It is significant for deeper understanding of features of ASR damages of concrete structures to reveal relations between expansive pressure under restraint and free expansions of mortars in laboratory tests. One of the purposes of this study is to estimate the amount of ASR gel produced within mortars by the combination of EDS analysis for the gels and pore solution analysis. In addtion, this study aims at elucidating relations between expansive pressure measured under a restaint condition, and the amount and composition of gels. The expansive pressure was approximately proportional to the amount of ASR gel formed, when alkali contents of ASR gels formed were less than a critical value. However, mortars containing ASR gels with a higher alkali content than the critical value showed extremely low expansive pressure, even when they greatly expanded in expansion tests without restraint. These results suggest that, in existing ASR affected concrete structures containing gels with a higher alkali content than a critical value, damages due to the secondary stresses caused by resraint might not be so significant, even if reactive aggregate used in the concrete have shown great expansions in mortar bar test in the laboratory.
Recently, the mass media pays attention to few cases of deterioration and damages on concrete structures. In order to prevent the deterioration and damages, it is necessary to improve the quality control. The anti-corrosion coating has been applied to some concrete structures as countermeasures against the deterioration since 1983 in NIHON DORO KODAN (Japan Highway Pubic Corporation : JH). However, the coating seldom satisfied the requirement in terms of the durability and elongation, depending on the conditions. Therefore, JH have hesitated to apply the coating to the concrete structures all over Japan. This paper describes a proposed evaluation method concerning durability and adhesion capability including the basic parameters, based on a follow-up survey on anti-corrosion concrete surface coating applied on piers of the URADO Bridge.
The model explaining the expansion mechanism of the cement added with an expansive additive is proposed on the basis of the measurement of autogenous volume change and the observation result of hydration products. It is inferred that the calcium hydroxide and ettringite generated from the expansive additive grow by entangling pores because the cement added with an expansive additive shows autogenous expansion while being accompanied by hydration shrinkage. It is suggests that calcium hydroxide forms on the surface of the expansive additive particles and ettringite on the surface of C3A and the expansive additive particles from the observation result of the hydration products. Based on these phenomena, the thickness of the hydration product layer was obtained by calculation. When a low addition-type expansive additive excellent in expansion property is used, chemical press effect is expected large compared with conventional expansive additives.
The frost damage is mainly caused by freeze of pore water. In a hardened concrete suffering from freeze-thaw action, volume expansion as a result of ice formation and frost shrinkage due to the movement of unfrozen water caused by the ice-lense mechanism are generally observed. Although mechanisms of frost damage have been investigated by many researchers, little discussion has been made on the numerical model to predict freeze-induced strain behavior of concrete. In this paper, a mathematical model was presented to predict behavior based on the thermodynamic theory. Then the theoretical prediction by means of the model was compared with the experimental results and a good agreement was obtained for mortar specimens of different water-cement ratios and sand-cement ratios.
For the purpose of applying composite material mixed with cement and asphalt-emulsion to structural member, the basic mechanical tests of the composite materials were herein conducted. The unconfined compression test and splitting tensile test were conducted u nder a constant rate of strain of 5mm/sec. These strength shows larger values with the increase of C/E. C/E is the ratio of cement and asphalt-emulsion. These tendencies are similar to the relationship between compression strength and the cement-water ratio in cement concrete. Special attention in the present research is paid to the consistency, bending and compressive strength, and the method of determine the mixing ratios of cement asphalt-emulsion mortar.
This study is concerned with the development of a new manufacturing machine of concrete aggregate which excels in grain shape and grading. We report the experimental results of concrete aggregate treated by the kinetic energy of many chains rotating at high speed in the presented stone crusher. In this investigation, many experiments of crushing treatment were carried out for some row stones, and the grain shape and grading of produced concrete aggregate were examined. The experimental factors were size and rotation speed of chain. The test results showed that the presented stone crusher could produce concrete aggregate with excellent grain shape and grading.