International Concrete Abstracts Portal

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.

The Akashi Kaikyo Bridge, with a center span of 1990 m, will be the world's longest suspension bridge when it is completed in 1998. The two main tower foundations are being constructed in water. A total volume of about 500,000 m3 of antiwashout underwater concrete has been placed, and about 180,000 m3 of ordinary reinforced concrete is currently being placed. Since this antiwashout underwater concrete had to be placed over a wide area and placed about 10,000 m3 per pour, it was necessary to choose a low-heat, high-flowability concrete. The cement used for this antiwashout underwater concrete was a three-component type containing about 80 percent granulated blast furnace slag and fly ash. Report describes the physical properties and workability of the antiwashout underwater concrete and the results of construction.

A considerable amount of natural zeolite has been used as an admixture for portland cement in the People's Republic of China. Paper first deals with a comprehensive characterization of inorganic admixtures such as natural zeolites with different mineralogical compositions, a fly ash, a fine blast furnace slag, and a silica fume. Binders, such as ordinary portland cement and a quick lime for the substitution of portland cement, were also subjected to the characterization. Next, bending and compressive strength and drying shrinkage of the test mortars were measured under the constant flow value. Standard test mortars were prepared by making use of the ordinary portland cement and quick lime-substituted portland cement, and blended cement mortars were also tested with the inorganic admixtures previously mentioned. As a result, natural zeolite was proven to be of sufficient applicability as an admixture for cement.

Study examines the microstructure properties of cement-based grout consisting of Type II rapid-hardening portland cement, Saskatchewan fly ash, and brine. The liquid brine is composed mainly of salts of sodium, calcium, potassium, and magnesium obtained from an underground potash mine. A scanning electron microscope (SEM), with an electron probe x-ray microanalyzer, was used to study the mechanism by which fly ash and brine alters the microstructure characteristics of cement grouts under confining pressures of 0, 3.4, and 6.9 MPa (0, 500, and 1000 psi). The SEM examination was conducted at 7, 14, and 365 days. This examination revealed that grout mixes containing brine had a gel-like substance covering the entire surface of the hydrated products. The probe x-ray microanalyzer identified the gel-like substance as consisting mainly of sodium chloride salt. Fly ash cement particles were also found to be encapsulated by the sodium chloride gel-like substance. This encapsulation may decrease the rate of pozzolanic reaction between fly ash particles and the lime available in the cement. Microscopic examination of specimens mixed with brine also showed the presence of long fibrous crystals with diameters ranging from 3 to 20 æm growing on the surface of the gel-like substance. Generally, at 7 and 14 days, the fly ash-cement grouts were found to have more such fibers than the grout containing no fly ash. This trend reversed at 365 days.