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  • Experimental results of a national technical assessment procedure on commercial FRP for structural strengthening: wet-lay-up systems
    Mater. Struct. (IF 2.548) Pub Date : 2020-01-14
    A. Occhiuzzi, F. Ceroni, A. Franco, P. Salzano, A. Bonati

    Abstract The paper shows the results of a large experimental activity for the qualification of wet-lay-up FRP products for structural repair and/or strengthening, required by the Italian national approval authority. The qualification procedure and the correspondent design rules are described in national guidelines. The analysis of the experimental results of a large number of qualification tests allows to highlight some aspects in the national procedure that could be addressed in a future revision of the guidelines. In particular, statistical analyses were carried out in order to assess the most suitable probabilistic models able to describe the experimental distribution of the tensile strength and the Young’s modulus of FRP wet-lay-up materials falling in the same class. The analyses were developed with reference to both ordinary and artificial environmental conditions. Nevertheless the paper is focussed on the case of wet-lay-up FRP materials, it can be considered exemplary of a problem common to other products.

  • Permeability and mechanical property measurements of reinforced asphalt overlay with paving fabrics using novel approaches
    Mater. Struct. (IF 2.548) Pub Date : 2020-01-14
    Ehsan Solatiyan, Nicolas Bueche, Michel Vaillancourt, Alan Carter

    In order to study the mechanical behavior of asphalt overlay reinforced with paving fabrics (a system composed of non-woven geotextile and asphalt cement) a new methodology was developed based on three new pieces of laboratory equipment including 3-point bending test (3-PBT) method on cylindrical specimens, crack widening device (CWD) and water-vacuum permeability device (WVPD). The 3-PBT and CWD were designed to simulate generation and propagation of thermally driven cracking from an existing discontinuity in the pavement system into a new asphalt overlay. In addition, the WVPD was assembled to accelerate the movement of water through a low porosity medium. On such basis, representative parameters have been suggested by the authors as: crack resistance index of the system to determine the reinforcement effect and coefficient of permeability (K) to evaluate the waterproofing benefit of the paving fabrics. The experimental results of two different rehabilitation strategies of bituminous pavements were compared during this research: a traditional strategy, as a reference case, in which asphalt overlay is directly attached to the existing surface with an asphalt emulsion and a new strategy with the inclusion of paving fabric as an interlayer system between two asphalt layers, as the reinforced case. The results indicate that the reinforced case has enhanced mechanical properties, in terms of lower crack width manifested at the surface and higher crack resistance index and reduced water permeability. In addition, the proposed methodology appears to be suitable to evaluate the mechanical performance of reinforced asphalt overlays.

  • Torsional vibration technique for the acoustoelastic characterization of concrete
    Mater. Struct. (IF 2.548) Pub Date : 2020-01-10
    Agustin Spalvier, Leandro D. Domenech, Gonzalo Cetrangolo, John S. Popovics

    Abstract There is no nondestructive evaluation method capable of determining stresses in concrete structural members in situ. Here, we propose and evaluate a torsional-vibration testing technique that offers an approach to estimate the stress state in concrete specimens by means of characterizing the material nonlinearity. We axially load three prismatic specimens comprising different concrete mixtures and measure their torsional vibration frequencies during four loading cycles. The fundamental torsional frequency shows a positive correlation with applied compressive stress for both loading and unloading stages after correcting for the effects of non-uniform torsion, geometric nonlinearity and changing boundary conditions. To quantify this behavior, we define the nonlinear parameter \(\beta_{G}\) to characterize the material nonlinearity (acoustoelasticity). The values of \(\beta_{G}\) of the initial loading cycle are lower than those of the subsequent loading cycles. However, the latter values of our concrete mixtures are consistent and similar to the values computed from previously published results. An estimate of the \(\beta_{G}\) parameter of a concrete structural member provides a pathway for nondestructive assessment of in situ compressive stress in the member.

  • Synergistic ethylcellulose/polyphosphoric acid modification of bitumen for paving applications
    Mater. Struct. (IF 2.548) Pub Date : 2020-01-08
    A. A. Cuadri, F. J. Navarro, P. Partal

    Abstract A lignocellulosic material, like ethylcellulose (EC), is assessed for bitumen modification, as a more sustainable alternative to polymers derived from non-renewable sources. However, ethylcellulose alone hardly enhances bitumen performance. This work studies novel bituminous binders prepared with ethylcellulose powder and polyphosphoric acid (PPA) as bitumen modifiers for paving applications. Rheological tests demonstrated that the addition of 0.5 wt% PPA to a binder containing 5 wt% EC, along with a thermal curing, leads to binders with improved rutting resistance at high in-service temperatures, compared to binders prepared solely with EC or PPA. TLC–FID chromatography, FTIR spectroscopy and modulated DSC were conducted on binders to shed some light on modification route. From them, it is possible to state that the rheological enhancement is related to a change in SARAs fractions (i.e., binder colloidal index), derived from the asphaltenes disaggregation and formation of new phosphorylated adducts. Therefore, the use of ethylcellulose as lignocellulosic raw material seems to be a promising alternative to design bituminous binders for paving applications with enhanced rheological properties at high in-service temperatures.

  • Development of failure criterion and fatigue model to characterize the fatigue resistance of asphalt binders under controlled-stress time sweep tests
    Mater. Struct. (IF 2.548) Pub Date : 2019-12-19
    Hanqi Liu, Rong Luo

    Abstract The fatigue resistance of asphalt binders is of great significance to the design and maintenance of asphalt pavements. This study aims to develop a fatigue model that is independent of material types for asphalt binders subjected to controlled-stress time sweep tests. The ratio of dissipated energy change (RDEC) method and the normalized stiffness ratio (NSR) method are first evaluated with regard to this objective. It is demonstrated that both methods fail to provide a fatigue model that is independent of material types. A new failure criterion is then developed through analysis of the three phases of the dynamic shear modulus versus load cycles graph. The fatigue life is defined as the load cycle corresponding to the second inflection point on such a graph. In accordance with the plateau value concept utilized in the RDEC method, a new fatigue-related parameter is defined as the RDEC value at the fatigue life determined by the NSR method. Combine the fatigue life with the new fatigue-related parameter in the form of power function yields a new fatigue model, which is then fitted to the data points of all tested asphalt binders. It is found that all of the data points are located at or close to the best-fit line with an R2 value of 0.978. Therefore, this new fatigue model has the potential of being material type independent.

