The Effect of Density on the Delicate Balance between Structural Requirements and Environmental Issues for AAC Blocks: An Experimental Investigation

Among other construction materials, Autoclaved Aerated Concrete (AAC) offers several advantages to face the pressing need to build more sustainable and energy-efficient buildings. From the building side, the low thermal conductivity of AAC allows the realization of energy-efficient building envelopes, with interesting savings in terms of heating and cooling processes. The equilibrium between structural performances (related to safety issues) and energy efficiency requirements is, however, very delicate since it is strictly related to the search for an “optimum” material density. Within this context, this work discusses the results of wide experimental research, showing the dependency of the most important mechanical properties (compressive strength, elastic modulus, flexural strength and fracture energy) from density, as well as the corresponding variation in thermal conductivity. In order to identify the better compromise solution, a sort of eco-mechanical index is also defined. The big challenge for future researches will be the improvement of this eco-mechanical index by working on pore structure and pore distribution within the material without significantly reducing the density and/or by improving the strength of the skeleton material.

A Numerical Study on Optimum Material and Design for Dental Trilayer Systems

This study investigated the impacts of geometry, thickness, and material on damage growth in a porcelain-metal restoration structure by utilizing a computational approach. Extended finite element method (XFEM) was used to find the critical loads causing the nucleation of radial cracks at the porcelain undersurface. Plastic deformation also was considered at the metal above the surface as another damage mechanism. The dental system consisted of a brittle outerlayer (porcelain)/metal (Pd/Co/Au alloys)-core/dentin-substrate trilayer system. A tungsten-carbide hemisphere as an indenter was used to apply a compressive loading on the structure. In addition, two different geometries were created to present the dental structure, cylinder, and tapered cylinder. The results showed that a harder and stiffer metal core can resist the initiation of radial cracks. It was also observed that the metal with thinner layers is more vulnerable to radial cracking. In all simulations, the tapered cylinder geometry showed to have higher critical loads in both damage modes. The optimum thickness for the porcelain layer was suggested to be 0.5 mm. The geometry of dental crown-like structures was found to be an important factor in damage initiation. The findings also proposed that the metal layer should not be designed very thin in order to prevent the formation of radial cracks. This numerical investigation also recommended that the stiffness of the metal layer is better to keep higher compared to other layers to hinder the initiation of radial cracks.

Morphological rationale of the optimum material searching for the conservative treatment of pulp inflammation (literature review)

Pulpitis is one of the most prevalence complication of dental caries. In the structure of visits for dental care, the diagnosis of pulpitis accounts for 14 – 20%. Preservation of the vitality of the pulp is very important for the tooth and for the body as a whole. Since the death of the neurovascular bundle leads to a abnormalities of the protective, trophic and plastic functions of the tooth, causing the loss of its functional signifcance, the development of complications and, as a consequence, removal of a tooth. So, conservative methods of pulpitis treatment must be used to prevent the spread of inflammation in the dental pulp. The success of both direct and indirect biological methods for treating pulpitis in more than 50% of cases depends on the drugs and materials used for the pulp. In the arsenal of dentists there are appropriate new generation drugs with a suffciently high evidential base, however, the problem of fnding the "ideal" material is still crucial.

Material of Choice in Pediatric Cranioplasty

Background Current evidence is lacking regarding the optimum material required for cranioplasty in the pediatric population when native bone cannot be replaced. The aim of our survey was to examine current practice in Australia and New Zealand regarding pediatric cranioplasty material. Methods The online tool SurveyMonkey was used to survey 244 neurosurgeons in Australasia. The survey consisted of five questions concerning preference of material and donor origin for pediatric cranioplasty. Results Twenty-two neurosurgeons (9%) participated. The results indicate that with small skull defects (< 3 cm) in patients aged 0 to 2years, conservative management with observation alone is the preferred option (65%). In patients aged 3 to 10 years, autologous donor bone was the most popular option, whereas for 11+ years, hydroxyapatite (HA) was the material of choice, followed by titanium. For defects of more than 3 cm, autologous donor bone was preferred in under 11 years. In patients older than 11 years, titanium was the preferred choice (46.67%). The preferred donor origin for autologous cranioplasty in small skull defects (< 3 cm) was split calvarial grafts for all age groups. However, 68.42% of respondents managed those under 2 years conservatively. In large skull defects (> 3 cm), the preferred donor origin was split calvarial grafts for patients older than 3 years (48.3%). In patients aged 0 to 2 years, exchange cranioplasty was the preferred option when cranioplasty was performed. Conclusion The current practice in Australia and New Zealand is to use autologous donor bone in preference to synthetic materials for cranioplasty in children under 11 years. In children older than 11 years, hydroxyapatite and titanium are the materials of choice.

Experimental Study on Physical and Rheological Properties of Trinidad Lake Asphalt Modified Binder

Mastic asphalt (MA) has been recognized as one of the most deformation-resistant and thus durable materials for bridge pavement. The performance properties of MA are highly dependent on the physical and rheological properties of the binder applied in the MA mixture. To modify the binder properties to obtain the expected performance of the MA mixture, Trinidad Lake Asphalt (TLA) is often applied. In this study, the TLA-modified binders to be used in mastic asphalt bridge pavement systems were evaluated to develop the optimum material combination using conventional and performance-related testing. Physical and rheological tests were carried out on TLA-modified binders with the different modifier content in the range of 10–50% on a weight basis. The tests revealed that the TLA modifier addition to the 35/50 base bitumen should be close to the value of 20%. Higher concentrations of TLA may make the binder very stiff and could induce low-temperature cracks in mastic asphalt.