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The conversion of cement to concrete is a reaction that requires precise measuring. You need a very precise water-to-cement ratio. If more water is added, the concrete hardens faster but is not as strong. If less water is added, the concrete hardens slower but it will turn out much stronger (Vaughan). You also need to carefully measure the other components to be added. If a more stable concrete is required, it is an option to add other products such as gravel, sand, and other fine rocks. It is also an option to add special compounds as admixtures to change the properties of the concrete, as discussed earlier (Vaughan). When water is added to cement the compounds in the cement undergo a reaction called a hydration reaction. The hydration reaction is the reaction that occurs when water is added to cement to harden it. This water is called the water of hydration. All of the compounds are slightly different, so here is the reaction for Tricalcium silicate: Tricalcium silicate plus water yields calcium silicate tetrahydrate plus calcium hydroxide plus heat 2Ca3SiO5 + 7H2O à 3CaO(SiO2)2 · 4H2O + 3Ca(OH)2 + 173.6 kJ (Vaughan) These reactions cause the concrete to harden over time (they are ongoing). Calcium and hydroxide ions are released and crystallize, slowing the reaction down. A lot of heat is also released in the reaction, as shown by the 173.6 kJ released in the reaction. |
