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Home > Publications > International Concrete Abstracts Portal
The International Concrete Abstracts Portal is an ACI led collaboration with leading technical organizations from within the international concrete industry and offers the most comprehensive collection of published concrete abstracts.
Showing 1-5 of 90 Abstracts search results
May 1, 1992
Hans S. Pietersen
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.
K. Sakai, H. Watanabe, M. Suzuki, and K. Hamazaki
In Japan, fly ash has been generally used as a material of low-heat cement for mass concrete, such as dams. As an alternative material for low-heat cement, granulated blast furnace slag can be considered. In this study, moderate heat portland cement, in which the fineness is 300 m¦/kg, and granulated blast furnace slag, in which the fineness is 300, 400, 500, and 600 m¦/kg, were made. The slag content in cement is 50, 60, 70, and 80 percent. Tests for setting and heat of hydration in cement, and for setting, compressive strength, freezing and thawing, adiabatic temperature rise, carbonation, and drying shrinkage in concrete, were carried out. The following results were obtained: 1) as the slag content increases, the time of setting increases; 2) the compressive strength of concrete increases with the increase of fineness of slag; 3) concrete with slag has a satisfactory resistance to freezing and thawing; 4) the adiabatic temperature of concrete is affected by the slag content and the fineness; 5) the depth of carbonation increases with the increase of slag content; 6) there is no great difference in drying shrinkage between concretes with slag and fly ash. From the test results, it is concluded that, by properly determining the slag content and fineness, it is possible to manufacture cement with similar or better quality compared to conventional moderate heat fly ash cement.
J. J. Brooks, P. J. Wainwright, and M. Boukendakji
Ten blended slag-cement concretes made with typical slags from four countries are compared with a control ordinary portland cement concrete. The slags replaced 30 to 70 percent of cement by mass. Concretes are compared on the basis of equal mass proportions of cementitious materials, aggregates, and water. Average strength, elasticity, and creep are quantified relative to the corresponding properties of the control concrete. The influence of type of slag on concrete properties is inconsistent and small. The influence of replacement level on strength and creep is time-dependent. For water-stored mature concrete, slag enhances the secant modulus of elasticity, but the opposite occurs for dry-stored concrete. Compared with OPC concrete, slag-cement concrete has a similar or greater long-term strength, similar shrinkage, lower basic creep, and similar or lower total creep.
A. Carles-Gibergues and B. Husson
Within the context of atmospheric pollution prevention, fly ash producers are brought to better desulfurize combustion gases. As a result, there are important modifications in the composition of the residues that are enriched with sulfur, especially in the case of calcium sulfite fly ash. The sulfitic fly ashes studied result from desulfurization by quick lime addition in dust removers of a thermal plant. Paper presents the physical, chemical, and mineralogical characteristics of this type of fly ash. Their examination by x-ray diffraction shows the presence of crystallized minerals: lime, calcite, and calcium sulfite, and the existence of a glass, the composition of which is given by electron microprobe. A special emphasis is given to the sulfite stability. In a second part of the paper, the behavior of these fly ashes in paste with water and slaked lime has been studied. It is shown that they are a very weak hydraulic binder but they present, on the other hand, pozzolanic activity. At last, the study has allowed determination of the influence on workability and mechanical properties of hydraulic mortars and concretes in which they have been introduced as partial replacement of cement. Corrosion and carbonation aspects have also been studied in mortars.
Examines the utilization of ultra-fine particles originated from fly ash, when a part of cement is replaced with the particles. The ultra-fine particles mainly consist of amorphous silica and alumina, and specific surface area of these particles can be changed from 200,000 cmý/g to 1,300,000 cmýg. To study the pore structures of mortar containing those fly ash particles, water-cement ratio, replacement ratio of the particles, and period of standard curing were varied. The properties, such as rate of hydration, rate of strength development, chemical components dissolved out to various alkali solutions during early ages, and pore-size distribution were measured. These properties were compared with properties of the cement mortar containing silica fume, meta kaolin, or fly ash for similar mortar specimens. It is shown that compressive strength of mortar containing the ultra-fine particles developed with age, and the pore structure of the mortar was like that of mortar with fly ash. Chemical components dissolved out to the particles were different from those dissolved out by other mineral admixtures.
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