| 1. |
- Ahmed, Lamis, et al.
(författare)
-
Numerical modelling and evaluation of laboratory tests with impact loaded young concrete prisms
- 2016
-
Ingår i: Materials and Structures. - : Springer Science and Business Media LLC. - 1359-5997 .- 1871-6873. ; 49:11, s. 4691-4704
-
Tidskriftsartikel (refereegranskat)abstract
- Numerical modelling in combination with in situ measurements, observations and laboratory testing will be important to future establishment of reliable guidelines for efficient civil and engineering work involving concrete casting close to e.g. blasting operations. Results from laboratory tests with impact loaded young concrete prisms are here evaluated using a 3D finite element model. Solid elements are used and a non-linear material model implemented, capable of describing cracking during stress wave propagation. The position of cracks and measured particle vibration velocities are calculated and compared with laboratory test results. The damaging effect of impact vibrations is evaluated using crack width and fracture energy as damage criteria. Alternative geometry for the test prisms, with a notched section, is analysed. This will give one wide crack at the centre of the prism instead of two or three cracks distributed over its length which will make future laboratory test more efficient and reliable. Recommended damage limits at concrete ages of 4, 6, 8 and 12 h are given, based on numerical calculations for concrete strength class C25 and C50.
|
|
| 2. |
- Arraigada, M, et al.
(författare)
-
Evaluation of Accelerometers to Determine Pavement Deflections under Traffic Loads
- 2008
-
Ingår i: Materials and Structures. - : Springer Science and Business Media LLC. - 1359-5997 .- 1871-6873. ; 42:6, s. 779-790
-
Tidskriftsartikel (refereegranskat)abstract
- The purpose of this work was to study the use of accelerometers to measure pavement deflections due to traffic loads. To this end, accelerometers were embedded in two sites: the full scale load simulator Circular Test Track (CTT) and the A1 motorway in Switzerland. Deflections were derived from acceleration measurements using an algorithm that double integrates the measured signal and corrects any errors derived from the procedure. In the motorway, deflections were monitored using a set of three magnetostrictive deflectometers. Additionally, the pavement's material viscoelastic parameters determined in the laboratory were incorporated in Finite Element (FE) models to estimate the theoretical deflections. The calculated deflections were then compared to the measured and to the theoretical deflections. Deflections calculated from acceleration showed a reasonable qualitative correlation to those measured by magnetostrictive deflectometers. In addition, the FE models revealed the inability of the accelerometers to measure very slow or quasi-static motion.
|
|
| 3. |
- Azinovic, Boris, et al.
(författare)
-
Experimental investigation of the axial strength of glued-in rods in cross laminated timber
- 2018
-
Ingår i: Materials and Structures. - : Springer Science and Business Media LLC. - 1359-5997 .- 1871-6873. ; 51
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents results from an experimental assessment of glued-in rods in cross laminated timber (CLT). For the purposes of the study more than 60 pull–pull tests were performed, where the specimens varied in terms of bonded-in length (from 80 to 400 mm), rod diameter (16–24 mm) and rod-to-grain angle (parallel and perpendicular). Several different failure modes that are not common for other applications of glued-in rods (e.g., a failure between CLT layers) were obtained for the analysed CLT specimens. It was found that these failure mechanisms can substantially influence the obtained ultimate tension loads. At the end, the experimental results were compared with empirical and semi-empirical equations for estimating the pull-out strength of glued-in rods in structural timber and glulam. The comparison showed that most of the existing equations overestimate the ultimate tension loads for specimens with the rod parallel to the grain and underestimate the ultimate tension load for specimens with the rod perpendicular to the grain. The results vary because the possible CLT failure modes were not included in previous studies. Further studies are proposed to improve the equations for glued-in rods in CLT.
|
|
| 4. |
- Babaahmadi, Arezou, 1985, et al.
(författare)
-
Development of an electro-chemical accelerated ageing method for leaching of calcium from cementitious materials
- 2016
-
Ingår i: Materials and Structures. - : Springer Science and Business Media LLC. - 1359-5997 .- 1871-6873. ; 49:1-2, s. 705-718
-
Tidskriftsartikel (refereegranskat)abstract
- To facilitate the long term durability predictions of nuclear waste repositories, acceleration methods enhancing calcium leaching process from cementitious materials are needed, even though mechanisms not necessarily comparable to those predominant in a natural leaching process may be developed. In the previously published acceleration methods the samples are very small, which limits further physical or mechanical tests. In this paper, a new acceleration method based on electro-chemical migration is presented. The method although not driven with the same kinetics as in natural leaching, was designed in such a way that unnecessarily destructive by-effects could be minimized while promoting a higher leaching rate for a sample size suitable for further testing the mechanical and physical properties. It is shown that approximately 1x10^6 C of electrical charge per paste specimen of size Ø50 x 75 mm (approximately 230 g) is required to leach out the total amount of Portlandite. The chemical and mineralogical properties of leached samples are characterized by various techniques. It is concluded that aged samples are comparable to those leached in a natural leaching process as both are characterized by a layered system comprising an unaltered core delineated by total dissolution of Portlandite followed by a progressive decalcification of the calcium silicate hydrate gel.
|
|
| 5. |
- Bader, Thomas K., 1980-, et al.
(författare)
-
Experimental characterization of the global and local behavior of multi-dowel LVL-connections under complex loading
- 2016
-
Ingår i: Materials and Structures. - : Springer Science and Business Media LLC. - 1359-5997 .- 1871-6873. ; 49:6, s. 2407-2424
-
Tidskriftsartikel (refereegranskat)abstract
- The thorough experimental characterization of a dowel-type connection under various combinations of bending moments and normal forces is presented in this study. Double-shear steel-to-timber connections with 12 and 20 mm steel dowels were tested in a 4-point bending test set-up. The load, between the connected steel and wood beams, was transferred by the dowels themselves and also via an additional (passive) contact device, which introduced an eccentric normal force in the timber beam. The behavior of the connections was studied at the global scale of the connection and at the local scale of the individual dowels. A non-contact deformation measurement system was used to assess the changes of the location of the center of relative rotation over the entire loading. At the same time, the head deformations of the individual dowels could be measured, giving a direct indication about the force distribution among the dowels. Due to reinforcement, connections behaved distinctly ductile with a global relative rotation of up to 3°. Pre-stressing of the contact device by a force of 40 kN yielded an even stiffer behavior. For the particular configurations tested herein, the center of rotation was found to be close to the vertical axis of symmetry of the joint and close to the top row of the dowels. Moreover, the superimposed vertical shift of the center of relative rotation in case of a delayed normal force could be quantified. © 2015 RILEM
|
|
| 6. |
- Bagampadde, Umaru, et al.
