Impact of corrosion on low-cycle fatigue degradation of reinforcing bars with the effect of inelastic buckling

The combined effect of inelastic buckling and chloride induced corrosion damage on low-cycle high amplitude fatigue life of embedded reinforcing bars in concrete is investigated experimentally. A total of forty-eight low-cycle fatigue tests on corroded reinforcing bars varied in percentage mass loss, strain amplitudes and buckling lengths are conducted. The failure modes and crack propagation are investigated by fractography of fracture surfaces using scanning electron microscope. The results show that the inelastic buckling, percentage mass loss and nonuniform corrosion pattern are the main parameters affecting the low-cycle fatigue life of reinforcing bars. It was found that the fatigue life of corroded reinforcing bars combined with inelastic buckling has a significant path dependency. The results show that in some cases the number of cycles to failure of corroded bars under constant amplitude fatigue test is increased.     

Effects of phosphate on the chloride-induced corrosion behavior of reinforcing steel in mortars

The influence of phosphate as a corrosion inhibitor on the corrosion behavior of as-received and pre-rusted reinforcing steels in mortar specimens was investigated after 360 days exposure in 3.5% NaCl solution. This involved the use of electrochemical techniques for studying the steel surface reactions and microscopic observations of the steel–mortar interface. The electrochemical methods, including electrochemical impedance spectroscopy (EIS) and measurements of corrosion potential (E_corr) and linear polarization resistance (LPR), were employed to evaluate the corrosion tendency and general corrosion rate of steel. In addition, the pitting corrosion resistance of steel was also determined by cyclic polarization (CP) measurements. The results indicate that different from nitrite, which is generally accepted as an anodic inhibitor, phosphate may be a cathodic inhibitor according to its reduced corrosion rate and more negative E_corr at the same dosage as nitrite in mortar specimens. The study also reveals that the inhibiting efficiency of phosphate against general corrosion of both as-received and pre-rusted specimens is lower than 10%, which is inferior to nitrite in some respects. However, as indicated by cyclic polarization measurements, the presence of phosphate provides slightly higher pitting corrosion resistance in comparison to nitrite. Furthermore, it suggests that the corrosion inhibition mechanism of phosphate in mortars mainly depends on a dual effect occurring at the steel–mortar interface. Furthermore, it is confirmed that phosphate has little effect on the long-term mechanical properties of mortars.     

Ermüdungsverhalten von Betonstahl unter Korrosionsbedingungen

In the 2001 completely revised version of DIN 1045‐1 for the first time an explicit proof against fatigue, more a fatigue analysis, have been published. A limit on the fatigue strength at two million cycles, as it was formerly common in civil engineering, is no longer in use. The influence of corrosion on the fatigue behaviour has been investigated insufficiently. It is thus not satisfyingly clarified. To fill this gap of knowledge, a research program was launched, in which fatigue tests at steel samples with a diameter of 16 mm were performed under going corrosion. The fatigue behaviour of the reinforcing steel was determined for four different corrosive media. The aim of the investiagtions was to show that the SN lines, which are the result of the fatigue tests, have exposure caused very different patterns. On the other hand it is examined, whether crack initiation and crack growth of the steel specimen can be recorded separately from each other. Therefore, different testing methods for crack detection were used. They differ especially with respect to their methodology. The article briefly describes the use of the testing methods for crack detection, explains the fatigue tests with the different corrosive liquids and discusses the test results.     

盐酸溶液中肉桂醛对铝的缓蚀作用及吸附热力学研究

本文通过对大量的单组份有机化合物和无机化合物的筛选,选出了肉桂醛这种缓蚀效果较好的化合物作为缓蚀剂,对其进行热力学研究,并分别绘制出不同温度下肉桂醛的吸附等温曲线,肉桂醛在金属铝表面的吸附符合Langmuir吸附规律,分析不同温度下对于肉桂醛缓蚀性能的作用,分别获得了吸附系数、焓变、熵变和自由能变的热力学参数。通过实验得出肉桂醛缓蚀剂的吸附过程是熵值减少的放热过程,随着温度的升高自由能逐渐变大,同时缓蚀率也随之降低。     

Lightweight geopolymer concrete containing aggregate from recycle lightweight block

In this research, the properties of lightweight geopolymer concrete containing aggregate from recycle lightweight block were studied. The recycle block was crushed and classified as fine, medium and coarse aggregates. The compressive strength and density with various liquid alkaline/ash ratios, sodium silicate/NaOH ratios, NaOH concentrations, aggregate/ash ratios and curing temperatures were tested. In addition, porosity, water absorption, and modulus of elasticity were determined. Results showed that the lightweight geopolymer blocks with satisfactory strength and density could be made. The 28-day compressive strength of 1.0–16.0 MPa, density of 860–1400 kg/m³, water absorption of 10–31% and porosity of 12–34%, and modulus of elasticity of 2.9–9.9 GPa were obtained. It can be used as lightweight geopolymer concrete for wall and partition.     

