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  • 1.
    André, Alann
    et al.
    Swerea SICOMP AB, Mölndal.
    Kliger, Robert
    Division of Structural Engineering, Chalmers University of Technology.
    Asp, Leif
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Compression failure mechanism in small scale timber specimens2014In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 50, p. 130-139Article in journal (Refereed)
    Abstract [en]

    Understanding the failure mechanism of wood loaded in compression parallel to the grain has been shown to be an important parameter in the design of timber beams strengthened with fibre-reinforced plastics (FRP). In this paper, a constitutive relationship for wood under uniaxial compression load parallel to the grain was determined experimentally. Several parameters, such as silviculture, moisture content and radial position in the log in relation to the pith from where the specimen was sawn, were considered. Small clear-wood specimens were used. The strain localisation in the failure region (kinkband) was monitored using the digital image correlation method. The results show that silviculture and moisture content are two very important parameters which influence the compression failure mechanism. Furthermore, there is a significant difference in behaviour between specimens from the juvenile region of the log and specimens from mature wood. Based on experimental results, two numerical models were built, considering either a global or a local constitutive relationship. It was demonstrated that both numerical models yield accurate results and that, depending on the experimental equipment available, a constitutive relationship could be extracted and used as input in these numerical models.

  • 2.
    Caprolu, Giuseppe
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Girhammar, Ulf Arne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Källsner, Bo
    School of Engineering, Linnæus University, Växjö, Linnéuniversitetet, Linnaeus University, Växjö.
    Comparison of models and tests on bottom rails in timber frame shear walls experiencing uplift2015In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 94, p. 148-163Article in journal (Refereed)
    Abstract [en]

    The authors present two different studies: one experimental study and one where analytical models developed to calculate the splitting failure capacity of bottom rails in partially anchored timber frame shear walls are evaluated and validated. The experimental study was divided into three parts with specimens matched to each other: (1) first the splitting capacity and failure mode of bottom rails subjected to uplift were studied; (2) then material properties such as tensile strength perpendicular to the grain; and (3) fracture energy were determined by testing specimens cut from the specimens belonging to study (1). The experimental results were compared with models based on a linear fracture mechanics approach presented earlier, using as input values results from (2) and (3). Almost all tested models show good agreement with the test results. The models showing the best agreement have been selected and proposed to be used as basis for calculation of the splitting failure capacity of bottom rails in partially anchored timber frame shear walls.

  • 3.
    Cwirzen, Andrzej
    et al.
    Department of Civil and Structural Engineering, Aalto University, School of Engineering, Espoo.
    Provis, John L.
    Department of Chemical & Biomolecular Engineering, University of Melbourne.
    Penttala, Vesa
    Department of Civil and Structural Engineering, Aalto University.
    Habermehl-Cwirzen, Karin
    Department of Civil and Structural Engineering, Aalto University, School of Engineering, Espoo.
    The effect of limestone on sodium hydroxide-activated metakaolin-based geopolymers2014In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 66, p. 53-62Article in journal (Refereed)
    Abstract [en]

    Blends of metakaolin and limestone can be alkali-activated with NaOH to form solid binders, which show relatively low strength but offer potential as a model system by which the reaction processes of more complex systems can be better understood. The effects of curing procedure, limestone content and alkalinity of the activator are able to be related to the mineralogy, mechanical properties and microstructure of hardened pastes. The presence of limestone enhances the release of Al and Si ions from metakaolin, with the Al released in the early stages of the reaction being bound into AFm-type phases. Dissolution of LS is slightly higher when a lower alkalinity sodium hydroxide activator is used. The heat treatment of pastes activated with 3 M NaOH solution resulted in a lower extent of reaction of limestone, while with 5 M solution, heat-curing at early age resulted in more reaction. The main alkali-activation product in metakaolin-limestone-NaOH pastes is a geopolymer gel with inclusions of unreacted metakaolin, limestone particles, zeolite A, and AFm phases, with different zeolites such as faujasite-like and hydrosodalite phases also identified at higher reaction temperatures. © 2014 Elsevier Ltd. All rights reserved.