(författare)
-
Impact of bitumen and aggregate composition on stripping in bituminous mixtures
- 2006
-
Ingår i: Materials and Structures. - : Springer Science and Business Media LLC. - 1359-5997 .- 1871-6873. ; 39:287, s. 303-315
-
Tidskriftsartikel (refereegranskat)abstract
- The impact of bitumen and aggregate composition on stripping was investigated using four bitumens and four aggregates. Moisture sensitivity was assessed based on retained resilient modulus and tensile strength ratio (MRR and TSR, respectively). The results indicate that mixtures from the bitumen with a high acid number exhibited high resilient modulus and tensile strength in the dry condition for all the aggregates. In wet condition, this conclusion did also hold except for one aggregate. Regarding penetration grade, mixtures made with lower penetration grade bitumen exhibited higher resilient modulus and tensile strength, in dry and wet conditions, than those of higher penetration grade. Bitumen characteristics like acid number, penetration grade and molecular size distribution did not influence moisture sensitivity. Mixtures with aggregates containing alkali metals (sodium and potassium) exhibited relatively high moisture sensitivity, regardless of the bitumen used. In contrast, indications of moisture sensitivity were not apparent in mixtures made with aggregates containing calcium, magnesium and iron. Data analysis revealed that variability in moisture sensitivity is attributed to aggregate rather than bitumen. No significant interaction effect between bitumen and aggregate was found on moisture sensitivity. The results indicated good correlation between MRR and TSR in ranking mixtures for stripping.
|
|
| 7. |
|
|
| 8. |
- Birgisson, Björn, et al.
(författare)
-
An optical strain measurement system for asphalt mixtures
- 2009
-
Ingår i: Materials and Structures. - : Springer Science and Business Media LLC. - 1359-5997 .- 1871-6873. ; 42:4, s. 427-441
-
Tidskriftsartikel (refereegranskat)abstract
- Knowledge of the conditions governing the initiation and propagation of cracks in hot mix asphalt (HMA) mixtures is a prerequisite for a comprehensive understanding of HMA cracking mechanisms. Traditional strain measurement sensors have proved to be not completely adequate in the sense that they do not provide pointwise measurements, thus not pinpointing the location of crack initiation, and not accounting for non-uniform strain distributions. This paper presents a digital image correlation (DIC) system for non-contact and full strain field measurements, conceived for the purpose of investigating the cracking behavior of HMA mixtures. The whole system was developed so as to account for the special nature of typical HMA testing configurations. An image matching technique (least squares matching) was employed for providing matches with sub-pixel accuracy. The performance of the method was investigated by several tests. The DIC system was shown to overcome the shortcomings of traditional on-specimen strain measurement devices achieving satisfactory accuracy compared to strain gauges.
|
|
| 9. |
- Bissonnette, B., et al.
(författare)
-
Recommendations for the repair, the lining or the strengthening of concrete slabs or pavements with bonded cement-based material overlays
- 2013
-
Ingår i: Materials and Structures. - : Springer. - 1359-5997 .- 1871-6873. ; 46:3, s. 481-494
-
Tidskriftsartikel (refereegranskat)abstract
- The recommendations presented in this publication are inspired by the State of the Art Report edited by the RILEM Technical Committee TC 193 RLS Bonded cement-based material overlays for the repair, the lining or the strengthening of slabs and pavements. The objective is to lay out all the practical aspects to be considered in the design of concrete overlay.bonded concrete overlay process, assessment of the existing structure, surface preparation, overlay materials, design methods, construction procedure and quality control/assurance system, and maintenance.
|
|
| 10. |
- Björk, Folke., et al.
(författare)
-
Roof membranes - The Swedish practice in light of EOTA TB 97/24/9.3.1 PT3 durability
- 2000
-
Ingår i: Materials and Structures. - 1359-5997 .- 1871-6873. ; 33:228, s. 270-277
-
Tidskriftsartikel (refereegranskat)abstract
- The practice for roof membranes for flat and low-slope roofs has substantially developed during the last two decades of the twentieth century. New technical solutions have been introduced and building codes and guidelines have been changed. The development of technical solutions preceded the scientific work. However, the scientific work did help to develop the technical practice for enhanced performance. The development described in this paper has much in common with recently published EOTA-guidelines regarding Assessment of service life.
|
|
| 11. |
- Boubitsas, Dimitrios, et al.
(författare)
-
The influence of reinforcement steel surface condition on initiation of chloride induced corrosion
- 2015
-
Ingår i: Materials and Structures. - : Springer Science and Business Media LLC. - 1359-5997 .- 1871-6873. ; 48:8, s. 2641-2658
-
Tidskriftsartikel (refereegranskat)abstract
- This paper describes a part of the work in the development of a "standard" test method for determining chloride threshold values required to initiate corrosion on reinforcement in concrete. The prerequisites of the test set-up are that the test conditions should be reasonably comparable to those in service and the test method should be fairly reproducible and as rapid as possible concerning the slow diffusion nature of the investigated phenomenon. This paper presents the results from a study on the influence of steel bar surface condition on chloride induced corrosion. Various electrochemical techniques were employed in the study to monitor the corrosion behaviour of the embedded bars with three different surface conditions. It is shown that the steel surface condition has a strong effect on the corrosion initiation of reinforcement in concrete, and can likely be the most decisive parameter attributing to the variability in the reported chloride threshold values.
|
|
| 12. |
- Bressi, S., et al.
(författare)
-
A new laboratory methodology for optimization of mixture design of asphalt concrete containing reclaimed asphalt pavement material
- 2016
-
Ingår i: Materials and Structures. - : Kluwer Academic Publishers. - 1359-5997 .- 1871-6873. ; 49:12, s. 4975-4990
-
Tidskriftsartikel (refereegranskat)abstract
- The reduction of virgin bitumen added to asphalt mixtures containing Reclaimed Asphalt Pavement (RAP) is based on the typical assumption that all the aged binder function in the same way as the virgin binder. However, recent studies conducted by the authors for a specific case show that a blend or mobilization of RAP binder are negligible. The aged bitumen becomes softer acting as glue facilitating cluster formation between small-size RAP particles. The reduction of small-size particles causes changes in the target grading curve and in the voids-fill, affecting the compactability of RAP mixtures. Therefore the target grading curve of RAP mixtures needs to be readjusted, using different proportions of virgin aggregates and taking into account the cluster phenomenon. The objective of this paper is to develop a new mix design approach for RAP mixtures, taking into account the cluster phenomenon and the contribution of the aged bitumen in the compactability. The virgin aggregates, filler and RAP are investigated and individually included in the calculation. 3D images of the virgin aggregates allowed the determination of new surface area factors; the concept of critical filler concentration led to the definition of the minimum bitumen quantity required to maintain the mastic in a diluted state and fill the voids. A RAP clustering model was introduced to predict the agglomeration of small-size RAP particles. The readjustment of the target grading curve was analytically calculated, allowing the correct estimation of the amount of virgin bitumen to be added to asphalt mixtures. Finally, a first verification of the entire process was carried out performing laboratory tests. These promising results enable the challenge of a new mix design optimization for HMA with high RAP content to be addressed.
|
|
| 13. |
- Briggert, Andreas, 1984-, et al.
(författare)
-
Prediction of tensile strength of sawn timber : models for calculation of yield in strength classes
- 2020
-
Ingår i: Materials and Structures. - : Springer. - 1359-5997 .- 1871-6873. ; 53:3, s. 1-15
-
Tidskriftsartikel (refereegranskat)abstract
- In Europe, strength classes for structural timber and glulam lamellae are defined by minimum requirements of characteristic values of the grade determining properties (GDPs). To fulfill these minimum requirements of characteristic values in the daily production at sawmills, indicating properties (IPs) to GDPs are calculated for each board and based on predetermined limits of the IPs (settings) boards are assigned to the graded class, or rejected. The aims of this paper is to address and discuss two different grading procedures/models that can be applied when settings for IPs that reflects a local board property are derived and to show how the yield in different T-classes depend on the model applied. It is not always that a board’s weakest cross-section is evaluated in a destructive test. An IP representing a local board property can therefore be determined either as the lowest property of the tested part of the board or as the lowest property along the whole board when applied to derive settings. Results presented in this paper show that too low settings and too large yields are obtained when the latter IP is employed. Similarly, IPs reflecting a global board property, like axial dynamic MOE, also give too low settings and too high yield in strength classes. This paper is the second and closing part of a series of two paper on prediction of GDPs and procedures for grading sawn timber into T-classes.
|
|
| 14. |
- Briggert, Andreas, 1984-, et al.
