• Proceedings of the Korean Institute of Building Construction Conference
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• 2007.04a
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• pp.25-28
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• 2007

In this study we measured the changes according to time respectively on the basis of 0, 30, 60 and 90 minutes, taking into consideration the decline in fluidity of concrete according to elapsed time to analyze manufacturing capability of batcher plant according to elapsed time of ready-mixed concrete manufactured in batcher plant, and offer basic data for mixture design of ultra-high strength concrete. The proportion of water-binder was 23.55, water content was 160kg/m3, proportion of replacement of crushed sand was 0, 20 and 40% at 3 level, and we applied to the same condition of triaxial component using blast furnace slag powder and silica fume as admixture. And to meet the demand of certain fluidity, we measured respectively on property before and after hardening of ultra-high strength concrete using superplasticizer. As a result of experiment, before hardening of ultra-high strength concrete showed the best fluidity in conditions of crushed sand replacement rates of 20% and superplasticizer composition of 1.95%, but it appeared that fluidity drops as time goes by in the same composition condition. And it appeared that when it comes to hardened, the changes of compression strength according to elapsed time by crushed sand replacement rates were within 1MPa. Therefore, it turned out that the difference of strength according to elapsed time was low and compression strength of 280dys in composition mentioned above appeared highly as 88MPa.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.11a
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• pp.731-734
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• 2005

Crushed sand is blended in order to investigate the quality changes and characteristics of concrete with variation of blend ratio of crushed sand (50, 60, 70, 80, 90, $100\%$). Slump and air content were measured to investigate properties of fresh concrete, and unit weight, compressive strength and modulus of elasticity in age of 7, 28, 60, 90, 180 days were measured to investigate properties of hardened concrete. Compressive strength, unit weight and modulus of elasticity were increased as time goes by and they are expected to keep on increasing in long-term age as well. As a result of measuring compressive strength and modulus of elasticity in age of 7, 28, 60, 90, 180days, compressive strength was highest when it is $70\%$ of blended ratio.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.05b
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• pp.145-148
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• 2006

Schmidt hammer and ultra-sonic method are commonly used for crushed sand concrete compressive strength test in a construction field. At present, various of equations for prediction of strength are present, which have been used in a construction field. The purpose of this study is to evaluate the correlation between prediction strength by presentation equations and destructive strength to test specimen, and find out which is a suitable equation for the construction site, In this study, a strength test was carried out destructive test by means of core sampling and traditional test. Non-destructive test was conducted Schmidt hammer and ultra-sonic method, the experimental parameter were concrete age, curing condition, test method and strength level. It is demonstrated that the correlation behavior of crushed sand concrete strength in this study good due to the perform analysis of correlation between core, destructive strength and non-destructive strength.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.11a
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• pp.459-462
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• 2005

Recently, interest grew on the quality of aggregates following the diminution of primary resources from river and the growing construction demand which exhausted high-quality sand sources around large cities and incited the use of low grade aggregates like shore sand and sea sand that can be supplied in natural state. Moreover, the most sensitive aspect highlighted by the unstability of aggregate supply is the quality. The extreme insufficiency of quality criteria about the materials currently used as substitute aggregates and about concrete mixed with such materials is also critical. This study investigated influence of qualities of concrete which is using mixed crushed sand and natural sand

• Advances in concrete construction
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• v.7 no.2
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• pp.87-96
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• 2019

Self-compacting concretes (SCC) are highly fluid concrete which can flow without any vibration. Their composition requires a large quantity of fines to limit the risk of bleeding and segregation. The use of crushed sand rich in limestone fines could be an adequate solution for both economic and environmental reasons. This paper investigates the influence of quarry limestone fines from manufactured crushed sand on rheological, mechanical and durability properties of SCC. For this purpose, five mixtures of SCC with different limestone fines content as substitution of crushed sand (0, 5, 10, 15 and 20%) were prepared at constant water-to-cement ratio of 0.40 and $490kg/m^3$ of cement content. Fresh SCC mixtures were tested by slump flow test, V-funnel flow time test, L-box height ratio, segregation resistance and rheological test using a rheometer. Compressive and flexural strengths of SCC mixtures were evaluated at 28 days. Regarding durability properties, total porosity, capillary water absorption and chloride-ion migration were studied at 180 days. For the two test modes in fresh state, the results indicated compatibility between slump flow/yield stress (${\tau}_0$) and V-funnel flow time/plastic viscosity (${\mu}$). Increasing the substitution level of limestone fines in SCC mixtures, contributes to the decrease of the slump flow and the yield stress. All SCC mixtures investigated achieved adequate filling, adequate passing ability and exhibit no segregation. Moreover, the inclusion of limestone fines as crushed sand substitution reduces the capillary water absorption, chloride-ion migration and consequently enhances the durability performance.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.05b
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• pp.93-96
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• 2006

