• 한국구조물진단유지관리공학회 논문집
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• 제3권2호
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• pp.191-198
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• 1999

The purpose of this study is investigating characteristics of the concrete containing Fly-ash according to different 4 mix design, that is, the first mix design is partial replace Fly-ash of cement, second is partial replace Fly-ash of cement and fine aggregate, third is partial replace Fly-ash of fine aggregate, fourth partial replacement of fine and coarse aggregate. For this purpose, selected test variables were water-binder ratio with two levels of 45%, 50%, and Fly-ash contents with four levels 0%, 10%, 20%, 30%, As the result of this study are as follow. 1) The result of mix design of a partial replacement of cement, the slump-flow value was appeared a promotive effect of viscosity. But in case of the over with Fly-ash 10% and the other mix design was not changed slump value. 2) The unit weight of the mixing rate with Fly-ash 0% was $1.875{\sim}1.884t/m^3$, the other mix design 10% over with Fly-ash was $1.846{\sim}1.615t/m^3$, the difference was appeared less about 15% than that. 3) In design, partial replace Fly-ash of fine aggregate, this compressive strength was appeared that the concrete age after 7 days was higher than in partial replacement of cement, therefore, the default of a concrete with Fly-ash, that is the earlier compressive strength was to lessen, was improved. 4) The thermal conductivity of the all mix design was $0.447{\sim}1.144kcal/mh^{\circ}C$, this value was as good as a lightweight aggregate concrete.

• Advances in concrete construction
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• 제11권4호
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• pp.335-345
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• 2021

It is known from the literature that there are relatively few studies on the engineering properties of ultra-high performance concrete (UHPC) in early age. In fact, in order to ensure the safety of UHPC during construction and sufficient durability and long-term performance, it is necessary to explore the early behavior of UHPC. The test parameters (test control factors) investigated included the percentage of cement replaced by silica fume (SF), the percentage of cement replaced by ultra-fine silica powder (SFP), the amount of steel fiber (volume percent), and the amount of polypropylene fiber (volume percentage). The engineering properties of UHPC in the fresh mixing stage and at the age of 7 days were investigated. These properties include freshly mixed properties (slump, slump flow, and unit weight) and hardened mechanical properties (compressive strength, elastic modulus, flexural strength, and splitting tensile strength). Moreover, the effects of the experimental factors on the performance of the tested UHPC were evaluated by range analysis and variance analysis. The experiment results showed that the compressive strength of the C8 mix at the age of 7 days was highest of 111.5 MPa, and the compressive strength of the C1 mix at the age of 28 days was the highest of 128.1 MPa. In addition, the 28-day compressive strength in each experimental group increased by 13%-34% compared to the 7-day compressive strength. In terms of hardened mechanical properties, the performance of each experimental group was superior to that of the control group (without fiber and without additional binder materials), with considerable improvement, and the experimental group did not produce explosive or brittle damage after the test. Further, the flexural test process found that all test specimens exhibited deflection-hardening behavior, resulting in continued to increase carrying capacity after the first crack.

• Advances in concrete construction
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• 제6권6호
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• pp.561-583
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• 2018

A variety of polycarboxylate ether (PCE)-based superplasticizers are commercially available. Their influence on the rheological retention and slump loss in respect of concrete differ considerably. Fluidity and slump loss are the cardinal features responsible for the quality of concrete. These are related to the dispersion of cement particles and the hydration process which are greatly influenced by type of polycarboxylate ether (PCE)-based superplasticizers. On the backdrop of relatively less studies in the context of rheological retention of high strength self-consolidating concrete (HS-SCC), the experimental investigations were carried out aiming at quantifying the effect of the six different PCE polymers (PCE 1-6) on the rheological retention of HS-SCC mixes containing two types of Ordinary Portland Cements (OPC) and unwashed crushed sand as the fine aggregate. The tests that were carried out included $T_{500}$, V-Funnel, yield stress and viscosity retention tests. The supplementary cementitious materials such as fly ash (FA) and micro-silica (MS) were also used in ternary blend keeping the mix paste volume and flow of concrete constant. Low water to binder ratio was used. The results reveal that not only the PCEs of different polymer groups behave differently, but even the PCEs of same polymer groups also behave differently. The study also indicates that the HS-SCC mixes containing PCE 6 and PCE 5 performed better as compared to the mixes containing PCE 1, PCE 2, PCE 3 and PCE 4 in respect of all the rheological tests. The PCE 6 is a new class of chemical admixtures known as Polyaryl Ether (PAE) developed by BASF to provide better rheological properties in even in HS-SCC mixes at low water to binder mix. In the present study, the PCE 6, is found to help not only in reduction in the plastic viscosity and yield stress, but also provide good rheological retention over the period of 180 minutes. Further, the early compressive strength properties (one day compressive strength) highly depend on the type of PCE polymer. The side chain length of PCE polymer and the fineness of the cement considerably affect the early strength gain.

