Effect of Nano-SiO2 on the Microstructure and Mechanical Properties of Concrete under High Temperature Conditions.

The aim of the research was to determine how the admixture of nanosilica affects the structure and mechanical performance of cement concrete exposed to high temperatures (200, 400, 600, and 800 °C). The structural tests were carried out on the cement paste and concrete using the methods of thermogravimetric analysis, mercury porosimetry, and scanning electron microscopy. The results show that despite the growth of the cement matrix's total porosity with an increasing amount of nanosilica, the resistance to high temperature improves. Such behavior is the result of not only the thermal characteristics of nanosilica itself but also of the porosity structure in the cement matrix and using the effective method of dispersing the nanostructures in concrete. The nanosilica densifies the structure of the concrete, limiting the number of the pores with diameters from 0.3 to 300 µm, which leads to limitation of the microcracks, particularly in the coarse aggregate-cement matrix contact zone. This phenomenon, in turn, diminishes the cracking of the specimens containing nanosilica at high temperatures and improves the mechanical strength.

Utility of the SYNTAX Score in the risk stratification of patients undergoing rotational atherectomy.

INTRODUCTION: The SYNTAX Score (SS) evaluates the angiographic complexity of coronary artery disease to assess the cardiovascular risk after coronary revascularization. The aim of the study was to evaluate whether SS results are associated with in-hospital and 1-year outcomes of patients undergoing percutaneous coronary intervention (PCI) requiring rotational atherectomy (RA). MATERIAL AND METHODS: We analyzed data of 207 consecutive patients who underwent PCI with RA. Patients were divided into two groups: those with high SS (> 33 points) and those with low/intermediate SS (0-33 points). RESULTS: In 21 (10%) patients SS was high and 186 (90%) patients had low/intermediate SS. Patients with high SS were older (76 vs. 71 years, p = 0.008) and more frequently diagnosed with chronic kidney disease (38% vs. 18%, p = 0.03) and heart failure (71% vs. 30%, p = 0.0001). In patients with high SS the RA procedure was longer (p = 0.004), required more contrast (p = 0.005) and higher radiation doses (p = 0.04), and contrast-induced nephropathy was more frequent (14% vs. 2%, p = 0.001). CONCLUSIONS: In our RA patients there was no significant difference between the frequency of in-hospital and 1-year adverse cardiovascular events depending on the SS result. High SS correlates only with parameters describing the extensity and technical complexity of the procedure. However, the unavailability of other risk assessment tools in this population raises the need to create a new more specific risk score for patients requiring RA.

Effects of Elevated Temperatures on the Properties of Cement Mortars with the Iron Oxides Concentrate.

Using the waste materials in the production of the building materials limits the storage of the wastes, burdensome for the environment and landscape, and makes possible to manufacture the materials and products with the use of the less volume of the raw materials. Cement concretes and mortars as the basic building materials offer the broad prospects of utilization of the recyclable or waste materials. The wastes from the iron ore processing are the solid wastes resulting from the process of enrichment of the ore concentrate. The paper presents the results of testing three mortars, in which a part of fine aggregate was replaced with the iron oxide concentrate (IOC) resulting from such a process. IOC has been used as a substitute of 10%, 20% and 30% (by mass) of the fine aggregate. The effect of the concentrate on the mechanical performance of the mortars at the high temperature (up to 600 °C) was also investigated. The IOC is a neutral material, not affecting chemically the process of cement hydration. The addition of IOC slightly improves the strength of the cement mortars (by 5% to 10%). In the case of the larger amount (20-30%) of the addition, the use of superplasticizer is necessary. The IOC significantly improves the high temperature resistance of the cement mortars (300 °C). The cement mortars containing 30% of the IOC addition keep 80% of the initial flexural and compressive strength when exposed to the temperature 450 °C.

Case report on successful 'bail out' aortic homograft implantation in a 81-year old woman with aortic ring rupture after double TAVI procedure.

A 81-year woman was admitted to our institution due to worsening chronic heart failure. The patient presented herself with severe aortic valve stenosis and mitral valve insufficiency. Due to estimated high operative risk a TAVI approach was chosen. Following the fist TAVI implantation (Sapien XT 26 mm) a big paravalvular leakage was diagnosed. Hence, in order to close the paravalular leakage, a second TAVI procedure with a Core Valve 26 mm was performed. A following CT scan showed signs of aortic ring rupture. We therefore decided to perform open heart surgery. After removal of both TAVI prosthesis, native valve excision a 21 mm sized aortic homograft was implanted. Additionally, a mitral valve annuloplasty with CE Physio 28 mm ring was performed. In the postoperative period the patient remained for three weeks in the ICU, followed by two weeks on general ward. The patient was discharged home in good condition, with good left ventricular function and regular homograft function in the aortic position. The open heart surgery should have had been performed primarily. Nevertheless, the decision on the treatment strategy is always difficult in case of borderline patients.