  • Effects of highly dispersed nano-SiO 2 on the microstructure development of cement pastes
    Mater. Struct. (IF 2.548) Pub Date : 2019-12-19
    Xin Liu, Pan Feng, Xin Shu, Qianping Ran

    The agglomeration of nano particles in cement systems remains a major challenge for their wide use in construction materials. A method of preparing highly dispersed nano-SiO2 in cement paste is introduced in this paper, and the effects of modified nano-SiO2 (SiO2@PCE) with a core–shell structure on cement hydration and microstructure development were investigated by isothermal calorimetry, quantitative X-ray diffraction, thermogravimetric analysis, scanning electron microscopy and nanoindentation. The results show that well-dispersed nano-SiO2@PCE particles in a cement system can significantly accelerate cement hydration at an early age. The highly dispersed nano-SiO2@PCE particles refine the pore structure of the hardened cement paste. More specifically, the number of harmless and less-harmless pores is increased, whereas the number of harmful and more-harmful pores is reduced. In addition, the proportion of high-density C–S–H and low-density C–S–H in the hardened cement paste at an early age increases by 69% and decreases by 27%, respectively, with the addition of 1.5% nano-SiO2@PCE. Through the seeding effect, cement hydration is accelerated pronouncedly with the addition of highly dispersed SiO2@PCE nano particles. In addition, the stiffness of the paste is enhanced by the pozzolanic reaction between SiO2@PCE and portlandite.

  • Integrative experimental and numerical study of ASR affected nuclear concrete containments
    Mater. Struct. (IF 2.548) Pub Date : 2019-12-17
    Victor E. Saouma, Mohammad Amin Hariri-Ardebili

    The alkali silica reaction (ASR) is a complex multifaceted deleterious one with broad implications on the structural integrity of a nuclear concrete containment (NCC). When compounded with seismic excitation, the structural assessment is even more complex, specially when its intrinsic shear strength is not yet well understood. This paper will highlight 3 years of a holistic research on the pre-cited problem, highlighting the interaction of various tasks, while details can be found in referenced publications. The reported work is broken into four integrated parts: (a) Design of a reactive concrete mix representative of the one in an NCC and likely to expand sufficiently within 6 months; (b) Specimens expansion monitoring in terms of different dimensions and reinforcement ratios for a year; (c) Large-scale testing of shear specimens to evaluate both material (no reinforcement) and structural (with reinforcement) components to assess impact of ASR; and (d) 3D probabilistic nonlinear seismic analyses of an NCC subjected to 40 years of ASR expansion followed by multiple dynamic excitation. It will be shown that the true shear strength of concrete material is affected by ASR, and that this reduction will reduce the seismic resistance of an NCC.

  • Correction to: Propagation of reinforcement corrosion: principles, testing and modelling
    Mater. Struct. (IF 2.548) Pub Date : 2019-12-16
    Carmen Andrade

    The article Propagation of reinforcement corrosion: principles, testing and modelling, written by Carmen Andrade, was originally published electronically on the publisher’s internet portal (currently SpringerLink) on 26 December 2018 without open access.

  • Correction to: Century-long expansion of hydrating cement counteracting concrete shrinkage due to humidity drop from selfdesiccation or external drying
    Mater. Struct. (IF 2.548) Pub Date : 2019-12-16
    Saeed Rahimi-Aghdam, Enrico Masoero, Mohammad Rasoolinejad, Zdeněk P. Bažant

    The article “Century-long expansion of hydrating cement counteracting concrete shrinkage due to humidity drop from selfdesiccation or external drying”, written by Saeed Rahimi-Aghdam, Enrico Masoero, Mohammad Rasoolinejad and Zdeněk P. Bažant, was originally published electronically on the publisher’s Internet portal (currently SpringerLink) on 24 January 2019 without open access.

  • Correction to: Structural effects of FRC creep
    Mater. Struct. (IF 2.548) Pub Date : 2019-12-12
    Giovanni Plizzari, Pedro Serna

    The article [Structural effects of FRC creep], written by [Giovanni Plizzari, Pedro Serna], was originally published electronically on the publisher’s Internet portal (currently SpringerLink) on 3 December 2018 without open access.

  • Correction to: Towards improved testing of modern asphalt pavements
    Mater. Struct. (IF 2.548) Pub Date : 2019-12-12
    M. N. Partl

    The article “Towards improved testing of modern asphalt pavements”, written by “M. N. Partl”, was originally published electronically on the publisher’s internet portal (currently SpringerLink) on 3 December without open access.

  • Correction to: Sustainability-based decision support framework for choosing concrete mixture proportions
    Mater. Struct. (IF 2.548) Pub Date : 2019-12-12
    Ravindra Gettu, Radhakrishna G. Pillai, Manu Santhanam, Anusha S. Basavaraj, Sundar Rathnarajan, B. S. Dhanya

    The article [Title], written by [AuthorNames], was originally published electronically on the publisher’s internet portal (currently SpringerLink) on 3 December 2018 without open access.

  • Correction to: RILEM and the National Institute of Standards and Technology (NIST) over the past 50 years
    Mater. Struct. (IF 2.548) Pub Date : 2019-12-12
    E. J. Garboczi

    The article [RILEM and the National Institute of Standards and Technology (NIST) over the past 50 years], written by [E. J. Garboczi], was originally published electronically on the publisher’s Internet portal (currently SpringerLink) on 20 September without open access.

  • Correction to: Biaxial bending of SFRC slabs: Is conventional reinforcement necessary?
    Mater. Struct. (IF 2.548) Pub Date : 2019-12-12
    Marco di Prisco, Matteo Colombo, Ali Pourzarabi

    The article “Biaxial bending of SFRC slabs: Is conventional reinforcement necessary?”, written by Marco di Prisco, Matteo Colombo and Ali Pourzarabi, was originally published electronically on the publisher’s Internet portal (currently SpringerLink) on 22 December 2018 without open access.

  • Correction to: Relating early hydration, specific surface and flow loss of cement pastes
    Mater. Struct. (IF 2.548) Pub Date : 2019-12-12
    Sara Mantellato, Marta Palacios, Robert J. Flatt

    The article “Relating early hydration, specific surface and flow loss of cement pastes”, written by “Sara Mantellato, Marta Palacios, Robert J. Flatt”, was originally published electronically on the publisher’s internet portal (currently SpringerLink) on 4 January 2019 without open access.

