Sulapha Peethamparan

Bio: Sulapha Peethamparan is an academic researcher from Clarkson University. The author has contributed to research in topics: Portland cement & Cement. The author has an hindex of 19, co-authored 44 publications receiving 1672 citations. Previous affiliations of Sulapha Peethamparan include Princeton University & Purdue University.

Use of nano-silica to increase early strength and reduce setting time of concretes with high volumes of slag

Abstract: The effects of nano-silica (NS) on setting time and early strengths of high volume slag mortar and concrete have been experimentally studied. Effects of NS dosages, size and dispersion methods on strength development of high volume slag mortars were also investigated. A constant water-to-cementitious materials ratio (w/cm) 0.45 was used for all mixtures. The results indicate that the incorporation of a small amount of NS reduced setting times, and increased 3- and 7-day compressive strengths of high-volume slag concrete, significantly, in comparison to the reference slag concrete with no silica inclusion. Compressive strength of the slag mortars were increased with the increase in NS dosages from 0.5% to 2.0% by mass of cementitious materials at various ages up to 91 days. The strengths of the slag mortars were generally increased with the decrease in the particles size of silica inclusions at early age. Ultra-sonication of nano-silica with water is probably a better method for proper dispersion of nano-silica than mechanical mixing method.

Very early-age reaction kinetics and microstructural development in alkali-activated slag

Abstract: The early age reaction kinetics and microstructural development in alkali-activated slag binder are discussed. In-situ isothermal calorimetry was used to characterize the reaction progression in sodium hydroxide and sodium silicate-activated slag binders cured at ambient temperature. Microstructure and strength development were monitored to correlate the heat evolution with the property development. In-situ isothermal calorimetric data for sodium hydroxide-activated systems exhibited only one major heat evolution peak with no dormant period. Sodium silicate-activated pastes exhibited multiple peaks and extended dormant periods. Microstructural evolution, monitored using BSE–SEM, showed rapid product formation on the surface of slag grains in sodium hydroxide-activated systems, forming thin reaction shells—the thickness of which was related to the activator concentration—and leading to diffusion controlled hydration at a very early stage. Sodium silicate-activated systems exhibited slow and progressive product formation, predominately nucleated from the solution. These results are supported by electron mapping and electron dispersive X-ray spectroscopy.

Structure and strength of NaOH activated concretes containing fly ash or GGBFS as the sole binder

Abstract: The influence of the concentration of the activating agent (4, 6, or 8 M sodium hydroxide solution), and activator-to-binder ratio (0.40, 0.50, or 0.60) on the compressive strengths, pore structure features, and microstructure of concretes containing Class F fly ash or ground granulated blast furnace slag (GGBFS) as the sole binder is reported. The starting material contents and the curing parameters (temperature and curing duration) are optimized to provide the highest compressive strengths. Statistical analysis of the compressive strength results show that the activator concentration has a larger influence on the compressive strengths of activated concretes made using fly ash and the activator-to-binder ratio influences the compressive strengths of activated GGBFS concretes to a greater degree. Activated fly ash concretes and pastes are found to be more porous and contains a larger fraction of pores greater than 10 μm in size as compared to activated GGBFS mixtures. The differences in the microstructure and the reaction products between activated fly ash and GGBFS pastes are detailed.

Pattern Recognition and Machine Learning

Abstract: Probability Distributions.- Linear Models for Regression.- Linear Models for Classification.- Neural Networks.- Kernel Methods.- Sparse Kernel Machines.- Graphical Models.- Mixture Models and EM.- Approximate Inference.- Sampling Methods.- Continuous Latent Variables.- Sequential Data.- Combining Models.

Modification of phase evolution in alkali-activated blast furnace slag by the incorporation of fly ash

Abstract: The microstructural evolution of alkali-activated binders based on blast furnace slag, fly ash and their blends during the first six months of sealed curing is assessed. The nature of the main binding gels in these blends shows distinct characteristics with respect to binder composition. It is evident that the incorporation of fly ash as an additional source of alumina and silica, but not calcium, in activated slag binders affects the mechanism and rate of formation of the main binding gels. The rate of formation of the main binding gel phases depends strongly on fly ash content. Pastes based solely on silicate-activated slag show a structure dominated by a C–A–S–H type gel, while silicate-activated fly ash are dominated by N–A–S–H ‘geopolymer’ gel. Blended slag-fly ash binders can demonstrate the formation of co-existing C–A–S–H and geopolymer gels, which are clearly distinguishable at earlier age when the binder contains no more than 75 wt.% fly ash. The separation in chemistry between different regions of the gel becomes less distinct at longer age. With a slower overall reaction rate, a 1:1 slag:fly ash system shares more microstructural features with a slag-based binder than a fly ash-based binder, indicating the strong influence of calcium on the gel chemistry, particularly with regard to the bound water environments within the gel. However, in systems with similar or lower slag content, a hybrid type gel described as N–(C)–A–S–H is also identified, as part of the Ca released by slag dissolution is incorporated into the N–A–S–H type gel resulting from fly ash activation. Fly ash-based binders exhibit a slower reaction compared to activated-slag pastes, but extended times of curing promote the formation of more cross-linked binding products and a denser microstructure. This mechanism is slower for samples with lower slag content, emphasizing the correct selection of binder proportions in promoting a well-densified, durable solid microstructure.