Browsing by Subject "Cementitious materials"
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Item Evaluation of natural pozzolans as replacements for Class F fly ash in portland cement concrete(2013-12) Cano, Rachel Irene; Juenger, Maria C. G.Most concrete produced today utilizes pozzolans or supplementary cementitious materials (SCMs) to promote better long term durability and resistance to deleterious chemical reactions. While other pozzolans and SCMs are available and provide many of the same benefits, Class F fly ash has become the industry standard for producing quality, durable concrete because of its low cost and wide-spread availability. With impending environmental and safety regulations threatening the availability and quality of Class F fly ash, it is becoming increasing important to find viable alternatives. This research aims to find natural, lightly processed, alternatives to fly ash that perform similarly to Class F fly ash with regards to pozzolanic reactivity and provide comparable compressive strength, workability, drying shrinkage, thermal expansion properties and resistance to alkali-silica reaction, sulfate attack, and chloride ion penetration. Eight fly ash alternatives from the US were tested for compatibility with the governing standard for pozzolans used in portland cement concrete and various fresh and hardened mortar and concrete properties. The results of this research indicate that six materials meet the requirements for natural pozzolans set by the American Society for Testing and Materials and many are comparable to Class F fly ash in durability tests. The primary concern when using these materials in concrete is the increase in water demand. The spherical particle shape of fly ash provides improved workability even at relatively low water-to-cement ratios; however, all of the materials tested for this research required grinding to achieve the appropriate particle size, resulting in an angular and rough surface area that requires more lubrication to achieve a workable consistency. So long as an appropriate water reducing admixture is used, six of the eight materials tested in this study are appropriate and beneficial for use in portland cement concrete.Item Sulfate Induced Heave: Addressing Ettringite Behavior in Lime Treated Soils and in Cementitious Materials(2012-02-14) Kochyil Sasidharan Nair, Syam KumarCivil engineers are at times required to stabilize sulfate bearing clay soils with calcium based stabilizers. Deleterious heaving in these stabilized soils may result over time. This dissertation addresses critical questions regarding the consequences of treating sulfate laden soils with calcium-based stabilizers. The use of a differential scanning calorimeter was introduced in this research as a tool to quantify the amount of ettringite formed in stabilized soils. The first part of this dissertation provides a case history analysis of the expansion history compared to the ettringite growth history of three controlled low strength mixtures containing fly ash with relatively high sulfate contents. Ettringite growth and measurable volume changes were monitored simultaneously for mixtures subjected to different environmental conditions. The observations verified the role of water in causing expansion when ettringite mineral is present. Sorption of water by the ettringite molecule was found to be a part of the reason for expansion. The second part of this dissertation evaluates the existence of threshold sulfate levels in soils as well as the role of soil mineralogy in defining the sensitivity of soils to sulfate-induced damage. A differential scanning calorimeter and thermodynamics based phase diagram approach are used to evaluate the role of soil minerals. The observations substantiated the difference in sensitivity of soils to ettringite formation, and also verified the existence of a threshold level of soluble sulfates in soils that can trigger substantial ettringite growth. The third part of this dissertation identifies alternative, probable mechanisms of swelling when sulfate laden soils are stabilized with lime. The swelling distress observed in stabilized soils is found to be due to one or a combination of three separate mechanisms: (1) volumetric expansion during ettringite formation, (2) water movement triggered by a high osmotic suction caused by sulfate salts, and (3) the ability of the ettringite mineral to absorb water and contribute to the swelling process.