Alexandra Bertron

Performance of cement-based materials in aggressive aqueous environments

Concrete and cement-based materials must operate in increasingly aggressive aqueous environments, which may be either natural or Industrial. These materials may suffer degradation in which ion addition and/or ion exchange reactions occur, leading to a breakdown of the matrix microstructure and consequent weakening. Sometimes this degradation can be extremely rapid and serious such as in acidic environments, while in other cases degradation occurs over long periods. Consequences of material failure are usually severe - adversely affecting the health and well-being of human communities and distrurbing ecological balances. there are also large direct costs of maintaining and replacing deteriorated infrastructure and indirect costs from loss of production during maintenance work, which place a great burden on society. The focus of this book is on addressing issues concerning performance of cement-based materials in aggressive aqueous environments, by way of this State-of-the-art Report. The book represents the work of many well-known and respected authors who contributed chapters or parts of chapters. Four main themes were addressed : I. Nature and kinetics of degradation and deterioration mechanisms of cement-based materials in aggressive aqueous environments. II. Modelling of deterioration in such environments. III. Test methodes to assess performance of cement-based materials in such environments, and which can be used to characterise and rate relative performance and inform long term predictions. IV. Engineering implications and consequences of deterioration in aggressive aqueous environments, and engineering approaches to the problem.

Plant aggregates and fibers in earth construction materials: A review

Abstract Earth as a building material is increasingly being studied for its low environmental impact and its availability. Plant aggregates and fibers have been incorporated into the earth matrix in the aim of enhancing performance for thousands of years but scientific studies began quite recently. The present paper reviews the state of the art of research on the influence of these various natural and renewable resources in unfired earth materials such as compressed earth blocks, plasters, and extruded and stabilized blocks. This review, based on 50 major studies, includes characterization of the particles and treatments, and recapitulative tables of the material compositions, and the physical, mechanical, hygrothermal and durability performances of earth-based materials. A lack of references on hygroscopic and durability properties was observed. Future research orientations are thus suggested to promote and develop this type of sustainable material, which provides a solution for saving energy and natural resources.

Attack of Cementitious Materials by Organic Acids in Agricultural and Agrofood Effluents

Agricultural and agrofood industries such as the breeding, dairy or sugar industries produce large quantities of effluents. As these waste waters may be important sources of pollution of the environment, notably of natural water resources (Muller and Heil 1998; Martinez and Le Bozec 2000), they cannot be released into the environment without treatment. They must be collected, stored and eventually treated to comply with chemical, physical, and microbial standards before being released into public streams.

Halomonas desiderata as a bacterial model to predict the possible biological nitrate reduction in concrete cells of nuclear waste disposals

After closure of a waste disposal cell in a repository for radioactive waste, resaturation is likely to cause the release of soluble species contained in cement and bituminous matrices, such as ionic species (nitrates, sulfates, calcium and alkaline ions, etc.), organic matter (mainly organic acids), or gases (from steel containers and reinforced concrete structures as well as from radiolysis within the waste packages). However, in the presence of nitrates in the near-field of waste, the waste cell can initiate oxidative conditions leading to enhanced mobility of redox-sensitive radionuclides (RN). In biotic conditions and in the presence of organic matter and/or hydrogen as electron donors, nitrates may be microbiologically reduced, allowing a return to reducing conditions that promote the safety of storage. Our work aims to analyze the possible microbial reactivity of nitrates at the bitumen - concrete interface in conditions as close as possible to radioactive waste storage conditions in order (i) to evaluate the nitrate reaction kinetics; (ii) to identify the by-products (NO2(-), NH4(+), N2, N2O, etc.); and (iii) to discriminate between the roles of planktonic bacteria and those adhering as a biofilm structure in the denitrifying activity. Leaching experiments on solid matrices (bitumen and cement pastes) were first implemented to define the physicochemical conditions that microorganisms are likely to meet at the bitumen-concrete interface, e.g. highly alkaline pH conditions (10 < pH < 11) imposed by the cement matrix. The screening of a range of anaerobic denitrifying bacterial strains led us to select Halomonas desiderata as a model bacterium capable of catalyzing the reaction of nitrate reduction in these particular conditions of pH. The denitrifying activity of H. desiderata was quantified in a batch bioreactor in the presence of solid matrices and/or leachate from bitumen and cement matrices. Denitrification was relatively fast in the presence of cement matrix (<100 h) and 2-3 times slower in the presence of bituminous matrix (pH 9.7). The maximal rate of denitrification was approximately 0.063 mM h(-1) and some traces of nitrite were detected for a few hours (<2%). Overall, the presence of solid cement promoted the kinetics of denitrification. The inspection of the solid surfaces at the end of the experiment revealed the presence of a biofilm of H. desiderata on the cement paste surface. These attached bacteria showed a comparable denitrifying activity to planktonic bacterial culture. However, no colonization of bitumen was observed either by SEM or by epifluorescence microscopy.