  • Correction to: Impact of carbonation on the chloride diffusivity in concrete: experiment, analysis and application
    Mater. Struct. (IF 2.548) Pub Date : 2019-12-12
    Kefei Li, Yiming Zhang, Shengnian Wang, Junjie Zeng

    The article [Title], written by [AuthorNames], was originally published electronically on the publisher’s internet portal (currently SpringerLink) on 3 December 2018 without open access.

  • Correction to: Cavitation of water in hardened cement paste under short-term desorption measurements
    Mater. Struct. (IF 2.548) Pub Date : 2019-12-12
    Ippei Maruyama, Jiří Rymeš, Matthieu Vandamme, Benoit Coasne

    This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits use, duplication.

  • Correction to: Understanding of historical masonry for conservation approaches: the contribution of Prof. Luigia Binda to research advancement
    Mater. Struct. (IF 2.548) Pub Date : 2019-12-12
    Anna Anzani, Giuliana Cardani, Paola Condoleo, Elsa Garavaglia, Antonella Saisi, Cristina Tedeschi, Claudia Tiraboschi, Maria Rosa Valluzzi

    The article [Title], written by [AuthorNames], was originally published electronically.

  • Correction to: Performance of Limestone Calcined Clay Cement (LC3) with various kaolinite contents with respect to chloride transport
    Mater. Struct. (IF 2.548) Pub Date : 2019-12-12
    Hamed Maraghechi, Francois Avet, Hong Wong, Hadi Kamyab, Karen Scrivener

    This article is distributed under the terms of the Creative Commons.

  • Correction to: A nearly self-sufficient framework for modelling reactive-transport processes in concrete
    Mater. Struct. (IF 2.548) Pub Date : 2019-12-12
    O. Burkan Isgor, W. Jason Weiss

    The article, A nearly self-sufficient framework for modelling reactive-transport processes in concrete, written by O. Burkan Isgor and W. Jason Weiss, was originally published electronically on the publisher’s Internet portal (currently SpringerLink) on 28 December 2018 without open access.

  • A novel nondestructive method to quantify fire-induced damage in RC structures based on their dynamic behavior
    Mater. Struct. (IF 2.548) Pub Date : 2019-12-12
    Ali Massumi, Kabir Sadeghi, Nafiseh Zifan

    The results of a research project on the dynamic behavior of fire-damaged RC structures are presented with specific reference to the fundamental period of the natural vibrations. Assessing the damage in fire-exposed RC structures is instrumental in understanding the features of the fire and in developing rational criteria to quantify structural post-fire safety. In this study, three moment-resisting frames were designed and tested to correlate the dynamic parameters with the temperature. Since the fundamental period of the natural vibrations can be easily measured for different levels of the thermal damage, the fire-induced variation of this parameter is a very efficient tool to quantify damage extension and allows introducing a novel fire damage index based on the relationship between the fundamental period and the temperature. This index is a contribution to facilitate decision-making concerning the repair and the partial or total demolition of fire-affected RC structures.

  • The influence of the glass transition temperature ( T g ) of polymers on early OPC hydration: a complete study of the heat flow, phase evolution, and pore solution chemistry
    Mater. Struct. (IF 2.548) Pub Date : 2019-12-11
    D. Jansen, Z. Lu, X.-M. Kong, J. Pakusch, E. Jahns, F. Deschner, Ch. Schmidtke

    The impact of two different dialyzed styrene-acrylate polymer dispersions on the early hydration of OPC was studied. The polymer particles of both dispersions show a similar particle size distribution and high charge due to carboxylic groups on the surface of the particles. Both dispersions also show similar adsorption behavior. The hydration of the OPC was studied at a polymer concentration below the initial adsorption in order to evaluate possible reasons for the interaction of the polymer particles with cement hydration. It can be shown that the polymer particle with the lower glass transition temperature Tg shows a stronger impact on cement hydration, which cannot be explained by any influence on the pore solution composition or the initial dissolution of cement phases. Hence, the adsorption mechanism seems to be the most likely cause of the interaction of the polymers with hydrating cement.

  • A practical creep model for concrete elements under eccentric compression
    Mater. Struct. (IF 2.548) Pub Date : 2019-12-10
    Haidong Huang, Reyes Garcia, Shan-Shan Huang, Maurizio Guadagnini, Kypros Pilakoutas

    Many prestressed concrete bridges are reported to suffer from excessive vertical deflections and cracking during their service life. Creep softens the structure significantly, and therefore an accurate prediction of creep is necessary to determine long-term deflections in elements under eccentric axial compression such as prestressed concrete girders. This study proposes a modification to the creep damage model of Model Code 2010 to account for the effect of load eccentricity. The modified creep model considers damage due to differential drying shrinkage. Initially, the creep behaviour of small scale concrete specimens under eccentric compression load is investigated experimentally. Twelve small-scale concrete prisms were subjected to eccentric axial loading to assess their shrinkage and creep behaviour. The main parameters investigated include the load eccentricity and exposure conditions. Based on the experimental results, an inverse analysis is conducted to determine the main parameters of the modified creep model. Subsequently, a numerical hygro-mechanical simulation is carried out to examine the effect of load eccentricity on the development of shrinkage and creep, and on the interaction between drying, damage and creep. The results indicate that eccentric loading leads to different tensile and compressive creep through the cross section, which contradicts the current design approach that assumes that tensile and compressive creep are identical. The proposed model also predicts accurately the long-term behaviour of tests on reinforced concrete elements available in the literature. This study contributes towards further understanding of the long-term behaviour of concrete structures, and towards the development of advanced creep models for the design/assessment of concrete structures.

  • Drying shrinkage of alkali-activated cements: effect of humidity and curing temperature
    Mater. Struct. (IF 2.548) Pub Date : 2019-12-07
    Maryam Hojati, Farshad Rajabipour, Aleksandra Radlińska

    Alkali-activated concrete (AAC) is a recycled and low-CO2 alternative to ordinary portland cement (OPC) concrete. One challenge with AACs is their propensity to shrinkage and cracking. In this work, drying shrinkage of four different structural-grade AACs was studied, namely: an activated class F fly ash, an activated slag, and two activated fly ash/slag blends. All four binders and a control OPC binder had the same (liquid/solid)vol and initial porosity. Drying shrinkage and mass loss of paste prisms were monitored as a function of time, relative humidity (RH), and the preceding moist-curing temperature. The results show that all AACs moist cured at 23 °C (73 °F) showed high shrinkage in comparison with the OPC binder and the shrinkage increased with higher proportions of fly ash. Steam curing at 60 °C (140 °F) substantially reduced the shrinkage of fly ash-rich mixtures, but it was less effective for slag-rich mixtures. Slag mixtures showed a significant time dependent response (creep), where the pastes continued to shrink after their mass loss had reached equilibrium.

