Washington Peres Nunez

Electric Arc Furnace Steel Slag: Base Material for Low-Volume Roads

The results of a study of the use of electric furnace slag as pavement aggregates are presented. Slag is generated as waste during steel production in industrial plants that use electric arc furnaces. Tests for the following were carried out to determine the characteristics of the aggregate: grain size distribution, soundness, Los Angeles abrasion, compaction, California bearing ratio, resilient modulus, and expansion. To use the slag as a granular layer, its grain size distribution had to be corrected. This procedure increased the bearing capacity and workability of the material. Evaluation of the expansion potential showed that the slag must be stocked in the open air for at least 4 months before it can be used in pavement construction. After correction of the gradation, the slag presented a resilient modulus that exceeded those of traditional granular materials; its use resulted in thinner and cheaper pavements. The results of the study led to the conclusion that the use of electric arc furnace slag as pavement material is possible and that it provides remarkably good technical quality and economic advantages.

SEASONAL VARIATIONS OF A SUBGRADE SOIL RESILIENT MODULUS IN SOUTHERN BRAZIL

The influence of suction on the resilient modulus of a shale residual lateritic soil was analyzed. Laboratory tests were carried out to obtain the moisture content-suction relationship and determine the resilient moduli of specimens submitted to drying, wetting, or wetting-after-drying paths. A supplementary study on the effects of compaction method on soil resilient modulus was carried out. Soil suction was measured in situ, with jet-fill tensiometers installed along test sections built in a pavement testing facility. Test sections were loaded by a traffic simulator, and periodically deflections were measured for modulus backcalculation. Laboratory and in situ results confirmed the consensus that suction remarkably affects soil elastic deformability. Wetting-after-drying paths proved to be an extremely severe condition that may lower resilient modulus up to four times. Static compaction led to resilient moduli higher than those of specimens compacted dynamically or by kneading. In situ results matched reasonably well with laboratory moduli of specimens compacted by kneading and tested at optimum moisture content. In general, the importance of drainage design and maintenance was clearly confirmed. In well-drained pavements, subgrade soils will not be saturated for long periods. Suction will control stress state and soil deformability and guarantee that the pavement will carry the designed traffic before failure.

Development of Roughness Prediction Models for Low-Volume Road Networks in Northeast Brazil

Roughness evaluation is the most effective way to diagnose pavement condition for design and decision making. The index most commonly used worldwide to indirectly describe the surface condition of asphalt pavements is the international roughness index (IRI). However, few studies have tried to predict the pavement performance of low-volume roads (LVRs) on the basis of the IRI, especially for LVRs in tropical regions. In an attempt to remedy that lack of knowledge, this paper presents IRI-based prediction models developed for asphalt pavement LVR networks in northeast Brazil. The following independent variables were considered to affect the IRI: Thornthwaites aridity index, which describes local climate; the modified structural number, representing pavement bearing capacity; and the cumulative number of equivalent single-axle loads, representing the traffic applied to the pavements. A multiple regression analysis was carried out, and the results showed that the IRI increases exponentially over time. The analysis of the model parameters confirmed their significance, and the R-square values were 0.87 and 0.94, respectively, for low-volume roads with hot asphalt mixes and bituminous surface treatments. The hot-mix asphalt model was compared with that of the Highway Development and Management Model and with other models developed in research also sponsored by the World Bank. Because of regional differences (especially climate and materials), the models proposed in this paper provide a better estimation of roughness progression in LVRs of the northeast of Brazil.

