Study on the Effect of Nano-Silica in Mechanical and Durability Properties of Concrete with Steel Fiber

This study presents experimentally the combined effect of using Nano-silica (NS) and steel fibers (SF) on the mechanical properties of hardened concrete. NS is used as partial cement replacement by different percentages, and SF is used as volume substitution by different percentages. Splitting tensile strength, modulus of elasticity, and flexural strength are evaluated using different combinations between NS and SF. Significant improvement in the mechanical properties of concrete is observed on using NS due to its high pozzolanic activity. The Optimum content of SF is improved splitting tensile strength with different percentages respectively compared to without either NS or SF. Utilizing NS with SF leads to improving modulus of elasticity compared to without either NS or SF. Flexural strength is doubled for using NS and SF compared to without NS and SF.

Contribution to the Study of the Durability of Rubberized Concrete in Aggressive Environments

Today, much of the world’s waste, in particular used tires, is accumulating as a potential source of major environmental and economic problems. In order to better preserve the environment, and in the face of changes in the legislation in force, many recovery actions have been carried out especially in the field of building materials.The present research aims to contribute to the study of the mechanical properties and durability of concretes based on rubber aggregates. To achieve this objective, we have contemplated incorporating therein amounts of rubber granules according to different volume substitution percentages being 10%, 17.5%, and 25%. A comparison of the results with a control concrete has been established.The obtained results make it possible to demonstrate that the substitution of a percentage of sand by rubber granules decreases the mechanical strengths and increases the expansion in water. On the other hand, it improves the resistance to attack from H2SO4, Na2SO4, and seawater. The latter is evaluated by the loss and gain in mass as well as the loss in mechanical resistance, especially in the long term (more than 90 days), decreases drying shrinkage, thus decreasing microscopic cracks and providing better durability.

P4736The Prognostic Impact of Volume Substitution on Cardiac Strain and the Development of Postoperative Atrial Fibrillation after Cardiac Surgery

Background Postoperative atrial fibrillation (POAF) represents a common complication after cardiac valve or coronary artery bypass surgery. Etiologically, multifactorial causes such as the patients' age, weight, comorbidities or local remodeling proved a strong association with this common arrhythmia. While strain of atrial tissue is known to induce atrial fibrillating impulses, less attention has been paid to potentially strain-promoting values during the peri- and post-operative period. Therefore, we aimed to determine the association of peri- and post-operative volume substitution on markers of cardiac strain and subsequently its impact on the promotion and development of POAF. Methods In this prospective observational study 271 patients undergoing elective cardiac surgery in our Medical University were enrolled (median age: 69 years [IQR: 60–75 years]; 195 [72%] male gender). Intra- and post-operative data was collected from anesthesiologic and intensive care unit protocols. Multivariate binary logistic regression analysis was used to identify the prognostic value of volume substitution on the development of POAF. Results A total of 123 (45.4%) individuals developed POAF. The average intra-operative transfusion volume was significantly elevated in the POAF subgroup (605.6ml [POAF] vs. 227.1ml [non-POAF]; p<0.001). Moreover, the fluid balance within the first 24 hours after surgery was significantly higher in patients developing POAF (+1129.6 ml [POAF] vs. +544.9 ml [non-POAF]; p=0.044). We found that N-terminal pro brain natriuretic peptide (NT-proBNP) values were significantly elevated in patients that received any volume substitution (2860.0 pg/mL [Transfusion] vs. 1486.5 pg/mL [no-Transfusion]; p=0.002). In line with those results, the postoperative fluid balance was also found to have a direct and significant correlation with postoperative NT-ProBNP values (r=0.287, p=0.002). Of note, the amount of substituted volume proved to be a strong and independent predictor for POAF with an adjusted odds-ratio (OR) per one standard deviation (1-SD) of 2.49 (95% CI: 1.25–4.96; p=0.009). Conclusion Within the present analysis we were able to demonstrate that substitution of larger transfusion volumes presents a strong and independent predictor for the development of POAF. Via the observed distinct association with NT-proBNP values, it can reasonably be assumed that post-operative atrial fibrillating impulses are triggered via volume-induced cardiac strain.

Effect of mineral admixtures on the rheological and mechanical properties of mortars

We propose in this study to determine the role of mineral admixtures on the properties of cementitious materials in order to define a formulation method allowing an optimization of their use and the improvement of the rheological and mechanical properties of the mortars. In order to meet the objectives of this study, and to evaluate the effects that mineral admixtures may have on the properties of mortars in the fresh and hardened state, we have proposed to use a specific method based on progressive volume substitution of cement by the mineral admixtures, in order to preserve the absolute volume of all the solid constituents and the consistency for all the mixtures. The use of the mineral admixtures in the mortars also has for objective to valorize a category of natural materials or coproducts available in Algeria. As a result, the mineral admixtures chosen for this study are Blast furnace Slag, natural pozzolan and silica fume. Then the effect of the mineral admixtures on the rheological and mechanical properties of the mortars was evaluated according to the substitution rate of the cement. We applied to the studied mortars the notion of equivalent binder in order to calculate the coefficient of activity (K) defined by the two theoretical formulas Féret and Bolomey. The specific chemical action of each mixture was evaluated by analysing the variation of the coefficient of activity K as a function of the rate of substitution of the cement.

