Nonlinear Model for Reinforced Concrete under Cyclic Loading

Most of the available shear models for reinforced concrete rely on empirical formulations. In this study, a rational shear stress function is used to define the shear stress–strain envelope for reinforced concrete. Cyclic rules are proposed to define the loading, unloading and reloading relationships for reinforced concrete under shear stress reversals. A normal stress function describing the cyclic relationship of concrete under axial stress is also introduced. The proposed functions are verified using experimental data of reinforced concrete panels tested under monotonic and cyclic loading. Subsequently, the normal and shear stress functions along with their cyclic rules are integrated in a non-linear finite element analysis code. The resulting model accounts for tension stiffening, crack opening and closing, compression hardening and softening, degradation of concrete strength and stiffness in the direction parallel to the crack, compression unloading and reloading, as well as non-linear steel behaviour (strain hardening and Bauschinger effect). The finite element model is then used to analyse two Portland Cement Association shear walls with different geometries tested under cyclic loading. The results show a good agreement between analytical and experimental data. The model showed an excellent capacity of predicting shear deformations of reinforced concrete elements under cyclic loading with minimal computational efforts

MAT-717: MECHANICAL PERFORMANCE OF HYBRID FIBRE-REINFORCED ENGINEERED CEMENTITIOUS COMPOSITE INCORPORATING NITISMA SHORT FIBRES

A new high-strength, high-tensile ductility hybrid fibre-reinforced engineered cementitious composite (HECCSMAF) incorporating randomly dispersed nickel-titanium shape memory alloy short fibres (NiTi-SMA) has been pioneered in this study. The mechanical properties of the HECC-SMAF produced with a combination of 2% polyvinyl-alcohol (PVA) and 0.5%, 1%, and 1.5% NiTi-SMA fibres by volume fraction have been explored. The experimental results indicate that utilizing a combination of those fibres can enhance the tensile capacity of ECC by up to 39% with a slight to no increase in compressive strength. An overall reduction in workability was observed compared to that of ECC made with only 2% PVA by volume fraction, which is typical of metallic fibre-reinforced cementitious systems. Among the tested ECC mixtures, HECC-SMAF made with 2% PVA and 1% NiTi-SMA presents the best mechanical performance

MAT-715: SUSTAINABLE HIGH-VOLUME FLY ASH GROUTS FOR TWO-STAGE CONCRETE

Two-stage concrete (TSC) is a special type of concrete in which coarse aggregates are pre-placed in the formwork and subsequently injected with a grout. Beneficiating fly ash in TSC grouts increases TSC sustainability through the ecological use of large quantities of fly ash, reduced carbon-dioxide emissions associated with cement production, and enhancement of resource productivity of the concrete industry. Limited research has explored the effects of using high volume of fly ash as partial replacement for cement in TSC grout mixtures. Therefore, the flowability of grout mixtures incorporating various fly ash addition rates (i.e. 0%, 30%, 50% and 70%) was evaluated using the flow cone method and spread flow test. Correlations between the efflux time and spread flow for the grout mixtures were developed. Results show that increasing the fly ash addition reduced the grouts efflux time while increasing its spread flow. The optimum high-volume fly ash dosage for achieving high flowability and acceptable TSC compressive strength was identified

MAT-741: IMPACT BEHAVIOUR OF SHAPE MEMORY ALLOY HYBRID FIBRE-REINFORCED ENGINEERED CEMENTITIOUS COMPOSITE

An experimental study was conducted to evaluate the impact behaviour of an innovative hybrid-fibre engineered cementitious composite (ECC) incorporating randomly dispersed short shape memory alloy fibres (SMA). A modified drop weight test was conducted on specimens from various ECC mixtures with and without SMA fibres. The impact behaviour was evaluated and compared based on the ability to dissipate energy and sustain impact load without damage. Results show that the addition of SMA to ECC mixtures significantly enhanced their performance under impact loading. The amount of dissipated energy by ECC increased by about 51% as a result of SMA fibre addition. This highlights the potential benefits of incorporating SMA in composite materials exposed to impact loads, paving the way for a wider implementation in the field of fortified structures

