Sufficiently high waterproof, moderate moisture permeability and extensibility are the necessary properties for a coating material to have in order to prevent the damage of concrete due to the alkali-silica reaction (ASR). A new inorganic coating material having all of these properties has been developed. In the present study, its physical properties were measured, first and then the durability under accelerated ultraviolet light exposure was examined. Lastly, practical performance tests were carried out by using the specimens made of concrete with alkali reactive aggregate and the actually damaged concrete structure due to ASR. As the result, it was confirmed that ASR was prevented for 2-years by coating the new material.
The slump loss with the lapse of time is one of the most significant disadvantages of superplasticized concrete. Recently, the slump retentive superplasticizer was developed to reduce the slump loss after flowing. The present paper describes the experimental results of the properties of concrete with such slump retentive superplasticizer. Four types of slump retentive superplasticizer were used in this experiment. The slump, air content, rheological properties and compressive strength of superplasticized concrete under various conditions were measured. The effects of the timing of superplasticizing, the amount of dosage of superplasticizer and the sand/aggregate ratio of the base concrete on the properties of superplasticized concrete were experimentally investigated. It has been proved that the slump retentive superplasticizer can be effectively used to prevent the rapid slump loss after flowing under the condition of proper adding time of superplasticizer and a suitable sand/aggregate ratio of concrete.
Prismatic concrete specimens were manufactured by surface vibrating compaction and cube test pieces cut from its upper and lower parts were prepared. The compressive and tensile strengths of the pieces were measured by applying load parallel or perpendicular to the placing direction. Furthermore, compaction mechanism was examined on the basis of the mix analysis test results and the compaction process observed through a transparent side panel of the specimen mould, and the maximum depth of voids contacted with upside and underside of each coarse aggregate was measured. The same tendency was observed on the relation between compaction time and compressive strength regardless of loading direction. At the time of 15 seconds, the strength in the upper part was considerably higher than that in the lower part, because the upper part was changed into relatively dense by sharp subsidence of specimen surface coincided with commecing compaction while the other was in the porous state as yet. Subsequently the strength increased and reached the maximum at the time of 120∼180 seconds. At this stage, air bubbles were dissipated and the voids were filled up by cement paste transfered downward. If compaction was continued moreover, the strength decreased. This resulted from the effect that the transfer direction was turned to upward. The relation between compaction time and tensile strength showed the same tendency as that observed on compressive strength. But, the ratio of cube strength to standard strength was lower than that of compressive strength on the whole, and the tensile strength loaded in parallel to the placing direction was higher than the others in case that crushed stones were used. It was thought that these resulted from the effects of void and bond property between coarse aggregate and mortar.
The silica fume having low silica content is a by-product from the dust-collector at a ferrosilicon plant in Kochi-city. The use of silica fume in the concrete with stiff consistency, being used for concrete products, was investigated in order to obtain the fundamental data relating the mixture proportions to the properties of concrete, such as slump, strength, drying shrinkage, water-permeability, etc.. Silica fume should be used with a high-range water-reducing agent, as the slump of concrete goes down with the increment of silica fume. The optimum content of silica fume addition is 10 percent substitution for cement in consideration of the workability, the strength and the economy of concrete. By the use of silica fume, the following effects can be obtained: reduced bleeding, increased strength and better water-tightness, although the drying shrinkage of concrete increases a little.
The damping characteristics of acoustic emission propagating through concrete were examined experimentally in order to establish the method of acoustic emission source wave analysis. The items chosen in the investigation were the effect of holding technique of sensor (Experiment-I), the effects of shape and size of specimen (Experiment-II), the effect of degree of heterogeneity of material (Experiment-III), and the effect of the degree of accumulative damage of specimen (Experiment-IV), respectively. The main results obtained in the present study are summarized as follows: (1) The frequency characteristics of acoustic emission picked up by the sensor were remarkably affected by its holding technique and the passing time after the sensor was held to the specimen, independently of the frequency characteristics of sensor or the degree of source acoustic emission. (2) The acoustic emission propagating through concrete diminished with increasing the length and the sectional area of specimen. The damping of the frequency components higher than 200kHz and 100kHz became more significant with increasing the propagating distance of acoustic emission and the sectional area of specimen, respectively. (3) Cement paste and mortar had the similar frequency characteristics of acoustic emission in the frequency range lower than 300kHz. In mortar, however, the frequency components higher than 300kHz diminished more than those of cement paste. On the other hand, the acoustic emission propagating through concrete diminished more remarkably in the whole frequency range than that of cement paste or mortar. (4) The frequency components of acoustic emission in the range of 100∼200kHz were prominent in undamaged concrete. But the frequency components in this range diminished gradually with the progress of accumulative damage of concrete by loading, and the low frequency components became prominent and the power of acoustic emission propagating through concrete decreased.
