Applied Mechanics and Materials Vols. 438-439

Abstract: Traditional concrete revetment technology mainly focuses on the safety of engineering without taking the river ecological system protection into account. The ecological concrete revetment can properly combines the river slope sclerosis with green to keep the river ecological system sustainable develop. Ecological concrete revetment includes excavating, laying concrete frame, pouring ecological concrete, filling nutrition soil, planting vegetation, management and observation processes. The revetment of concrete hexagonal tile is suitable with excellent resistance to water washing out and good capability of fixing soil. Slop protection of concrete rectangular frame is used for its large scale and high efficiency of construction. Selecting native plants for greening materials is convenient of transplanting, it has low cost and high survival rate.

Abstract: Based on the generalization and analysis of laboratory experimental results on mix ratio, the effects of various factors such as cement content, water-cement ratio, curing time, curing conditions and types of cement on the mechanical properties of unconfined compressive strength of cement soil are presented. Results show that the unconfined compressive strength of cement soil increases with the growing curing time, and it is greatly affected by the cement content, water-cement ratio, cement types and curing time, while the effect of curing conditions is weak with a cement content of more than 10%. Moreover, the stress-strain of the cement soil responds with the cement content and curing time, increasing curing time and cement content makes the cement soil to be harder and brittle, and leads to a larger Young's modulus.

Abstract: The concrete structure in the cold area is often strengthened or demolished in advance due to freeze-thaw damage, so as to cause waste of fund and energy, therefore, the research on the prediction of concrete freezing resistance under field environment is of profound practical value. In this paper, the equivalent relation model of indoor freeze-thaw cycles is established by using RBF network and can be effectively perfected by establishment of concrete freeze-thaw test and test database and data accumulation. On one hand, the establishment of this model can provide a solution for researches on the concrete freezing resistance under field environment and some guidance for the freezing resistance design, construction, late maintenance management and durability evaluation of concrete works. On the other hand, it can also provide references for establishment and management of experimental database and engineering field database to lay a foundation for the further research on the freezing resistance of hydraulic structure in the cold area.

Abstract: A new fracture ceramic proppant was prepared using the low-cost raw bauxite mineral as raw material, by adding the auxiliary material such as potash feldspar, manganese powder and nanocalcium carbonate. The obtained proppants were characterized by XRD and SEM. The crushing rate, particle size, sphericity and roundness of the products were satisfied the recommendation in the standard of the American Petroleum Institute APIR-60.

Abstract: The removal of Zn (II) ions from aqueous solution was studied using raw diatomite and MnO₂ modified diatomite samples at different adsorption parameters such as contact temperature, contact time, initial metal ions concentration and dosage of diatomite. The results showed that modified diatomite had a better adsorption than raw diatomite; adsorption increase with increase of time and then become almost stable, appropriate time is 15 min; adsorption increase with increase of dosage of Mn-ditomite, adsorption reached up to 95.7-97.2 % at 0.8-1.0g/mg dosage of Mn-diatomite to Zn (II) .

Abstract: This paper extends the study of Dharan on the stress state in an elastic solid specimen subjected to axial strain acceleration to compressible materials. And an improved Dharan model is presented. Based on the Drucker-Prager strength criterion, analytical equations of the radial inertia confinement effect on dynamic compressive strength of concrete in split Hopkinson pressure bar tests is derived. Comparison and discussion on the analytical, experimental and numerical results are performed. It is proved that the strain rate effect of compressive strength of concrete materials is a pseudo material property partly caused by the radial inertia confinement. Special attentions should be paid to dynamic tests of low-strength concrete to get the real mechanical properties.

Abstract: Cube concrete (150×150×150mm) of five ages (7, 14, 21, 28 and 35 days) under different stress conducted the ultrasound examination by non-metallic detector and universal testing machine. The results show that the relationship curve of the stress and the ultrasonic velocity can be divided into three stages, the smooth straight stage, the linear deceleration stage and the attenuation destruction stage from the load beginning to the ultimate strength for the same age. There is a growing trend about the ultrasonic velocity with the increase of the age to concrete samples of C10 and C20 in the same loading; however, the overall growth trend of the velocity is not obvious to concrete samples of C30, C35, C40 and C45. It also shows that the relationship curve of strength level and the velocity can be divided into two distinct stages, the sharply increasing stage (C10-C30) and the fluctuating stage (C30-C45). Simultaneously, the paper further illustrates and explains the reasons to appear these stages and the phenomena.

Abstract: Based on double-K fracture model, adopt three-point bending beam which has been recommended by RILEM, the fracture properties of three groups reinforced concrete beams were studied. Refer to the relevant literature, fracture parameters of reinforced concrete three-point bending beams are examined. Through the analysis of whole process of crack propagation of reinforced concrete three-point bending beams, the results show that the reinforcement ratios can't preventing the cracking effectively, but can increase the maximum loads, thus improving the relative toughness; the precritical crack propagation length relative values show a linearly increasing trend with the increase of reinforcement ratios; the initial fracture toughness is not affected by the reinforcement ratios, but the unstable toughness has little effects by the reinforcement ratios.

Abstract: Based on specimen size, which is the main reason of the shear fracture toughness of concrete, experimental research was carried out by 5 groups including 40 symmetrically loading specimens with different length and height. Through load and crack tip sliding displacement curve P-CTSD, load and strain curve P-ε and load and time curve P-t, the effects of length and height of specimens to shear fracture toughness were studied. Specimen stability is strengthened with increasing of length and weakened with increasing of height. Size effect of fracture toughness is weakened with increasing of length, is strengthened with the increasing of height. Fracture toughness increases with the increasing of length, decreases with the increasing of height. Research Background The size effect exists in parameters of concrete, such as concrete strength, modulus of elasticity, fracture toughness, fracture energy and so on [1-. In 1961, the theory of fracture mechanics was applied to concrete structure for the first time by Kaplan [. A vast majority of research work about concrete fracture mechanics was carried out by international scholars [6-. As the development of fracture theory of concrete, the size effect of fracture parameters became the focal point in theory study. Karihaloo [ pointed out that the size effect of concrete strength strengthens with the increasing of components size, however, the size effect weakens when crack length decreased relative to the size of specimens. Hu [3, 10, 11] accounted for the size effect by applying the theory of boundary effect and carried out the concept of local fracture energy which changes with width of fracture process zone. Based on the fictitious crack model, an analytical method [12, 13] for predicting the effective fracture toughness of concrete of three-point bending notched beams is proposed and the effects of initial seam height ratio and height on fracture parameters were carried out by Wu and Xu. At present, research on shear fracture toughness of concrete is immature and there are almost no papers about the size effect of shear fracture toughness of concrete. Aiming at the issue, this paper conducts a study on the size effect of shear fracture toughness of concrete by using symmetrically single-edge notched specimen.

Abstract: The young-old concrete can work together as a whole is the key issue of structural strengthening. Aiming at the technical selection problem appeared frequently in the bridge strengthening about the young-old concrete interface treatments between bonded rebar and grooving, 12 specimens were designed to compare with the shear performance and failure modes of the young-old concrete interface. The test results show that the failure characteristics of specimens which embedded steel bars are ductile, but the failure characteristics of specimens which slotted are brittle and the new concrete in slot position were cut off. And the young-old concrete interface shear strength of the specimens which embedded steel bars was distinctly stronger than that of the slotted specimens. So, the treatment of bonded rebar is proposed during the structural strengthening design. At the same time, the depth and distance of the bonded rebar should be well controlled.