En-Hua Yang

Rheological Control in Production of Engineered Cementitious Composites

A study of fresh property rheological control during engineered cementitious composite (ECC) processing for the purpose of more effective realization of mechanical properties using micromechanical design theory optimization is reported on in this paper. To determine their effects on fresh and hardened ECC properties, there was investigation of four factors (amount of viscosity-modifying admixture, amount of high-range water reducer [HRWR], water-binder ratio [w/b], and Class C fly ash [FA] to Class F FA ratio). That the w/b, among investigated factors, most strongly affects ECC mortar (without fiber), which in turn significantly impacts ECC composite tensile strain capacity and ultimate tensile strength, is indicated in test results. The mini-slump flow test and marsh cone flow test were shown to be simple and practical methods for ECCC mortar rheological property characterization. Self-consolidating ECC with optimum rheological properties promoting uniform fiber distribution through the matrix can be produced easily, and micromechanically based optimized ECC mixture design optimized tensile properties can be realized through compliance recommendation for rheological control for ECC production as summarized in this paper.

Gas Generation from Incinerator Bottom Ash: Potential Aerating Agent for Lightweight Concrete Production

AbstractIncinerator bottom ash (IBA) has great potential to be utilized for civil engineering applications. This paper is to investigate the characteristic of gas generation from IBA and to study the potential of IBA as an aerating agent. Results show the aeration capacity of IBA used in this study is approximately 1% that of pure aluminum powder by mass. Finer particles, higher alkali molarity, and higher reaction temperature encourage the reaction and more gas is generated per gram of IBA. Type of alkaline solution does not seem to be an important factor for gas generation from IBA. Several exemplary lightweight mortars were produced by incorporating IBA as an aerating agent. It is highly plausible IBA can be used as an aerating agent to replace pure aluminum powder in the production of aerated concrete.

Controllable mullite bismuth ferrite micro/nanostructures with multifarious catalytic activities for switchable/hybrid catalytic degradation processes

In this work, controllable preparation of micro/nanostructured bismuth ferrites (BFOs) were used to investigate multifarious heterogeneous catalyses, including Fenton/Fenton-like reaction, photocatalysis, photo-Fenton oxidation, and peroxymonosulfate (PMS) activation. Results showed that BFO can be used asa novel catalyst to activate switchable catalytic degradation of organic matters. Additionally, a novel catalytic system for degradation of organic pollutants, which integrating all-above heterogeneous catalyses is denoted as BFO/H2O2/PMS hybrid reaction, is introduced for the first time. BFO/H2O2/PMS system effectively degraded>99% for both methyl orange (MO) and sulfamethoxazole (SMX) within 60min, which shows better efficiency than above BFO-driven catalyses. The major SMX degradation pathway in BFO/H2O2/PMS system is proposed via detecting intermediates using LC/MS/MS. It was found that catalytic activities of BFOs are in the order of BFO-L (co-precipitation, micro/nanosize, single crystals exposing facet (001))>BFO-H (hydrothermal, nanocluster with a higher surface area than other BFOs)>BFO-C (fabricated using calcination process, microsize), which demonstrated that crystallographic orientation is more significant in heterogeneous catalyses than specific surface area at micro/nanoscale. Besides, the required H2O2 consumption for achieving 99% TOC removal was identified in BFO-driven photo-Fenton oxidation. The other effects on degradation efficiency, such as H2O2 dosage and pH, were investigated as well. In Fenton/Fenton-like reaction, reaction conditions suggested are ∼61.5mM H2O2 dosage and pH≥4.5 to avoid quenching of HO into HO2 by excessive H2O2 and Fe leaching.

