Mitigation of early age shrinkage of UHPFRC by using spent equilibrium catalyst

Abstract

Strengthening of structural concrete elements with ultra-high performance fibre reinforced composites (UHPFRC) layers is being successfully performed in recent years. The main advantage of UHPFRC in this context is that it can play a double function (water tightness and strengthening), while enabling short-time interventions. UHPFRC material exhibits remarkable mechanical properties namely, strain hardening in tension and extremely low water permeability. However, due to the very low water/binder ratio it is prone to autogenous shrinkage. The restraint provided by the substrate to the free shrinkage of the new layer generates built-in stresses which can impair its performance. As such, seeking strategies to reduce the autogenous shrinkage is an objective to pursue. The spent equilibrium catalyst (ECat) is a waste generated by the oil refinery industry with very high pozzolanic activity and high specific surface (150 m2 /g) which promotes a significant water absorption (about 30%, by mass), thus has a great potential to work as an internal curing agent in UHPFRC. Within this scope, this paper describes research on the viability of using ECat to mitigate autogenous shrinkage of UHPFRC. Test results showed a significant reduction of autogenous shrinkage in UHPFRC mortars without fibres and 20% and 30% of sand replacement by ECat.