Measurement of Pozzolanic Activity Index of Scoria, Pumice, and Rice Husk Ash as Potential Supplementary Cementitious Materials for Portland Cement

Hieronimi A Mboya,Karoli N Njau,Cecil K King’Ondu,Alex L Mrema

doi:10.1155/2017/6952645

Abstract

This work investigated the properties of scoria and pumice as supplementary cementitious materials (SCMs) for Portland cement and compared to those of rice husk ash (RHA). X-ray fluorescence, X-ray diffraction, and pozzolanic activity index (PAI) tests confirmed the suitability of these two materials as potential SCMs. Scoria and RHA samples achieved over 75% PAI at 7 days whereas pumice did this after 28 days. Initial and final mean setting times observed for the composite cement blended with these materials were 166 and 285 min, respectively. These setting times are longer than that of ordinary Portland cement but shorter compared to that of common Portland pozzolana cement. The ultimate mean compressive strengths achieved at 28 days of curing were 42.5, 44.8, and 43.0 MPa for scoria, pumice, and RHA, respectively, signifying that these materials are good SCMs. Higher fineness yielded higher ultimate mean strength. For instance, a scoria sample with a fineness of 575 m2/kg achieved the strength of 52.2 MPa after 28 days.

Highlights

Mortar is a workable paste prepared by adding water to a mixture of sand and binding materials like cement or lime
Pumice, and rice husk ash materials were successfully characterized according to ASTM C 618 criteria and tested to establish their potential as supplementary cementitious materials (SCMs)
Milled uncalcined samples of scoria and pumices and rice husk ash calcined in uncontrolled condition with specific surface area of 575, 506, and 611 m2/kg, respectively, showed high pozzolanic activity index (PAI) of 82, 70.7, and 87.8% at 7 days and 89.0, 85.5, and 88.9% at 28 days in that order

Summary

Introduction

Mortar is a workable paste prepared by adding water to a mixture of sand and binding materials like cement or lime. SCMs are pozzolans with a high amount of silica (SiO2) and alumina (Al2O3) As such, they react, in the presence of water, with calcium hydroxide (CH) at ordinary temperature to form calcium silicate hydrates (C-S-H) and calcium aluminosilicate hydrates (C-A-H). The influence of SCMs on the properties of blended cement in mortar and concrete such as setting times and early strength depends on the quantity and quality of the reactive SiO2 and Al2O3 present, particle size distribution (PSD), and the specific surface area. These three dictate the amounts of CH consumed by SCMs and the degree of C-S-H and C-A-H formation.

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