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Controlled Permeability Formwork (CPF) is a system proven to significantly enhance the durability of surface concrete during the casting process.
All concretes cast against wood or steel in the concrete cover zone, have a reduced cement content and increased water/cement ratio (i.e. less dense and more porous) compared to concrete located beyond the reinforcement. Within the core of any structural element the matrix is generally a denser and of better quality compared to the surface as a direct result of the concrete compaction. This compaction process drives excess mix air and water within the cover zone towards the formed surfaces.
As conventional wood or steel formwork is impermeable, the migration within the mix ceases as the concrete/formwork interface is reached. Visually, this may be observed on all concrete surfaces through the presence of blowholes following formwork removal.
This is a problem because the first line of defence of all structural elements against carbonatation, chlorides, frost and abrasion, is the cover zone. It is therefore imperative this region is durable.
CPF liners are typically constructed of 100% polypropylene fibres, spun and thermally bonded, with a woven texture of 0.7 mm thickness. Some systems may be laminated to a plastic latticed net to ensure drainage whilst providing stiffness to the liner.
They are robust and chemically inert and may be supplied in rolls of varying length to construction sites.
The basic elements of CPF systems are:
CPF liners are secured in place on vertical or inclined surfaces with staples or other fixing devices, having first been tensioned onto the formwork shuttering. Once attached, concreting is performed in the normal way. Release agents are not required as CPF liners easily debond from the concrete during formwork striking.
Throughout the concreting process and as a result of concrete pressures, entrapped air and excess mix water that would otherwise become trapped at the surface causing blemishes, can instead pass through the liner. A proportion of this mix water is held within the liner and under capillary action, imbibes back into the concrete to assist curing. Liners generally have a pore structure that is designed to retain the majority of cement and other small fines.
This results (for vertical and inclined surfaces) in the creation of a uniform surface relatively free from blowholes and other surface blemishes when compared to impermeable concrete. But more importantly the achievement of a cover area with significantly enhanced durability.
Concrete is a composite material composed of aggregate bonded together with a fluid cement that cures over time. Concrete is the second-most-used substance in the world after water, and is the most widely used building material. Its usage worldwide, ton for ton, is twice that of steel, wood, plastics, and aluminium combined.
Reinforced concrete, also called ferroconcrete, is a composite material in which concrete's relatively low tensile strength and ductility are compensated for by the inclusion of reinforcement having higher tensile strength or ductility. The reinforcement is usually, though not necessarily, steel bars (rebar) and is usually embedded passively in the concrete before the concrete sets. However, post-tensioning is also employed as a technique to reinforce the concrete. In terms of volume used annually, it is one of the most common engineering materials. In corrosion engineering terms, when designed correctly, the alkalinity of the concrete protects the steel rebar from corrosion.
Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials by chemical or electrochemical reaction with their environment. Corrosion engineering is the field dedicated to controlling and preventing corrosion.
A road surface or pavement is the durable surface material laid down on an area intended to sustain vehicular or foot traffic, such as a road or walkway. In the past, gravel road surfaces, macadam, hoggin, cobblestone and granite setts were extensively used, but these have mostly been replaced by asphalt or concrete laid on a compacted base course. Asphalt mixtures have been used in pavement construction since the beginning of the 20th century and are of two types: metalled (hard-surfaced) and unmetalled roads. Metalled roadways are made to sustain vehicular load and so are usually made on frequently used roads. Unmetalled roads, also known as gravel roads, are rough and can sustain less weight. Road surfaces are frequently marked to guide traffic.
Prestressed concrete is a form of concrete used in construction. It is substantially "prestressed" (compressed) during production, in a manner that strengthens it against tensile forces which will exist when in service.
In chemistry, efflorescence is the migration of a salt to the surface of a porous material, where it forms a coating. The essential process involves the dissolving of an internally held salt in water, or occasionally in another solvent. The water, with the salt now held in solution, migrates to the surface, then evaporates, leaving a coating of the salt.
Ferrocement or ferro-cement is a system of construction using reinforced mortar or plaster applied over an "armature" of metal mesh, woven, expanded metal, or metal-fibers, and closely spaced thin steel rods such as rebar. The metal commonly used is iron or some type of steel, and the mesh is made with wire with a diameter between 0.5 mm and 1 mm. The cement is typically a very rich mix of sand and cement in a 3:1 ratio; when used for making boards, no gravel is used, so that the material is not concrete.
