Laboratoire Central Des Ponts Et Chaussees Research Articles

Effect of Binder Rheology and Aggregate Gradation on the Permanent Deformation of Asphalt Mixtures

Rutting is one of the main sources of distress in asphalt pavements and has been widely studied because it influences safety and maintenance costs. To mitigate this distress, the selection of adequate asphalt binder and aggregates and an appropriate balance between them are key elements. This paper analyzed seven asphalt binders (2 neat, 3 polymer-modified, and 2 rubber-asphalt binders) and asphalt mixtures with different gradations (19-mm dense-graded and 12.5-mm gap-graded asphalt mixtures). The asphalt binders were evaluated in terms of rheology with the use of a dynamic shear rheometer (DSR) and a bending beam rheometer (BBR) to obtain the high- and low-performance grade (PG) temperatures. Additionally, multiple stress creep and recovery (MSCR) tests were performed to analyze the rutting potential of the materials at different temperatures. To evaluate the effect of the mineral skeleton on the asphalt mixtures, the Laboratoire Central des Ponts et Chaussees (LCPC) wheel tracking rutting test was performed. The polymer-modified binders (PMBs) and the asphalt mixtures produced with them were the most resistant to permanent deformation with low values of rut depth (< 2.5%). In general, the gap-graded mixtures had better resistance than the dense-graded mixtures; however, this comparison is dependent on the type of asphalt binder. Relationships between the binder and mixture parameters were also proposed and they demonstrated a good relationship between the nonrecoverable creep compliance of the binders (Jnr) and the rut depth of the dense mixtures (R2 = 0.81); however, no significant relationship was found for the gap-graded mixtures (R2 = 0.52).

Influence of particle size distribution, test time, and moisture content on sandy stratum LCPC abrasivity test results

This paper focuses on the influence of particle size distribution, test time, and moisture content on the Laboratoire Central des Ponts et Chaussees (LCPC) abrasivity coefficient (LAC). Image analysis and X-ray diffraction were used to analyze the particle shape characteristics and equivalent quartz content (EQC) of a sandy stratum. The test results show no significant differences in the shape characteristics and EQC of particles with different diameters obtained from the same sandy stratum. For the same EQC, the main factors affecting the LAC are particle size distribution, test time, and moisture content. An optimized effective size (ESop) index was established to represent different particle size distributions. The test results showed that the ESop index is more accurate than other indices in determining the LAC of soil samples, and the LAC had a linear relationship with the ESop index. Soil samples with moisture content less than the saturated moisture content have an LAC larger than that of a dry soil sample, and soil samples with moisture content greater than the saturated moisture content have an LAC similar to that of a dry soil sample. The influence of test time on the LAC of the soil samples could be divided into two stages, where the first and second stages are represented by a quadratic function and a linear function, respectively.

A comparative study of the influence of shift factor equations on master curve construction

This paper evaluates the applicability of different shifting techniques for constructing complex modulus master curves using the time-temperature superposition principle (TTSP). A database of complex modulus results of unmodified bitumens, polymer modified bitumens (PMBs), bitumen-filler mastics, unaged and aged bitumens was used together with a Generalized Logistic Sigmoidal Model to assess the validity of seven different shifting approaches. Except for the Laboratoire Central des Ponts et Chaussees (LCPC) method, the construction of master curves was done using the Generalised Logistic Sigmoidal Model and non-linear least squares regression optimization with the aid of the Microsoft Excel Spreadsheet Solver function. The goodness-of-fit for the various shifting techniques and functions was assessed through graphical and statistical methods. From the study, it was found that a numerical shift approach using non-linear least squares produced the best fit between experimental and predicted data in terms of both graphical and goodness-of-fit statistics. The ranking of the other shifting techniques consisted of the LCPC approach, followed by the William, Landel and Ferry (WLF), Modified Kaelble, Viscosity Temperature Susceptibility (VTS), Arrhenius and Log-Linear methods. However, most of the equations are basically empirical and they are not expected to be strictly obeyed by any materials. Discrepancies were still evident, even for the better functions, for those materials that demonstrated a deviation from the thermorheological simplicity of the rheological behaviour as found for highly structured bitumens following high degrees of polymer modification and/or oxidative ageing.

