Titel Deelnemers "Korte inhoud" "Finite element analysis of the effect of cementing concepts on implant stability and cement fatigue failure" "Dennis Janssen, Jantien Van Aken, Thierry Scheerlinck, Nico Verdonschot" "Background and purpose Two contradictory cementing techniques (using an undersized stem versus a canal-filling stem) can both lead to excellent survival rates, a phenomenon known as the ""French paradox"". Furthermore, previous studies have indicated that the type of bone supporting the cement mantle may affect implant survival. To further evaluate the mechanical consequences of variations in cementing technique, we studied the effect of implant size and type of bone supporting the cement mantle on the mechanical performance of cemented total hip arthroplasty, using finite element analysis. Methods In a generic 2-dimensional plane-strain finite element model of a transverse section of a cemented total hip arthroplasty with a Charnley-Kerboull stem, we varied implant size and type of bone supporting the cement mantle. The models were subjected to 2 × 106 cycles of an alternating loading pattern of torque and a transverse load. During this loading history, we simulated cement fatigue crack formation and tracked rotational stability of the implant. Results Canal-filling stems produced fewer cement cracks and less rotation than undersized stems. Cement mantles surrounded by trabecular bone produced more cement cracks and implant rotation than cement mantles surrounded by cortical bone. Interpretation Our investigation provides a possible explanation for the good clinical results obtained with canal-filling Charnley-Kerboull implants. Our findings also indicate that inferior mechanical properties are obtained with these implants if the cement is supported by trabecular bone, which may be minimized by an optimal cementing technique." "LAYERED FINITE ELEMENT (FE) MODELLING OF CEMENT COMPOSITES COMBINING CONTINUOUS TEXTILES AND SYNTHETIC MICROFIBRES: A FLEXURAL ANALYSIS" "Michael El Kadi, Ciska Gielis, Danny Van Hemelrijck, Didier Snoeck, Tine Tysmans" "This research presents a layered, semi-smeared modelling approach for the prediction of the flexural response of Textile Reinforced Cement (TRC) beams with combined continuous textiles (0.7v%) and short microfibres (1%). The constitutive behaviour of the composites was obtained from tensile experiments on TRC configurations and subsequently implemented in two different smearing approaches. The first approach concentrated the cross-sectional resistance in the load-bearing textile layers, whereas the second distributed the contribution of the short microfibres over the entire thickness. A satisfactory agreement was obtained between the experimental results and both numerical approaches, however, the distributed approach slightly underestimated the flexural response of the material." "Finite element analysis of glass fibre reinforced composites with inorganic phosphate cement matrix: comparison of inbuilt abaqus concrete models." "Maciej Wozniak, Johnny Vantomme" "Cement composites are promising particularly for the construction industry as they overcome crucial drawbacks of more commonly used polymer matrix composite materials. Contrarily to traditional organic resins (epoxy), the Inorganic Phosphate Cement (IPC), developed at Vrije Universiteit Brussel, is incombustible. The IPC matrix moreover has a neutral pH after hardening, such that it is not chemically aggressive for E-glass fibres, which are cheap in production. Finally, the fine grained IPC can impregnate very dense chopped strand mats, as a result of which fibre volume fractions of more than 20% can be obtained instead of the 5% that is commonly achieved with textile reinforced concrete.The main objective of this paper is to compare the inbuilt models for concrete offered by the commercial FEM software Abaqus for their adequacy in modelling the cement composite material. The main difficulty with the modelling of the GFR-IPC is the nonlinearity of the tensile behaviour after cracking of the matrix. Models taken into consideration are Concrete Damaged Plasticity and Concrete Smeared Cracking. Both models have high potential of modelling the cement composite when assuming homogeneity of the material, which is valid due to the high fibre volume fraction(>20%), and the homogenous distribution and random orientation of the fibres using chopped strand mats. Both numerical models were based on the uniaxial tensile laboratory tests performed on GFR-IPC with a fibre volume fraction of 23%. Models were verified by biaxial tension-tension tests on both a square plate and a cruciform specimen. Comparison of numerical and experimental results yields conclusions on the validity of both concrete models for the modelling of cement composites." "Finite element modelling of the biaxial behaviour of high-performance fibre-reinforced cement composites (HPFRCC) using Concrete Damaged Plasticity" "Maciej Wozniak, Olivier Remy, Johnny Vantomme" "High-performance fibre-reinforced cement or