Optimization of mixture proportions for concrete pavements - influence of supplementary cementitious materials, paste content and aggregate gradation

Adam Kajetan Rudy, Purdue University

Abstract

The main purpose of this research was to evaluate the influence of supplementary cementitious materials, paste content and aggregate gradation on the statistical optimization of mixture proportions for concrete pavements. The research program was divided into three main PHASES. In PHASE I, the influence of the amount and type of supplementary cementitious materials (as well as the paste content) on selection of optimum proportions for concrete pavement mixtures was studied. The Response Surface Methodology (RSM) was utilized to design test matrices of concrete mixtures consisting of three binder systems: the fly ash system, the GGBFS system and the fly ash plus GGBFS system. For each binder system, the paste content varied from 21 to 25% by mixture volume. The optimum composition of concrete mixtures was found to be 29% of fly ash and 22% of paste for the fly ash system, 37% of GGBFS and 23% of paste for the GGBFS system, and 15% of fly ash, 27% of GGBFS and 22% of paste for the ternary system. In PHASE II, three concrete mixtures (each representing near optimum composition of variables studied in PHASE I) were selected and produced with six different aggregate gradations. These aggregate gradations varied with respect to coarseness (CF) and workability (WF) factors (as defined by Shilstone's chart), packing density and maximum aggregate size. The results revealed that the best performance was obtained for mixtures with CF of about 67 and WF of about 40. In addition, the paste-aggregate void saturation ratio (k"), which relates paste content to aggregate packing density, was found to be important in controlling scaling and drying shrinkage of concrete mixtures produced in PHASE II. The focus of PHASE III of the study was on numerical modeling to determine the optimum combination of (k") and aggregate packing density with respect to concrete performance. The results revealed that the most desirable concrete mixtures were produced with a (k") value ranging from 0.925 to 1.000 and with packing density in the range from 0.755 to 0.786. Finally, selected concrete mixtures produced in Phase III were evaluated with respect to their cracking potential. The mixtures selected for the cracking potential study were those which showed elevated level of drying shrinkage and were characterized by relatively high k" values and poor aggregate packing density. The cracking potential of these mixtures was evaluated using the modified AASHTO ring test procedure which involved demolding of specimens immediately after the concrete reached the final setting time. The final setting time was determined using the Time Domain Reflectometry (TDR) method.

Degree

Ph.D.

Advisors

Olek, Purdue University.

Subject Area

Civil engineering

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