Luiz Carlos Pinto da Silva Filho

Estimativa da resistência à compressão a partir de resultados de ensaios de aderência tipo Pull-Out para controle da qualidade do concreto na obra

O controle de qualidade do concreto estrutural vem sendo realizado, ha varias decadas, baseado principalmente nos resultados de ensaios de compressao axial. Este tipo de ensaio, embora amplamente utilizado, nao esta isento de erros e tem algumas desvantagens consideraveis que podem afetar sua confiabilidade, tais como a necessidade de condicionamento adequado e cuidadoso dos corpos-de-prova e de adocao de adequadas tecnicas de nivelamento e capeamento. Por estas razoes, seria util ter maneiras complementares ou alternativas para verificar a resistencia a compressao, a fim de melhorar o processo de controle de qualidade do concreto. O uso de um ensaio de arrancamento para monitorar a resistencia do concreto esta sendo proposto por um consosrcio internacional de pesquisadores da Franca, Tunisia e Brasil como um meio potencial de atingir essa meta. Dado que a existencia de uma relacao direta entre a tensao de aderencia e a resistencia do concreto ja esta bem estabelecida, este tipo de teste parece ser uma alternativa viavel aos metodos tradicionais. No entanto, para verificar se o principio subjacente e valido quando usado em diferentes circunstâncias, o grupo tem buscado recolher dados de varios estudos, realizados por diferentes pesquisadores, em diversos paises, com concretos e barras de armadura de distintos tipos. Uma analise dos dados coletados confirma que ha uma correlacao clara e um forte vinculo entre a tensao de aderencia e a resistencia a compressao, independentemente da influencia de outras variaveis. Esses resultados validam a ideia basica de usar um teste de Pull Out adequado (denominado APULOT) para avaliar a resistencia do concreto. Se o principio geral e valido para dados aleatorios obtidos em diferentes estudos, a definicao de um procedimento de teste claro e adequado provavelmente levara a reducao erros experimentais e aumentara a estimativa da precisao obtidas por esse metodo.

Experimental investigation on the use of steel-concrete bond tests for estimating axial compressive strength of concrete. Part 2: APULOT

A presente pesquisa se propoe a estudar a viabilidade do uso de ensaios de aderencia aco-concreto para estimativa da resistencia a compressao axial do concreto, com o objetivo de emprega-los como um complemento no controle de qualidade do concreto armado. Lorrain e Barbosa (2008) e Lorrain et al. (2011) justificam a utilizacao de um ensaio de aderencia modificado, denominado APULOT, para estimar a resistencia a compressao do concreto, incrementando as possibilidades de controle tecnologico do concreto armado em canteiros de obras. Os mesmos propoem uma adaptacao do metodo pull-out test (POT) tradicional, normalizado pela CEB/FIP RC6 (1983), por ser este um ensaio de baixa complexidade e de custo reduzido. Para viabilizar o uso do ensaio APULOT como ensaio de controle tecnologico do concreto em canteiro de obras e necessario definir um padrao para o mesmo e adapta-lo da pratica experimental do laboratorio para o campo. O presente trabalho buscou avaliar num primeiro momento, a potencialidade de efetuar estimativas da resistencia a compressao a partir dos dados da tensao de aderencia obtidos com uso do pull-out test (POT) tradicional. Para tanto, foram ensaiadas 2 composicoes de concreto de classes distintas, aos 03, 07 e 28 dias. Foram, ainda, usadas na confeccao dos corpos de prova barras nervuradas com diâmetros nominais de 8; 10 e 12,5 mm, totalizando 108 ensaios do tipo POT. Os resultados obtidos mostram que, sob condicoes padronizadas de ensaio, a correlacao entre a tensao ultima (maxima) de aderencia e a resistencia a compressao do concreto e satisfatoria, em todas as idades ensaiadas, fortalecendo o proposito de consolidar este ensaio como uma alternativa complementar para controle de qualidade do concreto armado. Na segunda parte deste trabalho serao apresentados os resultados obtidos para as mesmas composicoes do concreto e as mesmas barras de aco, usando porem o ensaio de aderencia APULOT.

Application of artificial neural network for interpreting ultrasonic readings of concrete

Concrete is an essential material for civil engineers. However, its properties can vary considerably, depending on the nature and proportions of the constituents, the construction methods and the loading and environmental conditions. Therefore, the development of methods to determine the state condition and ascertain the quality of concrete elements is critical. This paper describes a study carried out to evaluate the feasibility of developing Artificial Neural Networks (ANN) that use data about concrete properties and ultrasonic readings to estimate compressive strength. The results obtained indicate that the estimation power of a neural network can surpass that of traditional statistical techniques and that this might become a very interesting tool to model certain problems in civil engineering.

Laboratory Evaluations of Long-Term Hydraulic Performance and Maintenance Requirements for Pervious Concrete Mixes: A Case Study in Southern Brazil

Widespread adoption and acceptance of pervious concrete systems in new areas using local materials and equipment are dependent on having information on the efficacy of the mix and their longterm needs for rehabilitation. In Porto Alegre, Brazil recent governmental mandates include incorporating permeable pavements into projects. This study expanded on research into the effectiveness of using readily available aggregate for adequate hydraulic performance and clogging resistance of pervious concrete to also determine the effectiveness of maintenance procedures. Laboratory specimens from three mixes with differently screened aggregate were cast and infiltration rates evaluated initially, post clogging, after sweeping and after powerwashing. The results indicate that all three mixes maintain similar hydraulic functionality after rehabilitation, and that powerwashing is more effective in rejuvenating infiltration capabilities than sweeping. In addition, it is recommended to perform infiltration testing twice after maintenance, as there is a slower rate measured on the second test, probably due to dislodged debris re-entering the system during the first test. Similar laboratory methodologies for mix design and maintenance evaluation might effect a faster and more efficient incorporation of this sustainable low impact development technology in other regions.