Formwork is molds into which concrete or similar materials are either precast or cast-in-place. In the context of concrete construction, the falsework supports the shuttering molds. In specialty applications formwork may be permanently incorporated into the final structure, adding insulation or helping reinforce the finished structure.
Engineered Cementitious Composite (ECC), also called Strain Hardening Cement-based Composites (SHCC) or more popularly as bendable concrete, is an easily molded mortar-based composite reinforced with specially selected short random fibers, usually polymer fibers. Unlike regular concrete, ECC has a tensile strain capacity in the range of 3–7%, compared to 0.01% for ordinary portland cement (OPC) paste, mortar or concrete. ECC therefore acts more like a ductile metal material rather than a brittle glass material, leading to a wide variety of applications.
Concrete cover, in reinforced concrete, is the least distance between the surface of embedded reinforcement and the outer surface of the concrete. The concrete cover depth can be measured with a cover meter. The purpose of concrete cover is to protect the reinforcement from corrosion, fire, and other potential damage.
Ground granulated blast-furnace slag is obtained by quenching molten iron slag from a blast furnace in water or steam, to produce a glassy, granular product that is then dried and ground into a fine powder. Ground granulated blast furnace slag is a latent hydraulic binder forming calcium silicate hydrates (C-S-H) after contact with water. It is a strength-enhancing compound improving the durability of concrete. It is a component of metallurgic cement. Its main advantage is its slow release of hydration heat, allowing limitation of the temperature increase in massive concrete components and structures during cement setting and concrete curing, or to cast concrete during hot summer.
Biogenic sulfide corrosion is a bacterially mediated process of forming hydrogen sulfide gas and the subsequent conversion to sulfuric acid that attacks concrete and steel within wastewater environments. The hydrogen sulfide gas is biochemically oxidized in the presence of moisture to form sulfuric acid. The effect of sulfuric acid on concrete and steel surfaces exposed to severe wastewater environments can be devastating. In the USA alone, corrosion is causing sewer asset losses estimated at $14 billion per year. This cost is expected to increase as the aging infrastructure continues to fail.
Polymer concrete, also known as Epoxy Granite, is a type of concrete that uses a polymer to replace lime-type cements as a binder. In some cases the polymer is used in addition to Portland cement to form Polymer Cement Concrete (PCC) or Polymer Modified Concrete (PMC). Polymers in concrete have been overseen by Committee 548 of the American Concrete Institute since 1971.
A cement accelerator is an admixture for the use in concrete, mortar, rendering or screeds. The addition of an accelerator speeds the setting time and thus cure time starts earlier. This allows concrete to be placed in winter with reduced risk of frost damage. Concrete is damaged if it does not reach a strength of 500 pounds per square inch (3.4 MPa) before freezing.
Lunarcrete, also known as "mooncrete", an idea first proposed by Larry A. Beyer of the University of Pittsburgh in 1985, is a hypothetical construction aggregate, similar to concrete, formed from lunar regolith, that would reduce the construction costs of building on the Moon. AstroCrete is a more general concept also applicable for Mars.
Concrete is produced in a variety of compositions, finishes and performance characteristics to meet a wide range of needs.
Concrete degradation may have many different causes. Concrete is mostly damaged by the corrosion of reinforcement bars due to the carbonatation of hardened cement paste or chloride attack under wet conditions. Chemical damages are caused by the formation of expansive products produced by various chemical reactions, by aggressive chemical species present in groundwater and seawater, or by microorganisms. Other damaging processes can also involve calcium leaching by water infiltration and different physical phenomena initiating cracks formation and propagation. All these detrimental processes and damaging agents adversely affects the concrete mechanical strength and its durability.
Sulfur concrete, sometimes named thioconcrete or sulfurcrete, is a composite construction material, composed mainly of sulfur and aggregate. Cement and water, important compounds in normal concrete, are not part of sulfur concrete. The concrete is heated above the melting point of elemental sulfur at ca. 140 °C (284 °F) in a ratio of between 12% and 25% sulfur, the rest being aggregate.
Giatec Scientific Inc. is a Canadian-based company with headquarters located in Ottawa, Ontario. It is a developer and manufacturer of nondestructive testing quality control and condition assessment devices for the construction industry.
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.