International Concrete Abstracts Portal

SP-132 Published in two volumes...The first volume contains papers dealing with fly ash and natural pozzolans. The second volume consists of papers dealing with condensed silica fume and ferrous and non-ferrous slags.

A study was made of the effects of Saskatchewan lignite fly ash on the resistance of concrete to freezing and thawing. Concrete was made with either ASTM Types I or V cement and different percentages of fly ash with an air content of 4 to 6 percent. Performance of the concrete was evaluated by measuring the changes in its dynamic modulus and its mass. A scanning electron microscope was also used to examine the changes in the microstructure of the cement paste due to exposure to freezing and thawing. Results show that the use of high percentages of fly ash in concrete (35 and 50 percent) reduced its resistance to freezing and thawing even though it contained about 6 percent air and was cured in water for 80 days. However, concrete containing 20 percent fly ash gave satisfactory performance, provided its air content and strength were comparable to control concrete that contained no fly ash. Results from the SEM examination show that the decrease in resistance of fly ash concrete to freezing and thawing may be due to the slow migration of portlandite and ettringite crystals from the dense C-S-H zones to the air voids. Concrete with fly ash was less susceptible to the migration of portlandite, but its air voids contained more fibrous hydrates, which may have led to an increase in the past porosity.

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.