• International Journal of Concrete Structures and Materials
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• v.9 no.4
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• pp.391-399
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• 2015

This study modeled the compressive strength and elastic modulus of hardened cement that had been treated with an expansive additive to reduce shrinkage, in order to determine the mechanical properties of the material. In hardened cement paste with an expansive additive, hydrates are generated as a result of the hydration between the cement and expansive additive. These hydrates then fill up the pores in the hardened cement. Consequently, a dense, compact structure is formed through the contact between the particles of the expansive additive and the cement, which leads to the manifestation of the strength and elastic modulus. Hence, in this study, the compressive strength and elastic modulus were modeled based on the concept of the mutual contact area of the particles, taking into consideration the extent of the cohesion between particles and the structure formation by the particles. The compressive strength of the material was modeled by considering the relationship between the porosity and the distributional probability of the weakest points, i.e., points that could lead to fracture, in the continuum. The approach used for modeling the elastic modulus considered the pore structure between the particles, which are responsible for transmitting the tensile force, along with the state of compaction of the hydration products, as described by the coefficient of the effective radius. The results of an experimental verification of the model showed that the values predicted by the model correlated closely with the experimental values.

• Journal of The Korean Society of Agricultural Engineers
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• v.52 no.3
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• pp.9-17
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• 2010

This study aims to evaluate a porous concrete using hwang-toh, blast furnace slag and blast furnace slag (BFS) cement instead of type I cement. The tests that were carried out to analysis the properties of porous hwang-toh BFS cement concrete included compressive strength, continuous void ratio, absorption rate, and pH value, repeated freezing and thawing test were conducted. Test results indicated that the performance in porous hwang-toh concrete are effective on the kaoline based binder materials. The pH value were shown in about 9.5 ~ 8.5. The compressive strength was increased and void ratio was decreased with increasing the kaoline based binder materials, respectively. The void ratio and compressive strength were in the range of about 21 ~ 30 %, 8 ~ 13 MPa, respectively. The increased in void ratio of more than 25 % is showed to reduce the resistance of repeated freezing and thawing. Also, the resistance of repeated freezing of thawing and the compressive strength of porous hwang-toh BFS cement concrete are independent with hwang-toh content and BFS cement amount. But, the void ratio was decreased with increasing the high volume hwang-toh contents (more than 15 %).

• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.653-658
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• 2001

The purpose of this study is to evaluate the compressive strength properties of hardening using the unrefined fly-ash and waste lime and to offer basic data to someone for recycling waste lime Waste limes are tested that specific gravity and pH value and observed microstructure of particle with SEM. The compressive strengths of Wast lime hardening which is mixed with regular ratio according to each admixture are measured. In the results of test, The pH of wast lime is very high by pH 12.1 and specific gravity is 2.22. Compressive strengths on hardening modified waste lime and fly ash is very effective. The vest compressive strengths is show that CaCl$_2$ existed in waste lime

• Journal of the Korean GEO-environmental Society
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• v.11 no.11
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• pp.77-85
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• 2010

Unconfined compressive strength tests were performed to evaluate curing characteristics of controlled low strength material(CLSM) made with coal ashes. It is found that unconfined compressive strength normalized by curing times, increases as decreasing the water contents of CLSM particularly during first three days. Dynamic cone penetrometer tests were also carried out to evaluate cost-effective CLSM lump strength characteristics with time. It takes around 10 days to reach target strength, 500kPa (penetration rate, 20mm/blow). Curing rate significantly decreases after 10 days elapsed regardless of CLSM formulation.

• Proceedings of the Korea Concrete Institute Conference
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• 1992.10a
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• pp.155-160
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• 1992

In this study , the size effect on diagonal shear failure of reinforced high strength concrete beams was investigated, For this purpose, ten singly reinforced high strength concrete beams without web reinforcement were tested for five different dimensions of effective depth which were varied from 67mm to 915mm. The compressive strength of concrete used in this study was 53.7 MPa. One type of reinforcing bar with nominal yield strength of 400 MPa was used. Test results were analyzed and compared with strength predicted by ACI code equation, Zutty's equation and Bazant &Kim's equation. As the results, ACI code equation was seriously unconservative for beams with d of 915mm. Bazant & Kim's equation predicted well the trend of test data. Within the scope of this study, there was no clear difference in size effect with variation of compressive strength of concrete.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.2
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• pp.198-203
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• 2020

