Mechanical performance of concrete with partial replacement of sand by sewage sludge ash

The production of sewage sludge from waste water treatment plants is increasing all over the world. Disposal of sewage sludge is a serious environmental problem. If we think of the areas needed for sludge ash disposal, we clearly understand the importance of reusing sewage sludge ash in concrete. This paper presents results related to the replacement of sand by sewage sludge ash. The sludge was characterized for chemical composition (XRF analysis), crystalline phases (XRD analysis) and pozzolanic activity. The effects of incineration on crystal phases of dry sludge were investigated. Two (W/C) ratios (0.55 and 0.45) and three sludge percentages (5%, 10% and 20%) by cement mass were used. The mechanical performance of SSAC at different curing ages (3, 7, 28 and 90 days) was assessed by means of mechanical tests. Results show that sewage sludge ash leads to a reduction in density and mechanical strength. Results also show that concrete with 20% of sewage sludge ash and W/C=0.45 has a 28 day compressive strength of almost 30MPa

Mechanical performance of concrete with partial replacement of sand by sewage sludge ash from incineration

"Advanced Materials Forum VI , vol. 730-732"The production of sewage sludge from waste water treatment plants is increasing all over the world. Disposal of sewage sludge ash is a serious environmental problem. If we think of the areas needed for sludge ash disposal, we clearly understand the importance of reusing sewage sludge ash in concrete. This paper presents results related to the replacement of sand by sewage sludge ash. The sludge was characterized for chemical composition (XRF analysis), crystalline phases (XRD analysis) and pozzolanic activity. The effects of incineration on crystal phases of dry sludge were investigated. Two (W/C) ratios (0.55 and 0.45) and three sludge percentages (5%, 10% and 20%) by cement mass were used. The mechanical performance of SSAC at different curing ages (3, 7, 28 and 90 days) was assessed by means of mechanical tests. Results show that sewage sludge ash leads to a reduction in density and mechanical strength. Results also show that concrete with 20% of sewage sludge ash and W/C=0.45 has a 28 day compressive strength of almost 30MPa

Optimal Location Design for Prediction of Spatial Correlated Environmental Functional Data

The optimal choice of sites to make spatial prediction is critical for a better understanding of really spatio-temporal data. It is important to obtain the essential spatio-temporal variability of the process in determining optimal design, because these data tend to exhibit both spatial and temporal variability. Two new methods of prediction for spatially correlated functional data are considered. The first method models spatial dependency by fitting variogram to empirical variogram, similar to ordinary kriging (univariate approach). The second method models spatial dependency by linear model co-regionalization (multivariate approach). The variance of prediction method was chosen as the optimization design criterion. An application to CO concentration forecasting was conducted to examine possible differences between the design and the optimal design without considering temporal structure

Assessment of the durability performance of fiber-cement sheets

According to standards, the durability performance of fiber-cement sheets must be evaluated by comparing the modulus of rupture (MOR) before and after durability tests (freeze-thaw, soak-dry, and warm water) are completed. This paper investigated the MOR of two different fiber-cement sheets samples before and after durability tests as well as its ductility and toughness. Results showed no significant difference between the MOR of control specimens and that of the specimens submitted to durability tests except in the case of the freezing and thawing test where after 100 cycles, a 7–9% decrease was observed. The differences between the MOR of the control specimens and that of the specimens submitted to durability tests were negligible and acceptable in accordance to the requirements of the standard. However, toughness and ductility decreased considerably in specimens of sample 1 by 25, 35, and 15%, respectively, when exposed to soak-dry (25 and 50 cycles) and warm water conditions. In turn, the reduction in toughness and ductility for specimens of sample 2 exposed to soak-dry (50 cycles) and warm water conditions were of 40 and 7%, respectively. The results of this investigation suggest that ductility and toughness should also be considered to assess the durability performance of fiber-cement sheets

Frequency-dependent anti arrhythmic effects of crataegus monogyna on the extracellular field potential recordings in the rabbit atrioventricular node, an experimental model of AF

Introduction: Despite extensive studies that have been performed on the effects of Crataegus monogyna in cardiovascular diseases, only few investigations have addressed the antiarrhythmic properties of this plant. Aims of the present study were: 1) To determine the protective role of methanolic extract of C. monogyna on the rate-dependent model and the concealed conduction of the AV node. 2) To explore the role of Na+-K+ ATPase in the protective role of C. monogyna Methods: Male New Zealand rabbits (1.5-2kg) were used in all experiments. Stimulation protocols were used to measure basic and rate-dependent AV nodal properties (recovery, atrial fibrilation and zone of concealment) in two groups (N=14). In the first group, all the stimulation protocols were performed before and after the administration of different concentrations of C. monogyna extract (n=7), while in the second group (n=7), all stimulation protocols were carried out in the presence of ouabaine (0.05 μM) and the plant extract. Results: Basic and rate-dependent properties of the AV node were inhibited after the addition of the extract of C. monogyna to Kerebs Henselite solution. At the maximum concentration of C. monogyna (30 mg/l), WBCL cycle length was significantly increased from 156.5±3.4 to 173±5.8 ms and the nodal functional refractory period was prolonged from 164.4±4.1 to 182.7±3.8 ms (P<0.05). Significant decreases of ventricular rhythm were recorded in both selective concentrations of the plant extract. The depressant electrophysiological effect of C. monogyna on the AV node was not abolished by ouabaine, a selective inhibitor of Na+-K+ ATPase enzyme. Conclusion: The results showed a potential anti-arrhythmic and protective effect for C. monogyna. The effect of the plant extract in increasing nodal refractory period and widening of the concealment zone might be the major mechanisms involved. The protective role of C. monogyna was not related to the Na+-K+ ATPase activity

