Evaluation Of Mechanical Properties Of Palm Oil Fuel Ash (pofa) Blended – Granite - Gravel Concrete

2.7 Properties of Cement
2.7.1 Physical properties of Cement
      According to Kirgiz, (2016) an ordinary Portland cement has a specific surface area of 0.325m2/g with a density of 3.11 g/cm3. The particle size distributions are in the range of 1.2 to 5.0 μm (Bahurudeen, 2015). The specific gravity of the cement mortar with OPC is 3.16 with a fineness and soundness value of 3.10 m2/kg and 1.61mm. It was also found that the cement mortars with OPC have a porosity of 12.21% and water absorption of 6.20% (Lertwattanaruk and Suntijitto, 2015).
2.7.2    Mechanical properties of Cement
      A cement paste has a compressive strength value of 41.5MPa with a modulus of rupture of 11MPa. Other than that it has modulus of elasticity of 1270MPa and toughness value of 340 J/m2. The value of bulk density of the cement paste is 1.85g/cm3 with water absorption and porosity value of 16% and 29% (Brasileiro et al., 2015). Results from previous research has recorded that the compressive and flexural strength of cement is 47 MPa and 9.23 MPa after 28 days while the drying shrinkage of cement at 28 days is 0.076% (Zheng, 2015).
2.7.3    Chemical Properties of Cement
      According to Aprianti, (2016), OPC contained high lime content (CaO) which is around 61.50% to 65.4% followed by silica (SiO4) in range 20.40% to 21.98%. It is followed by alumina (Al2O3) with range 3.68% to 5.27%. Iron (Fe2O3) and magnesia (MgO) with range content of 2.27% to 4.19% and 1.20% to 4.80% each.
2.7.4    Cement hydration
      Cement hydration is a process when cement is mixed with water and become a cement paste. It was a complex chemical reaction and these process cannot be reversed. This reaction is influenced by several factors, both internal and external factors. An examples of factors that influenced the hydration process is temperatures and the superplasticizer presence in the mixture. These factor are important because it plays an important role in hydration process and significantly influence the characteristics time. Porosity and pore size of the produced cement based materials also important for hydration process because it influences the final strength and durability of the concrete (Pop, and Ardelean, 2015). There are 5 stages during the hydration process. The stage is namely as initial reaction period, induction period, acceleration period, deceleration period and slow reaction period. The peaks process occur twice which is at initial reaction period and at the end of acceleration period and both of them known as first peak and second peak. The first peak is important for production of calcium sulfoaluminate hydrate (AFt) that formed from ion dissolution between C3A and calcium sulphate. The second peak is producing C-S-H and calcium hydroxide (CH) from the C3S hydration that happen during the stage (Han et al., 2015).