bluuebunny/crossref_metadata_2025 huggingface dataset:
Load Induced Thermal Strains in Steel Fibre Reinforced Concrete Subjected to Uniaxial Compression
Authors: Buttignol Thomaz E.T. , Colombo Matteo , di Prisco Marco
Published: September 2016

The effect of fibre reinforcement on Load Induced Thermal Strains (LITS) has not yet been significantly investigated up to now. Creep is becoming a key research topic only in the last few years. A semi-empirical model able to take into account both the thermo-mechanical damage associated to coarse aggregates and the thermo-chemical damage induced in the matrix and calibrated on the basis of the main results on plain concrete available in the scientific literature is presented. Some tests in uniaxial compression on Fibre Reinforced Concrete (FRC) cylinders characterized by a long age – 11-years-old – have been investigated and compared with the model to highlight fibre effects, if any. The uniaxial compressive strength at 28 days of the SFRC was 75 MPa; the specimens after 11 years showed a compressive strength exceeding 110 MPa. A strong increase of SLS residual strength was observed in post-cracking tension due to the long aging, while ULS residual strengths weakly increased. The cylindrical specimens were exposed to a maximum temperature of 200°C and 400°C and loaded with two load thresholds corresponding to 20% and 40% of the compressive strength detected at 28 days of aging, that means about 12.5% and 25% of the 11-years-old specimens. Two paths were investigated: pre-heated specimens up to 200°C or 400°C, then loaded with a compression stress equal to 0.2fc,28 and 0.4fc,28; and pre-loaded specimens up to 0.2fc,28 and 0.4fc,28 and then heated up to 200°C or 400°C. The duration of each test did not exceed 12 hours. Two main fibre effects were observed: a significant reduction of irreversible strains when the specimens were loaded and then heated and cooled and a different evolution in LITS passing from 200°C to 400°C, characterized by a significant reduction of the expected deformation.
Concrete Permeability and Explosive Spalling in Fire
Authors: Lu Fang Xia , Fontana Mario
Published: September 2016

Permeability of concrete is a good indicator of the risk of explosive spalling, concrete with low permeability is more prone to explosive spalling. To study explosive spalling of concrete, experimental tests on the concrete permeability have been carried out at ETH. The influences from temperature and moisture content have been investigated. The permeability of concrete is found to increase with the temperature and to decrease with moisture content. Based on the test results, a permeability model has been proposed. The explosive spalling has been predicted and an engineering boundary permeability for the liability to spalling is recommended to be 2 × 10-17 m2 for a concrete slab heated according to ISO fire curve. The boundary permeability is influenced by moisture content, tensile strength and heating rate.
Fire Performance of Columns Made of Normal and High Strength Concrete: A Comparative Analysis
Authors: Gernay Thomas
Published: September 2016

The use of high strength concrete (HSC) in multi-story buildings has become increasingly popular. Selection of HSC over normal strength concrete (NSC) allows for reducing the dimensions of the columns sections. However, this reduction has consequences on the structural performance in case of fire, as smaller cross sections lead to faster temperature increase in the section core. Besides, HSC experiences higher rates of strength loss with temperature and a higher susceptibility to spalling than NSC. The fire performance of a column can thus be affected by selecting HSC over NSC. This research performs a comparison of the fire performance of HSC and NSC columns, based on numerical simulations by finite element method. The thermal and structural analyses of the columns are conducted with the software SAFIR®. The variation of concrete strength with temperature for the different concrete classes is adopted from Eurocode. Different configurations are compared, including columns with the same load bearing capacity and columns with the same cross section. The relative loss of load bearing capacity during the fire is found to be more pronounced for HSC columns than for NSC columns. The impact on fire resistance rating is discussed. These results suggest that consideration of fire loading limits the opportunities for use of HSC, especially when the objective is to reduce the dimensions of the columns sections.
Statistical Comparison of the Results of Applying Several Methods in Checking Concrete Columns’ Fire Resistance
Authors: Ramalho Maria Alzira Barros , Gonçalves Miguel Chichorro
Published: September 2016

The main objective of this study is to help the structural designers so they can, quickly and efficiently, study the concrete columns’ fire resistance. The most expeditious methods of fire resistance verification in terms of ease of application by structural designers, the methods given in EN 1992-1-2 [1] in the form of tables (Method A, Method B and Method C), were used in the fire resistance verification of 12243 rectangular columns inserted in the stability projects of 63 buildings, carefully selected in order to be representative of the ones licensed in Portugal [2]. Noting that these methods lead to excessively conservative results, the authors developed an alternative methodology, also with expedite application, but leading to substantially less conservative results (although designed on the safety side). This methodology consists on the consultation of adimensional interaction diagrams in fire situation, Nfi/Mfi, developed using the 500oC Isotherm Method. In the development of these diagrams unexpected results were obtained in some columns’ cross-sections, for which the resistance at room temperature was lower than the one corresponding to a fire situation at level R60. Some of the factors that can contribute to the occurrence of these results are pointed out.
Electrochemical Tests for the Determination of the Critical Chloride Threshold of Steel in Concrete with Blended Cements
Authors: Lollini Federica , Redaelli Elena , Bertolini Luca
Published: September 2016

