Soil cement has been used as a means of stabilizing highway pavement layers, airport pavement layers, embankments, and foundations for decades. The technology uses a compacted mixture of soil, cement, and water to form a hardened material layer that has specific strength and durability properties. Even after decades of utilization, however, design of soil cement pavement layers has room for enhancement. This thesis investigates factors that influence the design and performance of cement stabilized pavement layers in Mississippi. A survey was conducted to collect information about soil cement design procedures from across the U.S. The factors examined in the laboratory investigation are strength gain with time, unconfined compressive strength variability, elastic modulus, and wheel tracking. More than 1,100 specimens were tested to determine the influence of these factors on the design and performance of soil cement pavement layers.

Seven distinctly different museum-quality concretionary morphotypes of elongate, spheroidal, banded, botryoidal, columnar, rosette, and speleothem in regolith at two small sites at the base of the Meski Plateau near Erfoud, Morocco are described. Although most are isolated hand samples, the largest concretions are meter-sized blocks. Not one sample resembles any surrounding outcrop or bedrock. The barite rosettes formed first via periodic mixing of Ba2+/SO42- saturated solutions. They provided nuclei for cyclical precipitation-based concentric concretion development. The speleothem formed via precipitation from a carbonate-saturated solution in a large void within porous sandstone. The sand concretions formed when calcite precipitated around grains in unconsolidated quartz sands with cyclic fluctuation of Ca2+/CO32- saturated ground water. Petrographic analyses, stable isotope data, sample morphology, coupled with light and scanning electron microscopy indicate that microbial processes induced the periodic cement precipitation that produced the unique concretions.

<p>Hydrated portland cement provides the solid adhesive matrix necessary to bind aggregate (sand and gravel) into concrete. The hydration reaction requires water, however the products of the reaction limit further diffusion of water to unreacted cement. Superabsorbent polymer (SAP) hydrogel particles absorb mixing water, then subsequently desorb when the relative humidity drops, serving as internal water reservoirs within the cement matrix to shorten diffusion distances and promote the hydration reaction in a process called internal curing. Internally cured cementitious mixtures exhibit an increased degree of hydration and reduced shrinkage and cracking, which can increase concrete service life. Increased service life can, in turn, reduce overall demand for portland cement production, thereby lowering CO2 emissions.</p> <p>This dissertation addresses practical implementation questions key to the translation of SAP hydrogel internal curing technology to from the benchtop to the field in transportation applications, including: (1) What effects do mix design adjustments made to increase mixture flow when using SAP have on cementitious mixture properties? and (2) What effect do cementitious binder characteristics have on SAP performance?</p> <p>The addition of SAP to a cementitious mixture changes the mixture’s flow behavior. Flow behavior is an important aspect of concrete workability and sufficient flow is necessary to place well consolidated and molded samples. Often, additional water is added to mixtures using SAP to account for the absorbed water, however cementitious mixture workability is often tuned using high range water reducing admixtures (e.g., polycarboxylate ester-based dispersants). Fresh and hardened properties of mortars were characterized with respect to flow modification method (using the mortar flow table test; compressive strength at 3, 7, and 28 days; flexural strength at 7 and 28 days; and microstructural characterization of 28-day mortars). At typical doses, it was found that the addition of extra water lowers the resulting compressive and flexural strength, while high range water reducing admixtures administered at doses to achieve sufficient mortar flow did not compromise compressive or flexural strength.</p> <p>The SAPs used in cement are generally poly(acrylamide-acrylic acid) hydrogels and are not chemically inert in high ionic-load environments, such as cement mixtures. The behavior of an industrial SAP formulation with characterized across five different cement binder compositions with respect the cement hydration reaction (using isothermal calorimetry, thermogravimetric analysis of hydration product fraction, and scanning electron microscopy (SEM)/energy dispersive x-ray spectroscopy (EDS) microstructural analysis), the absorption behavior of the SAP, and the fresh and hardened properties of SAP-cement composites (mortar flow and compressive and flexural strength). The change in properties induced by the addition of SAP was similar across ASTM Type I cements from three manufacturing sources, suggesting that SAP internal curing can be implemented predictably over time and geography. Excitingly, in analysis of cement systems meeting different ASTM standards (Type III and Type I with 30% replacement by mass with ground blast furnace slag), synergistic and mitigating reaction behaviors were observed, respectively, in Type III and slag cement, suggesting that further study of SAP with these cement systems could be of particular interest.</p>