Leaching of Cementitious Materials by Pure Water and Strong Acids (HCl and HNO3)

Ordinary Portland cement (OPC) is highly alkaline with pH values normally above 12.5, and is easily attacked by pure water and acidic solutions (Chandra 1988; Revertegat et al. 1992; Pavlik 1994a; Faucon et al. 1996, 1998; Israel et al. 1997; Allahverdi and Skvara 2000a; Kamali et al. 2008; Glasser et al. 2008). In fact, all hydrated cement compounds are stable only in solutions with well defined ranges of concentrations for Ca2+ and OH− ions. It is well known that in contact with a solution with low mineral content and/or as the pH of the solution decreases, hydrolytic decomposition of the hydrated cement compounds disturbs the equilibrium of the cement matrix, and causes severe degradation of the material, leading to a deterioration in its technical properties (Allahverdi and Skvara 2000a; Pavlik 1994a; Adenot and Buil 1992; Reardon 1990; Biczok 1967; Bertron et al. 2007; Haga et al. 2005a, b; Mainguy et al.2000; Kamali et al. 2008; Jain and Neithalath 2009; Faucon et al. 1996, 1997, 1998). Leaching involves a deterioration of many physical and mechanical properties of cement-based materials such as porosity, elastic modulus, compressive strength, internal friction angle and creep (Burlion et al. 2006; Haga et al. 2005b; Constantinides and Ulm 2004; Bernard et al. 2008; Heukamp et al. 2001; Stora et al. 2009; Sellier et al. 2011).

Microbial Catalysis of Redox Reactions in Concrete Cells of Nuclear Waste Repositories: A Review and Introduction

In order to be able to simulate the behaviour of radionuclides (RN) in waste repositories in space and time it is important to know their chemical speciation. 14C in its reduced form (CH4) does not have the same behaviour as in its oxidised form (CO2, CO 3 − ). Similarly, tritium in the reduced gaseous form, HT, does not at all behave as its oxidised form (liquid water, HTO). For other RN such as U, Se, Tc, Np and Pu the impact is less striking as the change in redox state does not generate a phase change but a change in the sorption behaviour. As a rule of thumb the oxidised form is more mobile than the reduced form. Nuclear waste repositories for both low and intermediate level wastes are characterised by the presence of cementitious phases and zero-valent metals as part of waste, waste containers or engineered materials; organic matter is also likely present in both waste and engineered barrier. Hydrogen gas can be formed either via radiolysis or anaerobic corrosion. We therefore have two main electron donors to participate in redox reactions within an “unnaturally” high pH environment. Oxygen, present during the exploitation phase, is quickly consumed and not considered to diffuse significantly into deep or near-surface repositories. Nitrate, Fe(III) or Mn(IV) are only in specific cases present in significant quantities. Consequently, H+ and C4+ present in water and carbonate will become the main electron acceptors in redox reactions after reduction of sulphates, present in some wastes, concrete and host rocks; H+ and C4+ are likely to control in fine the overall redox potential and the speciation of RN. There is more and more evidence for the microbial control of reactions implying electron transfer within H and C species [Hoehler TM (2005) Biogeochemistry of dihydrogen (H2). In: Sigel A, Sigel H, Sigel RKO (eds) Metal ions in biological systems. Taylor & Francis, Boca Raton, FL, pp 9–48]. Furthermore, the impact of microbial activity on the degradation of complex organic matter (i.e. polymers) adds to the need to evaluate their catalytic impact on waste cell redox potential [Askarieh MM, Chambers AV, Daniel FBD, FitzGerald PL, Holtom GJ, Pilkington NJ, Reesb JH (2000) The chemical and microbial degradation of cellulose in the near field of a repository for radioactive wastes. Waste Manag 20: 93–106]. Quantification of reaction dynamics in alkaline systems involving Fe(0), H2 or organic matter as electron donors and nitrates/sulphates (if present) as well as carbonates or water (and RN in their possibly oxidised form) as electron acceptors will have to consider a microbial catalysis. There are many analogues for testing simulation approaches for microbial catalysis of related redox reactions, but few are in alkaline systems. With H2 almost omnipresent as an energy source, essential and trace nutrients most likely present in the heterogeneous waste cell environment, with space and water available depending on depth, architecture and re-saturation, the high pH may become the most critical parameter controlling microbial activity in space and time. In this chapter, we will review the importance of oxyanions in the nuclear industry and their impact together with concrete, steel and organic matter on the redox state in the near field of a waste storage cell. Particular consideration will be given to the knowledge in relation to alcaliphilic microbial activity in some cases derived from existing natural analogues. Case studies will consider specific redox-sensitive radionuclides in both near surface and deep storage settings. This information will serve as input to two ongoing experimental endeavours dealing with the specific reaction of nitrate reduction by organic matter and/or H2 in the concrete cells for bituminous waste disposal.