(författare)
-
Prediction of tensile strength of sawn timber : definitions and performance of indicating properties based on surface laser scanning and dynamic excitation
- 2020
-
Ingår i: Materials and Structures. - : Springer. - 1359-5997 .- 1871-6873. ; 53:3, s. 1-20
-
Tidskriftsartikel (refereegranskat)abstract
- The presence of wood irregularities such as knots are decisive for the mechanical properties of sawn timber, and efficient utilisation of timber requires methods by which grade determining properties can be predicted with high accuracy. In the glulam and sawmilling industries today, there is a potential and a need for more accurate prediction methods. This paper concerns the performance of a set of indicating properties calculated by means of data from surface laser scanning, dynamic excitation and X-ray scanning, the latter used to obtain boards’ average density. A total number of 967 boards of Norway spruce originating from Finland, Norway and Sweden were used to determine statistical relationships between the indicating properties and the grade determining properties used to grade sawn timber into T-classes. Results show that the indicating properties give coefficients of determination to tensile strength as high as 0.70. Furthermore, results also show that laser scanning of boards with sawn surface finish give basis for almost as accurate grading as what scanning of planed boards do. The results imply that more accurate grading of timber into T-classes is possible by application of a new set of indicating properties. This paper is part one of a series of two papers. In the second paper, two models to derive settings and calculate yield in different strength classes using the indicating properties presented herein are compared and discussed.
|
|
| 15. |
- Buasiri, Thanyarat, et al.
(författare)
-
Monitoring temperature and hydration by mortar sensors made of nanomodified Portland cement
- 2024
-
Ingår i: Materials and Structures. - : Springer Nature. - 1359-5997 .- 1871-6873. ; 57
-
Tidskriftsartikel (refereegranskat)abstract
- Mortar beams incorporating carbon nanofibers (CNFs), which were synthesized in situ on Portland cement particles, were used to produce nanomodified Portland cement sensors (SmartCem sensors). SmartCem sensors exhibited an electrical response comparable to a thermistor with a temperature coefficient of resistivity of − 0.0152/ °C. The highest temperature sensing was obtained for the SmartCem sensor, which contained ~ 0.271 wt.% of CNFs. The calculated temperature sensitivity was approximately 11.76% higher in comparison with the mortar beam containing only unmodified Portland cement. SmartCem sensors were used to monitor the cement hydration in large-scale self-compacting concrete beams. The measurements were conducted after casting for 7 days. Additionally, commercially available thermocouple and humidity sensors were used as references. The results showed that changes in electrical resistivity measured by the SmartCem sensor were well aligned with the ongoing hydration processes.
|
|
| 16. |
- Bueno, M., et al.
(författare)
-
Fracture toughness evaluation of bituminous binders at low temperatures
- 2015
-
Ingår i: Materials and Structures. - : Springer Science and Business Media LLC. - 1359-5997 .- 1871-6873. ; 48:9, s. 3049-3058
-
Tidskriftsartikel (refereegranskat)abstract
- When asphalt roads turn brittle at low temperatures, they are no longer able to relax completely from traffic induced stresses and may also suffer damage through crack initiation and propagation. In order to avoid early structural damages, the bituminous binders must be selected very carefully. However, conventional test methods for assessing performance of bituminous binders at low temperatures are often unsatisfactory reliable, in particular in case of polymer modified bituminous binders. In this study, an alternative experimental method based on fracture mechanical principles was performed on pre-notched specimens in the brittle state inside a cooling media. This fracture toughness test was evaluated in terms of its suitability for distinguishing different types of polymer modified and unmodified bituminous binders. In addition, the feasibility to evaluate different ageing states was also analysed by testing samples after artificial short-term and long-term ageing procedures. The repeatability obtained from the experimental results showed that the fracture toughness test is a suitable candidate for being introduced in a standardization framework.
|
|
| 17. |
- Chen, Feng, 1987-, et al.
(författare)
-
Vibration-induced aggregate segregation in asphalt mixtures
- 2020
-
Ingår i: Materials and Structures. - : SPRINGER. - 1359-5997 .- 1871-6873. ; 53:2
-
Tidskriftsartikel (refereegranskat)abstract
- Aggregate segregation in asphalt mixture is a bothersome engineering issue during pavement construction. The practitioners have some measures to mitigate the segregation potential based on experiences which, however, can only reduce the risk to a certain extent. In this research, the authors aim to contribute to the discussion in a rational non-empirical way, by using novel experimental and numerical techniques. A case study is carried out to investigate the vibration-induced segregation in asphalt mixtures, corresponding to the circumstance arising during material transportation to the construction site. A novel experimental test is conducted for evaluating the segregation characteristics of asphalt mixtures under vertical vibration in laboratory conditions. A numerical investigation based on discrete element method is further performed to study the phenomenon from a micromechanical point of view. The obtained experimental and numerical results indicate that vibratory loading induces aggregate size segregation in asphalt mixtures, and the degree of segregation is influenced profoundly by the adhesive properties of bituminous binders and the aggregate gradation.
|
|
| 18. |
- Chen, Teresa E, 1988, et al.
(författare)
-
Correlation between concrete cracks and corrosion characteristics of steel reinforcement in pre-cracked plain and fibre-reinforced concrete beams
- 2020
-
Ingår i: Materials and Structures/Materiaux et Constructions. - : Springer Science and Business Media LLC. - 1359-5997. ; 53:2
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents results on corrosion characteristics of 66 rebars extracted from un- and pre-cracked plain concrete and fibre-reinforced concrete (FRC) beams suffering from corrosion for more than 3 years. The influences of fibre reinforcement, flexural cracks, corrosion-induced cracks and loading condition on the maximum local corrosion level (defined as the maximum cross-sectional area loss percentage) and pit morphology were examined. With 3D-scanning, the corrosion characteristics were analysed, and pit types were classified based on the maximum local corrosion level and geometric parameters of pits. Corrosion pits were observed near some flexural cracks, while the bars at other cracks were free from corrosion. Most rebars in FRC had less maximum local corrosion level than those in plain concrete under the same loading condition and maximum flexural crack width. However, the maximum local corrosion level was not dependent on the maximum flexural crack width (0.1 and 0.4 mm). Longitudinal cracks (corrosion-induced cracks) aggravated the total steel loss and changed the pit morphology by promoting the pit length development. However, longitudinal cracks did not always form, even with severe pitting corrosion. A hypothesis about the time-dependent interplay between transverse and longitudinal cracks and corrosion development was proposed. Further studies on predicting the pitting corrosion evolution and experimental work on specimens exposed for longer periods are needed to understand and quantify the long-term durability of concrete structures reinforced with both conventional reinforcing bars and fibres.
|
|
| 19. |
- Coureau, J. L., et al.
