Tatsuya Numao

Moisture migration and drying properties of hardened cement paste and mortar

Abstract The moisture migration and drying properties of hardened cement paste and mortar are studied experimentally and analytically. Thin-wall cylindrical specimens with a thickness of about 1.0 mm are used to reduce hygral gradients. The specimens are loaded with different compressive stresses in the range 0–11 MPa. Two test series are perfirmed: loss of water (test 1) and migration of moisture through the thin wall of the specimens (test 2) are measured: Furthermore, the experimental results are analyzed as a non-linear diffusion process, by means of the finite element method. The effects of the compressive stress and aggregates are discussed, referring to the diffusion coeffients obtained.

Relationships between Surface Roughness Indexes and Tensile Bond Strength between CFRP Sheets and Concrete.

The FRP adhesion method which uses carbon or aramid fiber sheets for the strengthening of the flexural member of building or bridge has lately become a subject of special interest. The bond strength between the FRP sheets and concrete influences the structural properties of the concrete elements which are strengthened by this method. The strength may be classified into three types according to the direction of force: the shear bond strength, the cleavage bond strength and the tensile bond strength. The authors have reported on the relationship between the shear bond strength and the surface roughness of the concrete. The present study describes the experiments concerning the tensile bond strength and the relations between the bond strength and various surface roughness indexes. The surface roughness of concrete varied by changing the treatment methods, such as, sandpaper polishing, diskgrinding, sandblasting and chipping. Surface roughness indexes, the maximum depth Dmax, the superficial area St, the form factor k, fractal dimension Df and the bearing ratio curve were determined based on the 3D profile measurements of the concrete surfaces. The mechanism for bonding between the FRP sheets and concrete was discussed based on the surface roughness indexes and the observations of the fracture surface of the tested specimens. The conclusions which were obtained from this study are as follows: 1) The superficial area St has the greatest influence on the tensile bond strength among the surface roughness indexes, 2) the chipping treatment reduces the bond strength significantly, and 3) the tensile bond strength increases as the concrete strength increases.

Remote sensing study of detecting of flaws in structural material

A new thermal radiation technique using an infrared radiometer has been developed to detect flaws of materials, such as inclusion, crack and pinhole. In the present study, several incident radiation energies like sun, lamp and gas, were injected to the test material with an artificial internal flaw. Transient radiation temperature image of the flaw on the CRT represents the existence of the internal flaw with higher radiation temperature than that of the surface without the flaw. The characteristics of various incident energy methods were compared with each other. The detecting limitation of internal flaws is determined by the surface temperature variance of the tested materials. The heat flow around the flaw was numerically analyzed by solving a heat conduction equation to verify the surface temperature behavior above the flaws.

Compressive Strength of Polymer Impregnated Mortars Using High Molecular Weight Methacrylate Monomers.

Recently, a relatively high molecular weight methacrylate monomer (HMWM monomer) has been developed. Since the monomer hardly evaporates under an ambient condition, it is possible to apply a thermal polymerization process under the atmospheric pressure in the production of polymer impregnated concrete or mortar (PIC). Furthermore, since it polymerizes at room temperature, it is possible to eliminate the thermal polymerization process.This paper describes the compressive strength of PIC using the mixtures of HMWM monomer and multifunctional acrylic monomers. The factors in the experiments were as follows: the number of functional groups of the multifunctional acrylic monomers and their contents, the water-cement ratio of base mortars, polymerization temperature and the polymerization time of PIC polymerized at room temperature (20°C). Compressive strength tests were made on 16×30mm cylindrical specimens. The water-cement ratio of the base mortars for PIC was varied from 30 to 60%, and their sand-cement weight ratio was 1.0. PIC using HMWM monomer or the mixtures of HMWM monomer and the multifunctional acrylic monomers were prepared as follows: (1) The base mortars were dried at 110°C for 48 hours, (2) evacuated at 8.0kPa for 1 hour, (3) impregnated with the monomers, (4) pressurized at 0.20MPa for 30 to 40 minutes, and (5) subjected to thermal polymerization at 70°C for 12 hours or storage at room temperature for 14 and 28 days. The principal conclusions obtained from the test results are summarized as follows:(1) The compressive strength of the base mortars is extremely improved by using mixed HMWM monomers, even though the compressive strength of PIC using mixed HMWM monomers is lower than that of PIC using MMA monomer.(2) When the number of functional groups of the multifunctional acrylic monomers increases 2 to 6, the compressive strength of PIC increases. In the range of the content of the multifunctional acrylic monomers 10 to 30%, the highest compressive strength of PIC is obtained when the content is 20%.(3) The compressive strength of PIC increases with the glass transition temperature of polymers.(4) The water-cement ratio of the base mortars influences the compressive strength of PIC, and the smaller the water-cement ratio becomes, the higher the compressive strength of PIC does.(5) In the use of a mixed HMWM monomer with a number of functional groups of multifunctional acrylic monomer of 6 and a multifunctional acrylic monomer content of 20%, the compressive strength of PIC polymerized at room temperature for 14 days is nearly equal to that of PIC polymerized at 70°C for 12 hours.

MECHANICAL BEHAVIOR OF HUME PIPES COVERED WITH REINFORCED CONCRETE

本文は, ヒューム管の周囲を鉄筋コンクリートで補強したコンクリート巻立てヒューム管に, その上下の中央部に集中荷重 (線荷重) が作用するときの力学的挙動に関するものである. 巻立て部厚さ, 巻立て部鉄筋量, ヒューム管の径, 載荷方法, 巻立て部形状の影響を実験的に検討した. 上記結果に基づきひびわれ・終局荷重の算定法を提案し, それらにより実測値を推定できることを示した.