The Adsorbing Effect of Calcined Layered Double Hydroxide for Chloride Ions in Simulated Concrete Pore Solutions

The adsorbing effect of calcined layered double hydroxide （CLDH） for chloride ions in simulated concrete pore （SCP） solutions was investigated with the potentiodynamic polarization method, impedance measurement, ion selective electrode analysis and XRD. CLDH could effectively adsorb Cl^- and increase pH value in SCP solutions containing NaCl. The chloride to hydroxyl ions ratio （[C1^-]/[OH^-]） of the solution greatly decreased by CLDH treatment. In CLDH treated SCP solution with CI-, the pitting potential of carbon steel notably increased, and the surface impedance was much higher, indicating strengthened passivation. The process of CLDH adsorbing chloride ions from SCP solutions was accompanied with the reconstruction of the layered structure.

Monitoring Chloride Concentrations in Concrete Pore Solutions Using Silver/Nano-silver Chloride Sensors

Corrosion of reinforcing steel is a major cause for degradation of concrete structures,especially when exposed to chloride ions.Thus,the Silver/Nano-silver Chloride (SNSC) electrodes as sensors of chloride concentration were prepared and encapsulated carefully.The properties of the electrode were studied by emerging them in a series of concrete pore solutions with different admixed KCl contents.These SNSC sensors show that good stability in concrete pore solutions at room temperature.Polarization disposal can shorten the stabilized period of the sensors.The electrochemical tests indicate the SNSC sensors with desirable linearity and reproducibility.The response time of SNSC sensors is short enough for monitoring the chloride ions concentration in concrete structures.The good performance of SNSC sensors indicate that they could be embedded in the concrete structures in the future.

Effect of Chromium Micro-alloying on the Corrosion Behavior of a Low-carbon Steel Rebar in Simulated Concrete Pore Solutions

A new low-cost corrosion-resistant rebar（HRB400 R） was designed and fabricated by chromium micro-alloying. The effects of Cr on the passivation and corrosion behavior of this rebar in the simulated concrete pore solutions were studied systematically, and its improved corrosion resistance was revealed. In the Cl--free saturated Ca（OH）_2 solution, the HRB400 R rebar presented nearly the same passive film and similar passivation ability compared to the common carbon steel rebar. In the long-term immersion corrosion test in the Cl--contained Ca（OH）_2 solution, the HRB400 R rebar presented improved corrosion resistance and obvious longer passivation-maintaining period. Micro-alloying of Cr element in the rebar matrix enhanced its corrosion resistance against Cl--attack and retarded the corrosion initiation in the matrix. In the alkaline Na Cl salt spraying test, the HRB400 R rebar also presented obviously lower mass-loss rate. The enrichment of Cr element in the rust layer improved its retardant effect to the penetration of aggressive medium, and decreased the corrosion propagation rate of the rebar.

Mass Balance and Viscosity of the Pore Solution during the Hardening of Cement Paste

In the presented work,the results are provided of examining the properties of a pore solution during the process of cement paste hardening.Based on the experimental data of W.P.Halperin et al,the evolution of the mass balance of structured physical water is analyzed as a combination of interactions of capillary,gel,and other components.The formation and development have been studied of the pore solution viscosity.The comparison of the reported dependences of the water viscosity on the size of the pores with the experimentally determined values of the pores’radius has allowed estimating the rise of avid the pore solution viscosity in the process of hardening of cement paste.The separation of the structured pore solution’s viscosity into capillary and gel components allows for a quantitative and qualitative consideration of the cement paste hardening as the process of forming a macrocapillary matrix,inside which a microporous structure is formed of the cement gel.

