International Concrete Abstracts Portal

The experimental program presented in this paper was a technical evaluation of an alternative cement and high-density (HD) concrete mixture design for HD concrete at mid-range temperature to meet specific target properties. The cement industry has moved away from manufacturing ‘special use’ portland cements, which were approved for some applications of mass HD concrete, for which temperature rise in the concrete is of importance. Potential replacement of these ‘special use’ portland cements by blending varying amounts of supplementary cementitious materials (SCMs) with ‘general use’ portland cement to provide ‘blended cements’ was investigated. The paper focuses on experimental results obtained in the laboratory showing the effect of the addition of high volume slag blended cement for HD concrete on temperature rise, as well as on mechanical properties and microstructure after aging and mid-range temperature exposure. Slag-blended cement was evaluated and determined to have acceptable properties in HD concrete, meeting or exceeding performance requirements.

The early age strength development of concretes containing slag cement (ggbs) at levels of up to 70% of the total binder have been investigated to give guidance for their use in fast track construction. 28-day target mean strength for all concrete specimens was 70 MPa (10,150 psi). Although supplementary cementitious materials such as slag cement (ggbs) are economical, their use has not gained popularity in fast track construction because of their slower strength development at early ages and at standard cube curing temperatures. There are however indications that supplementary cementitious materials are heavily penalised by the standard cube curing regimes. Measurements of temperature rise under adiabatic conditions have shown that high levels of cement replacement by ggbs, e.g. 70% are required to obtain a significant reduction in the peak temperature rise. Even though the temperature rise using slag cement is lower than from using portland cement, it is still sufficient to provide the activation energy needed for a significant reaction acceleration. Maturity measurements are needed to take advantage of the enhanced in-situ early age strength development of ggbs concrete. The contractor should confirm that the actual compressive strength of the concrete in the structure at the time of formwork removal exceeds the required strength. Maturity functions like the one proposed by Freiesleben Hansen and Pedersen (FHP), which is based on the Arrhenius equation, have been examined for their applicability to ggbs concrete. Activation energies, required as input for the FHP equation, have been determined according to ASTM C1074-98.

Synopsis: Economic and environmental considerations have promoted the use of supplementary cementing materials (SCMs) such as slag cement (SC) and fly ash (FA). Ternary mixtures containing both slag cement and fly ash have gained popularity due to environmental issues and shortages in the supply of cement. However, in the 2003 Arkansas State Highway and Transportation Department (AHTD) Standard Specifications, ternary mixtures were prohibited for use in Portland Cement Concrete Pavement (PCCP). Previous research conducted by the University of Arkansas examined ternary mixtures containing SC and FA and cured at 70°F (21°C). This research program examined the strength gain and time of setting characteristics of ternary mixtures cured at lower temperatures. In the study, SC contents ranged from 0 to 40%, and the FA contents ranged from 0 to 60%. Six different mixtures containing Class C FA and Grade 100 SC were batched and tested at temperatures of 70°F (21°C) and below. The curing temperatures for the study were 40, 50, 60, and 70°F (4, 10, 16, and 21°C). The concrete properties measured were concrete temperature, slump, unit weight, air content, time of setting, and compressive strength.

This CD-ROM contains eight papers that provide insight on recent slag cement concrete developments in academia, the concrete industry, and in real life applications of slag cement concrete. Topics include materials aspects related to the benefits of adding slag in concrete to prevent alkali-silica reactions, reducing drying shrinkage, and reducing the potential for thermal cracking during the curing period. Also covered are high-volume applications of slag cement in: concrete for transportation structures, high-performance concrete pavements, mass concrete, and high-density concrete. Note: The individual papers are also available. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP-263

This report details the results of a critical review of the literature on the effect of ground, granulated, blast-furnace slag (slag cement) and slag-blended cements on the drying shrinkage of concrete. Drying shrinkage values from the literature were collected, and concretes containing slag were compared to otherwise identical concretes that did not contain slag. Overall, while individual data may indicate a higher drying shrinkage, on average, the drying shrinkage for concretes containing slag cement was the same as concretes without slag. From examination of the data it was determined that the only parameter of the mixture design that had a significant influence on the drying shrinkage was the total aggregate volume. Any increase in drying shrinkage of the slag cement concrete was typically reduced with increasing aggregate content. The level of slag replacement and the w/cm of the concrete mixture were not found to affect the relative drying shrinkage, at least over the typical range used for concrete mix designs. The relative values of the drying shrinkage were also unaffected by whether slag cement was added as a separate ingredient or if a blended hydraulic cement containing slag was used. The aggregate content of concretes made with slag was often lower than a comparable concrete made without slag due to the lower density of the slag relative to portland cement when slag cement was used as a replacement on an equal mass basis, rather than on an equal volume basis. A correction for this would reduce any additional shrinkage attributable to the use of slag cement. In addition, the increase in relative shrinkage of some slag-containing concretes may, in several cases, also be partially due to the reduced gypsum content of the cementitious mixture, although this is unclear and needs further investigation. Although the data are limited, the restrained shrinkage cracking of concrete containing slag appears to be less than that of concrete without slag. Cracking was delayed to later ages and resulted in smaller total crack widths. The effect of the inclusion of slag on restrained cracking needs to be further investigated.