The effect of metakaolin on the corrosion behavior of cement mortars

In this paper the effect of metakaolin addition on the corrosion resistance of cement mortar is studied. A poor Greek kaolin with a low kaolinite content was thermally treated and the produced metakaolin (MK) was ground to the appropriate fineness. In addition, a commercial metakaolin (MKC) of high purity was used. Several mixture proportions were used to produce mortar specimens, where metakaolin replaced either sand or cement. Mortar specimens were then exposed to the corrosive environment of either partial or total immersion in 3.5% w/w NaCl solution. For the evaluation of the performance of metakaolin, the following methods were used: compressive strength, corrosion potential, mass loss, electrochemical measurements of the corrosion rate by the Linear Polarization method, carbonation depth and porosity. It is concluded that metakaolin improves the compressive strength and the 10% w/w addition shows the optimum contribution to the strength development. In addition, the use of metakaolin, either as a sand replacement up to 20% w/w, or as a cement replacement up to 10% w/w, improves the corrosion behavior of mortar specimens, while when metakaolin is added in greater percentages there is no positive effect.     

Lightweight mortar made with recycled polyurethane foam

This paper presents results of an experimental study on the use of rigid polyurethane foam wastes with cement-based mixtures to produce lightweight mortar. Several mortar grades were obtained by mixing cement with different amounts of polyurethane, aggregate and water. Dosages were varied to replace aggregates with recycled polyurethane, while the amount of water was optimized to obtain good workability. Rigid polyurethane was ground to particle sizes of less than 4 mm prior to use as an aggregate substitute. The characteristics of the test specimens were defined and they were tested in both a fresh and a hardened state. Results show that an increase in the amount of polyurethane affects the mortar, decreasing its density and mechanical properties while increasing its workability, permeability, and occluded air content. These results confirm that mortar produced with recycled polyurethane is comparable to lightweight mortar made with traditional materials.     

Corrosion behaviour of rebars in fly ash mortar exposed to carbon dioxide and chlorides

Addition of fly ash has beneficial effects on some mechanical properties of concrete, as well as on the corrosion process induced by the chloride ion. The aim of this study was to investigate the effect of fly ash addition on the corrosion process occurring in reinforced concrete exposed simultaneously to carbon dioxide and chloride. The corrosion process of steel rebars embedded in mortar with 15% and 30% of fly ash was tested under carbon dioxide and sodium chloride contamination. Monitoring of open circuit potential and electrochemical impedance spectroscopy (EIS) were used to follow the corrosion process. Results have shown that under accelerated carbonation fly ash mortar shows higher corrosion rates. The chloride content in mortar exposed to accelerated carbonation increases with the amount of fly ash. However, under natural carbonation it decreases with the addition of fly ash.     

A short-term test method to determine the chloride threshold of steel–cementitious systems with corrosion inhibiting admixtures

Now-a-days, multiple types of corrosion inhibiting admixtures (CIAs) are being used to enhance the chloride threshold (Cl_th) of steel–cementitious systems. However, due to the application of external potential to drive chlorides, some existing short-term test methods are not suitable to assess the Cl_th of S–C systems with CIAs containing anions. This paper presents the development of a Modified Accelerated Chloride Threshold (mACT) test to determine the Cl_th for S–C systems with CIAs. The test specimens consisted of a mortar cylinder with an embedded steel piece and electrodes forming a 3-electrode corrosion cell. The specimens were exposed to chloride solution and the linear polarization resistance tests were conducted every 3.5 days. The corrosion initiation was detected using statistical analysis of the repeated R _p measurements. After corrosion initiation, the chloride content in mortar adjacent to the embedded steel piece was determined and defined as Cl_th. The time required to complete mACT test for an S–C system with CIAs is about 120 days. The Cl_th of eight specimens each with S–C system containing (i) without inhibitor, (ii) anodic inhibitor [calcium nitrite] and (iii) bipolar inhibitor [both calcium nitrite and amino alcohol] were determined. Both anodic and bipolar CIAs showed enhanced corrosion resistance. Also, the bipolar inhibitor performed better than anodic inhibitor. It was concluded that the use of CIAs could significantly delay the initiation of chloride-induced corrosion. The mACT test can be used to determine the Cl_th and estimate the service life during the planning and design stages of a project and help select durable materials.     

