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Muroran, Japan

Ishida T.,University of Tokyo | Luan Y.,University of Tokyo | Sagawa T.,Nittetsu Cement Co. | Nawa T.,Hokkaido University
Cement and Concrete Research | Year: 2011

A multi-scale system called DuCOM was enhanced to model behaviors of blast furnace slag (BFS) concrete. Tests on the strength and micro-hygro-physical properties of BFS concrete and Portland cement concrete were conducted. The current model was found to underestimate the strength of BFS concrete at later ages owing to underestimation of the water content inside C-S-H gel pores. To remedy this, enhanced modeling of porosity allowing proper simulation of the porosity of the BFS paste matrix and higher strength development at later ages is proposed. Furthermore, based on the enhanced porosity model, the moisture loss and pore size distribution of the BFS paste matrix were investigated. The pore size distribution was found to be coarser than the test at later ages in the model, resulting in overestimation of moisture loss. Hence, the pore size distribution was enhanced as well, allowing simulation of a finer pore structure of the BFS matrix. Finally, verifications showed that the enhanced model better predicts water desorption, moisture loss and drying shrinkage behaviors. © 2011 Elsevier Ltd. All rights reserved. Source

Luan Y.,University of Tokyo | Ishida T.,University of Tokyo | Nawa T.,Hokkaido University | Sagawa T.,Nittetsu Cement Co.
Journal of Advanced Concrete Technology | Year: 2012

A hydration model for cementitious materials was applied to slag blended cement. The original model was found to overestimate the hydration degree of slag, and the influence of the slag ratio on the hydration degree not to be well simulated either. The hydration mechanism of slag was investigated, considering the role of calcium hydroxide as activator and the Ca/Si ratio of C-S-H. It is assumed that for low Ca/Si ratio, the C-S-H inner product has a stronger resistance against ion diffusion and thus influences the hydration process significantly. Accordingly an enhanced model for slag hydration is proposed. Finally, the enhanced model is verified by both hydration degree and heat generation tests. Copyright © 2012 Japan Concrete Institute. Source

Na S.H.,Muroran Institute of Technology | Hama Y.,Muroran Institute of Technology | Taniguchi M.,Japan Building Research Institute | Katsura O.,Japan Building Research Institute | And 2 more authors.
Journal of Advanced Concrete Technology | Year: 2012

This paper investigates the hydration rate in fly ash blended cement paste and self-healing ability in mortar incorporating fly ash for long-term period. The hydration rate of fly ash and consumption of calcium hydroxide in fly ash paste containing calcium hydroxide reagents were examined at different ages and curing temperatures. Five types of fly ash blended cement paste, each of which with 10% by mass fly ash replacement ratio, were prepared for the acceleration test at 80°C. Four fly ash cement pastes, with two types of fly ash and with fly ash replacement ratios by mass 10% and 30%, were tested to measure the rate of reaction of fly ash in the mixtures. Ten mixtures were tested to evaluate the self-healing ability of mortar incorporating fly ash, considering different types of cement and fly ash. Compressive strength, bending strength, accelerated carbonation depth, after applying freeze/thaw cycling until 60% and 80% relative dynamic modulus of elasticity, and porosity were examined. The experimental results revealed that incorporating fly ash in cement paste would affect the hydration rate of fly ash and consumption of calcium hydroxide. Curing temperature can affect hydration rate, acceleration rate and velocity of reaction rate in fly ash cement paste. Moreover, it is confirmed that self-healing ability, carbonation rate coefficient and the pore volume modification in mortar incorporating fly ash rely on the curing conditions. Finally, it is suggested that the practical fly ash replacement ratio in concrete could be 10% to 15% and 11% to 20% for water to cement ratios 0.50 to 0.55 and 0.55 to 0.60, respectively. Copyright © 2012 Japan Concrete Institute. Source

Yoshida S.,Japan Civil Engineering Research Institute for Cold Region | Taguchi F.,Japan Civil Engineering Research Institute for Cold Region | Nawa T.,Hokkaido University | Watanabe H.,Nittetsu Cement Co.
Concrete under Severe Conditions: Environment and Loading - Proceedings of the 6th International Conference on Concrete under Severe Conditions, CONSEC'10 | Year: 2010

When a concrete structure is built on the acid sulfate soils found around volcanic zones, the concrete may be deteriorated due to chemical attack. In this study, sulfuric acid resistance of belite-based concrete with ground granulated blast-furnace slag was examined by immersion test in sulfuric acid to improve the sulfuric acid resistance of concrete structures built on the sulfuric acid soils. The results showed that the degree of erosion due to sulfuric acid attack varied by the concentration of the sulfuric acid, and that erosion of concrete due to sulfuric acid attack could be controlled by using these binders. © 2010 Taylor & Francis Group, London. Source

Koizumi Yu.,Kajima Corporation | Tanaka T.,Kajima Corporation | Takeuchi J.,NITTOC Construction Co. | Kanazawa T.,Nittetsu Cement Co. | Nishigaki M.,Okayama University
Zairyo/Journal of the Society of Materials Science, Japan | Year: 2012

Grouting is an important part of construction in rock and soil for such as controlling the flow of water, filling voids in the ground and strengthening grounds. Grouting method has advantages over other soil improvement methods of not discharging slimes and requiring large spaces. However, conventional cement grout was difficult to permeate into fine sand. Chemical solution grout shows high permeability ; on the other hand, the solidified ground is not strong and durable enough. The purpose of our work is to develop grouting methods with ultrafine cement (the average particle size 1.5ìm) grout. The authors conducted both laboratory and field grouting tests. As a result, the grout permeated into a one-meter long artificial ground composed of fine sand, where conventional superfine cement grout was not able to permeate. Furthermore, unconfined compressive strength of the solidified ground was 10 times as large as that of solidified ground with chemical solution grout. As for the field test, the ball-shaped solidified ground was observed in the grouted area, and its diameter was 190cm as designed. It is concluded from the tests that ultrafine cement grout showed a great permeability and high solidified strength. © 2012 The Society of Materials Science, Japan. Source

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