  • 4.
    Enochsson, Ola
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Lundqvist, Joakim
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Rusinowski, Piotr
    Technical University of Denmark.
    Olofsson, Thomas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    CFRP strengthened openings in two-way concrete slabs: an experimental and numerical study2007In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 21, no 4, p. 810-826Article in journal (Refereed)
    Abstract [en]

    Rehabilitation and strengthening of concrete structures with externally bonded fibre reinforced polymers (FRPs) has been a viable technique for at least a decade. An interesting and useful application is strengthening of slabs or walls where openings are introduced. In these situations, FRP sheets are very suitable; not only because of their strength, but also due to that they are easy to apply in comparison to traditional steel girders or other lintel systems. Even though many benefits have been shown by strengthening openings with FRPs not much research have been presented in the literature. In this paper, laboratory tests on 11 slabs with openings, loaded with a distributed load are presented together with analytical and numerical evaluations. Six slabs with openings have been strengthened with carbon fibre reinforced polymers (CFRPs) sheets. These slabs are compared with traditionally steel reinforced slabs, both with (four slabs) and without openings (one slab). The slabs are quadratic with a side length of 2.6 m and a thickness of 100 mm. Two different sizes of openings are used, 0.85 × 0.85 m and 1.2 × 1.2 m. The results from the tests show that slabs with openings can be strengthened with externally bonded CFRP sheets. The performance is even better than for traditionally steel reinforced slabs. The numerical and analytical evaluations show good agreement with the experimental results.

  • 5.
    Escalera, Edwin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Garcia, Gustavo
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Terán, R
    Chemistry Department, San Simon University.
    Tegman, Ragnar
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Antti, Marta-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Odén, Magnus
    The production of porous brick material from diatomaceous earth and Brazil nut shell ash2015In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 98, p. 257-264Article in journal (Refereed)
    Abstract [en]

    Diatomaceous earth was mixed with Brazil nut shell ash (BNS ash) in different amounts between 0 and 30 wt% and sintered at temperatures between 750 and 950 °C. The BNS ash contains 33 wt% K2O and 11 wt% CaO mainly in carbonate form. The addition of BNS ash into the diatomaceous earth caused significant changes of the microstructure after sintering. The BNS ash addition produces lightweight porous bricks with acceptable strength at lower sintering temperature. The best combination of strength and porosity was achieved for a mixture of 10 wt% of BNS ash in the diatomaceous earth sintered at 850 °C. The achieved high porosity was 49%, density 1.06 g/cm3, thermal conductivity 0.20 W/(m K) and the compressive strength was 8.5 MPa.

  • 6.
    Gaff, Milan
    et al.
    Department of Wood Processing and Biomaterials, Faculty of Forestry and Wood Sciences, Czech University of Life Sciences, Prague, Czech Republic.
    Kačík, František
    Department of Wood Processing and Biomaterials, Faculty of Forestry and Wood Sciences, Czech University of Life Sciences, Prague, Czech Republic;Department of Chemistry and Chemical Technologies, Faculty of Wood Sciences and Technology, Technical University in Zvolen, Zvolen, Slovakia.
    Gašparík, Miroslav
    Department of Wood Processing and Biomaterials, Faculty of Forestry and Wood Sciences, Czech University of Life Sciences, Prague, Czech Republic.
    Todaro, Luigi
    School of Agricultural, Forestry, Food and Environmental Sciences, University of Basilicata, Potenza, Italy.
    Jones, Dennis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Corleto, Roberto
    Department of Wood Processing and Biomaterials, Faculty of Forestry and Wood Sciences, Czech University of Life Sciences, Prague, Czech Republic;School of Agricultural, Forestry, Food and Environmental Sciences, University of Basilicata, Potenza, Italy.
    Makovická Osvaldová, Linda
    Department of Fire Engineering, Faculty of Security Engineering, University of Žilina, Žilina, Slovakia.
    Čekovská, Hana
    Department of Wood Processing and Biomaterials, Faculty of Forestry and Wood Sciences, Czech University of Life Sciences, Prague, Czech Republic.
    The effect of synthetic and natural fire-retardants on burning and chemical characteristics of thermally modified teak (Tectona grandis L. f.) wood2019In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 200, p. 551-558Article in journal (Refereed)
    Abstract [en]

