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About this book

This book is mainly based on the results of the EU-funded UE-FP7 Project EnCoRe, which aimed to characterize the key physical and mechanical properties of a novel class of advanced cement-based materials incorporating recycled powders and aggregates and/or natural ingredients in order to allow partial or even total replacement of conventional constituents. More specifically, the project objectives were to predict the physical and mechanical performance of concrete with recycled aggregates; to understand the potential contribution of recycled fibers as a dispersed reinforcement in concrete matrices; and to demonstrate the feasibility and possible applications of natural fibers as a reinforcement in cementitious composites. All of these aspects are fully covered in the book. The opening chapters explain the material concept and design and discuss the experimental characterization of the physical, chemical, and mechanical properties of the recycled raw constituents, as well as of the cementitious composite incorporating them. The numerical models with potentialities for describing the behavior at material and structural level of constructions systems made by these composites are presented. Finally, engineering applications and guidelines for production and design are proposed.

Table of Contents


Recycled Aggregate Concrete


Chapter 1. State of Knowledge on Green Concrete with Recycled Aggregates and Cement Replacement

Since the construction industry is characterized by a huge demand for both energy and raw materials, it is fully concerned by the need for enhancing sustainability, which is certainly the main challenge for all industrial sectors in the twenty-first century. Therefore, several solutions are nowadays under investigation to reduce the environmental impact of concrete production. They often consist of partially replacing the ordinary concrete constituents with recycled ones, in view of the objective of reducing both the demand of raw materials and the amount of waste to be disposed in landfills. The most recent advances in this field are summarized in this chapter, which is intended at drawing the line of the current state of knowledge on “sustainable” structural concrete.
Enzo Martinelli, Eduardus A.B. Koenders, Marco Pepe

Chapter 2. Concrete with Recycled Aggregates: Experimental Investigations

The mechanical behaviour of Recycled Aggregate Concrete (RAC) is investigated by reporting the main results of experimental tests intended at understanding the influence of Recycled Concrete Aggregates (RCAs) on the resulting mechanical properties of concrete. The focus is placed on the higher porosity of RCAs and their higher water absorption capacity. Consequently, the role of the initial moisture conditions of RCAs at mixing is also unveiled and its consequences on both the hydration reaction and the time evolution of compressive strength are highlighted. The influence of processing procedures intended at reducing the aforementioned porosity is also discussed.
Carmine Lima, Marco Pepe, Ciro Faella, Enzo Martinelli

Chapter 3. Cement Replacement: Experimental Results for Concrete with Recycled Aggregates and Fly-Ash

The experimental activity reported in this chapter was aimed at enhancing the knowledge about the mechanical behaviour and durability of concretes made with Recycled Concrete Aggregates (RCAs) and coal Fly Ash (FA) and their possible use for structural purposes. To this end, starting from a reference concrete composition, twelve mixtures were designed by replacing part of the ordinary constituents (i.e. cement, sand and coarse aggregates) with the FA and RCAs. The time evolution of the compressive strength, as well as the splitting strength, were measured with the aim to monitor the mechanical performance, whereas the durability performance was scrutinised by measuring water permeability, carbonation depth and chloride-ions ingress. The obtained results unveil the influence of both RCAs and FA on the resulting concrete performance and highlight that their combined use can lead to a synergistic effect in terms of the relevant physical and mechanical properties of structural concrete.
Carmine Lima, Ciro Faella, Marco Pepe, Enzo Martinelli

Chapter 4. Insights into the Triaxial Behaviour of Recycled Aggregate Concrete

In this chapter, the results of an experimental programme aiming to investigate the incidence of different replacements ratios of natural coarse aggregates by recycled ones on the mechanical behaviour of Recycled Aggregate Concrete (RAC) under tri-axial compression stress states are presented and discussed. The experimental campaign performed at the University of Buenos Aires considers four concrete mixtures including a reference or parent concrete and RACs with 30, 60 and 100% of coarse aggregate replacements. Besides the aforementioned tri-axial compression tests, the results of splitting tensile and uniaxial compression experimental tests are also presented. It is showed that increasing levels of recycled aggregates lead to concretes more sensitive to confinement.
Paula Folino, Hernán Xargay