Numerical and Experimental Analysis of a Waffle Slab Parking Floor

AbstractRational and sophisticated structural solutions are essential requirements for structural designers, as a consequence of architectural design evolution and new building management concepts. Thus, waffle slabs turn out to be an interesting alternative, despite their laborious numerical modeling. It is necessary to increase knowledge about the structural behavior of and improve the theoretical models used for the simulation of these slabs. To better understand the behavior of RC waffle slabs, and more realistically quantify stresses and displacements of this kind of element under actual work conditions, a real-scale ribbed slab was tested and the results are presented in this paper. The chosen structure, designed to serve as a parking floor, was instrumented with strain and deflection gauges to assess the deformations and deflections developed under some induced loading conditions. A grillage model and a three-dimensional finite-element model were used for the numerical study. The data collected ind...

Investigation of the Potential for Evaluation of Concrete Flaws Using Nondestructive Testing Methods

Adoption of periodic or continuous monitoring strategies to assess condition state of infrastructure elements is a vital part of service life management (SLM). NDT methods are increasingly seen as an attractive and viable strategy to support condition monitoring. Over the last 15 years, the LEME research group at UFRGS has investigated several aspects related to the use of the ultrasonic pulse velocity (UPV) method and its potential for real field applications. One of the main advances involved the development of artificial neural network (ANN) models for correlating compressive strength and UPV measurements. Another examined problem was how to deal with the large amount of raw data derived from inspection of large structures. Several studies were carried out to check different mapping techniques, as reported by Lorenzi et al. 2011. This paper relates one investigation where UPV and rebound hammer (RH) measurements were collected from a beam containing several induced defects, simulated using different materials. The results were processed using a mapping strategy, which indicated suspicious points where core extraction was undertaken. All cores taken from points derived from UPV results were found to have flaws providing evidence that this may be a suitable tool to assess concrete structures, when data is properly interpreted.

Application of heat-activated films as a new generation of adhesives used for bonding fiber reinforced polymers to concrete

The application of FRP for post-strengthening of concrete structures induces the use of elevated temperatures to minimize the curing time of the adhesive. The replacement of traditional adhesives by Heat-Activated Films (HAF), with higher glass transition temperatures (Tg), is na interesting prospect, and has been motivating studies regarding the viability of applying termo-activated adhesives. For this study, notched beams post-strengthened with CFRP bonded with two types of heat-activated films (epoxy and phenolic based) and one classical adhesive were tested in bending at EMPA (Swiss Federal Laboratories for Material Testing and Research). To verify the stress redistribution on the notched beams, a computational model, which divides the structure in solid elements, was implemented. The analysis of the behavior of the concrete-laminate interface demonstrates that numerical models are an efficient tool to supplement and explain experimental data.

Numerical and experimental study of a waffle slab designed to serve as a tennis court floor

Reinforced concrete waffle slabs have become a common option for designers due to a need of rationalization in construction with reduction in costs and deadlines. To better understand the behavior of this structural system, and more realistically quantify stresses and displacements, a full scale waffle slab was tested. The structure, designed to serve as a tennis court floor, was submitted to a load of 12 kN/m2 and instrumented to measure strains and deflections at different locations. The loading process used the floors constructive base filling material and readings were taken at different loading stages and arrangements during the floors construction. Test data was compared to results obtained from the matrix analysis program Sistema Computacional TQS v11.0 and from the finite element model program SAP2000 v14.2.2. Slab behavior was as expected, with deflection and bending moments close to those determined by the numerical analysis.

Applying Post-Tensioning Technique to Improve the Performance of FRP Post-Strengthening

Reinforced concrete structures are, frequently, submitted to interventions aiming to restore or increase their original load capacity. According to Garden & Hollaway [1], the choice be‐ tween upgrading and rebuilding is based on factors specific to each individual case, but cer‐ tain issues are considered in every case. These are the length of time during which the structure will be out of service or providing a reduced service, relative costs upgrading and rebuilding in terms of labor, materials and plant, and disruption of other facilities.

Development of artificial neural networks for interpreting ultrasonic pulse velocity tests in concrete

Nondestructive Testing (NDT) techniques are useful tools for analyzing reinforced concrete (RC) structures. The use of Ultrasonic Pulse Velocity (UPV) measurements enables monitoring changes in some critical characteristics of concrete over the service life of a structure. Nonetheless, the current techniques for UPV data analysis are largely based on the sensitivity of the professionals who apply these tests. For accurate diagnosis it is necessary to consider the different factors and conditions that can affect the results. In order to properly control and inspect RC facilities it is essential to develop appropriate strategies to make the task of data interpretation easier and more accurate. This study is based on the idea that using Artificial Neural Networks (ANNs) is a feasible way to generate workable estimation models correlating concrete characteristics, density and compressive strength. The study shows that this goal is achievable and indicates that neural models perform better than traditional statistical models.