Cementitious composites reinforced with polypropylene, nylon and polyacrylonitile fibres

This paper compares the adhesion strength between three polymeric fibres (polypropylene (PP), nylon66 (N66) and polyacrylonitrile (PAN)) embedded in a cement paste. The specimens were prepared at a water to cement ratio (w/c) of 0.5, and tested after 7, 14 and 28 curing days. It was found that although the adhesion between the polymeric fibres to the cement matrix is an important factor, the energy absorption capacity or energy dissipation ability of the fibres plays a more important role in the improvement of the cementitious composites fracture toughness. Scanning electron micrographs was used to characterize the fibres surface before and after the Pullout tests

Evaluation of adhesion in polymeric fibre reinforced cementitious composites

In this study adhesion of some polymeric fibres to a cement matrix was evaluated both by a theoretical and by an experimental approach. In common methods adhesion of the fibres to the cementitious materials is determined by pull-out test. This test evaluates the energy failure during the fibre drawing out. This paper analyzes the adhesion theory for fibre reinforced cementitious composites to separate the share of the chemical and mechanical adhesion expressing new parameters, which are effective in the adhesion behaviour. Explanations about how the different fibres, matrix properties, test factors and environmental conditions can affect the adhesion results are given. It was found that for fibre/cement composites the fracture energy due to the interfacial interactions is for several orders of magnitude smaller that the polymeric fibre losses function. By employing adhesion theory, fibre/cement interac- tions are better described by a simple relationship of their surface free energy. Determination of the loss function (energy dissipation) leads us to predict the fibre behaviour in the cement matrix and the selection of the appropriate reinforcement

Spatial Factors Affecting the Frequency of Pedestrian Traffic Crashes: A Systematic Review

Context: Considering the importance of pedestrian traffic crashes and the role of environmental factors in the frequency of crashes, this paper aimed to review the published evidence and synthesize the results of related studies for the associations between environmental factors and distribution of pedestrian-vehicular traffic crashes. Evidence Acquisition: We searched all epidemiological studies from 1966 to 2015 in electronic databases. We found 2,828 studies. Only 15 observational studies out of these studies met the inclusion criteria of the study. The quality of the included studies was assessed using the strengthening the reporting of observational studies in epidemiology (STROBE) checklist. Results: A review of the studies showed significant correlations between a large number of spatial variables including student population and the number of schools, population density, traffic volume, roadway density, socio-economic status, number of intersections, and the pedestrian volume and the dependent variable of the frequency of pedestrian traffic crashes. In the studies, some spatial factors that play an important role in determining the frequency of pedestrian traffic crashes, such as facilities for increasing the pedestrians’ safety were ignored. Conclusions: It is proposed that the needed research be conducted at national and regional levels in coordination and cooperation with international organizations active in the field of traffic crashes in various parts of the world, especially in Asian, African and Latin American developing countries, where a greater proportion of pedestrian traffic crashes occur

Influence of acrylic fibers geometry on the mechanical performance of fiber-cement composites

This article analyses the influence of acrylic fibers shape on the flexural behavior of cement composite. The fibers differ in their cross-sectional shapes due to the spinning process (wet-spun and dry-spun). The fibers were characterized by optical microscopy, and the shape factors were calculated on the basis of their geometric characteristics. Results showed that both types of acrylic fiber remarkably improved the flexural performance of the composites. Wet-spun acrylic fibers lead to high flexural strength and toughness. It was found that by increasing the fibers’ shape factor by a factor of 10%, flexural strength and toughness increase to 26% and 23%, respectively

Durability of alkali-activated binders: a clear advantage over Portland cement or an unproven issue?

The alkali activation of alumino-silicate materials is a complex chemical process evolving dissolution of raw materials, transportation or orientation and polycondensation of the reaction products. Publications on the field of alkali-activated binders, state that this new material is likely to have high potential to become an alternative to Portland cement. While some authors state that the durability of these materials constitutes the most important advantage over Portland cement others argue that it’s an unproven issue. This paper presents a review of the literature about the durability of alkali-activated binders. The subjects of this paper are resistance to acid attack, alkali–silica reaction, corrosion of steel reinforcement, resistance to high temperatures and to fire, resistance to freeze–thaw. Special attention is given to the case of efflorescences, an aspect that was received very little concern although it is a very important one