International Concrete Abstracts Portal

Concrete specimens were manufactured by completely replacing natural aggregates with recycled aggregates from a crushing plant in which rubble from building demolition was ground. Various concrete was prepared by using silica fume or fly ash as a partial fine aggregate replacement and by using an acrylic polymer based superplasticizer to achieve the prefixed workability. Three types of recycled aggregate concrete were manufactured with the same water/cement (0.40) and the same fresh workability (fluid consistency). A reference concrete was also prepared by using natural aggregates with the same particle size distribution as the recycled aggregate, and having a water/cement of 0.56 and a similar fluid consistency. The results obtained show that because of mineral addition and W/C reduction, recycled aggregates can be used instead of natural aggregates since concretes with similar compressive strength can be obtained. The use of the recycled aggregates with fly ash replacements also has significant cost and environmental advantages over ordinary concrete.

Materials prepared by agglomerating white sand and slag with lime were subjected to infiltration with supercritical CO2 at temperatures from 3 1 to 40 OC, pressures from 7.4 to 10 MPa, and for periods from 20 to 120 min. This technique quickly promotes the carbonation reactions which are responsible for the development of the cementitious properties of the composite material. T h e extent of carbonation inside 50 mm cubes was monitored by using phenolphthalein, and the crystalline species were determined by X-ray diffraction. The results showed a high conversion (greater than 74%) of lime to calcite. After infiltration, all specimens exhibited a significant increase in compressive strength. From these results, we conclude that it is possible to produce improved carbonated materials in short processing times. The infiltration technique may be useful for producing construction materials from a number of siliceous waste products such as slag, construction rubbish and sludges from water-treatment plants.

Corrosion is one of the dominating causes of deterioration of reinforced concrete structures. Carbonation of concrete can initiate the corrosion of reinforcements. Many parameters are affecting the concrete carbonation process. Due to the combination of these parameters, phenomenon of concrete carbonation is very complex. It is therefore necessary to implement numerous experimental works to find the relationship between input and output parameters. These tests are slow and time-consuming. On the other hand t h e great number __ of __ r eq uir ed tests makes the investigations costly. Thus it is worth to use numerical methods as new tools to find the relationships between input and output parameters. Neural Networks are capable of showing the relationships of inputs and outputs even in complex nonlinearity. They can be used even in the cases of little background of the theoretical rules, which govern the phenomenon. Due two these advantages of neural networks, a new model of concrete carbonation (NNCC) have been developed to show the appropriateness of the neural networks in civil engineering fields especially in advanced concrete technology, together with its usage as a new prediction model instead of conventional fitted type models.

For the repair and strengthening of historical masonry structures, high penetrability injection grouts which use lime, natural pozzolan, portland cement and some with silica fume have been developed. The type, morphology and evolution of the microstructure and hydration products as evidenced by mercury intrusion porosimetry and X-ray diffraction are presented. Furthermore, the evolution of the insoluble residue and soluble silica contents is also presented. The results of mechanical and bonding tests are presented. Grout mixtures at different ages up to 180 days are compared. The results indicate that ternary blends of the type lime-natural pozzolan-normal portland cement with or without addition of silica fume are highly sensitive to curing conditions. If appropriate curing and quality control are applied, the grout mixtures developed very good mechanical properties and address both durability and economy issues.

Both material and fiber rebound in dry-mix shotcrete are high, and the use of an appropriate mineral admixture is known to alleviate the problem. However, the exact influence of the admixture particle size, gradation and shape on the rebound and the ultimate mechanical properties of shotcrete are poorly understood. This study is divided into two parts: in the first part, the effectiveness of four mineral admixtures-fly ash, silica fume, high reactivity metakaolin (HRM) and carbon black-with varying particle size gradations and shapes was investigated from a rebound reduction point of view. In the second part, HRM and silica fume were compared on the basis of hardened mechanical properties with special emphasis on flexural toughness in the presence of fiber reinforcement.