Hey-Zoo Hwang

Effects of Water-Binder Ratio and Fine Aggregate–Total Aggregate Ratio on the Properties of Hwangtoh-Based Alkali-Activated Concrete

Fifteen hwangtoh-based alkali-activated concrete mixes were tested to explore the significance and limitations of the development of cementless concrete without carbon dioxide emissions while maintaining various beneficial effects. Hwangtoh, which is a kind of kaolin, was incorporated with inorganic materials, such as calcium hydroxide, to produce a cementless binder. The main variables investigated were the water-binder ratio and fine aggregate–total aggregate ratio to ascertain the reliable mixing design of hwangtoh-based cementless concrete. The variation of slump with elapsed time was recorded in fresh concrete specimens. Mechanical properties of hardened concrete were also measured, including compressive strength gain, splitting tensile strength, moduli of rupture and elasticity, stress-strain relationship, and bond resistance. In addition, mechanical properties of hwangtoh-based cementless concrete were compared with those of ordinary portland cement (OPC) concrete and predictions obtained from the design equations specified in American Concrete Institute 318-05 and Comite Euro-International du Beton-Federation International de la Precontrainte for OPC concrete, wherever possible. Test results show that the mechanical properties of hwangtoh-based concrete were significantly influenced by the water-binder ratio and to less extend by fine aggregate–total aggregate ratio. Based on the measured mechanical properties and code provisions, it can be proposed that the hwangtoh-based alkali-activated concrete is practically applicable as structural concrete when the water-binder ratio is less than 40%.

Hydration Heat and Shrinkage of Concrete Using Hwangtoh Binder

In this paper, the applicability of Hwangtoh, as an alternative of cement paste, is investigated for the solution of internal heat and shrinkage caused by the hydration of cement paste. Several small-sized specimens of Hwangtoh and ordinary portland concrete (OPC) were compared as to compressive strength, heat of hydration, and shrinkage strain. Moreover, the applicability to the construction structures was reviewed through the test of large-size specimens. The 28-day compressive strength of Hwangtoh concrete (HBC), ranged 18 to 33 MPa, can reach that of OPC. Not only the maximun internal temperature of HBC was read about 1/4 of OPC as it is cured, but also its shrinkage decreased more than the OPC did. Therefore, Hwangtoh binder is more favorable than cement binder in terms of its hydration heat and shrinkage under the construction of concrete.

2-D DIGE and MS/MS analysis of protein serum expression in rats housed in concrete and clay cages in winter.

In a previous study, we examined the physiological responses of male Sprague–Dawley rats over a 4‐week exposure to concrete and clay cages. No general toxicological changes were observed in rats exposed to either of the two cage types in summer. Under winter conditions, however, various general toxicological effects were detected in rats housed in concrete cages, although rats housed in clay cages showed no such effects. The infrared thermographic examination indicated that skin temperature in the concrete‐housed rats was abnormally low, but not so in the clay‐housed rats. We examined proteomic changes in the serum of rats housed in winter in concrete and clay cages using two‐dimensional differential in‐gel electrophoresis and mass spectrometry/mass spectrometry. Five proteins were identified and quantitatively validated; all were cold stress‐induced, acute phase proteins that were either up‐regulated (haptoglobin) or down‐regulated (alpha‐1‐inhibitor III, alpha‐2u globulin, complement component 3, and vitamin D‐binding protein) in the concrete‐housed rats. These results suggest that the 4‐week exposure to a concrete cage in winter elicited a typical systemic inflammatory reaction (i.e. acute phase response) in the exposed rats.

Effect of Superplasticizers and Admixtures on the Fluidity and Compressive Strength Development of Cementless Mortar Using Hwangtoh Binder

This paper reports test results to assess the influence of superplasticizers and different admixture on the flow and compressive strength development of cementless mortar using developed hwangtoh binder. Test specimens were classified into four groups: series for I the mixing ratio of superplasticizers, series II for a kind and replacement level of admixtures according to the variation of water/hwangtoh binder ratio, series III for the specific surface area and replacement level of ground granulated blast-furnace slag and series IV for the replacement level of powered superplasticizer agent developed to improve slump loss of concrete. The proper replacement level of each admixture is proposed for enhancement the flow and compressive strength of the hwangtoh binder mortar.

Stress-Strain Relationship of Ca(OH)2-Activated Hwangtoh Concrete

This study examined the stress-strain behavior of 10 calcium hydroxide (Ca(OH)2)-activated Hwangtoh concrete mixes. The volumetric ratio of the coarse aggregate (V agg) and the water-to-binder (W/B) ratio were selected as the main test variables. Two W/B ratios (25% and 40%) were used and the value of V agg varied between 0% and 40.0%, and 0% and 46.5% for W/B ratios of 25% and 40%, respectively. The test results demonstrated that the slope of the ascending branch of the stress-strain curve of Ca(OH)2-activated Hwangtoh concrete was smaller, and it displayed a steeper drop in stress in the descending branch, compared with those of ordinary Portland cement (OPC) concrete with the same compressive strength. This trend was more pronounced with the increase in the W/B ratio and decrease in V agg. Based on the experimental observations, a simple and rational stress-strain model was established mathematically. Furthermore, the modulus of elasticity and strain at peak stress of the Ca(OH)2-activated Hwangtoh concrete were formulated as a function of its compressive strength and V agg. The proposed stress-strain model predicted the actual behavior accurately, whereas the previous models formulated using OPC concrete data were limited in their applicability to Ca(OH)2-activated Hwangtoh concrete.

A Study on the Method of Measurement of Heavy-Weight Floor Impact Sound Considering the Room Mode in Low Frequency Ranges

Most of receiving rooms for the measurement of floor impact sound have rectangular shapes with couple of meters of dimension, with reflective finishing, no furniture and no curtains. Modal overlaps in those conditions are the major reason for the low reproducibility, and as a matter of course, low credibility in measurement. Especially the standard sound source that is currently being used for measurement of heavy-weight floor impact sounds, would cause many social problems due to the excessive low-frequency energy created, within a range from 63 to 125 Hz, and is difficult to evaluate and measure. To solve this problem, space-time average SPL’s through combinations of rotating microphones was suggested in the preceding research. In this study, measurement method using rotating machine and fixed microphones were compared and analysed by the field measurement. The measurement method using rotating machine has good consistencies with average SPL of entire receiving room. This method is expected to reduce the measurement time and measurement deviation as well as to support building regulation/standard development in Korea for Korean apartment buildings.