The service life of reinforced concrete (RC) structures exposed to marine environments or the action of de-icing salts is limited by the corrosion of steel bars. To predict the service life of a RC structure, and especially the initiation time, a reliable estimation of the critical chloride threshold is required. This parameter is strongly influenced by many factors related to the environment and the concrete. This paper presents the results of chloride penetration tests carried out on concrete specimens made with different types of binder, with bars in free corrosion conditions, in order to detect the critical corrosion threshold. During the exposure period of two and a half years, the corrosion behaviour of bars was monitored through measurements of corrosion potential and corrosion rate. Afterwards, potentiostatic polarization tests, during which the potential was increased by step +50 mV per hour and the circulating current was monitored, were carried out on selected specimens. Results of the tests allowed the investigation of the relationship between the potential at which corrosion occurred, during ponding or potentiostatic polarization tests, and the critical chloride content. Considering a range of potential of -100/+100 mV vs SCE, some effect of pozzolanic additions in leading to higher values of the chloride threshold could be observed in this work
Utilization of Fabric Formwork for Improving the Durability of Concrete from Supersulfated Cement
Authors: Ioannou Socrates , Badr Atef , Kostova Kaloyana , Paine Kevin , Ibell Tim
Published: September 2016

In this paper, the durability of fabric formwork-based concrete made from supersulfated cement was studied. The study involved comparison of chloride and carbonation resistance, pH values, and water absorption between of surfaces of SSC, the one being cast and the other cast in fabric formwork. It was shown that the use of fabric formwork minimized the pore volume near the surface, maintained the pH values at higher profile depths and showed improved durability when compared to the mould-cast surface. Carbonation depths were reduced by approximately 35% and calculated ab sorption rates were found to be approximately 40% lower at the fabric cast surface, indicating that fabric formwork is a promising aspect towards promoting the comeback of SSC in construction.
Durability Modeling for Enhancing the Service Life of a Building Constructed on a Reclaimed Land in the Sea
Authors: Muhammad K. Rahman , Mohammed Ibrahim , Zaki Al Omran , Mohammed S. Barry , Fahad Al Nahdi
Published: September 2016

In reinforced concrete structures constructed on the coastline of the hypersaline Arabian Gulf water, corrosion of reinforcing steel causes cracking, delamination and spalling of concrete, within a time span of a few years. The King Abdullah Civic Center (KACC), being constructed on a reclaimed land off the coastline in the Eastern region of Saudi Arabia, is a major complex with wharves, quay walls, and breakwater and commercial buildings. To ensure the durability of buildings in the harsh marine environment and to provide a minimum service life of 35 years, a concrete mix in which 70% of Portland cement is replaced by granulated ground blast furnace slag (GGBFS) was recommended based on durability modeling conducted using the software STADIUM®. Concrete with 70% GGBFS provides for the dual objective of achieving a green concrete and an enhanced service life of the building. Based on durability modelling it was concluded that corrosion inhibitor should be used preferably in the concrete. A detailed experimental program was conducted to assess the durability and strength properties of the 70% GGBFS concrete, with and without corrosion inhibitor. This paper presents the results of experimental investigations and durability modeling conducted for the project. A 70% GGBFS concrete mix without corrosion inhibitor was adopted for the raft foundation and subsequently for the entire building to make it a green concrete building.
Thermoviscoelastic Analysis of Concrete Creep at Mesoscale
Authors: Bary Benoit , Bourcier Christophe , Helfer Thomas
Published: September 2016

Concrete is a heterogeneous material made up at mesoscale of linear elastic aggregates distributed in a mortar matrix whose behavior is time and temperature dependent. The Interfacial Transition Zone (ITZ) between aggregates and matrix also influences the overall behavior. We investigate here analytically and numerically by means of 3D simulations the creep behavior of concrete and mortar subjected to moderate temperatures at mesoscale. The numerical specimens consist in unstructured periodic meshes of polyhedral aggregates with various size and shapes randomly distributed in a box. Specific interface finite elements are introduced between aggregates and matrix to model the ITZ. Both matrix and ITZ are considered as linear thermoviscoelastic materials. Averaged stresses and strains in the matrix and aggregate phases are compared to analytical estimations obtained with classical mean-field approximation schemes applied in the Laplace-Carson space, where the ITZ are introduced via imperfect interfaces modelled with the Linear Spring Model (LSM). The effects of ITZ thickness, aggregate shape and temperature are then studied to evaluate their respective influence on mortar and concrete creep behavior.
Macrocell Corrosion Formation in Concrete Patch Repairs - A Laboratory Study
Authors: Eldho Choorackal A. , Nanayakkara Ominda , Xia Jun , Jones Stephen W.
Published: September 2016

