Research

Structural performance evaluation of concrete structures

Shear failure is a brittle and dangerous mode in reinforced concrete structures. It is important to predict the shear strength correctly and take appropriate countermeasures to prevent the collapse of concrete structures. Our research group is working on the evaluation of the structural performance of concrete structures considering the material properties such as shrinkage of concrete, fracture characteristics of aggregates used in concrete, and expansion of expansive concrete.

Related publications

• Kenichiro Nakarai, Shigemitsu Morito, Masaki Ehara, and Shota Matsushita: Shear strength of reinforced concrete beams: concrete volumetric change effects, Journal of Advanced Concrete Technology, Vol.14, pp.229-244, 2016.
• Kenichiro Nakarai, Ryoichi Sato, Yuko Ogawa, Kenji Kawai: Shear strength of reinforced limestone aggregate concrete beams, ACI Structural Journal, Vol. 114, Issue: 4, pp.1007-1017, 2017.
• Halwan Alfisa Saifullah, Kenichiro Nakarai, Van Piseth, Nobuhiro Chijiwa, Koichi Maekawa: Shear creep failures of RC slender beams without shear reinforcement, ACI Structural Journal, Vol.114, No.6, pp.1581-1590, 2017.

Durability performance evaluation of concrete structures

Durability of reinforced concrete structures is an important issue these days. In addition to research on deterioration mechanisms, our research group has been actively conducting research on quality inspection, especially for newly constructed structures. We will establish a new approach to construct high quality concrete structures by confirming the durability performance of concrete structures immediately after construction using non-destructive tests such as surface air permeability test and water absorption test.

Related publications

• Nakarai, K., Shitama, K., Nishio, S., Sakai, Y., Ueda, H., and Kishi, T., Long-term permeability measurements on site-cast concrete box culverts. Construction and Building Materials, 198: pp.777-785, 2019.
• May Huu Nguyen, Kenichiro Nakarai, Yasutaka Kubori, Sohei Nishio: Validation of simple nondestructive method for evaluation of cover concrete quality, Construction and Building Materials, Vol.201, pp.430-438, 2019.
• May Huu Nguyen, Kenichiro Nakarai, and Sohei Nishio: Durability index for quality classification of cover concrete based on water intentional spraying tests. Cement and Concrete Composites, Vol 104: p. 103355, 2019.
• Verónica Bueno, Kenichiro Nakarai, May Huu Nguyen, Roberto Juan Torrent, Isao Ujike: Effect of surface moisture on air-permeability kT and its correction, Materials and Structures 54 (2), 1-12, 2021.

Performance evaluation of expansive concrete

The expansive additive is a suitable material to solve the shrinkage problem of concrete and to improve the performance of concrete structures. Our research group is studying the fundamental properties of expansive concrete, such as a new simple measurement of constrained expansive strain, durability, and structural performance. Since expansive concrete is often used in precast concrete plants, we are also conducting detailed investigations on the effects of steam curing.

Related publications

• Hoang Viet Nguyen, Kenichiro Nakarai,  Akeru Okazaki, Hideaki Karasawa, Yuji Tadokoro, Masato Tsujino, Applicability of a simplified estimation method to steam-cured expansive concrete. Cement and Concrete Composites, 95: p. 217-227, 2019.
• Hoang Viet Nguyen, Kenichiro Nakarai, Kien Hoang Pham, Saeko Kajita, Takahiro Sagawa, Effects of slag type and curing method on the performance of expansive concrete, Construction and Building Materials, Vol 262(30), 120422, 2020.

Performance evaluation of cement-treated soils

Ground improvement using cement or cement-based materials has been widely used to solidify soft ground and construct soil structures. Although cement treatment has been mainly studied in the field of geotechnical engineering, our research group has been working on the performance evaluation of cement-treated soils by physicochemical analysis based on the knowledge of cement chemistry and concrete engineering, considering them as intermediate materials between concrete and natural soils.

Related publications

• Kenichiro Nakarai and Tomomi Yoshida: Effect of carbonation on strength development of cement-treated Toyoura silica sand, Soils and Foundations, Volume 55, Issue 4, pp.857–865, 2015.
• Lanh Si Ho, Kenichiro Nakarai, Yuko Ogawa, Takashi Sasaki, Minoru Morioka: Effect of internal water content on carbonation progress in cement-treated sand and effect of carbonation on compressive strength, Cement and Concrete Composites, Vol.85, pp.9-21, 2018.
• Lanh Si Ho, Kenichiro Nakarai, Myriam Duc, Alain Le Kouby, Abdelhak Maachi, Takashi Sasaki, Analysis of strength development in cement-treated soils under different curing conditions through microstructural and chemical investigations. Construction and Building Materials, 166: p. 634-646, 2018.

Performance evaluation of engineered barrier system for nuclear
waste management

The disposal of radioactive waste generated from nuclear power plants has become a global issue. In Japan, as in other countries, underground disposal facilities have been implemented or planned, and engineered barriers using cementitious materials are utilized for safe disposal. Our research group is studying the long-term stability of cementitious materials, especially focusing on the chemical interaction with the surrounding bentonite.

Related publications

• Kenichiro Nakarai, Masahito Shibata, Hiroyuki Sakamoto, Hitoshi Owada and Georg Kosakowski, Calcite precipitation at cement–bentonite interface. Part 1: Effect of carbonate admixture in bentonite, Journal of Advanced Concrete Technology 19 (5), 433-446, 2021.
• Kenichiro Nakarai, Masaki Watanabe, Kiyoshi Koibuchi and Georg Kosakowski, Calcite Precipitation at Cement–Bentonite Interface. Part 2: Acceleration of Transport by an Electrical Gradient, Journal of Advanced Concrete Technology 19 (5), 447-461, 2021.