Earticle

The objective of the study is to investigate the effect of impregnation of alkali activator on the strength enhancement of hardened high volume fly ash mortar. Sodium hydroxide (12 mol) is adopted for alkali activator of hardened mortar in this study. Four different contents of fly ash(FA) are chosen ranged from 30~90 % by cement weight. Alkali activator was applied on the surface of hardened specimen at 3 days. Curing temperatures ranged from 40~80℃ are varied. Mortars with 40 % of Water to binder ratio were fabricated. Test results indicated that the specimen impregnated with sodium hydroxide subjected to high curing temperature exhibited higher strength enhancement than that without sodium hydroxide by as much as 100~300 % due to accelerated pozzolanic reaction by sodium hydroxide. For the curing temperature effect, water curing at 40℃ of the specimen with 60 % of FA for 24 hours resulted in an highest enhancement of the strength regardless of age among other conditions, while the specimen with 90% of FA showed remarkable increase of strength at 60℃ of the curing temperature.

본 연구는 $CO_2$발생으로 인한 지구 온난화에 따른 해결책으로 고로슬래그, 레드머드, 실리카 흄 등을 시멘트를 대체하기 위한 기초적인 연구를 수행한 것으로 고로슬래그, 레드머드, 실리카 흄 및 알칼리 자극제를 사용하여 시멘트와 같은 성질을 가지는 경화체의 제조가 가능한지에 대한 실험적 검토를 실시하였다. 이를 위하여 시멘트 대체재로 고로슬래그, 레드머드, 실리카 흄 등의 무기결합재와 수산화나트륨(NaOH), 규산나트륨($Na_2SiO_3$)등을 사용하여 비빔시간 변화에 따른 강도특성을 선행실험에 실시하였다. 선행실험을 바탕으로 본 실험에서는 기건양생, 수중양생, 피막양생, 한지양생을 실시함으로써 경화체의 강도특성에 대하여 분석을 실시하였다. 그 결과, 수중양생 $80^{\circ}C$의 경우 재령 28일에서 압축강도 및 휨강도가 가장 우수하였으며 무시멘트 경화체의 제조가 가능해서 친환경적인 콘크리트 생산에 커다란 영향을 미칠 수 있을 것으로 판단된다.

This study was conducted as the basic research for the replacement of Blast Furnace Slag, Red Mud, Silica Fume, etc., with cement as a solution to the problems arising from the global warming caused by the generation of $CO_2$, and conducted the experimental review to examine the feasibility of matrix having properties identical to those of cement by using the Blast Furnace slag, Red mud, Silica fume, and alkali-activator. For this, by using the the inorganic binder, such as Blast Furnace Slag, Red Mud, Silica Fume, etc., and NaOH, $Na_2SiO_3$ and others as the cement substitute material, the strength characteristic according to the mixture time variation was performed in the tentative experiment. Based on the preceding experiment, this study performed the experiment to analyze the strength properties of hardener through the curing by air-dry temperature, curing by temperature in water, coating curing, and Korean paper curing. For the water curing at $80^{\circ}C$, the compressive strength and flexural strength were found to be the most excellent at the age of the 28th day, and furthermore, it was found that the non-cement hardener could be made, which is considered to affect the production of eco-friendly concrete.

콘크리트의 품질판정기준(品質判定基準)은 재령(材令) 28일(日)의 압축강도(壓縮强度)이지만, 실질적인 품질관리(品質管理)를 위해서는 조기(早期)에 강도(强度)를 파악해야 한다. 콘크리트 강도(强度)를 조기판정(早期判定)하는 방법은 크게 "강도촉진법(强度促進法)"과 굳지 않은 콘크리트의 "분석법(分析法)"이 있으나, 본(本) 연구(硏究)에서는 $70^{\circ}C$의 열수양생법(熱水養生法)으로 다양한 양생방법을 시도하여 기존의 외국기준(外國規準)보다 개선된 방법을 제시하였다. 실험자료의 분석(分析)에 있어서는 각 강도의 변동을 검토함은 물론, 합리적인 추정식(推定式)을 제안하기 위하여 각 강도의 분포(分布)를 고려하고 확률적(確率的) 관계(關係) 및 품질기준(品質基準)의 적합성(適合性)을 검토하였다. 실험결과 촉진강도(促進强度)의 변동은 비교적 작게 나타났으며, 본 연구에서 제안한 대부분의 방법이 좋은 상관성(相關性)을 가지고 있어 유용한 조기판정방법(早期判定方法)으로 판명되었다.

