The Retardation Process of Crack Propagation in Unconfined High-Strength Concrete Columns Due to the Introduction of Silica Fume

High-strength concrete (HSC) has been in high demand as it can offer superior performance, and it is more cost effective over normal strength concrete. Without any addition of admixtures, fillers or supplementary materials, the greatest strength achievable by standard concrete mixes is 80 MPa. Amongst currently available supporting cementitious materials, silica fume offered several benefits. Firstly, its ultrafine particles can fill in the void between the hydrated concrete paste and aggregates. Secondly, as silica fume contains about 97% of silica dioxide, it can prolong the chemical reaction to produce a concrete paste. In other words, the introduction of silica fume in concrete mixes will enhance the structure packing density as the interstitial voids are significantly reduced. Although it is a common practise to have silica fume in concrete mixes, its performance and behaviour have not been accurately analysed. HSC with silica fume is treated as usual HSC or NSC during the analysing process, but studies show that the different is significant (Xiao et al. in J Compos Constr 14:249–259, 2010; Lim and Ozbakkaloglu in Constr Build Mater 63:11–24, 2014). Therefore, a new model that can truly reflect the HSC with silica fume performances needs to be derived and developed. In addition, the HSC column is very brittle, whether it consists silica fume or not. Studies showed that lateral confinement could significantly enhance its axial strength and deformability (Mander et al. in J Struct Eng 114:1804–1826, 1988; Saatcioglu and Razvi in J Struct Eng 125:281–289, 1999; Saatcioglu and Razvi in J Struct Eng 118:1590–1607, 1992). External confinement by steel tubes and fibre reinforced plastic (FRP) tubes provided the best solution as they can act as a formwork hence improving the construction process time. Various studies on these two types of confinement have been carried out, but the model proposed only covers the effectiveness of the confinement material and the behaviour of the confined concrete as a whole composite. The composition of concrete mixes is not clearly discussed hence, the effective contribution of silica fume in term of volume, and improved strength in this system are unknown. Therefore, this project will highlight the differences between HSC with and without silica fume concerning axial stress–strain behaviour, lateral-axial strain performance and peak axial stress. The research also will undertake a study on unconfined HSC with silica fume to determine the pre-axial stress peak performance. Experimental investigation on both unconfined and confined HSC with silica fume will be carried out with steel tube and glass fibre reinforced plastic (GFRP) winding tube will be used as a confining material. Then, a more representative model to denote the behaviour of unconfined and confined HSC with silica fume will be presented.