• Proceedings of the Korea Concrete Institute Conference
• /
• 1999.10a
• /
• pp.163-166
• /
• 1999

In this paper, strength development of concrete using blast-furnace slag cement(BSC) and ordinary portland cement(OPC) are discussed under varius W/C and curing temperatures. According to the experimental results, strength development of BSC concrete is lower than that of OPC concrete in low temperature at early age and maturity. In high curing temperature, BSC concrete has higher strength development than that of low temperature regardless of the elapse of age and maturity. BSC has much effect on the strength development of concrete at the condition of mass concrete, hot weather concreting and the concrete products with the steam curing, which is influenced by high temperature.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2005.11a
• /
• pp.707-710
• /
• 2005

This experimental study investigate temperature dependency affecting setting and strength development of concrete using mineral admixtures such as CKD, FA and BS. For the properties of setting at $5^{\circ}C$, setting time of concrete with mineral admixture was delayed about $3\~14$ hour compared with that of plain concrete. Use of CKD had a desirable effect on reducing setting retard under $5^{\circ}C$ because of $CaCO_3$ of CKD while use of FA and BS retarded setting time greatly. For compressive strength under $5^{\circ}C$, concrete with CKD had the most compressive strength in early age compared with the other mineral admixtures but exhibited slight strength loss in $-5^{\circ}C$ at 28days. Especially, concrete with FA and BS was observed in early stage at low curing temperature because of strength loss remarkably in $-5^{\circ}C$.

• Journal of the Korea Concrete Institute
• /
• v.13 no.5
• /
• pp.447-456
• /
• 2001

Many investigators have tried to represent the nonlinear behavior of stress-strain relationship of concrete using mathematical curves. Most of empirical expressions for stress-strain relationship, however, have focused on old age concrete, and were not able to represent well the behavior of concrete at an early age. Where wide understanding on the behavior of concrete from early age to old age is very important in evaluating the durability and service life of concrete structures. In this paper, effect of 5 different strength levels and ages of from 12 hours to 28 days on compressive stress-strain relationship was observed experimentally and analytically. Tests were carried out on $\phi$100${\times}$200mm cylindrical specimens water-cured at 20${\pm}$3$^{\circ}C$. An analytical expression of stress-stain relationship with strength and age was developed using regression analyses on experimental results. For the verification of the proposed model, the model was compared with present and existing experimental data and some existing models. The analysis shows that the proposed model predicts well experimental data and describes well effect of strength and age on stress-strain relationship.

• Proceedings of the Korean Institute of Building Construction Conference
• /
• 2003.05a
• /
• pp.99-102
• /
• 2003

This study discusses the determination of removal time of forms with early strength development in high strength concrete. According to the results, as W/B increases by 10％, the setting time is shortened by about 2 hours. The time when compressive strength of 8 MPa is gained is about 20 hours. Bond strength between form and concrete is highest around final setting time, but decreases drastically after that. Amount of concrete sticking on the form is large before setting, but after that, it is little. The rebound value of P type schmidt hammer is measured faster by 2-3 hours than compressive strength. It is also confirmed that the removal of forms is possible when the rebound value of P type schmidt hammer is more than 34

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.22 no.2
• /
• pp.154-160
• /
• 2018

Cement industries are considered key industries for reducing carbon emissions, and efforts are off the ground to reduce the use of cement in the concrete sector. As a part of this effort, research is off the ground to utilize a large amount of industrial by-products that can be used as a substitute for a part of cement. Concrete using industrial by-products has advantages such as durability, environment friendliness and economical efficiency, but there are problems such as retarding and early-age strength deterioration. Therefore, this study aimed to reduce the use of cement and solve the problem of early-age strength deterioration while using fly ash, which is an industrial by-product. Accordingly, it was confirmed that the strength was improved at all ages irrespective of curing temperature by accelerating the hydration reaction by using high fineness cement. Subsequently, high fineness cement was partially replaced with fly ash and the strength development characteristics were examined. As a result, it was possible to exhibit strength equal to or higher than ordinary portland cement even at the early age. Also, it was confirmed that even when the fly ash is replaced by 30%, it is possible to shorten the time for dismantling the forms of vertical and horizontal members.

• Journal of the Korean Ceramic Society
• /
• v.53 no.1
• /
• pp.18-23
• /
• 2016

The development of a binder system with a lower carbon footprint as an alternative to Portland cement has been intensely researched. In the present study, alkali-activated fly ash exposed to carbon dioxide at an early age was characterized in compressive strength tests and by MIP, XRD and FT-IR analyses. The compressive strength of carbonated specimens experienced a dramatic increase in comparison to uncarbonated specimens. The microstructural densification of the carbonated specimens was evidenced by MIP. The XRD pattern showed peaks assigned to nahcolite, indicating that the pH was lower in the carbonated specimens. Under the carbon dioxide-rich environment, the aluminosilicate gel reached a more Si-rich state, which improved the mechanical properties of the alkali-activated fly ash.

