|
Concrete Cancer
Concrete cancer may refer to: * Rebar corrosion and spalling of the concrete cover above rebar caused by the rust expansion and accelerated by chloride attack and pitting corrosion of the steel reinforcements. * Alkali–silica reaction (ASR), also known as alkali-aggregate reaction (AAR), when reactive amorphous silica aggregates exposed to alkaline conditions (high pH) swell inside the concrete matrix leading to the development of a network of cracks. It may also refer to: * Sulfate attacks, an hat appellation covering different concrete degradation mechanisms: ** Delayed ettringite formation (DEF), also known as internal sulfate attack (ISA) when the temperature of fresh concrete exceeds 65 °C during its setting and hardening; ** External sulfate attack (ESA), and; ** Thaumasite form of sulfate attack (TSA). {{Disambiguation Concrete Corrosion Materials degradation ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Reinforced Concrete Structures Durability
The durability design of reinforced concrete structures has been recently introduced in national and international regulations. It is required that structures are designed to preserve their characteristics during the service life, avoiding premature failure and the need of extraordinary maintenance and restoration works. Considerable efforts have therefore made in the last decades in order to define useful models describing the degradation processes affecting reinforced concrete structures, to be used during the design stage in order to assess the material characteristics and the structural layout of the structure.. Service life of a reinforced concrete structure Initially, the chemical reactions that normally occur in the cement paste, generate an alkaline environment, bringing the solution in the cement paste pores to pH values around 13. In these conditions, passivation of steel rebar occurs, due to a spontaneous generation of a thin film of oxides able to protect the steel fr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Alkali–silica Reaction
The alkali–silica reaction (ASR), also commonly known as concrete cancer, is a deleterious internal swelling reaction that occurs over time in concrete between the highly alkaline cement paste and the reactive amorphous (''i.e.'', non-crystalline) silica found in many common aggregates, given sufficient moisture. This deleterious chemical reaction causes the expansion of the altered aggregate by the formation of a soluble and viscous gel of sodium silicate (Na2SiO3, also noted Na2H2SiO4, or N-S-H (sodium silicate hydrate), depending on the adopted convention). This hygroscopic gel swells and increases in volume when absorbing water: it exerts an expansive pressure inside the siliceous aggregate, causing spalling and loss of strength of the concrete, finally leading to its failure. ASR can lead to serious cracking in concrete, resulting in critical structural problems that can even force the demolition of a particular structure. The expansion of concrete through reaction be ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sulfate Attack In Concrete And Mortar
Sulfate attack typically happens to ground floor slabs in contact with soils containing a source of sulfates. Sulfates dissolved by ground moisture migrate into the concrete of the slab where they react with different mineral phases of the hardened cement paste. The attack arises from soils containing ions, such as MgSO4 or Na2SO4 soluble and hygroscopic salts. The tricalcium aluminate (C3A) hydrates first interact with sulfate ions to form ettringite (AFt). Ettringite crystallizes into small acicular needles slowly growing in the concrete pores. Once the pores are completely filled, ettringite can develop a high crystallization pressure inside the pores, exerting a considerable tensile stress in the concrete matrix causing the formation of cracks. Ultimately, Ca2+ ions in equilibrium with portlandite (Ca(OH)2) and C-S-H and dissolved in the concrete interstitial water can also react with ions to precipitate CaSO4·2H2O (gypsum). A fraction of ions can also be trapped, or sor ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
AFt Phases
AFt Phases refer to the calcium Aluminate Ferrite trisubstituted, or calcium aluminate trisubstituted, phases present in hydrated (or hardened) cement paste (HCP) in concrete. AFm and AFt phases in cement hydration products Calcium aluminates can form complex salts in combination with different types of Ion, anions. Two series of calcium aluminates are known in cement chemist notation, cement chemistry: AFm phases, AFm and AFt phases, being respectively mono- or tri-substituted with a given divalent anion X (''e.g.'' , , or hosting a divalent impurity such as ...), or with two units of a monovalent anion, ''e.g.'' , , or hosting a monovalent impurity such as , or ...). Their general formulas are respectively: in which n, the number of water molecules present in the hydrate, is in the range 10 to 12 for the AFm phases, and around 32 for the AFt phases. AFt phases AFt phases are important mineral hydration, hydration products of the cement clinker. They are Crystal, cry ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Thaumasite
Thaumasite is a calcium silicate mineral, containing Si atoms in unusual octahedral configuration, with chemical formula Ca3 Si(O H)6( C O3)( SO4)·12 H2O, also sometimes more simply written as CaSiO3·CaCO3·CaSO4·15H2O. It occurs as colorless to white prismatic hexagonal crystals, typically as acicular radiating groups. It also occurs as fibrous masses. Its Mohs hardness is 3.5 and it has a specific gravity of 1.88 to 1.90. Optically it is uniaxial negative with indices of refraction of nω = 1.507 and nε = 1.468. It occurs as a hydrothermal alteration mineral in sulfide ore deposits and geothermal alteration of basalt and tuff. It occurs with zeolites, apophyllite, analcime, calcite, gypsum and pyrite. Thaumasite can also be formed in man-made concrete structures at the detriment of calcium silicate hydrates (C-S-H, with dashes denoting the non-stoichiometry of this hydrated cement phase acting as the "glue" in hardened cement paste) during cement alteration, especially ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Concrete
Concrete is a composite material composed of aggregate bound together with a fluid cement that cures to a solid over time. It is the second-most-used substance (after water), the most–widely used building material, and the most-manufactured material in the world. When aggregate is mixed with dry Portland cement and water, the mixture forms a fluid slurry that can be poured and molded into shape. The cement reacts with the water through a process called hydration, which hardens it after several hours to form a solid matrix that binds the materials together into a durable stone-like material with various uses. This time allows concrete to not only be cast in forms, but also to have a variety of tooled processes performed. The hydration process is exothermic, which means that ambient temperature plays a significant role in how long it takes concrete to set. Often, additives (such as pozzolans or superplasticizers) are included in the mixture to improve the physical prop ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Corrosion
Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engineering is the field dedicated to controlling and preventing corrosion. In the most common use of the word, this means electrochemical oxidation of metal in reaction with an oxidant such as oxygen, hydrogen, or hydroxide. Rusting, the formation of red-orange iron oxides, is a well-known example of electrochemical corrosion. This type of corrosion typically produces oxides or salts of the original metal and results in a distinctive coloration. Corrosion can also occur in materials other than metals, such as ceramics or polymers, although in this context, the term "degradation" is more common. Corrosion degrades the useful properties of materials and structures including mechanical strength, appearance, and permeability to liquids and ga ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
