Utilization of processed fly ash in mortar

Grinding process is introduced to provide fine particles of coal fly ash that enhances the strength gain of cement mortars. It is discovered that grinding can make all the studied fly ashes more suitable for concrete use at higher replacement value than previously anticipated even when the effect of high carbon content is considered. In this study, new mechanisms for strength gain of fly ash mortars are proposed. They are dispersion and nucleation, which are results from the presence of fly ash in the cement mortar. These effects are shown to enhance the hydration of cement. The pozzolanic action of fly ash contributes strength at a later stage. Pozzolanic activity of fly ash is shown to increase with fineness of the ground fly ash. Several types of fly ashes, wet bottom, dry bottom and low NOx, fly ashes are chosen as representative of the waste products of existing and the new burner technology. They were ground to different particle size distributions. Tests were conducted to determine the physical properties of these fly ashes and their performance in cement mortars. Optimum ranges of the grinding process were explored along with particle size analysis, chemical composition, mineralogy, and morphological aspects of raw and ground fly ash. In order to see whether these processed fly ashes can be used at high percentages in cementitious products, the performance of mortars made from these fly ashes is examined. The strength contribution of fly ash in cement mortars through dispersion, nucleation, and pozzolanic action were investigated and found to perform equally or better than normal cement mortars as early as seven days. Furthermore, the study on the properties of mortars made of high-carbon ground fly ash from low NOx, furnace also showed similar strength enhancement. The major conclusion of this study is that grinding is a suitable mean to increase utilization of fly ash as cement replacement. The processing technique has economically been demonstrated to yield quality fly ash for us in concrete, thus reducing the amount of fly ash that needs to be disposed of in landfills

Sulfuric acid resistance of fly ash mortar

Crown corrosion of concrete pipe and its subsequent repair is a topic much discussed in recent years. Present protective methods have not worked effectively. Due to its properties and its low cost, fly ash was used as a cement replacement of mortar to investigate its sulfuric acid resistance. Different types and different percentages of fly ashes were mixed with and without admixtures including microsilica, and superplasticizer. The main parameters investigated included the chemical compounds, the fineness and the volume of fly ash. 2 x2 cubes were immersed in a 10% sulfuric acid pond. The weight of each cube was determined continuously up to 28 days. The results indicated that fly ash can be used effectively to improve sulfuric acid resistance of mortar in term of weight loss when using the finest fly ash in the optimum percentage, 50%. However the strength of these samples under the same conditions was significantly deteriorated. Microsilica and superplasticizer cannot inhibit the strength deterioration when mixed with fly ash mortar

Solid-state nuclear magnetic resonance spectroscopy of cements

Cement is the ubiquitous material upon which modern civilisation is built, providing long-term strength, impermeability and durability for housing and infrastructure. The fundamental chemical interactions which control the structure and performance of cements have been the subject of intense research for decades, but the complex, crystallographically disordered nature of the key phases which form in hardened cements has raised difficulty in obtaining detailed information about local structure, reaction mechanisms and kinetics. Solid-state nuclear magnetic resonance (SS NMR)spectroscopy can resolve key atomic structural details within these materials and has emerged as a crucial tool in characterising cement structure and properties. This review provides a comprehensive overview of the application of multinuclear SS NMR spectroscopy to understand composition–structure–property relationships in cements. This includes anhydrous and hydrated phases in Portland cement, calcium aluminate cements, calcium sulfoaluminate cements, magnesia-based cements, alkali-activated and geopolymer cements and synthetic model systems. Advanced and multidimensional experiments probe 1 H, 13 C, 17 O, 19 F, 23 Na, 25 Mg, 27 Al, 29 Si, 31 P, 33 S, 35 Cl, 39 K and 43 Ca nuclei, to study atomic structure, phase evolution, nanostructural development, reaction mechanisms and kinetics. Thus, the mechanisms controlling the physical properties of cements can now be resolved and understood at an unprecedented and essential level of detail

Quantitative study of the reactivity of fly ash in geopolymerization by FTIR

Fourier transform infrared (FTIR) spectroscopy has been applied to analyse the environments of Al–O and Si–O bonds in fly ash, which are used as raw materials of geopolymer synthesis. It is noted that the relative intensities of the bands at around 1000, 910 and 700 cm-1 are much higher in fly ash with higher reactivity, as reflected by the compressive strength of geopolymer. Deconvolution analysis of the band from 400 to 1400 cm-1 shows that the cumulative area of these three resolved bands, together with the band at 1090 cm-1, which is assigned to the asymmetric stretching of Si(Al)–O–Si, is proportional to the reactivity of fly ash. If it is assumed that the area of the resolved bands is proportional to the concentration of the corresponding bonds, a general indication is therefore that fly ash containing more reactive bonds will exhibit higher reactivity in geopolymerisation. FTIR spectroscopy in combination with particle size analysis provides a fast approach to predict the reactivity of fly ash,from the perspective of aluminosilicate glass chemistry