Accelerated strength testing is a available method for quality control of concrete. This paper presents the improved hot water ($70^{\circ}C$) methods and discusses how these methods can be adapted for predicting 28 day strength. The strength results have been analyzed by statistical techniques and correlation between early and 28 day strength are showed by prediction line. The test results show that the methods proposed in this paper are usable to predict the potential quality of concrete with low variation and good relationship between two strengths.

The objective of the paper is to provide effective insulation curing method for cold weather concrete considering temperature condition in cold weather. Concretes were placed at the slab for deck plate and column executed at construction field for newly constructed department store building. Surface insulation curing materials studied by the authors were applied. According to results, under chilly climate condition, the combination of double layer bubble sheet and fabric sheet at the top surface of slab concrete made it possible to maintain its temperature above 15℃, which did not require any additional heating. At slight freezing condition in cold weather, the combination of double layer bubble sheet and fabric sheet at the top surface of slab concrete made it possible to maintain its temperature above 15℃ for over 2 days, which can prevent frost damage at early age. However, at severe freezing condition, as substantial measure against freezing is necessary, at top surface of concrete, the combination of double bubble sheet and fabric sheet and temporary tent around bottom section resulted in an effective curing, which maintained the concrete temperature above 5～10℃ for over 1.5 days and also, saved the cost for temporary works. This method may be the cost effective heat curing system. For column concrete, the wrapping of bubble board around the column can secure the stability against frost damage at early age by protecting the edge of column concrete vulnerable to cold weather.

The study is progressing dynamically to reduce the amount of CO2 worldwide. Cement manufacture is known as industry which is emitting about a lot of CO2. In this study, test piece of non-sintered cement mortar was made with the effects of granulated blast-furnace slag with phospho-gypsum which is made a process of fertilizer produce and slaked lime which is a essential material to make a strong alkali stimulant. There is a purpose to evaluate each test piece of non-sintered cement mortar comparing flexural strength and compressive strength by water curing and steam curing.

Purpose: This study aimed to evaluate the effect of post-curing method on the flexural strength of provisional restorative resins produced by a digital light processing printer. Methods: A total of 20 specimens were produced, with a length of 64 mm, width of 10 mm, and thickness of 3.3 mm using a digital light processing printer. Two types of provisional restorative resins made with different post-curing methods were investigated and divided into conventional and vacuum groups. For the flexural strength test, each group was prepared by each method according to ISO 10477, and the flexural strength was measured with a universal testing machine. For statistical analysis, data were analyzed by independent t-test and Mann–Whitney U test. Results: The flexural strengths of the conventional and vacuum groups were 151.89 MPa and 131.94 MPa, respectively, showing a statistically significant difference (p<0.05). Conclusion: Within the limitation of this study, provisional restorative resins produced with vacuum demonstrated lower flexural strength than those produced with conventional postcuring method.

A novel evaluation method is investigated for measuring the ability of acid amplification of acid amplifier. The method is based on the measurement of conductivity change by the acid generation according to UV radiation. It is found that the decrease of conductivity is caused by photopolymerization of epoxy monomer during UV curing process of ink film and the by the rate of UV curing. In this paper, the novel acid amplifiers were synthesized and measured thermal stability by means of DSC. It was found that mono-type acid amplifiers were more stable than di-type. It is possible to make the dynamical evaluation the curing rate of UV curable ink in curing process by this method.

