Advanced Materials Research Vols. 250-253

Abstract: With the experimental objects of the C₃S pastes curing at 60 days with water-solid ratio of 0.5, the micro mechanical characteristic between C-S-H clusters and tip has been investigated in the low scale. The results show that the experimental method is feasible for bonding force between C-S-H clusters and tip using atomic force microscopy (AFM) in the real atmospheric conditions. Though bonding force values are discrete in view of the anisotropy character of the cement-based material, the normal distribution can be fitted for the variation of bonding force between C-S-H blusters in the C₃S pastes and AFM tip with a mean of 6.2nN. Even if bonding force values is somewhat higher due to the roughness and the measuring conditions in the paper, the experimental method using AFM could still be effective for the lateral correlation for bonding force of the different systems. The research on bonding force between C-S-H clusters would play the important role in establishing the new microscopic structural model.

Abstract: The damage evolution laws of high strength and high performance concrete (HSHPC) are obtained by a large number of experiments on mechanical properties. Based on stochastic damage model, a new damage variable with two parameters is proposed to describe the damage constitutive relationship of HSHPC and the damage constitutive equation is established by boundary conditions. Compared mechanical test result of HSHPC with theoretical calculation, it is shown that the damage constitutive equation can reflect the damage characteristics of HSHPC reasonably. The research identifies a certain theoretical basis for further studying on dynamic and stochastic damage constitutive relationship of HSHPC.

Abstract: High strength and high performance steels used in structural engineering have been developed, but the application is constrained and the design work changes as a result of the different material property. In order to study high strength steel material property features, the production process, steel grade and code limit requirement were reviewed and discussed. Some important mechanical property indexes including the stress-strain relationship, yield-tensile strength ratio (i.e. Y/T ratio), ductility and toughness, were analyzed based on a large amount of tension coupon test data reported in the available literature. The stress-strain relationship model used for finite element analysis was proposed. It is concluded that high strength structural steels have excellent toughness but lager Y/T ratio and lower elongation compared with those of traditional steels, some of which even exceed the code limit values. It is necessary to do deep research on the relationship between the steel mechanical property indexes and structure safety and to make further development of high strength steels. This research work is helpful to comprehend the material property of high strength structural steels and relevant code limit requirements.

Abstract: As a new type of fibrous material, CaCO₃ whisker has played an increasingly important role in the fields of instrumentation, polymerscience and artificial bones. In order to give full play to CaCO₃ whisker’s novel micro structure, excellent mechanical properties and stability, we initially applies it to advanced cement based construction materials. The preparation methods, characterization of CaCO₃ whisker and its applicability in advanced construction materials were studied thoroughly, based on the latest literatures and our newest research works.

Abstract: Base on the practical experience of reinforcing engineering and the application of new type of cement based grouting material in recent years, a new type of cement-based concrete for strengthening engineering with high-bonding, low-shrinking, self-compacted was developed in this paper. Fast-speed strengthening and repairing of structures can be realized by combining this new strengthening material with the traditional method of increasing section area for strengthening, and by the adoption of the technology of perfusion pumped on-site. This new strengthening concrete can be applied to both reinforced concrete structures strengthening and masonry structures strengthening. Compared with the traditional strengthening method of increasing section area, due to smaller section needed, the construction speed is quicker, and the quality can be more easily guaranteed. Therefore, this new type of material possesses a wide application prospect. And a series of experimental researches on the mechanical properties of this new strengthening concrete is conducted in this paper.

Abstract: A designed experimental study has been conducted to investigate the effect of clay dosage on mechanical properties of plastic concrete. The mechanical properties include compressive strength, splitting tensile strength, shear strength and elastic modulus. On the basis of the experimental results of the specimens of eight sets of mix proportions, the mechanism of action of clay on these mechanical properties has been analyzed in details. The results indicate that there is a tendency of decrease in the compressive strength, splitting tensile strength, shear strength and elastic modulus of plastic concrete with the increase of clay dosage. However, the internal friction angle of the shear specimens is increasing gradually with the increase of clay dosage. Further, the clay appears can improve the ductility of plastic concrete and this can help plastic concrete to bear larger deformation before failure.

Abstract: Energy conservation is a hot topic in the field of construction. To increase the thermal resistance of the enclosing structure of buildings, a T-shaped self thermal insulating block is designed. The particular shape, light weight concrete shell and heat insulating materials filled in the cavities result in a good heat insulating effect. Thermal bridges on the wall can significantly be reduced, which leads to a great improvement in thermal resistance, and performance of energy conservation. The thermal conductivity of wall made of this kind of blocks could be as low as 0.088W/ m·K, by which energy consumption could be saved by 65% comparing with wall made of bricks in 1980s.

Abstract: Based on the evaluation of fibrous concrete materials and the experiments of freezing-thawing resistance home and abroad, the present experiment takes relative dynamic modulus of elasticity and rate of mass reduction as an analytical index to conduct a comparative study on the effects of the mixing of four kinds of polypropylene fiber on the cement concrete freezing resistance. The results show that different kinds of polypropylene fiber have different influences on cement concrete freezing resistance. And some polypropylene can improve it while others may make it decreased.

Abstract: Grafting method was used to modify polypropylene (PP) fiber to enhance the fiber reinforced concrete in this study. Polyacrylamide (PAM) was grafted onto PP surface by UV radiation using benzophenone (BP) as a photoinitiator. The microstructure of PP, and the interaction force between PP and the polar probe were observed with an atomic force microscopy (AFM). Experimental results showed that the roughness of PAM-grafted PP surface decreased significantly in comparison with that of the untreated PP surface. In addition, instead of smooth force curve as that of the untreated PP, the interaction between the probe and PAM-grafted PP surface appeared an oscillation. The above results gave the evidences that PAM had been successfully grafted onto the PP surface as discussed . The high hydrophilic property of PAM modifies the surface property of PP fiber and strengthens PP fiber reinforced concrete.

Abstract: In fuel gas project, the foundation of carburetor is in circumstance which concrete occurred freeze-thaw circulation. To meet durability of structure, polypropylene fibrous concrete was used in design to solve concrete freeze-thaw. By means of a project, this paper talks about its crack control mechanism, impermeability, frost resistance and wear-resisting strength. Furthermore, some attention is listed to use polypropylene fibrous concrete successfully.