Conference papers by Julien Ston
IABSE Symposium 'Construction’s Role for a World in Emergency', 2024
The use of lightweight concrete could overcome some of the disadvantages of normal-weight concret... more The use of lightweight concrete could overcome some of the disadvantages of normal-weight concrete. However, the fabrication of lightweight aggregates is energy intensive and considerably draws on non-renewable resources. The positive consequences from lighter weight on supporting structural components' dimensions are frequently outrun by the increase in carbon footprint of up to 65% stemming from the lightweight aggregates. On this background, fabrication of lightweight aggregates in a low-energy cold-bonding pelletizing process, using bio-based waste and byproducts, and alternative binders in combination with or instead of cement was explored. Presented results cover reflections for recipe mix design, observations made in the pelletizing and hardening process, results obtained for density, strength, thermal properties, and carbon footprint of this alternative way to produce lightweight aggregates for concrete.
Papers by Julien Ston
Report, 2024
The use of lightweight concrete could overcome some of the disadvantages of normal-weight concret... more The use of lightweight concrete could overcome some of the disadvantages of normal-weight concrete. However, the fabrication of lightweight aggregates is energy intensive and considerably draws on non-renewable resources. The positive consequences from lighter weight on supporting structural components' dimensions are frequently outrun by the increase in carbon footprint of up to 65% stemming from the lightweight aggregates. On this background, fabrication of lightweight aggregates in a low-energy cold-bonding pelletizing process, using bio-based waste and byproducts, and alternative binders in combination with or instead of cement was explored. Presented results cover reflections for recipe mix design, observations made in the pelletizing and hardening process, results obtained for density, strength, thermal properties, and carbon footprint of this alternative way to produce lightweight aggregates for concrete.
Sustainable Construction Materials and Technologies (SCMT), 2019
Limestone Calcined Clay Cements (LC 3) permit to continue decreasing the clinker factor in cement... more Limestone Calcined Clay Cements (LC 3) permit to continue decreasing the clinker factor in cement. Two widely-available Supplementary Cementitious Materials (SCMs) are used in LC 3 : calcined kaolinitic clays and limestone. The combination of these two SCMs allows additional reactions compared with conventional cements, leading to a high space-filling and excellent properties. Clays with only 40% of kaolinite can be used in LC 3 , providing sufficient strength, higher resistance to chloride ingress and alkali-silica reaction.
Hypothesis: During total shoulder arthroplasty (TSA), humeral head subluxation may be difficult t... more Hypothesis: During total shoulder arthroplasty (TSA), humeral head subluxation may be difficult to manage. Furthermore, there is a risk for postoperative recurrence of subluxation, affecting the outcome of TSA. An accurate evaluation of the subluxation is necessary to evaluate this risk. Currently, subluxation is measured in 2 dimensions (2D), usually relative to the glenoid face. The goal of this study was to extend this measure to 3 dimensions (3D) to compare glenohumeral and scapulohumeral subluxation and to evaluate the association of subluxation with the glenoid version. Materials and methods: The study analyzed 112 computed tomography scans of osteoarthritic shoulders. We extended the usual 2D definition of glenohumeral subluxation, scapulohumeral subluxation, and glenoid version by measuring their orientation in 3D relative to the scapular plane and the scapular axis. We evaluated statistical associations between subluxation and version in 2D and 3D. Results: Orientation of subluxation and version covered all sectors of the glenoid surface. Scapulohumeral subluxation and glenoid version were highly correlated in amplitude (R 2 ¼ 0.71; P < .01) and in orientation (R 2 ¼ 0.86; P < .01). Approximately every degree of glenoid version induced 1% of scapulohumeral subluxation in the same orientation of the version. Conversely, glenohumeral subluxation was not correlated to glenoid version in 2D or in 3D. Conclusions: Orientation of the humeral subluxation is rarely within the arbitrary computed tomography plane and should therefore be measured in 3D to detect out-of-plane subluxation. Scapulohumeral subluxation and glenoid version measured in 3D could bring valuable information for decision making during TSA.
