Aires Camões

Performance of Concrete in Aggressive Environment

Surface treatments act as a barrier between the environment and the concrete, preventing or retarding the entry of harmful substances and cutting off the transportation path into concrete. The effectiveness of a surface protection preventing the permeation depends on how close and strongly connected are the resin molecules. This work intends to contribute to a better understanding of the performance of protected concrete in chemically aggressive environments, by presenting results of ion diffusion and resistance to aggressive solutions of several hydrophobic agents and coatings used to protect concrete. Three different types of surface protections were tested: silicone hydrophobic agent, acrylic and epoxy coatings. The obtained results indicate that the overall performance of epoxy resin was better than the other selected types of protections.

Durability Indicators Comparison for SCC and CC in Tropical Coastal Environments

Self-compacting concrete (SCC) demands more studies of durability at higher temperatures when subjected to more aggressive environments in comparison to the conventional vibrated concrete (CC). This work aims at presenting results of durability indicators of SCC and CC, having the same water/binder relations and constituents. The applied methodologies were electrical resistivity, diffusion of chloride ions and accelerated carbonation experiments, among others, such as microstructure study, scanning electron microscope and microtomography experiments. The tests were performed in a research laboratory and at a construction site of the Pernambuco Arena. The obtained results shows that the SCC presents an average electrical resistivity 11.4% higher than CC; the average chloride ions diffusion was 63.3% of the CC; the average accelerated carbonation penetration was 45.8% of the CC; and the average open porosity was 55.6% of the CC. As the results demonstrated, the SCC can be more durable than CC, which contributes to elucidate the aspects related to its durability and consequent prolonged life cycle.

Carbonation Resistance of High Volume Fly Ash Concrete

The cement industry is responsible for a large part of the global environmental problems: is the largest consumer of natural resources; the most responsible for the emission of greenhouse gases, including about 1.8 Gt of CO2; and requires huge amounts of energy, corresponding to between 12 and 15% of industrial energy use. The cement is also not used in the most appropriate manner, since 40% of the consumption of concrete is due to the renovation and repair of buildings, making concrete structures inefficient because its durability is relatively low. However, in the future, concrete can and should evolve in order to improve its eco-efficiency, with a smaller amount of cement in its composition, replacing it with high quantities of mineral additions, particularly fly ash. Nevertheless, current technology may not allow this type of concrete to be very efficient, because its long-term durability may be compromised. In fact, with increasing dosage of pozzolanic mineral additions, alkali paste components are consumed in the reaction leaving it vulnerable to concrete carbonation which may compromise the passivation layer needed for steel rebar protection against corrosion. This article explores a promising approach to mitigate this problem, which consists in the careful addition of hydrated lime in the concrete composition, highlighting the synergy of its components, significantly enhancing its carbonation resistance. It is proposed, therefore, to manufacture a concrete with high volume of fly ash, low cement content and high service life period: an efficient and sustainable concrete. In this context, an experimental campaign was developed with the aim of characterization of pastes behavior with high fly ash content, in particular with respect to its durability. The results will be presented and properly analyzed.

New Eco-Friendly Gypsum Materials for Civil Construction

The sustainable world’s economic growth and people’s life improvement greatly depend on the use of alternative products in the architecture and construction, such as industrial wastes conventionally called “green materials”. This paper concerns the main results of an experimental work carried out with the objective of developing new composite materials based on gypsum and incorporating waste material as granulated cork, a by-product of cork industry, and cellulose fibres, a waste of paper industry. Such materials are intended to be used as composite boards for non structural elements of construction, such as dry walls and ceiling. Cork (bark of the plant Quercus Suber L), a substance largely produced in Portugal, is a material whose characteristics are of considerable interest for the construction industry. It is regarded as a strategic material with enormous potential by its reduced density, elasticity, compressibility, waterproof, vibration absorption, thermal and acoustic insulation efficiency [1]. During the first stage of this research work the gypsum binder and its properties were studied. Then, composites with mineral additions (added to increase the waterproofing and resistance) were also developed and submitted to tests to determine their physical and mechanical properties. In last stage, reinforced composites using different industrial by-products have been developed. This paper will present the properties and the manufacture methods used to produce the above mentioned eco-friendly composites that can ease ways for using industrial wastes as new construction materials, with excellent inherent thermal and acoustic properties.

