Basic creep and autogenous shrinkage of Limestone Calcined Clay Cement (LC3)

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 grade clays and does not depend on the clay purity if it has at least 40% of calcined kaolinite. A two-dimensional finite elements model was used to simulate the creep response of the tested microstructures in order to try to determine whether the compliance reduction originated from a different phase assemblage or a higher viscosity of the C-S-H. The outputs pointed towards a different rheology of C-S-H gel. Autogenous shrinkage measurements on LC3 binders showed that these ternary blends had a lower or comparable shrinkage to plain cement reference during the two first months of hydration. Shrinkage rate and amplitude was found to be close for LC3 mixes usingmedium to high grade clays of natural origin. A study of the evolution of microstructure with shrinkage demonstrated that if the calcined clay contained enoughmetakaolin to consume most of the available portlandite, the porosity and desaturation of the microstructure were very similar regardless of the clay. As these features play a large role on the origin of shrinkage force, the macroscopic response is comparable among these specific mixes

A semi-automated quantitative CT method for measuring rotator cuff muscle degeneration in shoulders with primary osteoarthritis

Background: Rotator cuff muscle degeneration is an important parameter to consider when planning shoulder arthroplasty. Hypothesis: We hypothesized that rotator cuff muscle degeneration is correlated with scapulohumeral subluxation in patients planned for anatomical total shoulder arthroplasty (TSA). Materials and methods: We developed a semi-automated quantitative CT method to measure rotator cuff muscle degeneration, and retrospectively analyzed 107 preoperative shoulder CT scans of patients with primary osteoarthritis. On a standardized sagittal-oblique CT slice perpendicular to the scapular axis, two observers measured the cross-sectional areas of residual rotator cuff muscle tissues, normalized by the estimated area of healthy muscles. Muscle degeneration was quantified in a semi-automated manner, and divided into atrophy and fatty infiltration. Scapulohumeral subluxation was determined in 3D as the distance between the humeral head center and the glenoid surface center, projected on the same CT slice, and normalized by the humeral head radius. We tested all potential correlations between muscle degeneration and scapulohumeral subluxation. Results: Muscle degeneration, primarily due to atrophy, predominated in the supraspinatus; it varied from 0.8% to 88.8%. Scapulohumeral subluxation varied from 2.5% to 72.9%, and was mainly in a posterior and postero-superior orientation. There was a significant but weak correlation between the amount of sublux- ation and both supraspinatus (R = 0.207, P = 0.032) and infraspinatus (R = 0.225, P = 0.020) degeneration. Inter- and intra-observer reproducibility of muscle degeneration measurements were both excellent (ICCs range = 0.955–0.987 and 0.971–0.988, respectively). Conclusion: This new semi-automated CT method allows to quantitatively and reproducibly measure rotator cuff muscle degeneration in shoulders with primary osteoarthritis. Muscle degeneration is weakly correlated with scapulohumeral subluxation in patients planned for anatomical TSA

Postoperative scapula fracture after reversed shoulder arthroplasty

Reversed shoulder arthroplasty (RSA) is recommended in case of severe muscle deficiency, along with important joint wear. Although having a correct placement of the prosthesis after the operation and a recovery of the mobility, several cases of scapula fracture are reported, in the region of the scapular spine or the acromion. Complication occurs 3 to 6 months after the surgery and may necessitate a second intervention. Such fractures are likely to be provoked by important stresses in the scapula, due to the poor muscle state, combined with the weakening of the bone induced by the implant. A 3D numerical model of the shoulder, including the prosthesis, was developed with Abaqus CAE to investigate the stresses in the different regions of the joint, when performing certain movement with the arm. The aim of the project is therefore to adapt the model to some known problematic cases, in order to identify the cause of fracture and propose an adapted solution, in function of the initial state of the joint

Basic creep of limestone-calcined clay cements: An experimental and numerical approach

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

Impacting factors and properties of limestone calcined clay cements (LC3)

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 reaction

Effect of humeral stem design on humeral position and range of motion in reverse shoulder arthroplasty

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

Importance of a three-dimensional measure of humeral head subluxation in osteoarthritic shoulders

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) = 0.71; P < .01) and in orientation (R(2) = 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