Key Engineering Materials Vol. 634

Abstract: Among the test-methods for evaluation of aggregates reactivity towards alkali-silica reaction (ASR), linear dilatation of mortar bars or concrete prisms is often used in several tests under various conditions, criteria and procedures of measuring and accelerating the reaction. As reactivity is an essentially kinetic property, the expansion limits in such tests, or even tests results for the same aggregate, should be kinetically inter-related.

Abstract: The heritage of fair-faced concrete, largely built in the twentieth century and nowadays recognized as heritage to be protected, is susceptible to attacks by graffiti, a form of vandalism that causes a major social and economic impact on society. Concrete is a porous material sometimes deteriorated over the years, and the interactions between the inks and the substrate and removal methods sometimes deteriorate or alter the concrete surface, especially if it is necessary to repeat the removal process. The anti-graffiti products are applied on the surface of the concrete, hindering the adhesion of paints or preventing its penetration into the pores of concrete, which in turn facilitates their removal. However, it appears that many of the existing protective products on the market may also alter the surface characteristics of the concrete irreversibly. Considering that the durability of concrete depends on the composition and characteristics of the surface, it is essential to know the effects of anti-graffiti protection systems on the durability of concrete and adopt the appropriate methodology to preserve this heritage. Thus, an experimental program was developed for analyzing changes in durability indicators and surface properties that protect concrete from deterioration (i) concrete without protection before and after application of spray paint, (ii) concrete with protection before and after application of spray paint and (iii) after paint removal were studied. Two anti-graffiti products were evaluated: a permanent and a sacrificial one. Effects of the anti-graffiti systems on the concrete durability are investigated and the tests performed include: water absorption by capillary and immersion at atmospheric pressure. The results of the water absorption tests show that the graffiti protection reduces the water absorption into the concrete and facilitates the removal of the graffiti without affecting negatively the characteristics of the surface and thus contributing to improve its durability.

Abstract: Unsaturated polyester based composites materials present several improved properties over conventional materials. However, these composites show great sensitivity to high temperatures and poor fire behaviour. In the present study, an effort is undertaken to develop new unsaturated polyester composites with improved fire reaction behaviour by matrix modification with hybrid flame retardant systems based on nanooxides and phosphinates. For this purpose, a series of composite formulations containing different contents and types of both metal oxide nano/micro particles and organic phosphinates were manufactured, with basis on the Taguchi L9 orthogonal array, and tested for fire reaction and mechanical properties. The data treatment was carried out through analyses of variance. Fire reaction properties were analysed and quantified by the vertical flammability test (UL-94), and the mechanical properties were studied by flexural, Shore D, and Charpy impact tests. The results were compared with those obtained for plain resin specimens. Test results revealed that the addition of hybrid flame retardant systems introduced reasonable improvements in at least one fire reaction property. However, it was verified that the filler addition led to a decrease in mechanical properties, probably due to poor matrix-filler adhesion. Further studies are required in order to improve the mix design formulations.

Abstract: The addition of fibers in order to obtain better performance of mechanical characteristics of concrete has been common place in the last fifteen years in Brazil. Following a request from the Faculty of Architecture at the Federal University of Bahia to replace the Eternit Wall panels with structural deterioration used in its mezzanine floor, this research was developed to analyze the flexural behavior of reinforced concrete slabs with the addition of PET (polyethylene terephthalate) fibers obtained from soda bottles. Selection of this material was based on sustainability since PET wastes represent a serious environmental issue although it can be recycled at a low cost. The importance of this work is based on verifying some of the characteristics of PET fibers reinforced concrete aiming sustainability of civil construction. After laboratory analysis of materials used for slabs, specimens and concrete slabs were shaped with and without PET fibers, being respectively submitted to standard axial compression and flexural tests. Despite the averages of compressive and flexural strengths of slabs with fiber being similar to those without fiber, the firsts presented a better result in terms of cracking, deformation and a less abrupt rupture.

Abstract: The present work features results on the possible increase of radioactive ²²²Rn gas in environments of human habitation, caused by the use of dimension stones inside constructions with poor air circulation. For the study, “granitic” stones were selected from Espírito Santo and Minas Gerais states, commonly used as decorative stones and as wall covering. They were subjected to petrographic analysis, determination of physical indexes and level of U, and were monitored to quantify the amount of ²²²Rn gas released. The rates of ²³⁸U in the rocks stood between 2.9 ppm and 37 ppm, and the amount of ²²²Rn gas released ranged between extremely low for six of the stones (up to 98 Bq/m3) and moderate to considerably high (between 471 and 2483 Bq/m3) for four others. From the calculations to cumulatively evaluate the radiation levels generated by radon release, nine samples are below the limit of 4 pCi/L set by the EPA– Environmental Protection Agency (U.S.A.) and one is above that limit, demonstrating the role of these stones in increasing radon levels in ill-ventilated environments.