Osteoporosis International, 2015
This study investigates the creep properties of limestone calcined clay cement. A series of paste... more This study investigates the creep properties of limestone calcined clay cement. A series of paste samples using limestone and calcined clays as replacement materials were tested under basic compressive creep. The ternary mixes showed lower creep compliance than the plain cement references, even when using low reactivity clays or lower replacement fraction. A finite element model was used to back-calculate the visco-elastic properties of the C-S-H matrix and C-S-H gel. Whereas the elastic properties of C-S-H were found to be similar between LC3 and plain cement, the viscous behaviour of C-S-H gel appeared to be noticeably different for LC3.
Theoretical and Applied Fracture Mechanics, 2019
This article presents a study on the creep properties of limestone calcined clay cement. A series... more This article presents a study on the creep properties of limestone calcined clay cement. A series of paste samples using limestone and calcined clays as replacement materials were tested under basic compressive creep. The ternary mixes showed a lower creep compliance than the plain cement references, even when using low reactivity clays or lower replacement fraction. A finite element model was used to back calculate the visco-elastic properties of the C-S-H matrix and C-S-H gel. Whereas the elastic properties of C-S-H were found to be similar between LC3 and plain cement, the viscous behavior of C-S-H gel appeared to be noticeably different for LC3. The higher viscosity of C-S-H gel in LC3 could be attributed to a different chemical composition, a filler effect from the clayey particles or a combination of both.
Cement and Concrete Research, 2019
This paper investigates the fundamental mechanisms behind the effect of supplementary cementitiou... more This paper investigates the fundamental mechanisms behind the effect of supplementary cementitious materials (SCM) on the basic creep behavior of cement pastes. The intrinsic creep properties of the C-S-H gel are assessed based on measurements of uniaxial compressive basic creep of cement pastes with different water-to-cement ratio (w/c), prepared either with pure cement or cement blended with fly ash or quartz. The viscoelastic response of the C-S-H was back-calculated from the macroscopic experimental creep results with Finite Element Method (FEM) homogenization. The numerical simulations show that the intrinsic viscoelastic behavior of the C-S-H gel follows a similar trend in different systems, independent of their w/c (in the range 0.35-0.63) and the binder used. The differences in the magnitude of the creep at the macroscopic scale in different cement-based systems appear to depend mainly on the volumetric fractions of the solid phases and on the porosity of the cement pastes.
Green Materials, 2018
This paper details the main factors influencing the performance of limestone calcined clay cement... more This paper details the main factors influencing the performance of limestone calcined clay cements (LC3). The kaolinite content plays a major role in the rheological properties as well as strength development. Even in the presence of secondary phases, kaolinite can be accurately quantified by thermogravimetric analysis. The performance of LC3 is slightly influenced by the calcination process of clay, but it can be optimized by using the correct calcination temperature and applying a specific mix design with adjusted sulfate and alkali content. The hydration reactions of LC3 are fully characterized. They vary slightly from plain cement. There is no significant change in terms of phase assemblage. The main properties of LC3 are also described. LC3 blends show a lower creep compliance and a delay in shrinkage strains compared with plain cement. Concerning durability, LC3 blends show outstanding performance with respect to resisting chloride ingress and expansion from the alkali–silica ...
RILEM Bookseries, 2017
This study explored the delayed strains in limestone and calcined clay ternary blends. Autogenous... more This study explored the delayed strains in limestone and calcined clay ternary blends. Autogenous shrinkage measurements are carried out over 2 months and compressive basic creep tests during 28 days after one month of curing. All tests are done using mixed with calcined clay at different metakaolin amounts or with variable mix designs. Results show that the presence of any type of clay, except pure metakaolin, has a similar impact on both autogenous shrinkage and basic creep. However, mix design seems to have an important contribution. Shrinkage rate is higher for blends than PC at 28 days, although reaching a similar amplitude at this age for most mixes. Creep amplitude and rate are reduced when using the blended systems.
