• Proceedings of the Korea Concrete Institute Conference
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• 2005.11a
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• pp.643-646
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• 2005

This paper reports the influence of super retarding agent(SRA) on the setting time of concrete incorporating mineral admixture including fly ash(FA), expansive additive(EA), silica fume(SF), blast furnace slag(BS) and blast furnace slag along with fly ash(BS+FA). An increase in SRA resulted in retarding the setting time of control concrete, while the use of mineral admixture led to a delay of setting time markedly, compared with that of control concrete under no SRA content. Meanwhile, An increase in SRA in concrete with mineral admixture exhibited comparable setting delay with control concrete. Furthermore, in case of the use of BS and SF, acceleration of setting time was observed with increase of SRA content. It is considered that proper dosage of SRA of concrete with SF and BS to secure similar setting delay with control concrete require rather larger than that of control concrete. Accordingly, For concrete with mineral admixture, in order to decide the proper dosage of SRA, application of correction factors is needed.

• Journal of the Korea Concrete Institute
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• v.13 no.6
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• pp.527-535
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• 2001

The watertight property of concrete was examined, that is affected by the sort of self waterproofing admixture and the change of the addition ratio of admixture. Various self waterproofing admixtures were made by changing the mixing ratio of silica fume, zinc stearate and silica sand. The result showed as follows. As the adding ratio of self waterproofing admixture increases, the fluidity is increased and the setting time is delayed. While compressive strength of concrete with self waterproofing admixture A which is currently using is increased until the adding ratio of self waterproofing admixture reached 18kg/㎥ and decreased over 24 kg/㎥, that with self waterproofing admixture B, C and D which are developed are higher than that of A. Absorption is decreased as the adding ratio of self waterproofing admixture and the increasing of age in concrete. Especially, when self waterproofing admixture has a lot of zinc stearate, absorption is decreased manifestly. The property of permeability is similar to that of absorption; permeability is decreased as the adding ratio of self waterproofing admixture and the increasing of age in concrete. Consequently, when the ratio of silica fume, zinc stearate and silica sand in self waterproofing admixture is 1 : 2 : 1 and addition ratio of self waterproofing admixture is 6kg/㎥, the high quality concrete is obtained comparing to the concrete with existent self waterproofing admixture.

• Journal of the Korea Institute of Building Construction
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• v.23 no.5
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• pp.547-558
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• 2023

This research delves into the fabrication of an ultra-high-strength concrete, enriched with oxidized graphene nanoplatelet(GO) and hollow glass powder(HGP), notably eschewing the conventional inclusion of silica fume(SF). The primary objective was to scrutinize the autogenous shrinkage characteristics of this innovative formulation. It was discerned that the NewMix specimen, which incorporated the cGO(sourced from Company C) and HGP, and intentionally bypassed SF, showcased a commendable 13% reduction in autogenous shrinkage relative to the benchmark(Ref) specimenthat incorporated SF. Moreover, the proclivity for crack formation owing to autogenous shrinkage in the NewMix was observed to manifested by NewMix at the juncture of cracking emerged as the apex value. Attributed to the expansive specific surface area and exemplary dispersibility of cGO, it was postulated that the concrete's pore structure benefitted from enhanced infill, leading to a reduction in autogenous shrinkage. Additionally, the cGO integration fortified the concrete's resistance to crack initiation. Consequently, such an enhancement is posied to be pivotal in mitigating crack propagation resulting from autogenous shrinkage in ultra-high-strength concrete.

