Smart concretes and structures are intelligent systems that have properties different from normal concrete, such as selfsensing and self-healing properties, or have the ability to react upon an external stimulus, such as stress and temperature. The ''smartness'' of concrete and structures is achieved through material composition design, special processing, introduction of other functional components, or modification of the microstructure. They are designed to meet specific requirements through tailored properties for improving serviceability, safety, reliability, longevity, and durability of the infrastructures and reducing the life-cycle costs of the infrastructures. This article reviews the recent researches of various smart concretes and structures, with attentions to their principles, fabrication, and properties. Future challenges in the development and applications of smart concretes and structures are also discussed.

Sex steroids can positively affect the brain function, and low levels of sex steroids may be associated with worse cognitive function in the elderly men. However, previous studies reported contrary findings on the relationship between testosterone level and risk of Alzheimer's disease in the elderly men. The objective of this study was to comprehensively assess the relationship between low testosterone level and Alzheimer's disease risk in the elderly men using a meta-analysis. Only prospective cohort studies assessing the influence of low testosterone level on Alzheimer's disease risk in elderly men were considered eligible. Relative risks (RRs) with 95% confidence intervals (95% CI) were pooled to assess the risk of Alzheimer's disease in elderly men with low testosterone level. Seven prospective cohort studies with a total of 5251 elderly men and 240 cases of Alzheimer's disease were included into the meta-analysis. There was moderate degree of heterogeneity among those included studies (I(2) = 47.2%). Meta-analysis using random effect model showed that low plasma testosterone level was significantly associated with an increased risk of Alzheimer's disease in elderly men (random RR = 1.48, 95% CI 1.12-1.96, P = 0.006). Sensitivity analysis by omitting one study by turns showed that there was no obvious change in the pooled risk estimates, and all pooled RRs were statistically significant. This meta-analysis supports that low plasma testosterone level is significantly associated with increased risk of Alzheimer's disease in the elderly men. Low testosterone level is a risk factor of worse cognitive function in the elderly men.

In this paper, carbon fibers with hydrophilic surface modification were added into cement mortar through ultrasonic treatment. The mechanical and electrical properties of carbon fiber filled cement mortar were tested to examine the reinforcing effect of carbon fiber. In order to understand the underlying modification mechanisms of carbon fibers to cement mortar at micro scale and in theory, scanning electron microscope (SEM) observation and theoretical calculations were carried out. Test results indicate that the adding of carbon fibers into cement mortar enhances the mechanical strength (especially compressive strength), and decreases the electrical resistivity of carbon fiber filled cement mortar. SEM results show that the enhancement of the properties of carbon fiber filled cement mortar owes to fiber ability of restraining the growth of microcracks and absorbing energy by overcoming its pulling out. The enhancing mechanism of carbon fibers on the properties of cement mortar analyzed by the calculated fiber numbers per unit volume, average center distance between two carbon fibers and the critical pull-out length well matches the experimental results.

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The botryoid hybrid nano-carbon materials were incorporated into cementitious materials to develop a new type of self-sensing cementitious composites, and then the mechanical, electrically conductive, and piezoresistive behaviors of the developed self-sensing cementitious composites with botryoid hybrid nano-carbon materials were comprehensively investigated. Moreover, the modification mechanisms of botryoid hybrid nano-carbon materials to cementitious materials were also explored. The experimental results show that the compressive strength and the elasticity modulus of the self-sensing cementitious composites botryoid hybrid nano-carbon materials decrease with the increase in the botryoid hybrid nano-carbon material content, while the Poisson’s ratio does the opposite. The percolation threshold zone of the self-sensing cementitious composites botryoid hybrid nano-carbon materials is from 2.28 to 3.85 vol.%. The optimal content of botryoid hybrid nano-carbon materials is 3.38 vol.% for piezoresistivity of the self-sensing cementitious composites botryoid hybrid nano-carbon materials. The amplitude of fractional change in resistivity goes up to 70.4% and 28.9%, respectively, under the monotonic compressive loading to failure and under the repeated compressive loading within elastic regime. The piezoresistive stress/strain sensitivity reaches (3.04%/MPa)/354.28 within elastic regime. The effective modification of botryoid hybrid nano-carbon materials to electrically conductive and piezoresistive properties of cementitious materials at such low content is attributed to their botryoid structures, which are beneficial for the dispersion of botryoid hybrid nano-carbon materials and the formation of conductive network in cementitious materials. The use of botryoid hybrid nano-carbon materials provides a new bottom–up design and fabrication approach for nano-engineering multifunctional cementitious composites.