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  • Acoustic emission characteristics of fracture modes in masonry materials
    Constr. Build. Mater. (IF 3.169) Pub Date : 2018-01-19
    G. Livitsanos, N. Shetty, D. Hündgen, E. Verstrynge, M. Wevers, D. Van Hemelrijck, D.G. Aggelis

    Acoustic emission (AE) is a powerful technique for detection and analysis of the elastic waves produced by the failure mechanisms in construction materials such as masonry. In this study, the different fracture mechanisms are studied in relation to the properties of bricks and mortars. The fracture process is being evaluated using the combination of AE and Digital Image Correlations (DIC) techniques. The isolation of the AE signatures of different types of failure mechanisms is done by testing bricks in flexure and brickwork couplets in compression. AE data are analyzed with a simplified AE parameter-based approach aiming to characterize the fracture mode. This is one of the first times where the relation between the shear and the longitudinal strain field is correlated in masonry with AE. This offers new insight in the material's behavior especially in relation to complicated structural geometries where the dominant stress mode is not known a priori.

    更新日期:2018-01-19
  • VOCs characteristics and their relation with rheological properties of base and modified bitumens at different temperatures
    Constr. Build. Mater. (IF 3.169) Pub Date : 2018-01-10
    Min Lei, Shaopeng Wu, Gang Liu, Serji Amirkhanian

    During heating process of bituminous materials, volatile organic compounds (VOCs) will be released, and it is harmful to the skin, the respiratory and nervous system of the human body, especially increasing its carcinogenic tendency. In this study, the VOCs emission of base and modified binder was characterized as the function of typical temperatures by gas chromatography coupled with mass spectrometry (GC/MS). The rheological behavior of each binder before and after the emission of VOCs was compared. The relation between the VOCs emission of bitumen and its rheological properties was researched. The results indicated that a higher temperature can lead to increase of VOCs components of binder. The addition of SBS modifier can reduce VOCs components of its base binder. However, the degradation of the SBS modifier decreased its inhibition effect on the VOCs emission of bitumen at 220 °C. Naphthalene release and carcinogenic index of polycyclic aromatic hydrocarbons (PAHs) increased with the increase of temperature. The complex-flow activation energy EaEa increased after VOCs emission. Naphthalene content exhibited a better linear relation with EaEa.

    更新日期:2018-01-10
  • Research on properties of bio-asphalt binders based on time and frequency sweep test
    Constr. Build. Mater. (IF 3.169) Pub Date : 2018-01-09
    Junfeng Gao, Hainian Wang, Zhanping You, Mohd Rosli Mohd Hasan

    Bio-asphalt is a binding agent that is made of bio-oil and petroleum asphalt, or bio-oil modified with incorporations of some other additives under certain conditions. This study was carried out to evaluate the properties of bio-asphalt binder-based in terms of the value of complex shear modulus (G∗) and the phase angle (δ) tested by dynamic shear rheometer (DSR). Four bio-oil dosages of 5, 10, 15, and 20% based on the weight of asphalt (S100) were used to alter the SBS-modified binder. Whereby, the SBS content is approximately 1% of the weight of the virgin asphalt. The complex shear modulus and frequencies of virgin and short-term aged binders were tested. The master curves of rutting factor (G∗/sinδ) of different bio-asphalt were then generated to survey its rheological properties in a broad range of frequencies and temperatures. Based on the results, it was found that the addition of bio-oil extracted from sawdust has significantly increased the complex shear modulus of asphalt binder at the same frequency conditions after going through rolling thin film oven (RTFO), which is desirable for rutting prevention of asphalt mixtures. The rheological properties of bio-binders are more susceptible to the RTFO aging condition compared to the reference binder. The master curve of rutting factor of bio-binder indicated that the rutting factor of bio-asphalt increased with the increase of frequency before and after RTFO. Additionally, incorporations of bio-oil into the SBS modified asphalt, has greatly increased the rutting factor (G∗/sinδ) after RTFO, regardless of the loading frequency. However, the degree of enhancement was dominated by the percentage of bio-oil and aging condition.

