International Concrete Abstracts Portal

The efficiency of finely ground blast furnace slags (BFS) was studied in relation to the fundamental physico-mechanical and structural properties of cement mortars. A positive effect of BFS fineness on the workability of fresh mortars was proved. Due to a small water content (20 percent by mass of the cementitious material) when combined with a high-range, water-reducing admixture (HRWRA), the compressive strengths of mortars ranging between 80 and 100 MPa are ascertained at normal curing conditions. Special curing conditions, such as autoclaving or hot water curing, produce specimens with compressive strengths in the range of 100 to 130 MPa, depending on the grading of BFS and the composition of the binder. With additional heat curing, the compressive strength of the mortars increase, in general, by about 10 to 50 percent over that of either autoclaved or hot water cured mortars. In this paper, some other properties of high-strength mortars incorporating finely ground BFS are discussed, including porosity and durability investigations. The efficiency of BFS addition is compared with other fine mineral powders, such as silica fume and fine silica powder, with special attention paid to binder compositions and curing conditions.

Cementless fine-grained concrete based on high-calcium fly ash and slag from thermal power plants was developed by the Siberian Metallurgical Institute in 1990. This paper presents the results of a study of schedules of heat treatment of the cementless concrete aimed at improvement of quality and durability of concrete. Prior to heat treatment, concrete was cured for three, six, and 12 hours at 60, 80, and 100 C. The temperature rise and cooling took three hours each. This cycle was provided by an automatic steam-curing chamber. After moist curing at high temperature using the above cycle, the specimens were tested for compressive strength immediately after cooling to room temperature and at the age of 28 days. It was found that the temperature of the isothermal heating should be in the range of 80 to 100 C. The best results were obtained with 100 C, although it is difficult to achieve this temperature, especially in cast-in-place construction. It also demands a great amount of electrical energy. Therefore, 80 to 90 C should be acceptable as the optimum temperature range. The optimum time of the isothermal heating is 9 to 12 hours. However, the computer processing of the results of the investigation showed that the optimum time of curing was six to seven hours. The technology and recommendations for heating of cementless slag ash concrete, by means of heating wires used in the construction of low-rise houses both in summer and winter periods, have been developed.

Presents a study on high-early-strength cements based on calcium sulfoaluminate, C 4A 3S. These cements can be produced at temperatures about 300 C lower than normal portland cement and can also be synthesized using industrial process wastes and byproducts, such as fly ash, blast furnace slag, chemical gypsums, and other waste materials containing reactive sulfate and alumina. Cements designed to contain C 4A 3S, Beta-C 2S, and CS or C 4A 3S, calcium sulfosilicate, C 5S 2S, and CS have been synthesized using (a) pure analytical reagent (AR) calcium carbonate or commercial limestone as the source of CaO; (b) fly ash, blast furnace slag, bauxite, clay, or alumina as the source of Al 2O 3 and SiO 2; and (c) natural gypsum, phosphogypsum, or desulfogypsum as the source of sulfate. Ettringite, C 6AS 3H 32, generated by the hydration of C 4A 3S and CS is responsible for the high early strength of these cements. The hydration of the silicate phase and the presence of C 5S 2S contribute to ultimate strength. These ettringite-containing cements do not expand and, in fact, have dimensional stabilities similar to portland cement. In these types of cements, durability problems may arise from the poor resistance of ettringite to carbonation. Due to the higher resistance to carbonation of another calcium sulfoaluminate hydrate, monosulfate (C 4ASH 12), the investigation has been extended to a composition which included brownmillerite, C 4AF, whose presence promotes the conversion of ettringite to monosulfate during hydration.

The geological characteristics of Mexico permit an important number of materials to be considered for use as pozzolans in the construction industry. These materials have great importance, due to the relevance to problems of concrete durability. This situation has caused an increase in the use of pozzolanic cement. This increase of use of pozzolanic cement creates a need for characterization of these products and evaluation of their performance based on the specifications related to their use in concrete. Mexican natural pozzolans meet the requirements of the specification, with some deficiencies in some pozzolans. The objective of this work was a detailed characterization of all pozzolans actually used in Mexico and evaluation of their use as an admixture in concrete, using for this purpose ASTM C 311 and C 618. Those particular points of the specifications that are not satisfied completely and the elements that contribute to the fact are discussed in this paper.

Due to increasing volumes of fly ash production each year, new utilization areas must be found. A new application had been developed at Bogazici University. Fly ash with various weight percentages of rubber tire chips were mixed and compacted at a water content wet side of optimum. Sealed single ring infiltrometer and falling head permeability tests were conducted on these specimens with water and gasoline as the permeants. Unconfined compression and split tensile strength tests were conducted to evaluate the mechanical behavior of the proposed liner material. When gasoline was permeated through rubber-fly ash specimens, a decrease was observed in the permeability as compared to that measured during water permeation. This decrease is due to the physical characteristic of rubber, expansion upon contact with gasoline. The expanded rubber holds some portion of the gasoline in itself, while sealing the voids and blocking the passageways for further leakage. For the above-mentioned technique, patent protection has been applied. This technique has a good application in the field because the liability for the underground petroleum storage tanks will decrease considerably when this technique is used.