Evaluation of SBS modified stone mastic asphalt pavement performance

The purpose of this study is to research SBS polymer modified stone mastic asphalt (SMA) pavement performance. With this scope Marshall test (ASTM D1559) test was verified and optimal bitumen contents were calculated with experimental stages. At the optimal bitumen content control and SBS SMA mixtures were evaluated with Marshall Quotient (MQ) approach, repeated creep test (RCT), indirect tensile strength test (ITST), Laboratoire Central des Ponts et Chaussees (LCPC) Wheel tracking tests. According to the MQ results SBS modified samples gives higher values than conventional control mixtures. Higher MQ can be thought as more resistance to the plastic deformation. Controversial results can be obtained with MQ approach for some types of asphalt mixture gradations. Because of structural integrity and stone on stone contact gradation for SMA MQ approach gives more harmonious results. Efficiency of SBS polymer was confirmed with MQ method. Modified samples gave higher indirect tensile strength than control ones. RCT and LCPC wheel tracking test results shows that SBS modified mixtures have lower rutting values than the conventional mixtures.

A newly developed soil abrasion testing method for tunnelling using shield machines

The importance of the effect of ground abrasivity on the performance of a tunnel boring machine (TBM) is important for many tunnelling projects. In recent years, many abrasivity devices have been developed to measure soil abrasivity for specific conditions. In this paper a new device is developed to estimate the abrasivity of the soil for a wide range of site conditions. The device is designed on the basis of simulating the site conditions regarding the ground water, ground stresses and confining pressure of the TBM chamber, and the performance of the rotating cutter-head and pressurized shield tunnelling during its operation. A number of abrasivity tests were carried out on 12 types of crushed rock samples including six sedimentary rocks and six crystalline igneous and metamorphic rocks. The results showed that the abrasivity of the samples increased as equivalent quartz percentages of the sample increased. It was also found that the texture of the samples has a great influence on their abrasivity. To evaluate the performance of the newly developed device, the same samples were tested by other current abrasivity methods including the Cerchar test, Laboratoire Central des Ponts et Chaussees (LCPC) test and soil abrasion test (SAT). Comparisons of the results indicated close correlations, especially with the results for the Cerchar and LCPC devices.

Nonlinear Mixed-Effects Model for the Evaluation and Prediction of Pavement Deterioration

Pavement deterioration models are important inputs for pavement management systems (PMS). These models are based on the study of performance data, and they provide the evolution law of pavement deterioration. Performance data consist of observations of pavement section conditions, and are collected through several follow-up campaigns on road networks. To characterize the pavement deterioration process, several statistical methods have been developed at the Laboratoire Central des Ponts et Chaussees (LCPC). However, these methods are suboptimal for modeling the evolution of pavement deterioration, as they ignore unit-specific random effects and potential correlation among repeated measurements. This paper presents a nonlinear mixed-effects model enabling accounting for the correlation between observations on the same pavement section. On the basis of this nonlinear mixed-effects modeling, we investigate and identify structural and climatic factors that explain differences in the parameters between pavement...

Contribution des fillers calcaires à l’adhérence pâte-granulat. Exemples tunisiens

This article presents compressive test results carried out on a series of hydraulic concrete mixes without admixtures based on Tunisian limestones aggregates. Their estimated strength was calculated with the French model of LCPC (Laboratoire Central des Ponts et Chaussees), which takes into account the effect of bond to the paste and the ceiling effect of the aggregates. To check the experimental values, the parameter of bond had to be associated the content of fillers aggregates, because the performances predicted by the model are lower than the measurements, at least beyond 10% of fillers. The assumption is that the presence of these fine elements, of comparable nature that the aggregates, improves adherence or linking between paste and aggregate, thanks to bringing together the properties of rigidity of the two materials and to a better homogeneity of the system. The relationship found between the calcareous filler ratio and the bond coefficient then makes it possible to extend the forecasts of the model to the hydraulic mixtures containing aggregates crushed limestones, naturally rich in fillers.