    更新日期:2018-01-09
  • Further evidence of interfacial adhesive bond strength enhancement through fiber reinforcement in repairs
    Constr. Build. Mater. (IF 3.169) Pub Date : 2018-01-08
    Cristina Zanotti, Giulia Rostagno, Brian Tingley
    更新日期:2018-01-09
  • Temperature predictions for asphalt pavement with thick asphalt layer
    Constr. Build. Mater. (IF 3.169) Pub Date : 2018-01-08
    Yi Li, Liping Liu, Lijun Sun

    Temperature is one of the most important factors affecting functional as well as structural performance of asphalt pavements with thick asphalt layer (>30 cm). For a successful pavement design, it is vital to accurately predict the pavement temperatures at various depths. However, most previous researches focused on the temperature predictions for conventional asphalt pavements, of which the asphalt thickness is less than 30 cm. This suggests their proposed models are applicable in top layers, but may not be so effective for temperature predictions at deeper depths. As a result, the primary objective of this research was to develop a statistical model to predict temperatures at deep depths. Three test sites were selected, and they were instrumented with a number of sensors and a data logger to record the pavement temperature hourly. Also, all test sections can provide meteorological monitoring to collect hourly air temperatures and hourly total solar radiation. The recorded meteorological conditions were found to have cumulative effect on the measured pavement temperatures at various depths. On basis of their relationship, a statistical regression was performed, and the temperature prediction model was determined as a function of depth, average air temperature and total solar radiation calculated in the cumulative time. For an improvement in applicability, historical mean monthly air temperatures were also incorporated into the mode. The accuracy and applicability of the improved model were validated by applying it to additional sites for which the measured pavement temperatures and meteorological data were available. Also, by comparing with existing models, the developed model was testified to be more effective for asphalt pavements with thick asphalt layer, promising the model’s potential use.

    更新日期:2018-01-08
  • Replacement of steel with GFRP for sustainable reinforced concrete
    Constr. Build. Mater. (IF 3.169) Pub Date : 2017-12-28
    Shamim A. Sheikh, Zahra Kharal

    Corrosion of steel in reinforced concrete structures has cost a significant amount of resources globally over the past few decades. Glass fiber reinforcement polymer (GFRP) bars present a feasible and cost-effective solution to the problem of steel corrosion. The aim of this paper is to let engineers gain a better understanding of the overall behavior of GFRP as internal reinforcement so that they have more confidence using it as a sustainable material. This paper provides a few significant outcomes from an extensive experimental program underway at the University of Toronto. The work discussed here provides a summary of the tests on 24 GFRP reinforced beams, 60 GFRP direct tension specimens and 20 GFRP confined columns, and evaluates the behavior of GFRP-RC in flexure, shear, tension and compression. A recently proposed tension-stiffening model has been incorporated in analytical modeling of GFRP-RC beams and the results show significant improvement in the prediction of deflection and stiffness of the beams. Results from column tests show that GFRP bars used as longitudinal reinforcement can resist compressive stresses in excess of 700 MPa and GFRP lateral reinforcement can confine concrete core more effectively than steel.

    更新日期:2017-12-31
  • Effect of graphene nano-sheets on the chloride penetration and microstructure of the cement based composite
    Constr. Build. Mater. (IF 3.169) Pub Date : 2017-12-13
    Baomin Wang, Ruying Zhao

    In this work, the effects of the non covalent surface modification method on the dispersion of graphene nano-sheets (GNS) in water and chloride diffusion of the cement paste incorporating these dispersions were investigated. Results showed that stable and homogeneous suspensions of graphene nano-sheets were prepared using polyoxyethylene (40) nonylphenylether (CO890) as a dispersant. In this research, water to cement ration is kept 0.30, the addition of GNS is ranging from 0.02% to 0.15% by weight of cement. It is found that introduction small quantities of GNS as little as 0.02% can decrease the chloride penetration depth and coefficient by as much as ∼37% and ∼42%, respectively. This improvement could be attributed to the enhanced degree of cement hydration, filling effect, barrier effect and crack-arresting effect of GNS in cement matrix. This work provides a new way to further understand the improvement of GNS in cement composites.

