International Concrete Abstracts Portal

Self-Compacting Concrete (SCC) was developed in the later 1980’s and has attracted a wide interest in the world due to its unique properties. This study investigatesthe workability and earthquake resistance of SCC. Several chemical admixtures are added to the concrete to adjust its workability. The workability of fresh concrete is tested using different methods including slump cone, inversion slump cone, L-box and Orimet apparatus. Then the best SCC mixture ratio is selected for microstructural and earthquakeresistance investigations. The earthquake resistance of SCC is investigated on concrete frame. Two frames with the same size are designed and but one cast with SCC and theother one with ordinary concrete. The two frames are tested under low-cyclic loadingusing MTS loading system. ANSYS software is used to simulate and analyze the statictest. The test results give indication how the materials characteristics and constructability of SCC affect earthquake resistance behavior of the frame.

Fresh concrete is a complex fluid consisting of a suspension in water of a high volume percentage of particulate solid having a very wide particle size distribution. The rheological properties of fresh concrete control the flow behavior of the material in mixing, placement, consolidation and finishing. Test methods that measure flow using a single parameter (e.g. slump) cannot properly evaluate the rheological properties of concrete in all uses. ACI committee 236A with the support of the Concrete Research Council and industry has tested four concrete rheometers specifically designed to evaluate rheological properties of concrete materials. The second test series expands the data from the first test series using the same approach of bringing the rheometers together at a common test site and testing the same concrete mixtures simultaneously. All of the rheometers can measure a flow curve for fresh concretes with slumps in the range from 100 mm to 250 mm or non-segregating concretes with slump flows in the range from 300 mm to 800 mm. Each rheometer evaluates yield stress and plastic viscosity by fitting a Bingham model flow curve to measurements of rotation rate and torque for each mix. All of the rheometers gave different absolute values for the Bingham constants of yield stress and plastic viscosity for each mix. But all of the rheometers ranked the mixes in the same order for both yield stress and plastic viscosity.

This research examines the effect of aggregate content and gradation on self-consolidating concrete (SCC) passing ability. Passing ability is defined as an SCC mixture’s ability to flow through narrow spaces (e.g. closely spaced reinforcement) without segregating or blocking. The mixtures tested ranged over two uniform aggregate sizes, two aggregate contents, two different mixture design philosophies, and a gradated aggregate mixture. Passing ability tests, slump flow tests, horizontal flow tests, and stereology tests were performed on these mixtures. Stereology is a statistical counting technique used primarily by natural scientists. Concrete researchers have used this to describe bubble size and distribution in concrete. A vertical flow box was developed by McBride to determine the passing ability of the various mixtures. Various bar spacings are tested. From the results of this study, it seems that two stereology parameters can be correlated to the minimum bar spacing that will allow SCC to pass. These parameters are the ratio of maximum aggregate size to mean aggregate free distance and the ratio of maximum aggregate size to mean aggregate random spacing.

The accurate determination of fresh concrete rheology is key to ensuring the successful production of self-consolidating concrete (SCC). Rheometers, however, are used infrequently in the field. Empirical test methods are most commonly used to determine SCC workability despite measuring quantities that are related to rheological parameters only in an indirect way, if at all. Instead of using multiple empirical test methods to measure the workability of SCC, it is desirable to use a rheometer in both the laboratory and field to determine the flow properties of SCC quickly. Existing rheometers are generally unsuitable for routine field use due to their large size, high cost, or both. This paper describes the use of the International Center for Aggregates Research (ICAR) rheometer, a low-cost, fully portable device that can measure concrete mixtures ranging in workability from approximately 50 mm in slump to SCC. Laboratory test results of SCC mixtures and field testing experience are presented to demonstrate the validity and practicality of the ICAR rheometer.

An experimental program which aimed at investigating the behavior of SCC containingClass F fly ash has been carried out. The fresh state properties of the concrete wereassessed using methods of segregation and flow. The rheology of the paste matrix wasalso characterized and compared with a previously developed paste rheology model. Inaddition, compressive strength, chloride permeability, and mold-finish were evaluated. The results indicate that it is possible to develop a SCC containing Class F fly ash that is high performing in its fresh state. Furthermore, the addition of fly ash was shown toreduce superplasticizer dosage, increase workability, and increase overall chloride permeability resistance. In addition, it was determined that the difference of densities between the aggregate and matrix influence the results of a previously developed pasterheology model.