Rutting of thin pavements: Full-scale study

Since 1992, the Federal University of Rio Grande do Sul, along with the roads department of the same Brazilian state, has undertaken comprehensive research on weathered basalts, with the purpose of reducing the cost of low-volume pavements. Laboratory studies have led to a criterion (on the basis of the point load test) used to select deposits of these intensely fractured rocks. A traffic simulator was designed and built, and a pavement test facility was constructed on the university campus. A study was done of rutting of thin pavements on which weathered basalts were used as base layers. The traffic simulator applied more than 267,000 axle loads, ranging from 82 to 130 kN, on five full-scale test sections. Two different weathered basalts and three base thicknesses were used. A postmortem evaluation revealed that the base layer contributed the most to rutting. The axle load applications caused the pavement structure to settle and consolidate. A total of 4,148 measurements of rut depth, made at intervals, provided a statistically significant data set. Rutting evolution was shown to depend not only on traffic characteristics but also on pavement structure. With consideration of rutting as a major failure cause in thin pavements and a rut depth of 25 mm as a terminal criterion, load equivalence factors were calculated by means of a reliability analysis.

Effect of burning temperature on alkaline reactivity of rice husk ash with lime

The rice husk ash (RHA) is a by-product of rice milling, being used as a soil stabiliser to build roads, an economical alternative with environmental benefits. A research of the influence of kind and temperature of burning on the reactivity of RHA and mixtures with sandy soil and lime was made. A no controlled temperature RHA and RHAs done with different controlled temperatures were used. X-ray diffraction analyses and loss on ignition tests were carried out on RHAs. X-ray diffraction analyses, unconfined compressive strength, and splitting tensile strength tests were conducted on mixtures of sandy soil with different RHAs and lime. The results showed that the optimal reactivity of the RHA is reached for a range of controlled temperature of 650–800°C, providing a significant increase on the strength and stiffness of mixtures.

Investigation of Thin Pavements Rutting Based on Accelerated Pavement Testing and Repeated Loading Triaxial Tests

This paper discusses the permanent deformation behavior of unbound aggregates used in accelerated pavement test (APT) sec- tions. A traffic simulator loaded two test pavements consisting of surface treatment, dense crushed rock bases, and macadam subbases. The dependence of rutting evolution on stress state was verified, and a model relating rut depth to load repetition was derived. A laboratory study was carried out to verify if pavement rutting could be estimated by permanent-strain laboratory testing. The first stage of the investigation focused on the strain behavior of the dense graded crushed rock used in bases. Specimens were tested in a triaxial chamber in which repeated loadings were applied. Laboratory results and APT showed similar trends even if some of the results were unexpected. Rut depths in the APT test sections were noticeably more than expected from the permanent deformation in specimens in the triaxial apparatus. Although it seems clear that the investigation must be extended to the macadam aggregate and to the subgrade soil, the approach presented seems suitable to predict rutting of thin asphalt pavements. DOI: 10.1061/(ASCE)TE.1943-5436.0000298.

Rational Approach to the Evaluation of Soils for Low-Volume Roads

Given the paramount importance of soils in unsurfaced or thinly surfaced roads, it seems worthwhile to evaluate soils on the basis of both pavement and soil mechanics. Such a rational approach is used to discuss the mechanical behavior of a residual soil found in southern Brazil. The experimental program included tests traditionally used in pavement engineering, such as grain size distribution, Atterberg limits, compaction, California bearing ratio, resilient modulus, and permanent deformation under repeated loading. The influence of water content and compaction degree on soil strength and stiffness was quantified. In addition, direct shear tests were performed to define shear strength parameters that were used to verify layer safety against failure. Water retention curves, which relate soil suction to saturation degree, were used to analyze permanent deformation evolution under repeated loads. The interpretation of test results confirmed the suitability of the suggested approach for evaluating soils for low-volume road construction.

Mechanistic behaviour under traffic load of a clayey silt modified with lime

The behaviour under traffic loads of a soil modified with lime was researched through a laboratorial mechanistic approach. A clayey silty soil from Cebollatí, eastern Uruguay, and a commercial calcic lime were used. Cyclic triaxial compression tests were carried out on the soil treated with different lime contents, curing periods and dry densities in order to study its resilient behaviour. The fatigue life was investigated through cyclic indirect diametrical tensile tests by varying the lime content and curing period. A model of resilient modulus as power function of the deviator stress was found, independent of the lime content and curing period and dependent on the compaction effort. The model is similar to that observed in the natural soil, which means that the treated soil behaves as modified material. Nevertheless, the material is susceptible to fatigue cracking. The fatigue life, expressed as the number of load cycles up to break, is an inverse power function of the initial tensile strain, being most sensitive to that parameter. It was found that the fatigue life can be better explained when expressed as function of the ratio between the initial tensile strain and the tensile stain at break.

