bluuebunny/crossref_metadata_2025 huggingface dataset:
Non-Abelian strings in N = 1 supersymmetric QCD
Authors: Ievlev Evgenii , Yung Alexei
Published: October 2018

Non-Abelian flux tubes (strings) are well studied in N = 2 supersymmetric QCD in (3+1) dimensions. In addition to translational zero modes they have also orientational moduli associated with rotations of their fluxes inside a non- Abelian group. The dynamics of the orientational moduli is described by the two dimensional CP(N - 1) model living on the world sheet of the non-Abelian string. In this paper we consider a deformation of N = 2 supersymmetric QCD with the U(N) gauge group and Nf = N quark flavors with a mass term μ of the adjoint matter. In the limit of large μ the theory flows to an N = 1 supersymmetric QCD. We study the solution for the non-Abelian string in this limit and derive an effective theory on the string world sheet. The bosonic sector of this theory is still given by the CP(N -1) model. We study also the fermionic sector of the world sheet theory. Upon the deformation the non-Abelian string is no longer BPS and we show that the fermionic superorientational zero modes are all lifted. This leaves us with the pure bosonic CP(N-1) model on the string world sheet in the limit of N = 1 QCD. We discuss what happens to confined monopoles at large μ.
On replica-nondiagonal large N saddles in the SYK model
Authors: Aref’eva Irina , Khramtsov Mikhail , Tikhanovskaya Maria , Volovich Igor
Published: October 2018

We study the saddle points of the SYK model, formulated in terms of the replica bilocal fields, beyond the replica-diagonal assumption. We find a family of replica-nondiagonal saddle points in the IR limit, where the saddle point equations are separable. We use the Parisi ansatz to find the replicanondiagonal solutions and take the replica limit. The free energy on these solutions is computed, and we find that some of the replica-nondiagonal saddles have lower free energy than the replica-diagonal saddle point.
Dispersion relations and dynamic characteristics of bound states in the model of a Dirac field interacting with a material plane
Authors: Pismak Yury , Wegner Franz
Published: October 2018

Symanzik’s approach for construction of quantum field model in inhomogeneous space-time is used as a basis for modeling the interaction of a macroscopic material body with quantum fields. In quantum electrodynamics it enables one to establish the most general form of the action functional describing the interaction of 2-dimensional material objects with photon and fermion fields. Results obtained within this approach for description of the interaction of the spinor field with a material plane are presented.
Functional Approach for the Description of Vacuum Influence on Electron States
Authors: Biryukov Alexander , Shleenkov Mark
Published: October 2018

In the path integral approach we describe evolution of interacting electromagnetic and fermionic fields by the use of density matrix formalism. The equation for density matrix and transitions probability for fermionic field is obtained as average of electromagnetic field influence functional. We obtain a formula for electromagnetic field influence functional calculating for its various initial and final state. We derive electromagnetic field influence functional when its initial and final states are vacuum. We represent the equations of the movement for the fermionic field and expression for energy of an electron taking into account influence of a vacuum of the electromagnetic field.
Horndeski Genesis: strong coupling and absence thereof
Authors: Ageeva Yulia , Evseev Oleg , Melichev Oleg , Rubakov Valery
Published: October 2018

We consider Genesis in Horndeski theory as alternative to or completion of inflationary scenario. One of the options free of instabilities at all comological epochs is putative strong coupling regime at the early Genesis stage. We address this issue to see whether classical field theory description of the background evolution at this early stage is consistent, nevertheless. We argue that, indeed, despite naive strong coupling, classical analysis is legitimate in a certain range of parameters. This opens up a posibility of a novel scenario for the beginning of the cosmological expansion.
Baryogenesis in the vMSM: recent developments
Authors: Timiryasov Inar
Published: October 2018

Extension of the Standard Model with two right-handed neutrinos provides an economic and testable explanation of the origin of the baryon asymmetry of the Universe. We review recent progress in understanding dynamics of the asymmetry generation. We also present results of a new study of the parameter space of the model. These results demonstrate that the region of the parameter space in which the observed value of baryon asymmetry can be reproduced is larger than it was previously obtained.
keV sterile neutrino with large mixing angle is still alive
Authors: Chudaykin Anton
Published: October 2018

We study production of keV scale sterile neutrinos with large mixing with the Standard Model sector [1]. Conventional mechanism of sterile neutrino generation in the early Universe leads to overproduction of the Dark Matter and strong X-ray signal from sterile neutrino decay. It makes anticipated groundbased experiments on direct searches of sterile-active mixing unfeasible. We argue that for models with a hidden sector coupled to the sterile neutrinos cosmological and astrophysical constraints can be significantly alleviated. In developed scenario a phase transition in the hidden sector modifies the standard oscillation picture and leads to significantly larger mixing angles, thus opening new perspectives for future neutrino experiments such as Troitsk v-mass and KATRIN.

