Cement Overview and History

Cement Overview

• Cement is a crystalline compound primarily composed of calcium silicates and other calcium compounds. It has hydraulic properties.

Cement History

• Lime and clay have been used as cementing materials for centuries.
• Romans are credited with significant developments in hydraulic cement, particularly employing pozzolan-lime cement, using volcanic ash from Mt. Vesuvius mixed with lime.
• The Pantheon in Rome is a prominent example of Roman cement use.
• Joseph Aspdin, from England, invented Portland cement in 1824.

Cement Types

• Hydraulic cements set and harden under or with excess water through hydration of mineral compounds.

• Two main types:

• Pozzolanic: Siliceous materials that develop hydraulic properties when interacting with hydrated lime (Ca(OH)2).

• Hydraulic lime: Commonly used in specialized mortars, derived from calcined clay-rich limestones.

• Natural cements (sometimes mistakenly called Roman cements): Made primarily from argillaceous (clayey) limestones or interbedded limestone and clay. They proved inferior to Portland cements, leading to their diminished use.

Portland Cement

• Artificial cement, created by combining clinker with gypsum in a 95:5 ratio.
• Portland-limestone cements: Portland cement blended with ground limestone as a filler, to reduce costs.
• Blended cements: Mixtures of Portland cement and one or more supplementary cementitious materials (SCM) like pozzolanic additives.
• Pozzolan-lime cements: Similar to original Roman cements, primarily employing pozzolans and lime. Relatively little is made in the USA.
• Masonry cements: Portland cement with added materials for enhanced plasticity.
• Aluminous cements: Employ limestone and bauxite, suitable for refractory applications needing fast hardening, but more expensive than Portland cement. (Only one production facility in the US)

Raw Materials for Cement Production

• Fundamental chemical compounds for cement clinker:

• Lime (CaO)

• Silica (SiO2)

• Alumina (Al2O3)

• Iron Oxide (Fe2O3)

• Raw materials sources:

• Limestone, marl, chalk (calcium carbonate sources)

• Clay, shale, sand, iron ore, bauxite(silicates), diaspore, diatomite, staurolite, loess, silt, sandstone, volcanic ash

• Fly ash, bottom ash, foundry sand, metallurgical slags (waste material substitutes).

Clinker Composition in Portland Cement

• Key compounds in Type I Portland cement:

• Tricalcium silicate (C3S): 45%

• Dicalcium silicate (C2S) :27%

• Tricalcium aluminate (C3A): 11%

• Tetracalcium aluminoferrite (C4AF): 8%

• Gypsum is added to regulate the setting time of concrete.

Limestone Sources

• Limestone originates through biological processes involving shells and skeletons of organisms.
• It forms in massive deposits over millions of years.
• Contains calcium carbonate (CaCO3) and smaller amounts of magnesium carbonate.
• Critical material in cement production. The ideal limestone would have 77 - 78% CaCO3, 14% SiO2 and 1.75% FeO3

Argillaceous Materials

• Clay and shale are sources of alumina (Al2O3) and silica (SiO2)
• Other sources of silica and alumina: Loess, silt, sandstone, volcanic ash, diaspore and diatomite.
• These materials often occur interbedded with limestone deposits, in sedimentary rock layers deposited by water.

Cement Marketing

• Wide distribution of production plants helps lower costs to customers.
• Other important factors dominating the market include:
• Delivered costs
• Product quality and consistency
• Technical assistance
• Sales relationships with companies

Factors Affecting Cement Consumption

• Economic growth
• Private and governmental investment.
• Population growth

Cement Mining Methods

• Limestone: Extracted through bench mining (explosives), with front-end loaders moving ore to haul trucks for transport to the crusher.
• Marl and chalk: Often mined without explosives.
• Underground mining (less common in the U.S. for limestone): Uses different methods (room and pillar).

Cement Processing

• Cement production has several key processing steps:
• Quarrying and blending of raw materials
• Proportioning and fine grinding of materials
• Kiln system (preheating, cooling, clinker storage)
• Final grinding and shipping

Cement Uses

• Concrete and mortar fabrication are the main uses.
• Modern Applications include:
• Buildings (floors, beams, columns, etc.)
• Transportation (roads, bridges, tunnels)
• Water infrastructure (pipes, canals, dams)
• Civil engineering (piers, docks, retaining walls)
• Agriculture and other industries.

Cement Substitutes and Production

• Competitors in the construction industry:
• Alumina
• Asphalt
• Clay brick
• Fiberglass
• Glass
• Steel
• Stone/wood
• Alternatives to Portland cement:
• Fly ash and ground granulated furnace slags (partial substitutes).
• Worldwide cement production and capacity data provided: Yearly clinker capacity, in various countries, and overall global totals (metric tons)

Cement Resources and Availability

• Cement raw materials (especially limestone) are abundant and widespread.
• Individual company reserves can be exhausted. However, shortages at a global level are not anticipated in the future because of the widespread availability of raw materials.