Effect of Steel Fibers, Polypropylene Fibers and/ or Nanosilica on Mechanical Properties of Self-Consolidating Concrete

This research concerned studying the combined effect of using nano-silica and/ or hybrid fibers on key mechanical properties of self-consolidating concrete SCC. A comprehensive experimental work has been carried out, using steel fiber (SF) with volume fraction (0, 0.5% and 1.5%), polypropylene fiber (PPF) (0%, 0.05% and 0.15%) and SiO2 nanoparticles (0%, 2% and 4%) by weight of powdered material (silica fume- Sf ) with constant w/c ratio (0.48) to produce eleven different mixtures and tested at different ages (7, 28 and 90 days). Results showed that adding fibers adversely affect SCC workability and thus more dosage of super plasticizer (SP) should be added to stay within the standard limits. comparable to conventional concretes, the presence of steel fibers with SCC provide slight increase in compressive strength at 28 days, (up to 11%), while significant enhancement in tensile properties were observed (up to 24% and 32% for splitting and flexural strength respectively). Polypropylene or hybrid fibers however, provide lower enhancement compared with steel fibers. In contrast, implementation of nanosilica leads to significant improvement in concrete strengths particularly at 4% dosage. Combined effect of 4% nanosilica and 1.5% of steel fibers provide the superior hardening effect on the flexural performance compared with softening effect provided by other added dosages. Scanning Electron Micrograph (SEM) images confirm the matrix densification effect due to nanosilica adding. Flexural strength of SCCs without nanosilica was generally higher than splitting testing results. This fact does not change even with the presence of nanosilica and/ or fibers

Effects of nano montmorillonite clay modified epoxy adhesive on confinement efficiency of adhesively bonded CFRP stay-in-place formwork column

The efficiency of load transfer between the concrete surface and carbon fiber reinforced polymer (CFRP) is greatly influenced by the adhesive agent used in any composite system. This study investigates the effects of using nano montmorillonite clay (nC) as a toughening agent with the epoxy adhesive, to improve the confinement efficiency of CFRP-wrapped stay-in-place (SIP) composite column. Twenty scaled columns were tested under axial compressive load including, unwrapped (reference columns) and wrapped with one layer (1 L) or two layers (2 L) of CFRP. Two cross-section column shapes, square and circular, were evaluated based on their nC-modified adhesive efficiency. Results revealed that SIP columns made with nC-modified epoxy adhesive showed superior compressive behavior, stress, and strain capacity, compared to unmodified composite columns, even when wrapped with 2 L of CFRP. Using 1 L and 2 L of CFRP bonded with unmodified adhesive of circular specimens, increased the confinement efficiency (CE) by about 134 % and 183 % respectively. However, the improvements for the circular specimens with nC-modified epoxy adhesive were higher by up to 15 % than their counterparts’ ones made with unmodified adhesive. For square specimens, the use of nC-modified adhesive improved the CE by up to 16 % as compared with their counterparts’ specimens made with unmodified adhesive.Scanning electronic images revealed that using adhesive modified with nC induces several shorter microcracks, instead of a few wide cracks appearing in the unmodified adhesive. This toughening mechanism as well as the enhancement in the IZ between the adhesive matrix and the fabric yarns, explain the improvements in the ultimate strain capacity of the column specimens made with modified adhesive