  • An evaluation of yield and Maxwell fluid behaviors of fly ash suspensions in alkali-silicate solutions
    Mater. Struct. (IF 2.548) Pub Date : 2019-11-29
    Anvit Gadkar, Kolluru V. L. Subramaniam

    The rheological behavior of fly ash suspensions in alkali-silicate solutions used to prepare geopolymers is investigated. The transient stress response of fly ash suspensions at a constant applied strain rate is influenced by both the solids loading and the rheological behavior of the activating solution. The alkali-silicate solution itself behaves like a Newtonian fluid. The fundamental response of alkali-silicate fly ash suspension under constant applied shear strain rate exhibits a transition from a yield type to Maxwell flow. The variability in the Maxwell flow to yield type behavior depends upon the solids loading given by the solution to binder ratio and the composition of the activating solution. In both Maxwell flow and yield type responses, the maximum stress before initiation of flow is directly influenced by the viscosity of the activating solution. At specific solid loading, the transition between the Maxwell flow to yield type behavior is controlled by the composition of the activating solution. The viscous nature of the alkali-silicate solution produces a rate dependent transient response under constant applied strain rate.

  • Influence of calcium nitrate and sodium nitrate on strength development and properties in quicklime(CaO)-activated Class F fly ash system
    Mater. Struct. (IF 2.548) Pub Date : 2019-11-28
    Jung-Il Suh, Woo Sung Yum, Haemin Song, Hong-Gun Park, Jae Eun Oh

    The single use of CaO has been regarded as relatively unsuccessful in fly ash activation when no other additives are used together, as it produces a considerably lower strength compared to other types of activators (e.g., alkaline activators). This study investigated two potential additives of nitrate compounds (i.e., Ca(NO3)2 and NaNO3) to improve the strength of a CaO-activated fly ash system. The results showed that the use of Ca(NO3)2 was greatly beneficial in the strength improvement of the binder system primarily due to the significant increase in (1) the dissolution degree of fly ash, (2) C–S–H formation, and (3) pore size refinement from early days; however, NaNO3 was much less advantageous in strength improvement, although it also aided in dissolving fly ash.

  • Compressive and shear bond strengths of grooved AAC blocks and masonry
    Mater. Struct. (IF 2.548) Pub Date : 2019-11-28
    Amit Raj, Arun Ch Borsaikia, Uday S. Dixit

    Autoclaved aerated concrete (AAC) is a light-weight cementitious product of sand, water, cement, lime and aluminium powder mix, used globally for brickwork. The AAC blocks in vogue have smooth surfaces, due to which they have less bond strength than that of traditional clay bricks. This work asserts that the shear bond strength of AAC masonry can be enhanced by using grooved AAC blocks. The compressive strength of the grooved AAC block as well as the shear bond and compressive strengths of the masonry have been investigated experimentally and compared with conventional AAC blocks and masonry. The study clearly demonstrated the superiority of grooved AAC blocks to conventional AAC blocks. Simple analytical models have been developed to estimate the masonry compressive and shear bond strengths. Analytical models are capable of obtaining lower, upper and most likely estimates of strengths. Significance tests have been carried out to support the findings.

  • Diagonal shear behavior of historic walls strengthened with composite reinforced mortar (CRM)
    Mater. Struct. (IF 2.548) Pub Date : 2019-11-25
    Tommaso D’Antino, Francesca Giulia Carozzi, Carlo Poggi

    Composite reinforced mortar (CRM) represents an innovative strengthening solution for existing masonry structures. CRM is comprised of a composite grid embedded within an inorganic matrix (mortar) and it is applied as externally bonded reinforcement of masonry members. The composite grid bears the tensile stresses whereas the inorganic matrix is responsible for the stress-transfer between the composite grid and the substrate. CRM showed promising results in improving the mechanical properties of different masonry members, such as walls and arches. However, a full understanding of the mechanical behavior of CRM strengthened masonry members is still missing, which hinders the formulation of reliable CRM design guidelines. In this paper, an experimental investigation of the in-plane behavior of masonry walls made by historical bricks and strengthened with a CRM comprised of a glass fiber composite grid embedded in a lime-based mortar is presented and discussed. The parameters studied are the wall dimension and type (double leaf with and without diatoni). Furthermore, the effect of steel anchors on the strengthened wall capacity is investigated. The results obtained are finally analyzed using simple analytical formulations.

  • On low temperature binder testing using DSR 4 mm geometry
    Mater. Struct. (IF 2.548) Pub Date : 2019-11-11
    Johannes Büchner, Michael P. Wistuba, Torsten Remmler, Di Wang

    The 4 mm parallel plate geometry in the DSR with a new sample installation method is proposed to evaluate low temperature rheological properties of asphalt binders. For this purpose, the influences of temperature conditioning and normal force were studied, and finally suitable test conditions were identified to run T-f-Sweep tests in oscillation mode. Appropriate shear stresses were identified by amplitude sweep tests considering the instrument limitations. Consequently, testing conditions and instrument limitations are determined, which need to be respected to obtain precise and repeatable rheological data.

  • Assessment of test methods for the durability of thermal mortars exposure to freezing
    Mater. Struct. (IF 2.548) Pub Date : 2019-11-09
    J. Maia, Nuno M. M. Ramos, R. Veiga

    Thermal mortars are a trend in the construction industry in recent years, owing to the required decrease of the thermal transmission of building envelopes. The high porosity of thermal mortars leads to permeability values that can affect their durability since it creates more favourable conditions for the penetration of aggressive agents. Water is observed as one of the most common and harmful degradation agents. Regarding the climatic variability in Europe, freezing is a usual degradation mechanism both in severe and moderate climates. Since thermal mortars have higher water absorption than a common insulation, the freezing may occur. As no durability assessment methodologies to evaluate the exposure of thermal mortars to freezing degradation mechanisms exist, the present work has the objective to analyse existing accelerated ageing procedures, which envisage freezing degradation mechanism. As such, the durability assessment described in EN 1015-21 and ETAG 004 was adapted and implemented in different thermal mortars. It was observed that the higher number of cycles and the severity of the freeze–thaw ageing cycles, according to ETAG 004, may reproduce the effect of the northern European climates, while the ageing cycles, described in EN 1015-21, combine degradation mechanisms that occur in central and southern European climates. This adaptation allowed collecting reliable data and inputs to the development of durability assessment methodologies directly applicable to thermal rendering and plastering systems.

