• Advances in materials Research
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• 제11권2호
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• pp.121-146
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• 2022

In the recent years, the use of agricultural waste in green cement mortar and concrete production has attracted considerable attention because of potential saving in the large areas of landfills and potential enhancement on the performance of mortar. In this research, microparticles of palm oil fuel ash (POFA) obtained from a multistage thermal and mechanical treatment processes of raw POFA originating from palm oil mill was utilized as a pozzolanic material to produce high-performance cement mortar (HPCM). POFA was used as a partial replacement material to ordinary Portland cement (OPC) at replacement levels of 0, 5, 10, 15, 20, 25, 30, 35, 40% by volume. Sand with particle size smaller than 300 ㎛ was used to enhance the performance of the HPCM. The HPCM mixes were tested for workability, compressive strength, ultrasonic pulse velocity (UPV), porosity and absorption. The results portray that the incorporation of micro POFA in HPCMs led to a slight reduction in the compressive strength. At 40% replacement level, the compressive strength was 87.4 MPa at 28 days which is suitable for many high strength applications. Although adding POFA to the cement mixtures harmed the absorption and porosity, those properties were very low at 3.4% and 11.5% respectively at a 40% POFA replacement ratio and after 28 days of curing. The HPCM mixtures containing POFA exhibited greater increase in strength and UPV as well as greater reduction in absorption and porosity than the control OPC mortar from 7 to 28 days of curing age, as a result of the pozzolanic reaction of POFA. Micro POFA with finely graded sand resulted in a dense and high strength cement mortar due to the pozzolanic reaction and increased packing effect. Therefore, it is demonstrated that the POFA could be used with high replacement ratios as a pozzolanic material to produce HPCM.

• 한국도로학회논문집
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• 제11권3호
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• pp.51-60
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• 2009

본 연구에서는 고강도 고내구성 시멘트콘크리트 포장을 위하여 도출된 배합 콘크리트의 굳지않은 콘크리트 특성, 강도발현 특성, 염소이온의 투수특성 및 동결-융해에 대한 저항성 등의 역학적 내구적 특성을 분석하였다. 제시된 배합의 목표스럼프와 공기량은 적절한 혼화제의 사용으로 확보가 가능하나, 혼화제의 적정사용량은 충분한 현장배합실험을 통하여 구하여야 할 것이다. 단위시멘트량을 증가한 경우 일반적으로 강도가 증가하였으며 특히 재령 28일 이후의 강도가 지속적으로 증가하는 양상을 나타내었다. 휨강도는 그 특성상 단위시멘트량을 증가하더라도 뚜렷한 효과는 나타나지 않았다. 염소이온 침투저항성도 단위시멘트량보다는 재령에 따른 영향을 더 크게 받는 것으로 나타났다. 공기량에 가장 많은 영향을 받는 동결-융해 저항성은 각 실험변수에 대한 시험체를 공기량이 3% 이하 및 이상인 경우에 대하여 그리고 동결시 수돗물을 사용한 경우와 현장의 열악한 환경을 모사하기 위하여 4%의 NaCl 용액을 사용한 경우로 구분하여 실시하였다. 공기량에 상관없이 수돗물을 사용한 경우에는 동결-융해반복회수가 300회까지 상대동탄성계수나 표면의 손상이 거의 발생하지 않았다. 4% NaCl 용액을 사용한 경우에는 단위시멘트량이 현재의 한국도로공사의 표준배합인 경우 손상이 발생하였으며, 단위시멘트량이 동결-융해 저항성에 미치는 영향이 큰 것으로 나타났다. 따라서, 동결-융해에 대한 저항성을 충분히 확보하는 고내구성의 시멘트콘크리트 포장을 위해서는 단위시멘트량을 현재의 수준보다 증가시키는 것이 유리한 것으로 판단되며, 실험결과로부터 이러한 요구성능을 발휘하기 위해서는 단위시멘트량을 400kg/$m^3$ 이상으로 할 것을 권장한다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1994년도 가을 학술발표회 논문집
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• pp.161-166
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• 1994

Production of high strength concrete requires a low water-cement ratio and this leads to the high cement content. Mineral admixture like fly ash(FA) is often cheaper than ordinary portland cement(OPC) and this factor in combination with possible improvement in workability and moderation of the heat evolution of the cement-rich mixes tends to encourage its use. The other mineral admixture that its use has been widly advocated is silica fume that increases compressive strength due to its pozzolanic reaction. The objective of this study is to assess the contribution of mineral admixtures(FA, SF) to the workability and the strength of concrete with low water-binder ratios. In this experimental study that investigates and analyzes the properties of fresh concrete, it is presented that using admixtures like flysh and silica fume as binding material increases properties of high strength flowing concrete having very low water cementitious ratios of 0.25 and 0.30.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1995년도 봄 학술발표회 논문집
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• pp.84-87
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• 1995

Production of high strength concrete requires a low water-cement ratio and this leads to the high cement content. Mineral admixture like fly ash(FA) is often cheaper than ordinary portland cement(OPC) and this factor in combination with possible improvement in workability and moderation of the heat evolution of the cement-rich mixes tends to encourage its use. The other mineral admisture that its use has been widly advocated is silica fume that increases compressive strength due to its pozzolanic reaction. The objective of this study is to assess the contribution of mineral admixtures(FA, SF) to the workability and the strength of concrete with low water-binder ratios. In this experimental study that investigates and analyzes the properties of fresh concrete. it is presented that using admixtures like flyash and silica fume as binding material increases properties of high strength flowing concrete having very low water cementitious ratios of 0.25 and 0.30.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1994년도 봄 학술발표회 논문집
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• pp.175-180
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• 1994

