Anchorage of steel rebars to recycled aggregates concrete: Fid-Bau Portal

Anchorage of steel rebars to recycled aggregates concrete

Guerra, M. / Ceia, F. / de Brito, J. / Júlio, E.

Highlights • Concrete made with coarse recycled concrete aggregates. • Anchorage strength of ribbed steel rebars with varying length and diameter. • The anchorage strength decreases with the incorporation ratio of recycled aggregates. • Numerical modelling of the experimental tests.

Abstract This research aims at evaluating the effect of the replacement ratio of natural course aggregates (NCA) by recycled concrete coarse aggregates (RCCA) on the anchorage strength of ribbed steel rebars to concrete. To accomplish this purpose, four concrete mixes were designed: a conventional NCA concrete (NCA by RCCA replacement ratio of 0%) to serve as reference and three recycled aggregates concrete (RAC) with 20%, 50% and 100% NCA by RCCA replacement ratios. Besides this parameter, all the remaining ones were kept constant. An effective water/cement ratio of 0.53 and a slump of 125±10mm were adopted. The mechanical properties of the considered mixes were characterized in terms of compressive strength, splitting tensile strength, and Young’s modulus. The anchorage strength of ribbed steel rebars to RAC was assessed for each of the four concrete mixes using pull-out tests. In addition to the NCA by RCCA replacement ratio, two other variables were evaluated: the diameter (12 and 16mm) and the anchorage length (5ϕ, 10ϕ and 15ϕ) of the steel rebars. The combination of these three variables led to 24 different testing conditions. For each of these, three equal specimens were produced, corresponding to a total of 72 pull-out tests performed. As main conclusions of this research study, it can be stated that NCA by RCCA replacement ratio has a negative impact on the mechanical properties of concrete, presenting an approximately linear correlation. Only for lower replacement ratios, namely 20%, there are not any clear changes in concrete mechanical properties, and a slight increase can even occur. Regarding the anchorage strength of ribbed steel rebars to concrete, the incorporation of RCCA has a similar effect: the increase of the NCA by RCCA replacement ratio leads to a decrease of this parameter. This effect can be well explained analysing the stress distribution inside the pull-out specimens using a finite-element model developed with this aim, also presented herein.