Corrosion inhibitors for steel in concrete: State-of-the-art report

Influence of fly ash on the water and chloride permeability of alkali-activated slag mortars and concretes

https://repositorium.sdum.uminho.pt/bitstream/1822/16351/1/Pacheco%20Torgal%20et%20al.%202012.pdf

Durability of alkali-activated binders: A clear advantage over Portland cement or an unproven issue?

A review of waste products utilized as supplements to Portland cement in concrete

In the last decade, there has been rapid growth in interest in alternative binders, as part of the toolkit of cement technologies needed to mitigate the carbon footprint associated with the construction industry. Alkali-activated materials (AAMs), including geopolymer binders and other related systems, have been identified as a key component of this move to lower CO2 cements and concretes. These are clinker-free cements which can exhibit comparable performance to conventional portland/blended cements, when they are adequately formulated and cured. However, AAMs have a somewhat limited record of durability in service, and this is one of the main limitations facing their commercial adoption at present. To provide the best possible answers to the question of long-term durability within an experimentally accessible timeframe, standardized accelerated degradation testing methods have been widely adopted, in an attempt to simulate natural processes. It has been identified that the interactions between material and environment, which take place on microstructural and nanostructural levels, have a very significant influence on the outcomes of the durability tests. Here, we present an overview of the results obtained when AAMs are exposed to aggressive testing conditions such as elevated concentrations of CO2, sulfates or chlorides. The key outcome of this article is a broader synthesis of the available data regarding the interactions between these new materials and their surrounding environment, which is then available to be used in the design, development, and implementation of environmentally sustainable, high-performance cements and concretes for the 21st century.

Durability of Alkali‐Activated Materials: Progress and Perspectives

The effect of various inhibitive ions (hydroxide, citrate, stannate) for the corrosion of steel in concrete was studied by weight loss measurements, chronopotential studies, anodic polarization technique and compressive strength tests. The salient features of the investigation were: in 100% OPC as well as in OPC + fly ash (3:1 ratio) extracts the passivity of steel was readily destroyed even by the presence of 10 000 ppm of chloride. However in 100% OPC and also in OPC + fly ash (3:1 ratio) extracts containing inhibitive and complexing agents like hydroxide, citrate and stannate, the passivity of steel was maintained even in the presence of 30 000 ppm of chloride. The addition of inhibitive ions like hydroxide, citrate and stannate not only decreased the corrosion rate of steel in simulated concrete environments but also increased the compressive strength of mortars. Citrates, stannates and CaO are effective inhibitors of the corrosion of steel in concrete.

Competitive role of inhibitive and aggressive ions in the corrosion of steel in concrete

At present the utilisaton of fly ash in cement and concrete in India is very minimal. Therefore, enhancing the activity of fly ash is the critical key to large scale applications. Physical, thermal and chemical activation methods have been effected and their performance characteristics tested by aggressive macro cell corrosion technique. The salient features of the investigations were: steel embedded in ordinary Portland cement (OPC) and unprocessed fly ash incorporated cements suffered severe corrosion under macro cell corrosion conditions. But OPC containing treated fly ashes improved the corrosion resistant properties to a greater extent. Chemically treated fly ashes showed superior performance when compared to thermally treated and physically treated systems. The tolerable limit of replacement level for various treated fly ashes under aggressive macro cell corrosion condition is found to be 20%–30%. Under 30% replacement level, chemically activated fly ash (CFA) system showed lowest corrosion rate, hi...

Activated fly ash cements: tolerable limit of replacement for durable steel reinforced concrete

An activated fly ash blended cement composition having improved mechanical and corrosion resistance properties, which comprises: Ordinary Portland cement (OPC) : 70 TO 90 wt.%; Activated fly ash : 10 to 30 wt. %; Sodium silicate : 1 to2 % by weight of OPC Calcium oxide : 2 to 5 % by weight of OPC.

An activated fly ash blended cement composition having improved mechanical and corrosion resistance properties

Evaluation of a composite corrosion-inhibiting admixture and its performance in concrete under macrocell corrosion conditions

Various activation techniques, such as physical, thermal and chemical were adopted. By adopting these methods of activation, hydration of fly ash blended cement was accelerated and thereby improved the corrosion-resistance and strength of concrete. Concrete specimens prepared with 10%, 20%, 30% and 40% of activated fly ash replacement levels were evaluated for their compressive strengths at 7, 14, 28 and 90 days and the results were compared with ordinary Portland cement concrete (without fly ash). Corrosion-resistance of fly ash cement concrete was studied by using anodic polarization technique. Electrical resistivity and ultrasonic pulse velocity measurements were also carried out to understand the quality of concrete. The final evaluation was done by qualitative and quantitative estimation of corrosion for different systems. All the studies confirmed that upto a critical level of 20–30% replacement; activated fly ash cement improved both the corrosion-resistance and strength of concrete. Chemical activation of fly ash yielded better results than the other methods of activation investigated in this study.

Influence of activated fly ash on corrosion-resistance and strength of concrete

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