4,019 research outputs found
Tecniche elettrochimiche per lo studio della corrosione di acciai annegati in matrici cementizie tradizionali e innovative
No full textCorrosione-erosione dell'acciaio a contatto con conglomerati cementizi allo stato fresco
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Concrete manufactured with crushed asphalt as partial replacement of natural aggregates
No full textThe paper focuses on the reuse of crushed asphalt (GA) as a partial replacement (up to 20%) of natural aggregates for concrete manufacture. Addition of GA aggregates produced a positive effect on workability loss. The GA mixes, however, showed a significant tendency to bleed and segregate at the highest replacement percentage applied. GA led to a decrease of compressive strength in concrete (with respect to that of the reference concrete) up to 50% due to the weakness of the cement paste / recycled aggregate interface. To compensate for this negative effect, a reduction of w/c for the GA concretes was necessary. A decrease of w/c allowed the GA concretes to show drying shrinkage values substantially similar to those of reference concrete with the same cement factor. The experimental results confirmed the possibility of partial substitution (max. 15%) of natural aggregates with crushed asphalt for making concrete
An experimental evaluation of the compatibilty of NSF and PCE superplasticizers with different cement types
No full textThis paper deals with variability in the performances of seven different superplasticizers chosen among those of most common use belonging to the naphthalene (NSF) and polycarboxylate-based (PCE) families. In particular, compatibility of two naphthalene-based and five polycarboxylate-based admixtures with six different cements available on the Italian market was evaluated by measuring water reduction to manufacture mortars with the same workability at the end of mixing. Two different lots of the same cement (same plant) were used: lot 1 and 2 produced, respectively, on September 2005 and March 2006. Flow retention up to sixty minutes and tendency to entrap air in the mortars were measured. Results confirmed that the average water reduction and flow retention properties are better for PCE compared to NSF superplasticizers. However, experimental data confirm as performances of PCE admixtures are more strongly dependent on the cement type than those of NSF polymers. No differences were detected in terms of the air entrapped between the two superplasticizer families, except for the ACR5 superplasticizer
Current and potential distribution modelling for cathodic protection of tank bottoms
No full textAbove ground tanks for storage of liquid hydrocarbon are often erected with secondary containment membrane installed below the tank bottom to prevent the soil contamination in case of leakage. The design of impressed current cathodic protection in presence of the plastic membrane is based on distributed anodes installed in the space between the tank bottom and the membrane; among available anodes, the most commonly used are the titanium grid or ribbon activated with noble metal oxides. The configuration of the grid or ribbon anode system confined in the closed space between bottom and membrane creates specific issues concerning the electrochemical reactions occurring at anode and cathode, the ohmic drops in the anode system and the potential and current distribution at the cathode. The paper shows results of a number of numeric simulations performed to predict the actual distribution of current and potential. Design criteria are discussed
Performance and Compatibility of Phosphonate-Based Superplasticizers for Concrete
No full textThe paper deals with the effectiveness of an innovative phosphonate-based superplasticizer (PNH) for ready mixed concrete. Concrete specimens were manufactured by considering a constant initial workability, equal to 220 mm slump at the end of the mixing procedure. Workability was measured at 0, 30, and 60 min to evaluate the workability retention performances of the innovative superplasticizer. Compressive tests at 1, 7, and 28 days were carried out to evaluate the influence of the phosphonate-based superplasticizer on concrete setting and hardening. The concrete mixes were designed by considering 13 different cements to assess the superplasticizer-cement compatibility. The PNH-based admixture showed a better performance in terms of water reduction and workability retention with respect to napthalenesulphonate based admixtures (NSF); however, a higher dosage of PNH with respect to polycarboxylate ethers (PCEs) was needed to get the same initial fluidity
Le scorie d’acciaieria: impiego di sottoprodotti industriali per il confezionamento di calcestruzzi
No full textComposition of a fluid mix applicable as dummy fluid in wear testing of pumps
No full textA composition of a fluid mix comprises water, stone aggregates and one or more binders in the form of pozzolanic additives comprising silicic fly ash, with the provision that it does not contain substantially other binding materials or substances which produce calcium hydroxide, in particular in the absence of cement or lime, both in the form of oxide and in the form of air-hardening lime or hydrated lime. This fluid mix does not harden or set over time in ambient temperature and is thus applicable as dummy fluid for testing wear in concrete pumps
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