Several studies have demonstrated the reliability of the Stiffness Damage Test (SDT) (a mechanical test) and the Damage Rating Index (DRI) (a petrographic test) as diagnostic tools for ordinary concrete (aggregate particle sizes up to 20 mm) under free expansion. There is however limited information on the application of these tools to mass concrete mixtures incorporating large coarse aggregate particles and subjected to several stress states. This paper presents the findings of a study aimed at evaluating the use of these tools for mass concrete with reactive coarse aggregate particle sizes ranging from 5 to 40 mm. The SDT and DRI tests were performed on concrete specimens subjected to different stress states (with or without sustained load and/or passive confinement) at 100

In the context of massive concrete structure ageing, such as nuclear power plant containments or hydroelectric dams, the study of cementitious material durability is of great interest. In particular, the Alkali-Silica Reaction (ASR) can drastically reduce the durability of such structures. A reactive transport model (species transport and chemical reaction) of ASR able to simulate the progressive aggregate dissolution, the silica gel precipitation and its localization depending on the aggregate characteristics (chemical composition, diffusion properties, size, and morphology) is proposed. The objective is to consider mainly physical measurable parameters and thermodynamic constants. The ion transport is given by Fick's second law of diffusion and the geochemical system models the aqueous complexation and solid reactions. The thermodynamic equilibrium of chemical processes is assumed, except for the dissolution of the reactive silica, that is modeled by a kinetic reaction. Two main reaction products of ASR are considered, a low Ca/Si ratio C-S-H and an expansive alkali-silica gel. The application focuses on the cement paste and aggregate interaction. The results fit well with the experimental observations where the ASR gel forms inside the aggregate particle and the C-S-H precipitates at the interface between paste and the particle. The effect of aggregate composition and particle size on the overall ASR kinetic and gel precipitated localization is investigated.

A promising prognosis approach developed at the Laboratoire des Matériaux et de la Durabilité de Constructions (LMDC) based on the reactive silica consumption kinetics was applied to an hydro-electric dam located in province of Quebec, Canada. Accelerated expansion tests in immersion conditions (1N NaOH solution) were carried out on mortar specimens of three different sizes made with unreacted rock material (metagrauwacke) crushed into four different particle sizes. The optimal combination of aggregate size (600–1180 µm) and mortar bar size (252 × 25 × 285 mm) for this aggregate was determined based on expansion results measured after 546 days. Accelerated tests in similar conditions with unreacted rock material and two gradations (5–20 and 20–40 mm) of aggregates recovered from the dam’s concrete and crushed to optimal aggregate gradation showed results well aligned with the reactive silica consumption model implied in LMDC’s method. LMDC’s testing method appeared effective in consuming reactive silica. However, mechanism of consumption of the reactive silica in site conditions differs from those of the accelerated expansion tests in alkali rich immersion conditions.

Mass concrete specimens, consisting of concrete cores drilled in various directions from large blocks cast in the laboratory, were stored under conditions favorable to the development of ASR (38 ℃; 100

In the context of concrete structures ageing, the study of cementitious material durability is of critical importance, particularly the degradations caused by the Alkali-Silica Reaction (ASR). This reaction is driven by the reactive silica dissolution of the concrete aggregate and can unfold in different manner according to the aggregate. The goal of the study is to improve the evaluation of the aggregate reactivity, in terms of quantity of reactive silica and dissolution rate, linked to the form and state (crystalline, amorphous, micro-crystalline) of the aggregate structure. Four aggregates were selected for this study: Potsdam sandstone, Springhill greywacke, Spratt limestone, and a non-reactive Quartzite (used as a reference). For dissolution properties assessment, the aggregates were immersed in a basic solution to promote the degradation of their reactive structure. To reproduce an idealized highly alkaline solution close to a concrete pore solution, dissolution tests were performed on a 1M NaOH solution. Two particle size fractions for each aggregate: 0.5 mm–1 mm and 1–2 mm (with a solid to solution mass ratio of 1:4) and three temperatures: 25, 38, and 60 ℃ were considered. Silica concentration in the solution was measured by complexometric titration. The study displays the dissolution rate constants and analyses the cause of the differences in dissolution.

This work aims to study the effects of alkali-silica reaction (ASR) on the fracture energy of reactive mass concrete mixtures (maximum aggregate sizes of 38 mm and 76 mm), characteristic of an existing hydro-electric facility. More than 40 large concrete blocks were casted and stored in a controlled environmental chamber for more than 1100 days. The blocks as well as cylindrical reference cores were monitored in expansion. Wedge splitting (WS) tests with different notch to depth ratios, were performed at different ASR advancements to assess the evolution of mechanical and fracture parameters of concrete. Digital Image Correlation (DIC) technique was used to monitor the tests. Damage Rate Index (DRI) technique was also performed on cores extracted from the blocks, following the completion of the splitting tests. Important size and heterogeneity effects were observed on the assessed ASR expansion and fracture energy. By filtering these effects, it was possible to assess for the first time in literature the evolution of size-independent fracture energy with respect to intrinsic volumetric expansion of concrete. The findings suggest that fracture energy increases for moderate levels of expansion, due to crack branching within the splitting crack, interacting with pre-existing ASR-induced cracks. This phenomenon was not observed for the case of a few horizontally cast blocks where the splitting crack ran parallel to pre-existing ASR cracks, indicating an anisotropy in ASR damage effects on the fracture energy of concrete.