  • Glucose addition improves the bio-remediation efficiency for crack repair
    Mater. Struct. (IF 2.548) Pub Date : 2019-11-07
    Xiaohao Sun, Linchang Miao, Chengcheng Wang

    This study developed a novel method of glucose addition for the crack repair of concrete samples, which improved the bio-remediation efficiency. Various amounts of glucose were added to the medium at different sequence and the resulting absorbances were measured. Urea, calcium salt, and various amounts of glucose were mixed with an absorbance-fixed bacterial suspension and the resulting effect on calcium carbonate production was analyzed. Concrete specimens with irregular cracks were subjected to glucose addition for bio-remediation. Glucose addition decreased the pH, which inhibited the growth of bacteria. However, in a strong alkaline environment, this procedure was beneficial for crack repair. Informed by the bacterial growth and precipitation rates for calcium carbonate, addition of 10 g/L glucose was identified as the optimum concentration. After repair, the area recovery ratios of all samples exceeded 79%, while water penetration rates decreased significantly. The sonic time values of measurement points decreased and the strength of samples reached about 35% of the initial strength. Adding glucose to the medium during the repair improved the effect of the repair. This method can repair irregular cracks, accelerate the bio-remediation reaction, and reduce the repair time.

  • Effect of marine sediments incorporation on the behaviour of alkali-activated GGBFS
    Mater. Struct. (IF 2.548) Pub Date : 2019-10-26
    Reine Karam, David Bulteel, Thomas Wattez, Dimitri Deneele

    This study deals with the development of a new binder using alkali-activated ground granulated blast furnace slag (GGBFS) and the fine fraction of non-calcined dredged sediments. The effects of sediment’s incorporation (23% in mass) on hydration heat, slump flow and mechanical properties are studied at two water/solid ratios (0.45 and 0.62). The results show that in absence of silicates in the alkali-activator, the addition of sediments maintains mechanical strengths comparable to those obtained without sediments except that reaction kinetics and setting times are slowed down. Whereas when adding 23% of sediments to the silicate activated systems, compressive strength decreases and reaction kinetics is slowed down. The presence of sediments in the mixture does not affect the initial setting time of the paste. Whereas at W/S = 0.62, a loss in the mechanical behavior is noted, the setting times and the kinetics of the reaction are decelerated. Tests on GGBFS in the absence of sediments showed that it’s the increase of water content (W/S increase from 0.45 to 0.62) that affects the mechanical properties of the binders more than sediment’s incorporation, but it’s the presence of sediments that affects the setting times more than W/S increase. These results show that the control of the quantity of water in the system allows the development of alkali-activated materials with good mechanical performance and regulated setting time.

  • FRP fibre-cementitious matrix interfacial bond under time-dependent loading
    Mater. Struct. (IF 2.548) Pub Date : 2019-10-17
    Mohammed Farooq, Nemkumar Banthia

    This paper presents the behavior of the interfacial bond between an innovative FRP fibre and cement mortar under time-dependent loading. Two types of FRP fibres—GFRP and CFRP were investigated. Particularly, the fibre pullout response under quasi-static loading is compared with the response under dynamic loading. To gauge the long term behavior of cracked fibre reinforced composites, fibre relaxation tests were conducted in which initial strain was imparted and sustained, and the relaxation of the composite in terms of drop in load over time period was monitored at room temperature as well as at 50 °C. FRP fibres were found to be to some extent sensitive to loading rate, with an increase in the range of 30–50% in the peak load under dynamic loading. The GFRP fibres itself depicted higher strengths under dynamic loading rate. Under a sustained fibre slip, FRP fibres showed a lower relaxation at both room temperature and at 50 °C compared to commercially available steel and polypropylene fibres. There was also no conclusive change in pullout response in specimen subjected to sustained strains compared to reference.

  • Effects of curing temperature and superabsorbent polymers on hydration of early-age cement paste containing a CaO-based expansive additive
    Mater. Struct. (IF 2.548) Pub Date : 2019-10-15
    Haitao Zhao, Kaidi Jiang, Yunfei Di, Wen Xu, Wei Li, Qian Tian, Jiaping Liu

    The early-age shrinkage can easily result in crack of concrete in the early age, which seriously affects the durability of concrete. The CaO-based expansion additive is a normally used and effective material for the shrinkage compensation and the reduction of early-age crack risk in concrete. The hydration is a factor that significantly influences the mechanical and durability properties of concrete, and the study on the hydration of the cement paste containing a CaO-based expansive additive under different curing temperature and with superabsorbent polymers addition is lacking. In this study, tests were conducted using the low-field nuclear magnetic resonance to assess the effect of curing temperature and superabsorbent polymers on the hydration of early-age cement paste containing a CaO-based expansion additive. The experimental results show that the incorporation of CaO-based expansive additive can promote the hydration of cement paste, and 2% dosage of CaO-based expansive additive has a better promotion than that of 3% dosage. High curing temperature can effectively accelerate the hydration of cement paste containing the CaO-based expansion additive. In addition, superabsorbent polymers can also effectively promote hydration.

  • Rate-dependence of the tensile behaviour of fibre reinforced concrete in the quasi-static regime
    Mater. Struct. (IF 2.548) Pub Date : 2019-10-09
    Stefie J. Stephen, Ravindra Gettu

    The effect of crack rate on the tensile stress–crack width relation of fibre reinforced concrete is studied experimentally, using the three-point bending test, where the post-peak flexural response of the material is determined over a range of loading rates covering 5 orders of magnitude. The tetralinear stress–crack opening (σ–w) relations are subsequently obtained from inverse analyses. Concretes with hooked-ended steel fibres at different dosages and with polypropylene fibres have been studied. The results show that the tensile strength is reduced and the initial drop in cohesive stresses is less steep at slower loading rates, with the changes being more significant in concretes with lower toughness. Numerical analysis shows that the fracture process zone at crack initiation extends further as the loading becomes slower. The variation in the σ–w relation with crack rate has been modelled empirically based on the rate-dependence of the concrete matrix and the tensile strength of the FRC. The general variation of flexural toughness with the loading rate has also been identified, reflecting the moderating influence due to steel fibres, especially at higher dosages.