• Corrosion Science and Technology
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• v.8 no.5
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• pp.171-176
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• 2009

The chloride threshold level (CTL) in mixed concrete containing, ordinary Portland cement (OPC), pulverized fuel ash (PFA) ground granulated blast furnace slag (GGBS), and silica fume (SF) is important for study on corrosion of reinforced concrete structures. The CTL is defined as a critical content of chloride at the steel depth of the steel which causes the breakdown of the passive film. The criterion of the CTL represented by total chloride content has been used due to convenience and practicality. In order to demonstrate a relationship between the CTL by total chloride content and the CTL by free chloride content, corrosion test and chloride binding capacity test were carried out. In corrosion test, Mortar specimens were cast using OPC, PFA, GGBS and SF, chlorides were admixed ranging 0.0, 0.2, 0.4, 0.8, 1.0, 1.5, 2.0, 2.5 and 3.0% by weight of binder. All specimens were cured 28 days, and then the corrosion rate was measured by the Tafel's extrapolation method. In chloride binding capacity, paste specimens were casting using OPC, PFA, GGBS and SF, chlorides were admixed ranging 0.1, 0.2, 0.3, 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0% by weight of binders. At 28days, solution mixed with the powder of ground specimens was used to measure binding capacity. All specimens of both experiments were wrapped in polythene film to avoid leaching out of chloride and hydroxyl ions. As a result, the CTL by total chloride content ranged from 0.36-1.44% by weight of binders and the CTL by free chloride content ranged from 0.14-0.96%. Accordingly, the difference was ranging, from 0.22 to 0.48% by weight of binder. The order of difference for binder is OPC > 10% SF > 30% PFA > 60% GGBS.

• Journal of the Korean Recycled Construction Resources Institute
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• v.1 no.1
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• pp.58-66
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• 2013

This study investigated quality properties of alkali activated cement free mortar using industrial by-product such as cement kiln dust(CKD), silica fume(SF) and quartz sand powder(SP) to compare with previous research about blast furnace slag(BS) and fly ash(FA). The results were as following. All materials were effective to increase compressive strength, however they showed different tendency on flowability. CKD and SP increased flowability, but on the other hand SF did not because it's blain was great difference with other materials. Flowability and compressive strength were related with grading distributions of binders because CKD, SP and SF which had small particle size filled up BS and FA. Application of industrial by-products with various grading distributions could be effective for the high early strength and flowability of alkali activated cement free mortar using BS.

• Computers and Concrete
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• v.30 no.2
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• pp.99-111
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• 2022

In this study, deep learning and k-Nearest Neighbor (kNN) models were used to estimate the sorptivity and freeze-thaw resistance of self-compacting mortars (SCMs) having binary and ternary blends of mineral admixtures. Twenty-five environment-friendly SCMs were designed as binary and ternary blends of fly ash (FA) and silica fume (SF) except for control mixture with only Portland cement (PC). The capillary water absorption and freeze-thaw resistance tests were conducted for 91 days. It was found that the use of SF with FA as ternary blends reduced sorptivity coefficient values compared to the use of FA as binary blends while the presence of FA with SF improved freeze-thaw resistance of SCMs with ternary blends. The input variables used the models for the estimation of sorptivity were defined as PC content, SF content, FA content, sand content, HRWRA, water/cementitious materials (W/C) and freeze-thaw cycles. The input variables used the models for the estimation of sorptivity were selected as PC content, SF content, FA content, sand content, HRWRA, W/C and predefined intervals of the sample in water. The deep learning and k-NN models estimated the durability factor of SCM with 94.43% and 92.55% accuracy and the sorptivity of SCM was estimated with 97.87% and 86.14% accuracy, respectively. This study found that deep learning model estimated the sorptivity and durability factor of SCMs having binary and ternary blends of mineral admixtures higher accuracy than k-NN model.

