Abstract
A very simple method based on electrical conductivity and pH measurements was proposed for assessing reactivity of pozzolans. Calcium hydroxide:pozzolan water suspensions were monitored by means of measurements of electrical conductivity and pH values. In these suspensions, Ca(OH)2 in solid state was initially present, being them, thus, saturated in this reagent. Three testing temperatures were selected (40, 50 and 60 °C). In the experiments carried out, calcium hydroxide was suspended in deionized water for yielding a lime saturated suspension. The addition of siliceous pozzolan (two types of rice husk ash RHA and two types of densified silica fume DSF were tested) to the saturated lime suspension can produce the unsaturation of the system, depending on the testing time, testing temperature and reactivity of pozzolan. When unsaturation was reached, the loss of electrical conductivity was higher than 30% and the variation of pH was higher than 0.15 units. These threshold values were selected for characterizing the reactivity of pozzolans by means of a proposed template, classifying the pozzolan in three different reactivity levels.
Highlights
A very simple method based on electrical conductivity and pH measurements was proposed for assessing reactivity of pozzolans
Several waste materials have been assessed as supplementary cementitious material (SCM) in blended cements, contributing on the reduction of landfilling areas and on diminishing the CO2 emission associated to the production of Portland cement clinker that is responsible for about 5–8% of the global CO2 emission (3)
A very simple method based on electrical conductivity and pH measurements of Calcium Hydroxide (CH):pozzolan suspensions was proposed for assessing reactivity of pozzolans
Summary
Calcium hydroxide (95% purity) supplied by Panreac S.A. was used to prepare CH suspensions. Plastic film, Erlenmeyer flasks of 100 mL were used for the analysis To validate this new method, four selected pozzolanic materials with different reactivity were as sessed: a high-degree densified silica fume (DSF-H), a low-degree densified silica fume (DSF-L), an amorphous rice husk ash (RHA-A) and a crystalline rice husk ash (RHA-C). DSF-L is a low-degree densified silica fume with a mean particle size of 23.2 mm and 90% of particles under 42.6 mm (17) Despite both DSF samples presented similar mineralogy, significant differences on particle size distribution were observed. This fact has an important influence on the content of amorphous silica: for the coarsest pozzolan (DSF-H), the amorphous silica content was only 80.5%, unlike the finest one (DSF-L) which had 98.2% of reactive silica. The low pozzolanic reactivity of RHA-C was previously reported by Payá et al (11)
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