Methods for Analyzing the Chemical Mechanisms of Bitumen Aging and Rejuvenation with FTIR Spectrometry

The recycling of asphalt is a process where old pavement is broken up and used as reclaimed asphalt pavement (RAP) in new asphalt pavement, often with the aid of recycling agents. The goal of asphalt recycling agents is to reintroduce the properties lost in bitumen and asphalt during aging such as penetration, softening point, viscosity, ductility, cohesion and adhesion to aggregate, reducing the performance of asphalt and requiring its replacement. The purpose of this study is to observe the chemistry of bitumen aging and the effects of recycling agents may have in reversing it. Fourier transform infrared spectroscopy (FTIR)-attenuated total reflectance (ATR) was used to analyse the bitumen aging and regeneration in terms of the evolution of carbonyl, sulfoxide and other bands. FTIR-ATR microscopy was used to study the distribution of these bands between the aggregates in order to understand the remobilization of the old asphalt (RAP) by the recycling agents through observing their penetration into the RAP. A method for aging bitumen and mastic in a ventilated oven was developed. An increase in C=O and S=O indices was observed with aging, plateauing after 7d.

Methods for Testing Cementitious Materials Exposed to Organic Acids

Concrete in agricultural and agro-industrial settings suffers severe degradation, notably linked with attack by waste waters (De Belie et al. 1997a, 2000a, b; O’Donnell et al. 1995a, b). Waste waters such as liquid manure, silage juices, whey, molasses and distillery residues contain organic acids that attack the concrete. Concrete is the most widely used material for the construction of structures intended for the production, collection, storage and treatment of such effluents as it complies with several requirements: it is economical, watertight, ensures good thermal inertia and respects the health standards imposed in agro-food industries.

General Introduction to Part I

Concrete structures are exposed to aggressive aqueous environments in very varied situations, and the range of aggressive species is wide. Among numerous examples, foundations and/or parts of structures in contact with groundwaters, soils or wastewaters may be subject to sulfate attack, and harbour and other maritime facilities are exposed to the action of seawater involving the combined action of magnesium, sulfates and chlorides. Dams, waterpipes and other structures exposed to the action of soft or carbonated waters suffer leaching and/or carbonation. Many agricultural and agrofood facilities (storage silos, animal houses etc.) suffer severe degradation notably linked with organic acids in waste water. The understanding of the mechanisms of degradation of cementitious matrices by these aggressive media is an essential step toward the development of concrete that performs well in these environments and toward the increase of the service life or the safety of the structures and facilities.

Distribution spatiale de la porosité des matériaux cimentaires : Une approche méthodologique pour leur caractérisation

ABSTRACT Degradation of cementitious matrix in aggressive aqueous environments among others is accompanied by modifications of the spatial distribution of connected porosity. The application of the 14C or 3H-PMMA (polyméthylmethacrylate) impregnation method gives a quantitative and multi-scale representation of this distribution. The first application concerns a mortar, allowing to visualise and to quantify the in situ cement porosity. The second application is related to a cement paste degraded by organic acids. This tool has many potential applications in the field of cementitious materials. It allows a sharp characterisation of internal porosity variations frequently found during durability studies, and furthermore, it provides a realistic geometrical representation of pore space that can be used for solute transfer modelling.