• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.727-730
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• 2004

The purpose of this study is to evaluate the fundamental properties of fine type cement grouts with redispersible polymer powders. Cement grouts with redispersible polymer powders are prepared with various polymer-cement ratios, and tested. for flow, water absorption, drying shrinkage, flexural and compressive strengths. From the test results, flow of the cement grouts with EVA and Va/VeoVa polymer powers decreased with increasing elapsed time. Regardless of polymer type, the flexural strength of the cement grouts tends to increase with increase in polymer-cement ratio. The maximum compressive strengths of the cement grouts are obtained at a polymer-cement ratio of $5\%$.

• Journal of the Korean Society of Safety
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• v.13 no.3
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• pp.45-50
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• 1998

The low grade domestic kaoline, such as pink-C and white-D, was converted to metakaoline, which has pozzolanic reactivity by heat treatment in the temperature range of $600^{\circ}C$ to 100$0^{\circ}C$ for preparing the spacer. The spacer was used for supporting the reinforced steel rod during construction to improve the safety of architecture. Pink-C and white-D were completely dehydroxylated when burnt at 80$0^{\circ}C$ for 1 hour and converted to metakaoline. The compressive strengths of specimens added calcined pink-C were lower than those of press molding mortar products inspite of calcining conditions. When white-D with calcined 80$0^{\circ}C$ and 100$0^{\circ}C$ for 1 hour was mixed 30% in the weight ratio of cement, the specimens cured 28 days had 338 $kg/cm^2$ and 347 $kg/cm^2$ of compressive strengths, respectively.

• Journal of The Korean Society of Agricultural Engineers
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• v.47 no.1
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• pp.25-32
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• 2005

This study was performed to evaluate strengths and non-destruction properties of super flow concrete using recycled coarse aggregate. At the curing age of 28 days, the compressive strength was 22.7-37.5 MPa, the splitting tensile strength was $2.65\~3.73$ MPa, the flexural strength was $5.78\~6.86$ MPa, the ultrasonic pulse velocity was $3,103\~3,480$ mis, the dynamic modulus of elasticity was $3.401{\times}104\~4.521{\times}104$MPa, respectively. The strengths, ultrasonic pulse velocity and dynamic modulus of elasticity of super flow concrete were decreased with increasing the content of recycled coarse aggregate. The super flow concretes using recycled coarse aggregate were improved by substitution in the range of less than the fly ash content 30010 and recycled coarse aggregate content $75\%$.

• Computers and Concrete
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• v.24 no.1
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• pp.85-94
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• 2019

The ACI building code is allowing for higher strength reinforcement and concrete compressive strengths. The nominal strength of high-strength concrete columns is over predicted by the current ACI 318 rectangular stress block and is increasingly unconservative as higher strength materials are used. Calibration of a rectangular stress block to address this condition leads to increased computational complexity. A triangular stress block, derived from the general shape of the stress-strain curve for high-strength concrete, provides a superior solution. The nominal flexural and axial strengths of 150 high-strength concrete columns tests are calculated using the proposed stress distribution and compared with the predicted strength using various design codes and proposals of other researchers. The proposed triangular stress model provides similar level of accuracy and conservativeness and is easily incorporated into current codes.

• Journal of the Korean Society of Safety
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• v.20 no.2 s.70
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• pp.84-90
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• 2005

This study is to use results of the experiment on the influence to the strength by mixing powders of wasted tires into regular remicon within a range of little effectiveness in durability, applicability, economic aspect, and workability, to put it to practical use and to apply as basic data from a view of recycling wasted tires as construction materials. And the concrete, which was mixed with 10mm particles with ratio of $0.5\%\;and\;1.0\%$ respectively at 270 of mixing strength, was reduced by $27\%$ in compressive strength compared to normal concrete, whereas concrete mixed with other than 10mm particles showed lower decrease ratio compared to the former by reducing only $1.0\%\~1.5\%$. it is found that as strength increases, the less in quantity of aggregate and the more increase in quantity of cement. When considered to the above result, it is estimated that concrete mixed with wasted tire particles could be better used in conditions of compressive force rather than tensile force, and could also be used for structures with flexural strengths as well. In conclusion, higher strengths could be made using waste tire mix.

• Magazine of the Korean Society of Agricultural Engineers
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• v.16 no.3
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• pp.3533-3538
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• 1974

This study was attempted in order to search for physical properties of sail cement. In this study, soil samples were specified according to soil particle analysis and used for compaction, strength, abrasion, absorption tests respectively according to different cement contents. Cement content sused in each treatment were 6%, 8%, 10% and 12% of total weight of soil-consent mixture. In the test, compressise strengths of the specimens were measured at the following ages; 3 days, 7-days, 14-days, 21-days and 28-days. Abrasion and absorption tests of the specimens were carried out at the 7-days age only. The results obtained from the tests are summarized as follows; 1. As the cement contents were in creased, the compressive strengths of soil-cement were almost proportionally increased. 2. The Compressive strength of soil-cement was not always proporportional to ages. The gradient of compressive strength of the soil-cement was steeper as the cement content was rucreased. 3. As the cement content was increased, the amount of the weight loss of the samples due to the abrasion was decreased remarkably, giving no abrasion for about 8% of the cement content. 4. As the cement content was increased, the absorption ratio of the specimens was not changed remarkably.