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.     

Properties of Al2O3 nano-particle reinforced copper matrix composite coatings prepared by pulse and direct current electroplating

Cu–Al₂O₃ nano-composite coatings have high potential for use in applications in which high mechanical properties together with high corrosion resistance are required. In the present study it is intended to produce copper nano-alumina composite coatings with various nano-alumina contents in order to investigate the effect of alumina reinforcement particles on corrosion resistance and mechanical properties such as hardness and wear resistance. The composite coatings were deposited using direct current (DC) and pulse current (PC) plating. The microstructures of the coatings produced from both methods were examined via scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques. The wear behaviors, micro hardness, coating thickness, corrosion rate and coating porosity were examined using appropriate methods. Compared to DC deposition, PC plating facilitated higher amounts of particle incorporation with more uniform distribution. The results indicated that the mechanical properties of the applied coatings with incorporated nano-alumina reinforcement were far more superior as compared to its own matrix as well as non-composite copper coatings. It was also found out that increasing the amount of nano-alumina content in the coating, led to enhanced general properties of the coatings.     

外墙保温系统界面砂浆黏强度性能试验方法

通过比对试验,分析采用JG158-2004《胶粉聚苯颗粒外墙外保温系统》和DB33/T1054-2008《无机轻集料保温砂浆及系统技术规程》中界面砂浆黏结强度性能试验方法的差异,JG158-2004中的方法不能客观反映界面砂浆黏结强度的主要原因,并指出浙江地方标准DB33/T1054-2008的试验方法能较真实反映界面砂浆的黏结强度。     

Recycling petroleum coke in blended cement mortar to produce lightweight material for Impact Noise Reduction

This work introduces a new way to use low-cost petroleum (pet) coke as lightweight aggregate in cement mortars to make sound barriers. The feasibility of adding pet coke in cement matrix was investigated: an in-depth characterization of as-received coke and the new lightweight mortar was made. The acoustic behaviour herein was assessed by constructing a large dimension mortar slab (made of cement and coke as aggregate) used as floor covering and measuring, according to the procedure described in international standards, the impact noise pressure level over the range of frequencies 100–5000 Hz. Impact Noise Reduction (INR) was also obtained and the results were compared to the ones experimentally obtained from a control mortar slab (made of cement and sand). Results showed that coke addition leads to a decrease in mechanical properties of resultant mortars, this is principally due to an increase of the porosity (∼60%). A gradual increase of impact noise insulation was observed in lightweight floor covering from middle to higher frequencies tested, reaching, within this range, a remarkable improvement of sound insulation compared to control slab (∼14 dB).     

Recycling petroleum coke in blended cement mortar to produce lightweight material for Impact Noise Reduction

This work introduces a new way to use low-cost petroleum (pet) coke as lightweight aggregate in cement mortars to make sound barriers. The feasibility of adding pet coke in cement matrix was investigated: an in-depth characterization of as-received coke and the new lightweight mortar was made. The acoustic behaviour herein was assessed by constructing a large dimension mortar slab (made of cement and coke as aggregate) used as floor covering and measuring, according to the procedure described in international standards, the impact noise pressure level over the range of frequencies 100–5000 Hz. Impact Noise Reduction (INR) was also obtained and the results were compared to the ones experimentally obtained from a control mortar slab (made of cement and sand). Results showed that coke addition leads to a decrease in mechanical properties of resultant mortars, this is principally due to an increase of the porosity (～60%). A gradual increase of impact noise insulation was observed in lightweight floor covering from middle to higher frequencies tested, reaching, within this range, a remarkable improvement of sound insulation compared to control slab (～14 dB).     