This work was made in collaboration with Fedor Bezrukov and Dmitry Gorbunov.
Biodeterioration mechanisms and kinetics of SCM and aluminate based cements and AAM in the liquid phase of an anaerobic digestion
Authors: Giroudon Marie , Peyre Lavigne Matthieu , Patapy Cédric , Bertron Alexandra
Published: October 2018

In biogas structures, concrete faces aggressive media during anaerobic digestion. Biological activities allow the conversion of organic matter into biogas, leading to a medium characterized by a variability of composition in time and space. In order to ensure the sustainability of this expanding industry, solutions for increasing concrete durability are needed. This study aims to analyse the deterioration mechanisms of different binders focusing on the impact of the binder nature on the medium (biochemical composition) during the digestion. Binders with favourable composition to chemically aggressive media were tested: slag cement (CEM III/B), calcium aluminate cement (CAC) and metakaolin-based alkaliactivated material (MKAA), and a reference binder: OPC (CEM I). They were exposed to three anaerobic digestion cycles in liquid phase in laboratory bioreactors. The organic acids and ammonium concentrations of the liquid phase were monitored by GC and HPIC. For OPC and slag cement pastes, the chemical and mineralogical changes were characterized by SEM/EDS and XRD. Locally, the presence of binder materials has an impact on the kinetics of the digestion reaction, and therefore on the quantities of gas produced. Ammonium concentrations were above the XA3 class range. Under the conditions explored, biodeterioration mainly led to the carbonation of cement pastes.
Optical pH imaging of concrete exposed to chemically corrosive environments
Authors: Grengg Cyrill , Mueller Bernhard , Mittermayr Florian , Mayr Torsten , Borisov Sergey , Dietzel Martin
Published: October 2018

Major types of chemical concrete degradation such as carbonation, leaching and acid attacks are strongly associated with decreasing internal or external pH. Thus a precise determination of the latter is crucial for the assessment regarding the degree of corrosion and corresponding development of prevention strategies. Conventional pH measure methods for concrete, such as phenolphthalein indicator, pore solution extractions and flat surface electrodes have proven to contain significant limitations and inadequacies. This contribution presents the application of sensor foils based on luminescent pH sensitive dyes entrapped in a polymeric hydrogel matrix, to quantify and image the distribution of surface pH of concrete based construction materials. An imaging technique called time-domain dual lifetime referencing (t-DLR) was used, which suppresses artifacts from scattering of the background and other light inhomogeneities. Using this methodology high-resolution pH profiles of concrete samples exposed to carbonation and biogenic acid corrosion were recorded.
Effects of concrete quality and natural Johannesburg environment on concrete carbonation rate
Authors: Ikotun Jacob Olumuyiwa
Published: October 2018

This study presents the results of a project undertaken to study the combined effects of concrete quality (binder type, w/b, and duration of initial moist curing) and natural Johannesburg environment on carbonation rate of concretes containing 100% PC, 35% fly ash (FA), 50% ground granulated blast-furnace slag (BS), 10% silica fume (SF) and (30% BS + 10% SF). The results show that apart from the SF blended concretes, the carbonation rate of the SCM blended concretes are higher than the PC concretes. Reducing the w/b and increasing the duration of initial moist curing reduced the carbonation rate in the concretes. The indoor exposed concretes have the highest carbonation rates and reducing the w/b ratio is more efficient and sustainable in lowering the carbonation rate rather than extending the duration of the initial moist curing.
Assessing the influence of self-healing capacity of lime-based mortars on brick-mortar interface strength in masonry units
Authors: De Nardi Cristina , Cecchi Antonella , Ferrara Liberato
Published: October 2018

Among the materials used in constructions, self-healing ones have been widely studied, including polymers, asphalts, cement binders; nonetheless the issue of the implementations and engineering of the self-healing capacity of lime-based mortars has been seldom investigated. As a matter of fact, the aforementioned capacity in restoration of building heritage, as well as in concrete structures, would provide an interesting contribution in terms of durability of the same restoration work as well as of the building as a whole. The aim of this research is to study the influence of healing capacity on the masonry behaviour by means of shear tests. The choice to perform shear tests, with or without lateral precompression is due to the representativeness of conditions truly occurring in masonry structural elements when in service. “Triplet specimens” have been fabricated, consisting of 3 clay bricks and 2 layers of purposed-design mortar, to mimic the compositions of mortars which can be actually found in existing heritage buildings. The methodology envisages three phases: a first series of specimens, after 28 days curing in lab environment, was tested to evaluate the shear strength. Then, on a second series of samples, a damage was induced by loading them to a prescribed fraction (70%) of the shear strength, determined as above in the previous stage; samples were subsequently immersed in water for 3 months and re-tested at the end of this curing period. Results clearly show that the autogenous healing capacity is responsible of an interesting recovery of the interface shear strength. The reliability of this approach has been also investigated by comparing the experimental results with a simplified FE model.
Performance of concrete with and without crystalline admixtures under repeated cracking/healing cycles
Authors: Ferrara Liberato , Cuenca Estefania , Tejedor Antonio , Gastaldo Brac Enricomaria
Published: October 2018

