Browsing by Subject "Supplementary cementitious materials"

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Evaluation of test methods and specifications for supplementary cementitious materials for concrete
(2019-05-10) Kalina, Ryan David; Juenger, Maria C. G.; Ferron, Raissa P.; Folliard, Kevin J.; Fowler, David W.; Wheat, Harovel G.
With the decrease in availability of Class F fly ash as a result of stricter emission standards imposed on coal combustion in power plants, the concrete industry is taking measures to find new sources of supplementary cementitious materials (SCMs) to be used in concrete that behave similarly to, or better than, Class F fly ash. A problem that is encountered when evaluating SCMs is that test methods and standards designed to evaluate fly ashes and traditional sources of natural pozzolans are inadequate for evaluating new sources of materials, including quarry by-products. The research presented in this dissertation examined several test methods used to qualify natural pozzolans and fly ashes in the US to determine their suitability for assessing new material sources. First, test methods specified by ASTM C618 were compared against results from advanced characterization techniques for material pozzolanicity, including calcium hydroxide (CH) content via thermo-gravimetric analysis (TGA) and the recently developed rapid, relevant, and reliable (R³) method. This was done to determine how whether or not ASTM C618 can effectively screen inert materials. The research also evaluated the use of standardized tests for resistance to alkali-silica reaction (ASR) and their application to natural pozzolans and fly ashes, particularly in the context of SCMs with high alkali contents. The literature suggests that the more rapid test for ASR, ASTM C1567, is ineffective for evaluating the contribution of high-alkali fly ash in controlling ASR expansion, and this research examined the role of alkali solubility on the test results for both high-alkali fly ashes and natural pozzolans. Concerns with the relevance of the ASTM C311 standard method for determining available alkalis were explored by evaluating modifications to the standard available alkali test method that included varying the length of curing and increasing the pH of the reagent solution to better represent conditions in real concrete. The results of the research showed that ASTM C618 does not adequately screen inert materials for use in concrete and fails to test for pozzolanicity. The research also showed that natural pozzolans behave differently than high-alkali fly ashes in standardized tests for ASR in that ASTM C1567 is sufficient in predicting the outcome of ASTM C1293 for natural pozzolans, primarily due to the lower available alkalis of natural pozzolans compared to fly ashes. It was also found that modifying the ASTM C311 standard method for determining available alkalis to better represent realistic conditions is not necessary, since the results of the modifications were not significantly different than the results of the standard method. For several of the materials, the available alkalis determined using the standard method were useful in understanding the role of alkalis in SCMs when assessing their performance in ASR testing
Increasing the reactivity of natural zeolites used as supplementary cementitious materials
(2014-08) Burris, Lisa Elanna; Juenger, Maria C. G.
This work examined the effects of thermal and chemical treatments on zeolite reactivity and determined the zeolite properties governing the development of compressive strengths and pozzolanic reactivity. Zeolites are naturally occurring aluminosilicate minerals found abundantly around the world. Incorporation of zeolites in cement mixtures has been shown by past research to increase concrete’s compressive strength and durability. In addition, use of zeolites as SCMs can decrease the environmental impact and energy demands associated with cement production for reinforced concrete structures. Further, in contrast to man-made SCMs such as fly ash, zeolite minerals provide a reliable and readily available SCM source, not affected by the production limits and regulations of unrelated industries such as the coal power industry. In this work, six sources of naturally occurring clinoptilolite zeolite were examined. The zeolites were first characterized using x-ray fluorescence, quantitative xray diffraction, thermal analysis, particle size analysis, pore size distribution and surface area analysis, and scanning electron microscopy. Cation exchange capacity was also tested for one of the zeolites. Following comprehensive material characterization, the six pozzolanic reactivity of the natural zeolites was determined by measuring the quantity of calcium hydroxide in paste after 28 or 90 days, by measuring calcium hydroxide consumption of the zeolite in solution and by tracking the development of strengths of zeolite-cement mortars. Pretreatments that attempted to increase the reactivity of the zeolites, including calcination, acid treatment, milling and cation exchange, were then tested and evaluated using the same methods of material characterization and testing mentioned previously. Last, the results of the reactivity testing were reanalyzed to determine which properties of natural zeolites, including particle size, nitrogen-available surface area, and composition, govern the development of compressive strengths, pozzolanic reactivity and improved cement hydration parameters of pastes and mortars using natural zeolites as SCMs. Pretreatment testing showed that milling and acid treatment successfully increased the reactivity of zeolites used as SCMs. Additionally, particle size was shown to be the dominant property in determining the development of compressive strengths while particle size and surface area of the zeolites contributed to zeolite pozzolanic reactivity.