A novel evaluation method is investigated for UV curing process in printing system. The method is based on the measurement of conducivity change by the photopolymerization of UV curable inks and paints. It is found that the decrease of conductivity is caused by photopolymerization of epoxy monomer during UV curing process of ink film and the by the rate of UV curing. It is possible to make the dynamical evaluation the curing rate of UV curable ink in curing process by this method.

Purpose: This study aimed to evaluate the effect of surface treatment methods on threedimensional printing resin by analyzing surface roughness, contact angle, shear bond strength, and failure modes when bonded with self-polymerizing resin. Methods: The study compared control (CON) group and three surface treatment methods, namely, sand blast (SB) group with 50 μm alumina, adhesive (AD) group, and a combination of SB and AD (SA) groups. The specimens measured 10 mm×10 mm×5 mm. The specimens were printed with 100 μm thickness, light-cured for 15 minutes, and then polished with SiC paper. The SB group involved SB group with alumina, the AD group used a bonding agent followed by light-curing, and the SA group combined SB group with AD group and light-curing. Results: The surface roughness was significantly different between the CON and AD groups and between the CON and SA groups. The contact angles were significantly different across all groups of specimens. Moreover, the shear bond strength was significantly different between the SB and AD groups. Conclusion: The use of 50 μm alumina during SB group or applying a bonding agent afterward significantly increased the shear bond strength with self-polymerizing resin; therefore, these methods effectively enhance the bonding performance.

According to the domestic specification, the curing of the specimen for strength management used to determine the time of the mold deformity of the structure concrete in early spring and early autumn is cured in the field structure condition. However, when the seal curing is performed in the field, the temperature of the specimen is very low compared to the temperature of the actual structure, so the strength of the structure concrete predicted based on the strength of the specimen is much undervalued than the actual one, which causes the mold to be deformed. Therefore, this study analyzed the temperature history and compressive strength characteristics of the specimen for strength management through other sealing curing at 5℃ and concrete of the actual structure, and presented the most suitable curing method.

The microstructure and compressive strength of a 0.38 water-to-cement mass ratio (w/c) cement paste when subjected to accelerated-curing by microwave energy and autoclave curing were compared with a normal curing method by soaking in saturated-lime deionized water at 25 oC. The morphology, atom ratio of Si/Ca versus Al/Ca, phase composition by XRD, and compressive strength were measured in this study. The results indicate the presence of needle-like ettringite (Aft) in pastes that had been cured using the autoclave method. However, the saturated-lime deionized water cured paste showed lath-like or plate-like shapes and did not appear to produce ettringite (Aft). In addition, the microwave-cured paste indicated some evidence of ettringite. The range of Si/Ca and Al/Ca ratios of the autoclave-cured paste were 0.039? 0.052, and 0.207 ? 0.234,respectively, while in the microwave-cured paste the ratio shifted to 0.079? 0.091. The compressive strength of the autoclavecured cement paste showed an increase in strength at an early age, while the strength decreased after 7 days of hydration.

This study used a temperature stress test machine (TSTM) to study the effects of the water-to-cement (w/c) ratio, curingmethod and the content of polyvinyl alcohol (PVA) fiber on the autogenous shrinkage of high-performance concrete (HPC). The experimental values were compared with theoretical values obtained from four sets of autogenous shrinkage models tocompare model accuracy. The study results indicated the followings: (1) the autogenous shrinkage value of concrete increasedwith decreases in the w/c ratio. (2) The natural and semi-adiabatic curing conditions caused the specimens to form a low- anda high-temperature rise, respectively. The higher the temperature rise, the larger the stable value of the autogenous shrinkage. (3) Among the CEB-FIP, EN-1992, RILEM and Tazawa models, the Tazawa model demonstrated the highest degree ofaccuracy. (4) PVA fiber contents of 0.75% and 0.25% had the most significant and minimal autogenous shrinkages,respectively.

