Eurocode Shear Design of Coarse Recycled Aggregate Concrete: Reliability Analysis and Partial Factor Calibration.

João Pacheco,Jorge De Brito,Luís Evangelista,Carlos Chastre

doi:10.3390/ma14154081

Abstract

This paper contributes to the definition of design clauses for coarse recycled aggregate concrete. One of the main reasons for scepticism towards recycled aggregate concrete is the perceived notion that the heterogeneity of recycled aggregates may increase the uncertainty of the behaviour of concrete. Therefore, the paper uses structural reliability concepts to propose partial factors for recycled aggregate concrete’s design for shear failure. The paper builds upon a previous publication by the authors, in which the model uncertainty of recycled aggregate concrete elements designed for shear, with and without shear reinforcement, was compared with that of natural aggregate concrete elements. In that paper, the statistics of the model uncertainty for recycled aggregate concrete shear design were indeed found to be less favourable than those of natural aggregate concrete. Therefore, a partial factor for recycled aggregate concrete design is needed to ensure safety. This paper presents partial factors calibrated with explicit reliability analyses for different cases of design concerning beams (in the case of shear design of elements with shear reinforcement) and slabs (for the design of elements without shear reinforcement). For full incorporation of coarse recycled concrete aggregates and the design of elements without shear reinforcement, the calibrated partial factor reduces the design value of shear resistance by 10% (design with EN1992) or 15% (design with prEN1992) in comparison to natural aggregate concrete’s design. For the shear design of elements with shear reinforcement, the partial factor decreases resistance by 5% but a sensitivity analysis showed that the reduction might be, under pessimistic expectations, of up to 20%.

Highlights

IntroductionResearch on the structural behaviour of recycled aggregate concrete (RAC) demonstrates the feasibility of using coarse recycled aggregates (RAs) for structural concrete applications [1,2]
If the reliability analysis developed in this paper finds that β is below expectations, γNAC will be calibrated. γRAC is calibrated using reliability analyses on representative cases of design
The partial factor calibrated for Assumption 2 of the shear design of elements with shear reinforcement is a conservative upper bound of the implications of recycled aggregates (RAs) for shear design, and its main purpose is to show that additional experiments on the shear resistance of elements with shear reinforcement are needed prior to a definite calibration of a partial factor for this resistance model

Summary

Introduction

Research on the structural behaviour of recycled aggregate concrete (RAC) demonstrates the feasibility of using coarse recycled aggregates (RAs) for structural concrete applications [1,2]. This is relevant since RAs are produced from construction and demolition waste (CDW), whose recycling is a key objective of the European Union’s strategy for a circular economy [3]. Notwithstanding abundant research arguing in favour of RAC as a structural material [4,5], clear design guidelines are lacking. Guidelines for RAC are needed since RAs are different from coarse natural aggregates (NAs), changing the properties of concrete. The main differences between NAs and RAs are the following:

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