In order to investigate the fatigue life of concrete under varying repeated load, several kinds of fatigue tests were conducted. They were: the constant-amplitude fatigue test, three kinds of variable load fatigue tests and the random load fatigue test in which the shape of the maximum stress level for the random repeated load was set to fit the exponential distribution. In these tests, concrete cylinder specimens were subjected to the repeated load, level of which was selected to lie between a constant minimum stress level and different maximum stress levels. Since the values of the fatigue life of concrete are known to scatter widely, the fatigue test results were evaluated statistically. From the experimental results, it can be concluded as follows. (1) At each test condition, the distribution of Miner sum follows a logarithmic normal distribution. (2) Miner's rule may possibly be applied to predict the fatigue life under varying repeated load. (3) The variable load fatigue test can be used to simulate the fatigue test under random load.
The influences of materials and environmental factors on the adhesion strength of unsaturated polyester (UP) resin mortar in water have been studied. The adhesion strength was found to be affected mainly by the shrinkage of UP resin at its early stage of hardening. The adhesion strength of conventional UP resin mortar varied widely because of its large shrinkage. It shrinked 0.3-0.4% in length just after the gelation. On the other hand, the low shrinkage UP resin mortar, which contains polyvinyl acetate as the low shrinkage additive and expands 0.2-0.3% in length, showed stable adhesion stregth in water. The effects of other factors such as the joint structure, adhesion interval, pH in water and residual raw materials were also investigated.
Hitherto, it has been recognized that the deterioration of the concrete structure exposed to chloride ion attack is caused by the expansion force of the rust layer growth in the embedded rebars. In order to prevent such concrete damage, various practical methods have been proposed. However, the use of these methods are limited in practice, because the application is very troublesome. Therefore, we have tried to improve the corrosion resistance of the steel rebar itself and discovered the key to achieve this purpose. The main concept of the present discovery is to add both Cu and W or 3.3% Ni to high purified rebar. In order to make clear the effect of this steel rebar, electrochemical tests and concrete deterioration accelerated tests using concrete blocks with various rebars were carried out. The results obtained are summerized as follow. (1) The corrosion prevension mechanism of the rebar and the role of various elements were clarified. (2) From the deterioration accelerated tests of concrete blocks, it was found that the resistances against rust formation and crack growth of the rebar were excellent. Cu-W bearing and 3.5% Ni containing high purified steel rebars are suitable for the concrete structure at seaside.
This study was carried out for giving the basic data to establish the structural design procedure of prestressed concrete beams based on the toughness as well as to develope the structural members having high ultimate and cracking strength. Prestressed concrete beams (10×18×170cm), having various amounts of prestressing tendon and compression steel, were loaded up to complete failure. The normal strength concrete, high strength concrete and steel fiber reinforced concrete were included in the study. Also unbonded beams were tested and their test results were compared with those of the corresponding bonded beams. The principal conclusions derived were: (1) The toughness value of prestressed concrete beams could be roughly estimated by the toughness index γ, which was calculated from the sectional constant and material properties. γ became larger with an increase of the toughness of compression zone. It was noted, however, that sudden failure due to the rupture of prestressing tendon took place when γ became too large. Therefore, the upper limit of γ should be determined so as to avoid the beam failure due to tendon failure. (2) Mechanically high performance prestressed concrete beams can be made by placing a large number of re-bars in both compression and tension sides and by introducing a large amount of prestressing.
Concrete structures such as offshore oil platform, nuclear power plant etc. are required to withstand the impulsive load in particular, and an accurate determination of the structural response to impulsive load in the critical region is needed. In this paper, the behavior of high strength concrete slabs under impulsive load was studied in the critical region. An experimental program was carried out to study the effects of both high strength concrete admixtures and curing conditions on the behavior of high strength RC slabs under a given impulsive loading. Four types of high strength RC slabs were tested and the deformation in the critical region, energy absorption at failure, local deformation etc. were compared with each other to examine the contribution of related variables on improvement of the impact resistance. Also the experimental results were compared with the calculated results obtained by using a non-linear dynamic finite element analysis.
Structures sometimes suffer from corrosive deterioration during their long service. In order to meet the increasing needs to protect structures from corrosion and further prolong service life, a variety of new diagnostic techniques have been developed as essential tools in the area of structural maintenance. This paper outlines several examples of such techniques that have been produced as the results of our R/D efforts. Particularly notable are the corrosion monitoring devices such as (1) a corrosion sensor for marine steel structure, (2) a sensor for detecting corrosion of reinforcing bar in concrete and (3) a diagnostic sensor to monitor the corrosion protectivity of the rust forms on weathering steel. These sensors utilize the most advanced electrochemical techniques to provide meaningful data for quick and accurate corrosion diagnosis and are expected to play increasingly important roles on various diagnostic fields in the future.