Replacement of condensed silica fume by rice husk ash for the production of high strength concrete

Rice husks were incinerated at temperatures below 750 degrees C, yielding an amorphous ash with a significant carbon content that was thereupon grinded for 18 hours in a laboratory ball mill in combination with a naphthalene-based superplasticizer. The grinding resulted in a structural collapse of the porous ash particles, dramatically reducing BET specific surface area. For the concrete specimens with PC contents between 260 and 400 kg/m(3) and significant RHA additions, compressive strength values were obtained exceeding 50 MPa at 7 days, 70 MPa at 28 days and 80 MPa at 180 days. The mortar specimens yielded compressive strength values exceeding at ages of 3, 7, 28 and 182 days respectively 20, 30, 45 and 50 MPa.