Rheology control of alkali-activated fly ash with nano clay for cellular geopolymer application

An efficient method of production for cellular geopolymer from an alkali-activated fly ash (AAF) binder paste by controlling its rheological behavior is presented. The AAF binder paste exhibits a complex rheological behavior, which is influenced by the solids loading and the composition of the activating solution. The constant strain rate response of the AAF binder paste varies between a yield-type and Maxwell flow behavior. Entrained porosity created in the hardened geopolymer matrix with the use of Aluminum powder exhibits a dependence on the constant strain rate response of the AAF binder paste. A cellular structure is achieved in pastes which exhibit a yield-type behavior. The addition of nano-clay fundamentally alters the constant strain rate response of AAF binder pastes producing a yield-type response in suspensions that exhibit a Maxwell flow behavior. There is also an increase in the peak stress in the constant strain rate response with nano-clay. A stable cellular structure is produced in the AAF binder pastes which exhibit a Maxwell-flow type response with the addition of clay. Montmorillonite is more effective than Bentonite in enhancing the yield stress of the AAF binder pastes. The importance of identifying the yield stress of the AAF binder pastes for creating a stable cellular structure within the hardened geopolymer matrix is established. The cellular structure in the geopolymer matrix can be tailored with the rheology control of the AAF binder pastes using nano-clay

Porosity and pore structure control in cellular geopolymer using rheology and surface tension modifiers

Cellular geopolymer is produced by aerating Alkali-activated Fly ash (AAF) binder paste using Aluminum powder. The cellular structure created in the geopolymer depends on the AAF binder paste rheology and the surface tension of the activating solution. The constant strain rate rheological behavior of AAF binder paste varies between Maxwell flow and yield type depending on the activating solution content. Aeration with a stable bubble structure is achieved in an AAF binder paste with a yield-type constant strain-rate response. AAF binder pastes which exhibit a Maxwell-flow type constant strain rate response cannot retain bubbles in suspension. Addition of clay transforms the constant strain rate rheological behavior of the AAF binder paste from Maxwell-flow to yield type response producing a stable aerated paste. Increasing the clay content in the AAF binder paste increases its yield stress. The total porosity in the cellular geopolymer is controlled by the size and quantity of aluminum powder. Equivalent total porosity is achieved with a lower dosage of finer aluminum powder. Yield stress and surface tension have opposing influences on the pore size without influencing the total porosity. Increasing the yield stress of the AAF binder paste by adding clay produces an increase in the mean pore diameter. Adding surfactant to the AAF binder paste decreases the mean pore diameter in the cellular geopolymer. The porosity and the mean pore diameter in the cellular geopolymer can be controlled with the use of clay, and surfactant and by regulating the content and fineness of the aluminum powder. © 2022 Elsevier Lt

Self-Leveling Geopolymer Concrete Using Alkali-Activated Fly Ash

Self-leveling concrete is developed with low-calcium alkali activated fly ash (AAF) binder paste. The rheological behavior of AAF pastes with different compositions is evaluated. AAF pastes are proportioned with alkali-silicate activating solutions to ensure specific reactive oxide ratios for comparable geopolymer strength. The yield stress and the viscosity of the AAF binder paste vary with the silica content and the silica modulus (SiO2/Na2O mass ratio) in the alkali-silicate activating solution. The slump and flow behaviors of concrete mixtures made with AAF paste are evaluated. The requirements of the AAF binder characteristics, paste content, and aggregate packing for achieving self-leveling flow characteristics under gravity-induced flow are assessed. The transition from a frictional to a flow-Type behavior in concrete mixtures depends on the AAF binder paste content. Self-leveling is achieved without the use of admixtures with an AAF binder paste of low yield stress and at a paste content of 45%. Improving the aggregate packing using the Fuller-Thompson curve and reducing the yield stress of the AAF binder paste increase the flow achieved in concrete mixtures. The specifications for cement-based self-consolidating concrete (SCC) are closely applicable for self-leveling AAF-based concrete

An evaluation of yield and Maxwell fluid behaviors of fly ash suspensions in alkali-silicate solutions

The rheological behavior of fly ash suspensions in alkali-silicate solutions used to prepare geopolymers is investigated. The transient stress response of fly ash suspensions at a constant applied strain rate is influenced by both the solids loading and the rheological behavior of the activating solution. The alkali-silicate solution itself behaves like a Newtonian fluid. The fundamental response of alkali-silicate fly ash suspension under constant applied shear strain rate exhibits a transition from a yield type to Maxwell flow. The variability in the Maxwell flow to yield type behavior depends upon the solids loading given by the solution to binder ratio and the composition of the activating solution. In both Maxwell flow and yield type responses, the maximum stress before initiation of flow is directly influenced by the viscosity of the activating solution. At specific solid loading, the transition between the Maxwell flow to yield type behavior is controlled by the composition of the activating solution. The viscous nature of the alkali-silicate solution produces a rate dependent transient response under constant applied strain rate