Chapter 5. Constitutive Formulations for Concrete with Recycled Aggregates

In this Chapter, a thermodynamically consistent gradient model is proposed for natural aggregate concrete and then, modified to take into account the addition of different contents of recycled aggregates and its influence on concrete mechanical response. A particular and simple form of gradient-based plasticity is considered, where the state variables are the only ones of non-local character. After describing the material formulation for natural and recycled aggregate concretes, the model calibration is performed with experimental data taken from literature. A comprehensive numerical analysis is presented, where the effects of the recycled aggregate content on the performance of concrete in pre and post-peak behavior are evaluated and discussed, for different stress states. Finally, the ability of the model to capture the variation of mechanical response of concrete with different recycled aggregate contents is demonstrated for different mechanical tests.
Antonio Caggiano, Guillermo Etse, Paula Folino, Marianela Ripani, Sonia Vrech

Chapter 6. Generalised Mix Design Rules for Concrete with Recycled Aggregates

A conceptual formulation for controlling the resulting mechanical properties of Recycled Aggregate Concretes (RACs) is proposed via a set of generalised mix-design rules intended at covering the specific features of Recycled Concrete Aggregates (RCAs). As a matter of fact‚ the RCAs are characterised by a higher porosity and water absorption capacity than ordinary aggregates and‚ thus‚ general mix-design rules for ordinary structural concrete cannot be applied to RACs as such. Therefore‚ the formulations proposed herein are intended at generalising those rules taking into account the key properties of RCAs‚ as they are possibly influenced by the alternative processing procedures‚ which can be applied when turning demolition debris into concrete aggregates. Particularly‚ these formulations aim at predicting both the final value and the time evolution of compressive strength of RACs depending on their production procedure and mixture composition. The proposed formulations are calibrated and validated on the results of various experimental campaigns covering the effect of several aspects and parameters‚ such as the processing procedures‚ the source for RCAs‚ the actual aggregate replacement ratio‚ the water-to-cement ratio‚ the water absorption capacity and the initial moisture condition of coarse recycled aggregates. Design charts of the proposed formulations show ease of the method as well as the potential of employing this rational design method for RAC.
Eduardus A. B. Koenders, Enzo Martinelli, Marco Pepe, Romildo Dias Toledo Filho

Cementitious Materials Reinforced with Recycled or Natural Fibers—Technology, Properties, Design and Applications


Chapter 7. Introduction

Without Abstract
Joaquim A. O. Barros, Liberato Ferrara

Chapter 8. Cementitious Composites Reinforced with Recycled Fibres

Pneumatic tyres are nowadays among the most widespread industrial products and, hence, handling tyres that have reached their end-of-life is indeed a critical issue. This Chapter provides readers with the key facts about tyre production and consumption. Particularly, it describes the raw materials which they are made from, and summarises the main classifications currently accepted worldwide. The typical product life-cycle is shortly outlined before analysing the possibility of recycling waste tyres for producing new products. Relevant properties of concrete reinforced with recycled fibres are presented, with special focus on the post-cracking behaviour of these composite materials. Emphasis is given to the suitability of using recycled fibres obtained from waste tyres as partial or total replacement of industrial steel fibres for obtaining fibre reinforced concrete.
Joaquim A. O. Barros, Cristina Frazão, Antonio Caggiano, Paula Folino, Enzo Martinelli, Hernan Xargay, Zia Zamanzadeh, Lúcio Lourenço

