| What is Portland Cement? | | | | calcium silicate hydrate, C-S-H and 2) calcium |
| Portland cement (PC) is the principal binder that, upon | | | | hydroxide |
| hydration and setting, holds aggregates (coarse and | | | | Calcium Silicate Hydrate (C-S-H) is insoluble in water. It |
| fine) together in concrete. It has the ability to stand in | | | | gives the title hydraulic to set PC's ability to stand in |
| water and increase its strength over time. This ability | | | | water without any detriment. Calcium hydroxide is |
| elicits the term hydraulic cement for this type of | | | | soluble in water and leaches out of set concrete and in |
| cement. | | | | a two step approach first, the solution is drawn to the |
| What is the Composition of PC? | | | | exterior wall of the structure and secondly, react with |
| PC is a manufactured product formed within narrow | | | | carbon dioxide of the atmosphere to form chalk, the |
| confines of specific elements and subjected to heat | | | | white, efflorescence salt found on concrete walls. |
| treatment to form a semi-finished product called clinker. | | | | MINERAL ADMIXTURE - Mineral admixtures used in |
| Raw materials used include: Limestone, Shale, Iron Ore | | | | concrete formulations contain oxides of silica and other |
| and Sand. | | | | oxides that are found in Portland cement. Examples of |
| The principal elemental ingredients in the raw materials | | | | mineral admixtures include fly ash, silica fume and |
| are:o Calcium Oxide (CaO)o Silicon (SiO2)o Aluminum | | | | volcanic ash. |
| Oxide (Al2O3)o Iron Oxide (Fe2O3) in addition to other | | | | Mineral admixtures used in concrete may be referred |
| elemental oxides. | | | | to as Pozzolans, or materials that won't harden in |
| It is possible sometimes to have all these elemental | | | | water but in the presence of lime, react and harden to |
| oxides in some limestones. Where the principal source, | | | | form a stone-like mass. |
| limestone, is deficient in any of the elemental oxides | | | | One important use of mineral admixtures in concrete is |
| then the other ingredients are added in the right | | | | the ability of the silica component to react with the |
| proportion in preparation for the manufacturing | | | | soluble calcium hydroxide formed in the hydrating |
| process. | | | | cement to form an insoluble calcium silicate hydrate |
| The latter process comprise of three phases: | | | | thus helping to form a dense, compact concrete |
| 1. Grinding the materials into a powder form | | | | cement paste. |
| 2. Heating the powdered material in a kiln up to about | | | | Concrete formulated with mineral admixtures are not |
| 2700°F | | | | likely to form efflorescence salts. The use of mineral |
| 3. Grinding the clinker formed with gypsum to form PC | | | | admixtures in concrete helps resist sulfate attack and |
| When PC is mixed with water either to form a | | | | alkali-silica reactivity. In the fresh concrete the |
| cement paste or concrete, in a process called | | | | presence of mineral admixtures often improve the |
| hydration, a chemical reaction takes place and for | | | | workability of the mix. |
| simplicity sake two principal products are formed: 1) | | | | |