Oxygen and Chloride Permeability of Alkali-Activated Natural Pozzolan Concrete

One of the important factors in the use of portland cement concrete is its durability, and most of the situations where durability is lacking have been identifi ed and strategies to manage durability have been implemented. Geopolymer concrete, made from an alkali-activated natural pozzolan (AANP), provides an important opportunity for the reduction of carbon dioxide (CO2) emissions associated with the manufacture of concrete but has a limited history of durability studies. Until its different properties are well understood there is no desire to adopt this new technology of unknown provenance by the concrete industry. This paper presents an experimental study of oxygen and chloride permeability of AANP concrete prepared by activating Taftan andesite and Shahindej dacite (Iranian natural pozzolans), with and without calcining, and the correlations between these properties and compressive strength. The results show that compared to ordinary portland cement (OPC) concrete, AANP concrete has lower oxygen permeability at later ages; but it shows moderate to high chloride ion penetrability.

Simplified model for prediction of compressive strength of alkali-activated natural pozzolans

The assessment of pozzolanic activity is essential for estimating the reaction of a material as pozzolan. Natural pozzolans can be activated and condensed with sodium silicate in an alkaline environment to synthesize high performance cementitious construction materials with low environmental impact. In this paper, the pozzolanic activities of five natural pozzolans are studied. The correlation between type and chemical composition of natural pozzolan, which affects the formation of the geopolymer gel phase, both for the calcined and untreated natural pozzolans, have been reviewed. The improvement in pozzolanic properties was studied following heat treatment including calcinations and/or elevated curing temperature by using alkali solubility, and compressive strength tests. A model was developed to allow prediction of the alkali-activated pozzolan strength versus their chemical compositions, alkali solubility, and crystallinity.