MULTISCALE INVESTIGATION OF ALTERNATIVE CEMENTITIOUS MATERIAL SYSTEMS

The necessity and the universality of concrete infrastructure prompt innovation in addressing the global challenge of meeting societal needs in the most sustainable and economical ways possible. Increasing the use of non-portland cements or "alternative cementitious materials" (ACMs) is of growing interest due to their unique properties and to their potential to reduce the environmental footprint of concrete. The unique properties of ACMs may vary by material, but include rapid setting, rapid strength development, higher ultimate strength, improved dimensional stability, and increased durability in aggressive environments. The increased strength and increased durability further contribute to enhanced service life which can help offset initially higher material costs, and also to enhanced sustainability. In the past, most ACMs were primarily used in limited specialty applications, and some of them have been shown in lab-scale studies to be feasible for the partial or full replacement of traditional portland cements used in concrete. However, there is a limited understanding of the scalability of construction with these material systems, their long-term performance, and durability in a range of environments, and their structural response when subjected to transportation-relevant loading conditions. This thesis presents the results from the comprehensive investigation of the applications of these commercially available ACMs in durable and sustainable transportation infrastructure, which include the early-age and long-term material properties as well as multi-scale durability investigations. A novel multi-scale approach was proposed to design concrete mixtures with these commercial ACMs to meet both the prescriptive requirements and the performance targets. The multi-approach involves (i) using multiple advanced material characterization techniques to understand how these commercially blends hydrate, (ii) changing their fresh properties to meet the prescriptive requirements without adversely affecting their long-term material properties to meet the performance targets. New test methods and protocols also involving multi-scale material characterization were proposed to gauge the long-term performance of these ACMs against wide range of exposure conditions. These new test methods were designed, relying as much as possible on existing test methods for traditional portland systems, to facilitate rapid adoption of the ACM formulations. From this, guidance for the lab-scale investigation and guidance for the ACM selection and mixture design for use in transportation infrastructure, primarily in the aspects investigated in this thesis, are provided. Successful concrete mixtures were developed by using a combination of isothermal calorimetry, x-ray diffraction, set time assessments, and flow tests to link cement characteristics, admixture type, and dosage to early-age behavior. For all ACMs, except for one calcium aluminate cement and one magnesium phosphate cement, concretes were designed that met both the early age requirements for the set time and slump, at w/c of 0.40 or less, and later age requirements for mechanical properties. Even though commercially available polycarboxylate based superplasticizers and citric acid based set modifiers are known to perform well with calcium sulfoaluminate (CSA) based systems, it was found out that CSA cements containing high iron content have compatibility issues with those admixtures. A new test method for measuring formation factor in both the low resistive and highly resistive systems that is easy to perform and that does not require pore solution extraction or even prior knowledge of pore solution composition and its resistivity is developed; was used to understand permeability and interconnectivity in the ACM systems at varied w/b. Understanding permeability and interconnectivity in ACM mixtures are essential for durability assessment in these systems. New insights were provided on the chemical sulfate attack mechanisms in ACM systems. (C,N)-A-S-H type gel was found to be forming on the outside exposed surface in all the ettringite based systems investigated in this thesis, and it is found to be one of the primary reason for the superior resistance of these systems in resistance external sulfate attack. A new accelerated cylinder mortar test method was developed to assess the alkali-silica reaction (ASR) in ACM systems without the need for alkali boosting and also addressing the leaching issues found the current ASTM C 1293 accelerated test method. This new test method can be used as a complementary test method for the ASTM C1293 test, or it can be used as a standalone test method upon further validation. Using the combination of these two test methods, it was found out that most of the ACMs investigated in this thesis offer excellent resistance to alkali-silica reaction. It was also found that portlandite and alkali content played an important roll in resisting ASR compared to the permeability of these systems. Accelerated carbonation studies were performed on both OPC and ACM systems at various exposure levels (0.04%, 1%, 7%, and 14%). Out of the accelerated CO2 exposure levels tested in this chapter, both 7% and 15% exposure levels were found to be aggressive in all the OPC and ACM mixtures, except in one calcium aluminate system. Even the 1% exposure level found to be aggressive in activated aluminosilicate systems and two of the CSA systems investigated in this thesis. However, accelerated carbonation at 1% or higher CO2 exposure levels underestimated the carbonation in calcium aluminate cements having higher amounts of CAH10 compared to the atmospheric CO2 level. Therefore, selection of CO2 exposure levels, to accurately test the ACM systems for carbonation in accelerated conditions, can be made only after taking their sensitivity towards CO2 exposure level into account.Ph.D

Carbonation in Alternative Cementitious Materials: Implications on Durability and Mechanical Properties

Understanding the rate and implications of carbonation on strength and durability in alternative cementitious materials (ACMs) is critical in designing ‘green’ concretes for intended service lives. In this paper, three commercially available ACMs, including one calcium aluminate cement (CAC), one calcium sulfoaluminate belite cement (CSA), and one alkali-activated binder using class C fly ash (AA), were evaluated against one portland cement (OPC). Thermogravimetric analysis (TGA) and x-ray diffraction (XRD) techniques were used to understand the effect of carbonation on ACM paste composition. Water sorption tests on both carbonated and uncarbonated cement mortar showed a significant reduction in porosity of this OPC and CAC system with carbonation, whereas no significant change in this CSA and AA system. In addition, the carbonation front in concrete made with these ACMs was measured using phenolphthalein and rainbow indicators at regular intervals of exposure to 7% CO2, and these results are compared to companion concretes made with this OPC. The rate of carbonation in this CAC, CSA and AA system were significantly higher than that of OPC. The carbonation in the systems made with the ACMs in this study results not only in a decrease in pH, which may lead to depassivation on embedded metal reinforcement but is also found to cause decomposition of main strength giving hydration products. Further research is required to understand the effects of carbonation on steel passivation and chloride threshold levels in the ACM systems

Data for Novel Alternative Cement Binders for Highway Structures and Pavements

The contents of data file include raw data for all the data plots included in the final report titled Novel Alternative Cement Binders for Highway Structures and Pavements. The excel spreadsheets were named based on chapter numbers in the final report.The ubiquity and the necessity of concrete infrastructure prompts innovation in addressing the global challenge of meeting societal needs in the most sustainable and economical ways possible. Increasing the use of non-portland cements or “alternative cementitious materials” (ACMs) is increasingly of interest due to their special properties and to their potential to reduce the environmental footprint of concrete. The special properties of ACMs may vary by material but include rapid setting, rapid strength development, higher ultimate strength, improved dimensional stability and increased durability in aggressive environments. The increased strength and increased durability further contribute to enhanced service life which can help offset initially higher materials costs, and also to enhanced sustainability. In the past, most ACMs have primarily been used in specialty limited applications and some of them have been shown in lab-scale studies to be feasible for the partial or full replacement of traditional portland cements used in concrete. However, there is limited understanding of the scalability of construction with these material systems, their long-term performance and durability in a range of environments, and their structural response when subjected to transportation-relevant loading conditions. This data presents the results from the comprehensive investigation of the applications of these commercially available ACMs in durable and sustainable transportation infrastructure, which include the early-age and long-term material properties as well as complete multi-scale durability investigations.Office of Infrastructure Research & Development, Federal Highway Administration, 6300 Georgetown Pike, McLean, VA 22101-2296. Grant number: DRFH61-14-H-000