Concrete beams submitted to various moisture environments

This paper deals with the effects of various moisture environments on the structural behavior of concrete beams. The presented results were obtained within a large experimental program carried out at the Laboratoire Central des Ponts et Chaussees (LCPC), with Electricite de France (EDF) as a partner. The aim of this paper is to point out and to quantity the strains resulting from unidirectional moisture conditions: a drying gradient applied during 14 months, followed by the re-wetting of the dried surface during 9 months. The effect of reinforcement on the shrinkage and on the deformation due to water absorption is pointed out. Moreover, a lot of tests on companion cylinders and prisms were carried out to determine the mechanical characteristics of the material and help checking analysis methods. The paper focuses on numerous measurements obtained during the 23 months on one plain concrete beam and one reinforced concrete beam: variation of water content, followed by precise weighing and gammadensitometry, relative humidity measurements, local and global deformations in the three directions and deflection of the beams. Thus, the effects of drying and water absorption on the behavior of concrete structures are documented and analyzed in comparison with existing representation of water diffusion.

Development of new cement composite materials for construction

For almost ten years ultra-high performance fibre reinforced concrete (UHPFRC) has been developed throughout the world. After a reviewing and carrying out a critical analysis of the different UHPFRCs which exist, and some prospects related to these materials, a new cementitious composite, patented by the Laboratoire Central des Ponts et Chaussees (LCPC) in France, is presented. This UHPFRC has such good mechanical behaviour in tension that it is possible to construct structures or manufacture structural members without reinforcement in addition to the fibres.

Structural Behavior of Concrete Beams Affected by Alkali-Silica Reaction

This article reports on an alkali-silica reaction (ASR) study that was carried out on beam specimens at the Laboratoire Central des Ponts et Chaussees (LCPC), with Electricite de France (EDF) as a partner. In the study, three-dimensional deformations were measured on five 3 m-long plain or reinforced concrete beams undergoing partial drying over a period of 14 months. The authors discuss the effect of a moisture gradient over the depth of the beams and the influence of reinforcement on the development of ASR-induced expansions. Tests on companion specimens (cylinders and prisms) were carried out to measure the material expansion and mechanical characteristics, including longitudinal strains and beam deflections, transverse strains, vertical strains, and cracking. The authors make three main conclusions: the anisotropy of ASR-induced expansions has been verified with vertical swellings twice as large as horizontal ones; significant ASR expansions (0.10%) can occur without an external water supply and can lead to significant structural degradation; and an increase in ASR expansions with an external water supply has been quantified by this work. The authors note that once models are validated in this framework, they will be used to assess the dimensional stability and the residual bearing capacity of real ASR-affected structures (e.g., bridges and dams).

Water distribution in concrete beams

Moisture transfers have a major effect on concrete durability. For Alkali-Silica Reaction (ASR), chemical swellings depend on water content, and drying can have important consequences. Within the framework of a large experimental study developed in partnership by the Laboratoire Central des Ponts et Chaussees (LCPC) and Electricite de France (EDF), the continuous measurements of moisture transfer in reactive concrete structures was one of the main purposes. This paper deals with the large data bank on concrete drying and water absorption, measured on six 3 m long beams with weighing and gammadensitometry devices specially designed for this study. These measurements enable some quantitative conclusions to be reached. Moreover, the data allows the validation of models of moisture transfer representing the mass variation with time in the beams. Profiles of mass variations thus obtained are the mandatory first step of calculations to estimate the mechanical behaviour of these reference or ASR damaged beams.

Water distribution in beams damaged by alkali-silica reaction: Global weighing and local gammadensitometry

Within the framework of an experimental programme developed by the Laboratoire Central des Ponts et Chaussees (LCPC) and Electricite de France (EDF), in the aim of increasing knowledge on Alkali-Silica Reaction (ASR) and understanding the effect of water on ASR development in structures, two techniques have been designed to measure water content vs. time in large-scale concrete specimens. Global weighing variations are monitored on six 900 kg beams; and the, gammadensitometry measurement allows evaluating water content profiles in the beams. These two complementary measurements serve to validate water content models and correlate the moisture gradient with measured deformations The measurement principle, execution, and qualification are first described. The accuracy of the weighing device is thus evaluated at 10 g, and the uncertainty of the gammadensitometry method is close to 0.4% of relative mass. The paper then presents the results of one-year monitoring conducted on one of these beams and proves the consistency of these methods. At last, it is shown that the square root of time kinetics allows a good representation of the global mass variations of the beams and that the drying depth reaches between 80 and 100 mm after one year exposure.