José Tadeu Balbo

Theoretical and field evaluation of interaction between ultra-thin whitetopping and existing asphalt pavement

Ultra-thin concrete overlays or ultra-thin whitetopping (UTW), are an attractive alternative to traditional practices for the rehabilitation of asphalt pavements. However, it is widely accepted that the exiting pavement should have substantial stiffness to make a UTW a rehabilitation option. This paper re-examines this hypothesis using the performance results and structural evaluation of two experimental sections in Brazil. It is shown that structural contribution of the existing pavement is important for good performance of UTW. However, it appears that the ability of the existing pavement to ensure composite action of the individual slabs in the UTW is more important than its contribution to the flexural stiffness.

Thermal Gradients in Concrete Pavements in Tropical Environment: Experimental Appraisal

Fifteen concrete slabs were instrumented with thermal resistors, allowing the monitoring of temperatures in concrete pavements slabs in São Paulo, Brazil, where a typical tropical hot and wet environment prevails. Over the course of 1 year, this research sought the influence of climatic conditions such as temperature and moisture on the daily and seasonal variations of temperature differentials through the slab depths. Daytime temperature differentials of more than 15°C were observed during typical summer days (e.g., high air temperature of 32°C and 7.6 h of solar radiation) and of about 10°C during typical winter days (e.g., low air temperature of 11°C and 3 h of solar radiation). The absolute values of nighttime temperature differentials are not as extreme as the daytime differentials and are significant mostly during spring and summer (from September to March). Nonlinear quadratic temperature distributions through the slab thickness were evident in most cases; nevertheless, distributions that are almost linear may be present at some times during the day and even at night. Positive temperature differentials were recorded even at night, and discussions of those particularities are addressed. The effects of tropical rains on temperature differentials are presented, and empirical models for the prediction of temperature differentials in slabs are suggested.

Relações entre resistências à tração indireta e à tração na flexão em concretos secos e plásticos

Medidas de resistencia a tracao indireta nao sao normalmente cotejadas na dosagem ou no controle tecnologico de concretos em pavimentacao; os resultados de ensaios de resistencia a tracao na flexao, em especial com dois cutelos, sao empregados para tais finalidades. Na realidade, nenhum de ambos os tipos de teste mede de fato a resistencia real do concreto acabado na forma de placa por nao representarem um componente estrutural que responde mecanicamente em estado plano de tensoes. Uma revisao critica dos conceitos relacionados a essas medidas de resistencia permite claramente enxergar as limitacoes de cada uma das formas de afericao da resistencia a tracao e as maneiras de melhor encaminhar avaliacoes dessa natureza. Correlacoes entre ambas as medidas por meio de ensaios em concretos secos e plasticos especificos para pavimentacao sao apresentadas, corroborando com resultados anteriores obtidos para concretos plasticos.

Rendering the loss of strength in dry concretes with addition of milled asphalt through microscopic analysis

Milled asphalt removed from old pavement carpets requires tenable handling easily reachable through its incorporation within other paving materials. This work deals with the effects of such incorporation to dry compacted concretes. Fine, intermediate, coarse and whole portions of milled asphalts were blended to a reference concrete. Mechanical tests disclosed remarkable losses on its strengths and modulus of elasticity; for the stereoscope and scanning microscopy pointed out impaired transition zones between the cement paste and the milled aggregates involved by thin asphalt films. Nevertheless, the mechanical results shown that the concretes with incorporated milled asphalt aggregates are suitable for use in pavement layers as bases and sub-bases even with reduced mechanical parameters.

Efeito das variações de temperatura na transferência de cargas em juntas de pavimentos de concreto

Medidas de deflexoes com o falling weight deflectometer permitiram a avaliacao do comportamento de juntas em pavimentos de concreto simples do ponto de vista de sua eficiencia de transferencia de cargas (LTE). As investigacoes mostraram importantes variacoes nesse parâmetro, quando nao ha dispositivos de transferencia de cargas, entre horarios de dias bem como entre estacoes climaticas distintas (inverno e verao); enquanto que juntas com barras de transferencia apresentam, pouca variacao nesse parâmetro e encontrando-se em geral entre 90 e 100% de capacidade de transferencia, quando ha quedas de temperatura, as juntas sem barras chegam a apresentar capacidade de transferencia reduzida para 50% no inverno e para 60% no verao. Valores estimados de transferencia de carga com um programa de elementos finitos permitiram confirmar a necessidade de tratamento teorico do problema em fases de analise estrutural e projetos de pavimentos de concreto com juntas.

