Sacral insufficiency fractures are an under-diagnosed source of acute lower back pain. A polymethylmethacrylate (PMMA) cement injection procedure called sacroplasty has recently been utilized as a treatment for sacral insufficiency fractures. It is believed that injection of cement reduces fracture micromotion, thus relieving pain. In this study, finite element models were used to examine the mechanical effects of sacroplasty. Finite element models were constructed from CT images of cadavers on which sacroplasties were performed. The images were used to create the mesh geometry, and to apply non-homogeneous material properties to the models. Models were created with homogeneous and non-homogeneous material properties, normal and osteoporotic bone, and with and without cement. The results indicate that the sacrum has a 3D multi-axial state of strain. While compressive strains were the largest, tensile and shear strains were significant as well. It was found that a homogeneous model can account for around 80% of the variation in strain seen in a non-homogeneous model. Thus, while homogeneous models provide a reasonable estimate of strains, non-homogeneous material properties have a significant effect in modeling bone. A reduction in bone density simulating osteoporosis increased strains nearly linearly, even with non-homogeneous material properties. Thus, the non-homogeneity was modeled similarly in both density cases. Cement in the sacrum reduced strains 40-60% locally around the cement. However, overall model stiffness only increased 1-4%. This indicates that the effects of sacroplasty are primarily local. / Master of Science

Lime-cement columns were constructed to improve soft ground at the I-95/Route 1 Interchange in Alexandria, Virginia. As part of the test embankment program, two different commercial laboratories performed laboratory tests on treated soil, and they produced strikingly different unconfined compression test results. Further, both sets of results are different from test results for similar soils available in the published literature. This situation created uncertainties and a conservative design philosophy, accompanied by increased construction costs compared to typical lime-cement column projects. The goals of this research project were to assess factors that influence strength gain of lime-cement-soil mixtures and to develop a detailed laboratory test procedure that produces consistent results. Key findings from the research are that a laboratory test procedure that produces consistent results has been developed, drying and subsequent restoration of soil moisture prior to treatment can decrease the strength of the mixture, the mixture strength decreases as the ratio of soil water content to cement content increases for 100 percent cement-soil mixtures, the addition of lime can increase the mixture strength for some soils and decrease the strength for others, and presenting the test results in the form of contour plots of unconfined compressive strength can be very useful. / Master of Science

A laboratory testing program was conducted on cement-treated soil mixtures fabricated to represent materials produced by the wet method of deep mixing. The testing program focused on investigating the influences that variations in laboratory testing conditions and in the mix design have on measured property values. A base soil was fabricated from commercially available soil components to produce a very soft lean clay that is relatively easy to mix and can be replicated for future research. The mix designs included a range of water-to-cement ratios of the slurries and a range of cement factors to produce a range of mixture consistencies and a range of unconfined compressive strengths after curing. Unconfined compressive strength (UCS) tests and unconsolidated-undrained (UU) triaxial compression tests were conducted. Secant modulus of elasticity were determined from bottom platen displacements, deformations between bottom platen and cross bar, and from LVDT's placed directly on the cement-treated soil specimens. Five end-face treatment methods were used for the specimens: sawing-and-hand-trimming, machine grinding, sulfur capping, neoprene pads, and gypsum capping. Key findings of this research include the following: (1) The end-face treatment method does not have a significant effect on the unconfined compressive strength and secant modulus; (2) a relationship of UCS with curing time, total-water-to-cement ratio, and dry density of the mixture; (3) the secant modulus determined by bottom platen displacements is significantly affected by slack and deformations in the load frame; (4) the secant modulus determined by local strain measurements was about 630 time the UCS; (5) typical values of Poisson's ratio range from about 0.05 to 0.25 for stress levels equal to half the UCS and about 0.15 to 0.35 at the UCS; (6) Confinement increased the strength at high strains from less than 20% the UCS to about 60% the UCS. In addition to testing the cured mixtures, the consistency of the mixtures were measured right after mixing using a laboratory miniature vane. A combination of the UCS relationship along with the mixture consistency may provide useful information for deep mixing contractors. / MS

