Key Engineering Materials Vol. 517

Abstract: A long time immersion test of concrete specimens in dilute sulfuric acid is carried out to study the permeable concrete material aging rule under the action of the sulfuric acid. The experiment is designed by uniform design containing 4 factors and 10 levels and the soaking solution pH value is 4.00. To measure acid consumption, titration sulfuric acid with concentration of 0.125mol / L is used to keep original pH value of soaking solution, through which the corrosion rate of specimens can be determined. After certain immersion time, the specimens are dried and weighted and the weight changes of the specimens are recorded. The results show that corrosion rate of permeable concrete shares the same family of corrosion rate functions with those of ordinary concrete and mortar. However, the weight of specimen fluctuates with the soaking time, so that it may not be a proper index of corrosion.

Abstract: Steel reinforcement corrosion is always one of the most significant incentives of concrete structure deterioration, especially under severe chloride erosion environment. In order to describe the whole process of concrete deterioration induced by reinforcement corrosion, the mechanism of rust expansion and crack propagation in concrete was analyzed from the perspective of elastoplastic mechanics and fracture mechanics firstly, and experimental study was carried out to use vibrating wire strain gauges for monitoring corrosion-induced concrete deterioration process. The mechanism analysis of corrosion-induced concrete deterioration indicates that the degradation process of cover concrete can be divided into aggressive medium transmission process, free corrosive expansion process, corrosive expansion stress development process, corrosive expansion crack generation and propagation process, and vibrating wire strain gauges can be used to monitor corrosion-induced cover concrete stress development, crack initiation and propagation process along with the procedure of reinforcement corrosion. The test curve seems to be generally consistent with that of the theoretic analysis, and the signals captured by vibrating wire strain gauges can successfully reflect the durability degradation process of reinforced concrete structure under severe erosion environment.

Abstract: Magnesium slag cementitious material was prepared successfully using the magnesium slag-furnace slag-clinker system and different activators in this paper. The effect of activator on the mechanical property of the material was studied. The hydration and microstructure of this composite cement were analyzed by X-ray diffraction and scanning electron microscopy and the interaction mechanism was researched. The results show that the activity of magnesium slag was enhanced significantly by adding a small amount of activator. Combined activators have the best effect. The hydration products of magnesium slag cementitious materials mortar were C-S-H, Aft and Ca (OH)₂ and so on.

Abstract: The effectiveness of corn straw Fiber, organic polymer latexes, organic polymer latexes and corn straw Fiber blending on vibration damping properties of cement-based materials were studied by filling organic polymer latexes, and corn straw Fiber. The functional mechanisms of various fillers were discussed. The experimental results showed that the vibration damping ratio of cement-based materials with organic polymer latexes is 149.77% higher than that of pure cement-based materials, the vibration damping ratio of cement-based materials with corn straw fiber is 152.58% higher than that of pure cement-based materials, the vibration damping ratio of cement-based materials with organic polymer latexes and fibers blending is 191.08%, also higher than that of pure cement-based materials. The impact of corn straw Fiber and polymer latexes modification on the microstructure and mechanisms were analyzed by FTIR and SEM.

Abstract: This test is mainly diatomaceous earth mineral admixture to study the content, calcination temperature, calcination time, grinding time on the properties of concrete, and through the use of SEM, XRD and other means of micro-theory analysis. The results showed that, after calcination or ball mill grinding, diatomaceous concrete admixture used to increase strength, improve durability of concrete. When the diatomite calcination temperature to 650 ,content is 2%, the volcanic activity to achieve the best value, the calcination time increased strength increases, strength increases flattened when the rate of more than 2h.

Abstract: The concrete-filled steel tubular structure is widely used in practices, as it shows perfect seismic performances such as ductility, and has strong ability of collapse under seismic loading. In this paper, firstly, the stiffness damage and stiffness recovery parameters of concrete constitute model under cyclic loading was calibrated and verified by examples. Then the finite element model was verified by numerical examples of reinforce concrete members and concrete-filled steel tubular members. At last, on the base of the result of analysis and verification, the hysteresis curves on beam-column connection of concrete-filled steel tubular structure under cyclic loading were simulated and compared with experimental results, and the hysteresis characters was analyzed in the end.