The present paper analyses the repeatability of self-healing capacity in fibre reinforced concretes, both autogenous or enhanced by the addition of crystalline admixtures. The behaviour of the investigated concrete mixes was analysed by means of the “Double Edge Wedge Splitting (DEWS)” test, whose configuration and specimen geometry (150x15x50 mm) allow to predetermine the failure plane and the relative orientation of fibres. Initially, specimens were pre-cracked up to a crack width of 0.25 mm, then they were subjected for 1, 3 and 6 months to different exposure conditions, including water immersion, open air exposure and wet/dry cycles After that, specimens were subjected to repeated cracking and healing cycles, alternatively for 1 and 2 months, and up to an overall duration of one year. The crack closure index was evaluated using photogrammetric methods. The results highlighted the potentials of crystalline admixture in guaranteeing a better persistence of the healing performance in the long term and under repeated cracking and curing cycles.
Pore structure of mortars containing limestone powder and natural pozzolan assessed through mercury intrusion porosimetry and dynamic vapour sorption
Authors: Alderete Natalia , Villagrán Yury , Mignon Arn , Snoeck Didier , De Belie Nele
Published: October 2018

Pore structure characterization is a key aspect when studying the durability of cementitious materials. When supplementary cementitious materials (SCMs) are used changes in pore structure are expected, and the complexity of its analysis is increased. The purpose of this paper is to describe the pore structure variation of mortars with two types of SCMs: natural pozzolan from volcanic origin (NP), and limestone powder (LP). We tested mixes with cement replacements (in weight) of 20 % and 40% by NP, and 10 % and 20% by LP. To analyse the pore structure, two widely accepted and complementary techniques were applied: dynamic water vapour sorption (DVS) and mercury intrusion porosimetry (MIP). With the DVS data, the Barret-Joyner-Halenda (BJH) model was used for pore size distribution assessment. Calculations with the Dubinin-Radushkevich (DR) model were also made for the smallest pore size range. Tests were performed at 28 and 90 days. MIP and DVS allowed evaluating the effect of the studied SCMs on different pore size ranges. Both techniques provided comprehensive information over a wide range of pore sizes. The mix with 40 % of NP had the best evolution, showing a significant volume decrease in the mesopore range.
Characterization of Polyacrylamide based Superabsorbent Polymers for potential use in PC Matrices with Supplementary Cementitious Materials
Authors: Almeida Fernando C.R. , Rostami Rohollah , Klemm Agnieszka J
Published: October 2018

This paper compares three types of polyacrylamide based Superabsorbent Polymers (SAP) with different water absorption capacities for potential application in Portland cement composites. The analysed matrices contain Supplementary Cementitious Materials (SCM) such as ground granulated blast-furnace slag (GGBS), fly ash (FA type F), silica fume (SF) and lime (NHL 5). SAPs were characterized in terms of shape, size and molecular structure by the Laser Diffraction, SEM, and the Raman Spectroscopy techniques. Kinetics and capacity of SAPs absorption in different environments (deionised water, PC solution and various PC-SCMs solutions) were evaluated by the tea-bag method. pH of all solutions was determined after 24 hours. The effect of different SCMs on SAPs sorption behaviour has been presented. The experimental results show that SAPs do not affect pH of cementitious solutions. However, SCMs addition reduces SAPs' absorption capacity and increase their desorption features. This is related not only to the type of SCM, but also to the level of substitution.
Outcomes of the round robin tests of RILEM TC 247-DTA on the durability of alkali-activated concrete
Authors: Provis John L. , Winnefeld Frank
Published: October 2018

Alkali-activated cements, including ‘geopolymer’ materials, are now reaching commercial uptake in various parts of the world, providing the opportunity to produce concretes of good performance and with reduced environmental footprint compared to established technologies. The development of performance-based specifications for alkali-activated cements and concretes is ongoing in several jurisdictions. However, the technical rigour, and thus practical value, of a performance-based approach to specification of novel cements and concretes will inevitably depend on the availability of appropriate, reliable testing methods, particularly regarding key aspects of durability where degradation mechanisms may be complex and depend on the chemistry and microstructure of the binder. This paper will briefly discuss the activities of RILEM Technical Committee 247-DTA in working to validate durability testing standards for alkali-activated materials, bringing scientific insight into the development of appropriate specifications for these materials.
Outdoor exposure site testing for preventing Alkali-Aggregate Reactivity in concrete – a review.
Authors: Fournier Benoit , Lindgård Jan , Wigum Børge J. , Borchers Ingmar
Published: October 2018

