Hirozo Mihashi

• Tohoku University

It has been confirmed that some types of fiber-reinforced cementitious composites (FRCCs) are capable of significant self-healing after formation of cracks by some previous research. In this study, waterproof layers made of self-healing FRCC are proposed as building material with maintenance-free potential. A couple of fundamental studies were carr...

The development of ultra-high-performance fiber-reinforced cement-based composites (UHP-FRCCs) was motivated by the need for a new and versatile material with high energy absorption capacity. With its excellent cracking resistance and consequent long life, UHP-FRCC is suitable for use in seismic design applications. The present study proposes a mat...

The purpose of this paper is to propose a material design method of lightweight cement-based composites that reduces the mass of building components and provides them with better insulation. To achieve this purpose, a number of special lightweight aggregates were tested. Furthermore, material design methods based on the packing density models and t...

This paper reports test results on the corrosion durability of reinforcing steel in three series of precracked beams of ordinary mortar; a high-performance fiber-reinforced cementitious composite (HPFRCC) containing polyethylene (PE) fibers, referred as mono HPFRCC; and hybrid combinations of steel cord (SC) and PE fibers, referred as hybrid HPFRCC...

A new ultra-high-performance hybrid fiber-reinforced cementbased composite (UHP-HFRCC) was developed in this study. The UHP-HFRCC exhibited a tensile strength of 20.1 MPa (2.9 ksi), a strain capacity of 1.06%, and energy-absorption capacity of 153 kJ/m3 (1356 lb-ft/ft3). The multi-scale fiber-reinforcement system employed herein effectively improve...

Various types of fiber reinforced cementitious composites (FRCCs) were experimentally studied to evaluate their self-healing capabilities regarding their watertightness and mechanical properties. Cracks were induced in the FRCC specimens during a tensile loading test, and the specimens were then immersed in static water for self-healing. By water p...

The synergy effects of reinforcing rebars and Hybrid Fiber Reinforced Cementitious Composites (HFRCC) were experimentally investigated on the mechanical behavior of structural elements and on the cracking distribution. Uniaxial tension tests with prism specimens were carried out in order to evaluate the influence by changing the fiber volume conten...

High-performance fiber-reinforced cementitious composites demonstrate very good self-healing capability after immersion in water due to the closely spaced multiple cracks. To investigate the self-healing capability of ultra-high-performance hybrid-fiber-reinforced cementitious composite (UHP-HFRCC), some experiments were carried out that focused on...

The purpose of this study is to suggest the material design method of lightweight mortar that reduces the mass of building components and provides them with better insulation. To achieve this, we applied a number of special lightweight aggregates and applied the packing density model, porous mortar, and a combination of both methods. A series of ex...

Multiple cracking and strain hardening can be achieved in cement-based specimens subjected to uniaxial tension by increasing the volume fraction of steel fibers with hooked ends, or by using plastic fibers with and without steel fibers, or by means of high bond steel fibers (e.g., twisted fibers or cords). To better understand why relevant mechanic...

In this paper, a material design concept based on Hybrid Fiber Reinforced Cement-based Composites (HFRCC) is applied to Ultra High Performance Concrete (UHPC) so that a multi-levelreinforcement system for cracking will enhance the peak stress after crack initiation (i.e. tensile strength) and tensile strain capacity (i.e. strain at the peak stress,...

Autogenic self-healing has been defined in chapter 1 as a self-healing process where the recovery process uses materials components that could also be present when not specifically designed for self-healing (own generic materials).

Micro-crack development associated with the aging of concrete structure may be concerned in terms of decrease in durability. This study developed a smart artificial lightweight aggregate (ALA) capable of preventing micro-cracks by the internal curing with a reactive solution housed in its pore spaces. Water releasing capability of the smart ALA was...