Estudio de fatiga en mezclas asfálticas recicladas con cemento a través de ensayo en viga cuatro puntos

El reciclaje profundo de pavimentos flexibles con cemento Portland es una tecnica de recuperacion estructural y funcional recurrente en la practica vial Brasilera, ya que la reutilizacion de capas degradadas de revestimiento asfaltico o RAP ( reclaimed asphalt pavement ) y de base, permite reducir costos y tiempo de ejecucion. Sin embargo, en Brasil no existe un criterio de dimensionamiento de pavimentos que considere este tipo de materiales. En este sentido, es aceptado que la capacidad estructural de capas cementadas es limitada por la deformacion de traccion en su base. Con el objetivo de establecer esta relacion, a traves de modelos de fatiga, fue desarrollado un programa experimental basado en la experiencia australiana, buscando verificar su aplicabilidad a materiales reciclados de origen brasilero. Conforme al protocolo adoptado, el programa consistio de ensayos de flexion estaticos y dinamicos del tipo cuatro puntos en vigas, con edades de cura mayores a 28 dias, moldadas en laboratorio usando energia de compactacion modificada brasilera. Las mezclas consideradas estan constituidas 4 % de cemento Portland, y por brita granular y RAP en proporciones 80:20, 50:50 y 30:70. El comportamiento mecanico fue evaluado a traves de la Resistencia a la Traccion a la Flexion (RTF) y el Modulo Flexural Estatico y Resiliente (MFE y MFR, respectivamente). Entre otras conclusiones, el comportamiento estatico indica que el incremento de RAP reduce el MFE, incrementando la deformacion de traccion de ruptura, mientras que la influencia del RAP en la RTF no fue notoria. De otra parte, la relacion entre el exponente de dano y el porcentaje de RAP apunta a una dependencia del fenomeno de fatiga y el contenido de material reciclado. En general, puede concluirse que el protocolo australiano puede ser usado como modelo para el desarrollo de un metodo brasilero para este tipo de mezclas, con algunas modificaciones. DOI: http://dx.doi.org/10.4995/CIT2016.2016.3486

Shear strength of hot-mix asphalt and its relation to near-surface pavement failure – A case study in Southern

Since the years 1970, several design methods of flexible pavements have considered fatigue bottom-up cracking as the most critical degradation mechanism. However, in recent times, premature distresses originated close to the surface of pavements, especially in those with thick asphalt layers. These distresses are cracks initiating close to the surface and rutting, which are considered as shear failures. Shear failure close to the pavement surface is a complex phenomenon caused by factors like: tirepavement shear stresses, asphalt characteristics and environmental conditions. In this article, besides discussing theoretical aspects related, the behavior of asphalt is characterized by shear strength tests and risk analysis of failure close to the pavement surface. It was found that bitumen modification with SBS remarkably increases cohesion and, consequently, the asphalt shear strength. While the shear strength parameters for asphalt with conventional bitumen, at 25°C, are: c = 480 kPa and angle of internal friction angle(fi) = 46°, the tests on asphalt with SBS modified bitumen, also at 25°C, resulted in c = 1,006 kPa andfi = 40°. Regarding SBS modified asphalt, the increase of test temperature from 25°C to 40°c significantly reduces the cohesive interception from 1,006 kPa to 722 kPa, while the friction angle, which is a function of aggregates internal friction and interlocking, remains the same (40°). The risk of shear failure near surface of a pavement consisting of 8.0 cm of SBS modified asphalt; 45.0 cm of crushed rock layers and 60.0 cm of sand was evaluated. The non-uniformity of contact stresses was taken into account using software EverStress FE. In spite of the structure being safe against shear failure (due to the SBS modified bitumen high cohesion), it was shown that considering the thermal gradient on critical shear stresses computations is of paramount importance in the case of overloading.