| Abstract | These days, considerations of energy and resource conservation are more important, and using pozzolanic materials to replace cement in concrete is an option for conserving energy and resources. However, pozzolanicity is still imperfectly understood. Specific surface and chemical composition are known to play an important role but, because they are inter-related, pozzolanic behavior is complex. Furthermore, rapid techniques such as particle size analysis by laser diffraction combined with X-ray diffraction (XRD) are rather complex to use and the apparatus expensive. On the other hand, assessing pozzolanic activity by ASTM Designation C 311 requires time to obtain the pozzolanic properties in terms of the strength activity index. In this research, the proposed rapid technique can be performed using readily available apparatus to the concrete industry and is affordable in developing countries. Firstly, the tested samples were prepared to be a wide range of populations by varied types, sources, finenesses and weathering period of samples in order to range from inert material to excellent pozzolan. Then, the quality and properties of cement, pozzolans (i.e. silica fumes, fly ashes, rice husk ashes, metakaolins, ground granulated blast furnace slag, volcanic ashes) and inert material (i.e. river sand) were identified based on fineness of the tested samples, average diameter, and chemical composition by Blaine air permeability measurement and/or light scattering techniques, X-ray fluorescence (XRF), respectively. Moreover, compressive strengths of 50x50x50-mm tested and standard mortar samples were determined in order to obtain the strength activity indexes at the ages of7, 14,28, 56, and 91 days according to ASTM C 311 based on a constant ratio of cementitious materials to sand of I to 2.75 by weight while the water-to-binder ratio (w/b) was kept constant at 0.484 by weight. The experimental results showed that the degree of fineness, chemical compositions could not represent all pozzolanicity of the pozzolan. However, results of the strength activity index indicate that the w/b ratio constant at 0.484 can be used to determine both the degree of pozzolanicity of the pozzolan as well as the consistency of fresh mortar. In the second part, experiments were attempted to set up a rapid method to evaluate the reactivity of pozzolans. The experiments of conductimetric technique were applied to consider the electrical conductivity in lime-microsilica suspension at different conditions based on suspension temperature, type of alkali-activated solution, and amount of sample to find the optimum conditions. Three types of alkali-activated solution, namely unsaturated lime solution, saturated lime solution and the ordinary Portland cement solution (OPC solution), were investigated. Three different suspension temperatures, namely 40°C, 60°C and 80°C, were attained .. The quantity of silica fume was varied from 0.5 to 1.5 grams whereas the volume of the tested solution was kept constant at 200 mL. Measuring was stopped when observed electrical conductivity had very low variation, which indicated the electrical conductivity had stabilized. The results reveal that raising the suspension temperature accelerates the pozzolanic reaction. Increasing the amount of microsilica also increases the chemical reaction rate. Furthermore, the OPC solution can be used as an alkali-activated solution for pozzolanic activity evaluation, and one which offers good accuracy. In the last part, the conductimetric technique at the optimum condition obtained from Part II was conducted with the same prepared samples in Part 1. Hence, the electrical conductivity was measured at 80°C in fixed concentration of ope solution while the quantity of pozzolan sample was only one gram in 200 mL of tested solution. The electrical conductivity of the suspension was continually recorded using an electrical conductivity meter and stored on a personal computer for a period of slightly over 1 day. Subsequently, the indicative parameters which can be related to pozzolanic reactivity were investigated in detail with database from the first part and existing knowledge. Finally, the rapid evaluation of pozzolanic activity of pozzolan was developed by the monitoring of electrical conductivity of ope solution, to which the material was added, over time which is applicable to wide range of cement replacement materials namely silica fume, fly ash, rice husk ash, metakaolin, ground granulated blast furnace slag, volcanic ash. The results demonstrate that it is possible to qualitatively determine and describe the pozzolanic reactivity 01 tested sample within 28 hours by identifying the stages of reaction and the corrected reduction in normalized electrical conductivity and the rate of changf of electrical conductivity, as compared to 28 days for the determination 01 strength activity index according to ASTM. This technique would help concrete technologists to speedily investigate the quality of fly ash and other pozzolans fo: use as a partial cement replacement with a low cost available apparatus, which i: affordable in developing countries. This substitution can help to alleviatt pollution caused by cement production and to solve disposal problems of waste ashes. |