• 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.

• Proceedings of the Korea Concrete Institute Conference
• /
• 1995.10a
• /
• pp.229-233
• /
• 1995

In this study we have the properties of drying shrinkage crack of hardened cement mortar using admixtures. The drying shrinkage cracking test process has been examined by the restrained drying shrinkage strain by restraining rate measuring properties of strain-with- restraint by JIS original proposal and keeps a flow value of mortar about 100$\pm$5%. The results show that the usage of shrinkage reducing agent 1.5% was effective on the control of drying shrinkage in OPC and CP by restraining rate 20% and strain-with-restraing 20~30 $\mu$, the usage of expansion agent 0.45% was effective by restraining rate 50~60% and strain-with-restraint 40~80$\mu$, and the effectiveness was increased with shrinkage reducing agent. Also. admixtures such as Flyash, CP and NC reduced restrained shrinkage and drying shrinkage cracking and more with shrinkage reducing agent

• Proceedings of the Korea Concrete Institute Conference
• /
• 2005.05b
• /
• pp.313-316
• /
• 2005

In the recent design of high ductile fiber-reinforced cementitious composite ECC, which exhibits tensile strain-hardening behavior in the hardened state, optimizing both processing mechanical properties for specific applications is critical. This study introduced a method to develop useful ECCs in field, which possess the different fluid properties to facilitate diverse types of processing (i.e., self-consolidating or spray processing). Control of rheological modulation was regarded as a key factor to allow the performance of the desired processing, while retaining the ductile material properties. To control the rheological properties of the composite, we first determined basic ECC compositon, which is based on micromechanics and steady-state cracking theory. The stability and consequent viscosity of suspensions were, then, mediated by optimizing dosages of chemical and mineral admixtures. The rheological properties altered by this approach were revealed to be effective in obtaining ECC hardened properties, allowing us to readily achieve the desired function of the fresh ECC.

• Proceedings of the Korea Concrete Institute Conference
• /
• 1995.10a
• /
• pp.56-62
• /
• 1995

In this study, the properties of super flowing cocrete containing gly ash were experimentally investigated and compared with those of ordinary concrete. Tests were carried out on five types of super flowing concrete mixes containing fly ash and three types of ordinary concrete mixes without fly ash. Flow test, O-funnel test, box test, Ltype thest and slump test were carried out to obtain the properties for the workability of fresh concrete. Compressime strength, splitting tensile strength, modulus of elasticity. creep and shrinkage test were also obtained as the mechanical properties of hardened concrete. In fresh concrete, it was found that super flowing concrete had excellent workability and flowability compared with ordinary concrete, and the volume ratio of coarse aggregate to concrete volume greatly influenced flowability. Super flowing concrete also had good mechanical properties at both early and late ages with compressive strengths reaching as high as 40 MPa at 28 days. The creep deformation of super flowing concrete investigated were relatively lower than that of ordinary concrete.

• Computers and Concrete
• /
• v.21 no.2
• /
• pp.199-207
• /
• 2018

With the development of concrete technology, producing concrete products that have the ability to flow under their own weights and do not need internal or external vibrations is an important achievement. In this study, assessments are made on using travertine, marble and limestone rock flours in self-compacting lightweight concrete (SCLC). In fact, the effects of these powders on plastic and hardened phases of SCLC are studied. To address this issue, concrete mixtures with water to cementitious materials ratios of 0.42 and 0.45 were used. These mixtures were made with 0 and 10% silica fume (SF) replacement levels by cement weight. To achieve lightweight concrete, lightweight expanded clay aggregate (Leca) with the bulk density of about $520kg/m^3 $was utilized. Also two kinds of water were consumed involving tap water and magnetic water (MW) for investigating the possible interaction of MW and rock flour type. In this study, 12 mixtures were studied, and their specific weights were in the range of $1660-1692kg/m^3$. To study the mixtures in plastic phase, tests such as slump flow, J-ring, V-funnel and U-box were performed. By using marble and travertine powders instead of limestone flour, the plastic viscosities and rheology were not changed considerably and they remained in the range of regulations. Moreover, SCLC showed better compressive strength with travertine, and then with marble rock flours compared to limestone powders. According to the results of the conducted study, MW showed better performance in both fresh and hardened phases in all the mixes, and there was no interaction between MW and rock flour type.

