International Concrete Abstracts Portal

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.

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.

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.

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.

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.

This paper reports the results of an investigation of the sorptivity of mortar that contains varying amounts of ground brick from different European bricks. Waste clay brick deriving from four European countries was ground to roughly cement fineness and used to partially replace cement in quantities of 0, 10, 20 and 30% in mortars. The sorptivity and water absorption of these mortars were tested for curing periods of up to one year. The presence of ground brick does not have a significant effect on the water absorption of mortar. Sorptivity however, is affected considerably by not only the presence of ground brick but also by brick composition. Initially, the presence of ground brick in mortar increases its sorptivity. As curing periods increase, the sorptivity values for ground brick mortars decrease at a rate that is greater than that seen in mortars whose binder is 100% portland cement. This indicates that the ground brick decreases the capillarity of the mortar and this is attributed to the production of additional C-S-H gel. The additional C-S-H gel, in effect, refines the pore structure of the mortar and this is reflected in the increase in the compressive strength obtained for these mixes.

This paper describes the process technology of the production of rice husk ash (RHA) as a supplementary cementing material. The incinerating tests of rice husks were carried out by changing the temperature and duration of incineration using a rotary kiln. From the incineration tests, it was concluded that the incinerating temperature should be lower than 550°C to obtain RHA with specific surface area larger than 50 m2/g, and the duration of incineration should be long enough to obtain RHA with ignition loss less than 3%. Based on the incineration test results with the rotary kiln, a new stirring type furnace is introduced in the present paper for the production of RHA with large specific surface area. An applicability of the stirring furnace is examined by changing the feeding rate of rice husks and rotation speed of stirrer. The RHA having specific surface area larger than 50 m2/g and ignition loss less than 3%, can be produced using the new stirring furnace at a temperature below than 5 0 0C. Using this high specific surface RHA, strength development properties of mortar were examined and compared to the mortar incorporating a lower specific surface RHA and silica fume. The compressive strength of mortar incorporating the high specific surface RHA was increased remarkably, and was higher than that of the lower specific surface RHA and silica fume. Furthermore, unlike other pozzolanic materials, mortar incorporating the higher specific surface RHA showed excellent early strength development.

In the process of a long-term study of fine cementless mortar from wastes of thermal power plants (TPP) and other industries, aspects of its tech-nology were determined which were as follows: power 1. Processing slag (also known as bottom plant to sand of 0 to 5 mm size fraction. ash) from the Abakan thermal 2. Grinding fly ash to a fineness of 700 to 750 m2/kg with the use of mechanochemical activation process. 3. Using two - stage thermal treatment of cementless mortar mixture and determining optimal regimes for secondary thermal treatment. 4. Using a model method for concrete development. The application of cementless ash slag mortars non- load - bearing concrete profitability respectively. to load - bearing and

Oil shale is used for energy production. It was found that burning at about 800°C, according to the ROHRBACH-LURGI Process, resulted in optimal hydraulic properties of the ash. The major problem associated with burning oil shale is the formation of huge quantities of the by-product generally referred to as burnt-oil shale. Depending on the composition of the burnt-oil shale it can be used as an addition to normal portland cement in an amount of 2530% and in various other building products. In view of the fact that huge quantities of burnt-oil shale will be generated, it is beneficial to find ways in using this by-product in a large scale. In some respects burnt-oil shale is a hydraulic material similar in nature to blast-furnace slag. It is cementitious, due to the formation of clinker-like phases, mainly dicalcium silicate and monocalcium aluminate. It also contains, besides small amounts of free CaO and calcium sulfate, larger proportions of pozzolanic reacting oxides, especially amorphous SiO2. Burnt-oil shale has a very slow strength gain and it reaches a compressive strength of about 30 MPa at 28 days. The reactivity of burnt-oil shale can be improved with a hydration activator so that high volume (>50%) burnt-oil shale binders can be produced which show highest reactivity, resulting in extremely high early and final strength and high durability for repair of concrete roads, bridges, runways and the like.

Different non-aqueous solvents (NAS), such as ethylene glycol, 1,2-propylene glycol and glycerol, were tested in the study of the behavior of NAS/SiOz-rich pozzolans (rice husk ash, RHA, and silica fume, SF). Dissolved SiOa in NAS/pozzolan mixtures was evaluated by several procedures: a) electrical conductivity measurements of the suspension; b) weighing of non-dissolved matter in reflux conditions; and c) titration using barium hydroxide solution. The obtained results were compared to those obtained by the reference method (solubility in boiling KOH solution). A good correlation between data obtained in NAS and the reference method was observed.