Thesis (MBA)--Stellenbosch University, 2000. / ENGLISH ABSTRACT: The changing political landscape, which culminated in the all-inclusive election of 1994, enfranchised the previously excluded majority voters and ushered into SA a government with a different agenda. This was an important landmark in the development of the SA business environment. Having pledged itself to improve the social and economic standards of the poor majority, the ANC-COSATU-SACP led government is committed to the elimination of barriers to enter any industry and stimulate the economy in order to improve employment opportunities. Until 1996 cement producers in SA co-operated under an official cartel that facilitated price-fixing and joint marketing and distribution. This study shows that during that period the industry recorded a healthy performance until 1996 when the cartel was dissolved. The industry performance suddenly plummeted in1996 and since then has remained on a downward trend. Analysis of the industry confirms that the industry has the characteristics of a monopoly. Three producers, namely PPC, Alpha and Lafarge, dominate the industry. The "big three" control almost 100 percent of the cement market with a cross ownership of assets which straddle the whole cement industry' in SA. Besides the assets along the cement value chain, the industry effectively has sole control of alternative cement materials businesses, namely ash and slag, and owns significant interests in aggregates and ready-mix concrete businesses too. The dissolution of the cartel in 1996 effectively disallowed price fixing, joint capacity planning and any other collusion as defined by the Competition Act of 1998. Subsequently, players are expected to fiercely compete in an industry that is an oligopoly. According to classical economics, co-operation is the effective conduct to survive in an oligopoly. Hence the contradiction between national expectations and structure of the industry creates a dilemma for asset owners. The principal barrier to entry into the SA cement industry emanates from the high capital investment requirements. This study shows that it is mainly the clinker manufacturing component of the value chain that requires very high investments. A group of small entrepreneurs, engaged in blending cement with ash or slag and selling the product in competition with equivalent products from traditional producers, has successfully entered the lower end of the industry. This is testimony to the fact that sections of the value chain have no barriers to entry. It is believed that as producers of clinker face high sunk costs they have reason to encourage more clinker content in their cement products. They may, therefore, stifle further development of alternative materials. The national imperative - to breakdown concentration of industries to allow for easy entry - seems to be in conflict with the profit motive that businesses to survive. This study therefore recommends an alternative strategy that could accommodate both views. An amenable strategy is for the industry to be redefined into three distinct subsectors with minimal cross-ownership of assets. The three sub-sectors are: 1. Clinker manufacturing: Clinker is a commodity that requires high investment costs. The sector should therefore be offered legal dispensation to operate as a monopoly but with enough regulation to ensure efficiency. It is recommended that players in this sector are allowed to co-operate for efficiency reasons and prices are strictly controlled by a regulator. The regulator must also ensure that the manufacturer is prohibited from owning interests in any other cement sub-sector, to eliminate industry control by a few. w Thus this sector must be rid of interests in aggregate, alternative materials and readymix businesses. 2. Cement manufacturing: A sub-sector for the manufacture of cement, clearly distinct from clinker production should be created. Processes for this sub-sector will commence with milling of clinker into cement and extend to marketing and distribution to end users. 