International Concrete Abstracts Portal

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.

Presents results of investigations carried out on high fly ash content concrete (HFCC) cores removed from several structures constructed in the U.K. since 1979. Structures investigated included a road pavement, a major road viaduct, water-retaining and industrial structures, and a slipway subjected to marine exposure. Concrete properties measured after 10 years of service include compressive strength, depth of carbonation, permeability, and chloride and sulfate penetration profiles. In addition, petrographic analysis of thin sections was also undertaken. The HFCCs studied were designed considering the fly ash to be just a further ingredient in the concrete rather than as a cement replacement. This led to higher fly ash contents and lower cement contents than is generally normal practice. The structures examined were in excellent condition after 10 years. Results show a durable concrete exhibiting increases in compressive strength beyond 28 days, little evidence of carbonation, low to average permeability, and resistance to chloride penetration. In this respect, it is significant that at the marine exposure sites, the chloride concentrations decreased significantly with depth. No evidence of alkali-silica reaction was detected in spite of reactive aggregates being present in some of the concretes.

The results of a great number of trial mixes for mix design of roller compacted concrete (RCC) are presented. This particular RCC used a local fly ash, rich in lime and sulfates, which does not meet any existing specification. This fly ash's performance in concrete has been studied for some time at the Laboratory of Reinforced Concrete of Aristotle University of Thessaloniki. Recently, this fly ash was used in the construction of a large RCC dam in northern Greece. Measurements of the strength development and the elasticity of RCC mixes showed that the 80 percent (by weight) of the cementitious material could be substituted for this fly ash. Therefore, it was proven that in RCC mixes this fly ash is more effective than in conventional concrete.