Abstract:
The utilization of by-products ; fly ash and waste sands (both fine and coarse particles) derived from paper drying process using a fluidized bed coal, as raw materials for concrete paving blocks and geopolymer concrete was studied. The work was divided into 2 parts: Portland cement-based blocks and geopolymer-based blocks. For the cement-based concrete, the replacement of Portland cement with fly ash (binder), and the ratio of binder to aggregate (mixed waste sand) were studied. The samples were formed by pressing method and cured for 1, 7, and 28 days. The results indicated that the optimum mix was 15 wt% replacement of cement with fly ash and 1:1 by weight of binder to aggregate ratio. It was found that the compressive strength of the samples achieved 45 MPa after 7 curing days which was qualitied Thai industrial standard (TIS) 827-2531. The selected mixture could be shaped into paving blocks using a block pressing machine. Meanwhile, the other part concerned one-part geopolymer-based concrete process using fly ash and alkali activator, consisted of sodium hydroxide (NaOH) and sodium silicate (Na2SiO3), as binders. The mixture with binder to aggregate ratio of 1:1 was prepared similar to the previous cement-based concrete work, but the water to binder ratio yielded 0.31 for pressing. The fly ash to alkali activator ratios and sodium silicate to sodium hydroxide ratio in alkali activator were studied. The experiments suggested that the specimen with 80 wt% fly ash and 20 wt% alkali activator (60 wt% NaOH: 40 wt% Na2SiO3) provided the compressive strength value of 5.45 MPa after 28 days. Such value was still lower thanTIS 827-2531. Thus, the geopolymer could not be used as paving blocks whatsoever. However, the value was good enough for hollow block products, according to TIS 58-2560.