Papers

The degradation of concrete structures caused by delayed ettringite formation (DEF) is a problem that affects many concrete structures worldwide [1]. This pathology is due to the formation of expansive ettringite inside the material and is very difficult to deal with, because presently there is no efficient method to repair concrete structures affected by DEF. Hence, there is an urgent need to find preventive methods that may enable the inhibition of DEF in new constructions. This paper presents the findings of a long-term study [2,3] on the expansion rate and microstructure of heat-cured concretes with different amounts of mineral additions, like fly ash, metakaolin, ground granulated blast-furnace slag, silica fume and limestone filler. For this purpose different concrete compositions were produced using the same binder, water/binder (w/b) ratios and aggregate type. The concretes were prepared and subjected to a heat-curing cycle and subsequently to two drying-humidification cycles. After these cycles the concrete specimens were immersed in water for long-term storage at 20 ± 2ºC. Length changes of specimens were measured at regular intervals. The microstructures of old heat curing specimens were investigated by optical microscopy and SEM-EDS analysis. The results of the blended-concrete compositions were compared with control compositions, and the conclusions were extracted.

The degradation of concrete structures caused by delayed ettringite formation (DEF) is a problem that affects many concrete structures worldwide [1]. This pathology is due to the formation of expansive ettringite inside the material and is very difficult to deal with, because presently there is no efficient method to repair concrete structures affected by DEF. Hence, there is an urgent need to find preventive methods that may enable the inhibition of DEF in new constructions. This paper presents the findings of a long-term study [2,3] on the expansion rate and microstructure of heat-cured concretes with different amounts of mineral additions, like fly ash, metakaolin, ground granulated blast-furnace slag, silica fume and limestone filler. For this purpose different concrete compositions were produced using the same binder, water/binder (w/b) ratios and aggregate type. The concretes were prepared and subjected to a heat-curing cycle and subsequently to two drying-humidification cycles. After these cycles the concrete specimens were immersed in water for long-term storage at 20 ± 2ºC. Length changes of specimens were measured at regular intervals. The microstructures of old heat curing specimens were investigated by optical microscopy and SEM-EDS analysis. The results of the blended-concrete compositions were compared with control compositions, and the conclusions were extracted.

A especificação da madeira para a construção assenta ainda hoje, muitas vezes, em critérios pouco objectivos, de difícil verificação e reduzida eficácia. Algumas especificações “tipo” repetidamente encontradas em Cadernos de Encargos, não só não encontram sustentação científica, como assentam por vezes em falsos pressupostos quanto ao efeito que diversos factores têm sobre a resistência e a durabilidade da madeira. É no mínimo curioso que, apesar da existência de um amplo conjunto de normas e princípios que permitem especificar a madeira e os derivados de madeira para a construção de forma simples e eficiente, se verifique que as disposições relativas a madeiras contidas em muitos Cadernos de Encargos não parecem ter registado evolução desde meados do século passado, altura em que a inadequação das especificações era já então assinalada (Anon., 1951).

Dissolved air flotation (DAF) performance with two different naturally occurring cyanobacterial morphologies was investigated with respect to the biomass removal efficiency, the toxin release to water and the coagulant demand by different water background natural organic matter (NOM). Coagulation (C)/Flocculation (F)/DAF bench-scale experiments (2 min coagulation at 380 s 1 with polyaluminium chloride (0.5e4 mg/L Al2O3, the dose depending on the water NOM content); 8 min flocculation at 70 s 1; 8 min DAF with 5 bar relative pressure and 8% pressurised recycle) were performed with single cells of Microcystis aeruginosa and Planktothrix rubescens filaments spiked in synthetic waters with different NOM contents (hydrophobic vs. hydrophilic NOM; moderate (2e3 mgC/L) vs. moderate-high concentration (ca. 6 mgC/L)). For both morphologies, the results show no apparent cyanobacterial damage (since the water quality did not degrade in dissolved microcystins and the removal of intracellular microcystins matched the removal of chlorophyll a) and high biomass removal efficiencies (93e99% for cells and 92e98% for filaments) provided optimal coagulant dose for chlorophyll a removal was ensured. Charge neutralisation by the polyaluminium chloride was the main coagulation mechanism of the M. aeruginosa cells and most likely also of the P. rubescens filaments. The specific coagulant demand was severely affected by NOM hydrophobicity, hydrophobic NOM (with a specific UV254nm absorbance, SUVA, above 4 L/(m mgC)) requiring ca. the triple of hydrophilic NOM (SUVA below 3 L/(m mgC)), i.e. 0.7 vs. 0.2e0.3 mg Al2O3/mg DOC.

Urban water infrastructures provide essential services to modern societies and represent a major portion of the value of municipal physical assets. Managing these assets rationally is therefore fundamental for the sustainability of the services and to the economy of societies. “Asset Management” (AM) is a modern term for an old practice—assets have always been managed. In recent years, significant evolution occurred in terms of the AM formal approaches, of the monitoring and decision support tools and of the implementation success cases. However, most tools developed are too sophisticated and data seek for small utilities. The European R&D network COST Action C18 ( E-mail: www.costc18.org) identified key research problems related to the management of urban water infrastructures, currently not covered by on-going projects of the European Framework Program. The top 1 topic is “Efficient management of small community”. This paper addresses challenges and opportunities for small and medium utilities with regard to infrastructure AM (IAM). To put this into context, the first sections discuss the need for IAM, highlight key recent developments, and present IAM drivers, as well as research and development gaps, priorities and products needed.

External renders based on air lime are used in historical buildings as decorative and protective coats. They act as sacrificial layers, particularly exposed to climatic actions and mechanical and environmental impact. They generally present good cohesion and adhesion to the background, although often suffering some degradation as detachments, superficial cracks or “lacunae”. Render solutions specified nowadays for old buildings repair are frequently incompatible with pre-existent materials and inappropriate for the specific situation, thus producing new pathology. The choice of adequate materials, formulation and curing conditions of substitution mortars become crucial for the success of the conservation action. These mortars must meet functional and aesthetic requirements, to fulfil the principles of compatibility, maintaining buildings integrity and durability. An analysis of ranges of results for different lime based mortars for old buildings external renders, obtained in several studies carried out at LNEC, is presented. The mortar formulations studied include: air lime, air lime and cement, air lime and hydraulic lime, air lime and pozzolans and air lime and other additions. Their main physical and mechanical characteristics are analysed and compared. Examples of case studies are presented and analysed. Their adequacy to be used in historical buildings and possible application fields are discussed.

In this paper the efficiency of two organic corrosion inhibitors, a migratory and an admixture inhibitor, was evaluated by electrochemical techniques in solutions simulating the interstitial electrolyte of concrete and on concrete slabs exposed to natural environmental conditions over a five-year period. From obtained results, the usefulness of the two products is discussed aiming its application in new structures to prevent chlorides induced corrosion and as a curative method for repairing reinforced concrete structures contaminated with chlorides and affected by reinforcement corrosion.

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