Effective low-energy mixing procedure to develop high-fluidity cementitious pastes

Preparing a high fluidity paste is a major step in ultra-high performance concrete (UHPC) development with respect to its self-compacting ability as well as its ultra-high strength. In this regard, some experiments have been carried out in order to study various superplasticizer (SP) addition methods and times. Among these procedures, stepwise and delayed methods seem to be more efficient compared to direct addition of SP with or immediately after water addition. However, few studies regarding water addition time and method have been conducted since now. In this research work, the effects of water and SP addition methods on the fluidity of paste were investigated. The results demonstrated that stepwise and delayed water beside delayed SP addition remarkably reduce the flow time. This maximum fluidity was achieved after totally 15 minutes of mixing including 3 minutes after 70% of water addition to powder, as first-part water, 6 minutes after SP addition and finally an extra 6 minutes after second-part water which is 30% of the total water. Based on this procedure, the opportunity for developing self-compacting and durable UHPC could be accessible. Furthermore, using higher content of aggregates and supplementary cementitious materials would be possible due to higher fluidity of the paste which finally results in an eco-efficient UHPC.

Carbonation Front Progress in Mortars Containing Fly Ash Considering the Presence of Chloride Ions

The incorporation of fly ash (FA) in cementitious matrices have been frequently used in order to make the matrix more resistant to the action of chlorides. On the other hand, it is known that Ca (OH)2 existing in the matrix is partially consumed by the pozzolanic reactions, which facilitates the advancement of carbonation. Given that the combined action between carbonation and chloride penetration is a fact little known, we speculate about the behaviour of the matrix in this context. This study investigates the influence of the presence of chlorides on the carbonation in mortars with FA. Samples with 0% and 40% replacement of cement CEM I 42.5 R for FA were molded with water/binder 0.56 and 0.52 respectively. After 90 days of curing the specimens were subjected to cycles of immersion/drying for 56 days. Half of the samples was subjected to the following cycle: two days in a solution containing NaCl (concentration equal to 3.5 %); 12 days in the carbonation chamber (4% of CO2). The other half was: two days in water; 12 days in the carbonation chamber. Then, the development of carbonation was evaluated. The results indicate that the presence of chlorides influences the carbonation. The specimens submitted to the exclusive action of CO2 showed a greater depth of carbonation compared to that presented by the specimens subjected to combined action. This may be related to changes in properties of the matrix which may lead to further refinement of the pores and related to the presence of the salt that can lead to partial filling of the pores and the increase in moisture content .

Effects of Anti-Graffiti Protection on Concrete Durability

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.

Ancient Materials and Techniques to Improve the Earthen Building Durability

A substantial part of the world building heritage has been performed by earthen building. The durability of this existing heritage and mainly of the new buildings built with earth is particularly conditioned by the erosion caused by water action, especially in countries with high levels of rainfall. This research aims to contribute to the increase of knowledge about the ancient building techniques that provide enhanced durability. It is possible to analyse the ancestral practices used to protect the earth material from the water action in order to understand how the old earthen buildings were preserved over the centuries, resisting to harsh weather conditions. Among these techniques are: the incorporation of biopolymers (such as oils or fats from animal or vegetable origin); the addition of some minerals; and the earth stabilization with lime. However, this knowledge seems to be forgotten, probably due to the prejudice related to earthen constructions, which several times are associated with a poor building. This research also focuses on the study of new methods of earth stabilization with lime and biopolymers, adapting the ancient knowledge to improve the durability related to the water action. Therefore, alternative solutions can be obtained to improve the performance of earthen buildings, mainly the resistance of the material in the presence of water, reducing its permeability to water. In addition, with the proposed solutions it is possible to obtain good levels of water vapour permeability, one of the major advantages of the construction with earth.