3. Alternative cement materials: In view of economic stimulation, the development of alternative materials to compete with clinker should be encouraged. This sub-sector should be charged with research and development of these materials, and be allowed to blend them for marketing and distribution to end users. There are many implications that emanate from the myriad of stakeholders. Besides local owners of cement assets in SA, international asset owners and entrepreneurs in SA form part of the stakeholders. Thus shrewd planners will be required to champion this idea. It is therefore recommended that a team of academics and business practitioners be commissioned to investigate this and take it further. / AFRIKAANSE OPSOMMING: Die veranderende politieke omgewing, wat uiteengeloop het op die 1994 verkiesing, het die meerderheid kiesers tesame met die nuwe regering in 'n nuwe bedeling ingelei. Dit was 'n belangrike baken in die ontwikkeling van die Suid Afrikaanse besigheidsomgewing. Die nuutgevonde ANC-COSATU-SACP regering het homself toegewy aan sy beloftes om die sosiale en ekonomiese standaarde van die arm meerderheid van die bevolking aan te spreek, en daarmee saam om toegang tot industrie te vergemaklik, die ekonomie te stimuleer en werksgeleenthede te bevorder. Tot 1996 het sement vervaardigers in SA onder 'n offisiele kartel geopereer. Die kartel het gesorg vir fasilitering van prysbepaling, en gesamentlike bemarking en distribusie. Hierdie studie dui aan dat die sement industrie floreer het tot 1996, waarna die kartel ontbind is. Sederdien het die industrie in duie gestort, en is steeds in 'n afwaartse tendens. 'n Analise van die sement industrie toon die karaktereienskappe van 'n monopolie. Drie vervaardigers, nl. PPC, Alpha en Lafarge, domineer die industrie. Die "groot drie" beheer byna 100 persent van die sement industrie, en het verdeelde besitting van alle bates. Daarbenewens beheer hulle ook gedeeltelik of ten volle alle alternatiewe sement materiale besighede en ander verwante belange. Die ontbinding van die kartel in 1996 het effektiewelik prysbepaling verbied, asook gesamentlike kapasiteitsbeplanning en enige ander sameswering soos bepaal deur die Wet op Kompetisie van 1998. Dit word dus van alle spelers in die industrie verwag om gelykmatig te kompeteer in 'n oligopoliese industrie. Dit het egter 'n dilemma veroorsaak rondom die eienaarskap van voorheen gedeelde bates. Kapitale investering is die primêre verhindering tot toegang tot die sement industrie. Hierdie studie toon dat dit hoofsaaklik die klinkersteen vervaardigings komponent is wat groot investering vereis. 'n Groep entrepreneurs het 'n produk ontwikkel deur sement met as te vermeng, en sodoende 'n laer kwaliteit steen te vervaardig waarmee hulle suksesvol in 'n sekere marksegment meeding. Dit is getuienis van die feit dat sekere dele van die waardeketting relatief maklik binnegedring kan word. Die huidige vervaardigers van klinker produkte is onwillig om alternatiewe podukte te vervaardig, aangesien hulle die hoë koste van hul toerusting en die dienooreenkomstige kapitale investing moet regverdig. Die regeringsvisie om groot industrie af te breek om sodoende toegang tot industrie te vergemaklik, blyk in teenstelling te wees met die winsgerigtheid van besigheid. Hierdie studie stel 'n alternatiewe strategie voor wat beide visies kan akkomodeer. Dit stel 'n strategie voor wat die industrie sal herdefinieer in drie sub-sektore met minimale deling van bates. Hierdie sub-sektore is: 1. Klinker vervaardiging: Klinker is 'n kommoditeit wat groot kapitale investering vereis. Hierdie sektor moet dus toegelaat word om binne perke as 'n monopolie te opereer, met genoegsame regulering om effektiwiteit te verseker. Dit word voorgestel dat spelers in hierdie sektor toegelaat moet word om te koopereer om optimale vlakke van produksiekoste te handhaaf, en dat pryse streng gekontroleer word deur 'n regulerende liggaam. Hierdie sektor moet ook verbied word om enige ander besigheids en finansiele belange te hou by enige ander sement industrie sektor. 2. Sement vervaardiging: 'n Subsektor vir die vervaardiging van sement, duidelik onderskei van klinker vervaardiging, moet geskep word. Prosesse vir hierdie subsektor sal begin met die maal van klinker en bemarking en distribusie insluit. 3. Alternatiewe sement materiale: Die ontwikkeling van alternatiewe produkte om te kompeteer met klinker moet aangemoedig word. Hierdie subsektor moet hul toewy aan navorsing en ontwikkeling, sowel as vervaardiging, bemarking en distribusie. Daar is baie implikasies wat voortspruit vanuit die magdom belanghebbenes. Bo en behalwe die plaaslike eienaars van sement bates in SA, vorm internasionale bateeienaars en entrepreneurs ook deel van die belanghebbenes. Dit word dus voorgestel dat 'n span bestaande uit akademici en besigheid aangestel word om hierdie voorstelle verder te ondersoek.

