No description available.

In the current study, SAPs of cationic monomer [2 - (Methacryloyloxy) ethyl] trimethylammonium chloride have been prepared by free radical solution polymerisation with different crosslinkers. They were subjected to repeated cycles of swelling and de-swelling in DI water and NaCl solution. The conductivity of the swelling medium was measured and related to the swelling/de-swelling characteristics of the SAPs. The swelling capacity was also determined in saline solution. The swelling and de-swelling processes were described by first-order kinetics. The SAPs exhibited varied swelling capacity for crosslinkers of the same functionality as well as different functionality. The SAPs were used to adsorb, the dye Orange G at different initial concentrations of the dye. The equilibrium adsorption data followed the Langmuir adsorption isotherms. The SAPs were also used to adsorb three other dyes, Congo red, Amido black and Alizarin cyanine green. They exhibited different adsorption capacity for different dyes. The adsorption phenomenon was found to follow first order kinetics. In the later part of the study, the co-monomers of [2 - (Methacryloyloxy) ethyl] trimethylammonium chloride with zwitter-ionic monomers [2-(Methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide and [3-(Methacryloylamino)propyl]dimethyl(3-sulfopropyl)ammonium hydroxide inner salt were prepared in turns at two different concentrations. The effect of the addition of the zwitter-ionic monomers and their concentration of the swelling capacity and dye adsorption capacity was studied. There was no effect on the swelling capacity of the polymers due to either the species of the zwitter-ionic monomer or their concentration. However, there was a reduction in soluble content of the polymers. The dye adsorption capacity decreased at the higher concentration of the zwitter-ionic monomer.

Submitted by Silvana Teresinha Dornelles Studzinski (sstudzinski) on 2017-02-09T14:38:55Z No. of bitstreams: 1 Angélica Koppe_.pdf: 2328574 bytes, checksum: d353be1d4946babddf72b551a2536afa (MD5) / Made available in DSpace on 2017-02-09T14:38:55Z (GMT). No. of bitstreams: 1 Angélica Koppe_.pdf: 2328574 bytes, checksum: d353be1d4946babddf72b551a2536afa (MD5) Previous issue date: 2016-12-21 / Plásticos Brandt Ltda / A falta de cura adequada e, consequentemente, os problemas de má hidratação do cimento e manifestações patológicas, como retração e fissuras, estão entre os principais responsáveis pela redução da durabilidade de estruturas de concreto. Aliados ao aumento da velocidade de execução das obras, esses tendem a piorar uma vez que há falhas recorrentes nas atividades de pós-concretagem. A cura, com o objetivo de manter a umidade necessária para a correta hidratação do cimento e minimização da retração, vem evoluindo para um novo campo de pesquisa, a técnica da cura interna. Essa se baseia na incorporação, a uma matriz cimentícia, de materiais capazes de reter água e liberá-la de forma gradativa ao logo do período de cura. Seu estudo tem sido voltado basicamente para o uso em concretos de alto desempenho, contudo, concretos convencionais também são frequentemente negligenciados na prática de cura úmida e tendem a evoluir para essa tecnologia. Entre os materiais mais estudados, os polímeros superabsorventes (PSA) têm apresentado desempenho satisfatório como agentes de cura interna, apresentando-se como reservatórios internos de água dispersos na matriz. Esses polímeros foram apresentados à indústria da construção civil em 2001, já na prática de cura interna, com o intuito de melhorar a durabilidade das estruturas, diminuir a retração e melhorar a hidratação das partículas de cimento, agindo de dentro para fora. Mesmo com a desvantagem de gerar poros internos, seu uso apresenta vantagens quanto ao efeito plastificante, com capacidade de reduzir a relação a/c e a retração do concreto. Dentre os estudos publicados até o momento, entretanto, não se tem registros do uso de PSA de origem residual. Sendo assim, o presente estudo objetiva avaliar a viabilidade de uso de PSA residual (FCPSA), composto de fibra celulósica e PSA, proveniente de empresas de produtos de higiene, em matrizes cimentícias como agente de cura interna, buscando melhores características microestruturais. Foram realizadas análises de absorção de água e efeito plastificante do FCPSA, de resistência mecânica e retração ao longo do tempo em argamassas curadas a 100%, 60% e 30% de umidade relativa (UR), e análises de fissuração e retração inicial, até a idade de 24h, em matrizes com cimentos Portland CP II-F 40 e CP IV 32. Os resultados mostram que o FCPSA melhora a trabalhabilidade das argamassas em estado fresco, quando adicionado pré-saturado, possibilitando uma redução da relação a/c em ambos os tipos de cimento. No estado endurecido, o FCSA (a) atua principalmente na minimização de fissuração inicial, podendo reduzir