Challenging studies of engineered self-healing and self-repairing functions in concrete structures are briefly reviewed. While self-healing of concrete has been studied for a long time, it was only recently noticed that some engineered technologies are useful to stimulate the potential of concrete to be self-healed. For example, fiber reinforced ce...

Influence of material components and mix proportions on the fresh properties and mechanical ones of Hybrid Fiber Reinforced Cementitous Compo-sites (HFRCC) was experimentally studied. It was shown that the relative yield stress and the relative plastic viscosity of HFRCC decreased as the excess paste thickness increased. However, changing tendency...

Some Fiber-Reinforced Concrete (FRC), commonly called Strain-Hardening Cement-based Composite (SHCC), can show a very ductile behavior under tensile actions. Specifically, in the post cracking stage, several cracks de-velop before complete failure, which occurs when tensile strains localize in one of the formed cracks. To better understand the high...

To develop Hybrid Fiber Reinforced Cementitious Composites which is high strength and toughness, it is necessary for appropriate mixture conditions and kinds of fiber to be chosen and for constitution conditions to be clarified. The present study aims to clarify combined effects of fiber cocktail on the tensile properties under uniaxial tensile str...

The study presented here concerns the development of high-strength lightweight Fiber Reinforced Cement-based Composites (FRCC). Parametric study was performed by varying the W/B, volume contents of lightweight aggregate and fiber. Influence of these parameters on the material properties were experimentally investigated. As for the material properti...

Experimental studies are carried out to evaluate the self-healing capability of FRCC using different types of synthetic fibers that have different chemical properties, i.e. poly vinyl alcohol (PVA), ethylene vinyl alcohol (EVOH), polyacetal (POM) and polypropylene (PP). FRCC specimens were subjected to tension tests in order to generate a crack, an...

Super high strength concrete with compressive strength of 150 to 200N/mm2 using hybrid fiber reinforcement of organic and steel fiber was developed. Properties of fluidity of fresh concrete and effect of curing condition on strength development were studied. Viscosity of fresh concrete was significantly reduced by newly developed Maleate polycarbox...

Experimental results on the strain hardening and multiple cracking behaviors of polyvinyl alcohol (PVA) fiber reinforced cementitious composites under bending are reported in this paper. Different hybrid combinations of PVA fibers with different lengths and volume fractions are considered to reinforce the mortar matrix. Among different hybrid combi...

For the purpose of global sustainability the long life of structures is essential and the durability performance of reinforced concrete structures is one of the key issues to be resolved. This paper reports the results of a series of long term corrosion tests onfiber reinforced cementitious composites containing polyethylene (PE) alone and hybrid s...

The ductility of high-performance fiber-reinforced cementitious concrete (HPFRCC) can be developed not only in tension but also in compression. This aspect is evidenced in the present paper by comparing the behavior of HPFRCC cylindrical specimens under uniaxial compression, with the mechanical response of normal vibrated concrete (NC) and self-con...

Among different approaches that can be considered for concrete rehabilitation, bonded overlays are often the most economical alternative. The primary purpose of overlays is to extend the life of the candidate structures, either by restoring the quality and integrity of the surface and/or the re-establishing or improving the load-carrying capacity....

The ductility of High Performance Concrete (HPC) can develop both in tension and compression. This aspect is evidenced in the present paper by measuring the mechanical response of normal vibrated concrete (NC), self-compacting concrete (SC) and some HPCs cylindrical specimens under uniaxial and triaxial compression. The post-peak behaviour of these...

Fire resistance of High strength reinforced concrete columns with specified design strength of 80N/mm2 to 200N/mm2 were conducted by loaded fire resistance tests. High strength concrete column without fiber showed explosive spalling and fire resisting period of columns were less than 2 hours. Incorporating polypropylene fiber to concrete of 150N/mm...

High strength concrete with specified strength of 150 to 200 N/mm2 using hybrid fiber as synthetic and steel fiber to improve fire resistance and toughness of concrete was newly developed. Effect of mixture proportion and content of hybrid fibers on properties of fresh concrete, toughness, bonding strength, autogenous shrinkage and compressive stre...