This thesis discusses and documents findings from an investigation of performance-based testing of asphalt cement (AC), warm mixed asphalt cement, asphalt rubber (AR), and warm asphalt rubber. A number of control, warm, and asphalt rubber binders from Ontario construction contracts were investigated for their compliance with conventional Superpave® test methods such as rolling thin film (RTFO), pressure aging vessel (PAV), dynamic shear rheometer (DSR), and bending beam rheometer (BBR), as well as additional specification tests such as extended BBR and double edge notched tension test. The quality and durability of those binders were determined. Quality means the ability of asphalt binder to reach a set of specific properties whereas durability is the measure of how well asphalt retains its original characteristics when exposed to normal weathering and aging process. One warm AC and two field-blended asphalt rubber samples showed high levels of physical hardening which can lead to premature and early cracking. The warm asphalt cement lost 8 °C when stored isothermally for three days at low temperatures according to Ontario’s extended bending beam rheometer (BBR) protocol (LS-308). The two asphalt rubber samples lost 10 °C and 12 °C following the same conditioning. Many of the studied asphalt samples showed deficient strain tolerance as measured in Ontario’s double-edge-notched tension (DENT) test (LS-299). In a study of warm rubberized asphalt cement with improved properties, a number of compositions were prepared with soft Cold Lake AC and a small quantity of naphthenic oil. These binders showed little chemical and physical hardening and reasonable critical crack tip opening displacements (CTOD). Strain tolerance was much improved by co-blending with a high vinyl type styrene-butadiene-styrene (SBS) polymer and a small amount of sulfur. / Thesis (Master, Chemistry) -- Queen's University, 2013-04-24 22:54:20.07

Student Number : 9900772K - MSc research project - School of Civil and Environmental Engineering - Faculty of Engineering and the Built Environment / The hydration of cement is an exothermic reaction, which begins almost immediately upon contact with water. This produces a large amount heat that subsequently raises the temperature of the concrete mixture, creating a temperature gradient across the member. The temperature rise associated with hydration induces thermo-mechanical stresses. These stresses can cause damage to the structure, affecting the durability and in extreme cases the functionality of the structure. If the maximum rate of heat evolution experienced can be minimised through the selection of the constituents of a concrete mixture, then the thermal stresses that develop in the concrete can be reduced. The main aim of this research is to develop a knowledge of how the heat evolution characteristics of concrete are affected by changing certain concrete mixture parameters and ingredients. The focus is on the addition of three different cement extenders and varying the water/cement ratio. This will be a step towards the development of a model for predicting the thermal properties of concrete. As a part of this investigation, a prediction model for the change in heat rate in concrete was developed. The model is intended to predict the contribution of the individual clinker crystallographic phases in cement and the heat liberated in concrete during hydration.

