Effects of nano-silica treatment on the flexural post cracking behaviour of polypropylene macro-synthetic fibre reinforced concrete

Abstract

The effects of a surface nano-silica treatment, carried out with the sol gel method, on the post-cracking behaviour of polypropylene macro-synthetic fibre reinforced concrete are experimentally investigated here for the first time. The present study extends previous experimental and analytical investigations on the corresponding improvement of the bonding properties of a single synthetic macro fibre, performed by means of pull-out test. Scanning electron microscopy is adopted here to explore the changes in the morphological characteristics of polypropylene macro synthetic fibres, before and after mixing in the concrete matrix. A comparative analysis, carried out with three-point bending tests on notched beam specimens, is used to evaluate the effects of the nano-silica treatment on the concrete post cracking behaviour. Increase in concrete toughness and residual post-cracking strength is recorded due to improved adhesion between fibres and the concrete matrix and to the consequent increase in the frictional shear stress generated during the fibre pull-out, especially for large crack opening. As shown by the SEM images, the nano-treatment favours the bonding of the concrete hydration products to the surface of the treated fibres, thus ensuring strengthening of the interface transition zone. In addition, the links between the nano-silica coating and the concrete hydration products improve the frictional shear stress and thus the overall energy absorption, as denoted by the increase of the residual strength during the post-cracking phase

Mechanical Performance of Fiber Reinforced Cement Composites Including Fully-Recycled Plastic Fibers

“…Conversely, the observed post-peak behavior largely varies, primarily depending on the shape of fibers, which turns out to be a crucial parameter in the design of highly-dissipative FRCC systems, as also pointed out in relevant contributions [49,50]. On the one hand, the inclusion of cylindrical draw-wire filaments (reference PP black dash-dotted line and RP violet dashed line) leads to a limited load drop immediately after first cracking, followed by a consistent monotonic softening branch (see [7,33]). Conversely, the presence of both AT (light-green solid line) and AT-S (dark-green solid line) fibers induces a more dramatic load drop, ascribable to the lower stiffness (i.e., smaller cross-section) of flattened fibers.…”

“…As also established in other fundamental contributions [3,4], the addition of fibers in plain concrete improves the resistance to crack formation and propagation, due to the bridging mechanism implemented by the fibrous reinforcement. Moreover, the use of short dispersed fibers assures a meaningful reduction of shrinkage cracking, a more favorable crack distribution, and hence an enhanced durability of the structural elements [5][6][7].…”

“…To address this problem, several surface treatments of fibers have been proposed in the literature, involving among others oxyfluorination [34], chemical attack [35], cold plasma [36], and silica coating [37,38]. The last, while being a relatively simple technique, turns out to be particularly suitable at improving the interface bonding between synthetic fibers and cement binder (see, e.g., [7,39]).…”

An Experimental Study on the Compressive Dynamic Performance of Polypropylene Fiber Reinforced Concrete for Retaining Structure under Automobile Collision Magnitude

“…Meanwhile, polypropylene fiber reinforced concrete is able to suppress the generation of early shrinkage cracks to a certain extent so as to improve the ductility of concrete. At present, polypropylene fiber reinforced concrete has been widely concerned and applied in engineering structures, such as dams, retaining walls, and culverts [1][2][3][4][5]. In actual engineering projects, concrete structures are subjected to not only static actions but also dynamic actions including earthquake, collision, and explosion.…”

Pullout modelling of viscoelastic synthetic fibres for cementitious composites

“…They observed slip hardening behavior, namely an increase in the frictional stress acting on the fibre surface as the fibre is pulled out of the cement matrix caused by the progressive wearing of the fibre surfaces and the accumulation of wear debris due to abrasion phenomena. The pullout hardening behavior is responsible, in turn, of the increase in the residual strength during the post-cracking phase and, thus, of the ductile behavior of FRC [18].…”