Enhanced self-healing capacity in cementitious materials by use of encapsulated carbonate precipitating bacteria : from proof-of-concept to reality

In this study, two bacteria-based self-healing systems were developed for the proof-of-concept and approach to a realistic self-healing. A self-healing system with glass capillaries and silica sol gel carried bacterial cells was first built. The bio-CaCO3 formed in-situ (in silica gel) after glass capillaries breakage preliminarily showed the feasibility of this system. The investigation on the selfhealing efficiency demonstrated that the water permeability was decreased by about two orders of magnitude due to self-healing. However, practical application of this system was limited by the use of the un-mixable and expensive glass capillaries. A second self-healing system therefore was built in order to approach a realistic self-healing, by using hydrogel encapsulated bacteria. Great superiority in healing efficiency was obtained in this system. A maximum crack width of 0.5 mm could be healed within 7 days in the specimens of the bacterial series; while the maximum crack width can be healed in other series was in the range of 0.2~0.3 mm. Water permeability was greatly decreased (68%) in the bacterial series

SL(2,Z) Modular Forms and Anomaly Cancellation Formulas II

By some SL(2, Z) modular forms introduced in [4] and [9], we construct some {\Gamma}^0(2) and {\Gamma}_0(2) modular forms and obtain some new cancellation formulas for spin manifolds and spin^c manifolds respectively. As corollaries, we get some divisibility results of index of twisted Dirac operators on spin manifolds and spin^c manifolds

Effect of water availability on microbial self-healing of concrete

Microbial-based self-healing is a promising solution for a sustainable concrete. The principle is that carbonate precipitating bacteria and bio-reagents are pre-added into concrete; upon cracking, bacteria will be activated to precipitate CaCO3 to heal the crack. Due to the harsh environment in concrete, encapsulation of bacteria is preferable before incorporation into the matrix. In this study, microcapsules and hydrogels were applied to encapsulate bacterial spores. Water is an essential element for bacterial activities. Therefore, water availability is a key factor to obtain considerable amount of healing. In this work, self-healing behavior of the specimens (with and without bacteria incorporated) were investigated at the conditions of 95%RH and wet-dry cycles (wdc). Two types of wdc were applied: 1) 8h in water and 16h in 60%RH; 2) 1h in water and 11h in 60%RH. Healing efficiency was evaluated by crack closure and the decrease of water permeability. No crack healing was visualized in the specimens stored at 95%RH. The specimens subjected to wdcs had much more crack healing. Water permeability of the specimens with microencapsulated bacteria was about one order of magnitude lower than that of the reference ones. About 40% and 80% of the crack area was healed in the reference and bacterial specimens (at wdc1), respectively. For the ones stored at wdc2, though with a reduced wet period, considerable amount of healing was obtained in the specimens with hydrogel encapsulated bacteria, which had crack healing ratio of 5%~30% and 50%~100% for the reference and bacterial series, respectively. This study indicates that incorporation of carbonate precipitating bacteria into concrete can enhance the self-healing efficiency. The amount of available water and the time during which the water can stay available in cracks are of crucial importance to obtain a sufficient healing. This water availability can be enhanced by encapsulating the bacteria in hydrogels

Surface consolidation of natural stones by use of bio-agents and chemical consolidants

Surface treatment is a frequently used method for conservation and restoration of building materials. . In this study, a novel and environment friendly strategy, bacterially induced calcium carbonate precipitation was applied to strengthen the surface of limestone. The treatment procedure for bio-deposition was first optimized regarding the aspects of treatment frequency and treatment time. Ultrasonic velocity was used to characterize the surface properties. It turned out that two subsequent applications of a one-step bio-deposition treatment had the best effect, where the transmitting velocity of the ultrasonic wave was increased with around 10~20%. The improvement mainly occurred from the surface till the depth of 4 cm and the largest increase was at the depth around 2 cm. Meanwhile, a commercial chemical ethyl silicate based consolidant, was applied under the same condition. Yet the efficiency measured by the increase in ultrasonic velocity was not significant

Study on the Influence of Ultrasonic Vibration on the Specific Energy of Sawing Ceramic

