Advanced Materials Research Vols. 250-253

Abstract: Carbonation curing was adopted to accelerate the hydration of foam concrete with lower density of around 450 kg/m³. After standard curing in mold for 2d, the foam concrete samples were marked into two groups. The first one is directly cured in ‘Carbonation Test Chamber for Concrete’ with CO₂ concentration 20%, RH 70% and temperature 20°C (it was called ‘carbonation curing’) for 3d to 56d. The second one is cured in ‘Standard Curing Room for Concrete’ with RH ≥95% and temperature 20°C (it was called ‘standard curing’) for 7d, and then at carbonation curing for 3d, 7d and 21d. The strengths of harden foam concrete were tested, the hydration products were analyzed by means of XRD and TG/DSC. The results were compared with those of standard curing samples. It indicates that foam concrete with lower density is easier to be carbonated; the hydration of both C₃S and C₂S accelerates by carbonation curing, which results in higher early strength improvement. Vaterite is popular in the second group of samples, while it only appears in the first group of sample with longer carbonation time of 56d. Vaterite was considered to be formed from the further carbonation of C_xSH_y.

Abstract: Under variable temperature curing conditions(30 oC ~70 oC), concrete with fly ash whose compressive strength, flexural strength, and dynamic elastic modulus are better than ones without fly ash.Compared with constant temperature 20oC, 50 oC and 70 oC, variable temperature curing(VTC) is benefit for the improvement of mechanical properties of 30% fly ash concrete, but which is no advantage to improve performance of 50% fly ash concrete.

Abstract: The compressive strength of ultrafine white cement samples at three ages: 3, 7 and 28 days and micro appearance of hydrates were tested. The influence of the usage of superplasticizers on the compressive strength of ultrafine white cement paste and hydrates were investigated. The results indicated that the 28d compressive strength of ultrafine white cement with 3% naphthalene based superplasticizers added was 92.9 MPa, 22.9% of that of pure ultrafine white cements (75.6 MPa). The addition of superplasticizers was beneficial to the density of white cement paste. A large number of hydrates (AFt, C-H-S, and so on) were generated in the capillary pores, which would improve the structure of capillary pores of hardened cement paste, increase the density and strength.

Abstract: As a simplify and effective method , electrical resistivity has been used in geotechnical engineering. In lab the experiment simulated that cemented soil had been polluted by industrial sulphuric acid after mixing. On different age time, the variation trend among electrical resistivity of cemented soil and solution, formation factor and solution concentration were studied. The results indicated that both of electrical resistivity and formation factor have close correlations with sulphuric acid solution concentrations and pollution level of cemented soil. This shows that the electrical resistivity method are very sensitive for groundwater and cemented soil after pollution in the engineering site.

Abstract: The strip replacement mining in short-distance thin coal seam is one of the effective methods controlling displacement deformation of overlying strata and surface subsidence in coal mining under buildings and railroads and water bodies. The method has a great theoretical significance and application value by increasing recovery rate of coal resources and cutting down the effect of coal mining on environment and surface of mining area. The numerical simulation method is adopted to study the surface deformation characteristics by the strip replacement mining in short-distance thin coal seam. Such conclusions are drawn as follows: the strip project of forty meters mining with forty meters reserving is quite suitably selected while half of mining rate; ten meters in replacement width of coal pillar is relatively optimum; the feasibility of the strip replacement mining technology is verified by the simulation. Therefore, the strip replacement mining technology has provided one kind of new thought to coal mining under buildings and railroads and water bodies.

Abstract: A new approach, which is suitable for analyzing steel frames-reinforced concrete shear wall hybrid structure considered the semirigid connection for beam and column in horizontal load, is presented. The new simplified method considered the semirigid connection for beam and column in hybrid structure is established. The inter-story drift stiffness of steel frames considered the semirigid connection of beam-column in hybrid structure is derived.The traditional continuum method used in RC frames-shear wall structure is expand to steel frames-reinforced concrete shear wall hybrid structure in the paper.The numerical examples of considered the semirigid connection for beam and column in hybrid structure are analysed. The analysis results show that the proposed method is suitable for adoption in practice.

Abstract: The chloride threshold to develop active corrosion of the reinforcing steel does not seem to be a unique value and it depends on several factors, such as concrete mix proportions, cement type, C₃A content of cement, blended materials, water/cement ratio, temperature, relative humidity, steel surface conditions and source of chloride penetration among others. Numerous studies have been already devoted to the study of the chloride threshold value for depassivation of the steel embedded in concrete. One of the reasons found for the scatter is the large number of variables that influence the chloride amount for depassivation. The other reason is the lack of accordance for the definition of the chloride threshold itself, either on the determining parameters (visual observation, corrosion potential or corrosion current) or on the expression of the threshold (as[Cl^-]/[OH^-] ratio or by weight of cement or concrete). The present paper presents chloride thresholds expressed as total, free and [Cl^-]/[OH^-] ratio.

Abstract: HRB400 reinforcing steel due to high strength and high ductibility is as the main reinforcing steel in “Code for design of concrete structures (GB50010-2002)” in China. Cyclic potentiodynamic polarization technique was used to investigate the electrochemical corrosion bebavior of HRB400 reinforcing steel in Simulated Concrete Pore solutions (SCP solutions) differently contaminated by bicarbonate ions and/or chloride ions. The evolution feature of the corrosion parameters was analyzed and was compared with that of HPB235 reinforcing steel. The results show that the corrosion characteristics of HRB400 and HPB235 were exceedingly similar before the destruction of the passivation film. However, HRB400 is remarkedly more susceptible to chloride ions and carbonation than HPB235 during the failure of the passivation films. The pH threshold for HRB400 is larger than that for HPB235, and the chlorides threshold for the former is smaller than that of the latter. When HRB400 and HPB235 were connected and exposed to an aggressive environment, the galvanic corrosion will occur where HRB400 is anode and HPB235 is cathode. To ensure the durability of the reinforcing concrete structures, it is necessary to make the connection points insulate.

Abstract: A multiscale approach based upon micromechanical fiber/matrix/interface scale in fiber-reinforced composites was established to simulate the progressive damage at macroscopic scales. The composite is reinforced with Boron fibers under conditions of matrix tensile yield and interface debonding. An analytical solution using a superimposition technique within the framework of shear-lag model was employed to derive stress profiles for any configuration of breaks under applied loading. A simulation scheme coupled with Monte-Carlo method was proposed to investigate evolution of damage-plasticity of the composites.

Abstract: Take the aggregate as subject, based on the water cement ratio, the compression strength of recycled water permeable concrete and evolution of water permeability with a water cement ratio from 0.30-0.43 was researched. And then optimal proportion of recycled water permeable concrete when the compression strength within 10-15MPa and 15-20MPa, and provide a basis for application of recycled water permeable concrete in urban ecological construction.