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

2.1.3 Mechanical properties of POFA
      According to Khankhaje et al. (2016), the compressive strength of concrete decrease with the increase in percentage replacement of POFA and it depends on the finest of the POFA particles. However, for tensile strength, it shows an improvement where a specimen with 0.4 POFA/cement ratio has a tensile value of approximately 3.52 MPa. This value is 9% higher compared to control mix and 16% higher than a specimen with 1.2 POFA/cement ratio. For modulus of elasticity (MOE), the specimen mixed with POFA either fine or coarse is in range of 25.0 to 28.0 GPa. The value is quite similar to OPC concrete which is 27.5GPa (Khankhaje et al., 2016). However, after POFA replaced cement by 50%, the compressive and tensile strength drop and recorded lower value than normal concrete (Khankhaje et al., 2016). Other than that, slow pozzolanic reactivity of POFA would decrease the early strength of concrete due to low C3S content that is only presence in cement (Momeen, et al., 2015).                        The Re-incinerated POFA (RePOFA) and POFA show similarity in their particle size though the RePOFA has undergone thermal treatment. From the result obtained by Altwair et al. (2011), the particles of the treated POFA showed no agglomeratio and it was supported by figure 2.1 which shows the cumulative passing percentage of the treated and untreated POFA particles. Therefore, the RePOFA which shows no negative effect in term of the particles size if compared with POFA and contributes to the distribution of a higher amount of required SiO2 provides a certain image that the RePOFA can act as a better SCM compared to POFA.