International Concrete Abstracts Portal

Some protective techniques, such as anti-carbonation coating, provide the concrete a protection due to the creation of a surface barrier that prevents the penetration of CO2 and moisture. However, these procedures are not always so effective when the carbonation process moves as a front through the concrete pores, reaching the reinforcement. In this case, the procedure often adopted is the repair technique, which can include the anchorage of the structure, the entire removal of the carbonated layer and localized or general repair. The purpose of this research was to study the non-destructive repair technique referred as realkalisation by the absorption and diffusion of alkaline solutions. In order to provide evidence for further analyses of the technical viability, besides the main realkalisation testing, some additional tests such as compressive strength, capillary absorption, electrochemical techniques and mortar adherence on realkalised substrates, were performed. The results obtained show that realkalisation through direct contact of the alkaline solution on the concrete surface is effective in re-establishing the high pH of the concrete, although it presented a slight decrease in the compressive strength. The realkalisation process does not interfere in the mortar adherence to realkalised substrates.

Lightweight concrete could be producing by incorporating expanded polystyrene in the conventional concrete. This paper discusses the results of an experimental investigation into the effects of binder materials on the engineering properties of polystyrene aggregate concrete (PAC), having the nominal density of 1800 kg/m3. Four types of binders, namely, general purpose cement, shrinkage limited cement, a combination of 60% general purpose cement and 40% low calcium fly ash, and blended cement with 62% granulated blast-furnace slag, were used. The results showed that as expected, the use of supplementary cementitious materials such as fly ash and slag reduced the early-age strength of the polystyrene aggregate concrete. The strength development of PAC was also affected by the curing condition. Although the use of shrinkage limited cement reduced the shrinkage of PAC by 12%, it increased the creep potential by 76%. The paper also discusses the relationships between: shrinkage and moisture loss; strength and rebound number; and strength and pulse velocity.

SP229 This special publication contains the papers presented at the Fourth International ACI/CANMET Conference held in Olinda, Pernambuco, Brazil, on September 6-7, 2005. It contains 32 papers on recent advances in concrete materials and testing on topics of chemical admixtures; deformations, creep, and cracking control; durability; fiber concrete; fire resistance; nondestructive tests; quality control; strengthening of structures; structural behavior; supplementary cementing materials; and sustainability. Specific papers include: Self Consolidating Concrete, High-Performance and Normal Concrete Affected by Creep at Different Age, Curing, Load Level, Strength, and Water-Cement Ratio with some Interrelated Properties; Properties of Concrete with Recycled Concrete Coarse Aggregates; Application of Different Curing Procedures in High-Performance Concrete; and many more.

The paper describes the results of research on the properties of concrete with the replacement of part of portland cement with bottom ash from municipal solid waste incinerators (MSWI). Results showed that MSWI bottom ash is potentially attractive as mineral addition for the production of concrete, provided that the risk of entrapment of hydrogen bubbles produced by corrosion of aluminium metallic particles in the fresh concrete is prevented. This could be achieved by wet grinding the bottom ash so that reactions leading to gas development could start within the slurry. A great variability was observed in the time required to exhaust the hydrogen gas production; a key factor for this variability was found in the pH of the slurry. A modest amount of cement added in slurry could increase the pH, reduce the time required to exhaust hydrogen evolution and allow manufacturing of quality concrete suitable for aggressive chloride bearing environments.

In this research, three types of different surface treatments were used: acrylic, vinylic and styrene-butadiene polymeric admixtures in order to improve the bond between rubber and cement. Specimens of concrete were evaluated considering the incorporation of three different sizes of tire rubber, and applied in five treated and untreated contents (5% to 25%), resulting in a total of 31 different conditions of analysis . It was observed that the concrete specimens with incorporating of treated tire rubber had its mechanical behavior improved compared to those without treatment. In addition, rubber particles with 1.5 mm in dimension featured a minor negative influence on the concrete properties when compared to the reference and the ones with 0.42 mm and 4.8 mm particles. Some concrete samples were selected to be analyzed by scanning electron microscopy in order to correlate microstructure with their properties.