Revue de Chirurgie Orthopédique et Traumatologique, 2017
Mots clés : Muscles de la coiffe des rotateurs Atrophie Infiltration graisseuse Dégénérescence Im... more Mots clés : Muscles de la coiffe des rotateurs Atrophie Infiltration graisseuse Dégénérescence Image quantitative Arthrose de l'épaule r é s u m é Contexte.-La dégénérescence des muscles de la coiffe des rotateurs est un paramètre important dont il faut tenir compte lors de la planification d'une arthroplastie de l'épaule. Hypothèse.-Nous avons émis l'hypothèse que la dégénérescence des muscles de la coiffe des rotateurs est corrélée avec une subluxation scapulo-humérale chez les patients pour qui une arthroplastie totale de l'épaule (ATE) anatomique est planifiée. Matériel et méthodes.-Nous avons développé une méthode tomodensitométrique (TDM) quantitative semi-automatisée visant à mesurer la dégénérescence des muscles de la coiffe des rotateurs, puis de manière rétrospective, nous avons analysé 107 TDM d'épaule préopératoires provenant de patients atteints d'arthrose primaire. Sur une coupe TDM sagittale oblique normalisée et perpendiculaire à l'axe scapulaire, deux observateurs ont mesuré les surfaces de section transversales des tissus musculaires résiduels de la coiffe des rotateurs, normalisées en fonction de la surface estimée de muscles sains. La dégénérescence musculaire a été quantifiée de manière semi-automatisée, puis répartie en atrophie et en infiltration graisseuse. La subluxation scapulo-humérale a été déterminée en 3D comme étant la distance entre le centre de la tête humérale et le centre de la surface glénoïdienne, projetée sur la même coupe TDM, et normalisée en fonction du rayon de la tête humérale. Nous avons testé l'ensemble des corrélations potentielles entre la dégénérescence musculaire et la subluxation scapulo-humérale. Résultats.-La dégénérescence musculaire, principalement due à l'atrophie, prédominait dans le muscle sus-épineux ; elle variait de 0,8 à 88,8 %. La subluxation scapulo-humérale variait de 2,5 à 72,9 %, et son orientation était principalement postérieure et postéro-supérieure. Il y avait une corrélation significative, mais faible, entre l'étendue de la subluxation et la dégénérescence des muscles sus-épineux (R = 0,207, p = 0,032) et sous-épineux (R = 0,225, p = 0,020). Les reproductibilités inter-et intra-observateurs des mesures de la dégénérescence musculaire étaient toutes deux excellentes (intervalle du CCI = 0,955-0,987 et 0,971-0,988, respectivement). Conclusion.-Cette nouvelle méthode TDM semi-automatisée permet de mesurer de manière quantitative et reproductible la dégénérescence des muscles de la coiffe des rotateurs dans les épaules affectées par de l'arthrose primaire. La dégénérescence musculaire est faiblement corrélée avec une subluxation scapulo-humérale chez les patients pour qui une ATE anatomique est planifiée. Niveau de preuve.-Niveau IV. Type d'étude.-Étude diagnostique rétrospective.
International Orthopaedics, 2015
Purpose The impacts of humeral offset and stem design after reverse shoulder arthroplasty (RSA) h... more Purpose The impacts of humeral offset and stem design after reverse shoulder arthroplasty (RSA) have not been well-studied, particularly with regard to newer stems which have a lower humeral inclination. The purpose of this study was to analyze the effect of different humeral stem designs on range of motion and humeral position following RSA. Methods Using a three-dimensional computer model of RSA, a traditional inlay Grammont stem was compared to a short curved onlay stem with different inclinations (155°, 145°, 135°) and offset (lateralised vs medialised). Humeral offset, the acromiohumeral distance (AHD), and range of motion were evaluated for each configuration. Results Altering stem design led to a nearly 7-mm change in humeral offset and 4 mm in the AHD. Different inclinations of the onlay stems had little influence on humeral offset and larger influence on decreasing the AHD. There was a 10°decrease in abduction and a 5°increase in adduction between an inlay Grammont design and an onlay design with the same inclination. Compared to the 155°model, the 135°model improved adduction by 28°, extension by 24°and external rotation of the elbow at the side by 15°, but led to a decrease in abduction of 9°. When the tray was placed medially, on the 145°model, a 9°loss of abduction was observed. Conclusions With varus inclination prostheses (135°and 145°), elevation remains unchanged, abduction slightly decreases, but a dramatic improvement in adduction, extension and external rotation with the elbow at the side are observed.
