EVALUATION OF A BLENDED CEMENT AND A MINERAL ADMIXTURE CONTAINING CALCINED CLAY NATURAL POZZOLANS FOR HIGH PERFORMANCE CONCRETE

Abstract

A blended cement system (Duracem™) meeting the requirements of ASTM C 595 (IP, IPMS) and C 1157 (GU, MS AND HS) was developed and commercially produced in 1993 by Ash Grove Cement Company in its efforts to address the durability problems related to alkali-silica reactivity (ASR) and sulfate attack in concrete pavement. The cement product is manufactured by combining a calcined clay manufactured pozzolan, gypsum and Portland cement. In 1995 the mineral admixture (Durapoz™) which meets ASTM C 618 was produced and subsequently introduced into the market. Careful selection of the raw clay materials followed by proper thermal activation, and finish grinding are used to "engineer in" the desired performance properties. Ash Grove Cement Company was issued a patent for the above mentioned products in May of 1997. During the last three years, more than 110 miles of highway and municipal pavements have been placed in Nebraska, Kansas, and Iowa using these new products. The manufactured pozzolan addition rate in the blended cement is typically 16-21%. Paving operations managers have been pleased with the workability of the concrete mixes when compared to Type I mixes. Long term testing of both the Type IP cement and the mineral admixture confirms their ability to mitigate ASR using ASTM methods C 227, C 441, C 1260, and C 1293. Excellent sulfate resistance characteristics are shown using the ASTM C 1012 test method when comparing specimens of Type V, Type IP and Type IP with 10% Class C Fly Ash substitution. Significant reductions in concrete permeability are shown with data from method ASTM C 1202, as well as, corroborative testing by AASHTO T 259, chloride ponding, and diffusion coefficient calculation comparisons. Freezing and thawing resistance, and deicer scaling resistance data were similar to the control Type I concrete mixes when tested using the ASTM C 666 and C 672 methodologies, respectively. In summary, the calcined clay modified blended hydraulic cements and manufactured mineral admixtures can provide many benefits to highway paving, public works, and other structural applications. When compared to Type I Portland cement concrete, a few of the benefits of the calcined clay modified systems are: 1. Reduced susceptibility to ASR when used with potentially reactive aggregates. 2. Improved sulfate resistance. 3. Reduced permeability. 4. Lower Heat of Hydration. 5. Increased ultimate compressive and flexural strengths. 6. Improved workability. 7. Cost effectiveness.