• Journal of the Korean Recycled Construction Resources Institute
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• v.6 no.1
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• pp.72-79
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• 2011

This study is performed to analyze the effects of CASB by applying the superplasticizer combined CASB on the ultra high strength mortar and concrete that uses different mineral admixture depending on whether the silica fume was used and the results are summarized below. From the characteristics of Fresh mortar and concrete, the fluidity was lower in B2-CASB than B2-PC from the mixing of CASB and based on the viscosity of the mortar and concrete in the binary proportion but in the ternary proportion, B3-CASB showed a larger fluidity than B3-PC because of a reduction in the restriction level due to the effects of an improvement of particle size distribution. The compression strength was higher in ternary proportion than in binary proportion and higher in CASB than in PC from the characteristics of hardening mortar and concrete and this is analyzed as a result of increased minuteness from the calcium silicate hydrates produced from the pozzolan reaction of a mineral admixture, SF, and also the charging effects of capillary pore of CASB. Overall, when using the nanomaterial, CASB in combination with a superplasticizer, the fluidity and the strength aspects of the ternary proportion of ultra high strength mortar and concrete with silica fume may be improved to a higher quality.

• Computers and Concrete
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• v.16 no.6
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• pp.865-880
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• 2015

Standard test method for bulk electrical conductivity (ASTM C1760) provides a rapid indication of the concrete's resistance to the penetration of chloride ions by diffusion. In this paper a new approach for assessing the bulk electrical conductivity of saturated specimens of hardened concrete is presented. The test involves saturating concrete specimens with a 5 M NaCl solution before measuring the conductivity of the samples. By saturating specimens with a highly conductive solution, they showed virtually the same pore solution conductivity. Different concrete samples yield different conductivity primarily due to differences in their pore structure. The feasibility of the method has been demonstrated by testing different concrete mixtures consisting ordinary and blended cement of silica fume (SF) and calcined perlite powder (CPP). Two standard test methods of RCPT (ASTM C1202) and Bulk Conductivity (ASTM C1760) were also applied to all of the samples. The results show that for concretes containing SF and CPP, the proposed method is less sensitive towards the variations in the pore solution conductivity in comparison with RCPT and Bulk Conductivity tests. It seems that this method is suitable for the assessment of the performance and durability of different concretes containing supplementary cementitious materials.

• Proceedings of the Korea Concrete Institute Conference
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• 1994.04a
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• pp.148-151
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• 1994

Up to now, sea sand without complete removal of salt is being used in the construction works because there is little satisfactory counterplan for the substitute aggregate. In the case that such sea sand is used in the reinforced concrete, the residual salt gives rise to deterioration phenmenon and iron corrosion, reducing durability of the ferro-concrete structures. The paper, an experimental study on the effect of corrosion protection by tighting concrete used SF and FA, is to investigate general steel bar's corrosion and to develop concrete using sea sand economically after it is analyzed and examinated ratio of the corrosion area affected by the autoclave cycle. As a test results, as for corrosion area ratio, it is very effective to use admixrutes such as SF and FA which decrease corrosion area remarkably with increasing the amounts of admixtures. Accordingly the use of admixtures is advantageous for tightening concrete and has an effect of salt damage prevention and rust protection in concrete used sea sand.

• International Journal of Concrete Structures and Materials
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• v.18 no.2E
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• pp.97-102
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• 2006

In this study, the effect of supplementary materials(GGBS, PFA, SF) on sulfuric acid corrosion resistance was assessed by measuring the compressive strength, corroded depth and weight change at 7, 28, 56, 91, 180 and 250 days of immersion in sulfuric acid solution with the pH of 0.5, 1.0, 2.0 and 3.0. Then, it was found that an increase in the duration of immersion and a decrease in the pH, as expected, resulted in a more severe corrosion irrespective of binders: increased corroded depth and weight change, and lowered the compressive strength. 60% GGBS mortar specimen was the most resistant to acid corrosion in terms of the corroded depth, weight change and compressive strength, due to the latent hydraulic characteristics and lower portion of calcium hydroxide. The order of resistance to acid was 60% GGBS>20% PFA>10% SF>OPC. In a microscopic examination, it was found that acid corrosion of cement matrix produced gypsum, as a result of decomposition of hydration products, which may loose the structure of cement matrix, thereby leading to a remarkable decrease of concrete properties.