Environmental Sustainability through Recycling Incineration Bottom Ash for the Production of Autoclaved Aerated Concrete

Municipal solid waste incineration bottom ash (IBA) has great potential to be utilized for civil engineering applications. This paper is to investigate the characteristic of gas generation from IBA and to study the potential of IBA as aerating agent to replace costly aluminum powder and as silica source to partially replace silica flour/fly ash in the production of autoclaved aerated concrete (AAC). Results show the aeration capacity of IBA used in this study is about 1% that of pure aluminum powder by mass. Finer particles, higher alkali molarity, and higher reaction temperature encourage the reaction and more gas is generated per gram of IBA. Type of alkaline solution does not seem to be an important factor for gas generation from IBA. Several exemplary lightweight mortars and AACs were produced by incorporating IBA as aerating agent. It is highly plausible IBA can be used as aerating agent to replace pure aluminum powder in the production of normal aerated concrete. IBA-AACs with density ranging from 600 to 800 kg/m3 were successfully synthesized by using IBA as aerating agent. For a given density, the compressive strength of IBA-AAC is higher than that of AAC due to the formation of more uniform pore structure with smaller pore size in IBA-AAC.

Micromechanics-Based Optimization of Pigmentable Strain-Hardening Cementitious Composites

AbstractArchitectural and decorative concrete (ADC) has become an enormously popular product for both building interiors and exteriors, combining an aesthetic finish with structural capabilities. Cracking and chipping of ADC product during handling and transportation, however, is of great concern due to the brittleness of ADC materials. This paper looks at the development of a white strain-hardening cementitious composite (SHCC) as an alternative ADC material to address the above-mentioned challenges. It was found that the replacement of ordinary portland cement and fly ash with white cement altered SHCC microstructure which is unfavorab to the tensile strain-hardening behavior. A micromechanical model was engaged for composite optimization through ingredients selection and component tailoring to reengineer white SHCCs.

Micromechanics-Based Design of Strain Hardening Cementitious Composites (SHCC)

This paper reviews the research and development of micromechanics-based design theory of strain hardening cementitious composites (SHCC) at different scale, linking the microstructure at micro scale with the composite tensile behavior at macro scale through fiber bridging properties at meso scale. Micromechanics relates macroscopic properties of SHCC to its microstructures, and forms the theoretical basis of SHCC design theory. So the single fiber pullout behavior at micro level lays the foundation of the scale-up research and has been investigated under various loading conditions. Based on the single fiber pullout behavior, analytic tools on micromechanics-based strain hardening model have been developed in closed or numerical forms. And it is widely applied as design guideline in guiding ingredients selection and component tailoring to achieve desired strain hardening performance. Afterwards, the micromechanics-based concept has been extended to develop models for tensile stress-strain properties and cracking process of SHCC. Therefore, the micromechanics-based design methodology of SHCC becomes holistic in the sense of obtaining the ultimate composite behavior with given micromechanical parameters, and versatile in various SHCC design, i.e. towards durability performance with charactering the crack pattern. It is expected that the micromechanics-based design tools capable of capturing the essence of SHCC behavior, should help structural designers take full advantage of SHCC material in infrastructure system design.

Healing of Interface Between Polyvinyl Alcohol (PVA) Fiber and Cement Matrix

Polyvinyl alcohol (PVA) fiber-reinforced strain-hardening cementitious composites (SHCC) are able to maintain the fine crack widths under tension; and thus have demonstrated autogenous healing capability in the presence of water. The autogenous healing of PVA-SHCC leads to certain degree of mechanical recovery, which indicates the constitutive fiber-bridging across the crack may be strengthened. Fundamentally the fiber-bridging behavior is subject to the fiber/matrix interfacial bond. It is known that under tension PVA fiber/cement matrix bond could be weakened as the fiber chemically debonding from the matrix; however the potential autogenous healing at the debonded interface is never studied. The current study investigated the effect of water conditioning on the PVA fiber/cement matrix interface by conducting single-fiber pullout tests to the debonded-and-healed group and the control group. The testing results indicate that water conditioning did not restore the chemical bond between fiber and matrix, but it remarkably enhanced the frictional bond at the debonded interface.

