidirectional characterization (without considering the orientation of the fibres in the matrix). However, from a design-oriented perspective, the anisotropy due to the dispersion and orientation of fibres has to be taken into account when characterizing the mechanical behaviour of the material. In this paper, an alternative to the conventional tests applied for the characterization of FRC is proposed. The multidirectional double punch test (MDPT) consists of a double punch test applied to a cubic specimen. Due to the specimen shape in a single procedure an estimation of the fibre orientation efficiency can be obtained, establishing a link between the mechanical properties of FRC with the fibre orientation. Thereby, this paper represents a meaningful contribution to provide a step towards the development of a rational and design-oriented constitutive model for real-scale structures.

고온노출된 강섬유보강 콘크리트의 인장성능에 대한 실험적 연구

본 논문에서는 고온 노출된 강섬유 보강콘크리트의 인장성능을 실험적 연구를 통하여 검증하고자 하였다. 실험방법은 낮은 변동성을 특징으로 하는 DPT를 이용하였다. 일반적인 후크강섬유와 트위스트 강섬유, 0.25~1.0%의 강섬유 혼입률, 섬유형상비를 변수로 하여 실험을 수행하였다. 시험체는 고온 전기로에서 <TEX>$300^{\circ}C$</TEX>, <TEX>$500^{\circ}C$</TEX> 및 <TEX>$700^{\circ}C$</TEX>의 온도에서 2시간 노출되었으며, 12시간 동안 자연냉각 된 후에 가력되었다. 실험결과, 섬유혼입률이 증가할수록, 형상비가 클수록, DPT 인장강도가 증가하는 것으로 나타났다. 섬유종류의 영향은 다른 변수에 비하여 그 영향이 미미한 것으로 판단되었다. 실험결과를 근거로 강섬유의 혼입량과 형상비의 영향을 고려할 수 있는 노출온도 수준에 따른 DPT 인장강도 예측식을 제시하였다. Tensile strength of steel fiber-reinforced concrete was investigated with experimental program. For the investigation, Double Punch Test, which is known as a test method with low validity, was used. Fiber type(hooked and twisted fiber), mix ratios by volume ranged from 0.25% to 1.0%, aspect ratio were used as variables for the tests. The specimens were exposed to the elevated temperatures(<TEX>$300^{\circ}C$</TEX>, <TEX>$500^{\circ}C$</TEX> and <TEX>$700^{\circ}C$</TEX>) for 2 hours and placed at ambient temperatures for 12 hours before testing. Results demonstrated that residual tensile strength increases as mix ratio and aspect ratio increase. The effect of fiber type was insignificant. Based on the test results, the linear equation for prediction of DPT residual tensile strength was proposed in terms of mix ratio and aspect ratio.

DPT 실험을 이용한 고온노출된 강섬유보강콘크리트의 인장강도 평가

Steel fiber-reinforced concrete (SFRC) is widely used for tunnel lining structure such as shot-crete in NATM tunnel and segment in TBM tunnel. In tunnel fire accidents, structural performance of a lining is very important because the lining is the structure that directly exposed to fire. In this study, the effects of high temperatures, mix ratios and types on failure pattern, DPT tensile strength and coefficient of variation were investigated through Double Punch Tests (DPT) of SFRC subjected to high temperatures. In the results, it is confirmed that the residual DPT tensile strength increases as for SFRC and this is more in SFRC with higher mix ratio. But, the equation for evaluation of DPT tensile strength does not involve the number of failure surfaces SFRC specimens subjected to high temperatures, therefore, it is required to investigate more fracture energy in DPT tests.

Double Punch Test: Simple Performance Test to Evaluate the Fatigue and Rutting Potential of Asphalt Concrete

The primary distresses of the asphalt pavement are rutting, fatigue cracking, and thermal cracking. Laboratory tests can be conducted to characterize the expected performance of asphalt concrete in the field. This study evaluated the double punch test (DPT) as an alternative test method to characterize the fatigue and rutting of asphalt concrete due to its simplicity. In DPT, a cylindrical asphalt concrete specimen is compressed vertically through two steel punches placed concentrically on the top and bottom. The specimen fails along the diametrical plane due to the tensile strain generated in the tangential direction. Double punch tests were performed at intermediate and high temperatures to characterize fatigue and rutting potential of asphalt concrete, respectively. The DPT results were found to correlate well with fatigue parameters from indirect tensile (IDT) tests for fatigue and flow number test results for rutting, both of which have been reported to correlate well with field fatigue and rutting performance, respectively. The results indicate that the DPT can serve as a viable alternative to evaluate the fatigue and rutting behavior of asphalt concrete.