(författare)
-
Influence of the fracture softening behaviour of wood on load-COD curve and R-curve
- 2007
-
Ingår i: Materials and Structures. - : Springer Science and Business Media LLC. - 1359-5997 .- 1871-6873. ; 40:1, s. 97-106
-
Tidskriftsartikel (refereegranskat)abstract
- A cohesive crack model is used to analyse failure of wood in mode I along the grain. Several configurations of the gradual fracture softening behaviour of an interface, meshed with joint-elements located on the potential crack path, are investigated. Different constitutive laws, obtained from a single normalized polynomial function, are tested in order to estimate the influence of parameters such as, the tensile strength, the fracture energy or the ultimate opening of the interface, on the macroscopic response of a fracture specimen. Numerical results are compared with experimental data obtained on DCB specimen. We argue that the fracture energy related to the constitutive law must correspond to the plateau value of the R-curve. Moreover, this study reveals that the peak load of a load-COD (Crack Opening Displacement) curve is strongly affected by the slope of the softening behaviour. Finally, we present a review of the influence of each parameter describing the softening function on: (1) the load-COD curve and (2) the corresponding R-curve.
|
|
| 20. |
- Das, Prabir Kumar, et al.
(författare)
-
Investigation of the asphalt mixture morphology influence on its ageing susceptibility
- 2015
-
Ingår i: Materials and Structures. - : Springer Science and Business Media LLC. - 1359-5997 .- 1871-6873. ; 48:4, s. 987-1000
-
Tidskriftsartikel (refereegranskat)abstract
- The main objective of this study is to investigate the influence that asphalt mixture morphology aspects have on its overall ageing behavior. Since mixture morphology is controllable, having insight into how the various morphological parameters influence the mixture’s long-term behavior can be of great value to optimize its design, regardless of the individual material properties. To do so, this study is utilizing a new framework to characterize the combined effect of aggregate packing, average air void size, porosity and level of compaction on ageing for a large set of data from different sources of field compacted and laboratory produced asphalt mixtures. The paper also hypothesizes about the mechanisms that lay behind the found influences and how thus mixture design improvements can be made. From all the investigated cases, it was found that the framework can be used to optimize the durability performance of asphalt mixtures. It was also observed that prediction of ageing behavior without considering the influence of mixture morphology may lead to erroneous conclusions and non-optimal mix design.
|
|
| 21. |
- Das, Prabir Kumar, et al.
(författare)
-
On the Oxidative Ageing Mechanism and Its Effect on Asphalt Mixtures Morphology
- 2015
-
Ingår i: Materials and Structures. - : Springer Science and Business Media LLC. - 1359-5997 .- 1871-6873. ; 48:15, s. 3113-3127
-
Tidskriftsartikel (refereegranskat)abstract
- This paper investigates the influence of mixture morphologies and microstructures on oxidative ageing of asphalt mixtures. For this, an oxidative ageing mechanism based on a diffusion–reaction process was developed. Previously, most asphalt oxidative ageing modeling research focused on unidirectional diffusion of continuous oxygen flow through bitumen films, which is far from the actual boundary conditions in asphalt mixtures. For this reason in the current study, a finite element (FE) analysis has been conducted in which 3D mixture morphology was considered. Mixture morphology is the combination of mineral aggregate packing, porosity, air-void distribution and their interconnectivity. One dense and one open graded field asphalt mixture core were scanned with a computerized tomography X-ray scanner. In the analyses, the developed oxidative ageing model was implemented. The FE analysis showed that the effect of the air-void distribution, their interconnectivity and the mineral aggregate packing has a significant effect on the resulting age hardening of the overall mixture. Furthermore, from the microstructural investigation done in this research, strong indications were found that, depending on the bitumen and its conditioning, water soluble thin films are formed due to ageing. This means that ageing and moisture damage are strongly interlinked and this should thus be considered in the design of the asphaltic materials and the prediction of their long term performance.
|
|
| 22. |
- Di Benedetto, H, et al.
(författare)
-
Fatigue of bituminous mixtures
- 2004
-
Ingår i: Materials and Structures. - 1359-5997 .- 1871-6873. ; 37:267, s. 202-216
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents an interlaboratory test campaign organized by the RILEM 182-PEB Technical Committee. In the campaign, 11 different test methods, comprising uniaxial tension/compression, 2-, 3- and 4-point bending and indirect-tension tests, were utilized in order to investigate fatigue characteristics of a dense graded asphalt concrete mixture. The testing conditions specified were sinusoidal excitation at 10Hz and 10degreesC using controlled strain and stress modes. In total, more than 150 fatigue tests were carried out during the investigation. The fatigue test results were analyzed using both classical as well as continuum damage mechanics approaches. The fatigue test results obtained using the classical fatigue approach are considerably influenced by test type and mode of loading (controlled stress or strain) used. Consequently, this approach has limited use in realistic fatigue characterization of bituminous materials and pavement structures. In contrast to the classical approach, models founded on continuum damage theory may serve to isolate intrinsic fatigue characteristics from the influence of so-called biased effects, which are largely caused by the accelerated laboratory testing. The continuum damage models investigated may constitute steps, towards a rational mechanistic fatigue characterization model, which are important for effective future pavement design.
|
|
| 23. |
- Dias Ferreira Da Silva, Nelson, 1978, et al.
(författare)
-
Application of LA-ICP-MS for meso-scale chloride profiling in concrete
- 2013
-
Ingår i: Materials and Structures/Materiaux et Constructions. - : Springer Science and Business Media LLC. - 1359-5997 .- 1871-6873. ; 46:8, s. 1369-1381
-
Tidskriftsartikel (refereegranskat)abstract
- Chloride represents a major risk for reinforced concrete structures because at a certain concentration, it can promote depassivation of the steel bars and initiate corrosion. Therefore it is important to be able to measure the chloride content in concrete. In this paper the application of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) for the study of chlorides in concrete is proposed. This scanning technique enables quick multi-element profiling, directly at the sample without the need for further preparation, within a range of sub-millimetre (meso-scale) resolution and with low limits of detection. Optimization of the operating conditions was performed in pressed concrete powder pellets. Linearity of the calibration was verified and limits of detection below 0.05 wt% of cement were determined. Chlorine, calcium and iron distributions were studied in cement based materials of increasing heterogeneity (paste, mortar and concrete). This technique is furthermore proposed for the study of the chloride induced corrosion process, by following element distributions along the concrete-steel interface at the time of depassivation.
|
|
| 24. |
- Edwards, Ylva, et al.
(författare)
-
Energy saving and environmental friendly wax concept for polymer modified mastic asphalt
- 2010
-
Ingår i: Materials and Structures. - : Springer Science and Business Media LLC. - 1359-5997 .- 1871-6873. ; 43, s. 123-131
-
Tidskriftsartikel (refereegranskat)abstract
- This paper focuses on the addition of commercial wax as flow improver in polymer modified bitumen intended for use in mastic asphalt pavements under Nordic climatic conditions. Different aspects are dealt with. The aim of the project is to make mastic asphalt used in Sweden today (for bridges, parking decks etc.) more environment friendly and easier to handle. However, wax modification must not have any noticeable negative impact on the performance of mastic asphalt at medium and lower temperatures. The project involves laboratory testing of wax and polymer modified binder mixtures as well as mastic asphalt mixtures. Effects of adding two commercial waxes to one polymer modified bitumen have been studied. The results show that both waxes have a flow improving/viscosity depressant impact on the polymer modified bitumen at higher temperatures, indicating a possible lower laying temperature for the mastic asphalt if modified with such waxes. Moreover, there is a stiffening effect at medium and high temperatures (below placing temperature), indicating a certain positive effect on stability. Concerning low temperature performance, there are results indicating some negative impact on crack susceptibility at low temperatures, more by the addition of one of the waxes than by addition of the other. However, it could be concluded that using up to at least 4% of either wax additive will improve workability for the mastic asphalt product under investigation making it possible to lower working temperatures without seriously affecting its good performance in any negative way.
|
|
| 25. |
|
|
| 26. |
- Edwards, Ylva, et al.