a área fissurada em até 22,5% para o cimento CP II-F e 76,2% para o CP IV 32; (b) atua na redução de retração em condições de temperatura elevada e baixa umidade relativa e (c) apresenta resistências à compressão similares às argamassas referência, com dosagem calculada, para ambos os cimentos. / The lack of adequate curing conditions, and related problems such as poor hydration, shrinkage and cracking, are among the main reasons for the reduction in durability of reinforced concrete structures. Considering the increasingly tight schedules practiced in current building construction projects, these reasons tend to worsen once there are recurring failures in the post-concrete placement and finishing activities. Concrete curing, which aims to keep adequate moisture conditions for the proper hydration of cement and to minimize shrinkage and cracking, has been evolving into a new field of research: the practice of internal curing. This is based on the incorporation, into a cement matrix, of materials able to retain water and release it in a gradual manner during the curing period. Most internal curing studies conducted so far have focused primarily on high performance concretes; however, conventional concretes are often neglected in the practice of proper wet curing and also tend to evolve and apply this technology. Among the most studied materials in this context, superabsorbent polymers (SAP) have presented satisfactory performance as an internal curing agent, presenting themselves as internal water reservoirs dispersed throughout the matrix. They were presented to the construction industry in 2001, as internal curing agents, employed to improve the durability of the structures, reduce shrinkage and promote better hydration of the cement particles. Even with the disadvantage of generating internal voids, its use presents advantages due to its plasticizing effect (when pre-saturated), with a capacity to reduce w/c ratio and shrinkage. Among the studies published so far, there are no records of the use of residual SAP. The objective of this study is to evaluate the technical feasibility of using residual SAP (FCSAP), composed of cellulose fiber and SAP, from hygiene products companies, in conventional cement matrices as an internal curing agent. The RSAP absorption and plasticizing effects were evaluated, as well as mechanical strength and shrinkage in mortars cured at 100%, 60% and 30% relative humidity (RH), in addition to analysis of cracking and plastic shrinkage up to 24h, for two types of cements (CP II-F and CP IV). Results show that the use of RSAP as an internal curing agent improves the workability of fresh mortars when added pre-saturated, thus allowing a reduction of w/c ratio for a given workability. In the hardened state: (a) it works mainly in the minimization of initial cracking, being able to reduce the cracked area by up to 22.5% for CP II-F and 76.18% for CP IV; (b) acts in the reduction of shrinkage in high temperature and low relative humidity conditions; and (c) presents similar compressive strengths to the control mortars, when mixed in proper amounts, for both types of cement tested.

abstract: “Smart” materials are used for a broad range of application including electronics, bio-medical devices, and smart clothing. This work focuses on development of smart self-sealing and breathable protective gear for soldiers against Chemical Weapon Agents (CWA). Specifically, the response of chemo-mechanical swelling polymer modified meshes to contact with stimuli droplets was studied. Theoretical discussion of the mechanism of smart materials is followed by development and experimental analysis of different modified mesh designs. A multi-physics model is proposed based on experimental data and the prototype of the fabric is tested in aerosol impingement conditions to confirm the barrier formed by rapid-self-sealing feature of the design. / Dissertation/Thesis / Masters Thesis Mechanical Engineering 2016

This thesis is focused on description of superabsorbents with controlled released of nutrients, specifically macronutrients nitrogen, phosphorus and kalium. Superabsorbents are polymers, mostly acrylic acid polymers, that can absorb huge amount of water without dissolving in it. In its structure they can hold water and thanks to this they are very perspective materials for agricultural usage. Experimental part was focused on growing corn with use of superabsorbents and control samples without use of superabsorbents. Plants were growth for 3 time periods, specifically 46, 60 and 74 days. During the experiments, plats were growth without water stress and in controlled conditions in growing box under UV lamp that simulated day and night by turning on and off after 12 hours. At the end, an image analysis was performed in HARFA program, from which we got information about branching of the roots. Results were supplemented by soil and plants analysis.