  • Chemical and rheological properties of polymer modified bitumen incorporating bio-oil derived from waste cooking oil
    Mater. Struct. (IF 2.548) Pub Date : 2019-10-08
    Zhaojie Sun, Junyan Yi, Zining Chen, Sainan Xie, Meng Xu, Decheng Feng

    The chemical and rheological properties of polymer modified bitumen incorporating bio-oil derived from waste cooking oil (WCO) were investigated in this paper. At first, the chemical composition and mixing mechanism of the experimental materials were analysed from the perspective of functional group, and the influence of bio-oil on the activation energy was also researched. Then, the effect of bio-oil on the rotational viscosities of polymer modified bitumen and construction temperatures of corresponding mixtures was studied. Finally, the shear and bending rheological properties of polymer modified bitumen containing bio-oil were investigated. The results show that the bio-oil and styrene–butadiene–styrene (SBS) modified bitumen is mainly physically mixed, the addition of bio-oil decreases the activation energy of SBS modified bitumen. Additionally, the SBS modified bitumen containing bio-oil has lower viscosity values, and corresponding mixtures also have lower construction temperatures. Furthermore, the addition of bio-oil in SBS modified bitumen reduces the shear modulus and increases the bending creep compliance, which means bio-oil has positive effect on the low-temperature thermal cracking resistance performance while sacrificing the high-temperature rutting resistance performance to some extent. Therefore, the incorporation of WCO-based bio-oil in polymer modified bitumen is a promising technique to be used in cold regions where the low-temperature problems are more crucial.

  • Effects of applied voltage on chloride binding and microstructure of cement pastes subjected to chloride solutions
    Mater. Struct. (IF 2.548) Pub Date : 2019-10-08
    Xiang Hu, Caijun Shi, Qiang Yuan, Nima Farzadnia, Geert de Schutter

    In this paper, the effects of applied voltage on cement paste subjected to chloride solutions were studied by comparing the microstructure and chloride binding of hardened cement pastes after bulk diffusion and rapid chloride migration (RCM) tests. The chloride concentration index, chloride binding, chemical composition and morphology of hydration products, pore structure and zeta potential of cement pastes after the bulk diffusion and RCM tests were measured. The results showed that the microstructure of cement paste was densified by the chloride binding; the applied voltage of 10 V increased the Ca/Si of C–S–H gel and modified the morphology of Friedel’s salt. The chloride content of the expressed pore solution and the C–S–H bound chloride content increased when external voltage was applied, while no difference was observed for Friedel’s salt bound chloride. The applied voltage increased the total chloride content in cement paste mainly by increasing the free chloride and C–S–H bound chloride.

  • Precast TRC sandwich panels for energy retrofitting of existing residential buildings: full-scale testing and modelling
    Mater. Struct. (IF 2.548) Pub Date : 2019-10-04
    Isabella G. Colombo, Matteo Colombo, Marco di Prisco

    In the 7th Framework Programme for Research and Technological Development, the European Commission financed the project EASEE (2012–2016), which was aimed at developing façade solutions for the energy retrofitting of multi-storey multi-owners existing residential buildings, built in an historical period in which no specific attention was paid to the energy issue. For the outer envelope, the consortium proposed textile reinforced concrete precast sandwich panels. The high durability, high aesthetic potential, low impact on occupant life during installation, and increase in impact resistance make this solution competitive with the exterior insulation and finishing system, now the most widespread energy retrofitting method adopted on existing buildings. Within the project, the panel has been mechanically investigated at multiple scales, and finally applied on some demo-buildings. This paper presents the investigation of the bending behavior of full-size panels up to failure when tested according to four-point bending scheme, focusing the attention on the effects of the production procedure and panel details on the structural behavior. The capability of expanded polystyrene in transferring shear stresses to the external TRC layers—already exhibited by specimens at lab-scale—is here verified on full-size elements. In addition, a numerical model—already validated for lab-scale sandwich beams—is here applied in order to check its reliability for the design of full-scale panel.

  • The re-swelling behavior of superabsorbent polymers (SAPs) in hardened cement paste with an artificial crack
    Mater. Struct. (IF 2.548) Pub Date : 2019-10-04
    Haitao Yang, Juanhong Liu, Qian Zhou, Hongguang Ji

    Re-swelling capacity is a key factor affecting the contribution of superabsorbent polymers (SAPs) to sealing cracks in concrete. In this paper, a new parameter (η), the ratio between the volume of the crack filled with the expansive SAPs and the volume of dry SAPs, is given to evaluate the re-swelling capacity of a single SAPs particle. Moreover, the influences of paste composition, solution properties, and crack width on the η value are studied by an innovative immersion test. The results show that the swollen volume ratio, the ratio of the swollen volume of SAPs during mixing to their dry volume, decreases with the reduction of the water-to-binder ratio and the addition of mineral admixtures. Furthermore, the swollen volume ratio, the solution properties, and the crack width have significant impacts on the η value. The η value rises with an increase in crack width (0.25–1 mm), revealing the restricting effects of cracks on the re-swelling capacity of SAPs. These results indicate that the paste composition, solution properties, and crack width should be considered when designing the self-sealing concrete containing SAPs.

  • Comparative study of the yield stress determination of cement pastes by different methods
    Mater. Struct. (IF 2.548) Pub Date : 2019-10-04
    Mokrane Bala, Rachid Zentar, Pascal Boustingorry

    Different methods have been proposed in the literature to determine the yield stress of cement grouts. These methods may present wide differences especially for thixotropic materials such as cement pastes. In this paper, different mixtures of water–cement–superplasticizer were studied for various w/c ratios and superplasticizer dosages. From shear tests of the mixtures in a rheometer, yield stress was determined in different ways: by identification on the experimental flow curve or by modelling flow curve through different rheological models. The conventional rheological models as Bingham model and Herschel–Bulkley model are not in agreement in the majority of the cases studied especially at low shear rates where thixotropy can be observed. In order to enhance the modelling in this area and allows to accurately determine the yield stress, we compared the results obtained through the conventional rheological models to that obtained by a thixotropy model. From the obtained results, it turns out that the latter allows to better predict the behaviour of thixotropic cement grouts and their yield stress.