MAT-716: GREEN SIDEWALKS USING SUSTAINABLE TWO-STAGE CONCRETE

Two-stage concrete (TSC) is a special type of concrete, which has a high potential for use in sidewalk construction owing to its high volume stability. TSC is characterized by its high coarse aggregate content. Hence, using recycled solid waste materials as a coarse aggregate will increase TSC sustainability, while providing a cost-effective alternative to natural aggregates. Aggregates are pre-placed in TSC. Hence, water absorption by recycled concrete aggregates and the associated rheology problems do not exist in TSC. This study explores the performance of green TSC sidewalks incorporating recycled concrete aggregates (RCA) and crumb rubber from scrap tires. Mechanical properties of the proposed green TSC including compressive strength, modulus of elasticity, flexural strength and toughness, as well as durability to freeze-thaw cycles were investigated. Results show a slight reduction in TSC mechanical properties due to the use of RCA. Moreover, incorporating tire particles reduced TSC mechanical properties significantly, while improving its toughness and freeze-thaw resistance. Addition of recycled tire steel wires allowed to overcome the negative effects on the mechanical properties induced by crumb tire rubber. Therefore, recycling solid waste materials in TSC sidewalks can be an effective strategy to beneficiate such waste materials

Changes in the composition and fatty acid profile of Najdi ewes’ milk before and after weaning

This trial aimed to study the changes in the yield, composition, and fatty acid (FA) profile of ewes’ milk during suckling and milking periods. Nineteen multiparous Najdi ewes were kept under identical management and feeding conditions during a 12-week trial that was divided into two periods. Milk samples were collected on each sampling day from the total yield during the suckling (3rd, 6th, and 9th week) and milking (12th week) periods. The milk yield and the total solids, fat, protein, and lactose contents of the milk remained constant throughout the suckling weeks, but the protein content increased and milk yield and lactose content decreased after weaning. There were no differences in milk saturated FA (SFA), unsaturated FA (UFA), and monounsaturated FA (MUFA) contents during the suckling and milking periods, whereas the polyunsaturated FA content increased during the milking period. There were no differences in the individual milk SFA during the weeks of suckling, but the contents of caproic acid (C6:0), caprylic acid (C8:0), margaric acid (C17:0), and stearic acid (C18:0) decreased. However, myristic acid (C14:0), lauric acid (C12:0), and isomers of pentadecanoic (C15:0) acid increased during the milking period. The percentage of vaccenic acid (C18:1△11t), rumenic acid (C18:2△9c,11t; conjugated linoleic acid (CLA)), ω-3 FA group, and the atherogenicity index did not differ during the suckling period, but increased after weaning in the 12th week of lactation. This study demonstrated that weaning lambs in Najdi ewes is probably a factor that strongly affects milk traits by changing yield, composition, and FA profile.Keywords: CLA, dairy ewes, milk fat, milk yield, stage of lactatio

Conversión de Oleum papaveris seminis en ésteres metílicos mediante un proceso de esterificación: Optimización y estudio cinético

This paper presents an acid pre-treatment process and a kinetic study for the esterification reaction of Oleum papaveris seminis oil with methanol in the presence of amberlite 120 as a solid catalyst to convert the oil into methyl esters. Response surface methodology (RSM) was applied to optimize the reaction parameters, i.e. reaction time, percentage of the catalyst and volume ratio of methanol to oil. The results revealed that 0.87% w/w of catalyst concentration and 44.70% v/v of methanol to oil ratio provided final free fatty acid (FFA) contents of 0.60% w/w at 102.40 min of reaction time. It proved that the contribution of Amberlite 120 in the esterification of FFA was highly significant. The kinetics of the esterification in Oleum papaveris seminis oil with methanol in the presence of the amberlite 120 catalyst were also investigated to establish the reaction rate constant (k), reaction order, and activation energy. The study was performed under the optimized parameters at three reaction temperatures (50, 55, and 60 ºC). The value of k was in the range of 0.013 to 0.027 min-1. The first-order kinetics’ model was suitable for this irreversible FFA esterification with the activation energy of about 60.9 KJ·mol-1.En este artículo se presenta un proceso de pre-tratamiento con ácido, y un estudio cinético de la reacción de esterificación. Se utiliza Oleum papaveris seminis con metanol en presencia de Amberlite 120 como catalizador sólido para la formación de los ésteres metílicos. Se aplicó una metodología de superficie de respuesta (RSM) para optimizar los parámetros de la reacción; es decir, tiempo de reacción, porcentaje de la relación de catalizador y volumen de metanol - aceite. Los resultados mostraron que el 0,87% w/w de la concentración de catalizador y 44,70% v/v de metanol en relación al aceite dan lugar a un contenido final de ácidos grasos libres (FFA) de 0,60% w/w en 102,40 min de tiempo de reacción. Se demostró que la contribución de Amberlite 120 en la esterificación de los FFA fue altamente significativa. La cinética de la esterificación del Oleum papaveris Seminis con metanol en presencia del catalizador Amberlite 120 también se investigó para establecer la constante de velocidad de reacción (k), orden de la reacción, y la energía de activación. El estudio se realizó bajo los parámetros optimizados a tres temperaturas de reacción (50, 55, y 60 °C). El valor de la constante k fué del rango de 0.013 a 0,027 min-1. El modelo de cinética de primer orden fue el adecuado para esta esterificación FFA irreversible con una energía de activación de aproximadamente 60,9 KJ mol -1

