bluuebunny/crossref_metadata_2025 huggingface dataset:
Dry powder alkali-activated slag cements
Authors: Kovtun Maxim , Kearsley Elsabe P. , Shekhovtsova Julia
Published: November 2015

This paper reports on the results of an investigation into the possibility of producing dry powder alkali-activated slag cements as a ready-to-use product which can be packed in bags and mixed with water to produce a concrete. The cements were produced using a neutral granulated blast-furnace slag and sodium carbonate. To accelerate strength development at ambient temperatures, a combination of silica fume and slaked lime was used as accelerating admixture in the cement's formulation. Powder sodium lingosulfonate was added into the formulation to reduce the water demand of the cements; it also delayed setting and increased compressive strength. Alkali-activated slag concretes were produced using the developed cements. Compressive strengths in the range from 30 to 85 MPa were achieved for the concretes at 28 d. The accelerating admixture increased 1-d compressive strength for the alkali-activated slag concretes cured at ambient temperature up to 25 MPa. The optimum concentration of sodium carbonate was equivalent to 3·5% and 4·5% sodium oxide (Na2O) for precast and in situ application, respectively. The accelerating admixture is recommended at 6% for dry powder alkali-activated slag cements. The accelerated ageing test showed that the dry powder alkali-activated slag cement had a sufficient shelf life.
Metakaolin-, fly ash- and calcium hydroxide-based geopolymers: effects of calcium on performance
Authors: Guo Xiaolu , Shi Huisheng
Published: November 2015

Effects of calcium on the performance of geopolymers prepared from metakaolin, class C fly ash (CFA) and calcium hydroxide are studied, including setting times and compressive strength testing. Leaching concentrations of calcium from prepared geopolymers are investigated by inductively coupled plasma atomic emission spectrometry. Relative contents of geopolymeric products and hydration products are studied by acid dissolving testing. The mineral composition, morphology and chemical groups of geopolymeric products and hydration products are analysed by X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy. Geopolymer setting time is much faster when calcium content increases. Calcium has a positive effect on compressive strength of geopolymers. By acid dissolving testing, the ratio of geopolymer value/ordinary hydration product value in metakaolin-based geopolymer was 4·4 : 1, whereas in CFA-based and CFA + 6% calcium hydroxide-based geopolymers the values were 1 : 1·7 and 1 : 1·5, respectively. Thus, the main product in metakaolin-based geopolymer is geopolymeric products, whereas in CFA-based geopolymer, hydration products also occur. In the alkali-activated condition, CFA-based geopolymer is a composite system with geopolymeric gel and calcium–silicate–hydrate gel co-existing.
Cementitious binder of phosphogypsum and other materials
Authors: Liu Laibao , Zhang Yunsheng , Tan Kefeng
Published: November 2015

This paper presents the properties of a binder developed to produce eco-friendly building products. The mixing ratio of the binder, comprising phosphogypsum, slag (ground granulated blast-furnace slag), lime and cement, was obtained based on orthogonal experiments. The test results showed that, under steam curing, calcium silicate hydrate gel and ettringite were formed in the hardened binder, leading to a higher strength. After steam curing at 90°C for 7 h and then air curing, the 28 d compressive strength of the binder reached 41·7 MPa. Using this binder and river sand, bricks with a 28 d compressive strength of 21·4 MPa were successfully manufactured.
Assessing the self-healing capability of cementitious composites under increasing sustained loading
Authors: Yildirim Gurkan , Alyousif Ahmed , Şahmaran Mustafa , Lachemi Mohamed
Published: November 2015

This study investigated the effects of progressively increasing sustained loading on self-healing behaviour of 180-d-old microcracked engineered cementitious composites (ECCs) incorporating different mineral admixtures. After introducing microcracks to the specimens with applied severe pre-loading, some were subjected to progressively increasing sustained loading. All of the specimens were then subjected to continuous moist curing for 150 d to evaluate self-healing performance. Mechanical property (modulus of rupture (MOR) and mid-span beam deflection) characterisations and ultrasonic pulse velocity measurements were used to assess self-healing capability. Experimental results showed that even under progressively increasing sustained mechanical loading, MOR results greater than the original values could be obtained, depending on mineral admixture selection. Although deflection results were more adversely affected by progressive sustained loading compared to MOR results, even the lowest deflection value obtained from different ECCs was still more than 100 times that of conventional concrete after healing. Under continuous moist curing, there were minimal changes in ultrasonic pulse velocity results of all ECCs subjected to progressively increasing sustained loading, so that recovery results similar to those of specimens without sustained loading were obtained, despite the fact that ultrasonic pulse velocity testing was not that sensitive in capturing the effects of self-healing.
Effect of competitive adsorption between polycarboxylate superplasticiser and sodium tripolyphosphate on cement paste fluidity
Authors: Tan Hongbo , Li Xin , Huang Jian , Ma Baoguo , Qi Changya , Chaoliang Lin
Published: November 2015