Prediction performance of compressive strength of cementitious materials containing rubber aggregates and filler using fuzzy logic method

Purpose The purpose of this paper is to focus on compressive strength modelling of cementitious mixtures like mortar and Roller-compacted concrete (RCC) containing rubber aggregates from shredded worn tires and filler using adaptive neuro fuzzy inference systems (ANFIS). Design/methodology/approach The volume substitution contains a ratio of rubber aggregates vs sand in mortar and with crushed sand in RCC and ranges from 0 to 50 per cent. As for the filler, they are substituted with sand by 5 per cent in mortar mixture. The methodology consists of optimizing the percentage of substitution in cementitious mixtures to ensure better mechanical properties of materials like compressive strength. The prediction of compressive strength and the optimization of cementitious mixtures encourage their uses in such construction pavements, in area games or in other special constructions. These cementitious materials are considered as friendly to the environment by focussing on their improved deformability. Findings The results of this paper show that the performance of the constructed fuzzy method was measured by correlation of experimental and model results of mortar and RCC mixtures containing both rubber aggregates and filler. The comparison between elaborated models through the error and the accuracy calculations confirms the reliability of the ANFIS method. Originality/value The purpose of this paper is to assess the performance of the constructed fuzzy model by the ANFIS method for two types of cementitious materials like mortar and RCC containing rubber aggregates and filler. The fuzzy method could predict the compressive strength based on the limited measurement values in the mechanical experiment. Furthermore, the comparison between the elaborated models confirms the reliability of the ANFIS method through the error and the accuracy calculations for the best cementitious material mixtures.

UTILIZAÇÃO DE FIBRA DE BORRACHA DE PNEU COMO AGREGADO NA COMPOSIÇÃO DE CONCRETO

Resumo A indústria do processo de recauchutagem de pneus gera resíduos que em sua maioria têm sido descartados sem nenhum controle. Este fato contribui para aumentar a poluição ambiental e favorecer a proliferação de vetores nocivos à saúde. Visando encontrar uma aplicação para esse tipo de resíduo, neste trabalho são apresentados resultados experimentais de amostras que tiveram o intuito de avaliar o comportamento e a viabilidade do uso de fibra de borracha proveniente de pneu, adicionada em forma de agregado no concreto, com o objetivo de obter um possível material alternativo para a indústria da construção civil, contribuindo para a proteção ambiental. Prepararam-se uma dosagem de concreto sem resíduos de borracha, para servir de referência, e três diferentes dosagens contendo resíduos de borracha, com substituição do volume do agregado em 5%, 10% e 15%. Aos sete e vinte e oito dias as amostras produzidas, no total de 80 corpos de prova cilíndricos de 15 x 30 cm2, foram submetidas ao ensaio de resistência mecânica à compressão simples. Conclui-se que com a utilização das fibras de pneu, o concreto sofre uma perca de resistência em todos os casos, contudo, os traços com as porcentagens de 5% e 10%, além de um custo menor, atingiram resistência para serem utilizados em elementos não estruturais, como calçadas. Palavras-chave: Pneus inservíveis. Fibra de borracha. Agregado. Concreto. Reciclagem. Abstract The tire retreading industry generates waste residues that has mostly been disposed of without any control. This contributes to increasing environmental pollution and promoting the proliferation of vectors that are harmful to people’s health. With the aim to find an application for this type of residue, experimental results of samples with the intention of evaluating the behavior and the feasibility of the use of rubber fiber from tires were presented throughout this article. Such samples were added as an aggregate in the concrete, with the objective of obtaining a possible alternative material for the construction industry that would contribute to environmental protection. A dosage of rubber-free concrete to serve as reference was prepared, and three different dosages containing rubber residues were prepared with 5%, 10% and 15% volume substitution of the aggregate. After the seventh and the twenty-eighth day, the samples produced, in the total of 80 cylindrical specimens of 15x30 cm², were submitted to the mechanical test of simple compression. We came to conclusion that, with the use of the tire fibers, the concrete undergoes a loss of resistance in all cases. However, the traces with the percentages of 5% and 10%, in addition to a lower cost, reached resistance that allowed it to be used in non-structural elements such as sidewalks. Keywords: Wasted tires. Rubber fiber. Aggregate. Concrete. Recycling.