Absorption and desorption properties of fine lightweight aggregate for application to internally cured concrete mixtures

Recently, substantial interest has developed in using fine lightweight aggregate for internal curing in concrete. Mixture proportion development for these mixtures requires the specific gravity, water absorption, and water desorption characteristics of the aggregate. This paper presents results from a recent study in which the properties of commercially available expanded shale, clay and slate lightweight aggregates (LWA’s) were measured. This research measured the time-dependent water absorption response for the lightweight aggregate. The results indicate that a wide range of 24 h water absorption values exist for commonly used fine lightweight aggregates (e.g., absorption between 6% and 31%). Desorption was measured and it was found that between 85% and 98% of the 24 h absorbed water is released at humidities greater than 93%. These properties can be normalized so that they can be efficiently used in proportioning concrete for internal curing. Normalized plots of absorption and desorption demonstrate benefits for a single function that describes a large class of expanded shale, clay, and slate aggregate for use in internal curing.     

Utilization of lignite power generation residues for the production of lightweight aggregates

A novel process is proposed for the utilization of lignite combustion solid residues in the production of inflammable lightweight aggregates (LWA). The process consists of two stages, pelletization and sintering, and carbon contained in BA was used as the process fuel. The main residues bottom ash (BA) and fly ash (FA) from Megalopolis power plant were characterized, mixed in different proportions and treated through pelletization and sintering process. Sintering benefits from combustion of BA carbon content and the product is a hardened porous cake. The energy required for achievement of high temperatures, in the range of 1250 °C, was offered by carbon combustion and CO₂ evolution is responsible for porous structure formation. Selected physical properties of sintered material relevant to use as lightweight aggregates were determined, including bulk density, porosity and water absorption. Bulk density varies from 0.83 to 0.91 g/cm³, porosity varies from 60% to 64% and water absorption varies from 66% to 80%. LWA formed is used for the production of lightweight aggregate concrete (LWAC). Thermal conductivity coefficient varies from 0.25 to 0.37 W/mK (lower than maximum limit 0.43 W/mK) and compressive strength varies from 19 to 23 MPa (higher than minimum limit 17 MPa). The results indicate that sintering of lignite combustion residues is an efficient method of utilization of carbon containing BA and production of LWA for structural and insulating purposes. Carbon content of BA is a key factor in LWA production. Finally, this research work comprises the first proposed application for utilization of BA in Greece.     

The effect of additives on the properties of lightweight aggregates produced from clay

In an attempt to improve the properties, lightweight aggregates were produced from clay with the addition of Na₂CO₃, SiO₂, Fe₂O₃, and Fe in quantities between 2 and 10 wt% and examined with respect to strength, density and expansion behavior. The additives were mixed into dry clay powder, water was added and pellets were formed by hand and fired at 1120 °C in a chamber furnace. Particle densities of the products ranged from 0.31 to 0.57 g/cm³, porosities from 78% to 89% and the solid strength from 0.54 to 1.58 MPa. The addition of Na₂CO₃ proved to decrease the viscosity of the glass phase at the surface of the pellets but resulted in a reduced expansion, irregular shape and pellets sticking together. SiO₂ addition did not give any major change in properties. The addition of Fe₂O₃ increased the pore size in the center of the pellets, however with insignificant change in strength and density. Adding 5 wt% metallic iron powder led to LWA pellets with increased porosity, reduced density, larger pores and low mechanical strength and could be a useful additive in applications where low density is more important than strength.     

双组分造纸助留增强剂的制备与应用

介绍了双组分造纸助留增强剂的配方、制备方法、产品性能和应用情况。     

Using aggregate flowability testing to predict lightweight self-consolidating concrete plastic properties

This paper presents the results of an experimental study on the flow properties of lightweight self-consolidating concrete (LWSCC) which utilizes a new test relating aggregate flow to concrete flow. Three types of LWSCC were tested containing differing proportions of lightweight and normal weight, coarse and fine aggregates, as well as a normal weight self-consolidating concrete (NWSCC) as a control. The flow properties of the aggregate mixes used in the LWSCC and NWSCC specimens were tested using a V-funnel. The concrete flow properties were also tested for comparison, as were the compressive and tensile strengths of the various mixtures. A relationship between the aggregate frictional resistance and the traditional concrete flowability tests—i.e., slump flow, J-ring, and T₅₀₀—was demonstrated. Compressive strengths were greater in LWSCC mixes that contained smaller sized coarse and normal weight aggregates. Finally, a design procedure is introduced that utilizes the aggregate frictional resistance, paste flow properties, and aggregate void ratio to predict the plastic properties of the concrete.     

