Tailored Calcium-Silicate-Hydrates

: a sol-gel approach to nucleation seeding

Abstract

The application of sol-gel technology for the synthesis of seeding admixtures to tailor the nanostructure of C-S-H in Portland cement systems was investigated. The principal focus was to tune the degree of silicate polymerisation of C-S-H to a higher level and to promote the nucleation of organic-inorganic C-S-H hybrids. The two main silicon precursors utilised were tetraethoxysilane (TEOS) and 3-glycidoxypropyltrimethoxysilane (GPTMS). A parametric study was conducted by varying the processing conditions of the seeding material. The effects on cement hydration, phase evolution, micro-nanostructure and mechanical performance were evaluated. It was found that the sol-gel synthesis parameters provide a pathway to tune both cement hydration kinetics and the C-S-H gel structure. Additive-free synthesis of TEOS led to an earlier onset of the acceleration stage, representative of enhanced C-S-H nucleation. Acid-catalysed synthesis facilitated a higher degree of silicate polymerisation within the C-S-H framework. Base-catalysed synthesis promoted jennite-like C-S-H with silicate chains more ordered in terms of polymerisation. Certain synthesis conditions could limit the catalytic and pozzolanic properties, which favoured polycondensation reactions with existing C-S-H to produce more polymerised C-S-H. Base-catalysed synthesis of GPTMS triggered a prolonged dormant period, which could be mitigated by increasing the synthesis duration. Optimal dosages promoted an enhanced nucleation and growth stage. New evidence for the incorporation of glycidoxypropyl groups within the silicate framework of C-S-H was presented. The structure of C-S-H rearranged via the simultaneous polymerisation of organic and inorganic functions. The potential of coupling different layers of C-S-H through the polymerisation of glycidoxypropyl groups into dioxane and polyethylene oxide was proposed. The synthesis parameter, H2O/GPTMS molar-ratio, and dosage, presented distinct effects on the performance. The 8-day flexural and compressive strengths were improved by 44% and 32%. The 28-day flexural and compressive strengths were improved by 18% and 20%. Tuning the physiochemical properties of the seeding agents by a sol-gel process provides a new approach to engineer the performance and durability of cement-based materials.

Date of Award	16 Sept 2020
Original language	English
Awarding Institution	University of Bath
Supervisor	Juliana Calabria-Holley (Supervisor), Kevin Paine (Supervisor) & Martin Ansell (Supervisor)