Mixes with lower water to cement (w/c) ratio and supplementary cementing materials produce strong and durable concrete. The consequence of lowering w/c is an increase in autogenous shrinkage (AS), which contributes to concrete cracking. Internal curing (IC) is shown to mitigate AS, however improper dosing of IC material can negatively affect the concrete properties. The effectiveness of IC material, such as superabsorbent polymer (SAP), depends on the 1) amount of water stored, 2) particle distribution, and 3) ability to deliver water. The objective of this research is to quantify the in-situ efficiency of SAP by investigating its effect on the cement chemical reaction using non-destructive testing methods, specifically isothermal calorimetry and nuclear magnetic resonance (NMR). IC was tested with varying quantities of SAP in plain cement paste using white Portland cement and three w/c (0.30, 0.32, 0.35). Overdosing of the SAP material was found to significantly affect the hydration reaction and reduce the efficiency of the material. The initial porosity of the paste influences the ability of IC to provide water. However, the extra porosity provided by SAP needs to be considered when calculating the degree of hydration. Particle agglomeration occurs when the mass of SAP to IC water is greater than 5% and is the main factor causing loss of efficiency. A new geometric model was developed to estimate the SAP distribution within the cement paste. The model employs the SAP absorption determined by NMR and assumes that the SAP particles are spherical, of equal diameter, and individual particles absorb the same amount of pore solution. The results reveal that particle spacing increases with agglomeration and reduces the IC efficiency. A hybrid 1-D finite element transient flow model was developed to reverse engineer the effective diffusion coefficient from the NMR water distribution. The gel solid volume fraction and its impedance to water transfer were accounted for through the cement degree of hydration and tortuosity factor, respectively. Model results reveal that the effective water diffusion coefficient depends on w/c, gel volume fraction, and tortuosity once the cement gel fractions start to connect, i.e., after 20% cement degree of hydration. The diffusion length quantifies the distance water can transfer from the SAP to the cement paste. / Thesis / Doctor of Philosophy (PhD)

<p>Superabsorbent polymer (SAP) hydrogel particles have been used as internal curing agents in concrete mixes as they are capable of absorbing and subsequently releasing large amounts of water. This reduces autogenous shrinkage during early stages of hydration. The size, shape, and composition of the hydrogel particles can be controlled during the synthesis, hence providing the opportunity to custom synthesize these internal curing agents to elicit desired structure-property relationships. Utilization of optimized dosage and formulation of SAP has the potential to improve the microstructure, durability, and strength of internally cured concrete. </p> <p>The first study focuses on the synthesis and application of novel composite hydrogel particles as internal curing agents in cementitious mixes. Composite polyacrylamide hydrogel particles containing two different amorphous silica–either nanosilica or silica fume–were used to investigate whether the internal curing performance of hydrogel particles could be enhanced. The dosage and type of silica, crosslinker amount were varied to identify the composite polyacrylamide hydrogel particle composition that provides optimum benefits to internally cured cementitious systems. The synthesized hydrogels were characterized by means of absorption capacity tests, compositional and size analysis. The beneficial impacts of the addition of composite hydrogels on cement paste microstructure are highlighted, including the preferential formation of cement hydration products (such as portlandite) within the hydrogel-induced voids that appeared to be influenced by the composition of the hydrogel particles. The interrelationship between extent of hydration, size of hydrogel voids, and void-filling with hydration products was found to strongly influence mechanical strength and is thus an important structure-property relationship to consider when selecting hydrogels for internal curing purposes. This study informs the design of composite hydrogel particles to optimize performance in cementitious mixes. Additionally, it provides a novel means of incorporating other commonly used admixtures in concrete without facing common challenges related to dispersion and health hazards.