    更新日期:2017-12-14
  • Effects of the incorporation of recycled aggregate in the durability of the concrete submitted to freeze-thaw cycles
    Constr. Build. Mater. (IF 3.169) Pub Date : 2017-12-13
    N.S. Amorim Júnior, G.A.O. Silva, D.V. Ribeiro

    Recycled concrete aggregates have been extensively studied in recent years. However, the studies that have addressed the use of the recycled aggregate in concrete subjected to freeze-thaw cycles are divergent. Thus, the present work suggests the use of recycled coarse aggregate (RCA), derived from civil construction waste, in concrete as a substitution to the natural coarse aggregate (NCA). To this end, concrete specimens were molded with replacement levels equal to 15%, 25% and 50% of the NCA for RCA, being the specimens evaluated according to the ASTM C 666-15 norm. In addition, the samples were characterized for apparent porosity and density, water absorption by capillarity, axial compression strength and dynamic modulus of elasticity. The use of recycled aggregates proved to be efficient as a possible alternative to the incorporation of air in the concretes, presenting a durability factor at the end of the cycle higher than presented by the reference mixture.

    更新日期:2017-12-14
  • Hybrid fiber reinforced self compacting concrete with fly ash and colloidal nano silica: A systematic study
    Constr. Build. Mater. (IF 3.169) Pub Date : 2017-12-11
    Chinmaya Kumar Mahapatra, Sudhirkumar V. Barai

    The current systematic study investigates properties of hybrid fiber reinforced self compacting concrete (HyFRSCC) with crimped steel fibers (CSF) and polypropylene fibers (PPF) along with class F fly ash (FA) and colloidal nano silica (CNS). Optimization of HyFRC mix is conducted using L16 Taguchi Orthogonal Array where additive has four levels. Combination of 10% FA, 0.4% CNS, 1.25% CSF and 0.167% PPF found to be optimal recommendation. Multiple linear regression analysis predicts equations of tensile strength as the function of cylinder compressive strength, for combination of FA, CNS, CSF and PPF. A good correlation between tested and predicted values is obtained.

    更新日期:2017-12-14
  • Solidification/stabilization mechanism of Pb(II), Cd(II), Mn(II) and Cr(III) in fly ash based geopolymers
    Constr. Build. Mater. (IF 3.169) Pub Date : 2017-12-11
    Yaguang Wang, Fenglan Han, Jingqiu Mu

    Geopolymers are new cementitious materials, which can effectively solidify/stabilize heavy metal ions. Fly ash is an industrial waste from the coal-consumed power plant. With thermal power projects continuously building in the world and the emissions and accumulation quantities of fly ash are increasing yearly. At the same time, with the development of modern industry, waste and waste water containing heavy metals are continuously discharged, so that heavy metal pollution has been the very serious world environmental problems. Aiming at the problem of fly ash and heavy metal pollution, this study referred to solidification/stabilization (S/S) of Pb (II), Cd (II), Mn (II) and Cr (III) in fly ash based geopolymers prepared using composite activator of sodium silicate and sodium hydroxide. The solidification (S/S) results had been explained by means of the leaching and compressive strength of the solidification (S/S) geopolymers (solidified bodies) acquired. The analysis was performed through chemical analysis, X-ray Diffraction (XRD), Fourier Transform Infrared Spectrometer (FTIR), Scanning Electron Microscope (SEM), Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES) and compressive strength tests. The results indicated that heavy metal ions could be effectively solidified in fly ash based geopolymers with a replacement of safe metal ions like Na (I) and Ca (II). Heavy metal ions had different effects on the compressive strength of geopolymers. (1.5 wt%) Pb (II) was beneficial to improve the compressive strength of geopolymers, and reached 49.34 MPa at 28 d. The XRD patterns indicated an amorphous structure and zeolite-like structure of aluminosilicate. The FTIR patterns study suggested changes of the Si-O-T (T = Si or Al) peak in the geopolymers. The SEM analysis revealed almost condensed homogenous surface of geopolymers. ICP-AES results showed that the geopolymer showed a high degree of solidification (S/S) of the heavy metal ions; in all samples, the solidification rates reached 99.9%. The mechanism of heavy metal ions being solidified was the interaction of physical fixation, adsorption and ion exchange. Finally, the pilot-scale test can achieve the same result on the basis of this study and made preparations for the future of industrialization.