Corrosion of reinforcement steel bars is a major threat to the durability of concrete structures exposed to chloride contaminated environment. Patch repairing is widely practiced in affected structures to avoid further damage due to corrosion. Macrocell formation within the patch repair is identified as one main reason for the failure of patch repairs. In the present study, a group of patch repairing materials is tested for their potential to form macrocell corrosion after repaired in a chloride contaminated environment. The influence of parameters such as level of chloride contamination, type of repair materials and the area of steel bar receiving repair are presented based on macrocell current measurements. The selected repair materials for study were cement based, GGBS based and polymer based in its composition. It is found that the severity of macrocell depends on the driving potential existing between the repair and substrate concrete. The quality of substrate concrete and repair material influences the macrocell formation. The surface area of the steel bar that receives the repair also affects the macrocell current. The study will be used for the evaluation of repair materials for macrocell corrosion formation potential before their field application in a chloride contaminated environment.
Cyclic Behavior of Composite Truss Beam-to-RC Column Joints in MRFS
Authors: Colajanni Piero , La Mendola Lidia , Monaco Alessia , Spinella Nino
Published: September 2016

In the present paper, the cyclic behavior of beam-to-column joints made up of Hybrid Steel Trussed Concrete Beams (HSTCBs) connected to Reinforced Concrete (RC) piers is investigated. HSTCBs are a typology of composite beam generally constituted by a steel truss with end zone added rebars embedded within a block of concrete cast in place. HSTCBs represent a structural solution for light industrialization in the civil constructions; the main advantages in their use are the higher construction speed with the minimum site labor, the possibility of covering wide spans with low depths and a final economical convenience. For these reasons, they are also increasingly adopted within seismic framed structures. In the present study, the examined joints are representative of framed RC structures subjected to seismic actions and designed according to the current Italian standard code. Cyclic tests are performed and interpreted by means of analytical and numerical models with the aim of verifying the strength capacity and ductility of the system, focusing on both the global behavior and the force transmission between steel truss and concrete in the joint region.
Performance of Fibre Reinforced Concrete Structures - Modelling of Damage and Reliability
Authors: Pukl Radomír , Sajdlová Tereza , Červenka Jan , Červenka Vladimir
Published: September 2016

Steel fibre reinforced concrete (FRC) has higher ductility, it can save amount of convention reinforcement, labour and in consequence costs of the structure. However, broader use of SFRC as construction material is limited among others by lack of design codes. According to the previous study, reliability and safety of ordinary reinforced engineering can be verified using non-linear finite element analysis and several safety formats that are proposed in fib Model Code 2010. In the presented paper, safety formats are applied for fibre reinforced structures such as tunnel lining precast segment and individual approaches are compared. As tensile and shear cracks or compressive crushing can develop in the fibre reinforced concrete under severe conditions, the design combining numerical and experimental investigations together with safety formats is appropriate method how to obtain safe and reliable structure. Finite element method and advanced material models taking into account FRC properties such as shape of tensile softening branch, high toughness and ductility are described in the paper. Since the variability of FRC material properties is rather high, full probabilistic analysis seems to be the most appropriate format for evaluation of structural performance, reliability and safety.
Design Issues about the Bar Lay-Out at the Dapped Ends of Simply-Supported One-Way R/C Slabs
Authors: Gambarova Pietro G. , Lo Monte Francesco
Published: September 2016

Directly-or indirectly-supported R/C slabs are frequently used in the covers of small-to-medium underground facilities, where the service loads are often rather limited, but very severe loads cannot be ruled out in accidental situations.To have fresh information on the structural performance and cracking of R/C slabs simply supported along their short sides via corbels (dapped ends), four rectangular slabs subjected to transversely distributed or concentrated loads have been recently tested in Milan (b x L = 1.30 x 2.20 m; simply-supported span = 2.10 m; thickness = 15 cm). The load was applied either at mid-span (in the bending tests, not presented in this paper), or at 1/10 of the span (in the shear tests).Two bar arrangements were investigated with straight or bent-up bars in the main body, and straight bars or hooks in the corbels.In the D zones of the slabs tested in shear, the concentrated load induces a rather complex 3-D crack pattern, with a limited reduction in the bearing capacity, compared with the cross-wise distributed load.Rather simple strut-and-tie models applied to the slabs with bent-up bars and hooks, and the equations provided by European and North-American codes for the beams devoid of transverse reinforcement are shown to yield realistic predictions for the bearing capacity at the ultimate limit state. In the former case, however, modelling the bond along the tension reinforcement of the corbel requires some care, because of bond local and global effects. Last but not least, refining bar layout confirms – once more – that slab performance can be markedly improved with little extra effort.
Alkali-Silica Reaction in Concrete Pavements
Authors: Voland Katja , Weise Frank , Meng Birgit
Published: September 2016