    This article deals with the effect of various temperatures of thermal modification and fire retardants on selected burning characteristics and chemical wood components of teak (Tectona grandis L. f.) wood. The thermal modification was carried out at temperatures 160 °C, 180 °C and 210 °C. Subsequently, thermally modified wood was treated by natural (arabinogalactan) and synthetic (ammonium phosphate) fire retardants. The effect of thermal modification as well as fire retardant was detected by burning characteristics such as weight loss, burning rate, maximum burning rate, ratio of the maximum burning rate and time to reach maximum burning rate. The chemical changes caused by the influence of these factors were determined by changing the content of cellulose, hemicelluloses, holocellulose, lignin and extractives. The relationship between burning characteristics and chemical changes in the thermally modified wood was analyzed using Spearman’s correlation. The results showed that the thermal modification of teak wood had a negative effect on its ignition and burning properties. Synthetic fire retardant had the highest retardation effect in all cases. The natural fire retardant caused a better retardation effect on thermally modified wood at temperature 180 and 210 °C. The relative content of lignin, extractives and cellulose increased, while the amount of holocellulose and particularly hemicelluloses decreased.

  • 7.
    Ge, Wenjie
    et al.
    College of Civil Science and Engineering, Yangzhou University.
    Zhang, Jiwen
    Key Laboratory of Concrete and Prestressed Concrete Structures of Ministry of Education, Southeast University, Nanjing.
    Cao, Dafu
    College of Civil Science and Engineering, Yangzhou University.
    Tu, Yongming
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Flexural behaviors of hybrid concrete beams reinforced with BFRP bars and steel bars2015In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 87, p. 28-37Article in journal (Refereed)
    Abstract [en]

    Flexural behaviors of hybrid concrete beams reinforced with BFRP (Basalt Fiber Reinforced Plastic) bars and steel bars are studied in this paper. Tensile test, standard pull-out test of BFRP bars, and static flexural experiment of five different hybrid reinforced concrete beams were made. The tests show that BFRP bars have high tensile strength and low elastic modulus compared with steel bars. The bond strength between BFRP bars and concrete is similar to the bond strength of steel bars and concrete and shows good bond performance. The bond strength relative coefficient of BFRP bars can be considered to be 1.0. The crack spacing and crack width are analyzed and suitable formulas for calculation are proposed. The flexural capacity of appropriate hybrid reinforced beams is analyzed and a simplified formula for calculating its value is proposed. Results show that the value of the flexural capacity calculated by the proposed simplified formula is close to the experimental value. This proves that the formula can be successfully applied. By controlling the reinforcement ratio and the value of Af/As appropriately, the ductility of hybrid reinforced beams can meet the requirements of normal service conditions.

  • 8.
    Ghasemi, Yahya
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Emborg, Mats
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Cwirzen, Andrzej
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Exploring the relation between the flow of mortar and specific surface area of its constituents2019In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 211, p. 492-501Article in journal (Refereed)
    Abstract [en]

    Mortars can be studied as mixtures of solid and flowable phases. The volume of the flowable phase required for deformation depends on the solid phase surface area according to excess layer theories. This paper examines the relation between the specific surface area of constituents in mortars and their flow. The flowable phase volume was divided by the solid phase surface area to obtain the layer thickness surrounding the surface of the particles. The results suggested that the amount of water and paste needed to ensure flow could be estimated from the packing density and specific surface area of the particles.

  • 9.
    Girhammar, Ulf Arne
    et al.
    Department of TFE - Civil Engineering, Faculty of Science and Technology, Umeå University.
    Pajari, Matti
    VTT Building and Transport, VTT Technical Research Centre of Finland, Espoo.
    Tests and analysis on shear strength of composite slabs of hollow core units and concrete topping2008In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 22, no 8, p. 1708-1722Article in journal (Refereed)
    Abstract [en]

    Prestressed concrete hollow core slabs are commonly used as load-bearing floors and roofs. The upper surface of the hollow core slabs is usually levelled with a cast-in situ screed or concrete topping. Reducing the thickness of the precast unit and increasing the thickness of the concrete topping, but maintaining the load-carrying capacity for the whole composite section is technically and economically an interesting alternative. The expensive screed could be replaced by a cheaper concrete and installations could be embedded in the topping layer. Proper shear and bond strength at the interface is required for composite action. An experimental and theoretical study on the effect of structural topping on the shear capacity of hollow core slabs and of the adequacy of the shear or bond strength of the non-treated interface is presented. It is concluded that concrete topping can be used to improve the shear capacity of hollow core units. For the test specimens, the theoretical increase was of the order of 35%, which was verified by the tests. The bond strength at the interface is adequate and the topping interacts with the slab in a proper manner.