Sodium tripolyphosphate is a common retarder used to delay the hydration and prolong the setting time of cement paste. It is also sometimes employed to enhance superplasticiser dispersity to improve the fluidity and workability of cement and concrete, but the reason for this effect is unclear. The work discussed in this paper investigated the early hydration process of cement paste and the adsorption of sodium tripolyphosphate and polycarboxylate superplasticiser (PCS). The results show that there is competitive adsorption between PCS and sodium tripolyphosphate, sodium tripolyphosphate inhibits PCS from adsorbing onto the surface of cement particles, and PCS also reduces the adsorption of sodium tripolyphosphate. When both of these are reduced, there is a significant increase in the thickness of the adsorption layer and the zeta potential, which is shown to be the main reason for the improvement in fluidity. This indicates that some salts can be used to adjust the adsorption process of PCS in order to improve the fluidity and workability of cement paste and fresh concrete.
Influence of the specific surface area of alumina fillers on CAC hydration kinetics
Authors: Klaus Sebastian Reinhold , Neubauer Juergen , Goetz-Neunhoeffer Friedlinde
Published: November 2015

For refractory application inert alumina fillers frequently are mixed with calcium aluminate cements to improve particle packaging and to reduce the demand of water for low-cement castables. This finally results in decreased porosity and higher strength. Investigations by isothermal heat flow calorimetry show that the presence of alumina filler material with high specific surface area leads to a shortening of the induction period of calcium aluminate cement hydration. The study also demonstrates that the specific surface area of the chosen alumina filler changes the starting point of the main hydration reaction and in consequence the setting time of the calcium aluminate cement mixture is strongly influenced. During the dormant period the heat flow of calcium aluminate cement hydration with coarse alumina filler material of lower specific surface area is characterised by negative values. By addition of filler with higher specific surface area, the surface available for heterogeneous nucleation can be increased. Owing to more available surfaces the critical energy barrier for stable nuclei formation can be reduced. This results in a positive heat flow during the dormant period and a shift of the main reaction to earlier points in time.
Ceramic tiles waste as replacement material in Portland cement
Authors: Mas María A. , Monzó José , Payá Jordi , Reig Lucía , Borrachero María V.
Published: November 2015

The pozzolanic reactivity of real ceramic waste from different tile manufacturing companies was evaluated and its suitability as a partial Portland cement replacement was analysed. The raw material was finely ground and physico-chemically characterised using X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM) and laser analysis particle size distribution (ADL). Percentages of ceramic waste (from 15 wt% to 50 wt%) to substitute Portland cement were used to assess this material's pozzolanic behaviour, and samples were cured at 20°C for different curing times. pH tests and conductivity measurements were used to evaluate its pozzolanic character, while mortars were utilised to evaluate compressive strength behaviour. The microstructural evolution of the developed binders was assessed in pastes by XRD, thermal analysis, Fourier transform infrared spectroscopy (FTIR) and SEM analyses. A strength gain due to pozzolanic activity was observed after 28 d and 90 d curing. The results prove that mortars with up to 35 wt% of tile ceramic waste comply with the requirements established for fly ash pozzolanic materials.
Civil engineering career management—the unwritten rules
Authors: Hipkiss Anna
Published: November 2015

Getting ahead in civil engineering today is, like most other professions, very much down to an individual’s own efforts. Based on in-depth interviews with senior civil engineers and human resources managers at five major UK engineering organisations, this paper concludes that the traditional hierarchical, linear and predictable nature of civil engineering career development no longer exists. Promotion today depends very much on how individuals manage their own careers. Civil engineers need to make the best use of the support resources available to them and then follow their passions, be proactive and grasp opportunities. They should also build and share expertise, take considered risks, use positive politics, raise their visibility, promote their profiles, network and find role models and mentors.
Use of risk-based methods to evaluate spillway capacity: case histories
Authors: Brown Alan , Gosden John , Hewitt Martin , Hinks Jonathan , Gardiner Keith
Published: November 2015

The term ‘risk-based’ in relation to dam safety has now been in use for many years with quantitative methods available for over a decade. This paper explores the meaning of the term ‘risk-based’ and provides examples of its use in relation to assessing the need for spillway upgrades, including its use to asses when risk has been reduced to ‘as low as reasonably practicable’ (Alarp); that is, when the costs of further upgrading are disproportionate to the additional reduction in risk achieved. The paper then discusses the issues arising, including reasons for the apparent adherence to deterministic standards and lack of take-up of the Alarp approach in the UK as well as the management of potential conflict between recommendations from Section 10 inspections under reservoir safety legislation and portfolio risk assessment. The paper does not cover the wider issues of other threats to dams, which may have higher annual probabilities of failure; however, similar principles can be applied to the management of these threats.
Studies on magnetron-sputtered V2O5/ZnO thin films
Authors: Therasa Ranjani Perchamy , Deepak Raj Pattabiraman , Lakshmi Shree Balakrishnan , Selva Priya Subramanian , Sridharan Madanagurusamy
Published: November 2015