Abstract: The properties of cement based composites depend not only on the properties of their individual components but also on their interfacial characteristics and transition zone between fiber and matrix. There has been a renewed interest in the use of cellulosic pulp as micro-fiber reinforcement in cement based composites. The addition of nanoparticles, such as colloidal silica, to fiber-cement could allow a better control of its microstructure and the enhancement of the matrix/fiber interface. The objective of this work is to evaluate the effects of colloidal silica on the microstructure and mechanical performance of cementitious matrices and fiber-cement composites. These cementitious materials were prepared with 0%, 1.5%, 3%, 5% and 10% w/w colloidal silica suspension content. Cementitious matrices without fibers were produced by vibration. Fiber-cement composites with unbleached Eucalyptus kraft pulp as a micro-fiber reinforcement were produced by the slurry dewatering technique followed by pressing. All composite materials were cured by water immersion. A splitting (Brazilian) test was carried out to determine the tensile strength of cementitious matrices. Mechanical behavior of the fiber-cement composites was evaluated via modulus of rupture and fracture toughness based on load-displacement curves (L-d curves) under continuous loading and 3-point bending arrangement. The energy of fracture was measured through a stable crack propagation test with SENB (single-edge notched bending) configuration also under a 3-point bending arrangement. The matrix with highest content of colloidal silica suspension (10% w/w) presented high values of water absorption and consequently presented the lowest splitting tensile strength. The average values of modulus of rupture and fracture toughness of fiber-cement tend to decrease with increasing colloidal silica content. However, the pullout mechanism increased significantly in the fiber-cement composites with additions between 3% and 10% w/w of colloidal silica suspension as compared to that without any addition, noted by degree of improvement in the energy of fracture and by scanning electron microscopy micrographs (SEM). These findings show the potential use of colloidal silica to improve the transition zone between the cellulosic fiber and the cementitious matrix. The results of this study show an important way to engineer and control the fracture process of the composites.

Abstract: A kind of lightweight sand was only used as the fine aggregate to make the all-lightweight aggregate concrete, which can significantly reduce the gravity load of a structure and the foundation loads. Accordingly, the application of all-lightweight aggregate concrete in the construction projects can reduce the cost of foundation as well as construction project. In order to develop a new multi-story structural system which has a multifunction of load-bearing, lightweight and energy saving, the paper carried out an experimental study on the mechanical behaviors of six all-lightweight aggregate concrete columns with symmetrical reinforcement under eccentric loading. The failure modes, deformation characteristics and load-bearing capacity of the columns were analyzed. The effect of reinforcement ratio, stirrup ratio and eccentricity on the mechanical behaviors of the columns under eccentric loading were discussed. The test results show that all-lightweight aggregate concrete columns were loaded to failure with high load-bearing capacity and good ductility. The excellent mechanical behavior and the possibility of replacing the normal concrete with all-lightweight aggregate concrete were verified.

Abstract: The use of lightweight and energy saving materials is the main trend of modern building and construction technology. All-lightweight aggregate concrete, which is a new type of lightweight aggregate concrete, not only has all the advantages of light weight concrete but also a lower apparent density of 600kg/m³. At present, the commonly-used energy-saving organic insulation materials include the EPS insulation and polyurethane insulation. The paper presents a new type of all-lightweight inorganic aggregate concrete by replacing organic material, in order to obtain a lightweight, energy-efficient building structure which synthesizes the load-bearing capacity, lightweight and energy-saving. Tests on the flexural behaviors of 11 all-lightweight aggregate concrete beams and 6 slabs were conducted. The effects of steel reinforcement ratio and loading distribution on the flexural and shear behaviors and method to calculate the load carrying capacity were carried out. The feasibility of application of all-lightweight aggregate concrete on multi-story buildings and to replace common reinforced concrete members in bending was discussed. The experimental study in the paper can provide a basis of the lightweight and energy-saving multi-story structure.

Abstract: The effect of ground limestone fineness on the properties and mechanism of cement-based composite materials was investigated. The setting times, fluidity and strength of cement mortar were measured. In order to identify the mechanism effect of ground limestone fineness on the microstructure of the hardened cement pastes, microstructure analyses such as calorimetry analysis and Mercury Intrusion Porosimetry (MIP) were also performed. Experimental results indicated that the setting times are shortened, and the fluidity and strength of cement mortar are improved with the ground limestone fineness increases. The increase of the ground limestone fineness can effectively inhibit the pore structure of hardened paste, which due to mortar and paste samples incorporating replacement levels of ground limestone, and improve the pore structure of hardened paste.