A significant number of German concrete motorway pavements have shown damage only a few years after construction. The alkali-silica-reaction (ASR) is often one of the reasons for this damage.
German guidelines and regulations focus on the optimisation of the concrete composition to avoid damage due to ASR. Moreover, diverse research projects have dealt with the development and optimisation of ASR performance test methods with and without external alkali supply.
However, the influence of other parameters on the occurrence and intensity of a damaging ASR had not yet been taken into account. Such parameters include, e.g., insufficient curing and the modifications of concrete’s porosity due to the use of slip form pavers. Likewise, the increased traf-fic loading had not yet been considered. The Federal Institute for Materials Research and Testing (BAM) assesses these parameters and processes in a number of projects. These projects aim primarily to increase the durability of the concrete pavements, in particular by improving preventive measures that may be taken before or after the construction of concrete pavements.
This paper gives a short overview of BAM’s projects concerning ASR in concrete pavements. Furthermore, results regarding the influence of the cyclic traffic loading on ASR are presented.
Performance Assessment of Precast RC Flooring Units Exposed 40 Years in Aggressive Industrial Environment
Authors: Pascu Radu , Georgescu Dan Paul , Apostu Adelina
Published: September 2016

Performance of RC members is tightly closed to their environment. A long exposition time in aggressive environment corresponds frequently with the use of RC elements designed and produced in an epoch when technical norms, reflecting the knowledge level of the time, were insufficient to insure the durability of the elements.This paper presents the assessment of precast flooring units after 40 years of exposition in an aggressive industrial environment, specific to the steel industry. The assessment was performed using chemical and mechanical tests performed in situ and in the laboratory, using destructive as well as non-destructive techniques, applied at material and member level. Experimental methods were corroborated with calculation results.The paper presents also the steps which were taken in order to asses the performance of the concrete structural elements.The results of this study allow concluding about the causes which led to the observed damage and the identification of the remedial measures needed to restore the security of the investigated elements.
An Experimental Study on Carbonation in the Tensile Zone of Fatigue-Damaged Plain Concrete Beams
Authors: Jiang Chao , Gu Xiang Lin , Zou Wei
Published: September 2016

This paper investigates the accelerating effect of fatigue damage on carbonation process through an experimental study. A total of 30 prism specimens, categorized by A or B according to the cement type used, were cast in this experiment program. Mid-span deflection-and beam bottom strain-based damage indexes were proposed to estimate fatigue damage states for type A and B specimens, respectively. After static and fatigue failure tests for 10 specimens, 16 specimens were subjected to fatigue loading up to the prescribed damage states. Subsequently, these fatigue-damaged specimens and four intact specimens were put together into a chamber filled with high concentration CO2 gas, and carbonation depths were measured after 14, 28, and 49 days. Carbonation tests showed that fatigue damage could increase the mean carbonation depth by 150% and that the regressed linear expression between the normalized mean carbonation depth and fatigue damage index for each type specimen agreed well with experimental data. Normal distribution models for carbonation depths in fatigue-damaged concrete were proposed and found to be comparable with the realistic frequency distribution histograms.
Fire Protection of Concretes: Formulation, Performances and Pathology
Authors: Lanos Christophe , Baux Christophe , Melinge Yannick
Published: September 2016

The efficiency of thin mineral passive fire protection layer applied on concrete is analyzed. The more suitable fireproofing material formulations are selected from results of laboratory scale fire test. Such tests consist in the direct exposure of protected concrete samples to the flame of a burner, at constant temperature (850°C). Various formulations of mineral fireproofing materials have been tested to identify the effects of binder type and the density. Formulation compromises are highlighted regarding requested fire performances. Selected formulations are used to protect real scale concrete slab exposed to standard fire (ISO 834). During the test, the concrete/fire protection layer interface temperature and the steel reinforcement temperature have been recorded. For small size slabs, fire proofing layer is completely efficient. The temperature increases are strongly delayed. For large size slabs, delamination of fire proofing layer appears, leading to rapid concrete degradation. To understand the mechanics of cracking and delamination of fire protection layer, laboratory scale tests are performed with two selected formulations varying the implementation methods (surface treatment of concrete, intervention on interface roughness, pre-cracking...). It appears that the occurrence of fire protection layer delamination can be avoided choosing the optimal implementation method without adjustment of the optimized formulations.
Fire Behavior of Sandwich Panels for Roofing Applications
Authors: Zani Giulio , Rampini Marco Carlo , Colombo Matteo , di Prisco Marco
Published: September 2016