Characteristics of Chamaerops humilis L. var. humilis seed oil and study of the oxidative stability by blending with soybean oil

Herein we examine the characteristics of date seed oil extracted from Chamaerops humilis L. var. humilis seeds (HSO) cultivated in a gardening zone in Tunisia. Its physicochemical properties, fatty acid composition, and thermal and antioxidant properties were evaluated and compared with those of seed oil from another variety of Chamaerops humilis. The results showed that HSO possessed higher contents of oleic (44%) and linoleic (20%) acids than the other seed oil. The total tocopherol and tocotrienol content was 88 mg/100 g oil, where α-tocotrienol (64%) was the major isomer. The total phenolic (91 μg/g oil) and flavonoid contents (18 μg/g oil) of the HSO were determined, and its antioxidant capacities, measured in terms of ABTS and DPPH radical-scavenging capacities, were 210 µM TEAC/g DW and 4.3 mM TEAC/g DW, respectively. The oxidative stability index (OSI) of the oil was 16 h at 110 °C. Furthermore, the OSI of soybean oil was significantly enhanced upon blending with HSO. HSO exhibited higher thermal stability than the other oils and significantly different thermal behavior. The determination of fatty acid composition, physicochemical properties, bioactive content, oxidative stability, and thermal behavior of HSO demonstrated that this renewable resource can be used for edible purposes

Characterization of the Trans Watson-Crick GU Base Pair Located in the Catalytic Core of the Antigenomic HDV Ribozyme

The HDV ribozyme’s folding pathway is, by far, the most complex folding pathway elucidated to date for a small ribozyme. It includes 6 different steps that have been shown to occur before the chemical cleavage. It is likely that other steps remain to be discovered. One of the most critical of these unknown steps is the formation of the trans Watson-Crick GU base pair within loop III. The U23 and G28 nucleotides that form this base pair are perfectly conserved in all natural variants of the HDV ribozyme, and therefore are considered as being part of the signature of HDV-like ribozymes. Both the formation and the transformation of this base pair have been studied mainly by crystal structure and by molecular dynamic simulations. In order to obtain physical support for the formation of this base pair in solution, a set of experiments, including direct mutagenesis, the site-specific substitution of chemical groups, kinetic studies, chemical probing and magnesium-induced cleavage, were performed with the specific goal of characterizing this trans Watson-Crick GU base pair in an antigenomic HDV ribozyme. Both U23 and G28 can be substituted for nucleotides that likely preserve some of the H-bond interactions present before and after the cleavage step. The formation of the more stable trans Watson-Crick base pair is shown to be a post-cleavage event, while a possibly weaker trans Watson-Crick/Hoogsteen interaction seems to form before the cleavage step. The formation of this unusually stable post-cleavage base pair may act as a driving force on the chemical cleavage by favouring the formation of a more stable ground state of the product-ribozyme complex. To our knowledge, this represents the first demonstration of a potential stabilising role of a post-cleavage conformational switch event in a ribozyme-catalyzed reaction