International Concrete Abstracts Portal

This paper presents the results of an experimental investigation to determine the validity of 0.45-power chart in obtaining the optimized aggregate gradation for improving the strength characteristics of high-performance concrete (HPC). Historically, the 0.45 power chart has been used to develop uniform gradations for asphalt mixture designs; however it has now been widely used to develop uniform gradations for portland cement concrete mixture designs. Some reports have circulated in the industry that plotting the sieve opening raised to the 0.45 power may not be universally applicable for all aggregates. In this paper the validity of 0.45 power chart has been evaluated using quartzite aggregates. Aggregates of different sizes and gradations were blended to fit exactly the gradations of curves raised to 0.35, 0.40, 0.45, 0.50 and 0.55. Five mixtures, which incorporated the aggregate gradations of the five power curves, were made and tested for compressive strength and flexural strength. A control mixture was also made whose aggregate gradations did not match the straight-line gradations of the 0.45 power curve. This was achieved by using a single size aggregate and sand. The water-cement ratio and the cement content were kept constant for all the six mixtures. The results showed that the mixture incorporating the 0.45 power chart gradations gave the highest strength when compared to other power charts and the control concrete. Thus the 0.45 power curve can be adopted with confidence to obtain the densest packing of aggregates and it may be universally applicable for all aggregates.

Discusses the need and requirements for a method of proportioning high-strength concrete mixes. The development of the method, which is based on a well-established method used for conventional concrete, is described. Design charts are given for various stone sizes, and an example of such a chart is illustrated. Because the method is based on easily determined aggregate properties, it is suitable for any type of aggregate: crushed or naturally occurring stone and sand, and graded or single-sized stone.

Presents a simple design aid for predicting long-term (up to 50 years) movements in reinforced concrete columns and bridge beams made of normal and lightweight aggregate concrete. The method is based on the principle of superposition using a creep factor chart, which takes into account varying sizes of members, age at loading, exposure conditions, and the percentage of reinforcement, and it requires only a knowledge of the concrete strength and the loading history of the member. The method is developed from the study of in situ movements in two reinforced concrete structures subjected to increment loading. The shrinkage strains in columns are predicted using a shrinkage chart, which requires only a knowledge of elastic modulus of concrete at 28 days. The predicted load-induced and basic strains show excellent agreement with measured strains in the two structures, and the method shows good agreement with literature. The paper demonstrates how the simple method of predicting long-term movements in buildings and bridges can be utilized by the structural engineer as a designer's tool.