Dynamic compressive properties of high volume fly ash (HVFA) concrete with nano silica

High Volume Fly Ash (HVFA) concrete enables the utilization of fly ash (FA) to diminish greenhouse gas emission by decreasing the demand of ordinary Portland cement. Structures made of HVFA concrete, such as roadside barriers, tunnel cushions and building walls could be subjected to impact and blast loads during service life. Thus, dynamic performance of HVFA concrete is worthy of investigating for better analysis and design of concrete structures. This paper presents the quasi-static and dynamic properties of HVFA concrete containing FA contents of 40 and 60% (by wt.) as partial replacement of cement. The effect of 2% (by wt.) nano silica (NS) on the quasi-static and dynamic properties of HVFA concrete is also studied. The dynamic compressive tests are carried out by using a split Hopkinson pressure bar (SHPB) with 100 mm diameter. The failure processes and patterns as well as stress-strain curves of plain and HVFA concretes under different strain rates are compared. The strain rate effects on the compressive strength, modulus of elasticity and energy absorption capacities are analysed. The experimental results show that quasi-static and dynamic performances of HVFA concrete are enhanced by the addition of NS. With the increase of FA content, the damage level becomes more severe, and modulus of elasticity and energy absorption capacities of HVFA concretes become lower at the similar strain rate. Dynamic increase factors (DIF) of compressive strength for HVFA concretes are quantified and compared with the empirical formulae recommended by Euro-International Committee for Concrete (CEB) for normal concrete. Adding NS leads to lower DIF for compressive strength of HVFA concrete. Empirical formulae for DIF of compressive strength, modulus of elasticity and energy absorption capacity of HVFA concretes with and without nano silica as a function of strain rate are proposed. It is worth noting that the NS modified HVFA C60F38N2 in this study has higher compressive strength, modulus of elasticity and energy absorption capacity than the plain concrete (PC), which shows the potential to replace the normal concrete as a sustainable construction material.