Microbially induced CaCO3 precipitation (MICP), mainly in the form of calcite, has been reported to be an efficient approach for self-healing cracks in concrete. However, little is known about the implementation of aragonite, the other common crystalline form of CaCO3, in bioconcrete. Therefore, a systematic investigation of the crystal polymorphs and the healing efficiency of different cultures, i.e., two microbial consortia under anaerobic (MC-Aa) and anoxic (MC-Ao) conditions and nonureolytic pure-culture bacteria (Bacillus cohnii), was conducted in this study. The results showed that the MC-Ao agent exhibited the maximum values of completely healed crack widths (1.22 mm) after 28 d of healing, which is larger than the values of 0.79 and 0.73 mm for B. cohnii and MC-Aa, respectively. Field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD) analyses confirmed that the biominerals induced by MC-Aa and B. cohnii are calcite, while those of MC-Ao were 82% aragonite and 18% calcite. It is noteworthy that this proportion of aragonite is the highest reported level for the MICP system to date. In addition, economic evaluation verified that the microbial consortia resulted in a 61% decrease in production costs compared to pure cultures. The intriguing findings obtained in this study may provide a scientific basis for the potential implementation of microbial consortia under anoxic conditions, such as a new self-healing agent, in bioconcrete. (C) 2019 Elsevier Ltd. All rights reserved.

In this paper, available structural models and equations for predicting the effective thermal conductivity (k(e)) of recycled aggregate thermal insulation concrete, including series, parallel, Maxwell-Eucken, eEffective medium theory, and Gong's model are discussed and extended to three phases by considering the effect of glazed hollow beads (GHBs). The solid porosity of GHBs is estimated and used in the equations. A unified model for calculating ke values is proposed, where the fractal dimension of GHBs is considered. A simple expression characterizing the fractal dimension of GHBs is derived. Nine batch specimens with different concrete mixtures are tested to determine the ke values which are compared with the predicted values. The predicted values from Unified-2 model are found to be in good agreement with the experimental results.

The objective of this study was to prepare a type of recycled aggregate thermal insulation concrete (RATIC), in which thermal insulation particles (TIPs) were used as solid sealed ‘holes' instead of air holes to allow the thermal conductivity coefficient of the concrete to be reduced. This paper presents the results of a laboratory study on the performance of natural and recycled aggregate concrete, which was prepared by the incorporation of TIPs and different mineral admixtures including ultrafine slag (UFS), nanosilica (NS) and nanocalcium carbonate (NCC). The compressive strength, thermal conductivity coefficient and dry density of the concrete mixtures were determined. The experimental results demonstrate that glazed hollow beads, at the optimal level of 130%, significantly reduced the thermal conductivity property of the recycled aggregate concrete. The properties of the concrete were improved by the addition of UFS and NS, while NCC produced a negative impact. As far as compressive strength was concerned, the replacement of cement by 10% UFS or 1% NS improved the mechanical performance, while the replacement of cement by 1·5% NCC and the addition of TIPs decreased the compressive strength of the recycled aggregate concretes. The effects of the UFS and NS mineral admixtures produced greater performance improvements in the concrete than the recycled coarse aggregate. Finally, the optimal mix proportion was determined. For this mix, the thermal conductivity coefficient and compressive strength of the concrete were 0·305 W/(m.K) and 46·7 MPa respectively.

In this paper, experimental investigations are conducted on the mechanical properties and stress-strain curve (SSC) of recycled aggregate thermal insulation concrete (RATIC), in which a volume percentage of 130% glazed hollow bead particles were added, with different replacement percentages of recycled coarse aggregate (RCA). Concrete specimens were fabricated and tested with different RCA replacement percentages of 0%, 30%, 50%, 70% and 100%. A water to cement ratio of 0.5 was adopted. Concrete workability was in the slump range of 150-180 mm. All tests were carried out after 28 days of wet curing. In addition, the concrete mechanical properties, elastic modulus and stress-strain relationship were evaluated.During the analysis, special attention was devoted to the failure behavior and the influences of the RCA replacement percentage on compressive strength, split tensile strength, flexural strength, elastic modulus, the peak and ultimate strains of the RATIC.The results indicated that when 70% of the virgin aggregate was replaced with recycled coarse aggregate a C40 strength class structural concrete could be produced. In addition, a correlation between the elastic modulus and compressive strength of the RATIC was found. Finally, it was possible to determine differences in the stress-strain relationship for a conventional concrete and the RATC with various different replacement percentages. (C) 2014 Elsevier Ltd. All rights reserved.

In this study, theoretical analysis and orthogonal test are carried out for five factors, including water consumption, sand ratio, cement dosage, gravel dosage, and admixture, which influence the working performance of thermal insulation glazed hollow bead concrete for the green building in Jincheng of shanxi province. The effect of five factors on the compressive strength and the work performance are studied. Finally, the optimal mix proportion is to be determined based on the experimental and orthogonal analysis in order to guide the construction.

For the poor thermal conductivity of ordinary concrete and fire-resistant performance, durability and other disadvantages of the organic building insulation material, a new type of insulating concrete thermal insulation glazed hollow beads concrete composed of inorganic insulation materials was proposed. The results indicate that the pre-wetting processing of inorganic heat preservation material and optimization of mixing procedure is able to reduce the slump loss of concrete. The addition of add the glassed hollow beads or expanded perlite can improve the heat preservation and insulation performance of concrete under the premise of strength.