  • 10.
    Gonzalez-Libreros, Jaime
    et al.
    Department of Civil, Environmental and Architectural Engineering, University of Padua.
    Sabau, Cristian
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Sneed, Lesley
    Department of Civil, Architectural and Environmental Engineering, Missouri University of Science and Technology, Rolla .
    Pellegrino, Carlo
    Department of Civil, Environmental and Architectural Engineering, University of Padua, .
    Sas, Gabriel
    Department of Infrastructure, Materials and Structural Engineering, NORUT.
    State of research on shear strengthening of RC beams with FRCM composites2017In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 149, p. 444-458Article in journal (Refereed)
    Abstract [en]

    This paper summarizes the state of research on the topic of shear strengthening of RC beams using externally bonded FRCM composites. In the first part of this paper, a detailed bibliographical review of the literature on the shear strengthening of RC beams using FRCM composites is carried out, and a database of experimental tests is developed. Analysis of the database shows that FRCM composites are able to increase the shear strength of RC beams. The effectiveness of the strengthening system appears to be influenced by parameters including the wrapping configuration, matrix compressive strength relative to the concrete compressive strength, and axial rigidity of the fibers. Different failure modes have been reported, including fracture of the fibers, detachment of the FRCM jacket (with or without concrete attached), and slippage of the fibers through the mortar. A possible interaction between the internal transverse steel reinforcement and the FRCM system has also been observed. In the second part of this paper, four design models proposed to predict the contribution of the FRCM composite to the shear strength of RC beams are assessed using the database developed. Results show that the use of the properties of the FRCM composite in Models 3 and 4 instead of the fiber mechanical characteristics does not significantly increase the accuracy of the models. A simple formulation such as that proposed by Model 1, based on the bare fiber properties, is found to be more accurate for beams with or without composite detachment.

  • 11. Hatem, Mohammed
    et al.
    Pusch, Roland
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Knutsson, Sven
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Warr, Laurence
    Greifswald University, Geographical & Geological Department, Germany.
    Hydrothermal alteration of clay and low pH concrete applicable to deep borehole disposal of high-level radioactive waste: A pilot study2016In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 104, p. 1-8Article in journal (Refereed)
    Abstract [en]

    In the very deep borehole (VDH) concept for high level radioactive waste disposal, the combined usage of clay and concrete provides an attractive way of achieving both high strength and low permeability required for sealing the various sections of the hole. The concrete is required for mechanical stability where water-bearing fracture zones are intersected, whereas the clay effectively seals sections in stable rock masses. As both the clay and concrete may be exposed to temperatures in the range of 60–150 °C in various parts of the hole, there is a need to address the stability of these materials under thermally enhanced aqueous conditions. In this pilot study, a new type of organic-free, low pH concrete based on granulated blast furnace slag is tested, which is hardened and altered under hydrothermal conditions in the laboratory. The results presented show that both adequate compressive strength (up to ∼9 MPa) and low hydraulic conductivity (down to ∼5.6 × 10−10) is attained at elevated temperatures ranging up to 150 °C, indicating that clay-concrete sealing can be a successful method used to prevent radionuclides from migrating vertically up through the borehole repository.

  • 12.
    Jacquier, Nicolas
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Girhammar, Ulf Arne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Evaluation of bending tests on composite glulam-CLT beams connected with double-sided punched metal plates and inclined screws2015In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 95, p. 762-773Article in journal (Refereed)
    Abstract [en]

    Composite beam elements made of glulam beams and cross laminated timber (CLT) panels, and connected with a new shear connection system were tested under four point bending. The beams tested represent a section of a cassette floor element to be used in a multi-storey CLT construction system. The shear connection is primarily made of double-sided punched metal plate fasteners, connecting the CLT and glulam members to form a T-cross-section. Due to the uncertainty about the capacity of the double-sided nail plates to resist possible separation forces between the timber members, the shear connection may be secured with screws. Bending tests were performed with three shear connection configurations: double-sided punched metal plate fasteners only, inclined screws only, and double-sided punched metal plate fasteners combined with inclined screws. An additional test with a screw-glued connection was made for comparison. The results show that a shear connection with double-sided nail plates can be designed to provide a sufficiently high level of composite action and load-carrying capacity and represents an alternative shear connection system for glulam-CLT composite floors