Cracking due to material behavior like drying shrinkage easily occurs since tensile strength in concrete is very low at initial curing stage. In this paper, workability such as air content and slump was evaluated on CFC(Cellulose Fiber Concrete) with 0.0 ~ 2.0% of fiber addition, and the tests for tensile/compressive strength were performed. With increasing addition ratio of fiber, air content and slump kept similar level to 1.0kg/㎥ of addition ratio, and this trend was effective to 2 hours after mixing. Strength was enhanced with increasing addition ratio, which showed 7.0 ~ 9.0% for compressive strength and 7.0 ~ 22.0% for tensile strength, respectively. The tensile strength increased relatively more, which show the addition of cellulose fiber was very effective to crack resistance. The workability in CFC can be guaranteed for 2 hours in the following conditions like 2 minutes of mixing period and 1.0kg/㎥ of addition ratio of fiber.

• Korean Journal of Materials Research
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• v.20 no.9
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• pp.488-493
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• 2010

Geopolymer is a term covering a class of synthetic aluminosilicate materials with potential use in a number of areas, but mainly as a replacement for Portland cement. In this study, geopolymers with fly ash and meta kaolin were prepared using KOH as an alkali activator and water glass. The effect of water glass on the microstructures and the compressive strength of the geopolymer was investigated. As the amount of water glass increased, the dissolved inorganic binder particles in the geopolymers increased due to polymerization, resulting in a dense microstructure. The meta kaolin-based geopolymer showed a better extent of polymerization and densification than that of the fly ash-based geopolymer. XRD data also suggested that polymerization in meta kaolin-based geopolymers should be active resulting in the formation of an amorphous phase with an increasing amount of water glass. The compressive strength of the geopolymer was also dependent on the amount of water glass. The compressive strength of the geopolymers from both fly ash and meta kaolin increased with an increasing amount of water glass because water glass improved the extent of polymerization of the inorganic binder and resulted in a dense microstructure. However, the addition of water glass to the geopolymer did not seem to be effective for the improvement of compressive strength because the meta kaolin-based geopolymer mainly consisted of a clay component. For this reason, the fly ash-based geopolymer showed a higher value of compressive strength than the meta-kaolin geopolymer.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.979-984
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• 2008

This paper discusses how to use basic strut-and-tie models(STM) for practical application. Construction of STM starts with drawing of load paths with equilibrium conditions. Understanding of structural systems including form active systems, vector active systems, and section active systems help us select appropriate systems for possible STM. Simple circular fans can be employed for load paths from concentrated forces to distributed forces. Strength of struts depends on configuration of their nodal zones which meet tension ties and effective compressive strength. The effective compressive strength of struts are assumed to be mainly influenced by transverse strain.

• Advances in concrete construction
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• v.4 no.4
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• pp.283-303
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• 2016

Several types of industrial byproducts are generated. With increased environmental awareness and its potential hazardous effects, the utilization of industrial byproducts in concrete has become an attractive alternative to their disposal. One such by-product is ground granulated blast furnace slag (GGBS), which is a byproduct of the smelting process carried out in the iron and steel industry. The GGBS is very effective in the design and development of high-strength and high-performance concrete. This paper reviews the effect of GGBS on the workability, porosity, compressive strength, splitting tensile strength, and flexural strength of concrete.

• Structural Engineering and Mechanics
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• v.46 no.1
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• pp.111-135
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• 2013

An experimental study has been carried out on square plain concrete (PC) and reinforced concrete (RC) columns strengthened with carbon fiber-reinforced polymer (CFRP) sheets. A total of 78 specimens were loaded to failure in axial compression and investigated in both axial and transverse directions. Slenderness of the columns, number of wrap layers and concrete strength were the test parameters. Compressive stress, axial and hoop strains were recorded to evaluate the stress-strain relationship, ultimate strength and ductility of the specimens. Results clearly demonstrate that composite wrapping can enhance the structural performance of square columns in terms of both maximum strength and ductility. On the basis of the effective lateral confining pressure of composite jacket and the effective FRP strain coefficient, new peak stress equations were proposed to predict the axial strength and corresponding strain of FRP-confined square concrete columns. This model incorporates the effect of the effective circumferential FRP failure strain and the effect of the effective lateral confining pressure. The results show that the predictions of the model agree well with the test data.