(författare)
-
Influence of commercial waxes and polyphosphoric acid on bitumen and asphalt concrete performance at low and medium temperatures
- 2006
-
Ingår i: Materials and Structures. - : Springer Science and Business Media LLC. - 1359-5997 .- 1871-6873. ; 39:7, s. 725-737
-
Tidskriftsartikel (refereegranskat)abstract
- The influence of adding four types of commercial wax and one polyphosphoric acid to a non-waxy bitumen was investigated with regard to binder and asphalt concrete mixture performance. Binder properties were determined using dynamic shear rheometer (DSR), bending beam rheometer, force ductilometer and various conventional test methods. Asphalt concrete performance was investigated using tensile stress restrained specimen test (TSRST), creep test at -25 degrees C, dynamic creep test at 40 degrees C and complex modulus test at 0, 10 and 20 degrees C. Totally eleven binders and eight asphalt mixtures were investigated. TSRST fracture temperatures of the asphalt mixtures were marginally influenced by the addition of any of the additives, and significant physical hardening of the binders, observed by BBR testing, could not be established using TSRST. Also in creep testing of asphalt mixtures at -25 degrees C, recorded effects were less pronounced compared to binder testing. In dynamic creep testing, the smallest permanent strains were recorded for the asphalt mixtures containing FT-paraffin or montan wax, indicating better resistance to rutting. Adding polyethylene wax or polyphosphoric acid to the non-waxy bitumen used, showed considerable positive stiffening effects on the binder at medium and higher temperatures. However, this increase in stiffness could not be shown in dynamic creep testing (at 40 degrees C) of asphalt concrete mixtures containing these additives.
|
|
| 27. |
- Ekblad, Jonas, et al.
(författare)
-
Precision of method for determining resistance of bituminous mixtures to de-icing fluids
- 2008
-
Ingår i: Materials and Structures. - : Springer Science and Business Media LLC. - 1359-5997 .- 1871-6873. ; 41:9, s. 1551-1562
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents the results of a Round-Robin test to estimate the precision of European method EN-12697-41 "Test methods for hot mix asphalt-Resistance to de-icing fluids". The purpose of the project was to determine precision data according to ISO 5725, ASTM E691 and ASTM C802. The examined test method is intended for use in requirements specifications for airfield de-icing chemicals and/or as a tool for development of such products. Precision statistics, repeatability and reproducibility standard deviations, are based on observed values from six laboratories and six levels, each level comprising four samples. From a general statistical analysis, which was conducted in addition to precision determination, it could be concluded that the most damaging de-icing agents (treatments) were identified by all participating laboratories both in terms of absolute values and by ranks.
|
|
| 28. |
- Ekblad, Jonas, et al.
(författare)
-
Soft bitumen asphalt produced using RAP
- 2017
-
Ingår i: Materials and Structures. - : Springer. - 1359-5997 .- 1871-6873. ; 50:1
-
Tidskriftsartikel (refereegranskat)abstract
- Soft bitumen asphalt concrete is a common paving material in Scandinavia. The purpose of this investigation was to indicate the possibility to compensate for the stiff binder of reclaimed asphalt pavement (RAP) by using softer binders compared to the mix design. Characterization of binder mixing and diffusion were carried out using viscosity measurements and tests on asphalt concrete comprised stiffness modulus and cyclic compression testing. Acquired results suggest that virgin and reclaimed binders mix and the viscosity can be predicted using simple mixing models. In the case of asphalt made from mixing virgin and recycled material, the mechanical properties indicates fully mixed binders and mixing occurs during sample manufacturing. In general, this study suggests that soft asphalt mixtures can be produced using RAP and that nominal binder viscosity of the final product can be obtained by compensating the stiff binder of the RAP by virgin bitumen of a softer grade.
|
|
| 29. |
- Ekblad, Jonas
(författare)
-
Statistical evaluation of resilient models for characterizing coarse granular materials
- 2008
-
Ingår i: Materials and Structures. - : Springer Science and Business Media LLC. - 1359-5997 .- 1871-6873. ; 41:3, s. 509-525
-
Tidskriftsartikel (refereegranskat)abstract
- Consistent material modeling is a prerequisite for a mechanistic approach to pavement design. The scope of this investigation was to statistically evaluate the efficiency of various resilient models commonly encountered in highway engineering. These models were categorized as describing either resilient modulus or shear and volumetric strains. Triaxial tests using constant and cyclic confining pressure were performed on coarse granular materials of various gradings (maximum particle size 90 mm). Two statistical methods, the extra sum of squares F-test and the Akaike information criterion, were used for model comparison. Concerning resilient modulus, the Uzan model provided, in general, a statistically significant improvement compared to the k-theta model. However, this improvement is lost if a constant Poisson ratio is used to predict shear and volumetric strains. In case of the shear-volumetric approach, no single model was most likely to be the best model for all gradings studied.
|
|
| 30. |
|
|
| 31. |
|
|
| 32. |
- Fadil, Hassan, et al.
(författare)
-
A spherical indentation test for quasi-non-destructive characterisation of asphalt concrete
- 2024
-
Ingår i: Materials and Structures. - : Springer. - 1359-5997 .- 1871-6873.
-
Tidskriftsartikel (refereegranskat)abstract
- The indentation test is a promising technique for the viscoelastic characterisation of asphalt concrete (AC). Indentation measurements are primarily influenced by the material properties in the direct vicinity of the indenter-specimen contact point. Accordingly, it may become a useful alternative for the characterisation of thin asphalt layers as well as for a quasi-non-destructive AC characterisation in the field. In this study, the spherical indentation test is used to measure the linear viscoelastic properties of AC mixtures extracted from a road test section. The measured complex moduli are compared to those obtained by the shear box test and are found to exhibit a linear correlation. The measurements are further analysed using the Gaussian mixture model to assign each indentation test to either aggregate-dominated or mastic-dominated response. The measurements attributed to mastic-dominated response are found to be more sensitive to the temperature and AC’s binder properties as compared to the average measurements. Accordingly, the proposed test method may provide a promising tool to measure AC viscoelastic properties and monitor the changes in AC binder phase in a non-destructive manner. A finite element micromechanical model is used to identify a representative scale for the response measured in mastic-dominated tests as well as to quantify the effect of measured properties on the AC damage propensity.
|
|
| 33. |
- Fadil, Hassan, et al.
