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- Alkali activation (2) (entfernen)
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The main objective of this work is to determine chloride migration coefficients for alkali activated fly ash-based mortars. The effect of various mixture composition is studied. The identified values will be used in simulations of chloride transport in the alkali-activated composites, mainly to determine a critical time span of exposition to chlorides causing corrosion of reinforcement. Rapid chloride migration experiments (RCM) are performed on cylindrical specimens, 100 mm diameter, 50 mm height. Low voltage electric field (10–30 V DC) is applied as a driving force for the accelerated chloride penetration. The chloride front in the sample is identified according to NT Build 492 standard after given time of penetration (depending on the electrical current ~ 3 hours) on a fracture surface using silver nitrate solution.
Further, accelerated diffusion experiments are performed in order to verify the migration coefficients obtained using RCM. The total chloride content is determined, and chloride profiles obtained on powder ground from separate layers of the specimen.
Alkali-activated fly ash foams – mechanical, chemical and physical properties
Alkali-activation of fly ash together with an aluminum powder blowing agent led to the synthesis of inorganic fly ash-based foam. The aluminium powder reacts with the alkalies from the activation solution. Hydrogen is released during this reaction and creates a closed-pore structure. The amount of liquid activation solution and aluminium powder was optimized considering proper pore distribution and feasible bulk density of the resulting foam. The viscosity of the initial mix was found as a crucial factor for the foaming process as well as for the stability of the fresh foam.
The fly ash foam is characterized in terms of its compressive and flexural strength, thermal conductivity and capacity, resistance to chemically aggressive environments, fire resistance and 2D morphology. The fire resistance test shows, that almost all mass loss occurres below 500°C and the biggest volume change take place between 800°C and 1100°C. An excellent chemical durability stems mainly from the closed-pore network and absence of leachable Ca in the system. Experiments and micromechanical simulations prove that reasonable bulk densities lie in the range of 400 to 800 kg/m3.