Papers by Keyword: Transport Mechanism

Abstract: Concrete is widely used construction material for the development of built environment which consumes huge amount of cement, around 4.3 billion metric ton all over the world. Reinforced concrete construction exposed to harsh environment such as chloride bound air causes deterioration in concrete through its pore structure by corroding the steel bar. The use of pozzolanic material i.e. metakaolin (MK), fly ash (FA), silica fume (SF), nano silica (NS) can be used as partially cement replacing material which not only reduces the pores in concrete but improves the mechanical, durability properties and microstructure of concrete. This paper reviews various transport mechanisms involved in ingress of deleterious material and incorporation of MK, FA and NS in concrete and their effects on concrete mechanical and durability properties. However, the research work provides an extended approach to evaluate combine effect using MK, FA, and NS and to produce a concrete with more refined pore structure for aggressive environment.

Abstract: When dealing with a specific development issue, designers have at their disposal a wide range of skills and their implicit knowledge, enabling them to conceptualize the appropriate solution pertaining to the problem. In developing and applying these solutions, the efficiency of the designers is often dependent on their appropriate use of analysis and creativity skills, their experience, as well as the existing knowledge stored in the company or other accessible databases. This paper presents a case study on a containers transport mechanism in order to highlight the activities, used tools and the advantages considered for the functional design based on functional-constructive knowledge stored in databases as a main phase of a new advanced product design process.

Abstract: Abstract. Impedance spectroscopies were used to investigate the electrical properties of spinel Ni_0.3Zn_0.7Fe₂O₄ (NZF) ceramics. Measurement was done using NOVO Dielectric Spectrometer from frequency 0.01 Hz to 3 x 10⁶ Hz at temperature 30°C to 200°C. Resistivity response phenomena had been observed in sample sintered at 1100°C and carriers involved are mainly due to electron hopping mechanism between n-type and p-type carriers. The high and low response of grain and grain boundary regions were determined by plotting imaginary part versus real part of resistivity. An equivalent RC circuit of the experimental result had been constructed using a model that had been proposed by Hill and Pickup (1985). The model consists of parallel combination of 2 Havriliak-Negami (1966) model, resistivity and dielectric constant where ρ = 5.79 x 10⁶ Ωm and ε = 4.45. It is found that 0.40 ± 0.01 eV, 0.14 ± 0.01 eV and 0.13 ± 0.01 eV and 0.38 ± 0.01 eV (extrinsic region) and 0.50 ± 0.01 eV (intrinsic region) for ac and dc activation energy respectively by using Arrhenius plot.

Abstract: The development of new materials for specific applications is an increasing field in the construction industry, so is the employment of nanotechnology for this goal. When poly(vinyl alcohol) (PVA) is added to a Portland cement mortar, a film is formed in between the hydration products. This film has low elasticity modulus and high tensile strength and it enhances the mortar’s mechanical properties in the fresh and hardened states. The addition of nano montmorillonites (MMT) gives the polymer a better compatibility with the cement matrix. In this work, the changes in the microstructure of Portland cement mortars modified with PVA and PVA with MMT are assessed by means of transport of fluids capacity as an indicator. The reference is a standard mortar according to EN 196-1. The parameters measured are: weight loss under drying and air permeability. Complementary measures, such as compressive and flexural strengths and drying shrinkage have also been performed. From the obtained results, it can be concluded that the inclusion PVA + MMT to Portland cement mortar doesn’t affect the microstructure, when compared with Portland cement mortar with PVA, and even increase its tensile strength.

Abstract: Hardened cement paste and concrete are porous materials. Most engineering properties of hardened cement pastes and concrete, such as strength, shrinkage, permeability, etc., are influenced or controlled by their pore structure characteristics. The ingress of chloride ion into concrete can cause steel corrosion and damage of steel reinforced concrete structure. This paper reviews the pore structure characteristics and transport mechanisms of chloride ion, such as hydrostatic advection, capillary suction, diffusion, thermal migration and electrical migration, in hardened cement pastes and concrete.