Concrete Technology

👉 Typical phase composition levels in ordinary Portland cement (OPC)

               C3S/Alite/Tricalcium Silicate  ⟶  45-60%

               C2S/Belite/Dicalcium Silicate  ⟶ 15-30%

                C3A/ Tricalcium Aluminate     ⟶ 6-12%

                C4AF/Tetra Calcium Aluminoferrite  ⟶ 6-8%

👉 The crystal structure of different phases are:

            C3S/Alite/Tricalcium Silicate   ⟶ Irregular Structure, Several polymorphs

            C2S/Belite/Dicalcium Silicate  ⟶ Rounded Structures, Several polymorphs

             C3A/ Tricalcium Aluminate     ⟶ Cubic in pure form

             C4AF/Tetra Calcium Aluminoferrite  ⟶ Series of solid solution

👉The temperature at which the reaction occur to form to different phases of cement:

           Formation of C3S  ⟶ > 1250 °C

           Formation of C2S  ⟶  900 - 1200 °C

            Formation of C3A  ⟶ Cooling Stage

           Formation of C4AF  ⟶ Cooling Stage

👉 Lime saturation factor (LSF) is particularly important because it indicates the amount of free lime. (Too much free lime can cause Unsoundness of the cement).

                                             LSF = C/ (2.8S + 1.2 A + 0.65 F)

                         C, S, A and F are the % amounts of CaO, SiO2, Al2O3 and Fe2O3

       The range of LSF in between 92 - 98 %

👉C3S/Alite/Tricalcium Silicate

• Responsible for early strength development
• High reactive due to irregular structure, high heat of hydration

👉C2S/Belite/Dicalcium Silicate

• Less irregular structure than C3S ⟶Less reactivity
• Later strength