Studies of Fracture Toughness in Concretes Containing Fly Ash and Silica Fume in the First 28 Days of Curing.

This paper presents the results of the fracture toughness of concretes containing two mineral additives. During the tests, the method of loading the specimens according to Mode I fracture was used. The research included an evaluation of mechanical parameters of concrete containing noncondensed silica fume (SF) in an amount of 10% and siliceous fly ash (FA) in the following amounts: 0%, 10% and 20%. The experiments were carried out on mature specimens, i.e., after 28 days of curing and specimens at an early age, i.e., after 3 and 7 days of curing. In the course of experiments, the effect of adding SF to the value of the critical stress intensity factor-KIcS in FA concretes in different periods of curing were evaluated. In addition, the basic strength parameters of concrete composites, i.e., compressive strength-fcm and splitting tensile strength-fctm, were measured. A novelty in the presented research is the evaluation of the fracture toughness of concretes with two mineral additives, assessed at an early age. During the tests, the structures of all composites and the nature of macroscopic crack propagation were also assessed. A modern and useful digital image correlation (DIC) technique was used to assess macroscopic cracks. Based on the conducted research, it was found the application of SF to FA concretes contributes to a significant increase in the fracture toughness of these materials at an early age. Moreover, on the basis of the obtained test results, it was found that the values of the critical stress intensity factor of analyzed concretes were convergent qualitatively with their strength parameters. It also has been demonstrated that in the first 28 days of concrete curing, the preferred solution is to replace cement with SF in the amount of 10% or to use a cement binder substitution with a combination of additives in proportions 10% SF + 10% FA. On the other hand, the composition of mineral additives in proportions 10% SF + 20% FA has a negative effect on the fracture mechanics parameters of concretes at an early age. Based on the analysis of the results of microstructural tests and the evaluation of the propagation of macroscopic cracks, it was established that along with the substitution of the cement binder with the combination of mineral additives, the composition of the cement matrix in these composites changes, which implies a different, i.e., quasi-plastic, behavior in the process of damage and destruction of the material.

Assessment of seawater quality and bacteriological pollution of rocky shores in the central coast of San Jorge Gulf (Patagonia, Argentina).

We assessed seasonal and spatial variability of seawater quality and bacterial pollution in two sewage-impacted and two reference rocky shores in the area of Comodoro Rivadavia, the largest city in central Patagonia. Samples taken from winter 2015 to autumn 2017 at different intertidal levels showed that the impacted sites experienced a decrease of salinity-more pronounced towards the autumn-, a slightly higher turbidity, the lowest values of dissolved oxygen, and significantly higher concentrations of nitrates throughout the year. They also were up to ten times above the legal limit of fecal indicator bacteria (FIB) for recreation and fishing areas. Enterococci increased particularly during winter. All bacteriological indicators decreased markedly during spring. Principal component analysis arranged the reference sites mostly by their higher salinity, and the impacted sites by concentration of FIB, nitrates and phosphates. Impacted and reference sites overlapped towards lower levels, where the explicative variables were more stable.

Congenital and acquired pulmonary artery anomalies in the adult: radiologic overview.

Various congenital and acquired anomalies may affect the pulmonary arteries in adult patients. Congenital anomalies (proximal interruption, anomalous origin of the left pulmonary artery [pulmonary artery sling], and idiopathic dilatation of the pulmonary trunk) are usually found incidentally at chest radiography or computed tomography (CT). Acquired anomalies include diffuse or focal enlargement of the arteries because of pulmonary hypertension, aneurysm, and intravascular pulmonary metastasis; decreased arterial diameter because of bronchial carcinoma, mediastinal fibrosis, and Takayasu arteritis; and intraluminal filling defects due to pulmonary thromboembolism and pulmonary artery sarcoma. An awareness of the radiologic manifestations of the disease entities and potential pulmonary artery complications secondary to infection or vasculitis may enable an early diagnosis. CT angiography is becoming the standard method for evaluating patients in whom the presence of pulmonary embolism is suspected. CT assessment of the extent of heart effects in patients with pulmonary hypertension and pulmonary embolism is particularly important because such effects largely determine the prognosis.