Use of blast-furnace slag fine powder blended cement is an important option for lowering carbon emission in the concrete construction sector. However, concrete with blended cement (hereafter denoted as BFS concrete) has been believed vulnerable to shrinkage cracking and its use in building construction has been avoided except for underground structural elements in Japan. To develop the use of BFS concrete in building construction, quantitative evaluation of its shrinkage cracking resistance is necessary. The scope of this study included experimental verification of shrinkage resistance of BFS concrete, in which the effects of ambient temperature were emphasized, and restraint shrinkage cracking tests with BFS concrete subjected to three levels of ambient temperatures of 10, 20 and 30°C compared with normal concrete. To improve crack resistance, an improved BFS concrete using additives such as water retaining shrinkage reducing agent (SRA) was added to the experiments. As a result, the following two major conclusions were obtained: 1) The crack resistances of BFS concrete deteriorated due to increasing free shrinkage strain at high temperatures, while this was not the case for the normal concrete, and 2) water retaining type SRA dramatically improved the crack resistance of BFS concrete at high temperatures.

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 for the field data demonstrated dominant influence of coarse aggregate type on drying shrinkage compared with other parameters like unit water content and led to establishing simple formula for predicting drying shrinkage. These results also inferred the risk in exaggerated expectation to restrict drying shrinkage only by selecting coarse aggregate type due to wide variety of drying shrinkage behavior among identical coarse aggregate type. Finally, mixing usage of multiple aggregate types was depicted effective via experiment to practically limit drying shrinkage.

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 gage showed highest reproducibility and consistency with the standard method and were revealed an appropriate for this proposal. This proposing method was also demonstrated robustness and high reliability in field experiment and is expected to contribute to rational shrinkage controlling at construction sites.

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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 first examined through laboratory tests that confirmed the improvement of water retaining capability within concrete. It was shown that water diffusion in concrete with the smart ALA was largely delayed leading to a decrease in micro-crack development and increase in compressive strength and improvement of durability indexes such as carbonation depth and air permeability.