GGBFS
Source: | Author:Wikipedia | Published time :2024-09-02 | 90 times view: | Share:
Ground granulated blast-furnace slag (GGBS) is a fine powder obtained from quenching molten iron slag in water or steam, then drying and grinding it. GGBS forms calcium silicate hydrates upon contact with water, enhancing concrete's durability and strength. It is commonly used in Europe, the USA, and Asia, particularly in Japan and Singapore, for its superior durability in concrete structures. GGBS reduces the risk of damage from alkali–silica reaction, chloride ingress, and sulfate attacks, and it also lowers the heat of hydration, making it suitable for large concrete pours. Additionally, GGBS contributes to sustainability by being a by-product of steel manufacturing, which is recognized by LEED and other environmental assessment methods.

Durability

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GGBS cement is routinely specified in concrete to provide protection against both sulfate attack and chloride attack. GGBS has now effectively replaced sulfate-resisting Portland cement (SRPC) on the market for sulfate resistance because of its superior performance and greatly reduced cost compared to SRPC. Most projects in Dublin's docklands, including Spencer Dock, are using GGBS in subsurface concrete for sulfate resistance.

Bulk Electrical Resistivity is a test method that can measure the resistivity of concrete samples. (ASTM 1876–19) The higher electrical resistivity can be an indication of higher ion transfer resistivity and thus higher durability. By replacing up to 50% GGBS in concrete, researchers have shown that some durability properties can be significantly improved.[2]

To protect against chloride attack, GGBS is used at a replacement level of 50% in concrete. Instances of chloride attack occur in reinforced concrete in marine environments and in road bridges where the concrete is exposed to splashing from road de-icing salts. In most NRA projects in Ireland GGBS is now specified in structural concrete for bridge piers and abutments for protection against chloride attack. The use of GGBS in such instances will increase the life of the structure by up to 50% had only Portland cement been used, and precludes the need for more expensive stainless steel reinforcing.

GGBS is also routinely used to limit the temperature rise in large concrete pours. The more gradual hydration of GGBS cement generates both lower temperature peak and less total overall heat than Portland cement. This reduces thermal gradients in the concrete, which prevents the occurrence of microcracking which can weaken the concrete and reduce its durability, and was used for this purpose in the construction of the Jack Lynch Tunnel in Cork.

Appearance

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In contrast to the stony grey of concrete made with Portland cement, the near-white color of GGBS cement permits architects to achieve a lighter color for exposed fair-faced concrete finishes, at no extra cost. To achieve a lighter color finish, GGBS is usually specified at replacement levels of between 50% and 70%, although levels as high as 85% can be used. GGBS cement also produces a smoother, more defect-free surface, due to the fineness of the GGBS particles. Dirt does not adhere to GGBS concrete as easily as concrete made with Portland cement, reducing maintenance costs. GGBS cement prevents the occurrence of efflorescence, the staining of concrete surfaces by calcium carbonate deposits. Due to its much lower lime content and lower permeability, GGBS is effective in preventing efflorescence when used at replacement levels of 50%-to-60%.

Strength

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Concrete containing GGBS cement has a higher ultimate strength than concrete made with Portland cement. It has a higher proportion of the strength-enhancing calcium silicate hydrates (CSH) than concrete made with Portland cement only, and a reduced content of free lime, which does not contribute to concrete strength. Concrete made with GGBS continues to gain strength over time, and has been shown to double its 28-day strength over periods of 10 to 12 years.[citation needed]