  • 13.
    Jacquier, Nicolas
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Girhammar, Ulf Arne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Tests on glulam–CLT shear connections with double-sided punched metal plate fasteners and inclined screws2014In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 72, p. 444-457Article in journal (Refereed)
    Abstract [en]

    A new shear connection system was tested in order to be used in off-site manufactured cassette floor elements made with glulam beams and cross laminated timber (CLT) panels. This type of floor element can present advantages from weight, structural and assembly point of view in multi-storey timber construction. The shear connection proposed is made of double-sided punched metal plate fasteners, connecting CLT and glulam members to form a T-cross-section. Inclined screws are used in combination with the double-sided nail plates to secure the shear connection. Shear test results are presented and compared with a simple calculation model for estimating the mean load-carrying capacity and stiffness of the combined joint according to methods available in the literature.

  • 14.
    Jensen, Jørgen L.
    et al.
    Department of Civil and Environmental Engineering, Faculty of Engineering, The University of Auckland, School of Engineering.
    Quenneville, Pierre
    Department of Civil and Environmental Engineering, Faculty of Engineering, The University of Auckland, School of Engineering.
    Girhammar, Ulf Arne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Källsner, Bo
    School of Engineering, Linnæus University, Växjö.
    Splitting of timber beams loaded perpendicular to grain by connections: combined effect of edge and end distance2012In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 35, p. 289-293Article in journal (Refereed)
    Abstract [en]

    The paper presents experimental results of tests on splitting of laminated veneer lumber beams subjected to loading perpendicular to grain by single bolts with small edge and end distances. Two different edge distances were used, and a total of eight different combinations of edge and end distances were tested. Material properties such as perpendicular-to-grain tensile strength and mode I fracture energy of the tested beams were also determined by testing. The experimental results are compared with a simple analytical model based on quasi-nonlinear fracture mechanics, which takes into account the effect of the edge distance as well as the end distance. A generalized model is proposed, which applies to small and large edge distances and to small and large end distances, and which contains as a special case the linear elastic fracture mechanics model, which is currently used as the basis for calculation of the splitting capacity in the Europeans and Canadian timber design codes.

  • 15.
    Orosz, Katalin
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Hedlund, Hans
    Skanska Sverige AB.
    Cwircen, Andrzej
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Effects of variable curing temperatures on autogenous deformation of blended cement concretes2017In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 149, p. 474-480Article in journal (Refereed)
    Abstract [en]

    Shrinkage tests have been performed on blended Portland cement based early-age concrete with different w/c ratios, undergoing variable temperature curing. Results showed presence of induced non-negligible autogenous swelling which could mitigate part of the stresses related to shrinkage at very young concrete age. Recorded swelling was higher at higher curing temperatures and longer duration, especially pronounced for the low w/c mix. The swelling continued for several days after the temperature stabilized. Although not investigated directly, evidence to the nonlinear nature of the thermal expansion coefficient in young concrete has also been provided

  • 16.
    Qin, Xiao-Chuan
    et al.
    School of Civil Engineering, Southeast University.
    Meng, Shao-Ping
    School of Civil Engineering, Southeast University.
    Cao, Da-Fu
    School of Civil Science and Engineering, Yangzhou University.
    Tu, Yong-Ming
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Sabourova, Natalia
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Grip, Niklas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Ohlsson, Ulf
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Blanksvärd, Thomas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Sas, Gabriel
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Elfgren, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Evaluation of freeze-thaw damage on concrete material and prestressed concrete specimens2016In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 125, p. 892-904Article in journal (Refereed)
    Abstract [en]

    The pore structure of the hardened concrete and the microscopic changes of a few selected pores throughout the freeze-thaw test were investigated by a method combining RapidAir and digital metalloscope. Traditional tests were also performed to evaluate the macroscopic change caused by freeze-thaw cycles (FTCs). The investigation shows that the concrete material, of which the spacing factor is 0.405 mm and the air content is 2.38%, can still withstand more than 300 FTCs. Severe microscopic damages occurred after approximately 200 FTCs and the freeze-thaw damage were gradually aggravated afterwards. Prestress forces have a remarkable impact on the failure pattern under FTCs. It was further found that the compressive strength as an indicator is more reliable than the relative dynamic modulus of elasticity in evaluating the freeze-thaw damage on concrete material. In addition, the test and analysis show that the measured prestress losses of bonded specimen are larger than that of unbounded specimen under the attack of FTCs due to the duct grouting effect. The ultimate freeze-thaw prestress loss is about 5% of σconσcon for both the bonded and unbonded specimens because the grouting cement paste will eventually be completely destroyed.