  • Waste glass as binder in alkali activated slag–fly ash mortars
    Mater. Struct. (IF 2.548) Pub Date : 2019-10-03
    G. Liu, M. V. A. Florea, H. J. H. Brouwers

    This paper illustrates the application of waste glass powder as part of the binder in slag–fly ash systems activated by NaOH and NaOH/Na2CO3 activators. To evaluate the reaction kinetics, reaction products, mechanical properties, and durability performance of glass powder modified alkali activated slag–fly ash systems, calorimetry test, X-ray diffraction, FTIR, strength test, drying shrinkage tests, and carbonation test were conducted. From the isothermal calorimeter results, glass powder shows a higher reactivity compared to fly ash but still lower than slag. The reaction products of glass power modified samples exhibit an enhancement of polymerization degree of Si–O–T, observed in FTIR. As a consequence, higher drying shrinkage exists in glass modified mortars. The mechanical performance of different samples is mostly controlled by the Ca/Si of dry mixtures and activator type. After the slag–fly ash binder system was modified by the waste glass, a significant enhancement of resistance to carbonation was identified, especially for NaOH/Na2CO3 activated mortars, which show an increase of 300% on the carbonation resistance ability compared to the reference sample. The Na/(Si + Al) ratio of dry mixtures exhibits a positive correlation with carbonation resistance.

  • A simplified model for the combined wicking and evaporation of a NaCl solution in limestone.
    Mater. Struct. (IF 2.548) Pub Date : 2018-01-01
    L Pel,R Pishkari,M Casti

    Salt weathering is one of the major causes of the damage both in cultural heritage as well as in civil engineering constructions. A special case develops when there is a continuous wicking of a salt solution into a material in combination with evaporation of the moisture at its surface. In this study we are interested in the case where the absorption rate is much higher than the evaporation and as a result a salt concentration will build up at the drying surface resulting in crystallization. To this end we propose a simplified model to describe this mechanism. In order to check the model the NaCl concentration profiles were measured non-destructively by Nuclear Magnetic Resonance during a combined wicking and evaporation experiment with limestone. A good correlation was found between the model and the measured NaCl concentration profiles.

  • Performance of single skin masonry walls subjected to hydraulic loading.
    Mater. Struct. (IF 2.548) Pub Date : 2018-01-01
    D M Herbert,D R Gardner,M Harbottle,T G Hughes

    Property owners are facing increasing threats from flooding and in response are likely to turn to products designed to waterproof or 'seal' the outside of the building in an effort to prevent the ingress of flood water. However, very limited research has been conducted on the effect of this sealing action and the consequent hydraulic load acting upon the structure of the building. The theoretical safe application of waterproofing products has been suggested to be between 0.6 and 1 m (published guidance suggests 0.9 m), although the experimental evidence supporting these suggestions is either absent or limited in nature. This paper presents the findings of an experimental programme that has examined the effect of out-of-plane hydrostatic loading on masonry walls typical of domestic or commercial buildings. The study, conducted at 1/6th scale using a geotechnical centrifuge considers wall panels constructed from a variety of masonry units (autoclaved aerated concrete block, brick and brick-block) bound together with two different types of mortar. The wall panels were subject to an axial load representative of 1 storey of loading and were simply supported on all 4 sides. The load-out-of-plane deflection response of the panels was captured by a 3D digital image correlation system, and the water level at failure was compared to that predicted from previous research and the established yield line analysis method with encouraging results. When partial material and load factors were taken into consideration the results illustrated that a safe sealing height of 0.9 m, as quoted in the literature, would generally be inappropriate, whilst the safe sealing height of 0.6 m was not suitable for every case investigated. This supports the need for a suitable approach for the calculation of water levels at failure rather than the use of fixed values given in published literature.

  • An experimental study of cathodic protection for chloride contaminated reinforced concrete.
    Mater. Struct. (IF 2.548) Pub Date : 2018-01-01
    Hayder M Oleiwi,Yu Wang,Michele Curioni,Xianyi Chen,Guowen Yao,Levingshan Augusthus-Nelson,A H Ragazzon-Smith,Igor Shabalin

    Cathodic protection (CP) is being increasingly used on reinforced concrete structures to protect steel reinforcing bars from corrosion in aggressive conditions. Due to the complexity of environmental conditions, the design specifications in national and international standards are still open to discussion to achieve both sufficient and efficient protection for reinforced concrete structures in engineering practices. This paper reports an experimental research to investigate the influence of chloride content on concrete resistivity, rebar corrosion rate and the performance of CP operation using different current densities. It aims to understand the correlation between the chloride content and concrete resistivity together with the CP current requirement, and to investigate the precision of the CP design criteria in standards.

  • How models can make a difference for a sustainable future of the building industry.
    Mater. Struct. (IF 2.548) Pub Date : null
    Klaas van Breugel

    Models play a vital role in science and technology and in the evolution of modern societies. They are used for describing processes and mechanisms, experimental observations, analyses and predictions. In spite of the fact that models are a reduction of reality, the achievements of modern societies are impressive and would have been inconceivable without the role of models. These achievements can be qualified with one term: growth. The impressive growth in past decades, however, now appears to be unsustainable. In this contribution the above-mentioned dilemma is dealt with. First the evolution and use of models is discussed from a more general sustainability perspective. In the second part of the paper the application of models for sustainable solutions in the field of cementitious materials is emphasized.

  • Active control of properties of concrete: a (p)review.
    Mater. Struct. (IF 2.548) Pub Date : 2018-11-06
    Geert De Schutter,Karel Lesage

    Concrete properties to a large extent depend on mix design and processing, currently leaving only limited options to actively modify concrete properties during or after casting. This paper gives a (p)review on a more advanced active control of properties of concrete, based on the application of external signals to trigger an intended response in the material, either in fresh or hardened state. Current practices in concrete industry that could be considered as active control are briefly summarized. More advanced active control mechanisms as studied in other fields, e.g. based on hydrogels and other functional polymers, are reviewed and some principles are listed. A specific focus is further given on potential methods for active rheology control. Based on the concepts developed in other fields, substantial progress could be made in order to achieve active control of fresh and hardened concrete properties. However, several challenges remain, like the stability and functioning of the responsive material in a cementitious environment, the applicability of the control signal in a cementitious material, and the economy, logistics and safety of a control system on a construction site or in precast industry. Finding solutions to these challenges will lead to marvelous opportunities in general, and for 3D and even 4D printing more particularly.

