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.

Gypsumless Portland cements (GPC) are inorganic binders, which may be described aas system of: ground Portland clinker (specific surface of 400-500 m2/kg - Blaine), a surface-active agent with hydroxyl groups and a hydrolyzable alkali metal salt (carbonate, bicarbonate, silicate). New cements, developed in recent years, are able to reach both higher strengths and fracture toughness than ordinary Portland cement (1,2,3). New developments in the making of very strong cements have resulted from modifying cement compositions and manipulating the microstructures (4).

In High-Strength Concrete in general high-quality aggregate is used. This aggregate has a high compressive strength and often a high modulus of elasticity. This high modulus of elasticity of the aggregate strongly influences the deformation behaviour of high-strength concrete. Results show that there is a direct and linear relationship between the shrinkage value and the modulus of elasticity of the concrete. The highest modulus of elasticity of concrete was 85 GPa. The compressive strength at the age of 28 days was in the range from 102 to 182 MPa. A design aid is given to show the interrelation between modulus of elasticity and shrinkage strain of the concrete on one side and modulus of elasticity of the aggregate, modulus of elasticity of the matrix and matrix content on the other side.