Crystalline vanadium oxide (V2O5) thin films were grown over zinc oxide (ZnO) buffer layer-coated glass substrates at room temperature by magnetron sputtering technique. Initially, ZnO thin films have been formed by oxidizing sputtered zinc films at different annealing temperatures (300–500°C) in ambient air for 1 h. The influence of ZnO buffer layer on the structural, morphological, optical and electrical properties of the V2O5 films was studied using the X-ray diffraction (XRD), field-emission scanning electron microscopy, energy-dispersive analysis of X-rays, ultraviolet–visible spectrophotometry and four-point probe method. The thickness values of the deposited films were measured using the stylus probe profilometer. XRD patterns of the V2O5 deposited over ZnO (VZO) showed reflection planes corresponding to V2O5 and ZnO buffer layer. The optical studies showed the enhancement on the optical properties of V2O5 films deposited over ZnO buffer layer. The electrical studies of the VZO films showed that the resistivity of VZO films varied from 400 to 60 Ω cm. The enhancement in the optical and electrical properties may be due to the improvement in the crystallinity of the film because of ZnO buffer layer.
Multimodal traffic assignment with traffic emission effects
Authors: Meng Meng , Shao Chunfu , Wong Yiik Diew , Zhang Jie
Published: November 2015

Traffic emissions are one of the most serious issues that affect urban sustainable development. Due to the heavy pollution from cars, public transport, including electric bicycles, has been regaining its proper position. A multimodal traffic equilibrium model with emission effects (MTEEE) is presented that considers energy use per person and pollutant emissions. MTEEE is based on a general traffic equilibrium model which jointly reduces congestion and emissions in a multimodal transportation network. Aiming for control of the total amount of carbon dioxide and limiting the link concentration of carbon dioxide, the model is expressed as a mathematical programming problem by combining the concept of environmental capacity with traffic capacity as constraints. The proposed MTEEE model is solved by a particle swarm optimisation (PSO) algorithm. Two experiments are conducted to demonstrate the effectiveness of the proposed model and the convergence properties of the PSO algorithm.
The paradox of public acceptance of bike sharing in Gothenburg
Authors: Nikitas Alexandros , Wallgren Pontus , Rexfelt Oskar
Published: November 2015

Bike sharing is one of the most promising urban planning interventions to facilitate an all-necessary transition towards a more sustainable transport paradigm. Regardless of the fact that hundreds of schemes run in more than 50 countries worldwide, bike sharing is still moderately investigated by research. This paper reports on a primarily quantitative study of 558 responses that was set to frame attitudes reflecting public acceptance towards the rapidly expanding bike-sharing scheme in Gothenburg, Sweden (Styr & Ställ), in an attempt to identify the ‘formula for success’. The respondents generally believed that Styr & Ställ is a pro-environmental, inexpensive and healthy transport mode, which complements the city’s public transport services and promotes a more human-friendly identity for Gothenburg. Even the respondents that self-reported a small (or no) likelihood to use bike sharing were positive towards the scheme. This means that they recognise that bike sharing has a significant pro-social potential and is not a system favouring a particular road-user segment over others that might not be interested or able to use it. The fact that the majority of the respondents do not use the scheme and yet its popularity is still vast indicates that there is much potential for more use in real terms.
Adapting building structures to new uses in the future
Authors: Xuereb Konrad , Parkin Ivan P.
Published: November 2015

This paper discusses the practical need to design building structures to adapt to new uses in the future through the introduction of data-acquiring systems in structural frames. It makes reference to civil engineering projects that incorporate data-acquiring systems and extrapolates the findings to inform strategies on how similar systems can be successfully implemented in buildings. Client-based interviews carried out with stakeholders to challenge this need are referred to. These solicited an appreciation of the main advantages and challenges related to implementing such systems in projects.
Effects of geogrid encasement on lateral and vertical deformations of stone columns in model tests
Authors: Gu M. , Zhao M. , Zhang L. , Han J.
Published: November 2015

