Assessing supplementary cementitious materials for use in concrete : long-term and rapid testing
Creators: name: Al-Shmaisani, Saif
Publisher: name: The University of Texas at Austin
Year: 2021
Subjects: Reactivity
Fly ash
Pozzolanicity
Rapid screening

description: Supplementary cementitious materials (SCMs) have been commonly used as a partial replacement for cement in concrete to reduce cost, reduce the carbon footprint, and improve long-term durability. In recent years, there has been an increased demand for new SCMs due to increased concrete production as well as decreased availability of traditional Class F fly ash, and suppliers are looking to extend the supply of fly ash by looking to non-traditional materials. For example, blending bituminous or Texas lignite coals and sub-bituminous coals has become more common for coal-fired power plants to reduce emissions of sulfur oxides (SO [subscript x]) and operation costs, resulting in fly ashes that differ slightly from a traditional Class F fly ash. Additionally, suppliers have started to blend Class F fly ash with other coal combustion products or natural pozzolans to meet the chemical and physical requirements of a Class F fly ash, thereby extending the supply of Class F fly ash. Suppliers are also treating fly ashes that do not meet Class F fly ash requirements using various methods, such as grinding, drying, and treating with chemical additives. The research performed for this dissertation showed that these non-traditional fly ashes performed comparably to a traditional Class F fly ash in most short and long-term testing, except for their impact on cement hydration and ability to improve sulfate resistance in some cases. Chemical and mineralogical compositions were important factors in determining material performance and should be analyzed prior to using these materials in concrete. Some of the long-term laboratory tests conducted on fly ashes and other SCMs take up to two years. Since this is time-consuming and expensive, rapid tests were evaluated to determine if they were effective at screening out poor performing materials. Materials used in rapid testing included some that are known to be inert, pozzolanic, hydraulic, or have combined hydraulicity and pozzolanicity. A modified version of the standardized strength activity index (SAI) test was found to be ineffective at screening poor performing materials as was bulk electrical resistivity on mortars at 28 days. The new rapid, relevant, and reliable (R³) calorimetry and bound water tests and a modified lime reactivity test, called the University of New Brunswick Pozzolanic Reactivity Test (UNBPRT), on the other hand, were both effective at distinguishing between inert and reactive materials. Pairing these tests with an added step in the R³ bound water test, called the R³P test, allowed for the separation of pozzolanic and hydraulic reactivity. Material reactivity determined from these tests was then compared to short and long-term testing to see if it could accurately predict performance of materials. Values from the R³ tests and the UNBPRT were found to predict compressive strength of SCM-mortars at 28 days well, except for fly ashes. The R³ tests were able to predict the performance of all SCMs in RCPT, but only “inert” materials in ASR and sulfate testing. It is clear that bulk oxide and X-ray diffraction analyses are necessary, in addition to reactivity testing, in order to predict the performance of “pozzolanic, less reactive” materials in ASR and sulfate testing.