concrete composites (HPFRCC) are increasingly used in structural applications exposed not only to uniaxial but also complex stress states. Current finite element models for these materials have however been only validated for uniaxial stress states, and mostly restricted to cement composites with relatively limited strain hardening capacity in tension. To facilitate the numerical analysis and design of more complex structures, this paper adapts and validates the Concrete Damaged Plasticity (CDP) model for both uni- and biaxial stress states, and for cement composites with a large strain hardening capacity (ratio of failure stress to linear stress limit more than 8). The validation of the numerical model is done by performing laboratory biaxial tension–tension tests under various load cases. For the latter, an adapted cruciform specimen was designed. The strain distribution in the specimen as well as its evolution with increasing load correspond well. As the results show, the adapted CDP model can simulate the nonlinear strain hardening behaviour in tension – different from the linear behaviour in compression – of high-performance cement composites for both uniaxial as well as biaxial stress states. Moreover, failure can be simulated. &" "Flash-calcined dredging sediment blended cements: effect on cement hydration and properties" "Ruben Snellings, Céline Van Bunderen, Lucie Vandewalle, Özlem Cizer" "Dredging of docks and waterways generates a large and continuous supply of sediments currently destined for disposal. Transforming this currently wasted materials into new resources still requires meeting technical challenges. One of the options is to process the sediments into a supplementary cementitious material by flash-calcination. This paper describes the effect of cement replacement by flash-calcined dredged sediments on cement hydration and key properties. The hydration kinetics, products and microstructure are studied to explain changes in cement properties such as compressive strength development and workability. The flash-calcined dredging sediments show clear pozzolanic activity which surpasses that of typical coal combustion siliceous fly ash (V, EN 197-1). This is manifested in (1) the rate of compressive strength development, (2) reduced portlandite and (3) increased ettringite and bound water contents. The results show that calcination can transform wasted dredging sediments into a new supplementary cementitious resource for producing large volumes of low-CO2 blended cements." "Mechanical implications of interfacial defects between femoral hip implants and cement: a finite element analysis of interfacial gaps and interfacial porosity" "Thierry Scheerlinck, Jeroen Broos, Dennis Janssen, Nico Verdonschot" "Two types of defect between femoral hip implants and cement have been identified. Interfacial porosity arises from cement shrinkage during curing and presents as pores randomly located along the stem. Interfacial gaps are much larger stem-cement separations caused by air introduced during stem insertion. To investigate the mechanical consequences of both types of defect, a finite element analysis model was created on the basis of a computed tomography image of a Charnley-Kerboul stem, and alternating torsional and transverse loads were applied. The propagation of fatigue cracks within the cement and the rotational stability of the stem were assessed in models simulating increasing amounts of interfacial gaps and pores. Anterior gaps covering at least 30 per cent of the implant surface promoted cement cracks and destabilized the stem. Anterolateral gaps were less destabilizing, but had more potential to promote cracks. In both cases, cracks occurred mainly outside gap regions, in areas where the stem contacted the cement during cyclic loading. Although random interfacial pores did not destabilize the implant, they acted as crack initiators even at low fractions (10 per cent). In conclusion, random interfacial pores were more harmful for the cement mantle integrity than were larger regions of interfacial gaps, although gaps were more detrimental for the rotational stability of the stem." "Comment on Taylor SJ, Allan K, Clemente R. Undetected Cortrak tube misplacements in the United Kingdom 2010-17: an audit of trace interpretation. Intensive Crit Care Nurs. 2019 Dec;55:102766" "Tim Torsy, Mats Eriksson, Dimitri Beeckman" "Cemented short-stem total hip arthroplasty: Characteristics of line-to-line versus undersized cementing techniques using a validated CT-based finite element analysis" "Fahimeh Azari, Amelie Sas, Harry van Lenthe" "Short stems are becoming increasingly popular in total hip arthroplasty as they preserve the bone stock and simplify the implantation process. Short stems are advised mainly for patients with good bone stock. The clinical use of short stems could be enlarged to patients with poor bone stock if a cemented alternative would be available. Therefore, this study aimed to quantify the mechanical performance of a cemented short stem and to compare