O progresso científico e tecnológico das últimas décadas registra um avanço significativo no processo de obtenção da cal, porém, há uma lacuna de conhecimento de base referente à sua ação quando empregada em conjunto com o cimento Portland. O uso da cal nas argamassas mistas de acabamento tem sido associado positivamente apenas à plasticidade no estado fresco e à sua deformabilidade no estado endurecido. Maiores informações são necessárias sobre a ação da cal na evolução das propriedades da argamassa no estado fresco, vinculadas à hidratação do cimento. Este conhecimento é importante para o desenvolvimento de formulações que atendam ao desempenho desejado em diferentes aplicações. O entendimento do mecanismo de hidratação do cimento em presença da cal constitui uma plataforma para estudos de adições minerais ativas ao clínquer, com adição de cal hidratada como fonte externa de cálcio, na produção de novos materiais cimentícios sustentáveis. O estudo em pasta realizado teve como foco a interação cimento-cal visando identificar os fenômenos químicos e físicos relevantes que se sucedem à adição de água ao sistema. Foram caracterizadas as idades iniciais de hidratação do cimento por meio de ensaios de calorimetria de condução, termogravimetria (TG/DTG) e difratometria de raios X em material no estado fluido e em regime consecutivo de coleta de dados. Os experimentos envolveram as proporções 1:1 e 1:2 de cimento Portland tipo CP II E com cales hidratadas tipos CH I e CH III de natureza cálcica e dolomítica, respectivamente. A cal CH I incorpora à mistura elevado teor de hidróxido de cálcio com imediata saturação do meio por íons hidroxila e íons cálcio; a cal CH III incorpora também, em maior quantidade, filler carbonático. Por efeito químico, devido à presença da cal, há alteração da velocidade de hidratação, mas com formação dos produtos de reação característicos da hidratação do cimento. Por efeito físico, o filler carbonático e a fração insolúvel do hidróxido de cálcio da cal, presente no meio saturado, atuam como nucleador para precipitação de fases hidratadas. O efeito combinado desses fenômenos promoveu aceleração da hidratação do cimento Portland, principalmente no período de indução, quando prevalecem as reações de formação de etringita e de aluminatos de cálcio hidratados. / In the last decades, scientific and technological progress has shown a significant advance in the process of obtaining lime; however, there is gap knowledge with relation to its action when employed together with Portland cement. The use of lime in finishing mix mortars has only been positively associated to the fresh state plasticity and ability to deformation in the hardened state. It is necessary to collect data about the role of lime in the gradual development of the properties of mortars in the fresh state, linked to cement hydration. Such knowledge is important to develop formulas which can meet the required performance in different uses. The current demand of sustainable materials has favored the addition of minerals to the composition of Portland cement, and hydrated lime as an extern source of calcium, is a feasible alternative to the composition of byproducts and mixtures to be used as alternative binders. This research focused the cement-lime interaction aiming at identifying relevant chemical and physical phenomena which succeed the addition of water to the system. The paste study characterized the early ages of hydration by means of isothermal calorimetric, thermogravimetric, X-ray diffraction in material in the fluid state analysis collecting data in a consecutive basis. The experiments were carried out by using two proportions of Portland cement type CP II E with hydrated lime types CH I and CH III, calcic and dolomitc, respectively. By adding lime CH I to the cement-water system, calcium hydroxide is abundantly incorporated, with immediate saturation by means of hydroxide ions and calcium ions. The addition of lime CH III, also incorporates, in greater amount, finely ground limestone. Due to chemical effect because of the presence of lime, there is alteration in speed of hydration, forming products characteristics to the cement hydration process. Due to physical effect, the filler and the lime insoluble fraction of calcium hydroxide, present in the saturated environment, work as facilitators to the precipitation of the hydrated phases. The combined effect of these two phenomena accelerated hydration of Portland cement, mainly in the induction period, when ettringite and hydrated calcium aluminates formation reactions prevail. The advancement made in terms of knowledge permits to broaden comprehension on the behavior of mixtures in early stages, when hardening and consolidation processes are applied to mortars and help rheologic studies which involve their application. The understanding of the hydration mechanism in the presence of lime sets a base to study additions of active minerals to the clinker and produce new sustainable cementious compounds.