Geosynthetic encasement of individual stone columns can provide additional confinement to the columns thus increasing their load capacities and reducing lateral and vertical deformations. Most of past studies have been focused on the load capacities and settlements (i.e. vertical deformations) of the encased stone columns. However, the load transfer mechanism and the lateral bulging deformation pattern of the encased stone columns are not thoroughly understood. In the present study, four series of laboratory model tests in a large-scale testing tank were performed to investigate the effect of geogrid encasement on the lateral and vertical deformations of stone columns installed in a clay bed. For comparison purposes, ordinary stone columns were also tested and evaluated. The main objective of this research is to investigate the lateral and vertical deformation patterns of the encased stone columns and the reinforcement mechanisms of the geogrid encasement with different encasement lengths. In addition, the stress–strain characteristics of the encasement were measured and analysed. The test results show that the ultimate load capacity of the soft soil was greatly increased by the geogrid-encased stone columns. The effective length of the encasement was three to four times of the diameter of stone columns based on the consideration of performance and economy. In comparison with the analytical solution based on the unit cell concept with full encasement of columns, the experimental tests on composite foundations with partially encased columns, which allowed lateral deformations of columns and soils and slippage along the column-soil interfaces (geogrid–soil, stone column–geogrid, and stone column–soil if the column is not encased), resulted in larger settlements, especially at higher vertical pressures.
Change in the permeability of clastic rock during multi-loading triaxial compressive creep tests
Authors: Zhang Y. , Liu Z. B. , Xu W. Y. , Shao J. F.
Published: November 2015

Permeability is a crucial factor for seepage analysis of porous clastic material. This research presents the change in permeability of clastic rock during multi-loading triaxial compressive creep tests. Clastic rock was cored from a critical fault zone of a hydropower station in southwestern China. Based on the physical properties and mineralogical characterisation of the rock material, a series of hydro-mechanical coupling creep tests was designed with three different confining pressures to correlate permeability and material deformation during triaxial compressive creep and reveal the effect of confining pressure on the permeability of the clastic rock. Scanning electron microscopy (SEM) was applied to identify the pore and crack features of the rock material after creep failure and consequently explain the differences in permeability at different confining pressures. The results show that the initial permeability decreased with an increase in confining pressure. During the creep tests, the permeability rapidly decreased during the initial creep and continuously decreased as material deformation increased. Near the accelerating creep, clastic rock permeability began to increase in the low confining pressure creep test but tended to stabilise in the high confining pressure creep test. This finding agrees well with the SEM results of the void features, that is, more connected pores in the sample failed under low confining pressure than under high confining pressure.
Electrical resistivity of sandy soil
Authors: Pandey L. M. S. , Shukla S. K. , Habibi D.
Published: November 2015

This paper presents the results of an investigation into the interaction between the various electrical factors pertaining to resistivity tests in Perth sandy soil (specifically AC input voltage and frequency) and those controlling the soil characteristics, specifically water content and relative density of the soil, and the type of water employed in the tests, whether distilled or tap water. The experimental apparatus was developed as per Australian standard AS 1289.4.4.1-1997 and was used for the electrical resistivity measurements. The test results indicate that the resistivity of the sandy soil is almost independent of both AC input voltage and frequency within the ranges used, while the choice of electrode material has an insignificant effect on the outcome of tests using this method. It was observed that the resistivity of sandy soil decreased rapidly with an increase in water content, but the rate of decrease reduced considerably for water contents over 12% in the case of distilled water and 10% for tap water, irrespective of the relative density. The resistivity was found to decrease almost linearly with an increase in relative density. However, the effect of relative density on the electrical resistivity of the soil was found to be negligible at higher water contents. Correlations between electrical resistivity, water content and relative density, which are applicable to the soil and water used in the study, are also presented.
Assessment of racking deformation of rectangular underground structures by centrifuge tests
Authors: Ulgen D. , Saglam S. , Ozkan M. Y.
Published: November 2015

Seismic safety of buried structures has become increasingly important over the past two decades, especially after the destructive earthquakes such as in Kobe, Japan (1995), Kocaeli, Turkey (1999) and Chi-Chi, Taiwan (1999). Some of the embedded structures including pipelines, subways and tunnels collapsed or suffered severe damage in those earthquakes due to inappropriate design. The main difficulty in seismic design is the incorporation of soil–structure interaction effect governed by the relative stiffness (flexibility ratio) between the soil and the embedded structure. This study aims to clarify the effect of flexibility ratio on the dynamic response of rectangular structures buried in dry sand. For that purpose, a series of dynamic centrifuge tests were conducted on two types of box-shaped models with different rigidities under various harmonic motions. The results reveal that the magnitude of dynamic lateral earth pressure and sidewall deformation is highly dependent on the flexibility ratio of the embedded structure. Based on the flexibility ratios, racking deformations observed in centrifuge tests and racking deformations estimated through analytical approaches were evaluated in a comparative manner.
Mechanical and hydrological impacts of tree removal on a clay fill railway embankment
Authors: Smethurst J. A. , Briggs K. M. , Powrie W. , Ridley A. , Butcher D. J. E.
Published: November 2015

