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Showing 2 results for Blended Cement

S. Nwaubani,
Volume 12, Issue 3 (9-2014)

This study assesses the kinetics of hydration of Pulverised Fuel Ash and Metakaolin cement pastes and compares how the rate of reaction affects the pore-characteristics and resistance to ionic ingress. The degrees of hydration for the different mixtures were evaluated, both as a function of the calcium hydroxide content and with respect to the chemically combined water contents. The reaction rates have been evaluated using a mathematical model (Jander model), which describes the hydration kinetics of the two materials. The results show that the reaction rate for specimens incorporating Metakaolin is several folds higher than those incorporating Pulverised fuel ash. The faster rate of reaction of the pozzolanic blends results in a faster rate of filling the pore spaces with hydration products, smaller pore volumes and reduced chloride ion diffusivity. The results from this investigation will provide engineers with a much needed uunderstanding of the kinetics of hydration and setting characteristics of these types of cement systems and help in gaining an appreciation of the early structural development, ease of placement and subsequent evolution of properties.
N. Kaid, M. Cyr, H. Khelafi,
Volume 13, Issue 4 (12-2015)

The paper presents the characterisation of an Algerian natural pozzolan (NP) intended to for use in cement-based materials. The experimental programme was based on different tests on paste and mortar. The pozzolanic activity was assessed by the means of lime consumption over time of mixtures of lime-pozzolan (75% NP and 25% Ca(OH)2, water-binder ratio of 0.45). The degree of reactivity was assessed by observing the crystallographic changes (XRD) and lime consumption (TG) up to 1 year of hydration. The effect of NP on cement-based mixtures was based on the measurement of the water demand and setting time of pastes, and on the compressive strength of mortars, up to one year. The replacement rates of cement by pozzolan were 5, 10 and 15%. A superplasticizer was used (0, 1, 2 and 3% of the binder mass). A calculation of the carbon footprint was investigated in order to assess if the natural pozzolan could be considered as eco-efficient when used in replacement of the clinker. The results showed that NP had a medium pozzolanic reactivity and with a medium-low silica content. The use of NP usually led to a small increase in the water/binder ratio (up to 10%) to maintain constant workability. The setting time was also increased by around 20%. Nevertheless, strength tests showed that the pozzolan had sufficient activity to counteract the water demand, since long-term compressive strength of the binary system (cement + pozzolan) were higher than those of cement alone. The use of NP in replacement of clinker involves a reduction in CO2 emissions for transport up to 1800 km, which is compatible with sustainable development. The results are most promising from both a performance-based and an environmental point of view

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