• 한국건설순환자원학회논문집
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• 제7권1호
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• pp.44-49
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• 2019

본 연구는 서로 다른 입도의 단일골재 및 반대 입도의 골재를 혼합한 혼합골재에 리젝트애시(Reject ash=Rj)의 치환율 변화에 따른 콘크리트의 기초적 특성을 분석함으로써 골재 제조공장에서 프리믹스하여 1개의 골재로 납품하는 혼합골재 시스템의 가능성을 분석하였다. 실험연구결과 입도규정의 경우는 혼합골재(CSb+SS)에 Rj를 5% 정도 치환할 경우 입도규정을 만족하는 것으로 나타났다. 유동성인 슬럼프 및 슬럼프 플로와 공기량의 경우에는 Rj의 치환율 증가에 따라 감소하는 것으로 나타났으나, 압축강도의 경우에는 Rj의 치환율이 증가함에 따라 증가하는 것이 확인되었다. 따라서 매립 처분되는 Rj를 5% 정도 혼합골재에 프리믹스하여 활용하면서 감수제 및 AE제 등으로 적정 유동성 및 공기량은 확보하여 준다면 압축강도 증진 등 품질향상에 크게 기여할 것으로 분석되었다.

• Geomechanics and Engineering
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• 제29권3호
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• pp.311-320
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• 2022

TBM concrete segment requires a higher level of material properties compared to general concrete structures due to difficulties in maintenance and uncertainty in ground conditions. In this regard, recently, as one of the methods to achieve enhancement effect on concrete strength, many researchers have been focusing on adding CNTs to concrete mixture. However, even CNTs do not compensate the weakness that concrete exhibits brittle behavior after cracking. Separately, over the past few decades, a number of studies have been conducted on fiber reinforced concrete which exhibits ductile behavior due to fibers bridging cracks. However, only limited studies have been conducted to employ the advantages of the both materials together. In this study, an experimental program has been conducted to investigate the effect of CNTs on the workability and the compressive behavior of PVA-ECC which exhibits ductile tensile behavior with well-distributed cracks even without a conventional rebar. In addition to the compression test, SEM analysis has been also conducted for detailed investigation in the microstructure. The variable was the CNTs mix ratio, which were set to 0.00, 0.25, and 0.50 wt.% to the binding materials. It was observed though the test results that as the CNTs mix ratio increased, the workability considerably decreased with the reduced slump and slump flow. From the compression test results, it was also investigated that the compressive behavior was improved since the compressive strength, the strain corresponding to the compressive strength, and the modulus of elasticity increased with an increase of CNTs mix ratio. The contents of this paper will be useful for relevant research areas such as fiber reinforced concrete with CNTs which might be applied for high performance TMB concrete segments.