</p> <p>The second study focuses on the utilization of two retarding admixture-citric acid and sucrose-to custom synthesize composite polyacrylamides to investigate whether the composite hydrogels could delay hydration of cement paste. Isothermal calorimetry analysis results showed that composite sucrose-containing polyacrylamide hydrogel particles were successfully able to retard main hydration peak of cement paste, beyond the retardation capabilities of the pure polyacrylamide hydrogels. Thus, this study provides avenues of exploring the utilization of common admixtures to formulate novel composite hydrogels that imparts specific properties to cementitious systems.</p> <p>In another study, SAP formulated by admixture industries were used to investigate the feasibility of internal curing of bridge decks and pavement patches with SAP particles. The microstructure and early age hydration properties of SAP-cured cementitious systems were studied. Mitigation of microcracks in the matrix, along with portlandite growth in SAP voids, were observed in SAP-cured mortars. Presence of SAP also mitigated autogenous shrinkage and improved early age hydration as observed by isothermal calorimetry analysis. This thesis highlights some of the beneficial impacts of SAP-cured cementitious systems, and the potential to harness those benefits in large-scale applications of SAP-cured concrete.</p> <br>

Application of smart curing concept called internal curing (IC) is the most promising strategy for mitigating autogenous shrinkage and related early-age cracking in cement-based materials with low water-to-cement ratio. There are still many theoretical and practical questions that need to be answered before IC could become a standard method. Many of these questions concern the most appealing of water-regulating additives for IC called Superabsorbent Polymers (SAP). The clear linkage between SAP material properties, the moment of water release and the effect on autogenous shrinkage is still missing, which blocks formulating recommendations for use of particular potential IC agents in concrete construction. In this treatise various aspects that are decisive for effectiveness of IC in mitigating autogenous shrinkage were examined. The choice of materials was purposefully limited to two compositions of Ultra-High Performance Concrete (UHPC), one fine-grained and one coarse-grained mixture, and one particular, in-depth characterized SAP. The objectives of examination which shaped the final experimental programme were: assessment of IC agent absorption capacity, specification of periods of water migration from fresh concrete mixture into SAP and from SAP back into hardening concrete, determination of effect of SAP addition on cement hydration, evaluation of IC influence on and determination of start of effective autogenous shrinkage and, finally, assessment of autogenous shrinkage with selfsame IC agent but for different matrices. Ideally, description of the mechanisms behind the action of IC at different stages of concrete life and reasoning of differences observed for the UHPCs under investigation had to be provided. First, the main components of the system – UHPC and SAP material – were characterized as to their suitability for IC application. Special attention was paid to the material properties which affect water transport. Usage of different testing methods was necessary here and included: testing with ESEM, FT-IR, tea-bag test, sol fraction content examination and X-ray computed tomography (for SAP) as well as air content measurement and various methods for characterization of the porosity and other features of the microstructure. The observed delay in the start of pozzolanic reactions in case of fine-grained UHPC was rather surprising, but, under consideration of porosity, shed new light on permeability of young UHPC. The work at hand revealed numerous methods that can be used for studying the absorption capacity of polymers, but hardly representative for the behaviour of those polymers within concrete matrix. Because of its general availability and the relatively