Seasonal shrinkage and swelling of clay fill railway embankments can disturb the track geometry, resulting in train speed restrictions that disrupt normal operations. Such movements are exacerbated by vegetation, but reliable analytical descriptions of the effects of trees on embankment behaviour are not yet established. This paper presents and analyses the results of a field experiment, carried out on a heavily vegetated clay railway embankment to investigate quantitatively the influence of trees. After the first year of monitoring, the mature trees initially present on the upper two-thirds of the embankment slopes were removed. The field monitoring data are used to assess and understand the mechanisms of soil water content and pore water pressure changes before and after tree removal, and their influence on the vertical and lateral displacements of the embankment slopes. Removal of the vegetation stopped seasonal volume changes in the clay fill at the crest of the earthwork, but also resulted in the loss of the deep-seated suctions generally beneficial to embankment stability. The wider implications for the management of vegetation on embankment slopes are discussed.
Assessing the punch-through hazard of a spudcan on sand overlying clay
Authors: Hu P. , Wang D. , Stanier S. A. , Cassidy M. J.
Published: November 2015

A complete analytical method to describe the full load-penetration resistance profile of a mobile jack-up spudcan footing penetrating a sand over clay stratigraphy is described. It is based on both large deformation finite-element analyses and geotechnical centrifuge experiments. The coupled Eulerian–Lagrangian (CEL) approach is used to accommodate the large deformations of a spudcan footing penetrating sand overlying clay. Modified Mohr–Coulomb and Tresca models describe the sand and clay behaviour, with modifications accounting for the effects of strain softening on the response of the soil. The CEL results are shown to match centrifuge tests well, allowing the numerical study to be extended parametrically, and with confidence, to cover the range of layer geometries, sand relative densities and footing shapes that are of practical interest to offshore jack-ups. The results are used to (a) assess the performance of an existing model to predict the peak resistance in the sand layer (extending its range of application to medium dense to dense sands and to conical footings of angle 0° to 21°), and (b) develop an expression for the bearing capacity factor when the footing penetrates into the underlying clay. Using the analytical formulas proposed, retrospective simulations of centrifuge tests show that the method provides a reasonable estimate of the peak punch-through load, the behaviour in the underlying clay, as well as the punch-through distance; the latter being a basic reflection of the severity of a potential punch-through failure.
Full-scale embankment failure test under simulated train loading
Authors: Lehtonen V. J. , Meehan C. L. , Länsivaara T. T. , Mansikkamäki J. N.
Published: November 2015

A full-scale embankment failure experiment was conducted in 2009 in Perniö, Finland. A small, extensively instrumented railway embankment on a soft clay foundation was brought to failure by loading over a period of 30 h. Instrumentation consisted of over 300 different measurement points, including 37 piezometers and nine automatically monitored inclinometer tubes. The relatively rapid loading simulated a heavy train coming to a standstill on the embankment. The primary purpose of the experiment was to gather field data of a failure caused by a rapidly applied load, with an emphasis on the pore pressure response in the clay foundation layer. The test was also used to assess the suitability of various instruments for real-time stability monitoring. The embankment failure was an asymmetric bearing capacity mechanism that is hypothesised to have been triggered by an undrained creep rupture. During the last 2 h of the experiment, pore pressure and displacements increased at an accelerating rate while the external load was kept constant. The time-dependency of the pore pressure and displacement responses was a key factor in the experiment. With regards to monitoring of similar in-service train embankments, proper placement of instruments according to predicted failure mechanisms was found to be important.
Effect of pore fluid osmotic suction on matric and total suctions of compacted clay
Authors: Thyagaraj T. , Salini U.
Published: November 2015

The experimental results of the present study on compacted expansive clay illustrate that matric suction increases with the increase in pore fluid osmotic suction due to changes in soil structure. Scanning electron micrographs show that particle stacking (aggregations) increases with increase in pore fluid osmotic suction and cation valence due to reduction in diffuse double layer thickness, and thus results in a reduction in micro pore size with a corresponding increase in macro pore size. At a given water content, the macro pore degree of saturation reduces with the increase in osmotic suction owing to the increase in macro pore size and leads to an increase in matric suction, as the matric suction is characteristic of the macro pore and the degree of saturation of the macro pore. The matric, osmotic and total suction measurements using the filter paper method also confirm that the matric and osmotic suction components are additive. This demonstrates that the method of obtaining matric suction from the difference between total suction and pore fluid osmotic suction determined using non-contact filter papers is reliable.
A new method for studying the evolution of particle breakage
Authors: Zhang S. , Tong C.-X. , Li X. , Sheng D.
Published: November 2015

This paper proposes a simple method for studying the evolution of particle breakage. A two-parameter statistical model is first proposed to describe the distribution of new particles generated from breakage of an initially uniformly graded sample. A Markov chain model is then proposed to describe the particle size evolution of non-uniformly graded samples. The two-parameter statistical model is shown to be able to capture different breakage patterns such as asperity breakage and particle splitting observed during breakage of uniformly graded samples. In the Markov chain model, it is shown that the concept of ‘effective breakage probability’, proposed to define the relative breakage extent of the whole sample, is comparable to a well-established breakage index in the literature. Both models are successfully validated against experimental data, where the characteristics of the model parameters and the engineering implications are discussed.
Another look at the stability of slopes with linearly increasing undrained strength
Authors: Griffiths D. V. , Yu X.
Published: November 2015

