• Journal of the Korea institute for structural maintenance and inspection
• /
• v.9 no.4
• /
• pp.261-269
• /
• 2005

The object of this research is to produce alkali activated fly ash-cement using low calcium fly ash as substitute for portland cement. The experimental program included activation of fly ash by a strong base(NaOH) at different concentration, temperature, and liquid-to-fly ash ratios. To achieve for higher compressive strength of the hardened product, sodium meta silicate is added to the alkaline solution. From the factors considered on strength development, the ratio of liquid/fly ash, the activator concentration and temperature always result to be significative factors. The optimization studied show that the alkaline solution concentration of $NaOH(210g)+Na_2SiO_3{\cdot}9H_2O(30g)+H_2O=1L$ at $50^{\circ}C$ produces the best alkali activation effect for the low calcium fly ash. SEM and XRD patterns showed that the components of alkali-activated fly ash consist mainly of mullite, quartz and amorphous aluminosilicate.

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.6 no.3
• /
• pp.69-78
• /
• 2011

As recent concrete products changed to pursue high class, high quality, and high strength, as translucent concrete was developed to meet esthetic effects and exhibition purpose of structures. This study aims at introducing fabrication methods of various shapes of translucent concrete and evaluating feasibility of using mineral admixture such as fly ash, ground granulated blast furnace slag and granulated glass throughout experimental tests. As the result, it was found that compressive strength of translucent concrete block at 28 days is 32.2MPa and higher elastic modulus and Poisson's ratio than ordinary concrete block, which means that translucent concrete is widely applicable to structural purpose. Application of fly ash as a replacement of cement showed lower strength of 85 to 96% than Portland cement. In the meanwhile, ground granulated blast furnace slag showed 82 to 96% depending on the amount of replacement. The use of granulated glass as replacement of optical fiber was not applicable due to invisibility of light in concrete.

• Journal of the Korean Institute of Landscape Architecture
• /
• v.28 no.5
• /
• pp.48-57
• /
• 2000

This paper is dealing with the fundamental properties of planting concrete, replacing the existing cover concrete on the roof of a building. This study is to find out the physical characteristics of the planting concrete and rearing characteristics of the grass throughout the modeling experimental materials. As the results of the experiment, the physical properties of planting concrete show the following results; when the paste to aggregate ratio is 0.2~ 0.4, voids volume : 30~17%, unit weight: 1,710~2,010kg/m3, compressive strength : 45~145kgf/$\textrm{cm}^2$, its pH is more than 11, but is reduced to the proper degree for planting after being neutralized. Kentucky bluegrass covered with planting concrete is grown well. The planting concrete used with blast furnace slag cement shows a better properties at the height, the width and the covering rate by 1.1cm, 0.5mm and 7%, respectively, than those used with ordinary portland cement. Also, the less the paste to aggregate ratio is, the better the plant grows. The orders of the effects of temperature control are as follows; the system of planting concrete with grass>the system of planting concrete without grass>the system of mixed soil>the existed roof system. In case, the planting concrete is placed to the roofs of buildings instead of normal concrete slab, and a number of favorable effect can be expected such as the improvement os environmental factors, the reduction of construction cost, the saving of energy and the reduction of environment load. The future research on the change of a variety of the aggregate conditions and the application of the practical structures should be made, and also the research of the endurance also be performed.

• KCI Concrete Journal
• /
• v.13 no.1
• /
• pp.43-51
• /
• 2001

Although portland cement concrete is one of the most universal construction materials, it has some disadvantage such as shrinkage, which is an inherent characteristic. Because of this shrinkage, combined with the low tensile strength of the material, cracks of varying sizes can be found in every reinforced concrete. To prevent this cracking, keeping the concrete in compression by mechanical prestress has been used. This study discusses application of expansive additives for concrete to improve the serviceability of precast concrete box culvert by inducing chemical prestress. For this purpose, both expansive concrete slabs and normal concrete slabs are tested to verify the effect of expansive additives. Then the failure tests of the fullscale precast box culverts were carried out and the critical aspects of the structural behavior were investigated. The result of the material testis shows that the optimal proportion of expansive additives is 13 percent of cement weight, and the properties of expansive concrete are the same as those of normal concrete in that proportion. Both the experimental cracking load and service load of the expansive concrete members are increased in comparison with those of the normal concrete, but the ultimate load is decreased slightly. In addition to the above results, the deformation of expansive concrete member is lets than that of normal concrete member, and permanent strain which results from cyclic load is decreased. It can be concluded that the use of expansive additives to induce chemical prestress in precast concrete box culvert greatly improves the serviceability.