  • Creep and cracking of concrete hinges: insight from centric and eccentric compression experiments.
    Mater. Struct. (IF 2.548) Pub Date : 2017-12-08
    Thomas Schlappal,Michael Schweigler,Susanne Gmainer,Martin Peyerl,Bernhard Pichler

    Existing design guidelines for concrete hinges consider bending-induced tensile cracking, but the structural behavior is oversimplified to be time-independent. This is the motivation to study creep and bending-induced tensile cracking of initially monolithic concrete hinges systematically. Material tests on plain concrete specimens and structural tests on marginally reinforced concrete hinges are performed. The experiments characterize material and structural creep under centric compression as well as bending-induced tensile cracking and the interaction between creep and cracking of concrete hinges. As for the latter two aims, three nominally identical concrete hinges are subjected to short-term and to longer-term eccentric compression tests. Obtained material and structural creep functions referring to centric compression are found to be very similar. The structural creep activity under eccentric compression is significantly larger because of the interaction between creep and cracking, i.e. bending-induced cracks progressively open and propagate under sustained eccentric loading. As for concrete hinges in frame-like integral bridge construction, it is concluded (i) that realistic simulation of variable loads requires consideration of the here-studied time-dependent behavior and (ii) that permanent compressive normal forces shall be limited by 45% of the ultimate load carrying capacity, in order to avoid damage of concrete hinges under sustained loading.

  • Low-Temperature Curing Strength Enhancement in Cement-Based Materials Containing Limestone Powder.
    Mater. Struct. (IF 2.548) Pub Date : 2017-08-02
    Dale P Bentz,Paul E Stutzman,Franco Zunino

    With the ongoing sustainability movement, the incorporation of limestone powder in cementitious binders for concrete in the U.S. has become a subject of renewed interest. In addition to accelerating the early age hydration reactions of cementitious systems by providing additional surfaces for nucleation and growth of products, limestone powder is also intriguing based on its influence on low-temperature curing. For example, previous results have indicated that the utilization of limestone powder to replace one quarter of the fly ash in a high volume fly ash mixture (40 % to 60 % cement replacement) produces a reduction in the apparent activation energy for setting for temperatures below 25 °C. In the present study, the relationship between heat release and compressive strength of mortars at batching/curing temperatures of 10 °C and 23 °C is investigated. For Portland-limestone cements (PLC) with limestone additions on the order of 10 %, a higher strength per unit heat release is obtained after only 7 d of curing in lime water. Surprisingly, in some cases, the absolute strength of these mortar cubes measured at 7 d is higher when cured at 10 °C than at 23 °C. Solubilities vs. temperature, reaction stoichiometries and enthalpies, and projected phase distributions based on thermodynamic modeling for the cementitious phases are examined to provide some theoretical insight into this strength enhancement. For a subset of the investigated cements, thermogravimetric analysis (TGA), quantitative X-ray diffraction (XRD), and scanning electron microscopy (SEM) are conducted on 7-d paste specimens produced at the two temperatures to examine differences in their reaction rates and the phases produced. The strength enhancement observed in the PLC cements is related to the cement hydration products formed in the presence of carbonates as a function of temperature.

  • Numerical Simulation of the Freeze-Thaw Behavior of Mortar Containing Deicing Salt Solution.
    Mater. Struct. (IF 2.548) Pub Date : 2017-01-14
    Hadi S Esmaeeli,Yaghoob Farnam,Dale P Bentz,Pablo D Zavattieri,Jason Weiss

    This paper presents a one-dimensional finite difference model that is developed to describe the freeze-thaw behavior of an air-entrained mortar containing deicing salt solution. A phenomenological model is used to predict the temperature and the heat flow for mortar specimens during cooling and heating. Phase transformations associated with the freezing/melting of water/ice or transition of the eutectic solution from liquid to solid are included in this phenomenological model. The lever rule is used to calculate the quantity of solution that undergoes the phase transformation, thereby simulating the energy released/absorbed during phase transformation. Undercooling and pore size effects are considered in the numerical model. To investigate the effect of pore size distribution, this distribution is considered using the Gibbs-Thomson equation in a saturated mortar specimen. For an air-entrained mortar, the impact of considering pore size (and curvature) on freezing was relatively insignificant; however the impact of pore size is much more significant during melting. The fluid inside pores smaller than 5 nm (i.e., gel pores) has a relatively small contribution in the macroscopic freeze-thaw behavior of mortar specimens within the temperature range used in this study (i.e., +24 °C to -35 °C), and can therefore be neglected for the macroscopic freeze-thaw simulations. A heat sink term is utilized to simulate the heat dissipation during phase transformations. Data from experiments performed using a low-temperature longitudinal guarded comparative calorimeter (LGCC) on mortar specimens fully saturated with various concentration NaCl solutions or partially saturated with water is compared to the numerical results and a promising agreement is generally obtained.

  • Standardization of peeling tests for assessing the cohesion and consolidation characteristics of historic stone surfaces.
    Mater. Struct. (IF 2.548) Pub Date : 2012-01-01
    Miloš Drdácký,Jaroslav Lesák,Silvia Rescic,Zuzana Slížková,Piero Tiano,Jaroslav Valach

    A peeling test known as the "Scotch Tape test" has been used for more than 40 years in conservation practice for assessing the consolidation efficiency of degraded stone. However, the method has not been supported by any standard or reliably verified recommendations for its application. Its applicability is overestimated, and its unrestricted use without adequate knowledge and sufficient understanding can lead to non-comparable, non-reproducible and, in many cases, incorrect and severely biased results and assessments. This paper presents the results of a recent study focused on establishing limits for application, reliable procedures and a "standard" protocol for testing the cohesion characteristics of brittle and quasi-brittle materials, mainly mortars and stones. The main application strategy exploits repeated peeling in the same place on a surface in order to eliminate the effect of the natural decrease in the detached material from the subsurface layers, which might be incorrectly interpreted as a consolidation effect. There is a discussion of factors influencing the performance of the peeling test method, and examples of peeling measurements on various natural and artificial stones are presented.

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