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

CHAPTER TWO
LITERATURE REVIEW
2.1 Properties of concrete with POFA
2.1.1 Physical properties
      For the physical characteristics of POFA, it is easily affected by the operating system in the factory. Based on the previous studies, it is observed that the temperature of the incinerator that the industries controlled in the combustion of the palm oil wastes are between 800-1000°C and the duration of the operation is different. Furthermore, the physical properties of POFA are greyish in colour and it changes into darker colour as the result of the increase of the proportion of unburned carbon (Altwair et al., 2013; Noorvand, 2013; Aprianti et al., 2015).                                 POFA has a varying specific gravity; however, its value never exceeded 3.0. The specific gravity of POFA would be increased after the grinding process because of a decrease of porosity. An increase of POFA replacement level would decrease the workability of concrete composites (Khankhaje et al., 2016). Drying shrinkage of POFA concrete has the same value as OPC concrete when 10% of OPC is replaced by POFA. However, the shrinkage increased slightly at 28 days because of the increasing of unground POFA percentage as a cement replacement (Khankhaje et al., 2016). Also, the water requirement for concrete with POFA is higher compared to normal concrete. So, the production of concrete with POFA will require more water (Khankhaje et al., 2016). The workability and density of the concrete also tends to decrease with the increase of POFA replacement (Awal, and Shehu, 2013; Ranjbar et al., 2014).
2.1.2 Chemical Properties of POFA
        The amount of the unburned carbon causes the chemical constituents existing in POFA to vary. The range of the amount of the chemical composition present in the POFA is displayed in Table2.1. In addition, Table2.1 also pictures the comparison of the chemical composition of the ordinary Portland cement (OPC) with the POFA. From the statement by Aprianti et al. (2015), the authors urged that the source of materials, combustion process and the efficiency of the palm oil industry are the factors that prompt the difference in the amount of the chemical components in the ash. In addition, the arising issue in order to have a promising outcome by using POFA as SCM is the inconsistent replacement ratio suggested by some researchers. For instance, as compared with the result obtained by researchers, Altwair et al. (2011) shown in Table2.2 and Zeyad et al. (2016), the performance of the concrete using same substitution ratio of POFA as the SCM displayed different performance. The former researcher suggested that POFA replacement percentage should be limited as 20 % while the latter repulsed the statement as he achieved better performance of POFA substituted concrete with high amount of POFA percentage.