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Earth buildings and adobe construction have been in use for thousands of years. Loam is locally available, environmentally friendly and has a small CO2 footprint mainly resulting from extraction and transport. Because of these reasons loam is one of the building materials of the future.
Water resistance is an important aspect when using loam as a construction material. If the structural option of building protruding roofs cannot be implemented, the water resistance of clay can be improved by stabilization.
Positive properties of the material should not be diminished by stabilization. For example, the desired regulation of air humidity, which however cannot be fully preserved by cement stabilization.
For an alternative and more appropriate stabilisation, different mixtures with calcined clays with alkali activator were examined. The calcination temperature for clays is usually lower than for cement and starts at 600° C. The calcined clays therefore also have a lower CO2 footprint compared to cement. To keep the mixture environmentally friendly potassium was used as alkali ion. It could be proven that the alkali activated polymer enhances water resistance of the loam mixture. Provided some further optimization the material shows potential to replace cement without compromising on the positive properties of clay.
The low calcination temperature for clays (600° C) and a low CO2 footprint compared to cement make them an interesting material. To find a stabilization method for loam using calcined clays, activation by alkalis was necessary. Therefore (and to keep the mixture environmentally friendly) KOH was used as alkali activator. It could be proven that the alkali activated polymer enhances water resistance of the loam mixture.
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.