冷轧带肋钢筋在砼排水管中的应用研究

简述了冷轧带肋钢筋的生产工艺及性能。4种不同管径的砼排水管按等强度设计原则，以冷轧带助钢筋替代原用的冷拔低碳钢丝后，可节省钢材10％～31％，并提高砼排水管的裂缝荷载，破坏荷载等质量指标和安全度。     

Mechanical performances and stress states of rock bolts under varying loading conditions

A comprehensive study including laboratory tests and numerical modeling was performed to investigate factors of rock bolt fracture. Experimental tests were performed to evaluate the mechanical performances of bolt ends including the thread and adjacent. The effects of installation angle, pretension and accessories (plate, washer and nut) were evaluated. It is found that a bolt installed with an oblique angle to roadway surface suffers a complex stress combination of tensioning, bending and twisting on the bolt. This complex stress is much greater than the tensile stress, leading to cracking and growth at the location of bending causing the thread to fail even though the tensile stress is less than the yield strength. Bolt thread is more vulnerable to fracture than rebar.     

Effect of fine crack width and water cement ratio of SHCC on chloride ingress and rebar corrosion

SHCC (Strain Hardening Cement-based Composite) is a material known for its strain-hardening behavior under tensile and bending stress and its characteristic numerous small cracks. SHCC is expected to show superior durability because of the fineness of the cracks. In this study, chloride ingress through cracks into SHCC and progress of rebar corrosion in three mixtures of SHCC with various water-cement ratios were investigated. Through a chloride solution immersion test, it was confirmed that chloride could penetrate through even very fine cracks. The resistivity of cracked SHCC against chloride ingress is mainly governed by the accumulated crack width and the water cement ratio. Chloride pre-mixed SHCC specimens were left in a high-temperature, high-humidity chamber for 11 months to promote rebar corrosion. While the accumulated crack width and the water cement ratio were both influential to an increase in corrosion area, only the water cement ratio had bearing on corrosion loss.     

热轧Φ6 ~40 mm HRB500E螺纹钢筋的生产实践

根据GB/T 1499.2-2018标准,水钢设计了Φ36～40 mm HRB500E螺纹钢筋的内控成分为（%）0.22～0.25C、0.60～0.70Si、1. 50～1.60Mn、0.11～0.13V、P≤0. 045、S≤0. 045。采用"100 t顶底复吹转炉冶炼-挡渣出钢-脱氧合金化-LF炉精炼-160方坯连铸-方坯加热-棒材轧制-空冷"的工艺流程,生产出的Φ36 mm HRB500E螺纹钢筋的屈服强度Re_L⁰ 540～580 MPa,抗拉强度R_m⁰ 705～735 MPa,断后伸长率A 15. 5%～20. 5%,最大力总延伸率A_gt 11.5%～14.0%,实测抗拉强度与实测屈服强度之比R_m⁰/R_eL⁰为1.25～1.32,实测屈服强度与GB/T 1499.2-2018标准要求的最低屈服强度之比R_eL⁰/R_eL为1.08～1.16,因此,钢筋的力学性能满足GB/T 1499.2-2018标准要求。生产出的Φ40 mm HRB500E钢筋的微观组织为铁素体+珠光体,晶粒度为9.5～10级。     

Field performance of concrete pipes during jacking in cemented sandy silt

Although many field investigations into pipe-jacking installation have been reported within the literature, there are few reports on the rebar stress in jacking pipes. This paper presents the field performance of concrete pipes during the jacking carried out under the Guan River in Jiangsu, China. Rebar stresses at two wings (the left and right side), the top crest, and the base in the longitudinal and circumferential directions for four different pipes were monitored. The maximum rebar stresses during the jacking were 37.1 MPa in the longitudinal direction and 36.6 MPa in the circumferential direction. However, the maximum rebar stresses after construction were only 18.5 MPa in the longitudinal direction and 20.3 MPa in the circumferential direction. A normalized jacking force “α” is proposed to evaluate the additional rebar stress in jacking pipes. The range of α is from 0.04 to 0.25. The relationship between the rebar stress and the construction procedure is presented and discussed. An excessive jacking force, an alignment deviation or an increased penetration rate would generate a large incremental rebar stress.     