the ""undersized"" cementing strategy (stem one size smaller than the rasp) with the ""line-to-line"" technique (stem and rasp with identical size). A prototype cemented short stem was implanted in eight pairs of human cadaveric femora using the two cementing strategies. Four pairs were experimentally tested in a single-legged stance condition; stiffness, strength, and bone surface displacements were measured. Subject-specific nonlinear finite element models of all the implanted femora were developed, validated against the experimental data, and used to evaluate the behavior of cemented short stems under physiological loading conditions resembling level walking. The two cementing techniques resulted in nonsignificant differences in stiffness and strength. Strength and stiffness as calculated from finite element were 8.7 ± 16% and 9.9 ± 15.0% higher than experimentally measured. Displacements as calculated from finite element analyses corresponded strongly (R 2  ≥ .97) with those measured by digital image correlation. Stresses during level walking were far below the fatigue limit for bone and bone cement. The present study suggests that cemented short stems are a promising solution in osteoporotic bone, and that the line-to-line and undersized cementing techniques provide similar outcomes." "Hydration degree of cement and slag in slag blended cement pastes" "Elke Gruyaert, Nele De Belie" "As hydration of pure cement pastes proceeds, unhydrated cement particles hydrolyse, hydration products are formed and the degree of hydration continuously increases. Moreover, the ultimate hydration degree mainly depends on the water/cement ratio and can be estimated by the formula of Mills. However, the situation becomes more complicated when the cement is partly replaced by blast-furnace slag since the hydration reactions of both components are influenced by each other. Furthermore, the hydration degree of slag in paste is difficult to predict and depends on the curing conditions, water/cement ratio, test age, cement/slag ratio and the slag reactivity. In this research, the extent to which slag particles are hydrolysed and take part in the hydration proces was visualized by backscattered electron (BSE) microscopy at 2, 7, 14, 74 days and 28 months. Besides, thermogravimetric analyses were performed to determine the bound water content, Ca(OH)2 and CaCO3 content : the differences between pastes wit hand without slag gave an indication about the extent to which slag hydration products are formed. The test results indicated that the cement hydration is enhanced in the presence of blast-furnace slag. The ultimate cement hydration degree of 74 %, which has been reached after about 2 years is pure cement pastes with a water/cement ratio of 0.5, increased above 90 % for slag blended pastes. The hydration of the slag itself strongly depended on the cement/slag ratio. For replacement levels of 50 % and 85 %, the hydration degree after about 2 years amounted to 70 %, respectively 39 %." "Combination of Portland cement and calcium-sulfoAluminate cement : the highroad for durable 3D printing ?" "Jolien Van Der Putten, Mahzad Azima, Karel Lesage, Geert De Schutter, Kim Van Tittelboom" "3D printing of cementitious materials opens new horizons for the construction industry. This newly developed technique uses a layer-by-layer fabrication process, inducing a higher porosity at the interface between the printed filaments. Consequently, this interface zone offers an ideal ingress path for chemical substances and affects the durability in a negative way. This in combination with a high content of ordinary Portland cement (OPC) in the composition of printable mixtures counteracts the many advantages of the construction type and decreases the eco-friendliness of the material drastically. To improve the ""green"" character of 3D printed cementitious materials, combinations of OPC and Calcium-Sulfoaluminate (CSA) cement are often made. This combination shows advancements regarding the evolution of cement hydration, but the expansive character of CSA cement also leads to the formation of additional voids which will affect the microstructure in a significant way. For the purpose of this research, 4 different mix compositions with OPC replacements up to 20% have been prepared and their effect in fresh state is investigated through measurements and isothermal calorimetry (TAM AIR). Scanning Electron Microscopy (SEM) analysis was performed on two layered printed specimens to examine the effect on the microstructure in hardened state and correlate the results with the mechanical performance, measured by compressive test and inter-layer bonding tests. These results showed that the setting time is lower for every combination of OPC and CSA, creating mixtures with a higher buildability. Due to the low amount of anhydrite, the expansive character of CSA is most pronounced in case of 10% and 15% OPC replacement, resulting in a higher amount of capillary pores and affecting the mechanical performance in the most negative way."