| 1. |
- Ahmed, Lamis, et al.
(författare)
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Numerical modelling and evaluation of laboratory tests with impact loaded young concrete prisms
- 2016
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Ingår i: Materials and Structures. - : Springer Science and Business Media LLC. - 1359-5997 .- 1871-6873. ; 49:11, s. 4691-4704
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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.
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| 2. |
- Alhede, Andreas, 1996, et al.
(författare)
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Monitoring corrosion-induced concrete cracking adjacent to the steel-concrete interface
- 2023
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Ingår i: Materials and Structures/Materiaux et Constructions. - 1359-5997. ; 56:9
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Tidskriftsartikel (refereegranskat)abstract
- Substantial research effort has been devoted on linking corrosion-induced cracking of concrete with the internal corrosion damage level. Still, numerical models of the corrosion and cracking process require internal parameters, that cannot be directly evaluated from experimental data. Therefore, this study provides a novel experimental method for monitoring the effects of steel corrosion adjacent to the steel-concrete interface. This non-destructive method is suited for small-scale laboratory-made specimen, and was designed to provide missing information required for subsequent calibration of numerical models. Hollow steel bars were cast into concrete and subjected to accelerated corrosion using the impressed current technique. The deformations of the hollow steel bars were measured using distributed strain sensing in an optical fibre, attached to the inner surface of the hollow steel bars. After the corrosion period, X-ray Computed Tomography scans were performed to evaluate concrete cracking and corrosion level. The results reveal a non-uniform distribution of strain around the perimeter of the steel, indicating a non-uniform radial stress distribution. The non-uniformity correlated very well with the position of the corrosion-induced cracks; with extension hoop strains in the steel at the location of these cracks and contraction hoop strains in between. Further, the corrosion level varied around the perimeter, with higher values near cracks. The combination of non-destructive monitoring techniques used in this study on small-scale laboratory-made specimens show great potential to reveal new insights on how the corrosion pattern, corrosion-induced cracking of the concrete cover and stress (indirectly measured through the strain in the steel) interact throughout the corrosion process.
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| 3. |
- Arraigada, M, et al.
(författare)
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Evaluation of Accelerometers to Determine Pavement Deflections under Traffic Loads
- 2008
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Ingår i: Materials and Structures. - : Springer Science and Business Media LLC. - 1359-5997 .- 1871-6873. ; 42:6, s. 779-790
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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.
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| 4. |
- Azinovic, Boris, et al.
(författare)
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Experimental investigation of the axial strength of glued-in rods in cross laminated timber
- 2018
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Ingår i: Materials and Structures. - : Springer Science and Business Media LLC. - 1359-5997 .- 1871-6873. ; 51
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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.
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| 5. |
- Babaahmadi, Arezou, 1985, et al.
(författare)
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Development of an electro-chemical accelerated ageing method for leaching of calcium from cementitious materials
- 2016
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Ingår i: Materials and Structures. - : Springer Science and Business Media LLC. - 1359-5997 .- 1871-6873. ; 49:1-2, s. 705-718
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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.
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| 6. |
- Bader, Thomas K., 1980-, et al.
(författare)
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Experimental characterization of the global and local behavior of multi-dowel LVL-connections under complex loading
- 2016
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Ingår i: Materials and Structures. - : Springer Science and Business Media LLC. - 1359-5997 .- 1871-6873. ; 49:6, s. 2407-2424
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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
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| 7. |
- Bagampadde, Umaru, et al.
(författare)
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Impact of bitumen and aggregate composition on stripping in bituminous mixtures
- 2006
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Ingår i: Materials and Structures. - : Springer Science and Business Media LLC. - 1359-5997 .- 1871-6873. ; 39:287, s. 303-315
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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.
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| 8. |
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| 9. |
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| 10. |
- Birgisson, Björn, et al.
(författare)
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An optical strain measurement system for asphalt mixtures
- 2009
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Ingår i: Materials and Structures. - : Springer Science and Business Media LLC. - 1359-5997 .- 1871-6873. ; 42:4, s. 427-441
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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.
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