Assessment of Pozzolanic Reactivity – An Attempt on Formulating a Pozzolanic Index

The use of Mineral Admixtures, such as fly ash, micro-silica, metakaolin, calcined clay pozzolana, volcanic ashes etc, as a blending component in OPC alters the hydration kinetics of the resultant blended cement. Due to the secondary hydration reactions of these admixtures with the available calcium hydroxide , their use results in a decreased  availability of the calcium hydroxide in the hydrated cement matrix , thus forming a much compacted, less pervious hydrated cement paste matrix on hydration. These aspects are however a function of the nature, fineness and pozzolanicity of the mineral admixtures / Supplementary Cementitious Materials (SCM).

At the authors laboratory substantial work has been carried out to assess the efficacy of the different blending components through evaluation of the hydrated OPC and the blended cement pastes (made with the blending materials) at different ages of hydration. The evaluations include analysis of free calcium hydroxide, mineralogy of the hydrated products, analysis of the % unhydrated blending materials in the hydrated cement pastes at different ages of hydration viz. 1,3, 7, 28,60, 100 days.

Based on these studies the authors evolved a Pozzolanic Index(Q_H).The details of these findings and the comparison of the Q _Hwith the conventional compressive strength based Hydraulic Index (H_in) were discussed in the paper put forward at the PAC RIM IV conference ^[5]. Summary of the findings is also presented in this paper.

The Q _H could be used to assess the efficacy / pozzolanic reactivity of blending materials and also for selection of the reactive size fraction as also for optimizing the fineness levels of the blending materials like fly ash for improved pozzolanic properties. The paper discusses these applications for fly ashes of different . The Paper was presented and Published at 11th ICCCC seminar Durban s.