    更新日期:2017-12-14
  • Control of radon emanation at determination of activity concentration index for building materials
    Constr. Build. Mater. (IF 3.169) Pub Date : 2017-12-08
    Andrey Tsapalov, Konstantin Kovler

    Radon emanation is a well-known source of uncertainty at determination of activity concentration index for building materials and NORM. To reduce this uncertainty both radon emanation coefficient of the sample material and radon leakage from the measuring container should be considered. Two different methods (the rapid method and precise method, which requires to keep the sample sealed for at least three weeks), which are based on the use of only gamma-ray spectrometer, are proposed for testing radon emanation. Both methods also allow simultaneous determination of the specific activity of radium and an assessment of radon exhalation rate from the surface of the finished building products. In addition, the method for determination of radon leakage from the container is proposed. The reliability of the sealing methods of containers is compared and standard PET-flasks with a high radon-tightness are offered. The criteria to control radon leakage and radon emanation coefficient are given for three types of test samples: (a) building materials, (b) natural materials of mineral origin (sands, clays, rocks etc.), and (c) artificial materials, such as absorbents, filters, radioactive wastes. A simplified screening test to control activity concentration index for building materials without a need to keep the sample sealed before the measurement is proposed.

    更新日期:2017-12-14
  • Integrated GPR and laboratory water content measures of sandy soils: From laboratory to field scale
    Constr. Build. Mater. (IF 3.169) Pub Date : 2017-12-06
    M. Ercoli, L. Di Matteo, C. Pauselli, P. Mancinelli, S. Frapiccini, L. Talegalli, A. Cannata

    In this study, laboratory and GPR water content measurements on two sandy soils are compared. A robust procedure to constrain GPR surveys is provided, aiming to obtain accurate and reliable soil moisture information at the field scale. The application of the well-known Topp’s equation, provided good results only for water contents (θv) from 5 to 17%. Therefore, integrated analyses are mandatory to better understand the subsurface structures and the water content pattern in unsaturated zones. Data and results here presented represent the first reference for typical sandy soils outcropping in Central Italy, providing solid constraints for engineering and hydrogeological applications.

    更新日期:2017-12-14
  • Radioactivity and Pb and Ni immobilization in SCM-bearing alkali-activated matrices
    Constr. Build. Mater. (IF 3.169) Pub Date : 2017-12-01
    M.M. Alonso, A. Pasko, C. Gascó, J.A. Suarez, O. Kovalchuk, P. Krivenko, F. Puertas

    Partial or total replacement of Portland cement clinker by SCMs (Supplementary Cementitious Materials) is a priority for the cement industry in its pursuit of global sustainable development and eco-friendly binder manufacture. The most widely used SCMs include industrial by-products such as blast furnace slag, fly ash and red mud. Alkali-activated cements manufactured with SCMs may reduce the need for Portland clinker by up to 90 wt%–100 wt% with no significant decline in material strength. The trade-off, however, is the risk of higher than legally allowable levels of radioactivity and unbound heavy metals (Cd, Hg, Ni, Pb, Cr), which may leach into the soil with the concomitant adverse implications for human health and the environment. This study assessed the mechanical strength, leachability and natural radioactivity of alkali-activated cement paste containing industrial waste-based SCMs (blast furnace slag, fly ash and red mud) and Pb and Ni compounds. Strength was highest in alkali-activated slag and slag/fly ash pastes and lowest in the red mud-containing materials. The addition of Pb or Ni sulphates had no adverse effect on this parameter. Alkaline and OPC pastes showed a high level of immobilization of both lead and nickel ions. According to the radiological findings, the Activity Concentration Index (I) was higher in red mud than in OPC, blast furnace slag or fly ash. With (I) values lower than 1, however, all the hydrated/activated materials studied would be EU directive-compliant. Nonetheless, the use of these new materials will depend not only on the activity concentration index, but also on their physical and chemical properties and the quality tests that must be passed to conform to legal requirements.

    更新日期:2017-12-14
  • Coupling effect of temperature and relative humidity diffusion in concrete under ambient conditions
    Constr. Build. Mater. (IF 3.169) Pub Date : 2017-11-20
    Ye Tian, Nanguo Jin, Xianyu Jin

    To accurately analyze the temperature and relative humidity (RH) distribution in concrete structures under ambient conditions, based on Krstulovic-Dabic hydration kinetics, an improved hydration model is proposed to geometrically bridge the relationship between hydration degree and microstructure of cementitious materials. Both the water content and hydration heat can be individually extracted from the model to evaluate the influence of ambient conditions variation. And the adsorption curve of concrete is acquired based on the microstructure obtained from hydration model and a redistribution of moisture content in pores is applied to evaluate the hydration process accordingly. Thus, the coupling effect of RH and temperature diffusion in concrete is decoupled in terms of hydration degree. An engineering verification indicates that the model can accurately predict the development of relative and temperature in concrete structures, and the construction procedure has significant influence on moisture and heat diffusion in concrete under ambient conditions.

