Artigos de Revista

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

Dissolved air flotation (DAF) performance with two different naturally occurring cyanobacterialmorphologies was investigated with respect to the biomass removal efficiency,the toxin release to water and the coagulant demand by different water backgroundnatural 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, thedose depending on the water NOM content); 8 min flocculation at 70 s 1; 8 min DAF with5 bar relative pressure and 8% pressurised recycle) were performed with single cells ofMicrocystis aeruginosa and Planktothrix rubescens filaments spiked in synthetic waters withdifferent NOM contents (hydrophobic vs. hydrophilic NOM; moderate (2e3 mgC/L) vs.moderate-high concentration (ca. 6 mgC/L)). For both morphologies, the results show noapparent cyanobacterial damage (since the water quality did not degrade in dissolvedmicrocystins and the removal of intracellular microcystins matched the removal of chlorophylla) and high biomass removal efficiencies (93e99% for cells and 92e98% for filaments)provided optimal coagulant dose for chlorophyll a removal was ensured. Chargeneutralisation by the polyaluminium chloride was the main coagulation mechanism of theM. aeruginosa cells and most likely also of the P. rubescens filaments. The specific coagulantdemand was severely affected by NOM hydrophobicity, hydrophobic NOM (with a specificUV254nm 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.

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

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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