T HIS WORK compares nano-structured rice husk ash (RHA) before grinding and nano-sized RHA after grinding in terms of the physical properties of cement and mortar performance. Blaine surface area, sieve analysis (45 µm mesh), water of consistency, expansion, initial and final setting time, and compressive strength (at 2, 7, 28, 60 and 90 d of curing) measurements were performed for 0, 2, 4, 6, 8 and 10% RHA replacement of cement by weight. RHA both before and after grinding enhanced the cement physical and mechanical properties, as well as the mortar performance in terms of the long-term aged strength, at a constant water/cement ratio and without the use of any type of super-plasticizer (SP). The enhancement became stable at all long-term ages for 10% replacement in the case of RHA before grinding and 4% replacement in the case of RHA after grinding. More considerable enhancements were observed with a high replacement percentage up to 10% nano-sized RHA due to the small size of its particles, which increased the pozzolanic reactivity and worked as a filler material to produce a denser mortar.

The objective of the study is developing a procedure for production and characterization of rice husk ash (RHA). The effects of rice husk (RH) amount, burning/cooling conditions combined with stirring on producing of RHA with amorphous silica, highest SiO2, lowest loss on ignition (LOI), uniform particle shape distribution and nano structured size have been studied. It is concluded that the best amount is 20 g RH in 125 ml evaporating dish Porcelain with burning for 2 h at temperature 700 °C combined with cooling three times during burning to produce RHA with amorphous silica, SiO2 90.78% and LOI 1.73%. On the other hand, cooling and stirring times affect the variation of nano structured size and particle shape distribution. However, no crystalline phases were found in RHA in all cases. Results proved that the Attritor ball mill was more suitable than vibration disk mill for pulverizing nano structured RHA with 50% of particle size (D50) lower than 45 mm and 99 % of particle size (D99) lower than 144 mm to nanosized RHA with D50 lower than 36 nm and D99 lower than 57 nm by grinding time 8.16 min to every 1 g RHA without changes in morphousity of silica.