International Concrete Abstracts Portal

This paper describes the enhancements made to the FHWA’s HIPERPAV software program for simulating early-age concrete pavement behavior. It gives a brief background describing the software, discusses the modeling improvements that have been made, and suggests future work for additional improvements. An enhanced moisture transport model has been developed and incorporated into the HIPERPAV software, and results show that the moisture distribution and associated stress/strength developments are significantly affected by the model parameters, environmental, and construction conditions. New inputs were included in the software to define the experimentally determined hydration curve parameters to improve predictions of degree of hydration and portland cement concrete (PCC) temperature development. A batch mode was added for analysis of multiple strategies at once, and a comparison module was created that allow users to compare simulation results from multiple strategies and run sensitivity analysis for multiple variables.

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

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.