Evaluation of Characterization and Performance Modeling of Cementitiously Stabilized Layers in the Mechanistic-Empirical Pavement Design Guide

Cementitious stabilization of aggregates and soils is an effective technique to increase the stiffness of base and subbase layers. Furthermore, cementitious bases can improve the fatigue behavior of asphalt surface layers and subgrade rutting over the short and long term. However, it can lead to additional distresses such as shrinkage and fatigue in the stabilized layers. Extensive research has tested these materials experimentally and characterized them; however, very little of this research attempts to correlate the mechanical properties of the stabilized layers with their performance. The Mechanistic–Empirical Pavement Design Guide (MEPDG) provides a promising theoretical framework for the modeling of pavements containing cementitiously stabilized materials (CSMs). However, significant improvements are needed to bring the modeling of semirigid pavements in MEPDG to the same level as that of flexible and rigid pavements. Furthermore, the MEPDG does not model CSMs in a manner similar to those for hot-mix asphalt or portland cement concrete materials. As a result, performance gains from stabilized layers are difficult to assess using the MEPDG. The current characterization of CSMs was evaluated and issues with CSM modeling and characterization in the MEPDG were discussed. Addressing these issues will help designers quantify the benefits of stabilization for pavement service life.

Estudo da Condutividade Hidráulica com Carga Constante e Variável em Concretos Permeáveis

Resumo The main goal of this paper is to show the analysis of the permeability characteristics of three different mixes of pervious concrete produced with the variation of the coarse aggregate size. Two different test methods were used to achieve the hydraulic conductivity of the samples: falling head and constant head permeability tests. Based on test results it is concluded that the pervious concrete mixes have shown to be good drainable materials. Besides, it was found that the permeability of the mixtures does not seem to depend on the size and gradation of the coarse aggregate.

Experimental continuously reinforced concrete pavement parameterization using nondestructive methods

Resumo Four continuously reinforced concrete pavement (CRCP) sections were built at the University of Sao Paulo campus in order to analyze the pavement performance in a tropical environment. The sections short length coupled with particular project aspects made the experimental CRCP cracking be different from the traditional CRCP one. After three years of construction, a series of nondestructive testing were performed - Falling Weight Deflectometer (FWD) loadings - to verify and to parameterize the pavement structural condition based on two main properties: the elasticity modulus of concrete (E) and the modulus of subgrade reaction (k). These properties estimation was obtained through the matching process between real and EverFE simulated basins with the load at the slab center, between two consecutive cracks. The backcalculation results show that the lack of anchorage at the sections end decreases the E and k values and that the longitudinal reinforcement percentage provides additional stiffness to the pavement. Additionally, FWD loadings tangential to the cracks allowed the load transfer efficiency (LTE) estimation determination across cracks. The LTE resulted in values above 90 % for all cracks.

Influence of curing procedures and porosity in the flexural resistance of concretes for paving

Flexural strength of high performance concrete submitted to several non-standard curing conditions was evaluated through bending tests on beams in order to allow comparisons among different curing procedures. The moist curing process resulted more effective than curing by chemical products leading to membrane formation over concrete surface; moreover, flexural strength of high strength concrete was increased when satu- rated specimens were tested, whereas conventional concrete flexural strength decreased when submitted to the same conditions. Such results were explained on the basis of concrete porosity with the support of air permeability tests. Results explained differences between the behavior of conventional and high strength concrete when water fills the specimen pores. As recommendation, high strength concrete specimens shall not be tested in bending in saturated condition under the risk of overestimation of flexural resistance.