The ductility of High Performance Fiber Reinforced Cementitious Composites (HPFRCC) can be developed both in tension and compression. This aspect is evidenced in the present paper by measuring the mechanical response of normal concrete (NC), self-compacting concrete (SC) and HPFRCC cylindrical specimens under uniaxial and triaxial compression. The...

Durability of reinforced, concrete structure depends on the quality of the concrete cover that inhibits the rebar corrosion in concrete. Hence, for evaluating the performance of concrete cover to resist the rebar corrosion in concrete, authors proposed "Drill-PR method" using the permeability velocity and resistivity measured by the hole drilled in...

Fiber-reinforced concrete (FRC) showing strain hardening after cracking is commonly defined as High Performance Fiber-Reinforced Cementitious Composite (HPFRCC). In the post-cracking stage, several cracks develop before complete failure, which occurs when tensile strains localize in one of the formed cracks. As is well known, multiple cracking and...

In this study, the uniaxial tensile performance of hybrid type strain hardening cementitious composites (SHCC) that contains two kinds of PVA fibers was clarified. Moreover, the influence on the ductility by the difference of the specimen shape and mixed volume of the hybrid type SHCC was examined.

In order to investigate the self-healing capability of fibre reinforced cementitious composites (FRCC), mechanical properties and surface morphology of crack in FRCC were studied. Three types of FRCC specimens containing (1) polyethylene (PE) fibre, (2) steel cord (SC) fibre, and (3) hybrid fibres composite (both of PE and SC) were prepared. These...

Problem statement: Shrinkage induced cracking cause damage to reinforced concrete structures. An experimental study was conducted on restrained shrinkage test of cement mortar and light weight High Performance Fiber Reinforced Cementitious Composites (HPFRCC). Approach: Two types of light weight HPFRCC and a premix mortar containing small amount of...

5週間の短期間で長期のコンクリートの乾燥収縮ひずみを判定する乾燥収縮迅速評価システムを開発し，多くの実工事に関連するレディーミクストコンクリートに適用した。本システムの開発にあたり，省力化の実現が可能な乾燥収縮の試験方法として省力化乾燥収縮試験法を提案するとともに，長期の乾燥収縮ひずみを短期データから予測する予測手法として外挿法を提案した。本システムを，実工事に関連する280調合のレディーミクストコンクリートに適用するとともに，長期の乾燥収縮ひずみを短期間の測定デ―タから高い精度で判定できることを確認した。

To increase the crack bridging capacity of concretes and mortars, fibers are often added to cement-based matrices. As a result, the fracture energy of a fiber-reinforced concrete (FRC) is the sum of the cohesive forces of the matrix and of the pullout resistance given by the fibers crossing the crack. In the case of fibers randomly inclined with re...

This study focused to clarify the status of drying shrinkage in ready-mixed concrete via field study using simplified drying shrinkage testing method, which has not been sufficiently examined. The field study results revealed that significant variation in drying shrinkage properties for ready-mixed concrete. Furthermore, stochastic investigation fo...

This study reports on the prediction for the wood construction wastes of Sendai city based on the house ledgers of fixed asset tax rolls. The survival rate of wooden houses has been supposed to follow a Gompertz-Makeham distribution. The estimated data indicates that the survival rate in 1997 was lower than in 2002-2004. The life expectancy for woo...

This study aimed at proposing a new drying shrinkage testing method which enables us to save testing labor. For this purpose, Four testing methods were experimentally investigated in comparison with standard testing method specified in Japanese Industrial Standard. As a result of this experiment, a method adopting cylinder specimen embedded mould g...

Shrinkage cracking controlling design scheme has been proposed by authors and allows us to estimate shrinkage cracking risk of planer R/C members constructed with regular concrete. This study focused to extend this scheme to involve shrinkage crack reducing concrete added expansive additive and shrinkage reducing admixture (NES, hereafter). This ex...

