Kyoji Tanaka

Development of technique for observing pores in hardened cement paste

Mercury intrusion porosimetry is a widely used technique to determine the pore size distribution in porous materials. However, this technique does not provide information about the shapes and locations of pores. A new technique is developed, in which gallium (Ga) is used as an alternative intrusion liquid because of its property of being solid at normal room temperature (melting point: 29.8 °C). This permits the examination of pores using image analysis. The technique is applied to hardened cement paste. The distribution of solid Ga is observed through an electron probe microanalyzer (EPMA), and the shapes and locations of pores in cement paste are discussed.

THE DYNAMIC BEHAVIOR OF MORTAR UNDER IMPACT‐LOADING

Plate impact experiments have been performed to determine the dynamic behavior of conventional and high strength mortars. Longitudinal stresses have been directly measured by means of embedded polyvinylidene fiuoride (PVDF) gauges up to 1 GPa. A 200 mm‐cal. powder gun enable us to measure longitudinal stresses at several point from the impact surface, simultaneously. The longitudinal stress profile of conventional mortar, which static compression strength is 35 MPa, shows a two‐wave structure associated with the compaction of pores and the onset of damage around 200 MPa. Although the longitudinal stress profile of high strength mortar, which static compression strength is 120 MPa, does not show a two‐wave structure, longitudinal stress to phase velocity relationship indicates the onset of pore collapse around 500 MPa.

Artificial Weathering and Cyclic Movement Test Results Based on the RILEM TC139-DBS Durability Test Method for Construction Sealants

The purpose of this study was to assess the effect of artificial weathering and cyclic movement in a laboratory test based on the RILEM Technical Recommendation (RTR) “Durability Test Method for Curtain Wall Joint Sealants.” Eleven sealants being used in Japan were tested, including two silicones, two silicon-modified polyethers, two polysulfides, two polyurethanes — each as one- and two-part products — one two-part silicon-modified polyisobutylene, one two-part urethane cure acrylic, and one one-part water-borne acrylic. The two-part polyurethane, the two-part urethane-cure acrylic, and the one-part water-borne acrylic were also evaluated with and without painting the sealant surface. Test specimens were prepared using anodized aluminum and mortar as substrate materials; primers were used for all sealant/substrate combinations as recommended by the manufacturers. All sealant specimens were conditioned according to Method A. The durability test, consisting of weathering and thermo-mechanical cycling, was carried out both with and without the influence of fatigue cycling. The durability cycles were repeated three times. Weathering was conducted in a fully automatic weathering machine using a xenon arc light source. Sealants without painting were observed to chalk and craze at an earlier stage in the durability cycles than the ones with painted surfaces, confirming the effectiveness of painting the sealant surface in protecting organic sealants from aging. A substantial difference in the behavior of sealants was observed for exposures with and without fatigue cycling, confirming the importance of fatigue cycling in the degradation of sealants. In order to obtain a good correlation between accelerated weathering and actual service performance, a proper balance of degradation factors is essential.

Effect of Cross-Sectional Shapes of Polysulfide Sealant on Shear Fatigue Resistance to Sliding Joint Movement

The effect of cross-sectional shapes of polysulfide sealing beads on shear fatigue resistance to sliding joint movement was studied experimentally and analytically. Six kinds of sealing beads that were different in the depth of their concavity were repeatedly deformed by shear joint movement. Cracks appeared in surface near substrates or in the middle of surfaces in some specimens, and developed in parallel to substrates or in X-shape. The time to cracking became shorter for the specimen with deeper concave shape. To learn the reason for these results, the surface stresses of the beads were studied using a finite element method. It was concluded from both experimental and analytical results that a durable cross-section of a sealing bead to shear joint movement in rectangular or slightly concave shapes.

Evaluation of Sealed Joint Performance for the Selection of Sealants Suitable for Use in Autoclaved Lightweight Concrete Panels

The strength of autoclaved lightweight concrete (ALC) is evidently lower than that of normal concrete. Therefore, when movement occurs at a sealed joint between ALC panels, the sealant is required to deform and remain intact without damaging the ALC substrate. However, there is currently not sufficient information to permit evaluation of the expected performance of sealants applied to ALC substrates. In this study, static and dynamic tests were carried out in order to obtain an index that could be used to select the modulus of a sealant that can be expected to provide long-term performance when applied to an ALC substrate. To develop this index, an initial study was carried out in order to clarify actual joint movement between ALC panels of buildings; the expansion and contraction at the joint were measured, and shear joint movement was calculated based on the expected story-to-story drift of an external wall due to earthquake loads. Thereafter, in a subsequent stage of the study, five types of two-component polyurethane sealant products, of different elastic modulus, were subjected to tensile and shear tests from which the relationship between stress and the type of joint fracture was determined. The results from these tests revealed that when the stress is greater than 0.6 to 0.7 N/mm2, the ALC substrate is more easily fractured than the sealant. In a final stage of the study, the cyclic fatigue resistance of the same two-component sealants was evaluated using tensile and shear fatigue tests. Results from the fatigue tests indicated that the high modulus sealants lost adhesion from the ALC substrate at an early stage in the test. As well, the fatigue resistance of test specimens with joints having three-sided adhesion was lower than that of specimens having normally configured joints with adhesion on two sides of the sealant. Therefore, on the basis of results derived from all the studies, it was determined that a suitable sealant for use on ALC substrates is a sealant having a low modulus that is applied in the normal fashion as a two-sided joint.

