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.

Conditioning coal-burning power-plant flue gases with ammonia reduces the emission of nitrous oxide compounds. But the ammonia often combines with available sulfur and other compounds that attach to the fly ash. If the ammoniated fly ash is then used in concrete, the high-pH environment causes a release of ammonia and a strong, objectionable ammonia smell. This can make the fly ash unmarketable. What’s the solution? Fly ash beneficiation processes that can remove ammonia and also reduce the unburned carbon content. Some of the processes are described in one of the 54 papers included in ACI SP-199, Seventh CANMET/ACI International Conference on Fly Ash, Silica Fume, Slag and Natural Pozzolans in Concrete. Other papers deal with effects of fly ash and admixture combinations on setting time, use of slag concrete to reduce corrosion of reinforcement, and the role of chemical and mineral admixtures in concrete made with recycled concrete as aggregate. Note: The individual papers are also available as .pdf downloads.. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP199

Effective lightweight concrete with highly porous bottom ash (by-product of thermal power stations) as aggregate and high volume of fly ash was developed at the Research Institute of the College of Judea and Samaria, Ariel (Israel). This lightweight concrete has sufficient strength and thermal insulation properties, based on a rational combination of the highly porous aggregate and the relatively dense hardened cement-fly ash paste. In addition, the dense structure of the hardened cement-fly ash paste in the concrete, with low and middle cement contents, improves the durability of the concrete. In the current paper, the results of further studies of this lightweight concrete are presented. These studies were concentrated on lowering the volume of air voids in the cement-fly ash paste of the fresh concrete, and thereby increasing the strength and density of the hardened concrete. This evaluation is based on studying concrete mixture proportions prepared with broad range of the cement and the fly ash content (maximum relation of fly ash FA to cement C in the experiments was FA/(C + FA) = 0.8). In addition, a method for optimization of the lightweight concrete mixture proportions is suggested. This method ensures that the manufacturing the concrete is in compliance simultaneously with two given parameters: density and compressive strength.

Two silica-manganese slags containing about 11 % MnO were ground to Blaine finenesses of 360 to 600 m*/kg. Their C/S (CaO/SiO2) modulus was very low (0.47 to 0.58) and, for this reason, these slags were considered likely to be unsuitable for use in the preparation of blended cements. They were therefore introduced in concrete instead of either fly ash or silica fume. The cement content of these concrete mixtures was in range of 2 1 0 kg/m3 t o 4 5 0 kg/m3. The quantity of each supplementary cementing material was adjusted according to the French standards and varied from 50 to 80 kg/m3. The slags behaved as well in concrete as fly ash or silica fume: no decrease in strength was observed and the water permeability was the same.

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.