The paper presents a new look at the stability of slopes with linearly increasing undrained strength with depth. Particular emphasis in the current work is focused on the influence of a firm stratum on the factor of safety and the location of the critical failure surface. Solutions have been obtained by the application of standard optimisation software with some independent finite-element checks. Results are presented in the form of improved charts that give the stability number, and hence the factor of safety, as a function of the depth ratio, strength gradient and slope angle. It is shown that when the strength at the crest is greater than zero, previously published results can greatly underestimate the factor of safety, as the depth to a firm stratum is reduced.
Numerical modelling of transient cyclic vertical loading of suction caissons in sand
Authors: Cerfontaine B. , Collin F. , Charlier R.
Published: November 2015

This paper presents numerical investigations of the monotonic and cyclic behaviours of suction caissons upon vertical transient loading. Both drained and partially drained conditions are investigated. Monotonic compression and traction simulations are carried out to qualitatively compare results with the literature and validate the model. They highlight the different modes of reaction of the caisson to both compression and traction loading. A sensitivity analysis points out the strong influence of some parameters on the resistance of the caisson but also on the failure mechanism. The transient behaviour of the caisson upon different kinds of cyclic load signals is analysed. Results reproduce the settlement and pore water pressure accumulations observed during experiments. The influence of the key design parameters on the settlement accumulation is also assessed. Finally a cyclic diagram is proposed to describe the evolution of the final settlement upon different magnitudes of loading.
Fabric evolution and the related swelling behaviour of a sand/bentonite mixture upon hydro-chemo-mechanical loadings
Authors: Manca D. , Ferrari A. , Laloui L.
Published: November 2015

This experimental study investigates the swelling behaviour of an 80/20 sand/bentonite mixture and the associated fabric evolution under different hydro-chemo-mechanical loadings. Free and confined swelling tests are performed on specimens compacted to different dry densities and wetted with different pore fluids. Controlled suction confined swelling tests are performed to determine the suction–swelling pressure relationship for two different densities. An extensive microstructural characterisation is performed to relate the observed swelling behaviour to the evolution of the different pore networks during wetting. Based on the microstructural analysis, an expression is proposed to determine the relative dry density of the bentonite. This parameter enables comparisons of the data on the swelling of different bentonite-based materials prepared at different mixing ratios. A unique relationship is determined to fit all of the experimental data satisfactorily. The results reveal that the generated swelling pressure depends on the applied matric suction and on the chemical composition of the pore water. At a low dry density, the mixture in contact with aqueous solutions loses most of its swelling capacity. At a higher dry density, the swelling capacity of the mixture is better preserved.
t–z curves for piles from pressuremeter test results
Authors: Abchir Z. , Burlon S. , Frank R. , Habert J. , Legrand S.
Published: November 2015

Pile design is not only based on the assessment of bearing capacity, but can involve settlement calculations when the structures supported by piles need high service requirements. In this context, the load transfer approach with t–z curve models is one of the calculation methods used. The main issue for this method is the choice and implementation of the t–z curve modelling the behaviour of the soil around the pile and accounting for the progressive shaft friction mobilisation. In this paper, three types of t–z curve models from pressuremeter test results are compared: one proposed previously by R. Frank and S. R. Zhao in 1982 and two others presented here. The stiffness of each model is studied and a comparison is performed by considering 90 full-scale static load tests extracted from the IFSTTAR pile database. Measured and calculated values of the pile head displacement are compared for several loading levels considering different soil and pile types. For the three t–z curve models, the ratio of the measured pile head settlement value to the calculated one is analysed and the scatter of each t–z curve model is studied. Some considerations regarding the safety of the pile settlement calculations are proposed.
A case study on the seismic performance of earth dams
Authors: Pelecanos L. , Kontoe S. , Zdravković L.
Published: November 2015

The seismic non-linear behaviour of earth dams is investigated by using a well-documented case study and employing advanced static and dynamic coupled-consolidation finite-element analysis. The static part of the analysis considers the layered construction, reservoir impoundment and consolidation, whereas the dynamic part considers the response of the dam to two earthquakes of different magnitude, duration and frequency content. The results of the analysis are compared with the recorded response of the dam and exhibit a generally good agreement. The effects of the narrow canyon geometry, the reservoir impoundment and the elasto-plastic soil behaviour on the seismic dam behaviour are investigated. Finally the implications of the adopted constitutive modelling assumptions on the predicted response are discussed.
Semi-renewable latex via step-photopolymerization of dithiol and dienic terpenes
Authors: Tarablsi Bassam , Jasinski Florent , Lobry Emeline , Chemtob Abraham , Le Nouen Didier , Criqui Adrien
Published: November 2015