氧化石墨烯负载铁酞菁涂层的制备及其防腐蚀性能

目前,鲜见将石墨烯用于防腐蚀涂料的研究报道。以氧化石墨烯负载铁酞菁复合材料(GO-Fe Pc)为填料、环氧树脂E-44和107胶为成膜剂、T-31为固化剂,采用共混法制备了双组分涂料,并涂覆于Q235钢基片制备防腐蚀涂层,通过中性盐雾试验、抗老化和电化学等手段研究并评价了填料含量对涂层防腐蚀性能的影响。结果表明:添加GO-Fe Pc填料的涂层具有较好的防腐蚀性能,且E-44与GO-Fe Pc的质量比为100∶1时效果最佳,涂层附着力为0级,氙灯老化30 d和中性盐雾试验15 d后,涂层无腐蚀现象,3.5%Na Cl浸泡15 d后的电极腐蚀电位最高,为-0.258 V,防腐蚀性能最佳。     

重防蚀涂装体系在广岛和重庆的自然环境试验

大量的工业设施受酸雨和海洋腐蚀较为严重,中国重庆和日本广岛的自然环境具有一定的特殊性和代表性,针对4种用途13种涂装工艺的重防蚀涂装体系进行了耐酸雨和海洋严酷环境腐蚀规律的自然环境对比试验.结果表明:在重庆的涂层腐蚀均比广岛严重;所有暴露3年的试样,在重庆的划痕单侧最大腐蚀宽度几乎都超过3 mm,而在广岛几乎都在3 mm以下;即使按耐强腐蚀环境设计的重防蚀涂装试样,在重庆的腐蚀也比较严重.重庆的自然环境腐蚀严酷度等级比广岛高1个等级,在酸雨地区对钢铁具有较好保护作用的涂装体系(防蚀性和装饰性保护层)有两种:(1)热浸Zn→环氧底漆→聚氨酯面漆;(2) 厚膜无机富锌漆→喷涂层→环氧底漆→环氧底漆→聚氨酯中涂漆→聚氨酯面漆.     

Corrosion properties of thermal sprayed aluminium (TSA) coatings deposited by powder flame spraying

Thermal sprayed aluminium (TSA) coatings are widely used for the protection of steels from aqueous corrosion, including offshore structures and components that are exposed to seawater immersion, tidal and splash zone environments. In this paper, the influence of deposition parameters of aluminium coating on its corrosion properties was studied. For different application parameters of TSA coatings, the thickness, the microstructure and corrosion properties were determined. Determination of thickness was performed according to EN ISO 2064:2000 relating to the definition and determination of the thickness of metallic and other inorganic layers. Microstructure was determined using a Olympus GX50 optical microscope. The corrosion properties of the coatings were compared using an accelerated electrochemical corrosion test method. Electrochemical studies were carried out in accordance with the requirements of ASTM standard G 102 – 89. The TSA coating performance was quantified in terms of its corrosion potential and the corrosion rate, which was estimated from Tafel polarisation resistance measurements.     

Influence of a new type of additive on the performance of polymer-lightweight mortar composites

This paper shows how a new powder polymer additive (PPA), containing a waterproofing agent, a rheology control agent and air-entrainers, affects the workability, mechanical properties and setting times of polymer-lightweight mortar composites (PLMC). The waterproofing agent was a mixture of redispersible polyethylene vinyl acetate and redispersible silane based polymer powder. The rheology control agent was a redispersible hydroxypropyl carboxymethyl ether of patato starch based polymer powder. Air-entraining agent was a redispersible and an unmodified sodium laurly sulphate based polymer powder. Pumice fine aggregate at 0–3 mm size fraction was used as lightweight aggregate throughout the research work. In order to examine the effects of powder polymer additive on flowability and the performance when the additive is mixed in a mortar, the mixture proportions were set in four trial batches. The volume proportions of cement and pumice lightweight fine aggregate were fixed at 1:9, 1:8, 1:7 and 1:6, respectively, defining the mixture of mortar for measuring the compressive strength and workability of lightweight mortar. In this research study, PLMC mortars with 28 different mixture proportions (M1–M28) by weight of cement contents of 0.2%, 0.4%, 0.6%, 0.8%, 1.0% and 1.2% were adopted for the mortar mixture batches, respectively. Flow value of mortar was measured using a flow table method in accordance with the regulation in ASTM C230, “flow table for use in tests of hydraulic cement”. The target flow was fixed at 130 mm for each mixture proportion, which is regarded as the most suitable fluidity to secure workability at a site. For each mixture, 12 fresh plastic mortar samples were prepared according to the method specified in ASTM C305 and cured in a humidified atmosphere for 24 h, removed from the mould after 24 h, cured in water for 7 days, and then cured in air. The compressive strength test results were evaluated in accordance with ASTM C270.The suitability of using a new powder polymer additive in terms of workability and required compressive strength in PLMC mortar applications is also presented in this paper. It is observed that PLMC mortars have adequate strength and more convenient workability for their use in general masonry construction applications.     

