Papers by Author: Li Jiu Wang

Abstract: For the purpose of enhancing concrete performance and conserving freshwater, we proposed a new technique of making desalinated sea sand concrete. Salinity qualified desalinated sea water with alkaline potential is obtained through a set of self-made dual membrane electrodialyzers and membrane electrolyzers. Sea sand is sluiced by the obtained desalinated sea water before it is made into concrete. The desalinating device is portable and easy operating, and outputs qualified sea water to the requirements of desalinating sea sand. The method of sluicing sea sand is proved to be practical and effective. It is found that, comparing to standard concrete, concrete made of desalinated sea sand and alkaline potential water has better mechanics performance and better protection for steel bars. Both desalinated sea water and sea sand contain a certain amount of OH^- ions, which helps reducing the ratio of Cl^-/OH^- in concrete and thus inhibit the Cl^- ions from rotting or carbonating concrete; concrete durability is therefore enhanced.

Abstract: Introduced the concept of “Cementitious Coefficient” of fly ash, theoretical formula of strength of HFCC at a certain age was found with two variables: actual water-binder ratio and micro-aggregate-binder ratio. Development regularity of compressive strength of HFCC was studied and formula of long-term strength coefficient D28t was settled. Influence of actual water-binder ratio and micro-aggregate-binder ratio on long-term strength of HFCC was analyzed. Experimental results showed that along with the single-factor increase of actual water-binder ratio and micro-aggregate-binder ratio, growth rate of long-term strength of HFCC increased; influence of actual water-binder ratio was deeper than that of micro-aggregate-binder ratio.

Abstract: As a kind of monocrystal reinforcing material, CaCO3 whisker has good characteristics of high strength, high module and high thermal stability. This research aims to optimize the microscopic structure of fiber cement mortar by adding CaCO3 whiskers and improve the macroscopic mechanical properties. The results showed that CaCO3 whiskers increased the flexural and compressive strength of cement mortar at 3d age by 29.5% and 19.8% at maximum respectively, which fell to 7.2% and 13.0% at 28d age; when CaCO3 whiskers content was 10% and polypropylene fibers content was 0.05%, compared with the pure cement mortar, the flexural and compressive strength were increased by 32.4% and 29.4% at 3d age and 7.6% and 4.6% at 28d age respectively; when the fiber length was 9mm, the composite effect of whiskers and fibers was more ideal; through the SEM analysis, the reinforcing mechanisms of CaCO3 whiskers and polypropylene fibers in cement mortar were discussed.

Abstract: The objective of this study is to propose a light weight and suitable strength material as roof surface which can detain rainwater during rainy day and lower room temperature in sunny day by passive evaporative cooling. So blast furnace slag was used as the main raw material and clay as the subordinate ingredient to synthesize an alkali-activated cement matrix at room temperature. Furthermore the cement matrix were made into porosity by injecting prepared foam and attempted to improve strength by incorporation of short polypropylene fiber. Finally, the dry density of 453 kg/m3 and compressive strength of 4.5MPa porous roof material (slag-clay porous material) was gained. Variations of room temperature and heat flux transfer across porous material roof slab have been measured. The results showed that roof covered with slag-clay porous material can satisfactorily lower room temperature and reduce heat flux, as compared with OPC (ordinary Portland cement) roof layer simply. Covering slag-clay porous material layer as roof surface can create a more effective cooling system by utilizing its water absorption and evaporation capability during canicule, which provides a new approach to low carbon and energy saving technological development.

Abstract: The fracture behavior of brittle materials under biaxial plane stress has been investigated by means of numerical simulation method with software MFPA2D (Material Failure Process Analysis). The aims of this study are to clarify the fracture dependence of brittle material on biaxial plane stress state. The observation of crack initiation and fracture behavior reveals that the biaxial stresses have strong influence on the fracture properties of glass. Thus, the fracture criterion by the stress intensity factor was questioned for the biaxial plane stress issues. It is confirmed that the tensile stress parallel to the crack plane is an important factor affecting crack arrest, while the compressive stress parallel to the crack plane contributes to crack opening.

Abstract: The aim of this study is to demonstrate the influence of the stress parallel to the crack plane on subcritical crack growth in brittle materials by using a numerical code MFPA2D. The mechanism of this influence is also discussed. The curves of subcritical crack extension vs. strain of brittle materials under uniaxial and biaxial stress were obtained through numerical tests with acoustic emission consideration. The results showed that the tensile stress parallel to the crack plane has the effect on crack arrest, while the compressive stress parallel to the crack plane plays important role in crack opening process. The numerical results were consistent with experimental observed result, which shows the reliability of the numerical method, and provides theoretic foundation for failure analysis and life estimation of brittle materials.