    更新日期:2017-12-14
  • The NORM4Building database, a tool for radiological assessment when using by-products in building materials
    Constr. Build. Mater. (IF 3.169) Pub Date : 2017-11-15
    Wouter Schroeyers, Zoltan Sas, Gergo Bator, Rosabianca Trevisi, Cristina Nuccetelli, Federica Leonardi, Sonja Schreurs, Tibor Kovacs

    Scientific data on natural occurring radioactive materials (NORMs) is available in unknown quantities and the data is fragmented over several different sources. The new EU-BSS is regulating the use of NORM in building materials, however a large scale database with country specific information that can support legislators and industry in the assessment of the radiological impact of the use of by-products in construction is missing. Currently the COST Action ‘NORM4BUILDING’ (2014–2017) is creating such a database using a semi-automated datamining approach. In this paper radiological aspects on by-products that can find application in concrete are discussed based on the database.

    更新日期:2017-12-14
  • Time-varying relative displacement field on the surface of concrete cover caused by reinforcement corrosion based on DIC measurement
    Constr. Build. Mater. (IF 3.169) Pub Date : 2017-11-14
    Xianyu Jin, Jing Tong, Ye Tian, Nanguo Jin

    To investigate the cracking process of concrete cover due to corrosion of reinforcement for concrete specimens subjected to semi-immersed accelerated corrosion, digital image correlation (DIC) was applied to quantitatively and visually characterize the development of relative displacement on the viewed surface. The impacts of stirrups and concrete cover thickness on the evolution of relative displacement were interpreted. And a detailed analysis covered the initial cracking time, position and relative displacement distribution on the surface during the cracking procedure. The study indicates that the corrosion of stirrups is prior to longitudinal reinforcement as the longitudinal reinforcement is cathodic protected by stirrups. The full-scale monitoring on the relative displacement reveals that a thicker concrete cover can retard the initial cracking but will promote the propagation speed of corrosion cracks. The investigation on the initial cracking zone implies that the initial cracking has high probability to appear within a region and its width is approximately close to the concrete cover thickness.

    更新日期:2017-12-14
  • Gamma exposure from building materials – A dose model with expanded gamma lines from naturally occurring radionuclides applicable in non-standard rooms
    Constr. Build. Mater. (IF 3.169) Pub Date : 2017-11-12
    Tom Croymans, Federica Leonardi, Rosabianca Trevisi, Cristina Nuccetelli, Sonja Schreurs, Wouter Schroeyers

    Building materials are a significant source of gamma rays exposure due to the presence of naturally occurring radionuclides. In order to protect the public from harmful radiation, the European Basic Safety Standards (Council directive 2013/59/Euratom) (European Council, 2014) introduced a one-size-fits-all building(s) (materials) activity concentration index (ACI) based on a limited set of gamma lines. The ACI is considered “as a conservative screening tool for identifying materials that may cause the reference level (i.e. 1 mSv/y) laid down in article 75(1) to be exceeded”. Regarding calculation of dose, many factors such as density and thickness of the building material, as well as factors relating to the type of building, and the gamma emission data need to be taking into account to ensure accurate radiation protection. In this study the implementation of an expanded set of 1845 gamma lines, related to the decay series of 238U, 235U and 232Th as well as to 40K, into the calculation method of Markkanen (1995), is discussed. The expanded calculation method is called the Expanded Gamma Dose Assessment (EGDA) model. The total gamma emission intensity increased from 2.12 to 2.41 and from 2.41 to 3.04 for respectively the 238U and 232Th decay series. In case of 40K a decrease from 0.107 to 0.106 is observed. The 235U decay series is added, having a gamma emission intensity of 3.1. In a standard concrete room, the absorbed dose rates in air (DA) per unit of activity concentration of 0.849, 0.256, 1.08, 0.0767 nGy/h per Bq/kg are observed. The use of weighted average gamma lines increased the DA with 6.5% and 1% for respectively the 238U and 232Th decay series. A decrease of 4.5% is observed in the DA of 235U decay series when using the weighted average gamma lines in comparison to its non-averaged variant. The sensitivity of the EGDA model for density, wall thickness, presence of windows and doors and room size is investigated. Finally, a comparison of the index and dose calculations relevant for the dose assessment within the European legislative framework applicable towards building materials is performed. In cases where the ACI and density and thickness corrected dose calculation of Nuccetelli et al. (2015) cannot provide guidance, the EGDA allows performing more accurate dose assessment calculations leading to effective doses which can be several 100 µSv/y lower.

