Comparative Study On Effect Of Particle Size And Silica Content Of Rice Husk Ash On Properties Of Self-Compacting Mortar Systems

Abstract

This research work reports the manufacturing procedure of local Rice Husk Ash (RHA), its use in Self-Compacting Mortar (SCM) systems and the comparison of locally made RHA with another source to study the effect of particle size and silica content of RHA on the properties of SCM systems. Local RHA was used in SCM systems in two states i-e as made (without milling, D50= 84 microns, SiO2= 88.5%) and reduced particle size (milled RHA, D50=21 microns, SiO2= 88.5%) while RHA for comparison was brought in from Germany courtesy Technical University Freiberg (RHAG, D50=81 microns, SiO2= 94.5%). All three RHAs were found to be amorphous and have been used in SCM systems to study the effect of particle size and SiO2 content of RHA on fresh and hardened properties of SCM systems. Four partial replacement levels 0, 10, 15, 20% with respect to cement weight and two w/b ratio 0.4 and 0.5 were used. Addition of RHAP-21 and RHAG-81 in SCMs showed increased strength at 28 days of age, better early age volumetric stability and delayed hydration kinetics as compared to control mix with larger particle size showing better volumetric stability delayed hydration peaks. RHAP-84 however showed lower strength values compared to control mix and RHAP-21 as well as RHAG-81 however showed better volumetric stability then its counterparts. For RHAP-21 and RHAG-81, 15% cement replacement showed best strength results of SCMs while for RHAP-84 it was observed that increasing the amount of ash in SCM systems decreased the strength. It appears that larger particle size make the systems more viscous, increases flow times and SP demand to overcome internal friction and entrains more air compared to finer particle size with same w/b ratio and RHA content. SiO2 reactivity has been determined in terms of electrical conductivity drop and XRD on hardened paste samples. RHAP-21 and RHAG-81 gave almost same strength level, though other properties are quite different, confirming indirectly the lower particle size with lower SiO2 may be considered equivalent in performance to bigger particle size and higher SiO2 of RHA in self-compacting systems and makes the role of SiO2 prominent in the absence of fine size of particles. This study confirms that the role of SiO2 in strength gain is 2 more important than the particle. RHAP-84 and RHAG-81 have comparable particle sizes but different silica content and the performance of RHAG-81 is comparable to control mix in terms of strength gain which confirms the role of silica content. Locally made RHA had to be milled in order for it to be made usable in SCM systems as the performance of local RHA when used without any processing is poor. It was also observed that RHAG-81 was useable without any post processing