J. Alexandre Bogas

Compressive strength evaluation of structural lightweight concrete by non-destructive ultrasonic pulse velocity method.

In this paper the compressive strength of a wide range of structural lightweight aggregate concrete mixes is evaluated by the non-destructive ultrasonic pulse velocity method. This study involves about 84 different compositions tested between 3 and 180 days for compressive strengths ranging from about 30 to 80 MPa. The influence of several factors on the relation between the ultrasonic pulse velocity and compressive strength is examined. These factors include the cement type and content, amount of water, type of admixture, initial wetting conditions, type and volume of aggregate and the partial replacement of normal weight coarse and fine aggregates by lightweight aggregates. It is found that lightweight and normal weight concretes are affected differently by mix design parameters. In addition, the prediction of the concretes compressive strength by means of the non-destructive ultrasonic pulse velocity test is studied. Based on the dependence of the ultrasonic pulse velocity on the density and elasticity of concrete, a simplified expression is proposed to estimate the compressive strength, regardless the type of concrete and its composition. More than 200 results for different types of aggregates and concrete compositions were analyzed and high correlation coefficients were obtained.

Microstructural analysis of Iberian expanded clay aggregates.

This article presents a detailed study of the microstructure of Iberian expanded clay lightweight aggregates (LWA). Other than more commonly used mercury porosimetry (MP) and water absorption methods, the experimental study involves optical microscopy, scanning electron microscopy (SEM), and microtomography (μ-CT). Pore connectivity and how it is deployed are shown to some degree, and the pore size spectrum is estimated. LWA are in general characterized by a dense outer shell up to 200 μm thick, encasing an inner cellular structure of 10-100 times bigger pore size. Aggregate pore sizes may span from some hundreds of nanometers up to over 1 mm, though the range of 1-25 μm is more typical. A noteworthy fraction of these pores is closed, and they are mainly up to 1 μm. It is also shown that macropore spatial arrangement is affected by the manufacturing process. A step forward is given to understanding how the outer shell and the inner pore network influence the mechanical and physical LWA properties, particularly the density and water absorption. The joint consideration of μ-CT and SEM seems to be the most appropriate methodology to study LWA microstructure. MP analysis is likely to distort LWA pore spectrum assessment.

Numerical and experimental study of the optical properties of venetian blinds

Shading devices are used to reflect direct sunlight, reduce glare and prevent overheating. A correctly designed shading system will strongly influence the entire building energy consumption, peak loads and indoor comfort. The use of the venetian blinds is particularly common due to its relatively low cost and high versatility. The present study focuses on the algorithms for calculating both short-wave (solar) and long-wave (infrared) transmittance, absorptance and reflectance of the venetian blinds. The model is based on the net radiation method, allows for different slat discretization schemes and is suitable for integration into the building energy simulation tools. Once the effective optical properties are computed, the system can be regarded as an additional layer in a multilayer glazing system. Computed blind solar transmittance has been compared with other numerical models and in situ experimental results. A general good agreement has been found, except in cases where incident radiation is mostly diffuse. In this study, the effect of different design parameters on effective optical properties of the venetian blinds is also investigated: (a) the sun profile angle, (b) the slat angle and (c) the venetian blind geometry. Moreover, the effect of the discretization of each slat is examined.

Unstabilized and stabilized compressed earth blocks with partial incorporation of recycled aggregates

ABSTRACT This article aims to characterize the physical, mechanical, and water-resistant behavior of unstabilized and stabilized compressed earth blocks (CEB) produced with partial incorporation of recycled fine aggregates from construction debris. The objective was to produce an alternative-earth construction material with lower embodied energy. To this end, different types of common CEB were covered, namely: unstabilized CEB; stabilized CEB with 8% cement; stabilized CEB with 4% cement and 4% lime. CEB were characterized in terms of density, thermal conductivity, compressive and tensile strength, water absorption, permeability, and resistance to water erosion from drip and spray tests. The influence of moisture content was also analyzed. Lime stabilization had little effect on the early age mechanical and durability behavior of CEB. Design coefficients are suggested for common cement-stabilized CEB under different environmental conditions. A minimum of 4% cement content was sufficient to produce water-resistant CEB with partial incorporation of recycled aggregates.