    更新日期:2017-12-14
  • Use of water reducer to enhance the mechanical and durability properties of cement-treated soil
    Constr. Build. Mater. (IF 3.169) Pub Date : 2017-11-04
    Liangxing Jin, Weimin Song, Xiang Shu, Baoshan Huang

    This study investigated the potential of using water reducer (WR) to enhance the mechanical and durability properties of cement-treated soil. WRs have long been used in Portland cement concrete (PCC) to increase the properties of PCC. When added at a small dosage, WR helps improve the dispersion of cement particles and release the water otherwise entrapped in cement clusters, thus reducing the water demand for the same consistency or increase the consistency of PCC without adding more water. Cement-treated soil uses similar raw materials and has similar chemical compositions to PCC. However, little research has been conducted to explore the potential of using WR in cement-treated soil to improve its compaction and thus its mechanical and durability properties. In this study, a laboratory experiment was conducted to examine the effects of WR on the compaction characteristics and engineering properties of cement-treated soil. As expected, similar benefits of water reduction and improved properties could be achieved by adding WR in cement-treated soil. The improved mechanical and durability properties of cement-treated soil were due to the fact that WR could improve the compaction behavior of cement-treated soil through reduced optimum moisture content and increased maximum dry density. Further studies are recommended for the interaction among WR, soil particles, and cement particles to achieve an optimal effect for engineering applications.

    更新日期:2017-12-14
  • Thermal and mechanical properties of alkali-activated slag paste, mortar and concrete utilising seawater and sea sand
    Constr. Build. Mater. (IF 3.169) Pub Date : 2017-11-04
    Ying-Lei Li, Xiao-Ling Zhao, R.K. Singh Raman, Saad Al-Saadi

    This paper presents an experimental study on the thermal properties of alkali-activated slag paste, mortar and concrete utilising seawater and sea sand exposed to elevated temperature. The thermal properties of paste and concrete utilising cement, fresh water and river sand were also investigated for comparison purpose. The samples were heated to different target temperatures up to 1000 °C at a heating rate of 5 °C/min, and tested both under hot and cooled conditions. The thermal properties, including temperature gradient, visual observation, mass loss, thermal strain and mechanical properties (i.e. strength, Young’s modulus and stress-strain curve) were investigated. X-ray CT scanning and scanning electron microscopy (SEM) were conducted to understand the macro/microscopic changes of the paste and concrete in response to heating. Degradation in mechanical properties of slag paste is attributed mainly to the cracks induced by temperature gradient, pore pressure and phase change. The degradation of concrete is caused by thermal mismatch between paste matrix and aggregates regardless of the use of cement or slag, freshwater or seawater, and river sand or sea sand.

    更新日期:2017-12-14
  • Discussion and experiments on the limits of chloride, sulphate and shell content in marine fine aggregates for concrete
    Constr. Build. Mater. (IF 3.169) Pub Date : 2017-11-04
    Wei Liu, Ruihua Huang, Jiyang Fu, Waiching Tang, Zhijun Dong, Hongzhi Cui

    Concrete is the most consumable building material in the world. Marine aggregates are the natural sand and gravels available in the sea or dredged from seabed. Contents of chloride, sulphate and shell in the marine aggregates can influence the properties of concrete and corresponding performance of the concrete structures. However, the limitations of chloride, sulphate and shell contents are set as different threshold values in different countries and/or regions. Some of them are inconsistent or puzzling for user. This paper presents a comprehensive review on the limit values of these contents used in different countries and provides a better understanding on the rationale behind these limit values thorough analysis on the limits of chloride, sulphate and shell content in marine fine aggregates for concrete. Except discussion, in this paper, an experimental study was carried out to evaluate the corrosion of reinforcing steel in concrete mixed with DMS as well. The experimental results of corrosion potential and corrosion current density showed that the rebar in DMS concrete should be safe from corrosion when the chloride content in DMS is less than 0.18% or the total chloride content in concrete is less than 0.34%. This study can contribute to fill the knowledge gap on concrete applications on dredged marine sand (DMS) and relative research.