Service life of concrete structures rehabilitated with polymers

Der Beitrag befasst sich mit verschiedenen Methoden zur Instandsetzung von Betonbauwerken, wobei insbesondere Instandsetzungsprodukte auf Polymerbasis im Vordergrund stehen. Beispiele zur Instandsetzung und zur Erhoehung der Lebensdauer von Bauwerken sind zum Beispiel externe Verstaerkung mit Kohlefaserstoffen, Erhoehung der tragenden Betonquerschnitte und Anordnung einer zusaetzlichen Bewehrung bei gerissenen Betonbauteilen. Bei den externen Verstaerkungen mit Kohlefaserkunststoffen kommen Polymere sowohl bei der Verklebung mit dem Untergrund als auch zum Verbinden der einzelnen Fasern zum Einsatz. Der Einsatzbereich dieser Verstaerkungsmethode haengt stark von den zu erwartenden Umgebungstemperaturen und deren Einfluss auf das Langzeitverhalten der Verklebung ab. Um den Temperatureinfluss auf die Verklebungen naeher zu untersuchen, wurde ein Forschungsvorhaben an Bauteilen aus Normalbeton und aus Hochleistungsbeton durchgefuehrt, die mit einer gleichen Menge von Betonstahl bewehrt waren. Die Haftbruecke bestand aus einem Epoxidmoertel, der direkt vor der Applikation der Kohlefaserbewehrung gemischt wurde. Nach dem Verkleben auf 28 Tage alten Betonproben wurden die Proben unterschiedlichen Temperaturen ueber jeweils 6 Stunden und 50 Temperaturzyklen ausgesetzt. Die Untersuchungen erfolgten bei Temperaturen von 20, 40, 60 und 80 Grad Celsius. Um die tatsaechlichen Temperaturen in der Haftbruecke bei Sonneneinstrahlung festzustellen, wurden gesonderte Messungen durchgefuehrt. Diese Messungen zeigten, dass in der Haftbruecke waehrend eines warmen und windigen Fruehlingstages durchaus Temperaturen von etwas ueber 60 Grad Celsius auftreten koennen. Nach der Temperaturbeanspruchung wurden die Probekoerper einem Dreipunkt-Biegeversuch mit konstanter Belastungsgeschwindigkeit unterzogen. Die Ergebnisse der Versuche zeigen, dass - wie zu erwarten war - mit hoeher werdenden Temperaturen die Wirkung der Kohlefaserverstaerkungen deutlich abnimmt. Lag die maximale Versuchstemperatur nahe am Glasuebergangspunkt (62 Grad Celsius) der Haftbruecke wurden einzelne Abloesungen an den Enden der Kohlefaserverstaerkungen festgestellt. Bei Versuchstemperaturen von 80 Grad Celsius loesten sich die Verstaerkungen vollstaendig vom Untergrund. Es wird daher vorgeschlagen, fuer die Haftbruecke nur Epoxidharze zu verwenden, deren Glasuebergangstemperatur mindestens 20 Grad Celsius ueber der maximal zu erwartenden Umgebungstemperatur liegt. ABSTRACT IN ENGLISH: The service life prediction of concrete rehabilitation works is nowadays more and more significant. The rehabilitation techniques appeared as a need to solve problems posed by the degradation of concrete structures. Some years ago the rehabilitation techniques were not widespread developed and it was important to find effective and economic solutions for the problems. Now, there is more preoccupation with the service life of concrete rehabilitation techniques, like external strengthening with FRP, increase of concrete sections or reinforcement of cracked sections. The service life increase started with the quality of the concrete rehabilitation works. This includes the quality of the design, the products and the execution. Some standards are now available and establish specifications for concrete rehabilitation works. This work presents the main questions related with this subject. The use of polymers in concrete rehabilitation imposes a different analysis related with durability. (A)

Using Thymolphthalein for Accelerated Carbonation Testing of High Volume Fly Ash Cementitious Blends

Phenolphthalein is the most common pH indicator used to measure the carbonation depth of cementitious materials. It is simple and quick to use, but according to some authors, is not an appropriate tool. Moreover, this substance is in the candidate list as a substance of very high concern by European Chemicals Agency. This article discusses the use of thymolphthalein rather than phenolphthalein. Accelerated carbonation tests were performed on cement mortars and high volume fly ash mortars. Once this kind of mixtures has low carbonation resistance additional alkalinity was provided by adding hydrated lime during its fresh mixture, and by curing the samples immersed in a calcium hydroxide solution. The results showed that the best indicator was the thymolphthalein, mainly for blends with lower carbonation depth. It was also checked that adding alkalinity can be useful for increasing the carbonation resistance.