Impedance of reinforcing steel with disbonded dual polymer–zinc coating

Dual polymer/zinc-coated concrete steel reinforcing bar (rebar) is a novel material intended to improve corrosion related durability in marine and deicing salt environments. Severe fabrication bending induces coating breaks and separation from the steel substrate, creating a crevice where some zinc corrosion takes place. EIS measurements to characterize that corrosion revealed spontaneous fluctuations that included variations in the size of the high frequency loop and sometimes strong intermediate frequency dispersion. This investigation examined the underlying causes for that behavior. The fluctuations were explained by formation and episodic release of hydrogen gas in the crevice underneath the disbonded coating, as a product of the cathodic reaction in corrosion of the zinc layer. The gas caused partial occlusion of the crevice and the crevice opening at tears in the coating. Gas occlusion increased the effective electrolytic resistance inside the crevice, and contributed to an enhanced transmission line configuration with associated frequency dispersion, especially notable in the intermediate frequency part of the impedance spectrum. A radial transmission line model was adopted as a simplified abstraction of the system. Properties of the radial transmission line impedance behavior are discussed. The model output replicated the key features of the measured impedance spectrum and its fluctuations, and permitted isolating the low frequency response as the most representative to evaluate corrosion conditions inside the crevice in subsequent research.     

φ40mm K20MnSi螺纹钢筋质量分析

φ４０ｍｍ Ｋ２０ＭｎＳｉ螺纹钢筋冷弯和反弯断裂进行的检验确认为与连铸坯夹杂物，表面缺陷，基体组织及表层淬透深度有关，建议改善钢液清洁度，连铸工艺及轧钢加热温度和轧后余热处理工艺为提高钢材质量的途径。     

Effect of prior damage on the performance of cement based coatings on rebar: macrocell corrosion studies

The performance of any rebar coating system depends upon its resistance to corrosion in the presence of chloride contaminated concrete. It also mainly depends upon its tolerance towards damage that may occur during handling, transporting and concreting. The severe corrosion of epoxy coated reinforcing steel in long key bridge and other structures in Florida gave raise to the concern over the influence of damages in the coating system [R.J. Kessler, P.G. Powers, Interim report on corrosion evaluation of substructure in Long key bridge, Corrosion Report No. 87-9A, Florida Department of Transportation, Florida, 1987]. The performance of rebar coating such as galvanizing and epoxy based coating with prior surface damage has been evaluated and reported. [J. Hartley, Concrete Jan/Feb (1994) 12–15; A. Sagues, Performance of galvanized rebars in marine substructure service, Project ZE-418, Part I, October, 1994]. To date, the performance of cement based coatings with prior damages has not been widely studied and reported. In the present investigation the effect of prior damage produced during concrete pouring has been studied on inhibited cement slurry coating. To simulate the marine substructure environment, macrocell corrosion has been created via a chloride ion concentration gradient. Test conditions and method of macrocell current measurement as described in ASTM G 109-92 have been followed. The above investigation revealed that the cement based coating appears to have better tolerance towards defects in chloride contaminated concrete as compared to epoxy based coating system. The performance of the coating is independent of the height of concrete pouring.     

Corrosion studies of rebar in contact with saturated solution produced by leaching of Portland Type-II cement: examining the effects of chloride,carbonation and an amorphous silica additive

This study examined the effects of silica addition on electrochemical behavior of rebar in native pH 12.5 saturated solutions prepared by leaching of Portland Type-II cement, and in solutions reduced by CO₂ to pH 9. Cyclic polarizations showed that at pH 12.5 the silica additive increased the threshold concentration required for pitting from 100 to 105mM, and from 0.3 mM to 0.5 mM at pH 9. Passivation kinetic exponents were consistently larger for solutions with either pH when silica was present. The silica additive provided the passive film with generally increased resistance and lower capacitance, as confirmed by electrochemical impedance spectroscopy. Charge carrier densities calculated from Mott-Schottky plots were on the order of 1020 (cm^-3), increasing significantly after the passive film breakdown. Raman spectroscopy of rebar samples immersed in saturated cement solutions showed films predominantly composed of iron oxyhydroxides with a new shoulder attributed to amorphous silica.