Alkali-silica reaction (ASR) is a deleterious chemical reaction affecting the durability and service life of concrete structures worldwide. Specifications and recommendations were produced in many countries to ensure that non-reactive aggregates are used in concrete construction or, when reactive aggregates must be used, appropriate preventive measures are implemented. Such recommendations, especially those related to the use of supplementary cementitious materials (SCM) to prevent ASR, are generally based on laboratory investigations, but preferably on field performance surveys of concrete structures where such measures have been implemented. Over the past 50 years, outdoor exposure sites have been developed in several countries with the objective of validating data obtained from laboratory testing for various combinations of reactive aggregates and SCM, as well as for determining long-term performance of specific mix designs. This paper reviews worldwide efforts regarding outdoor exposure site testing for ASR prevention.
Determining alkali leaching during accelerated ASR performance testing and in field exposed cubes using cold water extraction (CWE) and µXRF
Authors: Lindgård Jan , Østnor Tone , Fournier Benoit , Lindgård Øyvind , Danner Tobias , Plusquellec Gilles , De Weerdt Klaartje
Published: October 2018

Considerable leaching of alkali metals was documented, both in concrete samples exposed to accelerated laboratory testing and field samples. CWE allowed to quantitatively determine the free alkali metal profiles as a function of the depth. However, CWE cannot account for the changes in the paste content towards a cast surface leading to a seemingly increase in alkali metals. The μXRF allowed to distinguish paste and aggregates. It allowed thereby to determine qualitative Na and K profiles in the cement paste phase of the concrete samples. The laboratory exposed samples showed a clear leaching profile into a depth of about 15 mm after 21 weeks of exposure at 60°C. Corresponding numbers for the 12 years field exposed cube were 50-60 mm. Alkali sorption by alkali silica gel was detected using the μXRF. For the laboratory exposed samples, the prisms prepared with Portland fly ash cement leached less alkali compared to the prisms prepared with ordinary Portland cement, as expected. The leaching in the middle of the prisms estimated based on the μXRF profiles agreed rather well with the level of alkali leaching determined based on the analysis of the leachate (i.e. the water below the samples during exposure).
Field Evaluation of Concrete using Hawaiian Aggregates for Alkali Silica Reaction
Authors: Robertson Ian , Shen Lin
Published: October 2018

Alkali Silica Reaction (ASR) occurs in concrete when the alkali hydroxides (Na+, K+ and OH-) from the cement react with unstable silica, SiO2, in some types of aggregate. The resulting gel will expand when it absorbs water, potentially leading to cracking and overall expansion of the concrete. Concrete aggregates available in Hawaii have not demonstrated a history of ASR, however, results of accelerated laboratory tests using ASTM C1260 indicated a potential for ASR with some aggregates. In order to assess the accuracy of the laboratory test results, a long-term field study of the potential for ASR in concretes made with Hawaiian aggregates was initiated in 2011. Forty concrete specimens were constructed of various concrete mixtures using aggregates from all Hawaiian aggregate sources, and some US mainland aggregates known to exhibit ASR expansion. The specimens are located in an open field site in Manoa valley on the Hawaiian Island of Oahu, exposed to relatively high humidity and frequent rainfall. A weather station at the site records the ambient conditions on a continual basis. This paper describes the field evaluation program and presents the results after six years of monitoring. Comparisons are made between the field observations and accelerated laboratory tests.
Towards understanding corrosion initiation in concrete – Influence of local electrochemical properties of reinforcing steel
Authors: Michel Lucas , Angst Ueli
Published: October 2018

The ageing of reinforced concrete (RC) structures in the industrialized countries increases the probability of durability issues. The mechanism of chloride-induced corrosion, the most common deterioration process in RC structures, is still not well understood. Improvement in the understanding of localized corrosion initiation is crucially required to allow for cost efficient and durable maintenance of the existing infrastructures and for service life design of new structures. This study reports results from localized electrochemical characterization of reinforcing steel surfaces taken with a local sensor positioned at different locations on the rebars. This permitted “mapping” the local Open Circuit Potentials for different rebars with different surface conditions. Moreover, local cyclic voltammetries on selected spots were also carried out. Subsequently, the samples were exposed to a chloride solution to provoke corrosion initiation. The corrosion initiation sites from visual inspection were correlated with the local electrochemical characterization. Results show a clear difference depending on the surface condition. Furthermore, for non-rusted surfaces, a spatial distribution of the local electrochemical behaviors seems to follow a pattern depending on the geometry of the steel bar and influencing the location of corrosion initiation.
Corrosion behaviour of rebars 1.4003 in cracks of RC structures containing chlorides
Authors: Dauberschmidt Christoph , Fraundorfer Andreas
Published: October 2018

The durability of chloride exposed reinforced concrete components is decisively determined by the corrosion behaviour of the reinforcement in the crack containing chlorides. In this case, high corrosion rates may occur using conventional rebar steel, which can lead to a significant cross-sectional loss of the rebar in a short period of time. One possible way to minimise the risk of corrosion in cracks containing chlorides is to use stainless rebars. Here, mostly expensive stainless steels of the material numbers 1.4571, 1.4401 etc. are used. An efficient alternative is the use of Chromium reinforcing steels (e.g. X2CrNi12) 1.4003. Corrosion tests on cracked reinforced concrete beams with chloride exposure and different chloride concentrations have been carried out in the laboratory of the University of Applied Sciences in Munich. The results of these investigations show a significant increase of the critical corrosion inducing chloride content of the rebars within the cracks. These results will be discussed in regard of the durability of reinforced concrete structures with Chromium reinforcing steels and cracked RC-structures in parking decks and floor slabs.
Monitoring DIAMOND device for corrosion state evaluation of reinforced concrete structures
Authors: Samson Gabriel , Deby Fabrice , Garciaz Jean-Luc , Perrin Jean-Louis
Published: October 2018

