International Concrete Abstracts Portal

Alkali silica reaction (ASR) causes premature and unrecoverable deteriorations of numerous civil engineering structures. ASR-expansions and induced cracking can affect the functional capacity of bridges and dams. Several hydraulic dams of Electricité de France (EDF) are concerned by ASR. Therefore, a behaviour model implemented in a finite element code has been developed in order to assess the safety level and the maintenance choices of these degraded structures. This approach has the particularity of modelling the ASR structural effects from the construction of the structure until today. It uses several ASR advancement variables, one for each aggregate size range of the affected concrete. These advancement variables depend on both the saturation degree and the temperature in the dam. The difficulty of using a classical residual expansion test on core samples to fit the model is pointed out, particularly when the swelling rate is slow due to low alkali content in the concrete. Thus, the authors propose an original approach combining additional tests and physical modelling to assess the chemical advancement of the ASR for each aggregate size of the affected concrete. Only the chemical advancement, which is a normalized variable linked to the residual reactive silica content, is measured in laboratory. The concrete residual potential expansion is not measured on laboratory tests but fitted through an inverse analysis based on a finite element structural calculation.

A simulation algorithm was developed for modeling the dense packing of large assemblies of particulate materials (in the order of millions). These assemblies represent the real aggregate systems of portland cement concrete. Two variations of the algorithm are proposed: Sequential Packing Model and Particles Suspension Model. A developed multi-cell packing procedure as well as fine adjustment of the algorithm’s parameters were useful to optimize the computational resources (i.e., to realize the trade-off between the memory and packing time). Some options to speed up the algorithm and to pack very large volumes of spherical entities (up to 10 millions) are discussed. The described procedure resulted in a quick method for packing of large assemblies of particulate materials. The influence of model variables on the degree of packing and the corresponding distribution of particles was analyzed. Based on the simulation results, different particle size distributions of particulate materials are correlated to their packing degree. The developed algorithm generates and visualizes dense packings corresponding to concrete aggregates. These packings show a good agreement with the standard requirements and available research data. The results of the research can be applied to the optimal proportioning of concrete mixtures.

Stresses develop in portland cement concrete pavement at early ages when volume changes associated with hydration reactions, moisture loss, and temperature variations are restrained. Saw-cuts are placed in concrete pavements to provide a weakened plane that enables cracks to form as intended, thereby relieving developed residual stresses. Although the idea of creating a weakened plane by saw-cutting is relatively straight forward, practically determining the timing and depth of saw-cut can be complicated in field construction. This study uses a finite element model (FEMMASSE) to evaluate influence of saw-cut timing on cracking behavior of concrete pavements. The model considers the influence of ambient temperature, cooling effect of wind, and time of casting. It is shown that the saw-cutting time window was reduced as ambient temperature was increased. Higher wind speeds influence the saw-cutting time window to a lesser degree at high ambient temperatures than they do at lower ambient temperatures. It was also shown that the time of casting influences the saw-cutting time window and it needs to be considered in estimating the saw-cutting time window especially at high ambient temperatures.

This CD-ROM consists of ten papers that were presented by ACI Committees 236 and 188, at the ACI Fall 2009 Convention in New Orleans, LA, in November 2009. The papers cover durability models, early age models, virtual testing and mechanical behavior models. Note: The individual papers are also available. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP-266

The alkali aggregate reaction (AAR) is affecting numerous civil engineering structures and is responsible for unrecoverable expansion and cracking which can affect their functional capacity. In order to control the safety level and the maintenance cost of its hydraulic dams, Electricité de France (EDF) has to get a better understanding and a better prediction of the expansion phenomena. In this context, EDF is developing a numerical modelling based on the finite element method in order to assess the mechanical behavior of degraded structures. Obtaining a good prediction of expansive phenomena requires the identification and realistic modelling of the underlying physical, chemical and mechanical phenomena. The model takes into account the mechanical damage, the creep of concrete and the stress induced by the formation of AAR gel. Coupling between the different phenomena (creep, AAR and anisotropic damage) are taken into account through a rheological modelling. First , experimental results obtained on concrete cylinders and beams affected by AAR are simulated to verify whether the model can describe the behavior of degraded structures.