Study on the Compressive Strength of Alkali Activated Fly Ash and Slag under the Different Silicate Structure

Abstract

Due to its high activation efficiency, waterglass has been widely used for alkali activations in geopolymer. In this study, the n(SiO2)/n(Na2O) (Ms) of waterglass was selected as the variable to investigate the role of the silicate structure on the mechanical properties of harden pastes. Ms was changed by the addition of NaOH to obtain the different silicate group, structure and experiments were performed by employing the liquid-sate 29Si nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FTIR), dynamic light scattering (DLS) and gel permeation chromatography (GPC) techniques. Furthermore, selected dissolution, scanning electron microscope (SEM-EDX), X-ray photoelectron spectroscopy (XPS) and FTIR experiments were used to measure the development of the amorphous gel and other materials with different curing condition. Results show that silicate structure of the waterglass was changed via the Si-ONa+ formation and the electric charge effect of Na+. Under the lower Ms waterglass, the Q0, Q1 and QC2 structure reverted to the main structure of the silicate group, which was kind of lower seize, molecule weight, linear or circular chain lower geopolymerization degree silicon structure. It would accelerate the geopolymerization speed of prepolymer formation. In addition, higher activity degree of Q0 and Q1 were useful to increase the formation amount of the gel structure with a low Si/Al ratio and size. Thus, silicate structure of waterglass controls the amorphous gel properties to adjust the compressive strength of alkali-activated materials.

Using Fly Ash Wastes for the Development of New Building Materials with Improved Compressive Strength

“…In the literature, there are mentions that the compressive strength values of the material are affected by the fly ash modification conditions [14]. The variation of the compressive strength values is explained especially on the basis of the Si/Al ratio [34]. On the other hand, there is also a relationship between the polycondensation products from the reactions during the mortar formation and the value of the compressive strength.…”

Experimental Study of the Mechanical and Microstructure Characteristics of Coal Gangue Road Stabilization Materials Based on Alkali Slag Cementation

“…Theoretically, this material can be produced by using any solid precursor containing active calcium, silicate, and aluminate to form C-A-S-H and N-A-S-H gels similar to Portland cement hydration products [27,28]. Wang [29] studied the effect of different silicates on the strength of alkali-activated fly ash and slag. Nur [23] studied the effect of sintering temperature on the microstructure, phase analysis, and electrical conductivity of alkali-activated materials.…”

Laboratory Study on Improvement of Expansive Soil by Chemically Induced Calcium Carbonate Precipitation

“…However, these traditional methods show some limitations in engineering applications. For example, the addition of lime or cement may have environmental impacts since the production of lime and cement is energy-intensive and emits substantial greenhouse gas into the atmosphere [ 16 , 17 ]. Moreover, the physical mixing of the stabilizers with soils is costly and resource-intensive, making it unsuitable for laboratory-scale applications.…”

“…The resulting calcium carbonate (CaCO 3 ) precipitation is expected to improve the properties of expansive soil by flocculation–agglomeration, densification and cementation effects [ 16 , 31 , 32 , 33 ]. This process is simply based on the reaction between calcium ions (Ca 2+ ) and carbonate ions (CO 3 2− ).…”