Tailoring lime properties to the modern construction industry. The effects of organic additives and alternative slaking methods on portlandite mineralogy

In a world where sustainability is a cardinal concept in the global public discourse, lime is becoming an increasingly valuable commodity for its importance in the development of more sustainable binders for construction. Lime has been manufactured and used since antiquity for a variety of applications including as binder for mortars and plasters. In the construction industry, its use gradually phased out during the 20th Century in favour of Portland cement. Nonetheless, a consensus on the beneficial properties of lime in construction has been growing over the past decades among practitioners, industry, and academics. The research described in this thesis focuses on the modifications induced to portlandite crystals by alternative slaking methods i.e., steam slaking and those entailing the use of organic additives. The goal of the research is to develop lime-based products with improved performances for the modern construction industry, able to overcome lime’s intrinsic limitations, such as the slow setting process and the need for a lengthy maturation to achieve optimal performance. In this study the effects of steam and of a range of organic additives (mono-, oligo- and polysaccharides as well as lignosulfonates) on portlandite crystals and air lime-based mixtures were assessed. Steam-slaked and additive-modified hydrated limes were characterised using a series of analytical techniques to obtain information on microstructural development, evolution of crystal growth and chemistry of the pore solution. Steam-slaked and additive-modified lime mixtures were prepared to study the influence of the slaking process on fresh- and hardened-state properties, and on the carbonation reaction. The results of this work demonstrate that both steam-slaking and the use of selected organic additives can affect the nucleation and growth of portlandite crystals and modify their size and shape, with an overall reduction in size and crystallinity. Such modifications are reflected in the behaviour of lime mixtures in terms of water demand, water retention, mechanical properties, and carbonation progression. These findings contribute to the understanding of the interaction mechanisms of lime with water vapour and with organic additives and their effects on the nucleation and growth of portlandite crystals. Furthermore, these results can be exploited to tailor the properties of lime to specific applications in the modern construction industry.