    更新日期:2017-12-14
  • Utilization of circulating fluidized bed combustion ash in producing controlled low-strength materials with cement or sodium carbonate as activator
    Constr. Build. Mater. (IF 3.169) Pub Date : 2017-10-06
    Jeong Gook Jang, Sol-Moi Park, Sangho Chung, Ji-Whan Ahn, Hyeong-Ki Kim

    The present study investigates the fresh and hardened properties of controlled low-strength materials (CLSM) utilizing circulating fluidized bed combustion (CFBC) ashes, activated with cement or sodium carbonate. Engineering properties such as flowability, settlement, setting behavior, compressive strength, and hydration characteristics were evaluated. The results provided new insights, demonstrating that CFBC ashes can be effectively utilized in producing CLSM with suitable material design as the CLSM could achieve the required performances specified in the ACI 299R-13. The CLSM mixtures showed a self-destruction characteristic due to the formation of ettringite, while it showed stable strength development in a dry condition.

    更新日期:2017-12-14
  • Concrete cover cracking and service life prediction of reinforced concrete structures in corrosive environments
    Constr. Build. Mater. (IF 3.169) Pub Date : 2017-09-14
    Zhen Cui, Alice Alipour

    Crack initiation of concrete cover due to corrosion defines the end of functional service life where repair or replacement is required for corroded reinforced concrete (RC) structures. This study provides a comprehensive and critical analysis for the analytical and numerical models of corrosion-induced cover crack initiation for both uniform and non-uniform corrosion. Parametric studies are conducted to investigate the effects of different factors on crack initiation time and crack propagation patterns using a thermal analogy approach defined in three dimensional nonlinear finite element (FE) models. The results show that the type of corrosion products, thickness of interfacial transition zone and rate of corrosion are the parameters that affect crack initiation time the most significantly. The developed FE models are able to study crack initiation and propagation for both uniform and non-uniform corrosion and quantify the extent of concrete damage due to cracks. The FE results show that crack patterns under uniform and non-uniform corrosion differ. Under uniform corrosion, the major crack occurs vertically in the cover. But under non-uniform corrosion, major cracks form diagonally at the location of the pit in the cover. The vertical crack appears later and then becomes the third major crack. The results also show that non-uniform corrosion causes high concentrated pressure at the pits which would lead to earlier cover cracking. It is shown that assuming uniform corrosion may result in non-conservative service life estimation. The efficiency and applicability of the existing empirical models have been analyzed using the outcomes from the finite element models. Recommendations on how to select proper models to estimate crack initiation time have been provided. The outcome of the research provides a reliable approach to predict corrosion-induced cover crack initiation and propagation for RC structures.

    更新日期:2017-12-14
  • The Diplomatic Hall of the Royal Palace of Naples: Structural characterization of the timber roof by in situ ND investigations
    Constr. Build. Mater. (IF 3.169) Pub Date : 2015-08-11
    Beatrice Faggiano, Anna Marzo, Federico M. Mazzolani

    Especially in monumental buildings the preservation is compulsory for perpetuating the history of the construction technologies and of the past used materials. Therefore, the evaluation of the residual bearing capacity of existing structures is necessary, in order to detect any structural deficiency and to select proper restoration interventions. First of all a comprehensive knowledge of the structures should be acquired through in depth surveys, aiming at the structural identification. In this context, the paper exemplifies the structural identification procedure with reference to the complex covering timber structure of the Diplomatic Hall of the Royal Palace of Naples. The focus is specially on the in situ investigation phase, as the first essential step prior to the structural analysis of stress and deformation. Both geometrical and visual surveys are presented, in addition to in situ ND tests, the latter being performed by the CNR IVALSA Institute according to the current Italian Rules. As a result, the geometrical and static schemes were identified, the wooden species distinguished, the moisture content assessed, defects and degradations due to both aging and biological attacks detected, the effective transversal section determined and the effectiveness of the connections evaluated.

    更新日期:2017-12-14
Some contents have been Reproduced with permission of the American Chemical Society.
Some contents have been Reproduced by permission of The Royal Society of Chemistry.
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