Chunxiang Qian

Development of hybrid polypropylene-steel fibre-reinforced concrete

Abstract This research first investigates the optimization of fibre size, fibre content, and fly ash content in hybrid polypropylene-steel fibre concrete with low fibre content based on general mechanical properties. The research results show that a certain content of fine particles such as fly ash is necessary to evenly disperse fibres. The different sizes of steel fibres contributed to different mechanical properties, at least to a different degree. Additions of a small fibre type had a significant influence on the compressive strength, but the splitting tensile strength was only slightly affected. A large fibre type gave rise to opposite mechanical effects, which were further fortified by optimization of the aspect ratio. There is a synergy effect in the hybrid fibres system. The fracture properties and the dynamic properties will be further investigated for the hybrid fibres concrete with good general mechanical properties.

Fracture properties of concrete reinforced with steel–polypropylene hybrid fibres

Abstract This research discusses polypropylene fibres and three sizes of steel fibres reinforced concrete. The total fibre content ranges from 0% to 0.95% by volume of concrete. A four-point bending test is adopted on the notched prisms with the size of 100×100×500 mm 3 to investigate the effect of hybrid fibres on crack arresting. The research results show that there is a positive synergy effect between large steel fibres and polypropylene fibres on the load-bearing capacity and fracture toughness in the small displacement range. But this synergy effect disappears in the large displacement range. The large and strong steel fibre is better than soft polypropylene fibre and small steel fibre in the aspect of energy absorption capacity in the large displacement range. The static service limitation for the hybrid fibres concrete, with “a wide peak” or “multi-peaks” load–CMOD patterns, should be carefully selected. The ultimate load bearing capacity and the crack width or CMOD at this load level should be jointly considered in this case. The K IC and fracture toughness of proper hybrid fibre system can be higher than that of mono-fibre system.

Experimental study on properties of polymer-modified cement mortars with silica fume

Abstract This paper discussed the flexural and the compressive strengths of polyacrylic ester (PAE) emulsion and silica fume (SF)-modified mortar. The chloride ion permeability in cement mortar and the interfacial microhardness between aggregates and matrix were measured. The chemical reactions between polymer and cement-hydrated product were investigated by the infrared spectral technology. The results show that the decrease of porosity and increase of density of cement mortars can be achieved by the pozzolanic effect of SF, the water-reducing and -filling effect of polymer. Lower porosity and higher density can give cement mortars such properties as higher flexural and compressive strength, higher microhardness value in interfacial zone and lower effective diffusion coefficient of chloride ion in matrix.

Comparing Monofractal and Multifractal Analysis of Corrosion Damage Evolution in Reinforcing Bars

Based on fractal theory and damage mechanics, the aim of this paper is to describe the monofractal and multifractal characteristics of corrosion morphology and develop a new approach to characterize the nonuniform corrosion degree of reinforcing bars. The relationship between fractal parameters and tensile strength of reinforcing bars are discussed. The results showed that corrosion mass loss ratio of a bar cannot accurately reflect the damage degree of the bar. The corrosion morphology of reinforcing bars exhibits both monofractal and multifractal features. The fractal dimension and the tensile strength of corroded steel bars exhibit a power function relationship, while the width of multifractal spectrum and tensile strength of corroded steel bars exhibit a linear relationship. By comparison, using width of multifractal spectrum as multifractal damage variable not only reflects the distribution of corrosion damage in reinforcing bars, but also reveals the influence of nonuniform corrosion on the mechanical properties of reinforcing bars. The present research provides a new approach for the establishment of corrosion damage constitutive models of reinforcing bars.

Hydrogen production by mixed culture of several facultative bacteria and anaerobic bacteria

Abstract The characteristic of hydrogen production by facultative anaerobic bacteria, obligate anaerobic bacteria and their mixed culture was studied by the batch culture method. The results showed that, due to the synergistic effect between facultative bacteria and anaerobic bacteria, the ability of hydrogen production in the mixed culture was much better than that in the pure culture. Especially, the culture Scheme No.7 mixed up with three strains ( Bacterium. E : Bacterium. B : Bacterium. P = 1:1:1) not only had the best hydrogen production capacity (1.885 mol H 2 /mol glucose) and maximum average hydrogen production rate (212.2 mL/(L·h)), but also had stable hydrogen production under continuous culture conditions, which was 1.968 mol H 2 /mol glucose.