  • 17.
    Schmidt, Jacob W.
    et al.
    Technical University of Denmark.
    Bennitz, Anders
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Goltermann, Per
    Technical University of Denmark.
    Pedersen, Henning
    COWI A/S.
    Mechanical anchorage of FRP tendons: a literature review2012In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 32, p. 110-121Article in journal (Refereed)
    Abstract [en]

    High tensile strength, good resistance to degradation and creep, low weight and, to some extent, the ability to change the modulus of elasticity are some of the advantages of using prestressed, unidirectional FRP (Fibre Reinforced Polymer) tendon systems. Bonded and non-bonded versions of these systems have been investigated over the last three decades with results showing that prestressing systems can be very efficient when the FRP properties are properly exploited. However, there are often concerns as to how to exploit those properties to the full and how to achieve reliable anchorage with such systems. This is especially important in external post-tensioned tendon systems, where the anchorage points are exposed to the full load throughout the life span of the structure. Consequently, there are large requirements related to the long-term capacity and fatigue resistance of such systems. Several anchorage systems for use with Aramid, Glass and Carbon FRP tendons have been proposed over the last two decades. Each system is usually tailored to a particular type of tendon. This paper presents a brief overview of bonded anchorage applications while the primary literature review discusses three methods of mechanical anchorage: spike, wedge and clamping. Some proposals for future research are suggested. In general, the systems investigated showed inconsistent results with a small difference between achieving either a successful or an unsuccessful anchorage. These inconsistencies seem to be due to the brittleness of the tendons, low strength perpendicular to the fibre direction and insufficient stress transfer in the anchorage/tendon interface. As a result, anchorage failure modes tend to be excessive principal stresses, local crushing and interfacial slippage (abrasive wear), all of which are difficult to predict.

  • 18.
    Tikkanen, Johanna
    et al.
    Department of Civil and Structural Engineering, Aalto University, School of Engineering, Espoo.
    Cwirzen, Andrzej
    Department of Civil and Structural Engineering, Aalto University, School of Engineering, Espoo.
    Penttala, Vesa
    Department of Civil and Structural Engineering, Aalto University, School of Engineering, Espoo.
    Effects of mineral powders on hydration process and hydration products in normal strength concrete2014In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 72, p. 7-14Article in journal (Refereed)
    Abstract [en]

    The use of fine material in concrete manufacture has received an increased attention during the last 10-20 years. A number of studies have been published on the influence of fillers on special types of concretes, however, the influence of fine material on ordinary concrete is less well examined. In this paper the effects of mineral powders on hydration process and hydration products of normal strength concrete were studied. Tests were carried out on concretes and cement pastes with quartz and limestone mineral powders. According to the results, heat evolution appeared to be affected by the use of mineral powders. Greater hydration heat and thus higher maturities, degrees of hydration and compressive strengths were obtained for concretes containing up to 40 wt% of added mineral powder. However, increasing the amount of mineral powder did not proportionally increase the amount of hydration heat. TGA tests on cement pastes revealed that the amount of Ca(OH)2 was slightly lower in the mineral powder pastes but the degree of hydration was greater. The use of mineral powder to replace 10 wt% of the cement had no effect or only a small one on the amount of Portlandite and compressive strength of the pastes. However, replacing a higher amount of cement reduced the amount of Portlandite and compressive strengths notably. In addition, the results from the TGA also suggested that some of the CaCO3 originating from the limestone was incorporated into the hydration phases. The XRD study confirmed the results obtained from the TGA. A 10 wt% cement replacement appeared to have almost no effect on the amount of Portlandite formed at the age of 28 days. However, using mineral powders to replace 30 wt% or more of the cement reduced the amount of Portlandite notably. In many of the cement pastes in which mineral powders replaced cement, the net intensity of C3S measured by XRD was lower than could be expected to happen as a result of mere cement replacement. It was related to a higher degree of hydration of cements with mineral powders which was additionally supported by the amount of Portlandite and the compressive strength results.

