Namshik Ahn

Evaluating Topological Optimized Layout of Building Structures by Using Nodal Material Density Based Bilinear Interpolation

Abstract This study presents a boundary representation of Eulerian-type in order to achieve conceptual structural layouts of building structures by relieving material discontinuities of structural topology optimization in comparison with classical ones. According to the partition of unity concept, a bilinear interpolation can be employed by nodal densities and shape functions with the use of discretization of four-node square elements and then material properties, i.e. here, densities in finite elements are not constant but variational values. As a result, the improvement of material continuity can be established as optimal topologies, and numerical singularity and zigzag material boundaries which may occur in classical topology optimization design are relieved. Numerical applications verify the efficiency of this method by evaluating this conceptual structural layout approach for designing building structures.

Sulfate Attack According to the Quantity of Composition of Cement and Mineral Admixtures

The primary factors affecting concrete sulfate resistance are the chemical composition of the Portland cement, and the chemistry and quantity of mineral admixtures. To investigate the effect of those on the sulfate attack, the testing program involved several different mortar mixes using the standardized test, ASTM C1012. Four different cements were evaluated, including one Type I cement, two Type I-II cements, and one Type V cement. Mortar mixes were also made with mineral admixtures, as each cement was combined with three different types of mineral admixtures. One Class F fly ash, one Class C fly ash, and one ground granulated blast furnace slag (GGBFS) were added in various percent volumetric replacement levels. Expansion measurements were taken and investigated with the expansion criteria recommended by ASTM.

Acid Resistance and Curing Properties for Green Fly Ash-geopolymer Concrete

Global warming has recently become a topical issue throughout the world, and the cement industry is widely seen as one of the prominent factors responsible for it. Therefore, the development of new binders with enhanced environment and durability performance is needed. In this regard, geopolymer technology is a breakthrough development as an alternative to Portland cement. In this study, such properties of geopolymer concrete as curing temperature, curing time, rest period before curing, and acid resistance are emphasized. Geopolymerization needs energy and time to occur, and higher curing temperatures result in larger compressive strength, while longer curing times result in higher compressive strength. For geopolymer concrete, the time for hardening can be extended up to 5 days. Geopolymer concrete shows good acid resistance. As products of geopolymerization have no sulfate, acid or salt attack mechanism, geopolymer concrete can be a good substitute for traditional building materials, and finding renewable materials to satisfy the increasing demand for building structures will eventually be a major issue.

A Study on Strength of Shear Stud in High Strength Concrete

For design of composite concrete members, the behavior between two materials; concrete and steel is considered significantly. And shear studs are generally used for effective composite action. The purpose of this paper are to propose an equation of strength of shear stud embedded in high strength concrete, and to evaluate the validity by comparing with the current design codes and existing proposed equations. The equation was proposed by regression analysis based on the test results of steel pipe encased composite members manufactured by considering diameter of shear stud and ratio of diameter to height of shear stud as variables. The comparisons of the test results with the design codes and existing proposed equations showed that KBC2009 and the equation of Cheong et al. have big error; 48.78% and 28.03%. And the equation proposed in this paper indicate relatively smaller error of 3.69%. It indicated that the proposed equation has higher accuracy for calculating the strength of shear stud embedded in high strength concrete.

Better Interpretation Techniques for the Alkali-silica Reaction of Aggregates

In the construction industry today, there is a need for improved testing procedures capable of accurately predicting the susceptibility of aggregates to the alkali-silica reaction (ASR). These new procedures will permit the use of some aggregates that have been excluded in the past on the basis of being classified as reactive. Effective mitigation methods will permit the economic use of reactive aggregates that would normally be excluded. Increasing the quality of the aggregate sources the target of this research, the results of which will help manufacturers sell more products while cutting prices for consumers. By modifying ASTM C1260, we expanded the length of testing from 14 to 56 days, changed the water content of the mixing proportion with the water to cement ratio controlled at 0.47, the molarity of the curing solution, and used different interpretation methods, specifically Avrami′s model and the polynomial fit procedures. If the results of this research enabled even 25 percent of these materials to be used, the increased volume available for use would increase substantially.

An Experimental Study of the Effects of Chloride Ions on the Corrosion Performance of Polymer Coated Rebar in Concrete Pavement

Construction materials have been greatly improved in recent years and reinforced concrete is no exception. However, corrosion inside reinforced concrete continues to be a primary problem in the construction field. This paper considers the corrosion rate of special kinds of steel inside reinforced concrete pavement. Corrosion is caused by chloride ions present in the deicing salts used to melt snow on pavement. These chloride ions cause endosmosis in the structure of steel and eventually destroy it. In order to prevent such corrosion, layers have been created to protect the steel. The authors use the polarization resistance method to check the ability of such barriers. The variables of this experimental study were four kinds of steel: black rebar, stainless steel 304 clad rebar, galvanized coated rebar A and galvanized coated rebar B. According to the test result, black steel corroded much more than the others with the presence of salt. Although the galvanized A rebar corroded more slowly than the galvanized B rebar in Ca(OH)2 plus the threshold amount NaCl, the corroding resistance of the galvanized B rebar was better in the presence of 3.5% NaCl. However, of the four kinds of steel, the pure stainless steel 304 clad rebar proved to be the best in terms of corrosion resistance.