Effect of Lignosulfonates on the Morphology of Calcium Hydroxide Crystals

Lignosulfonates is commonly used in concrete as superplasticisers. Its presence can affect crystallisation and carbonation kinetics of calcium hydroxide (CH), which is an important phase in hydrated cement since it plays a crucial role in the durability and performance of concrete. In this work, lime pastes were produced by slaking quicklime in distilled water. Ca lignosulfonate (CaLS) was added to them, either before and after the slaking process to investigate the effects of temperature on the CaLS-CH interaction. All samples were characterised at 0 and 6 months from slaking with the aim of investigating the effects of CaLS on CH crystallisation. Scanning electron microscopy and X-ray diffraction were used to investigate CH crystal size and morphology, whereas micro-chemical analyses contributed to the investigation of the chemistry of pore solutions. Results suggest that the addition of CaLS (both, during and after slaking) affects the CH crystals habit and size, which, in turn, can have an effect on the reactivity of CH and, consequently, on the properties of fresh and hardened concrete.