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In tunnels built according to the New Austrian Tunnelling Method, the shotcrete shell is often in contact with ground water. Depending on the amount and type of water, chemical compounds in the shotcrete are dissolved and transported into the drainage pipes and the main outfall. Due to precipitation of the dissolved compounds, the maintenance of the drainage systems is very expensive. Furthermore, the main outfall is loaded with water of a high pH-value. It was found that as well as Ca(OH)2, the alkalies in the shotcrete are responsible for the degree of leaching. Therefore, the accelerators needed for such shotcretes, which are based mostly on alkalies, have to be reduced as much as possible. This can be done sufficiently if silica fume is used in connection with slag cement to make the shotcrete sticky enough, so that it adheres to the rocks.

Paper presents the results of an experimental investigation to determine the influence of curing on pore volume, pore structure, and absorption of the surface zone of blended cement pastes and concretes. The cement replacement materials used were fly ash, ground granulated blast furnace slag, and silica fume. Temperature and relative humidity were the main variable parameters of the early age (up to 14 days) curing regimes adopted--the temperatures used were 20 and 45 C and the different relative humidities were 25, 55, and approximately 100 percent (specimens covered with wet burlap). In addition, a curing membrane was used in one set of experiments. Mercury intrusion porosimetry was carried out on ordinary portland cement and blended cement pastes. Capillary water absorption tests and shallow immersion tests were carried out on samples obtained from the surface zone of concrete cubes, and the latter test was also conducted on whole cubes. The cement replacement level and water-cementitious materials (water-total binder) ratio of the pastes and the concrete mixes were the same, the water-cementitious materials ratio being 0.45. Results show that dry curing at early ages results in higher intruded pore volume, coarse pore structure, and higher absorption of the surface zone compared with initial moist-curing. The effect is more pronounced in fly ash and slag-blended mixes than in control and silica fume mixes. Higher temperatures of curing have a detrimental effect on pore volume of ordinary portland cement paste and silica fume-incorporated cement paste, whereas the effect is beneficial for cement pastes blended with fly ash or slag. Cement pastes and concretes blended with slag are prone to surface crazing, which results in greater porosity of the surface zone of specimens. Surface crazing in slag-blended mixes becomes negligible under initial curing at higher temperature.

With more than 3 million underground storage tanks located throughout the U.S., and mass oil drilling, production, and transportation, leaking problems generate large quantities of petroleum-contaminated soils (PCS). With the limited availability of solid waste disposal facilities, research is needed to investigate viable reuse options for PCS. Paper presents an attempt to apply stabilization/solidification techniques to PCS to bind the hydrocarbons in a structure formed by cement, fly ash, and aggregates to produce a construction material suitable for bulk applications. An experimental program was developed to examine the potential for using PCS as a fine aggregate replacement in concrete. Two PCS types with different levels of heating oil contamination were investigated (0.11 and 0.66 percent contamination concentration by weight). For each soil type, nine mixtures were obtained by replacing sand with PCS (PCS-sand ratio of 10, 20, and 40 percent by weight) and Class C fly ash with cement (fly ash-cement ratio of 10 and 20 percent by weight). Compressive and flexural strengths, permeability (hydraulic conductivity), and leachability of benzene-to-water tests were conducted. Results indicate that the addition of PCS reduces both the compression and flexural strengths of concrete. However, the obtained strength is adequate for structural applications. Concrete containing higher PCS-sand replacement ratio develops lower strength. That strength loss increases with higher contamination concentration. Given longer curing time, the fly ash presence can reduce such loss. The permeability coefficient of PCS concrete is slightly higher than control. Fly ash addition yields a more impermeable PCS concrete. For both soil types, at 40 percent PCS-sand replacement ratio, the leachability of benzene was nondetectable after 24 hr and 10 days of casting.

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.

This paper gives the results of an investigation on the performance of high-volume fly ash concrete made with ASTM Class F fly ashes from three different sources. Cementitious materials contents of 300, 370, and 430 kg/m3 were used. The percentage of fly ash used was 58 percent of the total cementitious materials content. All the concrete mixtures were air-entrained and superplasticized. A large number of concrete specimens were subjected to the determination of compressive and flexural strengths, Young's modulus of elasticity, creep strain, drying shrinkage, abrasion resistance, deicing salt-scaling resistance, and resistance to chloride-ion penetration. High-volume fly ash concrete with adequate early-age strengths and excellent later age strengths can be produced with cement and total cementitious materials as low as 125 and 300 kg/m3, respectively. The Young's modulus of elasticity, creep, and drying shrinkage of high-volume concrete are comparable to those of the plain portland cement concrete. The high-volume fly ash concrete shows excellent resistance to chloride-ion penetration and outperforms plain portland cement concrete. The total charge in coloumbs at 91 days, a measure of resistance to the chloride-ion penetration, ranges from 278 to 1078. The corresponding values for reference concrete range from 1003 to 2313. Further research is needed to explain the relatively poor performance of the high-volume fly ash concrete under deicing salt scaling and abrasion tests.