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

2.4 Workability of Concrete with Replaced POFA
      According to Asrah et al. (2015), the treated POFA with bigger size of particles will suffer from a reduction of its workability. From the research, the replacement of POFA with an increasing number of bigger particles leads to a lower flow ability of the fresh mortar. However, when the particles size of the POFA was ground to fine or ultrafine, a better workability of the mortar was observed. The rationality is that the fine particles of the POFA show low porosity and this will avoid the excess absorption of the water added while mixing the mortar. Besides, it is agreed by Megat-Johari et al. (2012) that the POFA with fine particles provide a lubrication effect to the mix and this result good flow ability of the fresh mortar.                                        Furthermore, the untreated POFA also causes the reduction of the workability of the concrete as the substitute percentage is increasing. The statement is proved by the experiment done by Oyejobi et al. (2016) as the author found that the height of the slump was reduced when the replacement of POFA was from 10 % to 30 %. The RePOFA with thermal treated will not have these consequences because of the lower LOI value for the RePOFA. According to Chandara et al. (2010), the POFA with a high value of LOI will absorb more water and this will cause the diminishing of the flow ability. The reason for the treated POFA assists in the flow ability of the fresh mortar or concrete is that the extra paste volume resulted by RePOFA enhances the packing effect between the aggregates. The paste acts as a filler to fill into the space present between the particles and this provides a coating to the particles which help in developing their flow ability characteristic (Alsubari et al., 2016). The Figure 2.5 shows the increasing workability with the increasing POFA content.