During the manufacturing of foam concrete, conventional chemical and physical foaming methods are still inadequate for regulating and stabilizing the bubble properties. In this work, a one-pot method, denoted as in-situ mechanical frothing, was proposed preparing foam concrete by vigorously stirring the mixture of water, cement, sandy soil, and foaming agent. Sandy soil (SS) was used in the content range of 25–75 % as cement replacement to decrease the binder consumption and reduce costs. The influence of in-situ mechanical frothing technology and SS dosage on the properties of paste rheology, pore structure , compressive strength , and thermal properties was investigated. The results showed that the average pore size of foam concrete prepared by this method is between 45.73 and 74.58 μm. The compressive strength of the formed foam concrete at dry density of 600–1000 kg/cm 3 was 2.78–16.37 MPa, which was 85%–231 % higher than that the standard values. The incorporation of SS resulted in smaller and homogeneous pore structure in foam concrete. Moreover, foam concrete with 25–75 % SS dosage showed 7–40 % decrease in thermal conductivity . The overall analysis showed that the 25–50 % S S-incorporated foam concrete enabled achieving higher standard properties through in-situ mechanical frothing.
Xanthan gum, as an environment-friendly biopolymer, holds great promise to replace conventional binders for engineering construction. Yet, the impact of curing temperature and relative humidity (RH) on the strength of xanthan gum-treated sand remains uncertain. In this study, xanthan gum-treated sand specimens were cured under different temperatures (20°C-70°C) and RH (10 %-80 %), respectively, until an equilibrium moisture content was reached. Through a series of Unconfined Compressive Strength (UCS) tests, an optimal curing humidity of 40 % was identified for all the testing temperatures. It was also found the UCS at 10 % RH is always slightly higher than that at 70 % RH, and the UCS increases linearly with the curing temperature under the same RH. The mechanisms of the findings were further studied by X-ray Computed Tomography (CT) scan tests and Scanning Electron Microscopy (SEM) tests. The strengthening of xanthan gum-treated sand was attributed to an internal hydrogel effect and an external hydrogel-particle network effect. In particular, the hydrogel breakage at low RH and the small hydrogel volume at high RH contribute negatively to the network effect and thus relatively small UCS at low/high RH. Meanwhile, elevating the curing temperature could trigger the conformation transformation of xanthan gum hydrogels and thicken the shells of hydrogels, both of which contribute positively to the hydrogel and network effects and thus provide a higher UCS.
Yang Guokun,Zheng Shaojun,Liu Tianle,Luo Enhao,Tang Chengxiang,Qu Bo,Lei Gang,Jiang Guosheng
Enhancing the efficiency of microbially induced carbonate precipitation (MICP) for soil stabilization is of significant importance for reducing costs and shortening construction timelines, ultimately improving the applicability of MICP technology in engineering. This study developed a novel biocarrier material (Dia@AP-DE) to enhance the efficiency of MICP in cementing sand by immobilizing microorganisms and diversifying calcium carbonate cementation forms. Dia@AP-DE was chemically modified to graft –NH 2 groups onto its surface. These groups protonate to form positively charged –NH 3 + groups, enabling the tight adsorption of negatively charged bacteria through Coulombic interactions. MICP was applied to reinforce sand columns from group B (free bacteria) and group BDAD (Dia@AP-DE immobilized bacteria), and a series of experiments were conducted to analyze the biocarrier’s effects on cementation efficiency, calcium carbonate morphology, and pore structure. Additionally, flow channel evolution within the sand columns was simulated using AVIZO software. The results showed that the BDAD group formed more diverse calcium carbonate cementation forms, particularly the formation of “calcium carbonate bridges.” The bacteria immobilized on Dia@AP-DE produced additional layers of calcium carbonate, which acted as bridges between sand particles, reducing the distance required for effective cementation. Furthermore, flow simulation results indicated that the “calcium carbonate bridges” optimized the uniformity of flow channels within the sand columns during the early stages of injection. Unconfined compressive strength (UCS) tests showed that the strength of the BDAD group was significantly improved at all injection cycles, with UCS values of 1.02 MPa and 5.88 MPa after 3 and 11 injections, respectively, which were 4.6 and 2.0 times higher than those of B group. This study provides a potential new approach for enhancing the efficiency of biocemented soils.
危险品化学品经营许可证（带存储）