Ground granulated blast furnace slag
Encyclopedia
Ground-granulated blast-furnace slag (GGBS or GGBFS) is obtained by quenching molten iron slag
(a by-product of iron and steel-making) from a blast furnace
in water or steam, to produce a glassy, granular product that is then dried and ground into a fine powder.
and/or other pozzolan
ic materials. GGBS has been widely used in Europe, and increasingly in the United States and in Asia (particularly in Japan and Singapore
) for its superiority in concrete durability, extending the lifespan of buildings from fifty years to a hundred years.
Two major uses of GGBS are in the production of quality-improved slag cement, namely Portland Blastfurnace cement (PBFC) and high-slag blast-furnace cement (HSBFC), with GGBS content ranging typically from 30 to 70%; and in the production of ready-mixed
or site-batched durable concrete.
Concrete made with GGBS cement sets more slowly than concrete made with ordinary Portland cement, depending on the amount of GGBS in the cementitious material, but also continues to gain strength over a longer period in production conditions. This results in lower heat of hydration
and lower temperature rises, and makes avoiding cold joints easier, but may also affect construction schedules where quick setting is required.
Use of GGBS significantly reduces the risk of damages caused by alkali–silica reaction (ASR), provides higher resistance to chloride
ingress — reducing the risk of reinforcement corrosion — and provides higher resistance to attacks by sulfate
and other chemicals.
The use of GGBS cement in concrete in Ireland is covered in the new Irish concrete standard IS EN 206-1:2002. This standard establishes two categories of additions to concrete along with ordinary Portland cement: nearly inert additions (Type I) and pozzolanic or latent hydraulic additions (Type II). GGBS cement falls in to the latter category. As GGBS cement is slightly less expensive than Portland cement, concrete made with GGBS cement will be similarly priced to that made with ordinary Portland cement.
, including Spencer Dock
, are using GGBS in subsurface concrete for sulfate resistance.
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 abutment
s 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 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
.
, 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%.
s (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.
Slag
Slag is a partially vitreous by-product of smelting ore to separate the metal fraction from the unwanted fraction. It can usually be considered to be a mixture of metal oxides and silicon dioxide. However, slags can contain metal sulfides and metal atoms in the elemental form...
(a by-product of iron and steel-making) from a blast furnace
Blast furnace
A blast furnace is a type of metallurgical furnace used for smelting to produce industrial metals, generally iron.In a blast furnace, fuel and ore and flux are continuously supplied through the top of the furnace, while air is blown into the bottom of the chamber, so that the chemical reactions...
in water or steam, to produce a glassy, granular product that is then dried and ground into a fine powder.
Applications
GGBS is used to make durable concrete structures in combination with ordinary portland cementPortland cement
Portland cement is the most common type of cement in general use around the world because it is a basic ingredient of concrete, mortar, stucco and most non-specialty grout...
and/or other pozzolan
Pozzolan
A pozzolan is a material which, when combined with calcium hydroxide, exhibits cementitious properties. Pozzolans are commonly used as an addition to Portland cement concrete mixtures to increase the long-term strength and other material properties of Portland cement concrete, and in some cases...
ic materials. GGBS has been widely used in Europe, and increasingly in the United States and in Asia (particularly in Japan and Singapore
Singapore
Singapore , officially the Republic of Singapore, is a Southeast Asian city-state off the southern tip of the Malay Peninsula, north of the equator. An island country made up of 63 islands, it is separated from Malaysia by the Straits of Johor to its north and from Indonesia's Riau Islands by the...
) for its superiority in concrete durability, extending the lifespan of buildings from fifty years to a hundred years.
Two major uses of GGBS are in the production of quality-improved slag cement, namely Portland Blastfurnace cement (PBFC) and high-slag blast-furnace cement (HSBFC), with GGBS content ranging typically from 30 to 70%; and in the production of ready-mixed
Ready-mix concrete
Ready-mix concrete is a type of concrete that is manufactured in a factory or batching plant, according to a set recipe, and then delivered to a work site, by truck mounted transit mixers . This results in a precise mixture, allowing specialty concrete mixtures to be developed and implemented on...
or site-batched durable concrete.
Concrete made with GGBS cement sets more slowly than concrete made with ordinary Portland cement, depending on the amount of GGBS in the cementitious material, but also continues to gain strength over a longer period in production conditions. This results in lower heat of hydration
Mineral hydration
Mineral hydration is an inorganic chemical reaction where water is added to the crystal structure of a mineral, usually creating a new mineral, usually called a hydrate....
and lower temperature rises, and makes avoiding cold joints easier, but may also affect construction schedules where quick setting is required.
