It has become an intelligent and environmental protection method to repair concrete cracks based on microbial-induced calcium carbonate precipitation (MICP). However, due to the high-alkali environment in concrete, even the microbial spores with strong alkali resistance find it difficult to survive for a long time, which affects the long-term self-healing effect of concrete cracks. In this paper, low-alkali sulfo-aluminate cement (SC) was used as a carrier to encapsulate spores, and the effects of the spore group and microbial group on the basic performances of concrete were studied. Then, the area repair ratio, water permeability, the repair ratio of anti-chloride ion penetration, and ultrasonic velocity were used to evaluate the self-healing efficiency of cracks, and the self-healing effects of two kinds of microbial self-healing agents on concrete cracks with different curing ages were further studied. Moreover, the growth, enzyme activity, and microbial morphologies of spores with and without encapsulation immersed in the simulated pore solution of cement-based materials at different times were studied to discuss the protective effect of the carrier on spores. Compared with the reference group, the results showed that the addition of two microbial self-healing agents would slightly affect the basic performances of concrete, but both were within the control range of concrete materials. For the early-age cracks, the two kinds of microbial self-healing agents could achieve a good self-healing effect, but for the later-age cracks, the concrete cracks of the microbial group could still be repaired well, while the self-healing effect of the spore group was greatly reduced. Moreover, the white precipitates generated at the crack mouth were all calcite CaCO3. In addition, the self-healing mechanism of different microbial self-healing agents on concrete cracks was discussed carefully. This study provides a new idea and method for the engineering application of microbial self-healing concrete.

No abstract

SUMMARY Acetylene in oil is an important characteristic gas which reflects early discharge faults of transformer and other oil‐immersed electrical equipment. Laser‐based photoacoustic spectroscopy techniques of high sensitivity and good selectivity can be well applied to detect trace gases. A portable and tunable experimental setup with a distributed feedback diode laser has been developed in this paper. The photoacoustic cell property parameters, the relationships between the photoacoustic signals and the laser power and the acetylene gas concentrations were analysed experimentally. By means of diode laser wavelength modulation, the high‐resolution acetylene photoacoustic spectrum near 1.5 µm in the first overtone band near infrared was investigated. A novel method of photoacoustic quantitative analysis was proposed on the basis of least square regression. The theoretical and experimental results show the feasibility of on‐line monitoring of acetylene and designing a tunable photoacoustic spectrometer with high sensitivity. Copyright © 2011 John Wiley & Sons, Ltd.

No abstract

No abstract