1.      Materials and Experimental details1.1  Concrete materialsPortland composite cement conforming to MS 522-1:2007 from a single source was used as the binder. POFA used was collected from a local palm oil mill located in Nibong Tebal, Penang, Malaysia. The collected ashes were oven dried in the temperature of 105±50C for 24hours before then sieved passing 300µm sieve to remove larger particle as well as to reduce carbon content. The sieved POFA was then passed through the grinding process to produce finer ash particle. Saturated surface dry river sand passing through 600µm (Figure-1) sieve with a fineness modulus of 1.35 and specific gravity of 2.74 was used as fine aggregate. The larger particles of sand were removed to avoid it settle in a lightweight mix resulted the foam will collapse during mixing (Brady et al., 2001). A protein based foaming agent was used with the dilution ratio of 1:30 and was then aerated to produce a stable foam having a density of 65kg/m3 using a portafoam machine with the air pressure of 70-75Psi. Tap water complies with BS EN 1008, polycarboxylate based superplasticizer (SP) and silica fume were used as the chemical admixture with a fixed dosage of 1% and 5% by weight of the binder, respectively, to improve workability and strength of concrete.   1.2  Characterization of POFAPOFA used in this study was a by-product of incinerated palm oil biomass at the temperature exceeding 10000C. The high burning temperature can remove the POFA’s unburned carbon. The unburned carbon particles in POFA result in the increasing water requirement and dosage of superplasticizer (SP) because carbon particles absorb SP (Sata et al., 2007).After the sieving, drying and grinding process, the median particle size (d50) of ground POFA is 4.03µm, indicating that POFA has finer particle size than cement with d50 of 4.92µm (Figure-2). Based on the chemical composition (Table-1), POFA contains 62.16% of pozzolanic materials (SiO2 + Al2O3 + Fe2O3) and LOI reading at 5.66%, hence, the POFA can be classified as between Class C and Class F pozzolana (ASTM C618).  The X-ray diffraction (XRD) analysis of POFA showed that the major crystalline phase is ?-Quartz (SiO2) which having the highest peak and it was identified there a minor crystalline phase of Gehlenite (Ca2Al(AlSiO7)), as shown in Figure-3.    Figure-3: X-ray diffraction patterns of POFA 1.3  Mixture Proportions and castingTable-2 shows the proportions of the foamed concrete mixes where POFA used as a partial cement replacement in the level of 20% to 60% by the weight of the total binder, with the control of 100% cement content. The foamed concrete mixes having a target density of 900kg/m3 and a mix ratio of (1:1.5). The fine sand and binder (cement and POFA) are mixed in a concrete mixer until completely mixed. Water is added gradually together with superplasticizer to the homogeneous mix until the spread achieved 160 to 240mm). The actual mortar density is measured by weighing a 1-liter cup of mortar to calculate the amount of foam before added to the mix. The actual wet density of the resultant mix is checked which should be equal to the targeted wet density of 1033kg/m3. The mix then poured into the moulds. After casting for 24hrs, the specimens were removed from the moulds and wrapped with plastic cling (film) until the testing age. This curing regime is called as sealed curing which typically practices followed by industry of foamed concrete (Jones and McCarthy, 2005).   1.4  Assessment of POFA foamed concrete properties

Cubes specimens of 100 x 100 x 100mm were cast to test for the compressive strength of foamed concrete. The specimen was dried in an oven at temperature 105±5ºC for 24 hours prior to testing day until constant weight was achieved. The compressive strength was determined according to BS EN 12390-3 (BS, 2009). The prism specimens with the dimension of 100mm x 100mm x 500mm were cast for the flexural test. The test conducted according to BS EN 12390-5 (BS, 2009). Cylinder specimens of 45mm in diameter and 50mm in height were used for porosity test. Each test has been conducted at the ages of 7, 14, 28 and 56 days. For microstructure analysis, the foamed concrete specimens were analyzed by SEM and EDX analyses at the age of 28 days. The SEM analysis was performed to investigate the micro-pore characteristic while EDX to investigate their chemical composition. The sample for investigation was obtained by cutting the specimens into smaller pieces. 

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