The influence of boundary effects on the experimental results of concrete specimens is a phenomenon known for several decades. They are believed to be the main cause of size effects affecting physico-chemical concrete parameters assessed in the laboratory. For the specific context of hydraulic structures affected by ASR, they have a considerable impact on the predictions of numerical multi-physical simulations. This work highlights and quantifies the chemical and mechanical boundary effects that have arisen during a large experimental program to characterize the mechanical properties and ASR kinetics of a reactive mass concrete mixture used in the construction of an existing hydro-electric facility (maximum aggregate size of 76 mm). The focus is made on the fracture energy and the ASR free expansion curve, two important parameters for constitutive macro chemo-mechanical concrete models. Influence of specimen free boundary effects is highlighted on both parameters using a chemical-mechanical analogy. Also, the laser-induced breakdown spectroscopy (LIBS) with fast high-resolution scan technology is explored for the context of concrete samples affected by ASR. LIBS was found in this work in-progress study, as an interesting quantitative tool to characterize the chemical size effects.

This paper summarizes an important R D industry-university collaboration project related to a hydro-electric facility affected by alkali-silica reaction (ASR). The work in progress started almost ten years ago and aims to predict the long-term behavior of the facility using advanced finite element method (FEM). After a presentation of the facility, extensive experimental investigation campaigns on concrete cores extracted from the dam and on specimens made from concrete mixtures similar in composition and constituents to the ones used for construction will be detailed. Three laboratories were involved in the characterization campaigns. At Hydro-Quebec (HQ) research institute (IREQ), basic concrete testing, expansion and long-term creep tests were performed. At Polytechnique Montreal, large concrete blocks were tested using wedge splitting tests to assess the impact of ASR on the concrete fracture energy (size independent), a fundamental input parameter for numerical modelling of mass concrete structures. At Laval University, the focus was on characterizing the kinetics of the reaction, the anisotropy effects from casting or coring direction and the effect of confinement upon expansion. The paper presents the results from an owner’s strategic perspective and discusses how they will be applied to the management of the dam. More advanced technical and scientific aspects are detailed in other papers presented at ICAAR 2024.

An existing hydroelectric facility affected by alkali-aggregate reaction (AAR) is considered in this study through numerical and experimental investigations. A new developed phenomenological hygro-chemo-mechanical approach for AAR is presented and is shown to be practical and effective in damage assessing of large-scale hydraulic concrete structures. Experimental investigations were conducted to characterize the AAR kinetics of mass concrete mixture with very large aggregates, used in the construction of the facility. By combining experimental, numerical, and monitoring investigations, it was possible to assess size effects related to the free AAR expansion of mass concrete. Numerical simulations allowed to obtain a damage pattern similar to the cracking profile of the existing facility, to provide mechanical interpretation of the jumps observed in the instrumentation data, and most importantly, to predict the remaining time before reaching the asymptotic expansion of the facility: a very important result for owners of hydroelectric facilities affected by AAR.

This work aims to fill the gap between experimentation on laboratory specimens and structural diagnosis of mass concrete hydraulic structures affected by alkali-aggregate reaction (AAR) by conducting numerical and experimental investigations on an existing hydroelectric facility affected by AAR. A large experimental program was performed to characterize the mechanical properties and the kinetics of the AAR chemical reaction for the original mass concrete used in the construction of the facility (maximum aggregate size of 76 mm). The importance of considering mechanical and chemical size effects is discussed, on the basis of the asymptotic fracture energy and the free AAR expansion curve. The developed phenomenological hygro-chemo-mechanical approach for AAR modelling in mass concrete hydraulic structures is presented. The efficient and yet simple approach is based on three analyzes: transient thermal analysis, transient hygral analysis, and final multi-physical analysis that includes mechanical loading. The modelling approach was validated with existing benchmarks from the literature and provided very promising results, despite the simplifications made and the assumptions for some uncertain input parameters. Application of the numerical modelling approach to the existing hydraulic facility demonstrated its feasibility in an industrial context. It also provided fairly similar damage pattern if compared to the existing cracking pattern and improved the understanding of the complex structural behaviour of the facility. Comparison of displacement model predictions and available monitoring data allowed to assess an important size effect between laboratory and in-situ expansions.