• Journal of The Korean Society of Agricultural Engineers
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• v.53 no.5
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• pp.25-33
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• 2011

In this paper, the effects of aggregate and curing temperature on strength development characteristics of UP (Unsaturated Polyester)-MMA (Methyl Methacrylate) based polymer mortar under sub-zero temperature are experimentally investigated to provide a criterion for repair and production of precast products. The result showed that the setting time of the binder was 4 minutes at $20^{\circ}C$ whereas 35 minutes at $-20^{\circ}C$. The result also revealed that the compressive, flexural, and splitting tensile strengths of UP-MMA based polymer mortar significantly decreased as the aggregate and curing temperatures decreased. However, sufficient strengths which can be implemented in actual practices -36.6 MPa of compressive strength, 6.11 MPa of flexural strength, and 5.81 MPa of splitting tensile strength - were obtained even though both aggregate and curing temperatures were $-20^{\circ}C$. Strength development of polymer mortar is largely affected by curing temperature rather than aggregate temperature. It was found that the effects of aggregate temperature on strength development become smaller as the curing temperature becomes lower. Also, toughness, a ratio of compressive strength to flexural strength, increased from 3.5 to 5.9 as both aggregate and curing temperatures decreased from $20^{\circ}C$ to $-20^{\circ}C$.

• International Journal of Concrete Structures and Materials
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• v.10 no.1
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• pp.113-124
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• 2016

This paper presents the effect of silica fume and nano silica, used individually and in combination with the set accelerator and/or hydrated lime, on the properties of class F high volume ultra fine fly ash (HV-UFFA) cement composites, replacing 80 % of cement (OPC). Compressive strength test along with thermogravimetric analysis, X-ray diffraction and scanning electron microscopy were undertaken to study the effect of various elements on the physico-chemical behaviour of the blended composites. The results show that silica fume when used in combination with the set accelerator and hydrated lime in HV-UFFA cement mortar, improves its 7 and 28 day strength by 273 and 413 %, respectively, compared to the binary blended cement fly ash mortar. On the contrary, when nano silica is used in combination with set accelerator and hydrated lime in HV-UFFA cement mortar, the disjoining pressure in conjunction with the self-desiccation effect induces high early age micro cracking, resulting in hindering the development of compressive strength. However, when nano silica is used without the additives, it improves the 7 and 28 day strengths of HV-UFFA cement mortar by 918 and 567 %, respectively and the compressive strengths are comparable to that of OPC.

• International Journal of Concrete Structures and Materials
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• v.10 no.1
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• pp.75-85
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• 2016

Fire ranks high among the potential risks faced by most buildings and structures. A full understanding of temperature effects on fiber reinforced concrete is still lacking. This investigation focuses on the study of the residual compressive strength, stress strain behavior and surface cracking of structural polypropylene fiber-reinforced concrete subjected to temperatures up to $300^{\circ}C$. A total of 48 cubes was cast with different fiber dosages and tested under compression after exposing to different temperatures. Concrete cubes with varying macro (structural) fiber dosages were exposed to different temperatures and tested to observe the stress-strain behavior. Digital image correlation, an advanced non-contacting method was used for measuring the strain. Trends in the relative residual strengths with respect to different fiber dosages indicate an improvement up to 15 % in the ultimate compressive strengths at all exposure temperatures. The stress-strain curves show an improvement in post peak behavior with increasing fiber dosage at all exposure temperatures considered in this study.

• Structural Engineering and Mechanics
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• v.49 no.6
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• pp.763-773
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• 2014

The recently developed Ultra High Performance Concrete (UHPC) displays outstanding compressive strength and ductility but is also subjected to very large autogenous shrinkage. In addition, the use of forms and reinforcement to confine this autogenous shrinkage increases the risk of shrinkage cracking. Accordingly, this study adopts a combination of shrinkage reducing admixture and expansive admixture as a solution to reduce the shrinkage of UHPC and estimates its appropriateness by evaluating the compressive and flexural strengths as well as the autogenous shrinkage according to the age. Moreover, the coefficient of thermal expansion known to experience sudden variations at early age is measured in order to evaluate exactly the autogenous shrinkage and the thermal expansion is compensated considering these measurements. The experimental results show that the compressive and flexural strengths decreased slightly at early age when mixing 7.5% of expansive admixture and 1% of shrinkage reducing admixture but that this decrease becomes insignificant after 7 days. The use of expansive admixture tended to premature the setting of UHPC and the start of sudden increase of autogenous shrinkage. Finally, the combined use of shrinkage reducing admixture and expansive admixture appeared to reduce effectively the autogenous shrinkage by about 47% at 15 days.