Steel–concrete bond strength of lightweight self-consolidating concrete

The bond behavior of lightweight self-consolidating concrete (LWSCC) must be understood in order to use this type of high performance concrete in structural members. The objective of this research program is to assess the bond behavior of reinforcing steel bars embedded in LWSCC members. Three different classes of LWSCC mixtures were developed with two different types of lightweight aggregates. In addition, one normal weight SCC (NWSCC) was developed and used as a control mixture. A total of twenty four pullout tests were conducted on deformed reinforcing bars with an embedded length of either 100 or 200 mm and the load-slip responses, failure modes and bond strengths of LWSCC and NWSCC were compared. Based on the results of this study, the bond strength of deformed bars for LWSCCs are found to be less (between 16 and 38%) as compared with NWSCC. Under the conditions of equivalent workability properties and compressive strength, bond slip properties were shown to be significantly influenced by the type of lightweight aggregate used. In this study, the use of expanded shale in the production of LWSCC significantly enhanced the pullout strength when compared with lightweight slag aggregate.     

Load-carrying capacity of lightly reinforced,prefabricated walls of lightweight aggregate concrete with open structure

The paper presents and evaluates the results of a coordinated testing of prefabricated, lightly reinforced walls of lightweight aggregate concrete with open structure. The coordinated testing covers all wall productions in Denmark and will therefore provide a representative assessment of the quality actually produced. Existing and new formulas for the capacity are evaluated by comparison to the test results and a new model with a good correlation with the test results is presented.     

五种船体结构钢在流动海水中的腐蚀行为

研究了５种船体结构钢在０～７．０ｍ／ｓ的海水中的腐蚀行为。结果表明,海水的流动对船体钢的腐蚀具有很大影响,１．５ｍ／ｓ的流速就会使腐蚀率产生数量级的增大,３．０２ｍ／ｓ的流速就会导致显著的冲击腐蚀。无镍铬钢主要表现为迎水侧边的质量耗损,含镍铬钢主要表现为流线形沟纹和马蹄形坑。     

Micro-stress analysis and identification of lightweight aggregate’s failure strength by micromechanical modeling

This work is based on a dual approach of experiments and micromechanical modeling in order to characterize the failure behaviors of lightweight aggregate concretes (LWAC). Many classes of LWAC were tested, based on five families of lightweight aggregates (LWA) and three types of mortar matrices: normal, high performance (HP) and very high performance (VHP). Micromechanical modeling is based on an iterative homogenization approach and associated localization: local stress distributions during the uniaxial compression tests can be predicted in LWAC’s components and at their interface. Experimental compressive strengths were measured on manufactured 16 × 32 cm cylindrical specimens. The confrontations between micromechanical modeling and experiments were used to identify LWA’s failure strengths which are difficult to measure, and to quantify the inaccuracies related to conventional methods. These corrected values of LWA’s failure strength were introduced into a failure criterion modeling: associated predictions of LWAC’s compressive strength are in good agreement with the experimental measurements.     

Effects of heat treatment on oil palm shell coarse aggregates for high strength lightweight concrete

In this study, the effects of heat treatment on oil palm shell (OPS) coarse aggregates are evaluated for high strength lightweight concrete (HSLWC). OPS coarse aggregates are subjected to heat treatment at two temperature settings (60 and 150 °C) and duration of heat treatment (0.5 and 1 h). The reduction in density is found to be within the range of HSLWC when heat-treated OPS aggregates are added into the oil palm shell concrete (OPSC). The results reveal that workability of the OPSC increases with an increase in temperature and duration of heat treatment of the OPS aggregates. It is found that the maximum achievable 28-days and 90-days compressive strength is 49 and 52 MPa, respectively. Furthermore, the ultrasonic pulse velocity (UPV) is examined and the results showed that a good condition is achieved for the OPS HSLWC at the age of 3 days. The average modulus of elasticity (i.e. (E) value), is found to be 15.9 GPa for all mixes, which is higher than that reported in previous studies and is within the range of normal weight concrete. Hence, the findings of this study are of primary importance as they reveal that the selection of a suitable temperature and duration of heat treatment for OPS aggregates can be used as a new eco-friendly alternative method to enhance HSLWC.