Cement-based multilayered panels represent a promising and cost-effective solution for the roofing of modern prefabricated buildings. Due to the spread of such technologies, it is deemed necessary to evaluate the structural performances also with reference to the fire scenario. In the framework of a research project financed by national and regional authorities, Politecnico di Milano coordinated a wide experimental campaign aimed at assessing the mechanical behavior of innovative composite elements (2.5 m wide, 5 m long). The paper presents the results pertaining to the full-scale test of a prototype at high temperatures - mainly focusing on Temperature-Time and Displacement-Time diagrams - and provides a fire resistance classification compatible with the observed failure mode.
Tensile Behaviour of Reinforcing Steels at High Strain Rate and High Temperature
Authors: Cadoni Ezio , Dotta Matteo , Forni Daniele
Published: September 2016

The performance of reinforced concrete structures under combined effects of blast and fire is growing in interest of the research and engineering communities specially after the recent terrorist attacks as well as severe accidents (i.e. Gotthard tunnel, etc.). The mechanical behaviour of concrete and reinforcing steel when are subjected to extreme temperatures, impacts or blast has still many aspects open to investigation. In this paper the behaviour of AISI304, B500B and B500A reinforcing steel at high strain rate (500 s-1) and at three levels of temperature (200, 400 and 600°C) is presented. The results were obtained by using a Split Hopkinson Tensile Bar (SHTB) equipped with a heating system.
Dynamic Shear Resistance of RC Beams Based on Modified Compression Field Theory
Authors: Fujikake Kazunori , Somraj Amornthep
Published: September 2016

The aim of this study was to develop an analytical model to estimate the dynamic shear capacity of RC beams which may exhibit diagonal tension failure under impact and blast loadings. Thus, the modified compression field theory has been extended to dynamic loading in this study. The developed analytical model has been applied to the experimental results obtained from rapid loading tests of RC beams. As a result, the developed analytical model has been in good agreement with the experimental results.
Utilization of the Capacity for Energy Absorption of Concrete Structures under Impact
Authors: Zanuy Carlos , Ulzurrún Gonzalo , Díaz Iván M.
Published: September 2016

Concrete structures subjected to impact have shown a higher sensitivity to develop a brittle shear failure than under quasi-static loading. The differences between the dynamic and static behavior are due to the strain-rate dependence of material properties and the presence of inertial forces. Both effects should be accounted for when performing analyses of structures under impact. In the present paper, a simplified three-degree-of-freedom model is used to understand the improved impact response of reinforced concrete when steel fibers are added to the concrete matrix. The analysis shows that the higher capacity for energy absorption of fiber-reinforced concrete (FRC) may avoid local shear failure when the FRC is able to develop strain hardening prior to the peak strength. Various analyses are presented in order to understand the influence of different types and contents of fibers.
Robustness of Reinforced Concrete Framed Buildings: A Comparison between Different Numerical Models
Authors: Bertagnoli Gabriele , Gino Diego , Giordano Luca , La Mazza Dario , Mancini Giuseppe
Published: September 2016

According to Eurocode, robustness is the ability of a structure to withstand events like fire, explosions, impact or the consequences of human error, without being damaged to an extent disproportionate to the original cause.Avoiding the progressive collapse of a building in presence of accidental loading conditions is one of the challenges for the designers.The tie-force method is actually one of the most used design techniques for resisting progressive collapse, whereby a statically indeterminate structure is designed with reference to local simplified models determined in accordance to the failure mode considered.In this work a computational study of a reinforced concrete frame is presented. The beam-column assembly represents a portion of the structural framing system of a ten-story reinforced concrete frame building and is subjected to monotonically increasing vertical displacement of the center column to simulate a column removal scenario.Two different finite element models, with distinct levels of modeling, are used in order to compare the numerical results with the experimental ones coming from a full-scale test, and evaluate the ability of the models to simulate the structural behavior of the frame.
A Reformulation of a Multi-Axial Failure Criterion for the Concrete
Authors: Coccia Simona , Como Mario , di Carlo Fabio
Published: September 2016

The research of a failure criterion for concrete under multi-axial stresses is a very important task because of the numerous civil engineering applications. Nowadays several concrete failure tests are available in literature and various criteria have been proposed. A multi-axial failure criterion for the concrete founded on a simple physical basis, has been proposed by one of the authors. In this paper a sharper foundation of this criterion is given. The hardened cement paste (hcp), the binder of all the aggregate particles, is responsible of the concrete strength. Consequently, a preliminary average evaluation of the stresses, occurring, when the concrete is loaded, into the various phases components, and particularly in the hcp, is necessary to analyse the failure. To that end, the paper revolves around the analysis of the thermal behaviour of the concrete at its early stage of setting. It is shown that the heat production during the cement hydration process, is responsible to produce clearances among the various particles and the surrounding hcp that, in turn, the consequent statically determined structure of the concrete. Validation of this result comes out by analysing the elastic moduli and the thermal expansion coefficients. The micro-macro failure condition of Como & Luciano thus receives a sounder physical basis.
An Experimental Study on the Equation of State of Cementitious Materials Using Confined Compression Tests
Authors: Karinski Yuri S. , Zhutovsky Semion , Feldgun Vladimir R. , Yankelevsky David Z.
Published: September 2016