Abundance, low-cost and ene functionality are the key assets of terpenes in view of a large-scale use as renewable monomers in radical polymerization. However, their sterically hindered ene structure has been mostly ineffective in a chain-growth mechanism, leading to sluggish activity. To address this challenge, the alternative of a step-growth diene–dithiol linear photopolymerization is investigated here. Four non-modified dienic terpenes – geranyl acetate, linalool, limonene and geraniol – are reacted with ethylene glycol dithiol in various conditions. In bulk and solution, limited conversions prevent the formation of high-molecular-weight polymers. By contrast, a mini-emulsion containing the two difunctional comonomer yields higher conversions (>98%) in less than 10 min of ultraviolet irradiation, making the formation of polythioether chains possible. The authors assume that a thiol–ene polymerization confined in nanodroplets may drive high conversion thanks to a radical compartmentalization effect. The resultant aqueous polymer dispersions show an average diameter ranging from 100 to 140 nm, low glass transition temperature (less than −30°C), but only moderate molecular weights between 4 and 5 kDa for the fraction soluble in tetrahydrofuran. These promising results pave the way for a novel semi-synthetic and eco-efficient approach to polymer latexes based on natural terpene monomers.
A Bayesian network model to predict accidents on Swiss highways
Authors: Deublein Markus , Schubert Matthias , Adey Bryan T , García de Soto Borja
Published: November 2015

Although in 2014, Switzerland had an average of less than two fatalities per billion vehicle-kilometres, making its roads among the safest in Europe, still more than 17 000 traffic accidents occurred on Swiss communal roads, cantonal roads and national highways. On the highway network of approximately 1800 km alone, there were almost 1700 accidents involving personal injuries. In order to further reduce this number of accidents, it is important that accident risks are assessed as accurately as possible. A state-of-the-art methodology is used to develop a Bayesian probabilistic network model to estimate the number of accidents involving personal injury on the Swiss highway network. The developed model predicts the number of accidents on a given highway segment and can be used to identify segments with a high expected number of accidents. During validation, the number of accidents was correctly predicted on 86% of the segments with a tolerance of 25%. The model can also be used to conduct parametric studies, which help to ensure that the risk reduction interventions are effective and efficient. Road traffic and road infrastructure engineers and managers can use the model during the decision-making processes in the planning, construction and maintenance of road networks.
Early age thermal cracking of mass concrete blocks with Portland cement and ground granulated blast-furnace slag
Authors: Saeed Muneer K. , Rahman Muhammad K. , Baluch Mohammed H.
Published: November 2015

Evolution of heat due to an exothermic reaction between cementitious materials and water plays a significant role in the temperature rise in mass concrete at an early age. The temperature gradient between the core of mass concrete and its surfaces leads to the development of thermal stresses and may cause cracking if these stresses exceed the evolving tensile strength of concrete. This paper presents the results of an experimental and finite-element investigation of heat generation and dissipation in full-scale mass concrete blocks 2 m × 2 m × 2 m in size. A concrete mix with 100% OPC and 70% cement replaced by GGBFS was used in these blocks. The temperature profile across the depth of the block was measured at the centre, side and corner of the block. A semi-adiabatic calorimeter was used to measure the heat of hydration of the two concrete mixes. Finite-element simulation of these blocks captured with good accuracy the measured evolution of temperature in the blocks. Numerical simulation was subsequently used to investigate the influence of the size of the blocks, placement temperature of concrete, ambient temperature, solar radiation and type of formwork on the temperature rise and the associated potential of cracking in the mass concrete blocks.
Seismic retrofit of short RC coupling beams using CFRP composites
Authors: Li Xian , Liu Lu , Lv Heng-Lin , Sha Shi-Yu
Published: November 2015

To improve the deformation and energy dissipation capacities of conventionally reinforced coupling beams with low shear span to beam depth ratios, a new method for seismic retrofitting coupling beams using carbon-fibre-reinforced polymer (CFRP) composites is proposed and studied. Experiments are conducted to test four large-scale coupling beams with identical geometries and reinforcement layouts but with different retrofitting schemes. The effects of the arrangement of CFRP sheets and CFRP anchors on the seismic behaviour in terms of strength, stiffness, ductility, energy dissipation capacity and failure modes are evaluated. The study indicates the proposed retrofitting technique is well suited to improving the seismic behaviour of low-slenderness coupling beams in moderate seismic zones. The use of CFRP U-wraps can significantly improve the deformation and cumulative energy dissipation capacities of coupling beams while the beam stiffness can remain nearly constant. By using diagonal CFRP sheets, the strength, stiffness and energy dissipation capacity of coupling beams can be increased. The delamination of CFRP U-wraps can be delayed by using CFRP anchors, but sufficient insertion depth of the anchors is required to avoid their pull-out failure.
Progressive collapse of RC frame structures after a centre column loss
Authors: Hou Jian , Song Li , Liu Huanhuan
Published: November 2015