robust testing procedure, it was decided to focus on possibilities and limitations of using tea-bag test for evaluation of absorption capacity of SAP. New interpretation of tea-bag test results was deduced which enabled assessment of maximum absorption capacity of SAP from measurement of consistency of concrete before and after modification with IC. Influence of IC on hydration process was revealed by using two non-destructive methods, in particular ultrasonic measurement and concrete temperature record. It could be shown that the ionic polymer exhibits complex effects including retardation and acceleration of individual chemical processes. Additionally, X-ray computed tomography (CT) and instrumented ring tests were performed in order to understand scientific significance of the characteristic event appearing during shrinkage measurements, taken as time-zero (= starting point for evaluation of autogenous shrinkage data). Linkage of time-zero with certain phenomenon, e.g., changes of the SAP particles volume or specific value of yield stress, but not with final set, was suggested for the future investigations. By using two setups based on corrugated tube protocol it was possible to register and compare autogenous shrinkage of both UHPCs without and with modification by IC. The effectiveness of IC was shown to be dependent on the matrix in which IC was implemented. This was related to the observed changes in pore percolation that resulted from different absorption behaviour of SAP in the two UHPCs under investigation. Furthermore, the effect of fibres on effectiveness of IC was discussed. Description and discussion of mechanisms behind IC was supported by measurement of capillary pressure, total shrinkage tests with simultaneous mass loss measurement, free autogenous shrinkage tests and the CT measurement. Valuable source of information was furthermore the in-depth literature review. The most appealing finding of the work and the biggest paradox revealed was high efficiency of IC in mitigating autogenous shrinkage and simultaneously appearance of stage where very clear reverse in mode of polymer volume change was observed. This suggests partial reabsorption of water initially released. This puts interpretation of operative shrinkage mechanisms and ones standing behind IC effect in a new perspective. / Die innere Nachbehandlung (Internal Curing – IC) ist die derzeit aussichtsreichste Strategie, um das in zementgebundenen Baustoffen mit niedrigen Wasser/Zement-Werten ausgeprägt auftretende autogene Schwinden wirksam zu verringern und die damit einhergehende Rissbildung in jungem Beton zu vermeiden. Vor einer breiten baupraktischen Anwendung des IC sind noch viele offene Fragen zu beantworten. Die meisten dieser Fragen betreffen die derzeit interessanteste Klasse von wasserregulierenden Stoffen für das IC – die superabsorbierenden Polymere (SAP). Von entscheidender Bedeutung ist hier der noch weitgehend unerforschte Zusammenhang zwischen den Materialeigenschaften der SAP, dem Zeitpunkt der Wasserabgabe und der Auswirkung auf das autogene Schwinden. In der vorliegenden Arbeit werden verschiedene Einflussfaktoren auf die Wirksamkeit von SAP zur Verringerung des autogenen Schwindens untersucht. Für die Experimente wurde ein feinkörniger und ein grobkörniger ultra-hochfester Beton (UHPC) sowie ein schon detailliert charakterisiertes SAP genutzt. Das experimentelle Programm wurde auf folgende Untersuchungsziele ausgerichtet: Absorptionsvermögen der SAP, Zeitfenster der Wassermigration aus dem Frischbeton in das SAP sowie vom SAP in den erhärtenden Beton, autogenes Schwindmaß sowie effektiver Beginn des autogenen Schwindens. Ziel der Arbeiten ist die Beschreibung der Mechanismen, die IC zugrundliegen – und dies zu verschiedenen Betonaltern und unter Berücksichtigung der an den untersuchten UHPC beobachteten Unterschiede. Bei der Charakterisierung der Hauptkomponenten des betrachteten Systems – UHPC und SAP – wurde auf die Materialeigenschaften fokussiert, die den Wassertransport beeinflussen. Dazu wurden u. a. folgende Untersuchungsmethoden angewendet: ESEM, FT-IR, Teebeuteltest, Sol-Fraction Test, Röntgentomographie (für SAP) sowie verschiedene Verfahren zur Charakterisierung der Poren im Beton. Im feinkörnigen UHPC wurde überraschenderweise ein verzögerter Beginn der puzzolanischen Reaktion festgestellt, der bei Berücksichtigung