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Indiana University-Purdue University Indianapolis (IUPUI) / The functional quaternary ammonium salts (QAS) and their constructed polyQAS or PQAS were synthesized, characterized and formulated into a novel antibacterial glass-ionomer cement. Compressive strength (CS) and Streptococcus mutans (S. mutans) viability were used to evaluate the mechanical strength and antibacterial activity of the cements. Fuji II LC cement was used as control. The specimens were conditioned in distilled water at 37 oC for 24 h prior to testing. The effects of the substitute chain length, loading as well as grafting ratio of the QAS and aging on CS and S. mutans viability were investigated. Chapter 2 describes how we studied and evaluated the formulated antibacterial glass-ionomer cement by incorporating QAS chloride-containing polymer into the formulation. The results show that with PQAS addition, the studied cements showed a reduction in CS with 25-95% for Fuji II LC and 13-78% for the experimental cement and a reduction in S. mutans viability with 40-79% for Fuji II LC and 40-91% for the experimental cement. The experimental cement showed less CS reduction and higher antibacterial activity as compared to Fuji II LC. The long-term aging study indicates that the cements are permanently antibacterial with no PQAS leaching. Chapter 3 describes how we studied and evaluated the formulated antibacterial cements by changing chain length, type of halide, loading, grafting ratio and aging time. The results show that the effects of the chain length, loading and grafting ratio of the QAS were significant. Increasing chain length, loading, grafting ratio significantly enhanced antibacterial activity but reduced CS. The experimental cement showed less CS reduction and higher antibacterial activity as compared to Fuji II LC. The long-term aging study indicates that the cements are permanently antibacterial with no PQAS leaching. There was no significant difference between QAS bromide and QAS chloride, suggesting that we can use QAS bromide directly without converting bromide to chloride. In summary, we have developed a novel PQAS-containing antibacterial glass-ionomer cement. The cement has demonstrated significant antibacterial activities. Our experimental cement is a promising system because the reduced strength of the cement with addition of PQAS is still above those demonstrated by original commercial cement Fuji II LC without any PQAS addition. It appears that the experimental cement is a clinically attractive dental restorative that can be potentially used for long-lasting restorations due to its high mechanical strength and permanent antibacterial function.

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The objective of this research was to compare the efficacy of portland cement to that of lime for improving the strength and durability of plastic clays. The scope of work associated with this research involved laboratory strength and durability testing of three plastic clays treated with portland cement or lime. To ensure a broad application of the work, the clays were obtained from three different regions of the United States, specifically from project sites near Bloomington, Indiana; San Antonio, Texas; and Monticello, Utah. Laboratory testing included evaluation of selected properties of the three clays in the untreated condition and in the treated condition. For the untreated condition, testing included measurements of soluble sulfate concentration, analysis of particle-size distribution, determination of treatment concentration using the Eades and Grim test, determination of Atterberg limits, development of moisture-density relationships, and measurement of California bearing ratio. In the treated condition, each clay sample was treated with either portland cement or lime, and testing included determination of Atterberg limits, development of moisture-density relationships, measurement of unconfined compressive strength (UCS), evaluation under wet-dry cycling, and evaluation under freeze-thaw cycling. For each of the three clay types, statistical analysis was performed to compare the strength and durability of the cement-treated specimens and the lime-treated specimens at each treatment concentration. Across all three clays, lime-treated specimens exhibited greater reductions in the plasticity index when compared to cement-treated specimens. In general, increased treatment concentrations corresponded to increased strength and strength retention. Percent strength retention of the cement-treated specimens was higher, on average, than that of the lime-treated specimens for the Indiana and Texas clays at low and medium concentrations. Similar strength retention was observed for cement-treated specimens and lime-treated specimens at high stabilizer concentrations across all three clays. In general, similar or significantly higher strengths were observed for specimens treated with cement than specimens treated with lime after 7 days, 28 days, and freeze-thaw cycling. Cement-treated specimens retained similar or greater mass after wet-dry cycling than lime-treated specimens. Cement-treated specimens also retained similar or greater strength after freeze-thaw cycling than lime-treated specimens, except for the Texas clay treated at the high concentration and the Utah clay treated at the medium concentration.

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Improvements in the strength and durability of frost-susceptible soils and aggregates can be achieved through chemical stabilization using portland cement, where the efficacy of cement stabilization for improving durability depends on the degree to which hydraulic conductivity is reduced. Hydraulic conductivity is commonly estimated from basic soil properties using Moulton's empirical equation. However, the hydraulic conductivity estimation does not consider the detrimental effects of freezing or the benefits of cement stabilization. The purpose of this research was to derive new equations relating hydraulic conductivity after freezing to specific material properties of cement-treated soils and aggregates stabilized with different concentrations of cement. This research included material samples from two locations in Alaska and from single locations in Minnesota, Montana, Texas, and Utah, for a total of six material samples. Each soil or aggregate type was subjected to material characterization by the Unified Soil Classification System (USCS) and the American Association of State Highway and Transportation Officials (AASHTO) classification system. Moisture-density curves were developed, and unconfined compressive strength (UCS) testing was performed to determine cement concentrations generally corresponding to low, medium, and high 7-day UCS values of 200, 400, and 600 psi, respectively. After being cured for 28 days at 100 percent relative humidity, the prepared specimens were subjected to frost conditioning and hydraulic conductivity testing. The Alaska-Elliott, Minnesota, Montana, and Utah materials exhibit decreasing hydraulic conductivity with increasing UCS, the Texas material exhibits increasing hydraulic conductivity with increasing strength from the low to medium cement concentration levels but decreasing hydraulic conductivity from the medium to high cement concentration levels, and the Alaska-Dalton material exhibits increasing hydraulic conductivity with increasing strength. Multivariable regression analyses were performed to investigate relationships between hydraulic conductivity and several material properties, including soil gradation and classification, fineness modulus, specific gravity, cement content, porosity, compaction method, dry density, and 7-day UCS for each specimen. The R2 values computed for the six-parameter, four-parameter, USCS, and AASHTO-classification models are 0.795, 0.767, 0.930, and 0.782, respectively. Further research is recommended to investigate the effects of cement on hydraulic conductivity for USCS and AASHTO soil types not covered in this research.