Effect of type, form, and dosage of activators on strength of alkali-activated natural pozzolans

It is possible to synthesize environmentally friendly cementitious construction materials from alkali-activated natural pozzolans. The effect of the alkaline medium on the strength of alkali-activated natural pozzolans has been investigated and characterised. This paper highlights the effect of the type and form of the alkaline activator, the dosage of alkali and the SiO2/Na2O ratio (silica modulus, Ms) when using water–glass solutions and different curing conditions on the geopolymerisation of natural pozzolans. Activation of natural and calcined pozzolan for production of geopolymeric binder was verified by using Taftan andesite and Shahindej dacite from Iran as a solid precursor. The optimum range for each factor is suggested based on the different effects they have on compressive strength. The concentration of dissolving silicon, aluminium and calcium in alkaline solution, the formation of gel phase and the factors affecting this have been studied by using leaching tests, ICP–AES, and FTIR.

Effect of adding mineral additives to alkali-activated natural pozzolan paste

Natural pozzolans are raw materials from geological deposits with a range of chemical compositions that when combined with suitable alkali activators can be converted to geopolymer cement for concrete production. In this paper the concept of adding mineral additives to enhance the properties of geopolymer cement is introduced. Taftan andesite, a natural Iranian pozzolan, was used to study the effect of adding mineral additives such as kaolinite, lime and other calcined pozzolans on the compressive strength of geopolymer cement under both normal and autoclave curing. Scanning electron microscopy (SEM)/energy dispersive X-ray (EDX) was used to determine the composition of the gel phase in both alkali-activated Taftan pozzolan with and without mineral additions. The work has shown that deficiencies in SiO2, Al2O3 and CaO content in the raw natural pozzolan can be compensated for by adding mineral additives for enhanced properties.

Effect of heat treatment on reactivity-strength of alkali-activated natural pozzolans

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. The nature of the starting materials including mineral composition, chemical composition and crystal structure groups affects the formation of the geopolymer gel phase. In this paper, the pozzolanic activities of five natural pozzolans are studied. From XRD and XRF results, most of the raw materials contain zeolite clay minerals and have a high loss on ignition. Therefore, before use, samples were calcined at 700, 800 and 900 °C, respectively. 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. The results show that pozzolan containing sodium zeolite clinoptilolite can be used to prepare a moderate to high strength binder by heat treatment and calcinations can impart disorder hornblende as a constituent of pozzolan with no amorphous phase to prepare a moderate strength binder.

Radiological characterization of clay mixed red mud in particular as regards its leaching features

The reuse of industrial by-products such as red mud is of great importance. In the case of the building material industry the reuse of red mud requires a cautious attitude, since the enhanced radionuclide content of red mud can have an effect on human health. The natural radionuclide content of red mud from the Ajka red mud reservoir and the clay sample from a Hungarian brick factory were determined by gamma spectrometry. It was found that maximum 27.8% red mud content can be added to fulfil the conditions of the EU-BSS. The effect of heat treatment was investigated on a red mud-clay mixture and it was found that in the case of radon and thoron exhalation the applied heat reduced remarkably the exhalation capacities. The leaching features of red mud and different mixtures were studied according to the MSZ-21470-50 Hungarian standard, the British CEN/TS 14429 standard and the Tessier sequential extraction method. The Tessier method and the MSZ-21470-50 standard are suitable for the characterization of materials; however, they do not provide enough information for waste deposition purposes. To this end, we propose using the CEN/TS 14429 method, because it is easy to use, and gives detailed information about the material's behaviour under different pH conditions, however, further measurements are necessary.