Synthesis of nano-hydroxyapatite via microbial method and its characterization.

Nanoparticles of hydroxyapatite were successfully synthesized by microbial method at ambient temperature and pressure, using calcium chloride and specific substrate as reactants. The compositional and morphological properties of products of the syntheses were studied by means of X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). The characterization data obtained showed that the phase composition, functional groups, and surface morphology of samples obtained by microbial method were mainly similar to that by chemical precipitation method. The hydroxyapatite powder was shown to be nanometer-grade in size and sphere-like in shape.

Development of Microbe Cementitious Material in China

Microbe cementitious material as a binder has been developed due to the ever increasing awareness of environmental protection. The new cementitious material relies on microbiologically induced precipitation of calcium carbonate to bind loose particles or repair surface defects and cracks of cement-based material. This paper elaborates the research on loose sand particles cemented by microbe cement from three aspects: compressive strength, pore structure and microstructure. In addition, the research on restoration surface defects and cracks of cement-based material by microbe cement is introduced from two parameters: surface water absorption and compressive strength recover coefficient. The results show that microbe cementitious material can bind loose particles and repair surface defects or cracks of cement-based material.

Self-healing of early age cracks in cement-based materials by mineralization of carbonic anhydrase microorganism.

This research investigated the self-healing potential of early age cracks in cement-based materials incorporating the bacteria which can produce carbonic anhydrase. Cement-based materials specimens were pre-cracked at the age of 7, 14, 28, 60 days to study the repair ability influenced by cracking time, the width of cracks were between 0.1 and 1.0 mm to study the healing rate influenced by width of cracks. The experimental results indicated that the bacteria showed excellent repairing ability to small cracks formed at early age of 7 days, cracks below 0.4 mm was almost completely closed. The repair effect reduced with the increasing of cracking age. Cracks width influenced self-healing effectiveness significantly. The transportation of CO2and Ca2+ controlled the self-healing process. The computer simulation analyses revealed the self-healing process and mechanism of microbiologically precipitation induced by bacteria and the depth of precipitated CaCO3 could be predicted base on valid Ca2+.

Effi ciency of Concrete Crack-healing based on Biological Carbonate Precipitation

The aim of this study was to improve the capacity for crack-repair in concrete by developing a new way. The self-healing agent based on biological carbonate precipitation was developed. Crack-healing capacity of the cement paste specimens with this biochemical agent was researched. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to characterize the precipitation in cracks. The healing efficiency was evaluated by measuring the water permeability after crack healing as well.The experimental results show that the applied biochemical agent can successfully improve the self-healing capacity of the cement paste specimens as larger cracks can be healed. The cracks with a width of 0.48 mm in the specimens with the biochemical agent are nearly fully healed by the precipitation after 80d repair. SEM and XRD analysis results demonstrate that the white precipitation in cracks is calcium carbonate, which displays spherical crystal morphology. Meanwhile, the water permeability test result shows that the biochemical agent can significantly decrease the water permeability of the cement paste specimens, the water permeability of specimens with the biochemical agent respectively decreases by 84% and 96% after 7 d and 28 d immersion in water, however the control specimens only respectively decrease by 41% and 60%, which indicates that the bacteria-based concrete appears to be a promising approach to increase concrete durability.

Study on Shrinkage and Cracking Performance of SAP-Modified Concrete

SAPs (Super Absorbent Polymers) are a group of polymeric materials that have the ability to absorb a significant amount of liquid many times their own weight from the surroundings and to retain the liquid within their structure without dissolving and to desorb it in the dry environment. The shrinkage and cracking performance of SAP-modified concrete was studied by experimental investigation, which express as total cracking area from early-age plastic cracking tests and shrinkage rate (restrained and unrestrained) from shrinkage tests respectively. The effect of SAP on shrinkage and cracking of concrete was compared with that of using pre-soaked ceramsite or perlite. The results show that SAP can effectively improve the cracking and shrinkage of concrete with achieving a 30-50% decrease. SAP particles improve the shrinkage and cracking performance of concrete in three ways as absorption-desorption, some absorbed water being bonded with hydrogen bond of macromolecule and filmforming on SAP particles. The coupling effect of SAP retards the water losing and change the moisture distribution in concrete, and thus reducing the cracking and shrinkage of concrete.