Properties of alkali-activated mortar and concrete using lightweight aggregates

This study reports the testing of 12 alkali-activated (AA) mortars and six AA concretes using lightweight aggregates. These tests aimed to explore the significance and limitations of the development of lightweight AA mortar and concrete. Ground granulated blast-furnace slag, which was used as source material, was activated by sodium silicate powder. The main parameter investigated was the replacement level of lightweight fine aggregates to the natural sand. The effect of the water–binder ratio on the compressive strength development was also studied in AA mortars. Initial flow and development of compressive strength were recorded for the lightweight AA mortar. For the lightweight AA concrete, many factors were measured: the variation of slump with elapsed time, the development of compressive strength, splitting tensile strength, moduli of rupture and elasticity, stress–strain relationship, bond strength and shrinkage strain. Test results showed that the compressive strength of AA mortar decreased linearly with the increase of the replacement level of lightweight fine aggregates, regardless of the water–binder ratio. The compressive strength of AA concrete, however, sharply decreased when the replacement level of lightweight fine aggregates exceeded 30%. In particular, the increase in the discontinuous grading of lightweight aggregate resulted in the deterioration of the mechanical properties of AA concrete.     

Influence of cement and aggregate type on thaumasite formation in concrete

In this study the influence of binder type on the formation of thaumasite in mortar prisms made with expanded clay lightweight aggregate (LWA) or quartz sand was examined. For this purpose mortar prisms were made, which after 28 days of curing in deionised water were exposed to a sulphate solution or deionised water. The length and weight change of the prisms was recorded in triplicate as a function of time of exposure to dry–wet cycles at 5 ± 1 °C.The influence of the binder type on the expansion in the sulphate solution can be ordered from strong to weak as follows: (1) CEM I + limestone filler, (2) CEM I, (3) CEM I + fly ash, and (4) CEM III/A. Because the porosity of the LWA was able to accommodate the growing sulphate crystals, the mortar prisms made with LWA were still largely intact after 3 years of exposure. The only exception being the mortar prisms containing limestone filler. The mortar prisms made with quartz sand and exposed to the sulphate solution were all bent, broken or disintegrated after 24 weeks. The prisms exposed to deionised water showed minimal expansion. Key factors controlling the formation of thaumasite are discussed.     

Preliminary study on mitigating steel reinforcement corrosion with bioactive agent

Corrosion causes over $100 billion in damage annually. Cinnamaldehyde, a bioactive agent derived from cinnamon bark, can mitigate the corrosion of metals but has a negative effect on hydration when incorporated in cementitious systems. In order to avoid these negative consequences while harnessing anti-corrosive properties, cinnamaldehyde was incorporated in a cementitious mixture through the use of lightweight aggregate (LWA). The same method was used for penetrating corrosion inhibitors in an attempt to reduce the time required for the inhibitor to reach and protect reinforcing steel. The setting time, compressive strength, heat evolution (via semi-adiabatic calorimetry), and autogenous shrinkage of the experimental mixtures were measured and an accelerated corrosion test (ACT) was used to quantify performance in a corrosive environment. Experimental mortars showed prolonged setting times, reduced compressive strength, heat evolution, and autogenous expansion. However, the experimental mortars showed an increase in time to cracking when exposed to a corrosive environment.     