In this study, heat curing technique (up to 320 oC) that allows the usage of sodium silicate solutions with un-calcined kaolinsto offer a durable geopolymeric binder in a short time was investigated. Samples containing up to 40 wt.% binder have beenproduced to observe the binder behaviour over a wide range of additions by heat curing for one hour. The cured samplesconsist of kaolinite and amorphous phase and crystallinity was decreased with increasing curing temperatures. 240 oC was thethreshold temperature for the strength development of the samples. Condensation reactions between Al-OH- units in uncalcinedkaolin and silanol groups in sodium silicate solution that yield sialate (Si-O-Al-O) bridges detected by infraredanalyses are the considered mechanisms of promoter effects of kaolinite. Optimum compressive strength (23.4 MPa.) wasobtained with the samples produced with 20 wt.% binder addition and 300 oC curing temperature.

육송 미송 포플라 등 국산 연질 목재에 단량체 또는 단량체 혼합물을 촉매와 함께 침투시키고 열중합함에 있어서 시간에 따르는 중합율을 구하고 이것을 방사선 중합으로 WPC를 제조할 때 얻은 간과 비교 검토하여 다음과 같은 결론을 얻었다. (1) 중합율로 보아서는 육송, 미송이 포플라보다 좋으며 M.M.A.가 다른 단량체보다 효과적이다. (2) 비닐아세테이트는 일반적으로 열중합에 의한 중합율이 저조한 편이며 특히 포플라에 침투된 경우 매우 낮아 W.P.C.를 만들기 곤란하다. 그러나 비닐아세테이트와 M.M.A.를 같이 침투시키면 나무종류나 중합방법에 별 관계없이 매우 빨리 중합하여 가장 효과적이다. (3) 나무에 침투된 단량체나 단량체 혼합물의 중합의 경향은 나무가 많은량의 수지를 함유하지 않는다면 중합방법에 관계없이 단량체나 단량체 혼합물 자체만일때의 중합의 경향과 같다.

The polymerization rates of monomer or monomer mixture impregnated with catalyst into domestic soft woods such as pinus densiflora, pinus rigida and poplus deltoides e. t. c. were measured. The results were compared with those obtained by radiation curing method and the following conclusions were derived ; (1) Pinus densiflora and pinus rigida are superior to the poplus deltoides, and methyl methacrylate(M. M. A. ) is more effective than other monomers as far as the polymerization rates are only taken into account. (2) The polymerization rate of vinyl acetate is generally slow. And the polymerization rate of the monomer is the slowest in case of being impregnated into poplus deltoides. However, the polymerization rate of the comonomer composed of vinylacetate and M. M. A. is the fastest among the other monomers or monomer mixtures in woods regardless of the curing method. (3) The general trend of polymerization of monomer in wood is similar to that of monomers themselves in both curing methods if the woods contain not much resin.

This paper investigates the temperature history of slab mock-up specimens with various surface curing sheets, in order to determine a favorable surface curing method in hot weather condition. Test showed that insulating double bubble sheets+aluminum foil simultaneously on the upper section of a specimen prevented an increase of sudden temperature and a decrease of vaporization when placed during the hot weather condition. It also secured the high strength in early age. Therefore it is found that using the double bubble sheets+aluminum foil on concrete surface declined the plastic and drying shrinkage and inclined the early strength, thus improving the concrete quality.

This study is tocompare and analyze the results of hydration heat analysis and on-field measurements using the method with hydration heat difference and insulation curing method for controlling hydration heat in mass concrete. As a result of the analysis, the temperature difference between the center and the surface was predicted very similarly, and the mass concrete surface was controlled to a safe level when evaluating with a temperature crack index, and after being finished, it was confirmed that there was no hydration crack.

In this study, the hydration heat differential method was applied to mass concrete structures, and the hydration heat analysis was compared and analyzed with on-site measurement results. The results showed that the temperature history measurements of mass concrete were managed at a difference of 8.4 ℃, and although there was some deviation in thermal stress, a similar trend was observed. Consequently, it was determined that the thermal stress on the surface of mass concrete is less than its tensile strength, which would prevent the occurrence of thermal cracks.