Optimisation of properties of inorganic phosphate cement (IPC) for construction and high temperature applications

Inorganic Phosphate Cement (IPC) is a new cementitious material, developed at the Vrije Universiteit Brussel (VUB), which sets at room temperature. Due to its non-alkaline environment during and after setting and hardening, IPC can be combined with glass fibre reinforcement. Such a textile reinforced cementitious is an interesting material in those applications where high load-bearing capacity, good temperature resistance and lightweight construction are demanded. Since IPC is a relatively new cement-based material, this work focuses on engineering and optimizing the material for a field which has not been thoroughly studied yet. Although the behaviour of textile (glass-fibre) reinforced IPC under mechanical load has been subject of study for many years, the chemical, physical and physicochemical mechanisms and subsequent macro-mechanical behaviour under thermal loading hasn't been studied systematically yet. Moreover, the possible rearrangements within the microstructure and mineral composition of IPC as a function of time under ambient conditions (ageing) are still not documented in detail. This thesis focuses on the IPC's macro properties, its microstructure and its chemical phases. In correlating these levels, we aim to establish a sturdy base for further research. The study is conducted in three main stages. In the first stage the thermal and long-term stability of so-called reference IPC (post cured at 60 °C) are investigated. This stage characterizes the macro properties of the reference IPC as a function of temperature and time and defines which evolutions are considered to be undesirable. It was found that glass fibre reinforced IPC tends to show cracking when kept on the shelf, indicating that even at ambient conditions restrained shrinkage of the IPC matrix can lead to the introduction of internal tensile stresses in the IPC, high enough to introduce cracking. In the second stage, chemical and micro structural changes are identified along with changes in macro properties, again as functions of time and temperature. It is found that during ageing of IPC at ambient conditions the meta-stable calcium phosphate phases show considerable dehydration during several months, even after the substance has set. These ongoing chemical transformations over a long time contribute significantly to the chemical instability of the material. Additionally, it is observed that calcium phosphate transformations are one of the main factors behind thermally induced chemical shrinkage when heating up from 105 °C to ~ 515 °C. Transformations of the meta-stable calcium phosphate phases (e.g. brushite) to more stable calcium phosphate phases (e.g. monetite) are accompanied with considerable shrinkage. The advantage of a heat treatment - which generally speaking transfers 'brushite-based' IPC into more stable 'monetite-based' IPC - is that monetite-based IPC shows excellent chemical stability under long-term ambient conditions. The drawback of the heat treatment is found in the high shrinkage, which accompanies the treatment. This unwanted effect is due to the fact that the abovementioned transformation leads to an increase of the skeletal density. Building on the work done in the first two stages, a new technique is developed in the third stage to optimize the properties of the material. A hydrothermal post curing (HTPC)technique is developed in the last stage of this thesis to overcome the above-mentioned challenges: long-term evolutions, cracking and