The behavior of concrete under severe loading is of interest, especially for problems like ballistic impact and penetration and near distance explosions, where very high pressures are developed. For these problems the behavior of concrete at very high hydrostatic pressures is of importance. There is very little data available on concrete behavior at that high pressure level. Therefore there is much need for an extensive experimental work in order to provide necessary data and illuminate the rather obscure area of concrete behavior at high pressures. However high pressure controlled testing requires special and expensive equipment, and the testing is associated with a wide variety of technical problems. Recently published experimental data, obtained by utilizing a high-capacity tri-axial press, indicates that concrete that is subjected to high pressures behaves differently than concrete under low uniaxial loading. When uniaxial loading is applied, without any confining pressure, the concrete specimen demonstrates a well-known brittle behavior where failure is caused by a localized damage. Quite to the contrary, at high levels of confining pressures, the concrete behaves like a ductile material, and its failure is associated with diffuse material damage. The experimental data at the very high pressure range is most important to understand the processes of damage evolution that governs the characteristics of the equation of state. This paper presents the development of an experimental setup that is capable of performing confined compression tests of mortar and concrete specimens at high pressures up to 400MPa. The experimental study aims at investigating the effect of water/cement ratio as well as the ratio of fine aggregate on the different branches of the equation of state: active loading and unloading/reloading. The paper presents some of the test results as well as a new equation of state that is based on the multi scale approach. The model is applicable for dry materials; cementitious paste and concrete in which the pores are filled with water should be treated differently to account for the liquid phase.
Some Insights on the Role of Relative Humidity and Compaction on the Carbonation Rate of CaO/SiO2 (50/50) Clinker
Authors: Agnelli Marco , Huet Bruno , Briaud Vincent , André Elodie , Pisch Alexander
Published: September 2016

This paper focuses on the carbonation of non-hydraulic binders based primarily on wollastonite (CaSiO3) in order to study the relationship between clinker composition, curing conditions and compaction on carbonation reaction rate. Decoupled carbonation and drying experiments are carried out using cements at different CaO/SiO2 ratio, at 60 °C, 1 bar of CO2 and multiple RH (relative humidity) and compaction degrees. Solid analysis include mass gain or loss, TGA, XRF and Carbon/Hydrogen (CH) to determine respectively the bound H2O content, CO2 content and the mineralogical assemblage. Relative humidity strongly influences carbonation intrinsic reaction rate, while compaction seems to be a second order mechanism. Testing procedure can be used to discriminate the reactivity of clinkers with various initial phase assemblage.
Bond and Corrosion: Experimental Studies
Authors: Cesetti Alessandro , Mancini Giuseppe , Tondolo Francesco
Published: September 2016

Bond between steel and concrete plays an important role in the structural behaviour of reinforced concrete structures. In the present paper, bond tests on r.c. specimens in presence of corrosion are performed in order to evaluate the effect of corrosion on bond mechanism. The results of the tests on concrete specimens with RILEM type shape, reinforced with ribbed steel bars of 12 and 16 mm of diameter, with and without confinement, in presence of an increasing level of corrosion up to 20%, are presented. An electrochemical procedure using a current density of 200 µA/cm2 is employed to produce corrosion. The test results show the effect of oxidation of the reinforcement at the interface with concrete and consequent surface cracking, the change of performance in terms of bond and the change of failure mechanism.
Underground Tunnels Exposed to Internal Blast: Effect of the Explosive Source Position
Authors: Colombo Matteo , Martinelli Paolo , di Prisco Marco
Published: September 2016

The design procedure recently proposed by the same authors and based on a simplified FE model for underground tunnels subjected to internal explosion is extended in this work taking into account different possible positions of the explosive source inside the tunnel. The situation in which the internal explosion is preceded by fire accidents is also analyzed. The reference situation is represented by the explosive source located at the center of the tunnel cross–section. The tunnel geometry considered is that of the metro line in Brescia, Italy. It has an internal diameter of about 8.15 m and is located about 23.1 m below the surface. Six segments and a smaller key segment (6+1) make up the tunnel. The ring has an average width of about 1.5 m. Dynamic analyses were carried out in order to reproduce the blast scenario. The aim of this work is to evaluate the influence of the position of the explosive source on the tunnel dynamic response. An ultimate limit state criterion based on the eccentric ultimate flexural capacity and capable of including fire–blast interaction is adopted. An innovative layered precast tunnel segment solution made of different fiber–reinforced cementitious composites is considered.
Modelling Basic Creep of Concrete at Elevated Temperatures and Stresses
Authors: Torrenti Jean Michel
Published: September 2016

