Strength development of concrete with rice husk ash

Strength development of concrete with rice husk ash
This paper presents a study on the development of compressive strength up to 91 days of concretes with rice husk ash (RHA), in which residual R%HA from a rice paddy milling industry in Uruguay and RHA produced by controlled incineration from the USA were material for comparison. Two different replacement percentages of cement by RHA, 10% and20%, and three different water/cementicious material ratios (0.50, 0.40 and 0.32), were used. The results are compared with those of the concrete without RHA, with splitting tensile strength and air permeability. It is concluded that residual RHA provides a positive effect on the compressive stregth at early ages, but the long term behavior of the concretes with RHA produced by controlledincineration was more significant. Results of splitting tensile and air permeability reveal the significance of the filler and pozzolanic effect for the concretes with residual RHA and RHA produced by controlled incineration.
INTRODUCTION
In Uruguay, rice production has had a dramatic increase over the past 10 years, becoming the most important crop since 2001, the main use of ice husk is as fuel in therice paddy milling process. The use of this fuel generates a huge volume of ash. The rice husk ash has no useful application, is usually dumped into water streams and causes pollution and contamination of springs. As a result, the use of rice husk ash has aroused great interest in Uruguay.
Rice husk ash is a mineral admixture for concrete; the behavior of cementitious products varies with thesource of RHA. The basic aim of this study is to investigate the influence of residual RHA from the rice paddy milling industry in Uruguay and RHA produced by controlled incineration from the United States, used for comparison, on strength development of concretes at diferent gases.
EXPERIMENTAL PROGRAM
tHE FOLLOWING MATERIALS WERE USED IN THE PREPARATION OF THE CONCRETE SPECIMENS; FINE AGGREGATE(LOCAL NATURAL SAND) WITH MAXIMUM AGGREGATE SIZE OF 4.75 mm ; coarse aggregate (crushed granite) with maximum aggregate size of 12.5 mm; Portland Cement type I (normal portland cement); and superplasticizer based on a a sulfonated naphtalene formaldehyde condensate. Two sources of ash were considered; a residual RHA from the unique rice paddy milling industry in Uruguay (UY RHA) and homogeneousash produced by controlled incineration from United States (USA RHA), for comparison.
The residual RHA used for this work was a processed waste dry milled for the necesary time to obtain a median particle size of 8 um, a defined specific surface by nitrogenadsorption, and with the maximum activity index according to the AST C311-98b. This procedure of optimization is presented in.Table 1 shows thechemical composition, psysical properties and activity index of the cementitious materials. Chemical analysisi indicate that the two ashes are mainly composed of SiO2. The median particle size of the two ashes is the same, and the activity index are similar. X-ray diffraction analysis indicated that the USA RHA can be considered to be non crystalline RHA; but the UY RHA showed crystallinematerials, which were identified as cristobalite. A rapid analytical method to evaluate amorphous silica in the rice husk ashes according to has been used; silica in the rice husk ashes according to has been used; the porcentage of reactive silica contained in the USA RHA was 98.5% and in the UY RHA was 39.55 %.
A total of 15 concrete mixes were made, and three concretes without RHA for comparison. Thedifferent mix proportion by mass of the material used are given in Table 2 . The replacement the RHA presents less specific gravity than the cement Portland, and the paste content in volume was kept the same (35% cement paste content) for the different mix proportions. The values of the slump test are also indicated relation to weight of cementitious materials. Superplasticizer was used in very...