The corrosion of steel rebars is a major issue with respect to the durability of reinforced concrete structure. Several corrosion evaluation methods exist: half-cell potential, concrete resistivity or linear polarization resistance (LPR) measurement. However, these techniques are employed at a given moment and are not suitable for continuous corrosion evaluation. This works belongs to the DIAMOND project which aims to produce a new corrosion state measurement monitoring device. The monitoring probe consists on a cylindrical probe. A ring shape counter-electrode CE is plated on the probe side. At the centre of the CE, a reference electrode (RE) is placed for potential measurement. The device is embedded in concrete at 25 mm of the inspected rebar. The instantaneous ohmic drop observed at the beginning of the polarization measurement is only linked with the concrete resistance which depends on concrete cover and resistivity. A numerical model was developed on Comsol® to create abacuses graph that link concrete resistivity and concrete resistance. Thus, the ohmic drop measure at the beginning of the polarization can now be used to determine regularly concrete average resistivity between the monitoring probe and steel rebar. Two other series of abacus graphs are then introduced in order to determine the polarization resistance of the rebar in front of the monitoring probe (the point of interest (PI)). Two monitoring probes were placed in two types of concrete (one sound concrete and one concrete with chloride). Corrosion potential, concrete resistivity and rebar corrosion rate were monitored over around 200 days. The experimental results obtained with the monitoring probe are finally compared to the results obtained with the surface DIAMOND probe (introduced in the ICCRRR 2018 paper “Alternative methodology for linear polarization resistance assessment of reinforced concrete structure [1]”).
Probability Distribution of Cross-sectional radius of Corroded Steel Bars in Concrete and Its application
Authors: Chongkai LI , Weiping ZHANG , Xianglin GU , Qinghua HUANG
Published: October 2018

The impress current method is applied to acquire corroded steel bars embedded in concrete, and three-dimensional(3D) laser scanning techniques are applied on corroded steel bars to obtain the cross-sectional radius of corroded steel bars. Statistical analysis shows that with the increase of corrosion degree, the variation of radius of corroded steel bars increases linearly. For different types of steel bars, plain round steel bars have a larger sensitivity to corrosion than ribbed ones. Original radius of steel bars and mixture proportion of concrete have negligible effect on the variability of radius of corroded steel bars. A normal distribution model is obtained to describe radius data of corroded steel bars. For the convenience of practical application, the indicator,R, which is the ratio of the average to the minimum cross-sectional areas of corroded steel bars, is introduced to quantify the longitudinal variation of the cross-sectional areas. By using Monte-Carlo simulation, the indicator, R, of corroded steel bars are achieved based on the probability distribution of radius. The indicator R can be fitted well by the Gumbel distribution, and the distribution parameters increase linearly with the increases of corrosion degree.
Impregnation Technique Provides Corrosion Protection to Grouted Post-Tensioning Tendons
Authors: Whitmore David , Lasa Ivan
Published: October 2018

Thousands of bridge structures rely on grouted post-tensioning (PT) tendons. Problems with grouting techniques and grout materials have resulted in bridges with grout voids, chloride contaminated grout and soft grout. These problems have promoted corrosion and failure of post-tension tendons, some within 6 to 17 years of service. The Florida Department of Transportation (FDOT) has spent more than $55 million (USD) repairing 11 post-tensioned bridges to date. A cost-effective corrosion mitigation technique has been developed to minimize the corrosion of PT tendons and extend the service life of bridges which have grouting issues. This paper describes the development and implementation of this technique on grouted PT bridges.
Demolition of Old Oak Bridge B4113: Condition of a 54-year old prestressed concrete bridge
Authors: Kramer Wandie , Martin William , Viljoen Harry
Published: October 2018

The extension of the 3rd lane on Trunk Road 9 Section 1 (N1) at Bellville in the Western Cape necessitated the demolition and replacement of the Old Oak Road Underpass Bridge B4113. This bridge had insufficient vertical clearance as well as insufficient horizontal clearance for the widening of the road. Furthermore, the existing precast beam and slab deck has suffered from repeated vehicular impact damage over the years, resulting in continued costly repairs. This paper describes the condition of this bridge after a 54-year service life. The primary objective is to report and comment on the condition of this bridge in order for other engineers who have to rehabilitate, raise or widen similar bridges built at the same time, to have an indication of the quality of materials, workmanship, condition and behaviour. During and after the demolition operation, a visual inspection of the rubble was undertaken to evaluate the condition of this bridge which was constructed in 1963. Concrete cores taken before the demolition revealed higher concrete strengths of 50% and more. Carbonation and durability tests done on concrete fragments indicated a robust and durable structure which would easily reach its intended 100-year design life. However, overlays under the bridge reduced the vertical clearance while the expansion joint details led to reduced durability.
Validation of artificial defects for Non-destructive testing measurements on a reference structure
Authors: Stefan Maack , Salvador Villalobos , David Scott
Published: October 2018