The prestressed concrete confinement vessel is the third and last barrier in Nuclear Power Plants (NPP). In case of a severe accident (loss of cooling agent of the reactor for instance), pressure and temperature will increase in the nuclear vessel (0,5 MPa and 180°C during 2 weeks). Due to elevated temperatures, the evolution of basic creep will be accelerated. In this case, due to internal pressure, some tensile stresses could appear in specific parts of the structure and induce cracking. The modelling of basic creep and its couplings with temperature is very important for the safety of the structure (tightness of the concrete vessel). Here we present a model considering the following elements: a coupling between creep and damage is introduced, kinetics of basic creep is affected by temperature by the means of an Arrhenius thermo-activation, damage due to the increase of temperature is taken into account. The model is compared with the available experimental results. This work is a part of the MACENA project.
Material and Geometric Heterogeneity Consideration for Cracking Risk Prediction of Young Age Behavior of Experimental Massive Reinforced Concrete Structure
Authors: Chhun Ponleu , Buffo-Lacarriere Laurie , Sellier Alain
Published: September 2016

This article presents the application of a thermo-hydro-chemo-mechanical (THCM) model to a real complex structure of reactor confinement (mock-up VERCORS from EDF) by taking into account the specificities of the construction (construction consequences), the distributed reinforcements and the material heterogeneity of massive structure. The experimental campaigns were conducted during and after the construction of VERCORS. The early-age behavior of concrete is first modelled based on a multiphasic hydration model to ensure the thermal evolution. Then a 3D mechanical model is used to predict the consequences of hydration, temperature and water variations on mechanical behavior. An alternative approach to consider the structural effect of distributed reinforcement without explicit meshing of reinforcements is implemented and is able to reproduce the influence of reinforcement on the crack patterns. Moreover, the “Weakest link localization” method is also adapted to deal with a probabilistic scale effect due to the material heterogeneity of massive structure. It permits to assess directly the most likely tensile strength which can treat the first crack in softening part of the loaded volume of structures.
Experimental Investigations on the Influence of Temperature on the Behavior of Steel Reinforcement (Strands and Rebars)
Authors: Toumi Ajimi Wiem , Chataigner Sylvain , Falaise Yannick , Gaillet Laurent
Published: September 2016

In the case of exceptional accidents, nuclear containment structures may be submitted to an internal temperature increase. This may have an influence on the prestressed concrete structures behavior regarding both its mechanical performance and its porosity. The presented study got interested on the impact that a temperature increase may have on the mechanical behavior of the steel reinforcement for both prestressing strands and rebars. In order to remain in realistic situations, it was chosen to study temperatures between 20°C and 140°C. Some experimental investigations regarding the tensile behaviour of steel rebars and their adherence within concrete will first be presented. Then, some investigations on steel strands will be described: some tensile tests at different temperatures, and some relaxation tests to check how the level of prestress loss may be affected by the temperature. This experimental study is part of a national French project (MACENA) aiming at assessing the impact of an accident on the behavior of nuclear containment structures. The gathered experimental data will be used for their damage assessment.
A Simplified Approach to Analysis of Reinforced Concrete Slabs Subjected to Hard Missile Impacts
Authors: Lulec Andac , Vecchio Frank J.
Published: September 2016

This paper presents a nonlinear finite element analysis (NLFEA) procedure employing a smeared rotating crack macro-modeling approach for analysis of reinforced concrete structures under hard missile impacts. It represents a middle ground between simplified methods based on single degree of freedom (SDOF) systems and complex meso-or micro-element hydrocodes. Three hard missile impact tests were modeled and the results were compared with experimental results in terms of residual velocity, damage shape, and impact depth. Good correlations were obtained.
Shell Modelling of a 1/13 Scaled RC Containment Vessel under Cyclic Actions with PARC_CL Crack Model
Authors: Belletti Beatrice , Scolari Matteo , Stocchi Alessandro
Published: September 2016

The energetic resources exploitation became a big issue in present days. Globally 30 countries in the world are also exploiting Nuclear Power Plants (NPPs) for the generation of energy. In this case energy production issue is correlated to the requirements for population safeguard against radiation leakage and to safe nuclear waste storing. However, many of these NPPs, which are still producing a large amount of energy, need or will need in short times a renewal process. Reinforced concrete members are of strong importance for the safety and for the proper operation of NPPs. One of the most important structural elements is then the reinforced concrete containment vessel, RCCV, of the reactor. The correct prediction of the RCCV behaviour under sever action is essential for the assessment of existing structure safety and for the design of new ones. In the paper it is described the modelling of a 1/13 scaled reinforce concrete containment vessel tested at the National Center for Research on Earthquake Engineering of Taipei, Taiwan, under cyclic loading. The RCCV was analyzed by means of non linear finite elements analysis using multi layered shell elements. A secant total strain fixed crack model called PARC_CL, implemented at the University of Parma in the user subroutine UMAT.for in ABAQUS code, has been used to evaluate the mechanical non-linearity of RC elements. The multi layered shell elements approach with PARC_CL crack model provided good results in terms of local and global EDPs and it was able to give a good estimation of the post cracking behaviour until failure. Simulations results are provided in terms of displacements, strains and crack patterns. Although analyses provided good results, some issues like the modelling of the structure to foundation interface are still open.
Steel Reinforcement Corrosion in a Low Calcium Fly Ash Geopolymer Concrete
Authors: Babaee Mahdi , Castel Arnaud
Published: September 2016

