• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.6
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• pp.33-40
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• 2021

Measuring the compressive strength of concrete is a very important factor in the safety review of concrete structures. Concrete compressive strength measurement methods include destructive and non-destructive methods. The destructive method includes the uniaxial compression failure method, and the non-destructive method includes the rebound hardness method and the elastic wave measurement method. In this study, the type of measurement method and the effect of reinforcing bars inside the concrete were tested to examine the relationship between them. Regardless of the type of specimen, the average compressive strength by the elastic wave measurement method among the three experimental methods was greater than the average compressive strength by the other methods. When the specimen type is the same, the standard deviation of the measured values of the elastic wave measurement method is smaller than that of the other measurement methods, so it can be seen that the elastic wave measurement method does not show large variance in the measured values compared to the other two measurement methods. When the average compressive strength according to the test method for each specimen was compared with the average compressive strength of the compressive failure test method, the average compressive strength was measured to be high in the order of the elastic wave measurement method, the compression failure test, and the rebound hardness method. Since the measured values of the compressive strength of concrete are different depending on the method of measuring the compressive strength of concrete and the presence or absence of reinforcing bars inside the concrete, further research is required considering the effect of various concrete covers.

• Polymer(Korea)
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• v.35 no.4
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• pp.342-349
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• 2011

The effect of the amount of vinyltriethoxysilane (VTEOS) in precipitated silica filled silicone rubbers was extensively investigated in terms of the change of mechanical properties, heat resistance, oil resistance, compression set, resilience, and curing characteristics. As the content of VTEOS increased from 0 to 2.0 phr, the hardness of the silicone rubber increased, however, tensile strength, elongation at break, and tear strength decreased. From heat resistance test, the change of mechanical properties was pronounced for silicone rubber treated with more VTOES. The best heat resistance was achieved at 2.0 phr VTOES. In addition, oil resistance was proportionally improved with VTEOS content. From oil resistance test. it was found that the decrease in hardness and maximum elongation was reduced for VTEOS-added systems. Finally, resilience, compression set, degree of cure and crosslink density were significantly enhanced with the amount of VTEOS.

• Korean Journal of Heritage: History & Science
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• v.50 no.2
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• pp.40-61
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• 2017

This study investigated material characteristics of composition and variable strength measurement using physicochemical and petrographic analysis for lime-soil mixture barrier tombs of Guri Galmae site in Joseon Dynasty. The tomb barriers are composed mainly of microcrystalline calcite, quartz, feldspar and mica with lime matrix. The lime matrix shows compact sheet texture, and some samples show hydration aggregates with needle-shaped textures. Gypsum occurred as a secondary process where carbonization reactions were poor. Concentrations of CaO in the tomb barrier very widely ranged from 4.43 to 36.19 wt.%, specific gravity and absorption ratio of the materials show of 1.35 to 1.62 and 20.1 to 32.6%, respectively. As the rebound hardness, the materials ranged from 10.0 to 28.4 (mean 15.7). The values are higher in the $-90^{\circ}$ direction rather than in the $0^{\circ}$ direction with the consequence that the values indicate more strength toward the vertical direction. Difference in strength by directions was caused by the directions of the tomb barriers, which is related to the processes in each stage. In the tomb barriers, ultrasonic velocity and unconfined compressive strength ranged from 1,049.2 to 1,728.9m/s and under 5.00MPa, respectively. Variation patterns between the two are very similar in values. As the result of composition and strength, the materials of higher contents on CaO are higher in strength values. Generally, techniques and skills to make the lime-soil mixture barriers are interpreted as low qualities in relatively.

• Proceedings of the KAIS Fall Conference
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• 2011.05a
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• pp.292-295
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• 2011

본 논문에서는 배수성(저소음)포장을 포함하는 2-Layer 아스팔트 포장의 상부층과 하부층의 역학적인 특성을 평가하는데 목적이 있다. 연구 방법으로는 슈퍼페이브 배합설계로 2-Layer 아스팔트 포장의 상 하부층 시편을 제작하였으며, 시편 상부층의 최대공칭치수는 4.75mm이고 하부층의 최대공칭치수는 13mm이다. 이 시편에 대한 기본 물성 시험 실시 후 마샬 안정도 시험에 대한 안정도와 흐름값을 평가하였다. 그리고 상부층과 하부층의 자유단 공진주 시험을 통해 탄성계수(E)를 측정하였고, 비파괴 시험법인 슈미트해머(Schmidt hammer)를 이용해 반발경도를 측정한 후 강도를 추정하였다. 또한 일축압축시험으로 측정된 압축강도로 탄성계수($E_{50}$)를 계산하였다. 마지막으로 각각의 역학적 시험을 통해 얻어진 결과값으로 강도(qu)와 탄성계수 ($E_{50}$)의 상관관계와 추정식으로 구한 강도와 일축압축강도 시험으로 얻어진 강도와의 상관관계를 분석하였고, 자유단 공진주 시험의 탄성계수(E)값과 일축압축시험의 결과로 얻어진 탄성계수($E_{50}$)의 상관관계를 분석하였다.