(författare)
-
Spherical indentation test for quasi-non-destructive characterisation of asphalt concrete
- 2022
-
Ingår i: Materials and Structures. - : Springer Nature. - 1359-5997 .- 1871-6873. ; 55:3
-
Tidskriftsartikel (refereegranskat)abstract
- The indentation test is a promising technique for the viscoelastic characterisation of asphalt concrete (AC). Indentation measurements are primarily influenced by the material properties in the direct vicinity of the indenter-specimen contact point. Accordingly, it may become a useful alternative for the characterisation of thin asphalt layers as well as for a quasi-non-destructive AC characterisation in the field. In this study, the spherical indentation test is used to measure the linear viscoelastic properties of AC mixtures extracted from a road test section. The measured complex moduli are compared to those obtained by the shear box test and are found to exhibit a linear correlation. The measurements are further analysed using the Gaussian mixture model to assign each indentation test to either aggregate-dominated or mastic-dominated response. The measurements attributed to mastic-dominated response are found to be more sensitive to the temperature and AC's binder properties as compared to the average measurements. Accordingly, the proposed test method may provide a promising tool to measure AC viscoelastic properties and monitor the changes in AC binder phase in a non-destructive manner. A finite element micromechanical model is used to identify a representative scale for the response measured in mastic-dominated tests as well as to quantify the effect of measured properties on the AC damage propensity.
|
|
| 34. |
- Fang, Xing, et al.
(författare)
-
Impact of rapid-hardening cements on mechanical properties of cement bitumen emulsion asphalt
- 2016
-
Ingår i: Materials and Structures. - : Springer. - 1359-5997 .- 1871-6873. ; 49:1-2, s. 487-498
-
Tidskriftsartikel (refereegranskat)abstract
- Cement bitumen emulsion asphalt (CBEA) is obtained by mixing bitumen emulsion, cement, aggregates and filler at ambient temperature. CBEA is thought to be a promising substitute for hot mix asphalt because of its low environmental impact and cost-effectiveness. Disadvantages of this material are the long time required to reach its full strength and the inadequate understanding of the hardening mechanisms. This study aims at accelerating the development of mechanical properties of CBEA by using rapid-hardening cements while at the same time gaining a deeper understanding of the role of cement in CBEA. With this purpose, cold mix asphalt mixtures with cationic and anionic emulsions and different types of cement (ordinary Portland, calcium sulfoaluminate and calcium aluminate cement) were studied by means of isothermal calorimetry, measurements of water evaporation and Marshall tests. The results indicate that both anionic and cationic bitumen emulsions may affect the initial hydration rates of the cements used but have no significant influence on their degree of hydration after a few days. The addition of calcium sulfoaluminate and calcium aluminate cement to CBEA leads to mechanical properties after 1-day curing similar to those obtained with Portland cement after 1-week curing. Cement hydration dominates the strength gain, especially for rapid-hardening cements, and the type of cement influences both the amount of bound water and the rate of water evaporation from the CBEA.
|
|
| 35. |
- Fernandez, Ignasi, 1984, et al.
(författare)
-
Evaluation of corrosion level of naturally corroded barsusing different cleaning methods, computed tomography,and 3D optical scanning
- 2018
-
Ingår i: Materials and Structures/Materiaux et Constructions. - : Springer Science and Business Media LLC. - 1359-5997. ; 51:3
-
Tidskriftsartikel (refereegranskat)abstract
- Reliable methods are necessary to assess the corrosion level to establish links between structural performance and reinforcement corrosion in concrete structures. Hence, in this study, a set of naturally corroded bars were subjected to metallic brushing, acid immersion, and sandblasting for rust removal. Additionally, 3D optical, CT scanning, and weight loss measurements were used to evaluate the levels of corrosion. The results indicate that sandblasting is an optimal cleaning method. Weight loss measurements are sufficient when detailed information about corrosion is not required, and 3D scanning is preferred if information on corrosion variation along the bar is needed.
|
|
| 36. |
- Fernandez, Ignasi, 1984, et al.
(författare)
-
Structural effects of steel reinforcement corrosion on statically indeterminate reinforced concrete members
- 2016
-
Ingår i: Materials and Structures/Materiaux et Constructions. - : Springer Science and Business Media LLC. - 1359-5997. ; 49, s. 4959-4973
-
Tidskriftsartikel (refereegranskat)abstract
- Steel corrosion in reinforced concrete structures produces loss of reinforcement area and damage in the surrounding concrete. As a consequence, increases in deflections, crack widths and stresses may take place, as well as a reduction of the bearing capacity, which depends on the structural scheme and redundancy. In this paper an experimental study of twelve statically indeterminate beams subjected to different levels of forced reinforcement corrosion is presented. Different sustained loads were applied during the corrosion phase to assess their influence on the effects of corrosion. An important increase in deflections was registered in all corroded beams, especially in those subject to higher load levels. It was also found that the rate of corrosion was affected by the load level. Internal forces redistributions due to induced damage were measured. Finally, the experimental results were compared with those predicted by a non-linear time-dependent segmental analysis model developed by the authors, obtaining in general good agreement. © 2016, RILEM.
|
|
| 37. |
- Garcia, Alvaro, et al.
(författare)
-
A parametric study on the influence of steel wool fibers in dense asphalt concrete
- 2014
-
Ingår i: Materials and Structures. - : Springer Science and Business Media LLC. - 1359-5997 .- 1871-6873. ; 47:9, s. 1559-1571
-
Tidskriftsartikel (refereegranskat)abstract
- Environmental conditions combined with traffic loads contribute to premature deterioration of asphalt concrete pavements, reducing their strength and durability over time. To improve it, fibers can be incorporated in the mixture. Additionally, electrically conductive fibers can be used for self-healing purposes. In this context, this paper evaluates the influence of flexible steel fibers (steel wool) on the mechanical and physical properties of dense asphalt concrete. With these purposes, 25 different mixtures, with the same aggregate gradation and amount of bitumen, but with two different fibers lengths, four different percentages, and four different diameters of steel wool have been considered. Additionally, the influence of fibers on test specimens with three different types of damage: water damage, salt water damage and ageing have been evaluated through particle loss tests. Moreover, the influence of different temperatures on the flexural strength of dense asphalt concrete with steel wool fibers has been studied. It was found that steel wool fibers do not significantly improve the mechanical properties and damage resistance of dense asphalt concrete. On the other hand, steel wool fibers can change the air void distribution of a mixture, and therefore even reduce its particle loss resistance. As a recommendation, it is indicated that, for induction heating purposes, short fibers, with big diameters should be used, since they do not seem to alter the original properties of dense asphalt concrete.
|
|
| 38. |
- Garcia, Alvaro, et al.
(författare)
-
Influence of cement content and environmental humidity on asphalt emulsion and cement composites performance
- 2013
-
Ingår i: Materials and Structures. - : Springer Science and Business Media LLC. - 1359-5997 .- 1871-6873. ; 46:8, s. 1275-1289
-
Tidskriftsartikel (refereegranskat)abstract
- Asphalt and cement concrete are the most popular materials used in the construction of roads, highways, bridge deck surface layers and pavements in airports and other areas with heavy wheel roads. Whereas asphalt possesses, compared to concrete, the advantages of a short curing period, high skid resistance and easy maintenance, it also shows lower fatigue durability, ravelling and rutting due to repeated concentrated loads and susceptibility to temperature changes and moisture. On the other hand, concrete pavements are initially more expensive, have lower driving comfort and are susceptible to cracking due to volume changes and to salt damage. A material with low-environmental impact and with advantages of both asphalt and concrete may be obtained by combining bitumen emulsions and a cementitious material. In this paper, cold asphalt mixtures with different amounts of cement were tested with Marshall stability tests. Selected mixtures were also cured at different environmental relative humidity (35, 70 and 90 % RH). By monitoring the mass of the specimens and estimating the water bound by the cement, the total water remaining in the mixtures was calculated. Details of the microstructure in the mixtures were examined with X-ray microtomography. According to the results of the present study, cement contributes to the hardening of cold asphalt mixtures both by creating cement paste bridges between the aggregates and by removing water from the mixtures through cement hydration. Asphalt and cement composites appear to be promising materials for implementation in real pavements, although their rate of hardening needs to be improved further.
|
|
| 39. |
- Gasch, Tobias, et al.