The progressive collapse of a reinforced concrete (RC) frame structure due to the loss of a centre column was investigated in a static experimental study. A two-span, two-bay, single-storey one-third scale model representing a segment of a larger space frame structure was tested. Downward displacement of the top of the removed centre column was imposed until failure, and frame collapse was defined as the rupture of tension steel bars in the floor beams. The study provides insight into the behaviour and failure modes of the structure under centre column loss, including the development of catenary action in the frame beams and tensile membrane action in the frame slabs. The experimental observations and theoretical analysis were used to establish a simplified calculation model of the resistance capacity of RC frame structures against progressive collapse due to the loss of a centre column. The reliability of the proposed model was verified using experimental results.
Bond behaviour between corroded steel bars and concrete under different strain rates
Authors: Zhang Wei-Ping , Chen Hui , Gu Xiang-Lin
Published: November 2015

The impressed current method was used to produce 42 corroded reinforced concrete specimens. Pull-out tests were conducted to study the effects of strain rate, corrosion degree, concrete cover and stirrups on the bond behaviour between corroded rebars and concrete. The results showed that the lag effect of radial cracking in concrete will occur with increasing strain rate. The failure modes of the specimens changed from splitting of the concrete cover to pull-out failure of rebars, and the bond strength of the splitting specimens increased significantly as the rebars were loaded at a higher rate. The bond strength of corroded specimens decreased with the development of reinforcement corrosion under both static and dynamic loading. Coupling effects of corrosion degree and strain rate on bond strength were found. The degradation trend caused by corrosion decreased with increasing strain rate, and the effect of strain rate on the ultimate bond strength also decreased with an increasing degree of corrosion. In addition, specimens with smaller diameter rebars, a thicker concrete cover and stronger stirrups exhibited higher bond strength. Considering the effects of strain rate and corrosion, a model is proposed to predict the bond behaviour between corroded rebars and concrete under different strain rates.
Performance of in situ stitches in precast segmental bridges
Authors: Leung Cliff Chun Yu , Au Francis Tat Kwong
Published: November 2015

In situ concrete stitching with subsequent prestressing is often used in construction to join together precast concrete segments. An example of an application is the stitching of the approaching decks of precast segmental bridges constructed using the balanced cantilever method. The relatively narrow stitches used in segmental bridges are often provided with nominal reinforcement only. Therefore, the in situ stitch is a location of potential weakness, but relatively little work has been done in this area. In light of this, extensive experimental and numerical studies on the behaviour of precast concrete members with in situ concrete stitches have been conducted. The effects of stitch width, prestressing force, concrete strength, bonding of tendon and provision of shear keys on the performance of such members are presented in this paper. Unlike members that are continuously cast, cracking initiates along the construction joint between the precast segment and the stitch at low load levels for members with in situ stitches, while no cracking is observed elsewhere. The cracks widen extensively as the load level increases and can become detrimental to the serviceability of the members. Such members should be designed so that the joints are subject to no tension under service load.
Component model for shear transfer in reinforced concrete
Authors: Lin Feng , Lu Haixia , Dong Yu
Published: November 2015

A component model was developed from tests on 24 specimens with the purpose of understanding the shear resistance mechanism and predicting the ultimate shear transfer capacities of reinforced concrete (RC) with any length of crack. Targeted specimens were designed and tested, and analytical studies were performed. The results revealed that the shear resistance mechanism is primarily the development of shear components in a whole shear transfer process of initially uncracked RC after microcracking. Certain components weaken or vanish in completely or partly precracked RC. Expressions based on the component model were proposed to predict the ultimate shear transfer capacities of RC. Satisfactory agreement was achieved between the calculated results and the test data in this study and in the literature.
Improved flame-retardant properties of HIPS/ATH system by organo Fe-montmorillonite
Authors: Zhang Xingguang , Li Yanjun , Yan Shuai , Kong Qinghong , Zhang Junhao
Published: November 2015

High-impact polystyrene nanocomposites (HIPS) with aluminium trihydroxide (ATH) and organo-modified Fe-montmorillonite (Fe-OMT) were prepared by melting intercalation. The nanocomposite structures were characterized by X-ray diffraction and transmission electron microscopy. The results show that the intercalated and exfoliated nanocomposites were formed. Accordingly, the thermal stability and flame-retardant properties were evaluated by thermogravimetric analysis, limiting oxygen index, UL94 and the cone calorimeter test. The results indicated that the nanocomposites had excellent thermal stability and the char yield was also improved. When 4 wt% organo-modified Fe-MMT was added in the HIPS/ATH (46 wt%) composites, the nanocomposites were able to achieve UL94 V-0 grade. The heat release rate, total heat release, and mass loss rate of the nanocomposites were reduced. Furthermore, the addition of Fe-OMT could further improve the smoke suppression property of HIPS composites. The improved flame-retardancy caused by Fe-OMT in the HIPS/ATH matrix maybe due to a reinforced char layer which prevents the diffusion of the oxygen and decomposed organic volatiles in the flame during combustion.