Non-destructive testing was established over the last decades as an important tool for assessing damages, material characterization and quality assurance in civil engineering. For example, Ground Penetrating Radar (GPR) can be used to scan large areas of concrete structures to determine the spatial position of the reinforcement. With the ultrasonic echo method, the thickness of concrete structures can be easily determined even if a high density of reinforcement is given. Various methods and processes have been developed for the validation of NDT procedures aiming at ensuring the quality of measurements in practical use. The Probability of Detection (POD) for example, is an available method to compare different technical devices with each other quantitatively regarding their performance. With this method, the best suited testing device for a specific inspection task under defined boundary conditions can be selected. By using the Guide to the Expression of Uncertainty in Measurement (GUM), it is possible to quantify the measurement uncertainty of an inspection procedure for a specific task. Another important aspect to improve the acceptance of Non-destructive testing methods is the development of reference specimens. Reference specimens serve for the calibration and further development of NDT methods under realistic conditions in different laboratories under the same conditions. A particular challenge here is the most realistic representation of a damage that can occur at building sites. Possible damages include for example horizontal and vertical cracks or honeycombs in concrete. Such a reference structure was built for the development of a new design of power plant constructions. Comparative studies on the manufacturing of realistic honeycombs and delaminations were carried out in advance on a test specimen. The results of this study are presented here.
Alternative methodology for linear polarization resistance assessment of reinforced concrete structure
Authors: Samson Gabriel , Deby Fabrice , Garciaz Jean-Luc , Perrin Jean-Louis
Published: October 2018

For reinforced concrete structures, several corrosion detection methods exist: concrete resistivity, half-cell potential or linear polarization resistance (LPR) measurement. The LPR value can be linked to the corrosion rate thanks the Stern-Geary equation if strong hypotheses are made. Existing commercial devices use a guard ring to canalize the current on specific steel rebar area and assume that the steel rebar is uniformly polarized. However, recent works reveal that the top part of the steel rebar, right under the counter electrode, is the most polarized point. The particular point is referred as the point of interest (PI). This works belongs to the DIAMOND project which aims to produce a new corrosion rate measurement device. Comsol® software was used to model the influence of concrete cover, resistivity and injected current on the current density at the PI. Moreover, a significant influence of the steel rebars diameter was also demonstrated. Two types of abacus are built. The first one links to polarization measured on the surface to the polarization on the rebar at the PI. The second links the ratio between the current density at the PI and the density of injected current to concrete cover and steel rebar diameter. The Stern-Geary equation can now be used at the PI without using the approximation of a uniformly polarized rebar. The corrosion state of reinforced concrete structure can be controlled more precisely. The methodology is then applied on two concrete slabs in which three metal bars are embedded at different concrete covers. The first slab is prepared with ordinary concrete while the second contain chloride to artificially activate the corrosion process. The results reveal that the rebars embedded on the first slab are not corroding (icorr ≤0.2 μΑ/cm2) while the second rebar are corroding (icorr>0.2 μΑ/cm2).
Design and Development of Concretes for Special Rehabilitation Tasks
Authors: Flohr Alexander , Osburg Andrea
Published: October 2018

The requirements for concrete restoration are not only aspects of retrofitting or restoration of bearing capacity but also aspects of preservation of historic structures, such as industrial monuments or civil engineering structures and buildings of the 1960s [1]. Thereby the facsimile replication of the concrete surface is a particular challenge. For the manufacture of delicate and complex structures with restricted accessibility self-compacting concrete (SCC) is well suited [2]. A modification with polymers normally ensures the durability of repair mortars or concretes (PCC) [3]. The combination of PCC and SCC to the Polymer-modified Self-Compacting Concrete (PSCC) for the restoration of historic concrete constructions is the logical consequence, to combine the advantages of both materials and is therefore an interesting alternative to well established materials and methods. Historic concrete constructions are often manufactured of concretes with very stiff consistencies, the so called tamped concretes. So there is a need to develop materials and methods for the rehabilitation of structures made of tamped concrete. For this reason, first investigations have been performed to the recipe development and optimization of its composition, but also properties, furthermore to the design possibilities and how polymers influence the concrete properties. In Germany between 1920 and 1970 industrial buildings and hydraulic structures have been built with concretes, where the content of Portland cement clinker was nearly complete substituted by latent hydraulic materials. The binders of those concretes contain large quantities of blast furnace slag and calcium sulphate and are called super-sulphated cement (SSC). Because of the high sulphate content, the compatibility of concrete structure with SSC is not given to concretes or mortars with other cements. If there is an adequate range of moisture, harmful new formations of phases will occur in the contact zone between SSC-concrete and the other concrete. In the field of rehabilitation PCC are well established. These are polymer-modified mortars or concretes with Portland cement, which are not suitable for the rehabilitation of structures of SSC-concrete. An alternative is the polymer-modification of SSC-concretes with polymers.
Underwater Abrasion Resistance of Cementitious Acrylic Coating on Repaired Surface of Concrete Dam and Stilling Basin
Authors: Šušteršič Jakob , Kryžanowski Andrej , Brodnik Aleš , Zajc Andrej
Published: October 2018