AbstractThe hard as well as brittle constituents are typically difficult-to-machined materials, and this character upsurges the machining cost. Many non-traditional machining methods were developed to improve its cost-effectiveness. Ultrasonic vibration assisted grinding has been improved the processing performance of a variety of brittle materials, and achieved good results in processing application. In this study, engineering ceramic was precisely sawn using a thin diamond blade with or without ultrasonic vibration conditions. During the sawing process, the specific sawing energy was investigated with the measurement of sawing forces to explore the influence of ultrasonic vibration. The results showed that the ultrasonic vibration made a significant reduction in specific sawing energy. The specific sawing energy decreased with the increase of the maximum undeformed chip thickness in both the sawing conditions; however ultrasonic vibration changed the trend of specific sawing energy in normal cutting mode from exponentially decreasing to a good linear decreasing. Under the ultrasonic vibration assisted sawing condition, the impact of the diamond grain on the engineering ceramic caused to much more material removal in brittle fracture mode. The reducing of the plastic transformation also reduced the energy consumption during the engineering ceramic sawing process

Optimization and Numerical Simulation of Multi-layer Microchannel Heat Sink

AbstractThe configuration sizes of multi-layer microchannel heat sink is optimized in order to enhance the performance of the high flux chip, which is 556W/cm2. Taking the thermal resistance and the pressure drop as goal functions, a double-objective optimization model was proposed based on the thermal resistance network model. The opimized microchannel heat sink is numerically simulated by computational fluid dynamics (CFD) software. The number of microchannel in width n1 and that in height n2 are 24 and 2, the width of optimized optimized microchannel and fin are 196 and 50μm, respectively, and the corresponding total thermal resistance of the whole microchannel heat sink is 0.4025°C/W. The highest temperature is less than 98°C, which can satisfy the requirement of chip to temperature. The maximum temperature difference is 77.8673°C, and the transferred power of heat flux is 200W, so the total thermal resistance is 0.3893°C/W, which agrees well with the analysis result of thermal resistance network model

Applying a biodeposition layer to increase the bond of a repair mortar on a mortar substrate

One of the major concerns in infrastructure repair is a sufficient bond between the substrate and the repair material, especially for the long-term performance and durability of the repaired structure. In this study, the bond of the repair material on the mortar substrate is promoted via the biodeposition of a calcium carbonate layer by a ureolytic bacterium. X-ray diffraction and scanning electron microscopy were used to examine the interfaces between the repair material and the substrate, as well as the polymorph of the deposited calcium carbonate. The approximately 50 mu m thick biodeposition film on the mortar surface mostly consisted of calcite and vaterite. Both the repair material and the substrate tended to show a good adherence to that layer. The bond, as assessed by slant shear specimen testing, was improved by the presence of the biodeposition layer. A further increase was found when engineering the substrate surface using a structured pattern layer of biodeposition. (C) 2017 Elsevier Ltd. All rights reserved

Computational Discovery and Characterization of New B2O Phases

We present computational discoveries of new structural phases of B2O compound exhibiting novel bonding networks and electronic states at ambient and elevated pressures. Our advanced crystal structure searches in conjunction with density functional theory calculations have identified an orthorhombic phase of B2O that is energetically stable at ambient pressure and contains an intriguing bonding network of icosahedral B12 clusters bridged by oxygen atoms. As pressure increases above 1.9 GPa, a structural transformation takes the orthorhombic B2O into a pseudo- layered trigonal phase. We have performed extensive studies to investigate the evolution of chemical bonds and electronic states associated with the B12 icosahedral unit in the orthorhombic phase and the covalent B-O bonds in the trigonal phase. We also have examined the nature of the charge carriers and their coupling to the lattice vibrations in the newly identified B2O crystals. Interestingly, our results indicate that both B2O phases become superconducting at low temperatures, with transition temperatures of 6.4 K and 5.9 K, respectively, in the ambient and high-pressure phase. The present findings establish new B2O phases and characterize their structural and electronic properties, which offer insights and guidance for exploration toward further fundamental understanding and potential synthesis and application