• Computers and Concrete
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• 제20권3호
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• pp.283-290
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• 2017

The aim of this study is to investigate the effect of the bond strength of self-compacting mortars (SCMS) produced from ground pumice powder (GPP) as a mineral additive. In this scope, six series of mortars including control mix were prepared that consist of 7%, 12%, 17%, 22% and 27% of ground pumice powder by weight of cement. A total of 54 specimens of $40{\times}40{\times}160mm$ were produced and cured at the age of 3, 28 and 90-day for compressive and tensile strength tests and 18 specimens of $150{\times}150{\times}150mm$ mortar were prepared and cured at 28 days for bond strength tests. Flexural tensile strength and compressive strength of $40{\times}40{\times}160mm$ specimens were measured at the curing age of 7, 28 and 90-day. Mini V-funnel flow time and mini slump flow diameter tests were also conducted to obtain rheological properties. As a result of the study, it was observed that the SCMs containing 12% of GPP has the highest bond strength as compared to control and GPP mortars. Compressive strength slightly increased up to 12% of GPP.

• Computers and Concrete
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• 제18권6호
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• pp.1065-1082
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• 2016

The main aim of this study is to predict the compressive and flexural strengths of self-compacting mortar (SCM) containing $nano-SiO_2$, $nano-Fe_2O_3$ and nano-CuO using wavelet-based weighted least squares-support vector machines (WLS-SVM) approach which is called WWLS-SVM. The WWLS-SVM regression model is a relatively new metamodel has been successfully introduced as an excellent machine learning algorithm to engineering problems and has yielded encouraging results. In order to achieve the aim of this study, first, the WLS-SVM and WWLS-SVM models are developed based on a database. In the database, nine variables which consist of cement, sand, NS, NF, NC, superplasticizer dosage, slump flow diameter and V-funnel flow time are considered as the input parameters of the models. The compressive and flexural strengths of SCM are also chosen as the output parameters of the models. Finally, a statistical analysis is performed to demonstrate the generality performance of the models for predicting the compressive and flexural strengths. The numerical results show that both of these metamodels have good performance in the desirable accuracy and applicability. Furthermore, by adopting these predicting metamodels, the considerable cost and time-consuming laboratory tests can be eliminated.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2015년도 춘계 학술논문 발표대회
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• pp.71-72
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• 2015

As this study is the one related to the ultra high strength concrete essentially used for high rise buildings, it has analyzed on the flowability of ultra high strength concrete according to the variation of coarse aggregate and fine aggregate. The coarse aggregate was planned as two types including Granite Aggregate (GA) and crushed coarse Limestone Aggregate (LA) while fine aggregate was planned as four types including Sea Sand (SS), Limestone Crushed Fine Aggregates (LFA), Electric Arc Furnace Oxidizing Slag Aggregates (EFA) and Crushed Sand (CS) to perform experiment with a total of eight variables. As a result of analyzing slump flow, 500mm concentration time, U-Box and L-Flow, etc. among the characteristics of fresh concrete, a mix using LA+LFA is determined to show high flowability in case of applying ultra high strength concrete.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2002년도 가을 학술발표회 논문집
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• pp.573-578
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• 2002

We carried out the feasibility study of super early self compacting concrete having the characteristics of 1 day demoulding without steam curing, high flowable concrete with self compacting, high strength and high durability etc. Here, We test and selected by several methods using high early cement with and without admixtures for the condition of super early strength self compacting concrete's manufacture (SSCC). We sucessed to meet at the goal of SSCC with 30∼35N/㎟ in 1 day, without steam curing and with slump flow about 60-65cm and suggest various concrete products to apply the developed SSCC for practical use in factory and in site place

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2002년도 가을 학술발표회 논문집
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• pp.3-9
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• 2002

Paper sludge ash was assured as material of a sort of pozzolan. For the reason of fluidity decrease caused by the strong absorption of paper stooge ash and the decrease of compressive strength in case of using over30% replacement by the weight of cement, paper sludge ash is not suitable for blending material. Therefore, it is necessary to find proper replacement ratios between paper sludge and blast furnace slag to insure compressive compensation and appropriate slump. Accordingly, as varied the blending ratios of paper sludge and blast furnace slag, testing mortar was made. This study was aimed to investigate the possibility of using blending replacement of paper sludge ash and blast furnace slag throughout compressive test, flow test, SEM(Scanning Eletron Microscope), MIP(Mercury Intrusion Porosity test), and TG-DTA(Thermal analysis).