Materials Science Forum Vols. 730-732

Abstract: The objective of this paper is to investigate the influence of chemical degradation effects on polyester polymer mortar (PM). For this purpose, different dosages of siliceous and limestone PMs and natural stone specimens were exposed to representative degradation agents. Since the motivation for the research was to determine the durability of polymer mortar, it was considered important to simulate the types of aggressive environments that could conceivably be brought into contact with the material in domestic and industrial environments. In this paper, the possible variation of the surface aspect, water absorption and mass of the tiles after being immersed the specimens in different solutions, was measured and considered by visual observation and optical microscopy. As a conclusion PMs stability is strongly affected by the adhesion between matrix and aggregates at interface, and it is also dependent of the nature and packing level of aggregates.

Abstract: A new development in the repair and strengthening of reinforced concrete systems is the use of carbon fiber reinforced polymers (CFRP) strips bonded to concrete substrate with epoxy resins. It has been reported that epoxy adhesive are extremely sensitive to high temperatures. Some authors conclude that the epoxy temperature should not exceed 70 °C in order to safeguard the adhesiveness of the epoxy and, thus, the integrity and adequate functioning of CFRP. It is noted that even frequently exposure to direct sunlight causes temperatures higher than 70 °C. Since geopolymers are known to possess high stability at high temperature, these materials can be an alternative to epoxy resins. This papers presents results about the use of metakaolin based geopolymers mortars to insure the adhesion between the CFRP and the concrete substrate. Several compositions of geopolymer mortars were executed by varying the percentage of binder, sand/binder ratio and the concentration of sodium hydroxide. It was found that geopolymer mortars demonstrate very promising performances, having obtained a high mechanical resistance and a good adhesion to concrete. On the other hand the adhesion between CFRP and geopolymer mortars proved to be smaller than expected which could be due, to the fact that the composition of the mortar was not optimized or even to the nature of the CFRP.

Abstract: Pozzolanicity is a very interesting issue regarding building materials, as a way to enhance mortars and concrete durability. This property results from the reaction between calcium hydroxide and silica and alumina based materials. Different types of natural and artificial pozzolans show pozzolanic activities that differ depending on the materials characteristics. Therefore, the study of this property, namely its reactivity with calcium hydroxide, reveals itself to be important in the selection of the type and content of these materials. This paper presents the results of several pozzolanic reactivity methods, applied to different pozzolanic materials. The selected pozzolanic methods include Chapelle method, Fratinni method and Strength Activity Index. Those tests have been applied to evaluate the reactivity of various kinds of artificial pozzolans. The correlation between the test methods are presented and discussed.

Abstract: The geotextiles may suffer damages during installation, often causing significant changes in their properties. This paper evaluates the effect of the installation process on the mechanical and hydraulic properties of non-woven geotextiles. The geotextiles were damaged in laboratory (using a standardized procedure) with different granular materials. The changes occurred in the properties of the geotextiles were evaluated by mechanical and hydraulic tests.

Abstract: The aim of this work was to analyse the fracture behaviour of commercial dense cordierite bodies sintered in an electrical furnace in static air at 1250°C, 1275°C and 1300°C for 30 min using different cycling schedules in order to obtain tougher materials at minimum energy costs. Using a stereomicroscope and a scanning electron microscope, fracture surfaces of as-sintered bars tested under four-point bending at room temperature were examined at different magnification levels in order to determine the origin of fracture in each sintered bar. Once the fracture origin was identified, it was possible to measure its size, and based on ASTM C1322-96a standard, we were able to estimate the fracture toughness of the sintered parts. Fracture toughness was found to increase with increasing of sintering temperature from 1.8 MPa∙m½ to 3.1 MPa∙m½ by rising the temperature from 1250°C to 1300°C as the fracture process is strongly influenced by the microstructure of the material.

Abstract: To analyze the chemical activity of admixture in mortars, we used a methodology which guarantees that the obtained mixtures still have a volume of the flexible phase and an initial porosity constant. Then, only the clean chemical effect of the admixture is taken into account in the variation of the mechanical strengths. The chemical contribution of admixtures on the strengths of mortars had been evaluated in the basis of the factors of activity K deduced from the concept of the equivalent binder and using the predictive model of strength of Feret. To study the influence of the parameters of formulation on the activity of admixtures in mortars, we used seven admixtures different by their mineralogical natures, their fineness, and their morphological characteristics, two types of cements and two types of superplasticizers. The main results achieved showed that the factors of activity are very sensitive to the nature fineness and proportion of admixtures substituted to cement, but the influence of the nature of cement or superplasticizer was less important. Consequently the activity of admixtures differs from the concept of the equivalent binder recommended by the standard of the ready-mixed concretes which are based on a coefficient of reactivity with contractual values.

Abstract: The use of mineral admixtures in cementing materials can generate significant modifications in the fresh and hardened mixes, which can depend on the parameters of formulation. To study the influence of the parameters of formulation on the rheological properties of cementing materials with admixtures, we used seven admixtures different by their mineralogical natures, their fineness, and their morphological characteristics, two types of cements and two types of superplasticizers. The experimental methodology used is based on the volume substitution of the cement by admixtures in mixtures whose the absolute volume of the solid phases and workability are preserved constant. The main results achieved showed that the rheological properties of the fresh mortars with admixtures are very influenced by the amount and the properties of admixtures, and the nature of the superplasticizer, but depended rather on the nature of the cement used.

Abstract: The production of sewage sludge from waste water treatment plants is increasing all over the world. Disposal of sewage sludge ash is a serious environmental problem. If we think of the areas needed for sludge ash disposal, we clearly understand the importance of reusing sewage sludge ash in concrete. This paper presents results related to the replacement of sand by sewage sludge ash. The sludge was characterized for chemical composition (XRF analysis), crystalline phases (XRD analysis) and pozzolanic activity. The effects of incineration on crystal phases of dry sludge were investigated. Two (W/C) ratios (0.55 and 0.45) and three sludge percentages (5%, 10% and 20%) by cement mass were used. The mechanical performance of SSAC at different curing ages (3, 7, 28 and 90 days) was assessed by means of mechanical tests. Results show that sewage sludge ash leads to a reduction in density and mechanical strength. Results also show that concrete with 20% of sewage sludge ash and W/C=0.45 has a 28 day compressive strength of almost 30MPa.

Abstract: The concrete degradation caused by internal expansive reaction (IER) is a problem that affects many structures in the world. These reactions, which include the alkali-silica reaction (ASR) and the internal sulphatic reaction (ISR) related with delayed ettringite formation, are very dangerous, due the expansive behavior of products formed, that cause the cracking of concrete. So it is urgent to find preventive methods to avoid or mitigate the onset of these reactions in new structures. This work aims to show the applicability of sludge from a tungsten mine in the mitigation of the IER. To evaluate the effect of sludge in the mitigation of ASR and ISR, mortar and concrete mixes were produced with 30% (%in mass) of cement replacement. The results obtained so far allow stating that tungsten mine sludge as Portland cement replacement could be effective in the ASR and ISR mitigation.

Abstract: The study of stone alterations in the Lisbon Metro stations allowed the discussion of the influence in the development of these alterations of stones characteristics and the actual conditions to which the stones are subjected. Alterations occur under what can be considered the usual conditions of use but also under abnormal situations that must be taken into account given its frequency. The diverse situations identified are considered in the discussion of possible recommendations bearing in mind the actual situations found at the stations.