The Influence of Ce(NO_3)_3·6H_2O on the Inhibitive Effect of Ca(NO_2)_2 in Simulated Concrete Pore Solution

The effects of cerium nitrite on corrosion behaviors of carbon steel in simulated concrete pore solutions were studied with the methods of linear polarization, electrochemical impedance spectroscopy and surface analysis. In pore solutions in the presence of Ce（NO3）3？6H2O, the corrosion potential, polarization resistance and impedance of carbon steel obviously increased in contrast to the situation in the absence of cerium salts. The pore solution with [NO2-] / [Cl-] = 0.3 and 0.1% Ce（NO3）3？6H2O, carbon steel shows better corrosion resistance than that in the pore solution with [NO2-] / [Cl-] = 0.6, which indicates that a small amount of Ce（NO3）3？6H2O in pore solutions can effectively promote passivation of the steel and reduce the threshold [NO2-] / [Cl-] ratio for corrosion control. The surface layer formed in cerium salt containing pore solutions is more compact and smooth and 1.36%Ce is examined on the sample surface. The addition of 0.1% Ce（NO3）3？6H2O in pore solutions can decrease the corrosion rate of steel in pore solutions and has little influence on pH change of the solutions. However, more cerium nitrate addition above 0.1% may result in pH decrease of the solution.

Effects of Mixing Volume and Initial Particle Size Distribution of Fly Ash on Pore Solution of Cement Paste

The effects of fly ash with different mixing volume and different particle sizes on pore solution of cement-based materials were studied. The pore solution was extracted by squeezing at scheduled ages. The particle size distribution of fly ash was classified as smaller than 45 μm and 45～80 μm,and the mixing volume was classified as 10% and 20%. The concentrations of K+,Na+ and Ca2+ were measured using Inductively Coupled Plasma Emission Spectrometer (ICP),and the pH was measured by acid-base titration. The results indicate that the concentrations of various ions were prompted at the initial time of the hydration. With further hydration,ion concentrations of K+ and Na+ raise again and finally stabilized,but there is a certain decline on Ca2+ later on. It also shows that fly ash exhibited great effect on the hydration of cement,it can lower the concentration of Ca2+ and pH of the pore solution,but raise the concentrations of K+ and Na+. More importantly,ion concentrations of K+,Na+ and Ca2+ reduced with smaller particle sizes of fly ash.

Application of Image Analysis Based on SEM and Chemical Mapping on PC Mortars under Sulfate Attack

The degradation mechanisms of cementitious materials exposed to sulfate solutions have been controversial, despite considerable research. In this paper, two methodologies of image analysis based on scanning electron microscope and chemical mapping are used to analyse Portland cement mortars exposed to sodium sulfate solution. The effects of sulfate concentration in solution and water to cement ratio of mortar, which are considered as the most sensitive factors to sulfate attack, are investigated respectively by comparing the macro expansion with microstructure analysis. It is found that the sulfate concentration in pore solution, expressed as sulfate content in C-S-H, plays a critical role on the supersaturation with respect to ettringite and so on the expansion force generated.

Oil／Gas Accumulation Characteristics and Exploration Methods of the Deltaic Lithologic Reservoirs in Northern Shaanxi Area

There are large deltaic systems in the Triassic Yanchang Formation in the northern Shaanxi area of the Ordos Basin, and developed two sets of good source-reservoir-caprock assemblages and many sets of oil-bearing beds. Exploration experience demonstrates that the formation and distribution of the reservoir were controlled by the generative depression of the Yanchang Formation, and deltaic reservoir sand body is the material basis for large-scale oilfields. In addition, secondary laumontite in a low permeable area was dissolved and then a high permeable area was formed. The updip lithologic variety of reservoir sand bodies is favorable to the formation of subtle lithologic traps, and the deltaic reservoirs are characterized by large multi-beds of oil-generation and abundant hydrocarbon resources. In this paper, the petroleum geologic settings of the studied area are analyzed, and the accumulation characteristics and exploration methods of lithologic reservoirs are summarized. It is of theoretical significance for the study of the exploration theories of lithologic reservoirs, and also expedites the exploration steps of deltaic reservoirs in the northern Shaanxi area.