La presente Tesis Doctoral se titula "Obtención y caracterización de nuevos cementos óseos de fosfatos de calcio en el sistema DCP&#8213;alfa-TCP". Los cementos de fosfatos de calcio (CFC) son materiales biocompatibles que tienen la propiedad de endurecer en condiciones fisiológicas formando una estructura porosa de cristales interconectados de hidroxiapatita, i.e. la fase mineral de los tejidos óseos. Estos materiales pueden ser diseñados para que sean inyectables y tengan distintos porcentajes de porosidad. Este hecho permite obtener cementos con distintas tasas de reabsorción ósea que pueden aplicarse con técnicas de mínima invasión. En general, estas propiedades otorgan a estos biomateriales un excelente interés en campos de aplicación de prevención, reconstrucción o estabilización ósea (p.e.: osteoporosis, cirugía craneofacial, vertebroplastia, cifoplastia).Esta Tesis Doctoral consta de 6 capítulos. El Capítulo 1 (Cementos óseos de fosfatos de calcio) recoge el estado del arte de los CFC. Se realiza una revisión bibliográfica crítica de toda la información de interés. Se concluye la necesidad de realizar estudios cinéticos que expliquen adecuadamente las propiedades de fraguado de estos cementos y permitan diseñar cementos con mejores propiedades. El Capítulo 2 (Materiales y métodos utilizados en la fabricación y caracterización de cementos óseos de fosfatos de calcio) describe el protocolo de trabajo seguido para caracterizar los CFC física y químicamente. Este protocolo permite establecer correlaciones entre la microestructura y las propiedades macroscópicas. El Capítulo 3 (Estudio de la cinética de la reacción de fraguado de un cemento óseo de fosfato de calcio) investiga la cinética de fraguado de un cemento octocálcico en el sistema DCP&#8213;alfa-TCP. Los resultados mostraron que: (a) sólo el alfa-TCP reaccionó para dar una hidroxiapatita deficiente en calcio (CDHA); (b) el porcentaje de reacción y la resistencia mecánica a compresión estaban correlacionadas; (c) el cemento presentó una estructura de cristales interconectados con distinto grado de compacidad. El Capítulo 4 (Estudio de nuevas formulaciones de cementos de fosfatos de calcio en el sistema DCP&#8213;alfa-TCP) investiga las propiedades de fraguado y de resistencia mecánica de cementos del sistema DCP&#8213;alfa-TCP en el intervalo de relaciones Calcio/Fósforo (Ca/P) 1.26<Ca/P<1.50. Se estudia cómo varían la trabajabilidad, los tiempos de fraguado y la resistencia a la compresión. También se estudia el efecto de la adición de carbonato cálcico (CC) sobre las propiedades de fraguado ya que se espera obtener como producto final de la reacción de fraguado una hidroxiapatita deficiente en calcio carbonatada y, por lo tanto, más semejante a la apatita de la fase mineral ósea. Los resultados mostraron que la adición de un 10 % de CC produjo un efecto fluidificante sobre los cementos con un incremento en los valores de los tiempos de fraguado. El análisis de la evolución de la resistencia a la compresión con el tiempo demostró que el CC actúa como un retardador. Sin embargo, la resistencia final alcanzada representa en muchos casos un incremento de más del 40 %. El Capítulo 5 (Discusión general) discute los resultados más relevantes analizados a lo largo de los Capítulos 3 y 4 para comprender las posibilidades clínicas que este tipo de materiales nos ofrece. El Capítulo 6 (Conclusiones) presenta una serie de conclusiones obtenidas a partir de los resultados de los Capítulos 3 y 4. Son conclusiones extraídas a partir del análisis de los resultados de determinadas poblaciones de muestras. Como los intervalos de variabilidad de los parámetros de cada población son diferentes, muchas de las conclusiones no son generalizables a todo el sistema DCP&#8213;alfa-TCP, sino que se han de leer dentro de este sistema y en las condiciones experimentales estudiadas. Finalmente, la Tesis Doctoral lista el conjunto de referencias bibliográficas utilizadas en este trabajo de investigación.

