2. Experimental 2.1. Materials (1)

2. Experimental 2.1. Materials (1) Chemical composition. Portland cement type I (PC), pulverized coal combustion (PCC) fly ash from Mae Moh Power Station, fluidized bed coal combustion (FBC) fly ash from COCO Power Plant, and river sand were used. The chemical composition is listed in Table 1. The amounts of Si O2, Al2O3, and Fe2O3 of PCC and FBC fly ashes are 81.54wt% and 75.92wt%, respectively. The SO3 contents of PCC and FBC fly ashes are less than 5wt%, and the loss on ignition (LOI) is less than the limit of 6wt%. It is well estab-lished that classifying and grinding do not affect the chemi-cal composition of fly ash [2, 4-7]. The main composition of river sand is Si O2 with 91.3wt% [8]. (2) X-ray diffraction patterns. Fig. 1 shows XRD patterns of PCC and FBC fly ashes. PCC fly ash consists mainly of a glassy matrix with a relatively small amount of crystalline phases, such as quartz, mullite, and anhydrite. FBC fly ash, however, contains a higher percentage of crystalline materi-als, and the majority can be identified as quartz and anhy-drite. This suggests that PCC fly ash should be slightly more reactive than FBC fly ash. (3) Median particle size and surface area. Each type of fly ash was classified to three different finenesses, viz., coarse original, medium and fine fly ash. The median particle size (d50) and surface area of all fly ashes are shown in Table 2. Particle size distribution was performed using a laser parti-cle size analyser. The median particle size of PC is 14.1 μm which is the same as that of coarse FBC fly ash, while that of coarse PCC fly ash is slightly coarser at 18.7 μm. The median particle sizes of classified medium PCC fly ash and medium FBC fly ash are 6.4 and 7.0 μm, respectively. The median particle sizes of fine PCC fly ash and fine FBC fly ash are 2.2 and 2.4 μm, respectively. To study the packing effect, an inert material, i.e. river sand, was used to compare the results. The median particle size of coarse original river sand is quite large at 71.6 μm, whereas those of ground me-dium and fine sand are similar to those of fly ash at 7.0 and 3.3 μm.