Use of GGBS significantly reduces the risk of damages caused by alkali–silica reaction (ASR), provides higher resistance to chloride
Chloride
The chloride ion is formed when the element chlorine, a halogen, picks up one electron to form an anion Cl−. The salts of hydrochloric acid HCl contain chloride ions and can also be called chlorides. The chloride ion, and its salts such as sodium chloride, are very soluble in water...
ingress — reducing the risk of reinforcement corrosion — and provides higher resistance to attacks by sulfate
Sulfate
In inorganic chemistry, a sulfate is a salt of sulfuric acid.-Chemical properties:...
and other chemicals.
How GGBS cement is used
GGBS cement is added to concrete in the concrete manufacturer's batching plant, along with Portland cement, aggregates and water. The normal ratios of aggregates and water to cementitious material in the mix remain unchanged. GGBS is used as a direct replacement for Portland cement, on a one-to-one basis by weight. Replacement levels for GGBS vary from 30% to up to 85%. Typically 40 to 50% is used in most instances.The use of GGBS cement in concrete in Ireland is covered in the new Irish concrete standard IS EN 206-1:2002. This standard establishes two categories of additions to concrete along with ordinary Portland cement: nearly inert additions (Type I) and pozzolanic or latent hydraulic additions (Type II). GGBS cement falls in to the latter category. As GGBS cement is slightly less expensive than Portland cement, concrete made with GGBS cement will be similarly priced to that made with ordinary Portland cement.
Durability
GGBS cement is routinely specified in concrete to provide protection against both sulphate 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 DocklandsDublin Docklands
Dublin Docklands is the area of the city of Dublin, Ireland, on both sides of the River Liffey, roughly from Talbot Memorial Bridge eastwards to the Point Depot.It is currently undergoing a large amount of development.-Projects:...
, including Spencer Dock
Spencer Dock
Spencer Dock is a location within North Wall, Dublin, Ireland. The dockland area was originally part of the end of the Royal Canal, which still reaches the River Liffey here...
, are using GGBS in subsurface concrete for sulfate resistance.
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
National Roads Authority
The National Roads Authority is a state body in the Republic of Ireland, responsible for the national road network. The NRA was established as part of the Roads Act 1993 and commenced operations on 23 December 1993 in accordance with S.I. 407 of 1993.County councils remain responsible for local...
projects in Ireland GGBS is now specified in structural concrete for bridge piers and abutment
Abutment
An abutment is, generally, the point where two structures or objects meet. This word comes from the verb abut, which means adjoin or having common boundary. An abutment is an engineering term that describes a structure located at the ends of a bridge, where the bridge slab adjoins the approaching...
s 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
Stainless steel
In metallurgy, stainless steel, also known as inox steel or inox from French "inoxydable", is defined as a steel alloy with a minimum of 10.5 or 11% chromium content by mass....
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 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
Jack Lynch Tunnel
The Jack Lynch Tunnel is an immersed tube tunnel and an integral part of the N25 southern ring road of Cork in Ireland. It is named after former Taoiseach, Jack Lynch, a native of Cork....
in Cork
Cork (city)
Cork is the second largest city in the Republic of Ireland and the island of Ireland's third most populous city. It is the principal city and administrative centre of County Cork and the largest city in the province of Munster. Cork has a population of 119,418, while the addition of the suburban...
.
Appearance
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 colour for exposed fair-faced concrete finishes, at no extra cost. To achieve a lighter colour finish, GGBS is usually specified at between 50% to 70% replacement levels, 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 efflorescenceEfflorescence
In chemistry, efflorescence is the loss of water of crystallization from a hydrated or solvated salt to the atmosphere on exposure to air.-Examples:...
, the staining of concrete surfaces by calcium carbonate
Calcium carbonate
Calcium carbonate is a chemical compound with the formula CaCO3. It is a common substance found in rocks in all parts of the world, and is the main component of shells of marine organisms, snails, coal balls, pearls, and eggshells. Calcium carbonate is the active ingredient in agricultural lime,...
deposits. Due to its much lower lime
Lime (mineral)
Lime is a general term for calcium-containing inorganic materials, in which carbonates, oxides and hydroxides predominate. Strictly speaking, lime is calcium oxide or calcium hydroxide. It is also the name for a single mineral of the CaO composition, occurring very rarely...
content and lower permeability, GGBS is effective in preventing efflorescence when used at replacement levels of 50% to 60%.
Strength
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 hydrateCalcium silicate hydrate
Calcium Silicate Hydrate is the main product of the hydration of Portland cement and is primarily responsible for the strength in cement based materials.-Preparation:...
s (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.