This study aims at evaluating shrinkage cracking risk in reinforced concrete structures, which has not been established in the past studies. To achieve this goal, analytical scheme capable of calculating the probability of shrinkage cracking was proposed. In this scheme, the variation of shrinkage restrained stress, that of concrete cracking streng...

On the basis of micromechanics consideration of frost damage, a theoretical model to describe the freeze-induced strain behavior of porous materials such as concrete is presented. The model is derived from the thermodynamic equilibrium condition. Fundamental equations are derived on the microscopic level where temperature-induced phase transitions...

The author thanks Masatoshi Yamazaki, for his discussion, and the answers are as follows;Method of testing on the adiabatic temperature rise is similar to the type A of referred paper 1). The close adiabatic temperature rise simulation is not confirmed.Cumulative strain is measured value accurately. It was observed shrinking in restraint by the equ...

In cold regions such as Tohoku and Hokkaido districts, many RC structures are suffered from frost damage. While a frost damage risk map produced by S. Hasegawa has been widely used to evaluate the required durability performance for concrete against frost damage, the capability of resolution is quite limited and engineers can guess only briefly the...

This paper deals with development of controlling technology for shrinkage cracking, which consists of prediction of drying shrinkage strain of concrete from short-term test, crack reducing concrete, and evaluating shrinkage cracking risk. This controlling technology was applied to construction process, and its validity was demonstrated via construc...

The theoretical approaches used for the evaluation of crack width in reinforced concrete (RC) structures, are generally based on the hypothesis of parallel crack surfaces. In this way, crack width measured on the concrete cover should be equal to that on the bar surface. The results of several experimental analyses, developed during the past years...

It has been shown that the post-peak response of cement-based materials in compression can be defined by means of stress-inelastic displacement relationships. A unique function, used to define these relationships for different cement-based materials, is introduced in the paper. The function is implemented in two numerical procedures able to compute...

Thermal cracking is caused by large hydration heat of early age concrete in massive structures. For investigating mechanical behavior of early-age concrete and thermal cracking, a kind of temperature-stress testing machine (TSTM) was employd. By controlling the hydration heat in the concrete specimen, different results were obtained on the mechanic...

The design and composition methods for wooden dome are described. Wooden spheric dome is transformed into spherical polygon in order to put standard sized lumbers to use. The surface of spherical polygon is replaced with a combination of units, which are consisted of lumbers and shaped six-pointed star. Each unit has wedges, which keep the adhesive...

This paper reviews and presents various durability properties of strain hardening fibre reinforced cementitious composites (SHFRCC). Published research results show that, due to its tight crack width properties compared to ordinary concrete and ordinary fibre reinforced concrete, SHFRCC significantly resists the migration of aggressive substances i...

A finite element (FE) model is proposed to simulate the corrosion-induced cracking of reinforced concrete (RC) beams. The smeared cracking approach is used to model the cracking of ordinary concrete, ductile fiber-reinforced cementitious composites (DFRCC), and engineered cementitious composites (ECC). The model simulates the cracking of ordinary c...

High-performance fibre reinforced cementitious composites (FRCC) are usually designed by using high-performance fibres and matrix of high bond strength to enhance fibre debonding mechanism. The crack formation in high-strength matrices results in considerable strain-energy release. In such a case, fibres may not be able to effectively bridge the in...

A series of bond tests on a deformed bar embedded in high-performance fiber reinforced cement-based composites (HPFRCC) were carried out. Bond cracks around the reinforcing bar were observed by an X-ray technique and strain distribution along the bar was measured, too. Based on these experimental results, the mechanism to enhance the ductility of r...

The theoretical approaches used for the evaluation of crack width in reinforced concrete (RC) structures, are generally based on the hypothesis of parallel crack surfaces. In this way, crack width measured on the concrete cover should be equal to that on the bar surface. The results of several experimental analyses do not justify this assumption. T...