• Journal of the Korea institute for structural maintenance and inspection
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• v.11 no.4
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• pp.71-78
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• 2007

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. The experimental parameter were concrete age, curing condition, and strength level.

• Proceedings of the Korean Institute of Industrial Safety Conference
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• 1998.11a
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• pp.159-164
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• 1998

포틀랜트 시멘트가 개발되어 콘크리트에 응용됨으로서 콘크리트의 적용범위가 무한히 확대되고 있는 상황에서, 최근, 구조물이 고층화, 대형화, 특수화됨에 따라 건설재료인 콘크리트의 고품질화가 요구되고 있다. 이러한 고품질화의 최우선과제로 콘크리트의 고강도화에 관한 많은 연구가 국내외에서 이루어지고 있고, 실제 시공된 사례도 급속히 증가하고 있다. (중략)

• Proceedings of the Korean Institute of Industrial Safety Conference
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• 1998.11a
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• pp.153-158
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• 1998

다양한 구성재료로 이루어진 콘크리트는 역학적 특성과 거동이 복잡한 것으로 알려져 있으며, 특히 초기재령시는 그 역학적 특성의 변화가 급격하므로 구조물의 품질관리를 위하여 그 기본 요소인 압축강도에 대한 정확한 평가가 필수적이라 할 수 있다. 이는 공사기간, 공사비용 및 안전성확보 등 시공관리 전반에 걸쳐 지대한 관심 사항이라 할 수 있다. (중략)

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.2
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• pp.98-104
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• 2018

Nondestructive strength Equations are commonly used to determine the strength of concrete. However, the application of the existing equations may include many errors because this method is proposed on the basis of limited experimental parameters while actual bridges have various parameters such as conditions of concrete mixtures, properties of concrete strength, etc. Also, the error among the existing equations causes the confusion when engineers select the proper estimation equation for the concerned bridge. In this study, a series of the field inspection and the test have been performed on 297 existing bridges, in order to evaluate the bridges, based on the test results of the in-depth inspection, and the estimated strengths by means of the nondestructive strength equations are analyzed and compared with results of the core specimen strengths. According to results of analyses, the nondestructive strength equation proposed by CNDT Committee of Architectural Institute of Japan had high relationship with core strength. However, the strengths predicted by this equation, are underestimated when concrete's strengths are over 30 MPa, otherwise, they are overestimated. Also in this paper, based on the relationship between the estimated nondestructive concrete strengths and the core specimen strengths the modified strength equation through simple correlation analysis is proposed.

• Journal of the Korea Concrete Institute
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• v.16 no.4 s.82
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• pp.459-465
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• 2004

The present paper is intended to investigate the influence of materials such as cement, mineral admixture and aggregate, on the estimation of compressive strength by P type schmidt hammer. According to the results, the materials of concrete, such as the types of cement, the replacing ratio of mineral admixture, the kinds and maximum size of aggregate, hardly influence on non-destructive test by P type schmidt hammer except for alumina cement, hence, P type schmidt can be applicable to most of the concrete with a wide range. Since the correlativity between the rebound value of P type schmidt hammer and compressive strength is very favorable(above coefficient of correlation 0.96) regardless of materials, it is considered that compressive strength can be estimated comparatively exactly by P type schmidt hammer. The estimating formula of compressive strength by rebound value are derived from this experiment as following. $\cdot$Horizontal strike : Fc = 0.765RH - 5.74 (R=0.965) $\cdot$ Vertical strike Fc = 0.793RV - 8.66 (R=0.959)

• Korean Journal of Agricultural Science
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• v.24 no.2
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• pp.194-206
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• 1997

This paper was performed to evaluate the properties of no-coarse lightweight concrete using perlite and expanded polystyrene bead on fine aggregate. The results were shown that w/c and unit weight was affected by absorption ratio and unit weight of using aggregate itself. The compressive strength of no-coarse lightweight concrete was showed $187kgf/cm^2$ by using natural sand, $170kgf/cm^2$ by using perlite. Tensile and bending strength were showed the same tendency of compressive strength, but when expanded polystyrene bead concrete dose not have strength nearly. The pulse velocity and static modulus of elasticity of no-coarse lightweight concrete were smaller than that of normal cement concrete. And stress-strain curves were shown that was increased with increase of stress, and when the stress-strain curve using expanded polystyrene bead was repeated at short intervals increase and decrease irregularly.