Aluminium alloys exposed to borderline solutions – a methodology to evaluate the susceptibility to corrosion fatigue with respect to corrosive de‐icers

In addition to high mechanical loads certain components for the automotive industry are exposed to corrosive environments, especially during winter, when corrosion promoting de‐icers are essential to sustain road traffic. The underlying research work contributes to the evaluation of the corrosion fatigue performance of aluminium alloys relevant for automotive application generally, while the present text focuses on wrought alloys. Aluminium alloys are of special interest because of the opportunity to reduce expenses for an additional corrosion protection and to support lightweight construction of vehicles. Components exposed to simultaneous mechanical and corrosive service loads as well as corrosion tests of different scale level (immersion and cabinet testing, long term outdoor exposure of components, usage on test carriers) were analysed to evaluate typical forms of corrosion. Based upon the prevailing damaging mechanism of material conditions with known differences in susceptibility to specific forms of corrosion, like intergranular corrosion or pitting, methods were derived to evolve service relevant types of corrosion during laboratory tests.     

Effect of zinc phosphate chemical conversion coating on corrosion behaviour of mild steel in alkaline medium: protection of rebars in reinforced concrete

We outline the ability of zinc phosphate coatings, obtained by chemical conversion, to protect mild steel rebars against localized corrosion, generated by chloride ions in alkaline media. The corrosion resistance of coated steel, in comparison with uncoated rebars and coated and uncoated steel rebars embedded in mortar, were evaluated by open-circuit potential, potentiodynamic polarization, cronoamperometry and electrochemical impedance spectroscopy. The coated surfaces were characterized by x-ray diffraction and scanning electron microscopy. First, coated mild steel rebars were studied in an alkaline solution with and without chloride simulating a concrete pore solution. The results showed that the slow dissolution of the coating generates hydroxyapatite Ca₁₀(PO₄)₆(OH)₂. After a long immersion, the coating became dense and provided an effective corrosion resistance compared with the mild steel rebar. Secondly, the coated and uncoated steel rebars embedded in mortar and immersed in chloride solution showed no corrosion or deterioration of the coated steel. Corrosion rate is considerably lowered by this phosphate coating.     

Entwicklung einer niedrigschmelzenden Legierung und deren Applikation zum Korrosionsschutz hochfester Stähle

Development of low‐temperature galvanizing and its application for corrosion protection of high‐strength steels Apart from reliability and quality, vehicle safety and cost efficiency are the decisive criteria for automobile manufacturers. Corrosion protection plays a decisive role because it increases the service life. The ultra‐high‐strength steels are materials which exhibit high lightweight potential as well as a very good energy absorption capacity because of their mechanical properties. In connection with the possibility of hot forming, they are predestined for the fabrication of complicated, load‐compatible shapes in the crash‐relevant frame and body construction. The application of these steel qualities has been carried out in structural parts which are protected from corrosion by a hot‐dip coat of FeAl7 – the so‐called Usibor. However, at the moment there is no ready‐for‐production solution for later corrosion protection of already hot‐formed parts. Therefore, a corrosion protection system on the basis of conventional low‐temperature galvanizing processes has been developed and utilized. First, the softening behavior of the highly‐resistant 22MnB5 substrate was analyzed. Afterwards, a galvanizing system was developed and applied. The corrosion protection coatings were characterized with regard to their structure and corrosion protection potential. As a result, a significant improvement of the corrosion behaviour has occurred.     

Steel rebars corrosion investigation with strain gages

The presentation of a new laboratory, non-destructive method of detection and checking the corrosion of steel rebars in mortar specimens is discussed in this paper. The method uses extensive meter sensors, such as the well known strain gages (SG) and is based on the phenomena of tension state, in which the mortar mass comes near the rebar area, after the formation of corrosion products. The SG are embedded in reinforcing mortar specimens during casting. Specimens are immersed in a 3.5 wt% NaCl solution and a constant potential is applied between steel rebar and graphite electrode in order to obtain fast corrosion conditions. As the embedded SG are affected by volume changes, caused not only by corrosion products, all other disturbing parameters have been compensated for by the measurement method described. The method was applied in different types of mortar specimens in order to have test and verification results. The reliability of the technique was evaluated by measuring: (a) the gravimetric weight loss of the reinforcing steel bars; (b) the electrical charge flow through specimens; and (c) the porosity of mortar mass. The test results obtained indicate that the method is reliable and suitable for the laboratory study of the corrosion factors and the influence of concrete admixtures in corrosion protection.