RILEM Bookseries, 2015
Reducing the clinker factor is a target with increasing priority in cement industry, as a solutio... more Reducing the clinker factor is a target with increasing priority in cement industry, as a solution to lower greenhouse gases emissions and increasing cement production. Replacing a fraction of the clinker from the kiln with supplementary cementitious materials (SCMs) has proven efficient for many decades. Calcined clays are good candidates for SCMs, as the raw material can be found in many parts of the world, especially developing countries. Limestone and calcined clay ternary cements show a great potential as building material and mechanical properties close to OPC. On the other hand, little is known about the shrinkage behavior of such systems. Assessing this phenomenon is of prime importance for the elaboration of blends bound to be used for building purposes, as those mixes are controlled by strict standards in each country. Therefore, the mechanisms causing autogenous strain in such systems need to be understood. Ternary blends, such as Portland cement with blast furnace slag and limestone, tend to have a different strength development than OPC, therefore modifying their response to internal stresses caused by self-dessication, among other phenomena. However, no precise study on shrinkage behavior of limestone and calcined clay systems has been reported yet. Autogenous shrinkage measurements were done according to the actual standards and compared to OPC. In addition, clays with different grades of kaolinite were tested. Kaolinite is transformed into reactive metakaolin by the calcination process. Therefore, the impact of impurities or other phases, in particular expanding clays such as smectite, is studied.
Biomaterials, 2014
Bisphosphonates are known for their strong inhibitory effect on bone resorption. Their influence ... more Bisphosphonates are known for their strong inhibitory effect on bone resorption. Their influence on bone formation however is less clear. In this study we investigated the spatio-temporal effect of locally delivered Zoledronate on peri-implant bone formation and resorption in an ovariectomized rat femoral model. A cross-linked hyaluronic acid hydrogel was loaded with the drug and applied bilaterally in predrilled holes before inserting polymer screws. Static and dynamic bone parameters were analyzed based on in vivo microCT scans performed first weekly and then biweekly. The results showed that the locally released Zoledronate boosted bone formation rate up to 100% during the first 17 days after implantation and reduced the bone resorption rate up to 1000% later on. This shift in bone remodeling resulted in an increase in bone volume fraction (BV/TV) by 300% close to the screw and 100% further away. The double effect on bone formation and resorption indicates a great potential of Zoledronateloaded hydrogel for enhancement of peri-implant bone volume which is directly linked to improved implant fixation.
Computer Methods in Biomechanics and Biomedical Engineering, 2012
The use of supplementary cementitious materials (SCM) to lower the clinker factor of cements is n... more The use of supplementary cementitious materials (SCM) to lower the clinker factor of cements is now commonplace, for it benefits performance, economics and ecology. This thesis focuses on ternary blends of limestone and calcined kaolinitic clays, two very promising SCM thanks to their worldwide availability. In particular, this research aims to get an insight on the delayed strains in sealed condition of such binders, christened LC3 for Limestone Calcined Clay Cement. Delayed strains refer to time-dependent deformations undergone by the material during its lifetime, such as shrinkage and creep. This work evaluates the impact of the calcined kaolinite content of the clay — which can vary in accordance with the origin of the clay — on the autogenous shrinkage and basic creep properties of LC3. Compressive creep tests on mature paste samples indicated that the presence of limestone and calcined clay dramatically reduced creep compliance. This reduction is significant even with lower gr...
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Conference papers by Julien Ston
Papers by Julien Ston