The purpose of this experimental study is to improve the workability and durability in high sulphated cement concrete with fly-ash. As a results, we can make high strength concrete by using only high sulphated cement but try to improve the workability and degree of strength by adding 10% fly-ash but the effect beyond my expectation to improve the workability and degree of strength does not show, and the improvable effect except the drying shrinkage of durability dose not show, either. So we must give attention to using fly-ash.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 춘계 학술발표회 논문집(II)
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• pp.609-612
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• 2006

The quality of the concrete compression strength can be determined after the passage of 28 days, but if any defect is found the quality of concrete after that length of time, there can be serious problems in dismantling and repair. Thus, in response to the use of concrete using non sintering cement (NSC), the present study purposed to propose a method of managing the strength of high strength concrete using NSC in comparison with high strength concrete using ordinary Portland cement (OPC) through early strength estimation using microwave, which enables the quick estimation of the strength of high strength concrete using NSC.

• 한국건축시공학회지
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• 제4권2호
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• pp.81-88
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• 2004

The purpose of this study is to investigate the chemical shrinkage and autogenous shrinkage of high strength cement paste and silica fume and fly ash and sand to cement ratio by the method of volumetric tests, and also investigate the autogenous shrinkage of high measurement method, and compare the results of volumetric test and linear length measurement test. A series of cement paste which have W/C ratio of 25%, 35%, 45% respectively were planed to study the effect of the W/C ratio to the shrinkages, and a series of cement paste which were replaced the cement by the silica fume and fly ash with 5%, 10%, 15% as the mass of cement respectively were planed to investigate the effects of poazolana to the shrinkages. A series of mortar which have a C/S ratio of 1:1, 1:1.5, 1:2 respectively were planed to investigate the shrinkage resistant effect of aggregate.

• 한국세라믹학회지
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• 제27권7호
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• pp.861-868
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• 1990

Investigation for the preparation of high strength hardened cement paste using ordinary portland cement, hydroxypropyl methyl cellulose(HPMC) with SiC powder was carried out. The cement paste was mixed with 0.1 of water cement ratio by twin roll mill and cured 60 days in humidity chamber. The hydration degree of cement paste cured with W/C=0.1 in 60 days was about 30% and most pores in the paste were found to be existed as gel pores of diameter less than 0.01㎛. The maximum flexural strength of hardened cement paste was about 960kg/㎠. When the SiC powder was added to the paste, the flexural strength was 1000∼1100kg/㎠ and the Young's modulus was 8∼9×105kg/㎠.

• 한국건축시공학회지
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• 제24권1호
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• pp.23-34
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• 2024

본 연구의 목적은 RC 구조물의 균열 보수용 폴리머 시멘트 복합체의 휨접착성능을 평가하기 위함이다. 시멘트 모르타르에 다양한 크기의 균열을 만들어 PCCs를 충전한 후, 소정의 양생을 거쳐 휨접착강도와 휨강도 개선 정도를 파악하였다. 연구결과, 균열보수용 PCCs의 휨접착강도는 시멘트의 종류, 폴리머 종류 및 폴리머 결합재비에 따라 영향을 받으며 실리카퓸을 혼입한 초조강시멘트를 사용한 경우가 보통시멘트를 사용한 경우에 비해 최대 19.0%의 휨접착강도 개선효과가 나타났다. PCCs로 충전된 시멘트 모르타르의 휨강도 개선 정도는 균열폭의 영향보다는 균열깊이에 따라 큰 차이를 보였으며 균열에 충전된 PCCs가 단순히 보수재료로서 기능뿐만 아니라 어느 정도 휨강도를 개선시키는 보강재료로서도 역할을 하였다. 본 연구결과, 초조강시멘트, 3종류의 폴리머 디스퍼전과 실리카퓸, 60%~80%의 높은 폴리머 결합재비로 제작한 PCCs가 균열을 충전하는 보수재료로서 현장에서 충분히 사용될 수 있을 것이다.

• 한국터널지하공간학회 논문집
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• 제5권1호
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• pp.23-31
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• 2003

최근 NATM 터널 현장타설 콘크리트 라이닝의 시공성 향상과 균열에 따른 유지관리비 절감을 위해 양질 암반의 배수형 터널 시공에 있어서는 숏크리트만으로 라이닝을 대체하려는 영구지보 개념의 터널시공 (Single-Shell Tunnel, NMT 등)이 세계적으로 증가하고 있는 추세이다. 이러한 영구지보 개념의 터널 시공을 위해서는 고성능 숏크리트의 개발이 선결되어야 하며, 이러한 목적에서 본 논문에서는 조강시멘트와 최근 주목받고 있는 환경친화적인 alkali-free 급결제의 조합을 통해 고성능 숏크리트의 개발 가능성을 확인하였다. 그 결과, 보통시멘트(OPC)를 사용한 숏크리트보다 약 25%의 높은 초기강도를 확보하였으며, 용수부에서도 뛰어난 부착특성을 확인할 수 있었다.