Chapter 9. Cementitious Composites Reinforced with Natural Fibres

Natural fibres as dispersed reinforcement in cement-based materials may represent an interesting alternative to industrial fibres, because of their good mechanical properties and inborn sustainability signature. In this section the mechanical properties of Natural Fibre Reinforced Cementitious Composites (NFRCCs) will be reviewed. Cutting-edge topics will be finally addressed, focusing, on the one hand, on the use of nano-sized cellulose-based constituents in cementitious composites, and, on the other, on the self-healing capacity that natural fibres may bring to cementitious composites. An appendix summarizing the main properties of the natural fibres so far most commonly employed in cementitious composites will complement this information.
Liberato Ferrara, Saulo Rocha Ferreira, Visar Krelani, Paulo Lima, Flavio Silva, Romildo Dias Toledo Filho

Chapter 10. Approaches for the Design of Structures Made by Concrete Reinforced with Sustainable Fibres

In this section design recommendations for Fibre Reinforced Concrete and Cementitious Composites (FRCC) are presented, with main reference to the ones proposed by RILEM TC 162-TDF (2003) for SFRC and the ones proposed by CEB-FIP Model Code 2010 (MC2010). As a matter of fact, no specific reliable design recommendations are available so far for concrete reinforced with sustainable, either recycled or natural, fibres due to the relative novelty of these composite materials. However, when short discrete natural or recycled fibres, herein encompassed within the common wording of sustainable fibres, are used as a randomly distributed reinforcement in a concrete matrix, the design recommendations of the MC2010 can, in general, be adopted for the design of sustainable FRCC elements. Nevertheless, to the aforementioned purpose, the fibre reinforced composite materials have to be experimentally characterized according to the procedures described in Sect. 8.​2.​5, in order to obtain the residual flexural tensile strength parameters (f Rj ) to model the post-cracking behaviour. Some design tools are also proposed to design specific aspects of sustainable FRCC, such is the case of composites reinforced with continuous (long) vegetable fibres.
Joaquim A. O. Barros, Liberato Ferrara

Chapter 11. Inverse Analysis for Deriving the Fracture Properties of RSFRC

This section is dedicated to the description of a numerical strategy to derive the parameters that define the fracture mode I and fracture mode II of fibre reinforced concrete (FRC). This strategy is herein designated by inverse analysis (IA), and it was used to determine the mode I and II fracture parameters of Recycled Steel Fibre Reinforced Concrete (RSFRC) developed in Chap. 8. From the theoretical point of view the proposed IA is applicable to any type of FRC, as long as the setup of the experimental tests, whose results are adopted in the IA, assures the fracture is limited to a unique crack.
Joaquim A. O. Barros

Chapter 12. Advanced Numerical Models for the Analysis of Sustainable FRC Structures

This chapter introduces some of the relevant modelling approaches that are being used to simulate the behaviour of cementitious materials reinforced with discrete fibres. The major part of these approaches were originally proposed for modelling non-fibrous reinforced cement based materials‚ therefore the main focus herein given is related to the aspects how fibre reinforcement mechanisms have been considered. These approaches were grouped in two classes‚ one where fibres are explicitly considered in the finite element mesh (FEMesh)‚ herein designated as Discrete Fibre Reinforcement Approaches (DFRAs). The other class is designated by smeared fibre reinforcement approaches (SFRAs)‚ where fibres are not part of the FEMesh and their contribution is basically considered attributing a constitutive law to the FRC that simulates the fibre reinforcement mechanisms in terms of the fracture modes of this composite material.
Antonio Caggiano, Joaquim A. O. Barros, Guillermo Etse

Chapter 13. Exploring the Use of Cement Based Materials Reinforced with Sustainable Fibres for Structural Applications

This section presents some construction applications where sustainable fibres (both natural and from tire recycling industry) are used as fundamental or complementary reinforcement of cement based materials. Recent significant advances have been achieved on the enhancement of durability performance of natural (also currently designated by vegetable) fibres for the reinforcement of cement based matrices, and research efforts have been demonstrating the reinforcement performance of RSF as well. Because of this, and of the increasing concern of the society on the aspects affecting detrimentally the environmental conditions, a new phase seems to appear in the scientific and technical communities dedicated to explore the use of cementitious composites reinforced with different kinds of sustainable fibres for structural applications by demonstrating their economic and technical advantages.
Paulo R. L. Lima, Joaquim A. O. Barros


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