(författare)
-
Three-dimensional simulations of ageing concrete structures using a multiphase model formulation
- 2019
-
Ingår i: Materials and Structures. - : Springer Netherlands. - 1359-5997 .- 1871-6873. ; 52:4
-
Tidskriftsartikel (refereegranskat)abstract
- The durability of concrete structures is in no small degree determined by the quality and integrity of the concrete, where structural damages such as cracks negatively affect many of the functions of the structure. Often cracks are formed due to restrained thermal and hygral deformations, where the risk is exceptionally high during the early stages after casting. This study presents a hygro-thermo-chemo-mechanical model that accounts for phenomena such as hydration, external and internal drying, self-heating, creep, shrinkage and fracture. The model is derived as a modified version of a fully-coupled multiphase model recently proposed by Gasch et al. (Cem Concrete Res 116:202–216, 2019. https://doi.org/10.1016/j.cemconres.2018.09.009) and implemented in the Finite Element Method. Here the governing equations are simplified, and a more efficient solution method is proposed. These modifications are made with the intention to obtain a model more suitable for structural scale simulations. To validate the model, one of the end-restrained beams tested within the French research project CEOS.fr is analyzed. Laboratory data on the concrete is used to calibrate to model and recordings of ambient conditions makes it possible to define accurate boundary conditions. Results from the simulation are compared to measured temperatures and deformations from the first 60 days after casting and are found to generally be in good agreement. Compared to the fully-coupled model by Gasch et al. (2019), the modifications proposed in this study reduce the computational cost by a factor five; without any noticeable differences to the structural results.
|
|
| 40. |
- Ghafoori Roozbahany, Ehsan, et al.
(författare)
-
A new test to study the flow of mixtures at early stages of compaction
- 2016
-
Ingår i: Materials and Structures. - : Kluwer Academic Publishers. - 1359-5997 .- 1871-6873. ; 49:9, s. 3547-3558
-
Tidskriftsartikel (refereegranskat)abstract
- Workability is one of the most commonly used indicators for the capability of asphalt mixtures tobe placed and compacted on the roads with long lasting quality and minimum maintenancethroughout its service life. Despite of valuable previous efforts for measuring and characterizingworkability, none of them has proven successful in representing the field conditions of roadconstructions. This paper is an attempt towards developing a systematic workability test methodfocusing on compaction, the so-called Compaction Flow Test (CFT), by simulating fieldcompaction at early stages and at laboratory scale with the main focus on mixture flow. The CFTwas applied for different mixtures in order to identify the parameters with highest impact on theasphalt particle movements under compaction forces. A new setting inside X-ray ComputationalTomography (CT) allowed tracing asphalt particles during the CFT and acquiring CT imagesunderlining the reliability of the CFT results. In addition, simple Discrete Element Models (DEM)were successfully generated to justify some of the CFT results.
|
|
| 41. |
- Ghasemi, Yahya, 1982-, et al.
(författare)
-
Effect of water film thickness on the flow in conventional mortars and concrete
- 2019
-
Ingår i: Materials and Structures. - Dordrecht : Springer. - 1359-5997 .- 1871-6873. ; 52:3
-
Tidskriftsartikel (refereegranskat)abstract
- Mortar and concrete can be divided into two phases of solids and water where water fills the voids between the grains and also coats the surface of particles. The current study investigates the influence of the thickness of coating water on flow spread of mortars and concretes. The article aims at correlating consistency of concretes to consistency of mortars. It was found that the flow behavior of granular mixtures can be directly related to the average water film thickness that envelops the particles. The concept was tested on mortar and concrete mixtures with different cement types, aggregate grading, aggregate shape, fineness and proportioning; proving water film thickness to be the most critical parameter affecting the flow. The results of the study indicate the possibility of predicting the flowability of mixtures by knowing the enveloping water film thickness. In addition, the relation between flowability of mixtures measured in different sizes of slump cone is explored to enable translating flow of mortars measured in mini-slump cone to flow of concrete obtained from Abram’s cone.
|
|
| 42. |
- Gil Berrocal, Carlos, 1986, et al.
(författare)
-
The interplay between corrosion and cracks in reinforced concrete beams with non-uniform reinforcement corrosion
- 2022
-
Ingår i: Materials and Structures/Materiaux et Constructions. - : Springer Science and Business Media LLC. - 1359-5997. ; 55:4
-
Tidskriftsartikel (refereegranskat)abstract
- This paper investigates the interplay between corrosion of reinforcement and corrosion-induced cracking in reinforced concrete structures with non-uniform corrosion distribution based on the experimental results of a concrete beam simultaneously subjected to sustained deflection and accelerated corrosion through impressed current. Unlike previous studies, this work encompasses various refined techniques for the measurement of surface cracks, such as digital image correlation and distributed optical fiber sensors, as well as for the assessment of reinforcement corrosion, namely 3D laser scanning, to explore previously hidden aspects of the relationship between the two parameters. The applied techniques proved very effective in providing an unprecedented level of detail of both the crack development and corrosion distribution. More specifically, the formation and propagation of corrosion-induced cracks were accurately and constantly monitored over time and subsequently compared to the distribution of corrosion. The results revealed that determining the maximum corrosion level or even the location of the section with maximum corrosion based solely on visual inspection of the surface crack width may not be possible. However, the width of corrosion-induced cracks was found to increase linearly with the local corrosion level, implying that crack width monitoring can still be used to estimate the rate of corrosion degradation.
|
|
| 43. |
|
|
| 44. |
- Gonzalez-Corominas, A., et al.
(författare)
-
Structural behaviour of prestressed concrete sleepers produced with high performance recycled aggregate concrete
- 2017
-
Ingår i: Materials and Structures/Materiaux et Constructions. - : Springer Science and Business Media LLC. - 1359-5997. ; 50:1, s. Article no. 94 -
-
Tidskriftsartikel (refereegranskat)abstract
- © 2016, RILEM.A comparative analysis of the structural behaviour of prestressed concrete sleepers made with high performance concrete (HPC) and high performance recycled aggregate concrete (HPRAC) is presented in this study. Two types of HPRAC sleepers were tested, using 50 and 100% of recycled concrete aggregate (RCA) in replacement of coarse natural aggregates. The RCA employed in this research was sourced from crushing rejected HPC sleepers. The aim of this study was to determine through analysis if the HPRAC sleepers’ behaviour fulfilled the European minimum requirements standards for prestressed concrete sleepers and compare their experimental behaviour with that of the HPC sleepers. The three types of prestressed concrete sleepers were subjected to static load tests at rail-seat and centre section (positive and negative load). In the centre section tests a comparative study between the experimental results and the proposed values of four assessment methods of ultimate capacity was carried out. Dynamic load and fatigue tests were also performed at the rail-seat section. The HPRACs and HPC sleepers met all the structural requirements for prestressed concrete sleepers. The experimental results determined the satisfactory performance of the HPRAC-50 and the HPRAC-100, which was very similar to that of the HPC sleepers. The load–strain behaviour recorded via the use of strain gauges on the prestressing bars revealed slightly higher stiffness of the HPC sleepers. The values obtained from the four assessment methods of ultimate capacity were also accurate when applied to HPRAC.
|
|
| 45. |
- Gram, Annika, et al.