TBM 터널 세그먼트용 강섬유보강 콘크리트의 인장특성 평가

TBM 터널 세그먼트의 철근량을 감소시키기 위한 연구로서, 강섬유 보강콘크리트의 사용이 시도되고 있다. 이와 같은 터널 세그먼트에는 철근의 감소로 인해 필요한 인장성능의 확보를 위하여 숏크리트에 사용되는 강섬유에 비해 매우 높은 형상비의 강섬유를 활용하는 것이 필요하다. 본 연구에서는 강섬유의 형상비가 80인 강섬유 콘크리트의 인장특성을 휨시험과 Double Punch Test를 통해 평가하였다. 휨시험결과, 사용된 강섬유의 충분한 부착강도로 인해 30%~150%의 강도 증진을 나타냈으며, 오영훈(2008)의 예측식을 통한 휨인장강도예측이 가능한 것으로 판단된다. 이 실험을 근거로 설계에 필요한 직접인장강도를 ACI와 RILEM의 식에 의해 평가한 결과, 적용기준에 따라 큰 차이가 있는 것으로 나타났다. 또한, DPT 실험을 통해 RILEM에서 권고하고 있는 직접인장강도의 정밀도 있는 예측이 가능한 것으로 판단된다. In order to reduce the amount of steel reinforcements in TBM tunnel segments, the use of Steel Fiber Reinforced Concrete(SFRC) is being tried. The steel fibers with higher aspect ratio than that used in tunnel shotcrete are preferred to compensate the deficiency in tensile strength of the segments. In this study, the tensile properties of SFRC with aspect ratio of steel fibers equal to 80 were evaluated through flexural test and Double Punch Test. In the results of flexural test, flexural strengths of the SFRC were increased about 30%~150% thanks to bond of steel fibers used to concrete and could be properly predicted by the equation proposed by Oh(2008). There was a great difference in the estimated direct tensile strengths of the SFRC by the equations presented in ACI and RILEM. It was found that the Double Punch Test could be suitable methodology to estimate the direct tensile strength presented in RILEM of the SFRC.

Crack localization in a double-punched concrete cuboid with time reverse modeling of acoustic emissions

Time reverse modeling (TRM) is successfully applied to localize acoustic emissions (AE) obtained from a physical experiment (double punch test) on a 118 × 120 × 160 mm concrete cuboid. Previously, feasibility studies using numerical (Ricker wavelet) and experimental (pencil-lead break) excitations are performed to demonstrate the applicability of TRM to real AE waveforms. Numerical simulations are performed assuming an uncracked and heterogeneous concrete model. The localization results from the numerical and experimental feasibility studies are compared and verified. The AE recorded during the double punch test are localized in a three-dimensional domain using TRM. The localization results are superposed with the three-dimensional threshold-segmented crack patterns obtained from X-ray computed tomography scans of the failed concrete cuboid. The presented TRM approach represents a reliable localization tool for signal-based AE analysis.

Determination of Tensile Strength of Compacted Loess by Double Punch Test

Through double punch test, the tensile strength of compacted loess is determined under different water contents and different dry densities, the relationship between tensile strength, water content and the dry weight density is discussed, and their relationship is established. Comparing with Brazilian test, it proved the feasibility of determining tensile strength of compacted loess with double punch tests.

Numerical modeling of the double punch test for plain concrete

Double punch test is used to indirectly assess the tensile strength of plain concrete, f t . For this normalized test, the tensile strength is obtained as a function of the failure load, P, which is expressed as f t = F ( P ) . Different authors have proposed different expressions for the relation F ( · ) , yielding scattered values of f t . None of these alternatives is universally recognized as being more suitable than the others. In fact, these expressions are mainly based on elastic models considering the maximum tensile stress under the load P and f t is obtained as an output of the linear model. A numerical simulation allows using models in which f t is an input of the material model and the corresponding failure load P is obtained associated with each value of f t . In the present work, double punch test is simulated numerically considering two alternatives for modeling plain concrete accounting for damage and cracking: (a) the nonlocal Mazars damage model and (b) an heuristic crack model including joint elements in an a priori defined crack pattern. Numerical results are validated with experimental data and compared with the analytical expressions available in the literature.

