Effects of experimental ternary cements on fresh and hardened properties of self-compacting concretes

Self-compacting concrete (SCC) is a concrete that flows alone under its dead weight and consolidates itself without any additional compaction and without segregation. As an integral part of a SCC, self-compacting mortars (SCMs) may serve as a basis for the mix design of concrete since the measurement of the rheological and viscosity properties of SCC is often impractical due to the need for complex equipment. This paper discusses the properties of SCM and SCC with mineral additions. ordinary Portland cement (OPC), natural pozzolana (PZ), and marble powder (MP) are used in ternary cementitious blends system following the cement substitution with PZ and MP in ratio 1/3. Within the framework of this experimental study, a total of 12 SCM and 6 SCC were prepared having a constant w/b ratio of 0.40. The fresh properties of the SCM were tested for mini-slump flow diameter, mini-V-funnel flow time, and viscosity measurement. Slumps flow test, L-box, J-ring, V-funnel flow time, and sieve stability were measured for SCC. Moreover, the development in the compressive strength was determined at 3, 7, 28, 56, and 90 days. Test results have shown that using ternary blends improved the fresh properties of the mixtures. The combination of natural pozzolana and marble powder increase the slump flow test up to 826 mm for the mixture prepared with 10% of mineral additions. Moreover, the use of mineral addition reduced the time flow to 4.27 s for SCC with 20% mineral addition, thus reducing the viscosity of all mixtures. Addition of MP increases the capacity of the passage through the plates between 88.75 and 93.50% for SCC with 7.5 and 15% of MP, respectively. The ternary system (PZ and MP) improve the sieve stability with the value for 4.07% of SCC with 50% of substitution compared for SSC without additions. The compressive strength of SCC at 90 days with 40% of PZ and MP was similar to that of OPC.     

Quantification of metallothionein-like proteins in the mussel Mytilus galloprovincialis using RP-HPLC fluorescence detection

A HPLC-fluorescence method, using the fluorophore SBD-F (ammonium-7-fluorobenz-2-oxa-1,3-diazole-4-sulfonate), was adapted for the quantification of metallothioneins and their isoforms from the Moroccan mussel Mytilus galloprovincialis. The method was first optimized using a rabbit liver metallothionein. The effects of EDTA, tris(2-carboxyethyl)phosphine, and SBD-F on the labeling efficiency were studied. The optimized method was then applied to evaluate the amount of metallothionein in the mussels either exposed to cadmium in the laboratory or collected from the Casablanca coast, Morocco. The concentrations of metallothioneins measured in the field samples describe the degree of contamination of the sites and are reflected by distinct isoform patterns.     

Photographic study of high-flux subcooled flow boiling and critical heat flux

This study examines both high-flux flow boiling and critical heat flux (CHF) under highly subcooled conditions using FC-72 as working fluid. Experiments were performed in a horizontal flow channel that was heated along its bottom wall. High-speed video imaging and photomicrographic techniques were used to capture interfacial features and reveal the sequence of events leading to CHF. At about 80% of CHF, bubbles coalesced into oblong vapor patches while sliding along the heated wall. These patches grew in size with increasing heat flux, eventually evolving into a fairly continuous vapor layer that permitted liquid contact with the wall only in the wave troughs between vapor patches. CHF was triggered when this liquid contact was finally halted. These findings prove that the CHF mechanism for subcooled flow boiling is consistent with the interfacial lift-off mechanism proposed previously for saturated flow boiling.     

Exploring isolated lignin material from oil palm biomass waste in green composites

Lignin obtained from oil palm biomass empty fruit bunches (EFB) fibers, has been used as curing agent in green epoxy composites. Epoxy–lignin composites, with varying lignin content (15%, 20%, 25% and 30%), reinforced with EFB fiber were prepared. The effect of EFB-based lignin on the mechanical, thermal and morphology properties of the composites were investigated and compared with the composites cured with isophorone diamine curing agent. The improved thermal stability and the observed microstructure of the fractured surface of the composites were attributed to good fiber–matrix interaction, induced by the curing agent. The epoxy composites cured with 25% lignin content proved to be a better matrix and gave optimum value compared with other formulations which was confirmed by its mechanical, thermal and morphological properties.     

Thermal Stresses in Spherical Shells

This paper presents an iterative finite-difference technique for the analysis of axisymmetric spherical shells with variable wall thickness. The formulation is based on thin elastic shell theory. One-dimensional finite-difference points are used to discretize the shell into strips along the meridian, and an iterative technique is employed to determine the normal and meridional displacements. The stress resultants and bending stresses are then evaluated. Unlike existing analytical and finite-difference techniques, the proposed method is applicable with ease to any variation in rigidity along the meridian, to general loading conditions, and to steep and shallow shells. Results are presented and compared with those of the finite-element method.     

Linear Programming Approach to Optimize Strategic Investment in the Construction Workforce

The construction industry in the United States and other parts of the world has been facing several challenges, including a shortage of skilled workers. A review of the relevant body of knowledge indicates that one of the key reasons for this problem is the absence of human resource management strategies for construction workers at project, corporate, regional, or industry levels. This paper addresses the issues of workforce training and allocation on construction projects. It presents a framework to optimize the investment in, and to make the best use of, the available workforce with the intent to reduce project costs and improve schedule performance. A linear program model, entitled the Optimal Workforce Investment Model, is built to provide an optimization-based framework for matching supply and demand of construction labor most efficiently through training, recruitment, and allocation. Given a project schedule or demand profile and the available pool of workers, the suggested model provides human resource managers a combined strategy for training the available workers and hiring additional workers. The input data to the proposed model consists of a certain available labor pool, cost figures for training workers in different skills, the cost of hiring workers, hourly labor wages, and estimates of affinities between the different considered skills. The objective of the model is to minimize labor costs while satisfying project labor demands. Results from application of the model to typical situations are presented, and recommendations for future developments are made.     

One-Dimensional Model for Multi-Barge Flotillas Impacting Bridge Piers

Abstract:   The serious consequence of barge-bridge collisions necessitates the study of barge impact loadings on bridges. This article introduces an elastoplastic spring-mass model for the analysis of multi-barge flotillas colliding with bridge piers at zero angle of attack. The model accounts for the essential factors pertaining to barge/flotilla impacts, such as pier geometry and stiffness, and dynamic interaction between barges. A method to identify the elastoplastic behavior of barge crushing is also presented. The proposed method generates impact force time-histories for a multitude of flotilla configurations in a matter of minutes, which is especially valuable in probabilistic analysis requiring many collision simulations. The results from this study are compatible with the respective impact time-histories produced by exhaustive finite element simulations. A bridge pier impacted by a three-barge and a 15-barge flotilla is studied.     

New Nonlinear Polyurethane: Synthesis and Optical Properties

The compound 3,4-di-(2′-hydroxyethoxy)-4-diphenyl-hydrazonomethyl was synthesized from the reaction of 3,4-dihydroxy-4-diphenyl-hydrazonomethyl with 2–chloro–1–ethanol in a 1:2 mole ratio, and subsequent reaction with methylene–4,4′–diphenyldiisocyanate (MDI) to produce the new nonlinear polyurethane. The chemical structures of the resulting monomers and polymer were characterized by CHN analysis, FT-IR, ¹H-NMR, and UV-Vis spectroscopy. The nonlinear optical properties of new polyurethane have been studied via second harmonic generation (SHG). The values of electro-optic coefficient d₃₃ and d₃₁ of the poled polyurethane film were 6.62 × 10^?8 and 3.05 × 10 ^?8 esu, respectively. Thermal behavior of this polyurethane was studied by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC).