Autogenous shrinkage of CARDIFRCRTM

Durability requirements have become a major issue in the design of concrete structures today. The hardening process plays a key role in the quality of the concrete. Autogenous shrinkage is considered to be a factor that may cause damage to the concrete structure during hardening. The concept of autogenous shrinkage is relatively new and in the case of conventional concrete with fairly high water to cement ratios these self-induced volume changes are found to be relatively small and therefore are neglected. Self-desiccation and autogenous shrinkage are pronounced phenomena in the case of low water to cement ratio concretes. The current study deals with the development of autogenous shrinkage strains in a new class of High Performance Fibre Reinforced Cementitious Composites (HPFRCCs) designated CARDIFRC that has been recently developed at Cardiff University. The scope of the study was to investigate how the self-induced shrinkage strains develop in CARDIFRC matrix without fibres and what was the effect of the inclusion of a large amount of fibre on the autogenous shrinkage. Both experimental and theoretical studies were undertaken as a part of this investigation. Autogenous shrinkage strains were measured on large and small prisms of CARDIFRC under isothermal conditions. The experiments revealed a relatively large scatter in the measured values for the case of large beams with fibres, whereas the beams of same size but without any fibres gave consistent results. This large scatter has been confirmed to be a result of the uneven distribution of fibres in the large prisms. Small prisms with and without fibres gave very consistent results, with autogenous shrinkage taking place up to 75 days. The autogenous shrinkage strains have been modelled using a thermodynamic approach which follows the continuous change in the moisture content, pore volume and stiffness of the mix with degree of hydration. The predictions of the model are in good agreement with the measured strains in all specimens with and without fibres