The paper presents and analyzes the results of the underwater abrasion tests of Cementitious Acrylic Coating (CAC), which was used to protect the repaired surface of concrete dam and stilling basin of power-plant Moste on river Sava in Slovenia. Behavior of the CAC obtained with laboratory tests is rather similar to the behavior obtained after 1 year of application on the power-plant. Relatively good underwater abrasion resistance of CAC was obtained. Results of bond strength show that pressure of capillary water decreases bond between CAC and concrete surface. If such coating is additional loaded with abrasion forces, bond between those two layers becomes worse. Similar conclusions can be made on the basis of the obtained results of surface resistance to freeze-thaw test of CAC has been carried out. The resistance is rather good, but CAC separated from concrete surface, when water is present in the interface between the CAC and concrete surface during freeze-thaw loading.
Polymer Injection Rehabilitation Technology for Lifting Differential Settlement of Turnout Ballastless Track
Authors: Liu Jing , He Yuanqing , Zhang Jiahai , Hong Jian , Wen Xihua , Xiao Jianhong , Wang Feng , Zheng Xinguo
Published: October 2018

The turnout ballastless track is an advanced track structure with high stability and integrity. However, due to complicated geological conditions, local groundwater level declined, and many other unavoidable objective reasons, the roadbed foundation of some railway lines appeared large uneven settlement deformation, so the above turnout ballastless track concrete structure also experienced uneven settlement accordingly. Compared with ballast track which could be restored by increasing the ballast under the sleepers simply, the smoothness of turnout ballastless track could only be restored by adjusting the thickness of the base plates of fastener system accordingly. But if continuous settlement deformation exceeded the specified allowed adjustable range of the fastener system, the smoothness of ballastless track diminished, the speed of passing trains had to be limited to ensure the safety. In order to solve this global challenging problem, we systematically studied polymer injection rehabilitation technology through a series of indoor reduced scale tests and field full scale simulations with real ballastless track concrete structure. We verified the effect of uplift rehabilitation and filling quality of grouting material through destructive experiment inspection. And combined with engineering practices and its coring samples strength test, the Polymer injection rehabilitation technology for turnout ballastless track in settlement roadbed sections had been studied and developed. This technology could restore the smoothness of railway and the adjustable range of fastening systems without affecting the normal daily operation of the railway lines. Compared with traditional cement grouting technology, this rehabilitation technology possessed significant advantages including small light construction equipment, simple logistics, flexible organization, high uplifting precision, and little additional load. This technology provided valuable technical support and useful references for restoring the smoothness of turnout ballastless track which appeared large uneven settlement deformation.
The influence of concrete substrate moisture condition on the tensile pull-off strength of protective coatings
Authors: Kay Sean , Beushausen Hans
Published: October 2018

A range of different surface coatings are available for the protection of concrete surfaces, typically aimed at reducing the ingress of deleterious substances into the concrete and providing adequate aesthetic appeal on patch-repaired elements. The coating systems are usually of high material quality and perform well when applied and maintained correctly. The long-term success of protective surface coatings is largely a function of application procedures. In particular, coating durability with regards to bond strength and crack resistance is dependent on the preparation of the concrete substrate prior to coating application. This research gives insight into the effects a sound, clean and profiled concrete substrate that is subjected to different moisture conditions has on coating bond strength. The influence of three different methods to precondition concrete substrates on the tensile pull-off strength of two commercial coatings, applied to substrate concrete with various strengths was investigated. The moisture condition was found to have a significant influence on the pull-off strength of the coatings, higher degrees of substrate saturation typically resulting in higher strengths. Similarly, with increasing substrate moisture content, the failure mode increasingly shifted towards substrate cohesion failure.
Performance of Concrete Overlays in Iowa
Authors: Taylor Peter , Gross Jerod , King Dan , Chen Yu-An , Ceylan Halil
Published: October 2018