• Journal of the Korea Concrete Institute
• /
• v.12 no.5
• /
• pp.59-68
• /
• 2000

A series of experiments were performed to investigate the strength characteristics of concrete which contain air cooled blast-furnace slag as coarse aggregate. The slag is a by product of GISC. The experimental conditions are varied with three different W/C(45%, 50%, 55%) and the weight of water and S/a are constant. The strength properties of the concrete at 7days, 28days, 90days are examined. Also the same strength properties are examined for the normal concrete which contain river gravel and crushed stone respectively as coarse aggregate. As the comparison results of the strength properties, it was found that the compressive strength development of concrete containing blast-furnace slag is better than that of concrete using river gravel at early age, however this is adversely at long-term age, and the tensile and flexural strength of the concrete were not nearly affected by water-cement ratio.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2003.05a
• /
• pp.737-740
• /
• 2003

In this study, the influence of cement factor on the early strength gain and the other properties of concrete is discussed. According to the result, the setting time is faster in order of alumina cement(AC), high-early-strength cement(HSC) and ordinary Portland cement(OPC), and when OPC are replaced with HSC and AC, the final setting time is faster than when only OPC is used. At 10% replacement of AC, the instant setting happens. As the particle of cement is minute, setting time is shortened. As the properties of hardened concrete, the time when compressive strength of 5㎫, which the form can be removed, is gained is about 18 and 16 hours in the case of OPC and HSC respectively, and in the case of AC, it is about 5 hours. It also shows 16 hours at the replacing ratio of HSC of 50%, and 26 and 72 hours at the replacing ratio of AC of 5 and 10% respectively. And it shows 21, 16 and 12 hours with variation of fineness of cement, so early strength gain is fast with an increase of fineness. The coefficient of correlation between compressive strength and the rebound value is over 0.97, is very favorable. Therefore, if the rebound value of P type Schmidt hammer is more than 25, it is thought that the side forms can be removed.

• Computers and Concrete
• /
• v.24 no.2
• /
• pp.151-158
• /
• 2019

The sustainable development principle of replacing natural resources with renewable material is an important research topic. In this study, waste LCD (liquid crystal display) glass powder was used to replace cement (0%, 10%, 20% and 30%) through a volumetric method using three water-binder ratios (0.47, 0.59, and 0.71) to make cement mortar. The compressive strength was tested at the ages of 7, 28, 56 and 91 days. The test results show that the compressive strength increases with age but decreases as the water-binder ratio increases. The compressive strength slightly decreases with an increase in the replacement of LCD glass powder at a curing age of 7 days. However, at a curing age of 91 days, the compressive strength is slightly greater than that for the control group (glass powder is 0%). When the water-binder ratios are 0.47, 0.59 and 0.71, the compressive strength of the various replacements increases by 1.38-1.61 times, 1.56-1.80 times and 1.45-2.20 times, respectively, during the aging process from day 7 to day 91. Furthermore, a prediction model of the compressive strength of a cement mortar with waste LCD glass powder was deduced in this study. According to the comparison between the prediction analysis values and test results, the MAPE (mean absolute percentage error) values of the compressive strength are between 2.79% and 5.29%, and less than 10%. Thus, the analytical model established in this study has a good forecasting accuracy. Therefore, the proposed model can be used as a reliable tool for assessing the design strength of cement mortar from early age test results.

• Structural Engineering and Mechanics
• /
• v.74 no.6
• /
• pp.747-756
• /
• 2020

High-strength concrete (HSC) generally is made with high amount of cement which may release large amount of hydration heat at early age. The hydration heat will increase the internal temperature of slab and may cause potential cracking. In this study, slab specimens with a dimension of 600 × 600 × 100 mm were cast with concrete incorporating silica fume for test. The thermistors were embedded in the slabs therein to investigate the interior temperature development. The test variables include water-to-binder ratio (0.25, 0.35, 0.40), the cement replacement ratio of silica fume (RSF; 5 %, 10 %, 15 %) and fly ash (RFA; 10 %, 20 %, 30 %). Test results show that reducing the W/B ratio of HSC will enhance the temperature of first heat peak by hydration. The increase of W/B decrease the appearance time of second heat peak, but increase the corresponding maximum temperature. Increase the RSF or decrease the RFA may decrease the appearance time of second heat peak and increase the maximum central temperature of slab. HSC slab with the range of W/B ratio of 0.25 to 0.40 may occur cracking within 4 hours after casting. Reducing W/B may lead to intensive cracking damage, such as more crack number, and larger crack width and length.