Validity of 0.45 Power Chart in Obtaining the Optimized Aggregate Gradation for Improving the Strength Aspects of High-Performance Concrete

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Title: Validity of 0.45 Power Chart in Obtaining the Optimized Aggregate Gradation for Improving the Strength Aspects of High-Performance Concrete

Author(s): R.K. Panchalan and V. Ramakrishnan

Publication: Special Publication

Volume: 243

Issue:

Appears on pages(s): 99-108

Keywords: 0.45 power chart; high-performance concrete (HPC); maximum density line; optimized aggregate gradation

Date: 4/1/2007

Abstract:
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.