Effects of Microbial Carbonate Precipitation on Transport Properties of Fiber Cement Composites

AbstractFibers have been used to improve the mechanical and physical properties of cement-based material since the late 1960s. The inclusion of high-dosage and high-aspect ratio microfibers, however, introduces new interfaces between the fiber phase and the matrix phase that may alter the transport properties of fiber cement composites. This paper reports the effects of microbial carbonate precipitation (MCP) on the transport properties of fiber cement composites (FCCs). The results show that the transport properties of untreated FCC increase with fiber dosage as well as fiber aspect ratio due to higher porosity and better pore connectivity. MCP treatment greatly reduced the transport properties of FCC. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) analyses confirm the precipitates were in the form of rhombohedral calcite, which suggests slower MCP due to the growing environment and culturing condition used in this study.

High Strength Lightweight Strain-Hardening Cementitious Composite Incorporating Cenosphere

High strength lightweight concrete was originally designed for potential structural applications. However, the brittle nature and higher permeability became the main drawbacks for further broad application. In this case, it is imperative to develop a special type of high strength strain hardening lightweight cementitious composite, offering higher ductility, lower permeability and considerable weight saving. Engineered cementitious composite (ECC) is a class of high performance fiber reinforced composite characterized by strain hardening behavior and tight crack width. In this study, the low density of below 1500 kg/m was achieve by introduce lightweight fine aggregates of cenosphere obtained from coalfired power station to fully replace silica sand generally used in ECC preparation. Binary and ternary binder systems (cement, silica fume and slag) were employed to tailor the matrix properties for obtaining higher strength of more than 50 MPa and lower permeability. Polymeric fibers having a good compatibility with matrix were used to implement strain hardening behavior and higher ductility. The permeability and thermal conductivity tests were conducted to evaluate the applicable performance of resulting lightweight cementitious composite. The correlation between mechanical, physical and thermal properties was build up to reveal the effect of cenosphere on the performances of high strength lightweight strain hardening cementitious composite. The single fiber pull out test and matrix fracture toughness test were conducted to reveal the micromechanical mechanism of strain hardening behavior of high strength lightweight composites.

Rate dependent behaviors of nickel-based microcapsules

In this work, nickel-based microcapsules with liquid core were fabricated through an electroless plating approach. The quasi-static and high speed impact behaviors of microcapsules were examined by in-house assembled setups which are able to evaluate properties of materials and structures in microlevel accurately. Results indicated that the fabricated microcapsules showed strong rate sensitivity and the nominal strength of the capsule increased (up to 62.1%) with the increase in loading rates (up to 8200 s−1). The reduced modulus of nickel-based microcapsules was three orders of magnitude larger than that of the traditional microcapsules. The findings revealed that the fabricated nickel-based microcapsules produced remarkable performances for both static and dynamic loading applications. A high speed camera with stereo microscope was used to observe the failure mode of the microcapsule during the impact, which is of great importance to study the mechanical behaviours of materials and structures. Different failure modes were identified as multi-cracks with more rough and tortuous fracture surfaces and debris were observed for the samples subject to impact loading. Finite element method was employed to further understand the physical phenomenon which fitted well with the experimental results. These results could inspire more fundamental studies on the core-shell microstructures and potential applications in multifunctional materials.In this work, nickel-based microcapsules with liquid core were fabricated through an electroless plating approach. The quasi-static and high speed impact behaviors of microcapsules were examined by in-house assembled setups which are able to evaluate properties of materials and structures in microlevel accurately. Results indicated that the fabricated microcapsules showed strong rate sensitivity and the nominal strength of the capsule increased (up to 62.1%) with the increase in loading rates (up to 8200 s−1). The reduced modulus of nickel-based microcapsules was three orders of magnitude larger than that of the traditional microcapsules. The findings revealed that the fabricated nickel-based microcapsules produced remarkable performances for both static and dynamic loading applications. A high speed camera with stereo microscope was used to observe the failure mode of the microcapsule during the impact, which is of great importance to study the mechanical behaviours of materials and structures. Different...