Concrete

• High strength • Good acoustics • Takes time to set allowing you to play with its form

Water Cement: • Provides strength to harden concrete. • Fills voids between the aggregate, providing lubrications of fresh concrete as well as water-tightness in the hardened concrete. Fine aggregate (sand) Coarse aggregate: • Provide a cheap fill for the cementing material. • Provide a mass of particles suitable for resisting the action of applied loads, abrasion and percolation. • Reduces volume change resulting from the setting process as well as moisture changes in cement paste. Air

• When you mix cement and water together you produce a paste. • You then mix this paste with your fine aggregate to form mortar. • You then mix the mortar with the coarse aggregate to produce concrete.

• Hydraulic cement prevents water and leaks in concrete. • It is a type of cement similar to mortar, that sets extremely fast and gardens after it has been mixed with water.

Limestone/chalk: • Lime (CaO) Clay / shale: • Silica (SiO2) • Alumina (Al2O3) • Iron oxide (Fe2O3) • Gypsum (CaSO4)

• Grind the raw materials. • Burn in a large rotary kiln at 1450oC to form balls known as clinker. • Cool the clinker and grind them to a fine powder. • Add gypsum. During burning the raw materials are firstly dried out, and then calcination occurs before the materials are finally sintered (a process where clay and limestone combine).

70%

Fuelling of kilns: • Traditionally use fossil shells leading to direct CO2 emissions. Calcination of raw materials: • During calcination, CO2 is released due to the decomposition of calcium carbonate (CaCO3) into lime (CaO). • CaCO3 + heat -> CaO + CO2 Consumption of natural resources Research has introduced a wide range of sustainable replacements such as: • Nanomaterials • Bacteria • Alternative sources of fuel

• Tricalcium Silicate (C3S) • Dicalcium Silicate (C2S) • Tricalcium Aluminate (C3A) • Calcium Aluminium Ferrite (C4AF) • Gypsum (CaSO4)

• Known as alite. • Responsible for the rapid hardening and early strength gain of cement. • Reaction generates significant heat so has limited presence in low heat Portland cements.

• Known as belite. • Responsible for the late strength gain of cement.

• Has a large influence on cement properties. • Rarely present in excess of 15%.

• Provides Portland cement with its characteristic colour.

• Slows down the hydration of C3A to prevent cement early set.

The hydration causes it to set and harden. Cement + Water -> Calcium hydroxide + Hydration products (gel) Hydration can occur through two mechanisms: • In solution - reactants dissolve to produce ions in solution which combine to form solid products. • In solid state - reactions take place directly at the surface without entering solution.

• Alite + Water -> Calcium hydroxide + Calcium silicate hydrate (C-S-H gel) • Belite + Water -> Calcium hydroxide + Calcium silicate hydrate (C-S-H gel) • Tricalcium Aluminate + Water + (Calcium hydroxide) -> Calcium Aluminate hydrate (C-A-H gel) • Tricalcium Aluminate + Water + Gypsum + (Calcium hydroxide) -> Ettringite (gel) • Calcium Alumino Ferrite + Calcium hydroxide + Gypsum + Water -> “solid solution of sulfoferrite and sulfoalluminate”

• Formed mainly from alite hydration. • Makes paste highly alkaline.

• Main source of concrete strength. • Dashes indicate there is no strict ratio of the compounds which make up the gel.

• Produces ‘flash set’. • Therefore we add gypsum in order to slow the rate of reaction. • This produces a gel known as ettringite.

• Ettringite gel forms on the surface of tricalcium aluminate particle, causing the pressure to increase. • This causes the Ettringite layer to burst, exposing part of the tricalcium aluminate particle. • Therefore, more Ettringite is able to form. • This process repeats until the tricalcium aluminate particle is fully immersed in paste.

• Consists of rod-like crystals. • Compound of water, Gypsum and tricalcium aluminate.

• Occurs in later stage of hydration, replacing Ettringite. • Compound of water, Gypsum and tricalcium aluminate.

• Tricalcium and dicalcium sulfate are the main compounds responsible for strength. • Tricalcium sulfate is the compound responsible for the early strength of the cement.