Geopolymer concrete (GPC) has significant potential as a more sustainable, low-embodied carbon alternative for ordinary Portland cement concrete (PCC). However; as a rather new engineering material, there are some concerns over the durability aspects of geopolymeric binders. In this study, performance of chloride contaminated reinforced GPC specimens manufactured using low calcium fly ash is investigated by long-term monitoring of corrosion parameters such as free corrosion potential and polarization resistance. It was found that low calcium fly ash GPC can perform as well as PCC during the propagation phase of corrosion; although, some conventional reference values of corrosion parameters which are indicative of severity of the steel corrosion in PCC are not suitable for GPC. Additionally, commonly used electrochemical test methods are successfully employed to assess the degree of reinforcement corrosion in geopolymeric binders within an acceptable level of accuracy.
Effect of Internal Activation Using Porous Ceramic Aggregate on Hardness and Pore Structure of Fly Ash Cement Paste
Authors: Ootaishi Kazuki , Bui Phuong Trinh , Ogawa Yuko , Kawai Kenji
Published: September 2016

The utilization of fly ash not only reduces the environmental impact but also improves some mechanical properties and durability of concrete. However, the early-age strength of fly ash concrete is sometimes lower than that of normal concrete due to the slow pozzolanic reaction of fly ash. In recent years, some researchers have suggested alkali or sulfate activation to accelerate the pozzolanic reaction. Some studies have used sodium hydroxide (NaOH) solution, while others have applied potassium sulfate (K2SO4) or sodium sulfate (Na2SO4) as activators which are effective in accelerating the pozzolanic reaction and increasing the strength at early age. On the other hand, the early-age strength of fly ash concrete is also improved by using porous ceramic aggregate (PCA) as an internal curing agent. Therefore, the present study aims at investigating the effect of an internal activating agent using PCA on hardness and pore structure of fly ash cement paste. In the experimental program, PCA immersed in two kinds of solution (K2SO4 and Na2SO4) was placed in the center of specimen with dimension of 21x21x20 mm. In addition, normal aggregate (NS) was used for reference. As a result, internal sulfate activation using PCA improved the hardness of interfacial transition zone (ITZ) between paste and PCA, and reduced the Ca(OH)2 content in cement paste with 40% replacement with fly ash significantly at the age of 1 day, but negligibly at the ages of 7 and 28 days when compared with reference specimen. K2SO4 was more effective in improving hardness of ITZ as an internal activating agent than Na2SO4. Although the total pore volumes of the fly ash cement pastes using PCA imbibing sulfate activators were not reduced at the age of 28 days, their pore volumes with diameters less than 0.05 µm were increased.
Safety Assessment of Existing Reinforced Concrete Beams Using Probabilistic Methods at Different Levels
Authors: Roy Anindya , Robuschi Samanta , Hendriks Max A.N. , Belletti Beatrice
Published: September 2016

Several reliability methods available in literature combined with various modelling approaches are compared in this current work in the context of two experimental reinforced concrete (RC) beams. One beam failed in bending while the other beam failed in shear due to diagonal tension. The structural behaviour is described by analytical models and nonlinear finite element models. The changes in predicted reliability of these structures with increasing loads are evaluated by different reliability methods and the results are compared
Seismic Performance of a Concrete Highway Tunnel Using a Concrete Damage Plasticity Model
Authors: Dulinska Joanna M. , Murzyn Izabela J.
Published: September 2016

In the paper a non-linear dynamic response of a concrete highway tunnel to a natural earthquake is presented. The acceleration time history of the registered shock was applied as seismic excitation acting in three directions. The peak ground acceleration (PGA) of the shock was 0.5 g. A three-dimensional FE model of the concrete tunnel section (600 m long) and surrounding soil layers was created with the ABAQUS software. To represent the inelastic behavior of the tunnel under the earthquake, a concrete damage plasticity model was assumed as a constitutive model for the concrete. A model of spatially varying ground motion, which takes so called “wave passage effect” was implemented for the dynamic analysis. Two velocities of seismic wave propagation were assumed: 500 and 1000 m/s. These velocities are typical for soft and stiff bedrock, respectively. It turned out that in case of stiffer bedrock, in which seismic waves propagate faster, the damage pattern shows less cracking than in case of soft bedrock. The distribution of plastic and damage computed indices also allowed to assess the impact of the shock on the structure. It turned out that the analyzed shock with PGA of 0.5 g was strong enough to cause severe destruction (cracking) in the tunnel lining. Finally, the transverse pattern of cracks, that was obtained from the calculations, was in good agreement with damages observed during severe earthquakes.