An external surface coating to protect concrete and steel from aggressive environments

Carbonation and chloride ions are known to be the two major factors responsible for the premature corrosion of steel reinforcement in concrete. Surface coatings on concrete can provide an effective and efficient protection for both concrete and the steel embedded in it, and can enhance the long-term durability of concrete materials and concrete structures exposed to aggressive environments. In practice, concrete is often cracked, and the crack-bridging ability of coatings is an important factor to be considered in evaluating their performance characteristics. Four different surface coatings were evaluated for their crack-bridging ability by tests of exposure to ozone and ultraviolet light, and for their ability to control chloride penetration and steel protection by accelerated wet-dry or continuous salt spray tests. From these results, a highly elastic acrylic rubber coating was chosen for further long-term stability tests. The data presented show conclusively that the acrylic rubber coating can prevent penetration of water, air and chloride ions, and ensure the long-term durability of steel embedded in concrete both when the concrete is free of chlorides and when it is contaminated with sodium chloride up to 1% of the mortar matrix. At high levels of chloride in the concrete, a high cover is also essential if the benefits of the surface coating are to be fully realized, and long-term serviceability of the concrete structure is to be ensured.     

Static indentation and impact behaviour of GRP pultruded sections

Static indentation and dropweight impact tests have been performed on three pultruded sections of glass fibre/polyester resin laminates using an instrumented test rig. Damage in the form of cracking of the lower surface has been related to permanent indentation of the contact surface. This damage relationship is independent of flexural stiffness for static loading but dependent on flexural stiffness for impact conditions. Backface cracking has been assessed in terms of residual compression and the results indicate that static loading is more severe than impact.     

Determination of physicochemical properties of some fatty acid methyl esters by gas liquid chromatography

Physicochemical data such as vapor pressures (p⁰), heats of vaporization (ΔH_v), activity coefficents at infinite dilution (γ^∞) and excess partial molar entropy (ΔS _e ⁰ ) are considered important for conducting unit processes and designing reactor equipment. Scanty information regarding such data is available in the literature for the higher fatty acid methyl esters. The objective of this research was to determine the physicochemical properties of higher fatty acid methyl esters (C₁₁–C₂₃) by a gas-liquid chromatographic technique with SE-30 and diethylene glycol adipate as stationary phases. Correlations between carbon numbers and various thermodynamic properties have indicated definite trends, which could be useful in predicting the properties of unknown fatty acid methyl esters. The data generated may be useful to chemical engineers in the construction of storage tanks, solvent extractors and distillation columns. IICT communication no. 2993.     

Recursive-in-order least-squares parameter estimation algorithm for 2-D noncausal Gaussian Markov random field model

We present in this paper a recursive-in-order least-squares (LS) algorithm to compute efficiently the parameters of a 2-D Gaussian Markov random field (GMRF) model. The algorithm is based on the fact that the least-squares estimation of the parameters of a 2-D noncausal GMRF model is consistent and the coefficient matrix in the normal equation has near-to-block-Toeplitz structure. Hence, it has a Levinson-like form for the updating of model parameters by introducing auxiliary variables. Moreover, this paper proposes the concept ofrecursive path for 2-D recursive-in-order algorithms, and points out that there exists a tradeoff between fast computation of the parameters and accurate choice of model support; a compromise recursive path is then suggested where the orders change alternately in two directions. The computational complexity of the developed algorithm is analyzed, and the results show that the algorithm is more efficient when either the image size or the model support is larger. It is found that the total number of multiplications (mps) involved in the new algorithm is only about 14% of that in the conventional LS method when the image size is 512 × 512 and the neighbor set of the model is a 17 × 17 window. Computer simulation results using the recursive-in-order algorithm developed in this paper and the conventional LS method are given to verify the correctness of the new algorithm.This work was supported by the NSERC under Grants A-4070 and A-7739, and by the FCAR, Grant H-70.     

Sensitivity invariants for active lumped/distributed networks

The invariant nature of the sum of the sensitivities of network functions of a general linear active lumped/distributed network is established. Results of Holt and Fidler on summed sensitivities are extended to networks containing tapered lines, v.c.t.s and c.v.t.s simultaneously.     

The strength and deformation characteristics of high early strength structural concrete

There are many possible structural applications of concrete with a compressive strength of about 100 N/mm². In practice, however, the development of early strength is far more important, but the combination of both can bring considerable economic benefits to the construction industry. Tests are reported on the strength and deformation characteristics of high early strength structural concrete. Tests using an ultra fine cement with expanded slate lightweight aggregate and granite produced concretes with a strength of 30–40 N/mm² and 60–70 N/mm² respectively in 24 hours. Tests with aluminous cement produced better aggregate-matrix bond and developed strengths of about 95 N/mm² in the same time. Equations are presented to predict the tensile strength and elasticity of the high early strength concrete. It is shown that the rapid hydration results in a high rate of shrinkage and creep initially but the long-term deformation characteristics are comparable to normal concrete. It is suggested that it is worth exploring methods to minimise the effects of conversion.     

Multiprocessor pyramid architectures for bottom-up image analysis

This paper describes three hierarchical organizations of small processors for bottom-up image analysis:pyramids, interleaved pyramids, and pyramid trees. Progressively lower levels in the hierarchies process image windows of decreasing size. Bottom-up analysis is made feasible by transmitting up the levels quadrant borders and border-related information that captures quadrant interaction of interest for a given computation. The operation of the pyramid is illustrated by examples of standard algorithms for interior-based computations (e.g., area) and border-based computations of local properties (e.g., perimeter). A connected component counting algorithm is outlined that illustrates the role of border-related information in representing quadrant interaction. Interleaved pyramids are obtained by sharing processors among several pyramids. They increase processor utilization and throughput rate at the cost of increased hardware. Trees of shallow interleaved pyramids, calld pyramid trees, are introduced to reduce the hardware requirements of large interleaved pyramids at the expense of increased processing time, without sacrificing processor utilization. The three organizations are compared with respect to several performance measures.     

Molecular transport of n‐alkanes through diol chain‐extended polyurethane membranes

Molecular transport of n‐alkanes was investigated by calculating sorption, diffusion, and permeation of liquids through the diol chain‐extended polyurethane (PU) membranes in the temperature interval 25–60°C. Sorption experiments were performed gravimetrically. Diffusion coefficients were calculated from Fick's equation. These results showed a dependency on the nature and size of interacting n‐alkane molecules as well as morphology of the chain‐extended PUs. Transport kinetics followed an anomalous trend. Using the temperature‐dependent transport parameters, activation energies were calculated for diffusion and permeation processes using an Arrhenius equation. The van't Hoff relationship was used to obtain enthalpy and entropy of sorption. Concentration profiles of liquids through PU membranes were computed using Fick's equation, solved under appropriate initial and boundary conditions. A correlation was attempted between transport properties of liquids and physicomechanical properties of PU membranes. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 874–882, 2005