Protective carrier is essential for the self‐healing of concrete cracks by microbially induced CaCO3 precipitation, owing to the harsh conditions in concrete. In this paper, porous ceramsite particles are used as microbial carrier. Heat treatment and NaOH soaking are first employed to improve the loading content of the ceramsite. The viability of bacterial spores is assessed by urea decomposition measurements. Then, the self‐healing efficiency of concrete cracks by spores is evaluated by a series of tests including compressive strength regain, water uptake, and visual inspection of cracks. Results indicate that heat treatment can improve the loading content of ceramsite while not leading to a reduction of concrete strength by the ceramsite addition. The optimal heating temperature is 750°C. Ceramsite particles act as a shelter and protect spores from high‐pH environment in concrete. When nutrients and spores are incorporated in ceramsite particles at the same time, nutrients are well accessible to the cells. The regain ratio of the compressive strength increases over 20%, and the water absorption ratio decreases about 30% compared with the control. The healing ratio of cracks reaches 86%, and the maximum crack width healed is near 0.3 mm.
Using recycled powders from solid waste is accepted as an effective strategy to realize the sustainable development of the construction industry. In our study, the cement was substituted by two kinds of recycled powders, i.e., spontaneous combustion gangue powder (SCGP) and recycled concrete powder (RCP), with a certain replacement ratio of 30%. The experimental variables were mainly the type of replacement powder (e.g., SCGP, RCP, and SCGP + RCP) and the grinding time of RCP (e.g., 25 min, 50 min, and 75 min). The fundamental properties, including mechanical properties, long-term properties, and carbon emission, were analyzed for all the mortar mixtures. Experimental results indicate that incorporation of RCP contributes to enhancing the toughness and dry shrinkage resistance of eco-efficient mortar, while SCGP positively affects the compressive strength and chloride resistance. The grinding process improves the activity of RCP to a certain extent, while a long grinding time leads to fusion and aggregation between powders. Investigation on CO2 emission demonstrates that carbon emission from cement production accounts for the largest proportion, 80~95%, in the total emission from mortar production. Combined with the AHP model, eco-efficient mortar containing 15% RCP ground for 50 min and 15% SCGP displays optimal fundamental properties.
This paper presents an experimental investigation on the effect of nano-montmorillonite, carbon nanotubes, and nano calcium carbonate on autogenous shrinkage of cement based materials. Cement paste with different nano-montmorillonite dosage (1.0 wt.%, 2.0 wt.%, 3.0 wt.%), carbon nanotubes dosage (0.1 wt.%, 0.2 wt.%, 0.3 wt.%), and nano calcium carbonate dosage (1.0 wt.%, 2.0 wt.%, 3.0 wt.%) were compared with the reference group to assess the effects of nano-materials on cement paste. Results show that autogenous shrinkage of cement based materials containing nano-materials mainly occurs in the first 72 h. Nano-materials decrease the autogenous shrinkage of the investigated cement based materials at all ages. Compared with that of the reference group at the age of 168 h, the autogenous shrinkage of NM-modified cement based composites containing 3.0 wt.% NM decreased by as much as 57.4%; the autogenous shrinkage of CNTs-modified cement based composites containing 0.3 wt.% CNTs decreased by as much as 19.4%; the autogenous shrinkage of NC-modified cement based composites containing 2.0 wt.% NC decreased by as much as 17.1%. Electrochemical AC (Alternating Current) impedance spectroscopy results show that the resistance of the pore solution electrolyte of specimens containing nano-materials increases with age, and is less than that of specimens without nano-materials, which illustrates that the pore size of nano-modified cement based material is finer and autogenous shrinkage is smaller. Scanning electron microscope results show that the structure of cement matrix is denser with more hydration products by adding nano-materials. Nano-montmorillonite releases water to reduce self-drying effect during the process of hydration for its well water swelling. Carbon nanotubes have the nanometer filling effect and form a continuous network to restrain the early autogenous shrinkage of cement paste. Nano calcium carbonate not only decreases the porosity of the cement paste, but also reacts with tricalcium aluminate to generate the expanded product calcium carboaluminate for compensating autogenous shrinkage of cement paste.
2 November 2020 in Fullerenes, Nanotubes and Carbon Nanostructures
Bi2Te3 was incorporated in carbon fiber-reinforced cement composites (CFRCs) as thermoelectric-reinforced component via three different doping methods (uniformity volume mixing, gradient volume mixing, and gradient layer mixing), forming Bi2Te3 enhanced CFRCs. Seebeck coefficient and resistivity were measured for evaluating its thermoelectric properties. Scanning electric microscope (SEM) and three dimension video microscope (3-DVM) were applied to characterize the microstructure of prepared composites. SEM images showed that carbon fibers (CFs) overlapped on each other, resulting in a 3-D continuous electric conductive path. The introduction of Bi2Te3 enhanced the electric conductivity of the composites due to the quantum tunneling effect, which was beneficial to improve its Seebeck coefficient and the linearity and reversibility of the Seebeck effect. The thermoelectric performance of the composites was further improved by the synergetic effect of gradient effect and low dimension. Thermoelectric power (TEP) of the composite fabricated by gradient layer mixing method was enhanced as much as 10 times comparing to conventional CFRCs. The mechanism of the enhanced effect was also discussed.
Super high‐rise building is a typical architectural form of urban modernization, and it is also the trend of urban architectural development. This paper reviews the development history of super high‐rise buildings in China combined with the engineering practice of representative super high‐rise buildings since the 1980s, such as the Shanghai Center, Shanghai Oriental Pearl Tower, Jinmao Tower, Shanghai World Financial Center, Canton Tower, and Shanghai Tower. The development process of the key technologies of super high‐rise projects from the aspects of several technologies, such as soft soil pile foundation and foundation pit technology, concrete structure construction technology, integral formwork equipment technology, and steel structure comprehensive installation technology, is also elaborated. At the same time, the Shanghai Tower is selected as a typical case to share the innovative technology of China’s tallest building. Finally, prospects for development of super high‐rise construction technology are presented.
A zeolite/TiO2 composite (ZTC) was applied to prepare a high-quality photocatalytic cement-based material (PCM). The acetone degradation experiment and micro measurements including XRD(X-Ray Diffractometer), SEM-EDS(Scanning Electron Microscope-Energy Dispersive Spectrometer), BET(BET Specific Surface Area Tester), FTIR(Fourier Transform Infrared Spectrometer) were conducted to characterize the photocatalytic efficiency and physicochemical properties of PCM, respectively. Results show that TiO2 particles disperse on the surface of a PCM homogeneously and provide abundant active sites for photocatalytic reactions. Compared to a normal photocatalytic cement-based material (NPCM), the TiO2 content of a PCM is lower and its photocatalytic efficiency is higher. The ZTC frees TiO2 particles from the impacts of cement hydration products and increases the adsorption volume of acetone. The photocatalytic performance of the PCM was stable after repeated tests. Using the ZTC as a photocatalyst has a prominent effect on the photocatalytic performance of the PCM.