International Concrete Abstracts Portal

Red mud is a by-product from the aluminum industry. To investigate the possibility of using this waste material as a pozzolan in the cement and concrete industries, tests were carried out to examine the pozzolanic properties of calcined red mud. Red mud was calcined for 5 hr at five different temperatures: 600, 650, 700, 750, and 800 C. Blended portland cements containing 30 or 50 percent of the calcined red mud were studied for hydration products, strength, and durability. The results indicated that the red mud had the maximum reactivity when calcined at 600 C, because on hydration the lime content of the blended cement was considerably reduced. The calcined red mud when used in combination with portland cement contributed to the formation of hydrated alumina-silicates and hydrogarnets. Very good compressive strengths were obtained with the blended cement containing 30 percent calcined red mud. Mortars cast with these blended cements were placed in solutions of seawater and acetic acid. The results indicated good stability of mortars to these environments.

29Si NMR has been employed as a tool to characterize the reaction mechanism of hydration in several blended cements up to 6 to 9.5 months. The cements investigated were blends with silica fume, fly ash, activated kaolinite, and blast furnace slag. Spectra deconvolution indicated that, in the silica fume as well as in the activated kaolinite blend, the reaction of the anhydrous calcium-silicates is initially accelerated with respect to the ordinary portland cement. In the fly ash blends, this effect is smaller. Both in the silica fume and fly ash blends, an increase in the amount of silica middle groups (Qý-type) at - 84 ppm, relative to the amount of silica end groups (Q1-type) at - 79 ppm, is notable, which indicates an increased tendency to form longer CSH chains. The size distribution and glass content of the fly ashes used seem to influence the hydration reaction, which is reflected by somewhat higher Qý/Qý ratios and an increased initial hydration. In the blends with activated kaolinite, it was not possible to deconvolute the Q1 and Qý chemical shifts at all ages, due to changes in the shift maxima Q1 and/or Qý. This may be due to the formation of amorphous noncrystalline alumina-containing reaction products. The chemical shift of the blast furnace slag appeared too broad for a successful deconvolution. In general, both the total (Q1 + Qý) as well as the Qý/Q1 ratio correlate with compressive strength data, Qý species contributing markedly. Paper contains a general overview of the application of NMR spectroscopy in cement and concrete research.

The lining of underground cavities for storage of natural gas requires a proper cementing paste as does the cementing of casing in boreholes placed in salt beds. The following properties of the cementing pastes are required: high corrosion resistance, minimal shrinkage, even some expansion, high leak tightness, good bond to steel and rock, proper rheology and strength. The following blended cements were investigated: cement "Nowa Huta" 25 with 40% blast-furnace slag (bfs), cement "Rejowiec" 45 for bridge construction and cement with 70% bfs. The cements were mixed with NaCl brine at a concentration 310 g NaCl/L at liquid to solid ration 0.45. The properties of pastes, such as density, rheological, sedimentation and filtration characteristics; time of setting; strength development and shrinkage were determined. The phase composition of pastes was studied by XRD and the microstructure was observed under SEM. The best results were obtained for the pastes with the blast-furnace slag.

The resistance to freezing-and-thawing and chloride diffusion of antiwashout underwater concrete was investigated to evaluate the applicability for tidal zone in cold districts or reinforced concrete structures in marine environments. Comparisons were made with ordinary portland cement concrete of similar mix design. Two types of cement (ordinary portland cement and portland blast furnace slag cement) were used. Two types of blast furnace slag (Blaine fineness 500 and 700 m²/kg) were used as a cement replacement (slag content 30 and 50 percent by weight). The results show that antiwashout underwater concrete without blast furnace slag shows poor resistance to freezing-and-thawing compared with normal concrete. But the freezing-and-thawing resistance can be improved with blast furnace slag. This is due to the fact that concrete containing blast furnace slag has dense pore structures. Pore volume in the range of 10 to 10 3 nm in radius decreases significantly with blast furnace slag. Similarly, chloride diffusion depth becomes smaller with blast furnace slag.

It is well known that curing concrete at elevated temperatures reduces the final compressive strength. The reduction depends on the temperature regime as well as the concrete composition. This program was based on recent data indicating that concrete containing condensed silica fume suffers less strength loss if a strength of about 10 MPa is reached at 20 C before heating. In this investigation, concrete characteristics were w/c + s = 0.30, 0.45, and 0.60 with and without 8 percent condensed silica fume. The temperature regime was to transfer specimens at 40 and 60 C, after delay times at 20 C. The delay times corresponded to strengths of about, 0, 3, 6, 9, 12, and 16 MPa. After 6 days, all specimens were cooled to 20 C and tested at 28d. The results show that the delay period had no significant influence on the final strength, except for the specimens with zero delay. The rest suffered some strength reduction compared to 20 C references, about 15 percent for w/c + s = 0.60, and less than 10 percent for the others. The reductions at 60 C were slightly greater than at 40 C. Concretes containing condensed silica fume generally suffered the smallest strength reductions.