In this study a relationship between permeability of concrete and fractal dimension of crack is established. For this purpose four series of specimens of fiber reinforced cementitious composites are prepared. Specimens are subjected to uniaxial tension in order to create targeted damage (cracking) prior to permeability test. Image analysis is done...

A fundamental study was carried out to develop a kind of smart concrete that has a self-healing system that incorporates a heating device. Self-diagnosis composite is employed as the heating device used to heat up cracked parts in the concrete. This heating device and a pipe made of heat-plasticity organic film containing a repair agent are embedde...

This paper reports the results of an experimental program on the effect of steel loss and corrosion induced-damage (cracking, delamination, spalling, etc.) on the post-corrosion flexural response of reinforced concrete beams incorporating supplementary cementing materials (fly ash, slag and silica fume) used as partial replacement of ordinary Portl...

In the performance-based design for shrinkage cracking in building, the reliable mathematical model for predicting shrinkage and creep strain of concrete is required. It is desirable that the mathematical model is simple and accurate, and every engineer can use it without any difficulties. Then, in this paper, the prediction formula of shrinkage st...

This paper reports the results of an experimental examination of the structural performance of steel structures employing a beam-column joint system with steel fiber reinforced cementitious composites. The beam-column joint was achieved by filling steel fiber reinforced cementitious composites into the gap between a U-section bracket and a middle b...

To build reinforced concrete structures able to mitigate steel corrosion produced by environmental attack, a reduced crack width should appear in tensile concrete. At least in the serviceability stage, fibers added to ordinary concrete could be a way to satisfy this requirement. Depending on the type, on the volume content and on the aspect ratio o...

Drying shrinkage of concrete exerts a serious influence toward the long-term reliability such as the durability of the structure. The estimation formula of drying shrinkage of concrete is necessary by using examine this behavior of properties. In this paper, the prediction estimation formula of drying shrinkage strain of concrete is obtained with t...

Development of highly ductile concrete members is one of the key issues for mitigating damage of concrete structures in strong earthquakes. Reduction of crack width is also required for durability and long life of concrete structures. For such purposes, a kind of high-performance fiber-reinforced cement composite (HPFRCC) was developed by means of...

Mesolevel simulations were used to describe fracture processes in concrete. A new stochastic–heuristic algorithm was developed for generating the composite structure of concrete in 3-D space, producing specimens with comparably high aggregate content and realistic distribution. Aggregate particles were described as ellipsoids, allowing control in s...

Durability of concrete structures is seriously compromised by cracking in early age concrete, particularly in high-strength or massive concrete structures. Since early age cracking is influenced by various highly interrelated factors that affect the hydration process and stress/strain development, its behavior is highly complex and no rational meth...

For high-strength and high-fluidity concrete, the water-cement ratio and the volume fraction of aggregate is lower than conventional concrete. In order to clarify systematically the deformation of these concrete, it is necessary to consider the effect of the volume of constituents in concrete. In this study, the estimation formula of modulus of ela...

The objective of this paper is to provide an analytical basis for the quantitative evaluation of damage to a reinforced concrete structure based on the vibration data obtained by using the damage detection technique. A partial reinforced concrete system of a weak beam/strong column moment frame is chosen as an example. A pushover analysis is carrie...

Three-point bending tests and uniaxial tension tests on Hybrid Fiber Reinforced cement-based Composites (HFRCC) were carried out. HFRCC contains both specially-processed steel fiber (steel cord) and synthetic fiber. As the result of the bending tests, it was confirmed that coarse and wide cracks were observed near the notch of the specimens reinfor...

Development of high-performance construction materials is one of the key issues for the sustainability of structures, and this is one of the reasons for the development of ductile fiber reinforced cementitious composites (FRCC). The purpose of this study is to observe microcracking in high-performance FRCC at the micro and meso levels to clarify th...