It has often been claimed that concrete overlays are a cost effective, low maintenance preservation tool used to extend pavement life. However, there has been relatively little data to confirm this. The State of Iowa has a long history of using concrete overlays as a means of extending the life of all types of roadways and as such provides an interesting opportunity to examine their performance over time. The work described in this paper summarizes the activities and findings of a study conducted for the Iowa Highway Research Board. Existing databases operated by the Department of Transportation and Iowa State University were analyzed to assess the performance of overlays. Pavement condition data such as IRI, transverse cracking, longitudinal cracking, D-cracking, spalled joints and faulting were compared with design details of the overlays such as bond type, thickness and joint spacing. The data indicate that in general overlay performance is very good in that about 90% of 3100 km of overlays are still in acceptable condition at ages up to 35 years. The paper discusses the details behind this finding.
The widening of structures over the Orange river on national route 12 section 9 near Hopetown, the Northern Cape
Authors: Massingue Tiago , Lourens Chris
Published: October 2018

The South African National Roads SOC Agency (SANRAL) identified two bridges on the N12, section 9 to be widened and improved. The bridges were to be repaired of their existing structural defects and widened to allow safer passage of traffic and pedestrians along the route. Repairs to concrete, replacement of existing structural elements and retrofitting of improved elements were undertaken simultaneously to bring the bridges up to specification and safety standards. Through this effort, the bridges durability and lifespans were greatly improved and prolonged. Further substantial benefits were injected into the local environment and community through job creation and education with the local population of the area.
A Case Study of the Retrofitting of the Great Fish River Bridge
Authors: Moodley Nerave , Moore Graham , Wylie David
Published: October 2018

In developing countries and economies such as South Africa, retrofitting is a vital tool to maximise and extend the service life of existing infrastructure. The transportation sector plays a pivotal role in stimulating economic growth, and retrofitting existing bridges to meet the growing capacity needs of South Africa’s roads supports continued economic growth and development. This paper outlines the technical and practical challenges encountered and the solutions developed by the design team to retrofit the existing 215 m long, 9-span, Great Fish River Bridge in the Eastern Cape of South Africa. These challenges included jacking up the existing bridge under traffic loading to replace 108 existing bearings and erecting 32.5t precast beams at heights of 10.5m above a major river whilst accommodating high volumes of traffic on a busy National road.
Partial replacement of conventional fine aggregate with crumb tyre rubber in structural concrete – effect of particle size on compressive strength and time dependent deformations
Authors: Mushunje Kudzai , Otieno Mike , Ballim Yunus
Published: October 2018

This paper presents results of a study into the effects of truck tyre crumb rubber particle size, as fine aggregate, on the compressive strength, shrinkage and creep behaviour of structural rubberised concrete. The study is motivated by a growing interest in the use of concrete with waste tyre rubber particles, rubberised concrete, for structural applications. Three tyre crumb rubber sizes (2.36, 1.18 and 0.425 mm) were used to replace 10% by volume of fine mineral aggregates to produce concrete with a target strength of 30 MPa. The concrete was cast water-cured for 28 days and tested for shrinkage and creep for 180 days. Half of the shrinkage and creep samples were sealed with a bitumen seal to prevent drying during testing. Results show a general a decrease in compressive strength with reduction in crumb rubber size. The strength decreases by 22%, 23% and 27% for the 2.36, 1.18 and 0.425 mm mix respectively. Preliminary results show a general increase in both shrinkage and creep deformations in both drying and sealed conditions. The observed increases were checked against the limits provided in design codes to assess the applicability of the material for structural purposes.
Effect of Hybridization of steel fibers on the mechanical properties of high strength concrete
Authors: Khan M. Iqbal , Abbass Wasim
Published: October 2018

The hybridization of fibers for arresting the crack in concrete is a key factor and play an important role to improve mechanical properties of high performance concrete with respect to mono fibers. The effect of hybridization of hooked end steel fibers with different length and diameter on mechanical properties of high strength concrete was investigated in this research work. The different percentages of hook ended fibers (60 mm and 40 mm) are hybridized in the concrete mixture while keeping total percentage of fibers by volume equal to 1%. The compressive and flexural properties with complete load verses deflection curves of hybrid steel fiber reinforced high performance concrete were investigated to find the optimized dosage of hybrid steel fibers. The results showed that the hybridization of fiber provided better compressive and flexural performance. It was also observed from the results that combination of 65% of 60 mm and 35% of 40 mm hooked end fibers proved to be best for enhancement in compressive and flexural properties.
Pullout simulation of post installed chemically bonded anchors in UHPFRC
Authors: Delhomme Fabien , Brun Michael
Published: October 2018

An experimental and numerical study was completed in order to examine the mechanical behaviour of post-installed bonded anchors in ultra-high performance fibre reinforced concrete with a compressive strength higher than 130 MPa. The aim was to analyse the failure mechanisms in static pullout tests and to suggest a simple numerical model, which can be employed in a design stage, to reproduce the global behaviour of the anchor. The experimental observations show that a combined pullout and concrete cone failure occurred for an embedment depth of 40 mm and a steel rod failure for an embedment depth of 100 mm. The numerical model was set up using Abaqus software, by adopting the concrete damage plastic model and a surface-based cohesive behaviour for the interface concrete-anchor. The obtained failure modes and ultimate loads are in good agreement with experimental results. A minimum embedment depth of 50 mm was assessed to prevent a pullout failure of the anchor.