• Journal of the Korea Concrete Institute
• /
• v.21 no.5
• /
• pp.611-617
• /
• 2009

This paper reports an experimental study on the damage mechanism and resistance of Type I portland cement mortar and paste samples exposed to 5% sodium sulfate solution with different solution temperatures; namely, $4^{\circ}C$, $10^{\circ}C$ and $20^{\circ}C$. The resistance of mortar samples was evaluated using expansion, compressive strength and flexural strength measurements. Some microstructural observations such as x-ray diffraction, differential scanning calorimetry and scanning electron microscopy were also introduced to elucidate reactants formed by sulfate attack, especially in a low temperature condition. From the results, it was found that the degree of damage in the mortar samples was significantly associated with the temperature of sulfate solution. Low temperature of the sulfate solution led to the formation of thaumasite in mortar and paste samples, and subsequently a poor resistance to sulfate attack. Thus, it is noted that when concrete structures are exposed to sulfate media in the condition of a cold region or whether, special care should be taken.

• Advances in concrete construction
• /
• v.6 no.6
• /
• pp.561-583
• /
• 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.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.29 no.4A
• /
• pp.365-371
• /
• 2009

It is time-consuming to estimate chloride diffusivity of concrete by concentration difference test. For the reason chloride diffusivity of concrete is mainly tested by electrically accelerated method, which is accelerating the movement of chloride ion by potential difference. In this study, portland cement concrete and concrete containing with ground granulated blast-furnace slag (40 and 60% of cement by weight) with water-cementitious material ratio 40, 45, 50 and 60% were manufactured. To compare with chloride diffusivity calculated from the electrically accelerated test and immersed test in artifical seawater, chloride diffusivity tests were conducted. From the results of regression analysis, regression equation between accelerated chloride diffusivity and immersed chloride diffusivity was linear function. And the determinant coefficient was 0.96 for linear equation.

• International Journal of Highway Engineering
• /
• v.12 no.1
• /
• pp.87-98
• /
• 2010

Surface of fine-size exposed aggregate Portland cement concrete pavements is consists of exposed coarse aggregate by removing upper 2~3mm mortar of concrete slab. Fine-size exposed aggregate PCC pavements have advantages of maintaining low-noise and adequate skid-resistance level during the performance period. In order to provide the successful exposed concrete aggregate pavement, uniform distribution of the coarse aggregate on pavement surface through adequate the mix design and exposing method. In this study, evaluated initial performance of fine-size exposed aggregate PCC pavement by experimental construction. And it was known that fine-size exposed aggregate concrete pavement which can reduce the noise and maintain the adequate level of skid resistance and strength.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.21 no.5
• /
• pp.12-20
• /
• 2017

This report presents the results of an investigation on the fundamental properties of mortars high fluidity high volume slag cement(HVSC) activated with sodium silicate($Na_2SiO_3$). The ordinary Portland cement(OPC) was replaced by ground granulated blast furnace slag(GGBFS) from 40% to 80% and calcium sulfoaluminate(CSA) was 2.5% or 5.0% mass. The $Na_2SiO_3$ was added at 2% and 4% by total binder(OPC+GGBFS+CSA) weight. A constant water-to-binder ratio(w/b)=0.35 was used for all mixtures. The research carried out the mini slump, V-funnel, setting time, compressive strength and drying shrinkage. The experimental results showed that the contents of superplasticizer, V-funnel, setting time and drying shrinkage increased as the contents of CSA and $Na_2SiO_3$ increase. The compressive strength increases with and an increase in CSA and $Na_2SiO_3$. One of the major reason for these results is the accelerated reactivity of GGBFS with CSA and $Na_2SiO_3$. The maximum performance was CSA 5.0% + $Na_2SiO_3$ 4% specimens.

• Resources Recycling
• /
• v.18 no.4
• /
• pp.31-37
• /
• 2009

The purpose of this study was to evaluate the effects of fly-ash and blast-furnace slag on strength development and durability of ternary blended concrete (TBC) and ordinary portland cement concrete as fly ash and slag contents. Main experimental variables were performed fly ash contents (0%, 10%) and slag contents (0%, 10%, 20%, 30%). The compressive and flexural strengths, chloride-ion rapid permeability and chemical attacks resistance were measured to analyze the characteristic of the developed TBC on hardened concrete. The test results showed that compressive and flexural strength of TBC increased as the slag contents increased from 0% to 30% at the long term of curing. It considers blast furnace slag used when fly ash content was up to 10%. The permeability resistance of TBC(fly ash 10%, blast 30%) was extremely good at the curing time 90 days. Also, the effects of added blast furnace slag on OPC and TBC were increased on the permeability and chemical attacks resistance.