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Title: Phase development in cement hydrate systems
Author: Okoronkwo, Monday Uchenna
ISNI:       0000 0004 5365 2758
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 2014
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Much progress has been made in understanding the physicomechanical properties of blended cement pastes of various formulations. However, unanswered questions abound, particularly as it concerns the long term chemistry of mineral distribution as clinker is diluted with progressively more supplementary cementitious materials (SCM's) and as a greater fraction of blending agent reacts with cement with time. This Thesis describes progress towards elucidating the mineralogical evolution mainly by isothermal equilibrium of known compositions. The evolution of mineralogy of two major systems: the calcium-alumina-silica-water (CASH) system and sodium-calcium-alumina-silica-water (NCASH) systems were studied at 20 – 85 °C, using ~70 compositions. Phase assemblage models have been developed for the systems, demonstrating the mode of occurrence and coexistence of phases with respect to temperature and composition. The coexistence of gels, one based on calcium silicate hydrate (C-S-H), the other based on aluminosilicate hydrate (A-S-H), and crystalline phases such as hydrogarnet solid solution, strätlingite and gismondine-Ca in the CASH system at 20 – 85°C, are illustrated. Transformation of gels to their corresponding crystalline phases has been predicted. Similarly, models are presented showing the mode of occurrence and coexistence of portlandite, alumina hydrate, silica, tobermorite, strätlingite, hydrogarnet solid solution, gismondine- type zeolite (Na,Ca)P solid solution, zeolite A, zeolite X, sodalite, etc., at temperatures 20 – 85 °C for the NCASH system. The stability and properties of the various crystalline CASH phases such as, hydrogarnet solid solution, strätlingite and gismondine, in relation to other phases relevant to cement hydration – such as C-S-H, AFts, AFms, gypsum and calcite – are characterized. The impact of sulfate, carbonate, alkali and solid solution on phase stability in systems relevant to aluminosilicate substituted cement paste are investigated. Concerns on long-term evolution of pH and its consequences to the passivation of cement-steel composite are discussed.
Supervisor: Not available Sponsor: Abia State University ; Uturu ; Tertiary Education Trust Fund (TETFund Nigeria)
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available