Study of Weatherability of Construction Sealants with Novel Testing Method

Although construction sealants are used for all kinds of construction joints such as static joints with little movement, dynamic joints with thermal or seismically induced movement, and so on, the general test methods employed in the evaluation of the weatherability of construction joint are based on weathering test without movement. In November of 2000, AIJ (Architectural Institute of Japan) established a subcommittee chartered with developing an accelerated weathering test method, which enables the determination of the durability of waterproofing materials and sealants. In this activity, we evaluated the weatherability of sealants with a new test method using newly developed test specimens, which enable exposing the cured sealants to compression and extension at the same time in a single test specimen. In this paper, we report the interim test results, which cover twelve months of natural weathering and 3500 hours artificial weathering with xenon lamp and carbon flame weathering device. In this evaluation, we confirm that the surface degradation of sealants is accelerated by the additional movement cycles, and the differences in the degradation among the sealants are becoming observable.

Evaluating Root Resistance of Asphaltic Pavement Focusing on Woody Plants’ Root Growth

Pavement failures like cracking and rising, caused by the growth of plant roots are often observed in asphaltic pavement around roadside trees. To avoid trouble, the resistance of pavements to root growth should be estimated using a suitable test before installation. The aim of this study is to develop a test method for evaluating pavements’ resistance to the thickening of roots as they grow. The method uses a simulated root developed to mimic the mechanical power of a growing root for evaluating the performance of pavements more easily and quickly.

MICROSTRUCTURAL OBSERVATION AND SIMULATION OF POLYMER CEMENT WATERPROOFING MEMBRANE

A polymer-modified cement waterproofing membrane is formed by simultaneous cement hydration and polymer film formation, these rates are affected by the moisture content of the polymer emulsion used. The moisture content gradually decreases due to cement hydration and evaporation from the surface. This study focused on the changes caused in the waterproof layer by differences in the moisture environment. Four test pieces with different cement, polymer, and moisture contents were prepared and cured at 20 °C and relative humidities of 25, 60, and 98 %. The basic physical properties of the test pieces were studied in tensile tests; the structures were observed using an EPMA. Furthermore a simulation was carried out using a model that considers cement hydration, polymer film formation, and moisture evaporation rate. The simulation results well reproduced the experimental results.

Proposed Design and Method for Providing Sealed Joint Performance under Relative Story Displacement

The fatigue resistance of sealed joints to relative story displacement movements caused by earthquakes was studied experimentally and analytically, and the new joint design method was proposed, providing adequate sealed joint performance over the joint’s service life. First, the story drift R of a curtain wall panel and the number of movement cycles of relative story displacement at a sealed joint over its service life were investigated using earthquake data of the Japan Meteorological Agency. The results indicate that the number of cyclic movements at a sealed joint over its service life is inversely proportional to the story drift of the adjacent curtain wall panels. In regions where earthquakes are numerous, R=1/300 cyclic movements of the total length of the curtain wall panel occur several thousand times over a period of 75 years, while R=1/100 cyclic movements occur only several tens of times. Second, the three criteria required to create a joint design method were investigated, i.e., type of sealant, effect of cross-sectional size and shape of the sealed joint, and fatigue resistance of the sealant at intersectional zones of sealed joints to the sliding and rocking motions of curtain wall panels. It was obvious that the fatigue resistance of sealed joints was lower in the intersectional area than in the linear sections of the joints, and was lowest in the event of the same movement occurring in both vertical and horizontal joints. The fatigue resistance of a sealant at the intersection of sealed joints is not sufficient to attain the targeted service life and the fatigue resistance of this area of the sealed joint must be improved by applying larger curvature radii at the corner of the curtain wall panel. Finally, the new joint design process for the linear section and the intersection of the sealed joints to relative story displacement movements was developed based on the experimental data. Further, we proposed the methodology to estimate the expected service life of a sealed joint.

Wind Resistance Evaluation to Dynamic Response of Mechanically Anchored Waterproofing Membrane System

Damages of mechanically-anchored waterproofing membrane system from strong wind have been occurring. Thus, this study provides investigation on the behavior of waterproofing sheets and fasteners exposed during typhoon, and the difference between the static pressure test and typhoon test. The polyvinyl chloride waterproofing membrane reinforced with polyester fiber was constructed on a flat roof with dimensions of 6 m by 6 m on the island of Miyako in Japan. At first, a pressure test was carried out by using a compressor. Afterwards, the response of waterproofing membrane system located atop a building when subjected to strong winds from a typhoon in 2009 was measured. Both axial force and lateral force of mechanically-anchored waterproofing membrane system were measured under high speed wind, and lateral force was significantly large. It is presumed that such lateral force causes waterproof membrane damage that ripped the sheet in the lateral direction as if in a typhoon. Next, this study provided the proposal of simple wind resistance test method for mechanically anchored waterproofing membrane system. At first, the pressure test on the flat roof of actual building was carried out to obtain basic data for wind resistance design of this system. As a result, Fastener’s force of waterproofing membrane was equivalent to the wind force. Then, the ring type specimen with 200 and 600 mm diameter was made, and the fatigue coefficient of this system after using 10 years was calculated by using the tension test and the SIGDERS test. Finally, the design method for fastener based on fatigue model was proposed in order to apply to construction system.