• Computers and Concrete
• /
• v.21 no.1
• /
• pp.87-94
• /
• 2018

This paper presents the results of an experimental study to investigate the influences of high temperatures on the mechanical properties of concrete containing recycled fine aggregate. A total of 150 concrete prisms ($100{\times}100{\times}300mm$) and 150 concrete cubes ($100{\times}100{\times}100mm$) are cast and heated under five different temperatures ($20^{\circ}C$, $200^{\circ}C$, $400^{\circ}C$, $600^{\circ}C$, $800^{\circ}C$) for test. The results show that the mass loss, compressive strength, elastic modulus, splitting tensile strength of concrete specimens containing recycled fine aggregate decline significantly as the temperature rise. At the same temperature, the compressive strength, splitting tensile strength, elastic modulus of concrete specimens containing recycled coarse aggregate and recycled fine aggregate (RHC) is lower than that of concrete specimens containing natural coarse aggregate and recycled fine aggregate (RFC). The shape of stress-strain curves of concrete specimens at different temperatures is different, and the shape of that become flatter as the temperature rises. Normal concrete has better energy absorption capacity than concrete containing recycled fine aggregate.

• Advances in materials Research
• /
• v.5 no.1
• /
• pp.21-34
• /
• 2016

Fire is one of the most destructive powers to which a building structure can be subjected, often exposing concrete elements to elevated temperatures. The relative properties of concrete after such an exposure are of significant importance in terms of the serviceability of buildings. Unraveling the heating history of concrete and different cooling regimes is important for forensic research or to determine whether a fire-exposed concrete structure and its components are still structurally sound or not. Assessment of fire-damaged concrete structures usually starts with visual observation of colour change, cracking and spalling. Thus, it is important to know the effect of elevated temperatures on strength retention properties of concrete. This study reports the effect of elevated temperature on the mechanical properties of the concrete specimen with polypropylene fibres and cooled differently under various regimes. In the heating cycle, the specimen were subjected to elevated temperatures ranging from $200^{\circ}C$ to $800^{\circ}C$, in steps of $200^{\circ}C$ with a retention period of 1 hour. Then they were cooled to room temperature differently. The cooling regimes studied include, furnace cooling, air cooling and sudden cooling. After exposure to elevated temperatures and cooled differently, the weight loss, residual compressive and split tensile strengths retention characteristics were studied. Test results indicated that weight and both compressive and tensile strengths significantly reduce, with an increase in temperature and are strongly dependent on cooling regimes adopted.

• Journal of the Korean Ceramic Society
• /
• v.39 no.10
• /
• pp.963-969
• /
• 2002

In this studies, methly celluloes was used as antiwashout admixture and when considering the physical properties and economical efficiencies of Underwater Concrete as the results of making an experiencing slump flow, flow loss, setting time, suspension and pH also compressive strength and underwater/an air compressive strength ratio according to the adding amount changes 5, 7, 9, 11 kg/$m^3$ to Underwater Concrete of melamine superplasticizer, the using amount of melamine superplasticizer in Underwater Concrete approximately represents 9 kg/$m^3$.

• Advances in concrete construction
• /
• v.5 no.4
• /
• pp.313-330
• /
• 2017

Geopolymer is a sustainable concrete, replaces traditional cement concrete using alternative sustainable construction materials as binders and alkaline solution as alkaline activator. This paper presents the strength characteristics of geopolymer concrete (GPC) developed with fly ash and GGBS as binders, combined Sodium silicate ($Na_2SiO_3$) and Sodium Hydroxide (NaOH) solution as alkaline activators. The parameters considered in this research work are proportions of fly ash and GGBS (70-30 and 50-50), curing conditions (Outdoor curing and oven curing at $600^{\circ}C$ for 24 hours), two grades of concrete (GPC20 and GPC50). The mechanical properties such as compressive strength, split tensile strength and flexural strength along with durability characteristics were determined. For studying the durability characteristics of geopolymer concrete 5% $H_2SO_4$ solutions was used and the specimens were immersed up to an exposure period of 56 days. The main parameters considered in this study were Acid Mass Loss Factor (AMLF), Acid Strength Loss Factor (ASLF) and products of degradation. The results conclude that GPC with sufficient strength can be developed even under Outdoor curing using fly ash and GGBS combination i.e., without the need for any heat curing.

• Proceedings of the Korea Concrete Institute Conference
• /
• 1997.04a
• /
• pp.335-340
• /
• 1997

The mineral admixtures, ground granulated blast furnace slag (GSB) and fly ash (FA), were mixed with ordinary portland cement(OPC) in order to reduce temperature rise and slump loss in concrete. In according to concrete replaced with 30% of GBS, the compressive strength of that developed to 574 kg/$\textrm{cm}^2$ at age of 28days and maximum temperature decreased to the extent of $5^{\cire}C$. When GBS and FA are mixed with concrete, it can be estimated that mix proportions of them have to be taken into consideration.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2008.11a
• /
• pp.613-616
• /
• 2008

Many researches on alkali-activated concrete that does not need the presence of cement as a binder have been carried out recently. Instead, the source of material such as fly ash and blast slag, that are rich in Silicon(Si) and Aluminium(Al), are activated by alkaline liquids to produce the binder. Hence concrete with no cement is effect reduction of CO$_2$ gas. In this study, we investigated the influence of the workability and compressive strength of mortar on water reducing agent, alkaline activator and curing method in oder to develop cementless blast slag based alkali-activated mortar. In view of the results, we found out that the flowability of mortar was lowered as increasing to mole concentration of NaOH, but not large the loss of flowability to 9M NaOH, most of water reducing agent was not effect. The compressive strength was improved as increasing to mole concentration of NaOH, was the most effect in 9M NaOH. The curing temperature and curing conditions on compressive strength of blast slag based alkali-activated mortar didn't influence.