(författare)
-
Numerical Simulation of Fresh SCC Flow : Applications
- 2011
-
Ingår i: Materials and Structures. - : Springer Science and Business Media LLC. - 1359-5997 .- 1871-6873. ; 44:4, s. 805-813
-
Tidskriftsartikel (refereegranskat)abstract
- Numerical simulation of self-compacting concrete (SCC) flow shows great potential for developing into a powerful tool for prediction of SCC form filling. Numerical simulation is also of interest for modelling small scale material phenomena. This paper presents three different applications useful for modelling different phenomena on different scales: (i) particles, each representing an aggregate in the concrete, (ii) fluid, modelling concrete as a homogeneous liquid and (iii) particle in fluid, studying details of flow. The methods are compared and evaluated in order to give the reader a quick guidance into the world of possibilities that open up with numerical simulation.
|
|
| 46. |
- Groot, Caspar, et al.
(författare)
-
RILEM TC 203-RHM: Repair mortars for historic masonry : Performance requirements for renders and plasters
- 2012
-
Ingår i: Materials and Structures. - 1359-5997 .- 1871-6873. ; 45:9, s. 1277–1285-
-
Tidskriftsartikel (refereegranskat)abstract
- This article gives a summary of functional_x000D_ and performance requirements for renders and plasters_x000D_ for historic masonry (design, execution and maintenance)._x000D_ Specific attention has been paid to degradation_x000D_ effects, such as caused by salt crystallization and_x000D_ freeze–thaw cycling. Traditional as well as designed_x000D_ prefab mortars are considered for repair intervention.
|
|
| 47. |
- Groth, Patrik, et al.
(författare)
-
Air cooling of concrete by means of embedded cooling pipes—Part II: Application in design
- 1998
-
Ingår i: Materials and Structures. - 1359-5997 .- 1871-6873. ; 31:210, s. 387-392
-
Tidskriftsartikel (refereegranskat)abstract
- This paper relates the second part of the investigation of air-cooling in concrete; the first part is presented in `Air cooling of concrete by means of embedded cooling pipes Part I: Laboratory tests and heat transfer coefficients'. Embedded cooling pipes are used to reduce the risk of thermal cracking in early age concrete. Traditionally, water has been used as a cooling medium, but air cooling has been shown to be advantageous for many applications. The experimentally-determined heat transfer coefficients of cooling pipes, have been used and verified in comparisons of in situ measurements at the Igelsta Bridge in Sodertalje, Sweden. The close agreement between measured and calculated temperatures of air-cooled sections seems to justify the use of the averaged heat transfer coefficients determined in [1]. Some exemplifying calculations are also shown, and the general behaviour of cooled structures is discussed. The principles of designing a cooling system for a general case are proposed. It is concluded that it is possible to design prismatic structures, such as a columns, by the use of existing models and measured heat transfer coefficients
|
|
| 48. |
- Gudmarsson, Anders, 1983-, et al.
(författare)
-
Application of resonant acoustic spectroscopy to asphalt concrete beams for determination of the dynamic modulus
- 2012
-
Ingår i: Materials and Structures. - : Springer Netherlands. - 1359-5997 .- 1871-6873. ; 45:12, s. 1903-1913
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, a new application of resonant acoustic spectroscopy (RAS) is examined for constructing asphalt concrete mastercurves from seismic testing. The frequency-dependent material properties can be characterized from multiple modes of vibration through the use of RAS. Beam-shaped asphalt specimens are tested at multiple temperatures to determine the resonance frequencies of the specimens. The resonance frequencies are estimated by applying a small load impulse and measuring the resulting acceleration through the specimens. Using RAS, the material properties of the specimens are determined numerically using the measured resonance frequencies. The results presented show that the frequency-dependent dynamic modulus of the asphalt concrete specimens can be characterized using several modes of vibration at each testing temperature.
|
|
| 49. |
- Hailesilassie, Biruk Wobeshet, et al.
(författare)
-
New experimental methods for characterizing formation and decay of foam bitumen
- 2015
-
Ingår i: Materials and Structures. - : Springer Science and Business Media LLC. - 1359-5997 .- 1871-6873.
-
Tidskriftsartikel (refereegranskat)abstract
- Formation and decay of foam bitumen is a highly dynamic temperature dependent process which makes characterization difficult. In this research, new experimental tools were applied for characterizing the bitumen foam during the foaming process. Ultrasonic sensors were used for accurately monitoring the expansion and decay of foam bitumen as a function of time. Assessment of foam bitumen viscosity was performed using high frequency torsional rheometer and in situ observation by X-ray radiography. A high-speed camera was applied for examining the foam bitumen stream right at the nozzle revealing that foam bitumen at a very early stage contains fragmented pieces of irregular size rather resembling a liquid than foam. Moreover, infrared thermal images were taken for obtaining information on the in situ surface temperature of foam bitumen during the hot foaming process. The result showed that the average surface temperature of foam bitumen depends on the water content of the bitumen and bubble size distribution, 108 and 126 °C for 4 and 1 wt% (by weight) water content respectively. The residual water content in the decaying foam bitumen was determined by thermogravimetric analysis. The result demonstrated that residual water content depends on the initial water content, and was found to be between 38 and 48 wt% of the initial water content of 4–6 wt%. Finally, X-ray computed tomography was applied for examining the decay of foam bitumen revealing that the bubbles of foam bitumen remain trapped close to the surface of the foam bitumen.
|
|
| 50. |
- Hailesilassie, Biruk W., et al.
(författare)
-
Testing of blister propagation and peeling of orthotropic bituminous waterproofing membranes
- 2015
-
Ingår i: Materials and Structures. - : Springer Science and Business Media LLC. - 1359-5997 .- 1871-6873. ; 48:4, s. 1095-1108
-
Tidskriftsartikel (refereegranskat)abstract
- Bridge decks are commonly subjected to harsh environmental conditions that often lead to serious corrosion problems, which are triggered by blisters under the hot mix asphalt bridge deck pavement with waterproofing membranes. These blisters are secretly evolving during weather exposure until often being detected too late. Formation of blisters under the waterproofing membrane is caused by a complex mechanism governed by bottom-up pressure and loss of adhesion. This paper primarily intends to adopt the analytical blister propagation energy approach for waterproofing membranes and compare it with adhesive fracture energy from standard peeling test methods, already described in the literature. Three different types of polymer modified bitumen membranes (PBM) were used for this purpose. The investigation includes a comparison between uniaxial and biaxial testing conditions for determining the modulus of elasticity of the membranes. Moreover, the influence of the displacement rate and temperature on the adhesive fracture energy in peeling tests is investigated. It was found that the biaxial modulus of PBM in the longitudinal and transversal direction is comparable with the uniaxial tension testing results in the main directions. In addition, it was observed that the ratio of longitudinal and transversal modulus of elasticity was similar. The energy calculated from tests with elliptical blister propagation showed a comparable value to the standard peeling fracture energy for similar types of PBM.
|
|