• Journal of the Korea Concrete Institute
• /
• v.18 no.2 s.92
• /
• pp.189-198
• /
• 2006

The composition of most engineering materials is heterogeneous at some degree. It is simply a question of scale at which the level of heterogeneity becomes apparent. In the case of cementitious granular materials such as concrete the heterogeneity appears at the mesoscale where it is comprised of aggregate particles, a hardened cement paste and voids. Since it is difficult to consider each separate particle in the topological description explicitly, numerical models of the meso-structure are normally confined to two-phase matrix particle composites in which only the larger inclusions are accounted for. 2-D and 3-D concrete blocks(Representative Volume Element, RVE) are used to simulating heterogeneous concrete meso-structures in the form of aggregates in the hardened mortar with nearly zero-thickness linear or planar interfaces. The numerical sensitivity of these meso-structures are Investigated with respect to the different morphologies of heterogeneity and the different level of coupling constant among fracture mode I, II and III. In addition, a numerically homogenized concrete block in 3-D using Hashin-Shtrikman variational bounds provides an evidence of the effective cracking paths which are quite different with those of heterogenous concrete block. However, their average force-displacement relationship show a pretty close match each other.

• Proceedings of the Korean Institute of Building Construction Conference
• /
• 2018.11a
• /
• pp.116-117
• /
• 2018

The aim of this study is to investigate the properties of hardened mortar with chlorine by-pass system(CBS) in cement production in blast furnace slag(BS) mixed cement. Compressive strength had a tendency to be increased when the CBS Dust was replaced by 10% at the BS replacement rate of 0%. The 65% combination of BS showed a tendency to decrease as the CBS Dust exchange rate increases. Flexural strength was reduced as CBS Dust exchange rate increases in BS replacement ratio of 0%. The use of 5% of CBS dust can contribute to enhance the quality of non reinforced concrete.

• Proceedings of the Korea Concrete Institute Conference
• /
• 1998.10c
• /
• pp.133-138
• /
• 1998

The purpose of this study is to offer basic information of fly ash concrete for field application. Through before study and fly ash in mortar, various properties as fly ash ratio in concrete were checked according to the experimental result, slump was increased and entrained air quantity was decreased as fly ash ratio is increased in fresh concrete. In hardened concrete, strength development of plain concrete(W/B 50%) was slower than water-reduced concrete(W/B 40%) at early age. Especially water-reduced concrete was remarkabily faster than no fly ash in concrete. Moduls of stastic elasticity and stress-strain relationship of fly ash in concrete nearly were effect on no fly ash concrete.

• Proceedings of the Korea Concrete Institute Conference
• /
• 1999.10a
• /
• pp.191-194
• /
• 1999

Recently in Korea, may workers have reported the effects of the granulated blast furnace slag[BFS] of high fineness on the strength development of slag cement. We have studied the effect of slag fineness on the strength development of mortar with curing conditions, in order to get the basic data of high strength concrete using BFS. In this paper, we discussed the effects of slag fineness and porosity of mortar and the reaction of slag in hardened slag cement.

• Proceedings of the Korea Concrete Institute Conference
• /
• 1994.10a
• /
• pp.151-156
• /
• 1994

This study is to investigate the quality of superplasticizers in domestic market. Therefore, the physico-chemical characteristics, the fluidity characteristics of fresh cement paste and mortar were tested. Also fresh and hardened properties of mortars and concretes using these superplasticizers were tested. From these results, differences of quality among superplasticizers are checked clearly in low water/cement ratio. And it is concluded that several superplasticizers have better dispersion ability than others in every tests. It has known that all samples are naphtalene sulfornate formaldehede types by the UV(ultra-violet) test.