• KCI Concrete Journal
• /
• v.11 no.3
• /
• pp.29-43
• /
• 1999

The effects of superplasticizers on fresh and hardened concrete were investigated. The experimental program included tests on the workability and slump loss, bleeding, setting time, air content, compressive, tensile and flexural strength, permeability, shrinkage, freeze-thaw durability and creep deformation. Properties of superplasticized concrete were compared with those of conventional and base concretes. Superplasticizers were observed to have an appreciable fluidifying action in fresh concrete. They permitted a significant water reduction while maintaining the same workability. Bleeding of superplasticized concrete was much lower than that of conventional concrete of the same consistency. This indicates that the use of superplasticizers did not affect the tendency of segregation of fresh concrete. The compressive, tensile, and flexural strengths of superplasticized concrete were significantly higher than those of conventional concrete. The permeability and drying shrinkage and creep of superplasticized concrete were less than those of conventional concrete, but there were no significant differences between base and superplasticized concrete. Compared with base concrete, non-air-entrained superplasticized concrete had slightly higher freeze-thaw durability. and superplasticized concrete with an appropriate amount of entrained air Eave even better resistance to freezing and thawing.

• Journal of the Korean Wood Science and Technology
• /
• v.29 no.2
• /
• pp.69-75
• /
• 2001

This study was carried out to investigate the properties of woodceramics made from thinned logs of Cryptomeria japonica. In order to find the effect of steam injection time on the woodceramics fabricated with boards, boards were made with the non-steamed treatment and steamed treatment 1, 5, 10 min. at $250^{\circ}C$. The percentage of weight loss was proportional to the increased density of board The reducing rate of length and thickness, however, decreased with increasing density of board. The rate of weight loss, length and thickness reduction in non-steamed board were slightly higher than those of steamed board. When the resin impregnation rate increased, the bending strength and compressive strength of woodceramics had a tendency to increase. The bending strength and compressive strength of woodceramics in non-steamed board was higher than those of steamed board. But there was little difference between dimensional and strength properties of woodceramics and steam injection time of board.

• Advances in concrete construction
• /
• v.10 no.5
• /
• pp.443-454
• /
• 2020

In recent years, many studies have been done on the performance of concrete containing glass powder (GP). For the purpose of widespread use of GP in concrete mixes, a knowledge of the performance of such a mixture after a fire is essential for the perspective of structural use. This research work was carried out to evaluate the performance of High Performance Concrete (HPC) made with GP after being exposed to elevated temperature. The studied mixtures include partial replacement of cement by GP with up to 30%. The mechanical performance and structural alterations were assessed after high temperature treatment from 200℃ to 800℃. The mechanical performance was evaluated by testing the specimens to the compressive and tensile strength. In addition, the mass loss and the porosity were measured to notice the structural alterations. Changes in microstructure due to temperature was also investigated by the X-ray diffraction (XRD) and thermal gravimetric analyses (TGA) as well as porosity adsorption tests. The results of the concrete strength tests showed a slight difference in compressive strength and the same tensile strength performance when replacing a part of the cement by GP. However, after high temperature exposition, concrete with GP showed better performance than the reference concrete for temperature below 600℃. But, after heating at 800℃, the strength of the concrete with GP drop slightly more than reference concrete. This is accompanied by an important increase in mass loss and water porosity. After the microstructure analysis, no important changes happened differently for concrete with GP at high temperature except a new calcium silica form appears after the 800℃ heating.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.30 no.2C
• /
• pp.109-117
• /
• 2010

Gas hydrate dissociation can generate large amounts of gas and water in gas hydrate bearing sediments, which may eventually escape from a soil skeleton and form voids within the sediments. The loss of fine particles between coarse particles or collapse of cementation due to water flow during heavy or continuous rainfall may form large voids within soil structure. In this study, the effect of void formation resulting from gas hydrate dissociation or loss of some particles within soil structure on the strength of soil is examined. Glass beads with uniform gradation were used to simulate a gas hydrate bearing or washable soil structure. Glass beads were mixed with 2% cement ratio and 7% water content and then compacted into a cylindrical sample with five equal layers. Empty capsules for medicine are used to mimic large voids, which are bigger than soil particle, and embedded into the middle of five equal layers. The number, direction, and length of capsules embedded into each layer vary. After two days curing, a series of unconfined compression tests is performed on the capsule-embedded cemented glass beads. Unconfined compressive strength of cemented glass beads with capsules depends on the volume, direction and length of capsules. The volume and cross section formed by voids are most important factors in strength. An unconfined compressive strength of a specimen with large voids decreases up to 35% of a specimen without void. The results of this study can be used to predict the strength degradation of gas hydrate bearing sediments in the long term after dissociation and loss of fine particles within soil structure.