Finite Cylinders of Si1 − x Ge x Alloy Under the Double-Punch Test and Effect on Three Valence-Bands

An analytical solution for the stress and strain fields within a finite circular solid cylinder of Si1 − xGex alloy under the double-punch test is presented. The method of solution uses the displacement function approach, together with proposing a new expression for the displacement function so that all of the boundary conditions are satisfied exactly. The present solution covers the solution by Wei and Chau [1] for isotropic cylinders under the double-punch test when the isotropic limit case is considered. Numerical results show that strain and stress distributions within the cylinder are not uniform, and strain or stress concentrations are usually developed near the end surfaces, but the strain and stress distributions within the central part are relatively uniform. Moreover, according to quantum mechanics and the energy band theory, the effects of strain on three valence bands, namely the heavy hole (HH) band, the light hole (LH) band and the split-off (SO) band of Si1 − xGex alloy and the corresponding conductivity masses are analyzed. It was found that the quantum behavior of the three valence bands, such as the energy distribution, the shape of constant energy surfaces, the magnitude and the distribution pattern of the conductivity masses can be modified considerably by the external force applied in the double-punch test, depending on the proportion between silicon and Germanium in Si1 − xGex alloy.

An analytical solution for inhomogeneous strain within cylinders of silicon and effect on quantum band structure under the double-punch test

An analytical solution for inhomogeneous strain distributions within a finite cylinder of silicon under the double-punch test is obtained. The stress function method is employed and a new expression for the stress function is proposed so that all of the governing equations and the boundary conditions are satisfied exactly. The solution for isotropic cylinders under the double-punch test is recovered as a special case. Numerical results show that the strain singularities are usually developed near two end surfaces, but the strain distributions are relatively uniform in the central part of the cylinder. The largest tensile strain is always induced along the axis of loading. In addition, based on the envelope-function method of energy-band theory and quantum mechanics, the effect of external loads on the valence-band structure of silicon is analyzed. The spin–orbit interaction is considered. It is found that external load under the double-punch test can alter considerably the quantum behavior of energy-band structure of silicon, which manifests in the change of the constant-energy surfaces of the heavy-hole band, the light-hole band, the split-off band and the corresponding conductivity masses. The present study provides an alternative method to investigate the electro-optic properties of strained silicon.

Double Punch Test to control the energy dissipation in tension of FRC (Barcelona test)

Current testing methods used to measure tensile properties of Fiber Reinforced Concrete (FRC) are mainly based on bending test of beam specimens. They normally show a considerable scatter that makes difficult the quality control, as in particular when such properties are intended to estimate the strength of structural members. In order to improve the material assessment procedure, the Double Punch Test (DPT) has been recovered for the quality control of the tension behaviour of FRC. Former experimental research showed the feasibility of the test and a reduction of the scatter in the values of the tensile strength and of the toughness. This paper describes the results of an experimental program carried out using both DPT and bending test on FRC with different type of fibers, concretes and fiber contents. In addition, a correlation between both tests is proposed. Its application to steel and polyolefin FRC specimens shows very good results.

Quality control test for SFRC to be used in precast segments

Current methods to measure tensile strength and toughness in Steel Fiber Reinforced Concrete (SFRC) show a considerable scatter. That scatter makes difficult the quality control, in particular when such properties are taken into account in the evaluation of overall strength of the precast tunnel lining segments, as in the case of the Line 9 of the subway in Barcelona. In order to improve the material assessment procedure, the Double Punch Test (DPT) has been recovered for the quality control of the tension behavior of SFRC. Results of an initial feasibility research are presented, showing a significant reduction of the scatter in the values of the tension strength and in the toughness. Other advantages shown by this test are: (1) the reduced size 150x150 mm of the cylindrical specimens, compared with those used in beam test, and (2) the use of a conventional compression press controlled by displacement. (A) This paper was presented at Safety in the underground space - Proceedings of the ITA-AITES 2006 World Tunnel Congress and the 32nd ITA General Assembly, Seoul, Korea, 22-27 April 2006. For the covering abstract see ITRD E129148. Reprinted with permission from Elsevier.