Wood pulp fibers are a unique reinforcing material as they are non-hazardous, renewable, and readily available at relatively low cost compared to other commercially available fibers. Today, pulp fiber-cement composites can be found in products such as extruded non-pressure pipes and non-structural building materials, mainly thin-sheet products. Although natural fibers have been used historically to reinforce various building materials, little scientific effort has been devoted to the examination of natural fibers to reinforce engineering materials until recently. The need for this type of fundamental research has been emphasized by widespread awareness of moisture-related failures of some engineered materials; these failures have led to the filing of national- and state-level class action lawsuits against several manufacturers. Thus, if pulp fiber-cement composites are to be used for exterior structural applications, the effects of cyclical wet/dry (rain/heat) exposure on performance must be known. Pulp fiber-cement composites have been tested in flexure to examine the progression of strength and toughness degradation. Based on scanning electron microscopy (SEM), environmental scanning electron microscopy (ESEM), energy dispersive spectroscopy (EDS), a three-part model describing the mechanisms of progressive degradation has been proposed: (1) initial fiber-cement/fiber interlayer debonding, (2) reprecipitation of crystalline and amorphous ettringite within the void space at the former fiber-cement interface, and (3) fiber embrittlement due to reprecipitation of calcium hydroxide filling the spaces within the fiber cell wall structure. Finally, as a means to mitigate kraft pulp fiber-cement composite degradation, the effects of partial portland cement replacement with various supplementary cementitious materials (SCMs) has been investigated for their effect on mitigating kraft pulp fiber-cement composite mechanical property degradation (i.e., strength and toughness losses) during wet/dry cycling. SCMs have been found to be effective in mitigating composite degradation through several processes, including a reduction in the calcium hydroxide content, stabilization of monosulfate by maintaining pore solution pH, and a decrease in ettringite reprecipitation accomplished by increased binding of aluminum in calcium aluminate phases and calcium in the calcium silicate hydrate (C-S-H) phase.

The quantitative nondestructive evaluation (NDE) of cement-based materials is a critical area of research that is leading to advances in the health monitoring and condition assessment of the civil infrastructure. Ultrasonic NDE has been implemented with varying levels of success to characterize cement-based materials with complex microstructure and damage. A major issue with the application of ultrasonic techniques to characterize cement-based materials is their inherent inhomogeneity at multiple length scales. Ultrasonic waves propagating in these materials exhibit a high degree of attenuation losses, making quantitative interpretations difficult. Physically, these attenuation losses are a combination of internal friction in a viscoelastic material (ultrasonic absorption), and the scattering losses due to the material heterogeneity. The objective of this research is to use ultrasonic attenuation to characterize the microstructure of heterogeneous cement-based materials. The study considers a real, but simplified cement-based material, cement paste - a common bonding matrix of all cement-based composites. Cement paste consists of Portland cement and water but does not include aggregates. First, this research presents the findings of a theoretical study that uses a set of existing acoustics models to quantify the scattered ultrasonic wavefield from a known distribution of entrained air voids. These attenuation results are then coupled with experimental measurements to develop an inversion procedure that directly predicts the size and volume fraction of entrained air voids in a cement paste specimen. Optical studies verify the accuracy of the proposed inversion scheme. These results demonstrate the effectiveness of using attenuation to measure the average size, volume fraction of entrained air voids and the existence of additional larger entrapped air voids in hardened cement paste. Finally, coherent and diffuse ultrasonic waves are used to develop a direct relationship between attenuation and water to cement (w/c) ratio. A phenomenological model based on the existence of fluid-filled capillary voids is used to help explain the experimentally observed behavior. Overall this research shows the potential of using ultrasonic attenuation to quantitatively characterize cement paste. The absorption and scattering losses can be related to the individual microstructural elements of hardened cement paste. By taking a fundamental, mechanics-based approach, it should be possible to add additional components such as scattering by aggregates or even microcracks in a systematic fashion and eventually build a realistic model for ultrasonic wave propagation study for concrete.