  • 19. Tossavainen, Mia
    et al.
    Lind, Lotta
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Leaching results of reactive materials2008In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 22, no 4, p. 566-572Article in journal (Refereed)
    Abstract [en]

    Leaching results are used in the assessment of slag for use in construction. The stability of the major phase in iron- and steelmaking slags has a direct influence on the leaching of all elements enclosed in the matrix. Steelmaking slags have varying content of glass and puzzolanic minerals, and water granulation is a means of enhancing the glass content. A crystalline and an amorphous blast furnace slag have been investigated with a long-term test to determine if diffusion or dissolution was the controlling leaching mechanisms for each slag type. Both slag types were leached by dissolution according to the results. However, leaching of slags with puzzolanic phases implies that reactions take place, resulting in both dissolution and stabilization of elements. The phase transformations probably hamper the evaluation of leaching results and should be considered.

  • 20.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Strengthening concrete beams for shear with CFRP sheets2003In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 17, no 1, p. 15-26Article in journal (Refereed)
    Abstract [en]

    The method of strengthening concrete structures with FRP composites has existed for over a decade; the most common way to strengthen structures is in bending, but also wrapping of columns is quite common. There are also needs for strengthening concrete structures in shear, for example concrete beams, slabs, columns, etc. A typical structure can be a parking garage. However, strengthening concrete structures for shear is not as common as for bending and confinement. This paper presents examples to strengthen concrete beams for shear. First traditional strengthening methods are presented briefly, then the use of CFRP (Carbon Fibre reinforced Polymers) composites for shear strengthening is presented. Tests on beams strengthened in shear with CFRP sheets are presented and a short presentation on how to design for shear strengthening with CFRP is given. Furthermore, a field application of a parking slab strengthened for shear with CFRP unidirectional fabric is presented. The laboratory tests show the importance of considering the principal directions of the shear crack in relation to the unidirectional fibre. The field application shows that it is easy to strengthen existing structures for shear with CFRP fabrics.

  • 21.
    Xue, Peng
    et al.
    School of Metallurgical and Ecological Engineering, University of Science and Technology, Beijing , Department of Ferrous Metallurgy, School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing.
    Xu, Anjun
    Department of Ferrous Metallurgy, School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing.
    He, Dongfeng
    School of Metallurgical and Ecological Engineering, University of Science and Technology, Beijing , Metallurgical and Ecological Engineering School, University of Science and Technology, Beijing, State Key Laboratory of Advanced Metallurgy, University of Science and Technology Beijing, Department of Ferrous Metallurgy, School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing.
    Yang, Qixing
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Liu, Guiqun
    School of Material Science and Engineering, Beifang University of Nationalities, Yinchuan.
    Engström, Fredrik
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Björkman, Bo
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Research on the sintering process and characteristics of belite sulphoaluminate cement produced by BOF slag2016In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 122, p. 567-576Article in journal (Refereed)
    Abstract [en]

    The sintering process of belite sulphoaluminate cement (CSA1) clinker is still not clear to date. Besides, there are few reports concerning producing CSA by recycled BOF slag. Therefore, the sintering process of CSA was investigated from this perspective and the results can be a reference for BOF slag disposal. Four kinds of CSA clinkers with different additions of BOF slag were sintered at 1300 °C for 30 min. The sintering process was traced by heating microscope and the characteristics were analyzed by XRD, SEM-EDS and TAM Air. The results showed that the sintering degree of CSA clinker could be predicted by analyzing its sintering process. Furthermore, BOF slag could improve the melting state of CSA clinkers due to its composition containing iron oxide, manganese oxide and magnesium oxide. However, expansion was detected when the temperature reached 420 °C, which was arose by combined factors, namely volatilization of CO2 decomposed from MgCO3 and the thermal expansion of raw materials itself. The rational ratios of C2S, C4A3View the MathML sourceS¯, C4AF in CSA clinker with 14% BOF slag as raw material stood at 50%, 30%, 20% and its early hydration behavior was better than that of ordinary Portland cement (OPC) at the initial 16 h.

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