Fracture processes in concrete specimens were observed in mesolevel simulations. For generating the composite structure of the concrete in the three-dimensional space, a new stochastic-heuristic algorithm has been developed which allows obtaining specimens with comparably high aggregate contents and realistic distribution. The aggregate particles w...

The objective of this paper is to examine the relation between the change of mechanical characteristics of structural frame due to an earthquake and the damage level of structural members. A part of the reinforced concrete frame is considered, and the story shear-relative displacement relation is analyzed in association with the damage level. The c...

An experimental study was carried out to find material parameters for making fiber reinforced cementitious composites (FRCC) more ductile. One of the dominant factors to control the ductility might be hidden in fracture property of matrix as well as the interface property between fiber and matrix. Therefore this study varied air content and water–b...

This paper is a summary report based on the discussion of JCI-DFRCC committee. The paper attempts to summarize the terminologies related to DFRCCs and the structural advantages and application concepts of DFRCCs. The attempt is made for the purpose of further discussion at JCI International Workshop on Ductile Fiber Reinforced Cementitious Composit...

Durability design of concrete structures is now one of the main issues in the field of structural engineering. Since the durability depends mainly on the pore structures of concrete and the environment to which concrete is exposed, data of concrete temperatures and moisture content are essential for the durability design. For collecting the data, c...

For the sake of finding the factors which influence the mechanical performance on short fiber reinforced cementitious composites, a parametric study was experimentally carried out. Nine parameters on fiber and four parameters on mortar matrix were varied. Then the experimental results on bend and compression tests were assessed for nine parameters...

Direct tensile and flexural tests on polypropylene short-fiber reinforced cementitious composites were executed. Thereafter a stochastic study was performed to investigate the effect of the specimen size on its tensile strength. The results are: 1. Size-effect in the tensile strength was clarified and the tendency was described by a function. 2. An...

One of the most useful methods of enhancing the flexural ductility of beams reinforced by high strength fiber rebars is to get tensile co-operation of matrix To discuss such a point of ductile flexural behavior, direct tension tests, flexural tests and related analysis were executed The followings are concluded 1) A reasonable agreement is observed...

A collaborative effort between US and Japanese researchers has focused on the development of high-performance elements for seismic structural applications based on a new materials technology as an Engineered Cementitious Composite (ECC) designed using micromechanical principles. ECC exhibits strain-hardening with strain capacity in excess of 1% in...

The tensile stress distribution model under bending, which consists of tensile behavior before crack, fiber pullout behavior after crack and tension-softening behavior, is proposed to compose an analytical model. The followings are concluded by analyses and experiments ; 1) Various tensile stress distribution models of previous studies are the spec...

The objective of this paper is to study analytically the transition phenomenon between a large single curvilinear crack and diagnoal multiple cracks observed during the shear-off failure sequence of concrete shear key joints. Based on the principle of the conservation of strain energy, well-known elastic solutions are applied to analyze the princip...

屋根上積雪の規則的な滑落処理を継続的に行う勾配屋根に用いる屋根用塗装鋼板の長期的な滑雪性能の評価および維持の手法について検討している。勾配屋根に用いる葺材は紫外線による化学的劣化と滑雪による機械的劣化が生じ,年数の経過に伴って材料表面の性状が変化する。実際に使用されていた屋根用の塗装鋼板における滑雪性能の経年劣化曲線には,初期劣化の後に18年経過頃まで滑雪性能が殆ど変化しない期間が長く存在する。なお,この滑雪性能の経年変化は,屋根雪と屋根葺材との凍着強度および摩擦係数で評価した。このことから,長期的な滑雪性能を評価する場合は,滑雪性能の経年劣化曲線に基づいて行うことが有効と考える。さらに,その劣化曲線を考慮して,屋根の滑落機能の維持保全を計画する必要がある。従って,屋根葺材の滑雪性能の耐久寿...