White José dos Santos

The Influence of the Water/Cement Ratio in the Open Porosity and in the Carbonation Front Advancing in Cementitious Matrix Composites

In this study involving cementitious matrix composites, the influence of the water/cement (w/c) ratio variation (0.48, 0.60, 0.70 and 0.75) was analyzed in its open pore structure and in the carbonation front advancing. Test specimens were molded in cylindrical dimensions of (5x10) cm and (2x4) cm for each mix proportions, and subjected into accelerated carbonation tests, at controlled exposure conditions. The open porosity of the material was obtained by using a helium pycnometer. A model based on Ficks second law was used to fit an equation to the curve of progress of the carbonation front over time. The results show that the water/cement ratio can highly influence the analyzed properties; the mathematical model used provided an excellent approximation of the advancing carbonation front trend, allowing a good evaluation of the carbonation coefficient (K) associated to each mixture proportioning.

Bond Strength between Old and New Concretes with Focus on the Strengthening of Reinforced Concrete Columns - Slant Shear Test versus Double Sleeve Test

The purpose of this paper is to present the main aspects and results of an experimental study to determine the bond strength between the concrete of a column of an existing structure (old concrete) and the concrete that will be used in its strengthening project (new concrete). For the bond strength tests, a specimen was conceived, called Double Sleeve specimen. The bond strength results obtained from the tests using Double Sleeve specimens, called Double Sleeve Tests, were compared to the results obtained from using the Slant Shear Test. The values for the bond strength between the two concretes, obtained from the Double Sleeve Tests, were either below or above the values obtained from linear regression of the Slant Shear Test results, depending on the sleeve diameter and the ratio of transverse reinforcement used. This fact, enabled concludes that the Double Sleeve Test is the most appropriate test to evaluate the bond strength between concretes of columns strengthened.

Sustainable Architecture with Bamboo Columns Technology

Compositions with different pipe segments for constructing structural columns were investigated. In this article there is shown a column type composed of five parallel bamboo bars, connected by screws 16 mm and 13 mm in diameter. Compression tests instrumented with displacement transducers are associated with numerical modeling analysis to describe the column load capacity, from the general criteria of dimensioning. The chosen Bamboos are from the species Phyllostachys pubescens due to its favorable characteristics to produce structures and their common use in China, Brazil and other countries of temperate zones. In this proposal, the load capacity is considerably increased and lateral displacements are insignificant compared to the bamboo tested separately. More usual columns 3 and 4 meters long were modeled and presented the load limits of use for these types of structures. Other dimensions of columns can be calculated by the same system, presenting great design opportunities in the construction of the architecture and built spaces. This article shows a great advantage in using columns with bamboo bars compared to other materials used in the architecture, with guarantee and good indexes of security.

ANÁLISE DA INFLUÊNCIA DA GRANULOMETRIA DO AGREGADO MIÚDO NAS PROPRIEDADES MECÂNICAS E DE DURABILIDADE DAS ARGAMASSAS DE REVESTIMENTO

The building has a high demand for products and construction technologies to ensure optimum performance and durability, requiring knowledge of the behavior of materials and the influence they exert on the properties of cement composites. This work aims to experimental verification of the particle size influence of the fine aggregate in mixed mortar coating, both fresh and hardened. The particle packing was evaluated by loose bulk density of the particle sizes specified in NBR 248: 2003 and each sieve individually. Then, mechanical properties were determined by means of mechanical analysis (compressive strength, tensile strength in bending and potential adhesion to the tensile and dynamic modulus of elasticity) and durability indicators (loose bulk density, consistency, density and mass entrained air content either fresh, surface porosity, for water absorption and capillary microstructure and images) for mortars made with natural aggregate through size distribution curves - NBR 248: 2003, Carneiro and Cincotto (1999) and Reed (1995). The tests were evaluated the ages of 7, 21 and 28 days. It was evident that the particle size distribution of aggregates significantly influences the properties analyzed and should be considered during the process of dosage and specification. Keywords: mechanical property, durability, coating mortar, aggregates.

ANÁLISE COMPARATIVA DE MÉTODOS DE OBTENÇÃO DO MÓDULO DE ELASTICIDADE PARA CONCRETO PREPARADO COM AREIAS NATURAL E ARTIFICIAL

It was studied the mechanical properties and durability of concrete indicators, focusing on ways of obtaining elasticity modulus. Using two fine aggregate, an artificial crushing and other natural. In the experimental program examined the absorption of water by immersion and capillarity, porosity, resistance to axial compression and tensile strength by diametrical compression, correlating them with the elasticity modulus. The elasticity modulus was evaluated under the bias of three methods: ultrasound, forced resonance and the stress-strain curve. The results allowed characterizing the materials and the composites and to identify the similarities and differences between the properties and methods presented and to generate good correlations. It was observed that the ABNT NBR6118:2014 provided values of the elasticity modulus closer to reality due to the type of aggregate. It is concluded that the aggregate to be used is an important factor and the determination of its properties become essential in getting a good approximation between the theoretical and the real cases. It was proved that the artificial sand increases the mechanical strength; improve the durability and increases the static and dynamic elasticity modules of the concrete. Keywords: mechanical properties of concret, durability, concrete, elasticity modulus, aggregates.

VERIFICAÇÃO DE VIABILIDADE ECONÔMICA DE HABITAÇÕES POPULARES PADRÃO “MINHA CASA MINHA VIDA”

Lancado em marco de 2009, o programa Minha Casa Minha Vida – MCMV e destinado a construcao de moradias no padrao popular para reduzir o deficit habitacional brasileiro. Apesar da oferta de credito, subsidios e alta demanda, os empreendimentos devem ser submetidos a analise de viabilidade economica para que seja constatado o real potencial de rentabilidade. Com auxilio de indices e ferramentas consagradas da engenharia economica (fluxo de caixa, taxa minima de atratividade, valor presente liquido – VPL, taxa interna de retorno – TIR e payback), e possivel estimar a lucratividade dos projetos, comparar investimentos concorrentes e obter resultados conclusivos quanto a viabilidade economica. Na fase de revisao bibliografica, foram abordados aspectos legais do MCMV, nocoes basicas de gerenciamento e metodos de avaliacao economica. Em seguida, efetuou-se o estudo de viabilidade economica de um empreendimento real, localizado em Araguaina-TO. Por fim, apresentou-se propostas que visam otimizar estudos futuros, aumentar a precisao das informacoes sobre o empreendimento em questao e maximizar os lucros atraves da analise de novas metodologias construtivas.