To investigate the properties of high flowing concrete with fly ash and crushed sand for CFT structure, many batches were performed by a trial-error method and the results were analyzed by SPSS software program. In the experiment W/B was set up as 0.25 and the variables were a substitution ratio of fly ash, a blend ratio of crushed sand and the ages of specimens (3, 7, 28 days). The results of this study are summarized as the follows; 1) The increase of the substitution ratio of fly ash, the decrease of dosage of SP and the increase of dosage of AEA due to very fine sphere particle of fly ash. 2) The increase of the blend ratio of crushed sand, the increase of dosage of S/a and water content related with viscosity. 3) Made the high flowing concrete, the increase S/a and the increase the water content.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.05b
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• pp.157-160
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• 2006

Recently, trouble of sand supply is occurred according to exhaustion of natural sand resources. To solve this problem, sea sand and crushed sand are used. But, necessity of water reducing agent because quality of concrete that use sea sand and crushed sand is deteriorated. Therefore in this study was examined on the engineering properties of concrete with kind of fine aggregate and addition ratio of water reducing agents. As a result, compressive strength appeared similar standard regardless of kind of fine aggregate. Compressive strength, durability was similar in decrease of the unit water content by increase of addition ratio of the water reducing agent. Also, drying shrinkage resistivity was improved because the unit water content decreased.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.11a
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• pp.463-466
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• 2005

This study examined the effects of comparatively widely used fine aggregates in the domestic construction fields on the quality of concrete through the analysis of the effects of such fine aggregates on the physical properties of fresh concrete and strength of hardened concrete. Results revealed that crushed sand degrades the fluidity and air entraining of concrete compared to natural aggregates like sea sand and river sand. Especially, the use of crushed sand exhibiting low grain shape and grade was seen to have larger adverse effect on the physical properties of concrete.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.11a
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• pp.739-742
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• 2005

In this study, we predicted the service life against the freezing and thawing. as a result, we found that in the case of using the low quality crushed sand with high water-cement ratio, there is the possibility of deterioration. but in any other case, we concluded that there is no chance to deteriorate if we have the required air contents by using AE agent. we are going to improve the method to evaluate more exactly the durability of the concrete with crushed sand by acquiring data from the specimen which are exposed to field for long time.

• Proceedings of the Korea Concrete Institute Conference
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• 1994.10a
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• pp.99-104
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• 1994

Recently, nonlinear fracture mechanics was applied to analyze concrete structures more accurately, and new materials property such as fracture energy(Gf) was used for its application. The fracture energy was influenced by many parameters, especially the strength of concrete. Many researches on the relation between the strength of concrete and the fracture energy were performed. In spite of many researches on the relation between the strength of concrete and the fracture energy, there is no distinct conclusion. This research includes various the strength levels from low-strength of concrete to high-strength, and then intends to estimate relation between the strength of concrete and the fracture energy. Concrete used crushed sand is also included, which is going to be used much. In this research, the wedge splitting test method proposed by Prof. Linsbauer is adopted to investigate the fracture energy. Fracture behavior of concrete used natrual sand and crushed sand has the similar trend. In the strength range of 200~500 kg/$\textrm{cm}^2$, the fracture energy and the maximum splitting forces(F) increase as the strength of concrete increases. In the range of the higher strength, however, the maximum splitting forces(F) increases but the fracture energy decreases as the strength of concrete increases. Through this investigation the fracture energy of concrete was not proportional to the strength of concrete.