International Concrete Abstracts Portal

The primary purpose of this paper is to introduce and demonstrate the applicability of a statistical concept, the average, for the modeling of the deformations of two-phase composites under load. Concrete is modeled as a well-compacted two-phase composite, the hardened paste as the matrix, and the aggregate as the dispersed phase. Only the paste has creep. The demonstration is done by the development of novel viscoelastic models and their mathematical equivalents for the instantaneous as well as time-dependent deformations of concrete, as a two-phase composite, under load. The underlying principle of the work is based on an extension of earlier publications by the writer in which averages of the averages of the related the phases, the composite averages are offered for the estimation of the modulus of elasticity of composites. Since experimental results supported the composite average method, CAM, quite well for this, it seemed worthwhile to investigate whether the method can be extended for the calculation of time-dependent deformations. The extension consists of the addition of dashboard elements to the existing composite average spring models for the modulus of elasticity of concrete, for the estimation of creep. This is the combinations of two existing spring-dash models for the calculation of the creep: the Poyinting-Thomson model with the Maxwell model the results of which are two CAMs that are determined by the type of combination between these two: one for normal-weight concretes when the two models are connected in a series, and the other, when they are in parallel for lightweight-aggregate concretes. Experimental data on creep with uniaxial loading taken from the literature support these composite models well. Among others, the data and the models show that during the period when the creep development is gradually decelerating: 1. creep values as a function of loading time, give straight lines, let us call them creep lines (compliance functions) in semi-log system as well as in log-log system of coordinates. Consequently, they can be approximated both by logarithmic as well as power functions. Such formulas are suitable for the estimation of creep at a later time from an earlier measurement; and 2. various creep lines of comparable concretes may be parallel, regardless at what age t' the loading started. It is shown that the new models are: well supported by experimental results within reasonable time limits; they are conceptually simple and logical; they are novel; they can consider the composition of the concrete; they represent both E and creep; and they are valid both normal-weight and lightweight-aggregate concretes.

The transport properties of concrete are critical to its field performance. Commonly encountered degradation mechanisms are dependent on ionic diffusivity, sorptivity, and permeability. In this paper, virtual testing of two of these concrete transport properties, diffusivity and permeability, will be reviewed. Virtual evaluations of ionic diffusion (and equivalently conductivity) will be presented as one example that spans the full range of applications, from computations on cement paste with micrometer resolution to a virtual rapid chloride permeability test (RCPT) that simulates the standard ASTM test method for conductivity of concrete cylinders. At the concrete scale, a hard core/soft shell (HCSS) microstructural model may be employed to estimate diffusion coefficients, while finite difference solutions of Fick’s laws that incorporate sorption/reaction may be employed to evaluate remediation strategies for real world bridge decks. Virtual evaluations of permeability are dependent on a sufficient resolution of the pore sizes that are critical for flow under pressure. Two recent successful evaluations will be presented in this paper: the permeability of cement pastes (hydroceramics) cured at elevated temperatures, where transport is controlled by micrometer-sized pores, and the permeability of pervious concrete that is dominated by its coarse porosity (scale of mm). Many of the presented computational (virtual) tools are freely available over the Internet, either for direct access (remote computation) or for downloading.

The NIST-Industry Virtual Cement and Concrete Testing Laboratory (VCCTL) Consortium has developed an integrated software package for performing simulations of a number of engineering test measurements, including isothermal calorimetry, adiabatic temperature change, chemical shrinkage, elastic moduli, and compressive strength. In the last two years, the software interface has been redesigned to be easier to navigate, with online tutorials and documentation for easy reference. As a result, VCCTL is now ready to be integrated in industrial settings as a supplemental tool to accelerate research on mix designs and to streamline routine quality testing procedures. This paper will demonstrate the software interface, and two applications will be described to illustrate the utility of the software to help solve practical problems. In the first application, we address sustainability issues by investigating the replacement of coarse clinker particles with limestone and its effect on elastic moduli and compressive strength. In the second application, we illustrate VCCTL’s potential for screening the quality of incoming cement clinkers by providing rapid estimates of compressive strength development in mortar specimens.

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.

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.