der vorliegenden Porosität zu einer Neubewertung der Permeabilität von UHPC in jungem Alter führte. In der vorliegenden Arbeit werden verschiedene Methoden zur Beschreibung des Wasserabsorptionsvermögens von SAP benannt, deren Aussagekraft bei Anwendung dieser Polymere im Beton aber sehr eingeschränkt ist. Aufgrund seiner einfachen Verfügbarkeit und Robustheit wurde daher der Teebeutetest zur Bestimmung der Wasserabsorption des SAP genutzt. Die Wasserabsorption der SAP im Beton wurde durch Gegenüberstellung von Konsistenzmessungen am Beton vor und nach Zugabe von SAP und Ergebnissen der Teebeuteltest abgeschätzt. Der Einfluss des IC auf die Hydratation wurde zerstörungsfrei mit Ultraschall- und Betontemperaturmessungen erfasst. Auf dieser Grundlage konnten Hypothesen zu den komplexen Wechselwirkungen zwischen ionischem Polymer und der Beschleunigung oder Verzögerung einzelner chemischer Prozesse formuliert werden. Mit Hilfe von instrumentierten Ringversuchen und X-ray Computertomographie wurden die Auswirkungen des IC mit SAP auf das autogene Schwinden, den Aufbau von Zwangsspannungen bei behindertem Schwinden und Time-Zero diskutiert. Dabei konnte ein Zusammenhang zwischen Time-Zero und verschiedenen Phänomenen, wie z. B. Volumenänderung des SAP oder der Fließgrenze des erhärtenden Betons, nicht aber zum Ende des Erstarrens aufgezeigt werden. Das autogene Schwinden beider untersuchter UHPC (jeweils mit und ohne IC) wurde mit Hilfe von Corrugated Tube-Versuchen gemessen. Es konnte gezeigt werden, dass wie Wirksamkeit des IC von der Betonzusammensetzung sowie der in den UHPC infolge Wechselwirkungen mit den SAP verschieden ausgebildeten Porenstruktur der Matrix abhängt. Weiterhin konnte ein Einfluss von Faserzugaben auf die Wirksamkeit des IC gezeigt werden. Die Beschreibung und Diskussion der Mechanismen des IC wurde durch Messungen des Kapillardrucks, des Gesamtschwindens, des freien autogenen Schwindens, des Masseverlustes und Computertomographie unterstützt. Eine wichtige Erkenntnisquelle war zudem die umfangreich gesichtete und diskutierte Literatur. Das interessanteste und zugleich paradoxe Ergebnis der Untersuchungen ist die Tatsache, dass die bei Einsatz von SAP beobachtete Verringerung des autogenen Schwindens eindeutig mit einer zeitgleichen Umkehr der Volumenänderung der SAP einhergeht: die bis dahin dominierende Wasserabgabe geht in eine erneute Wasseraufnahme über. Dies stellt die Interpretation der Triebkräfte des Schwindens und die dem IC zugrundliegenden Mechanismen in einen neuen Zusammenhang.

Application of smart curing concept called internal curing (IC) is the most promising strategy for mitigating autogenous shrinkage and related early-age cracking in cement-based materials with low water-to-cement ratio. There are still many theoretical and practical questions that need to be answered before IC could become a standard method. Many of these questions concern the most appealing of water-regulating additives for IC called Superabsorbent Polymers (SAP). The clear linkage between SAP material properties, the moment of water release and the effect on autogenous shrinkage is still missing, which blocks formulating recommendations for use of particular potential IC agents in concrete construction. In this treatise various aspects that are decisive for effectiveness of IC in mitigating autogenous shrinkage were examined. The choice of materials was purposefully limited to two compositions of Ultra-High Performance Concrete (UHPC), one fine-grained and one coarse-grained mixture, and one particular, in-depth characterized SAP. The objectives of examination which shaped the final experimental programme were: assessment of IC agent absorption capacity, specification of periods of water migration from fresh concrete mixture into SAP and from SAP back into hardening concrete, determination of effect of SAP addition on cement hydration, evaluation of IC influence on and determination of start of effective autogenous shrinkage and, finally, assessment of autogenous shrinkage with selfsame IC agent but for different matrices. Ideally, description of the mechanisms behind the action of IC at different stages of concrete life and reasoning of differences observed for the UHPCs under investigation had to be provided. First, the main components of the system – UHPC and SAP material – were characterized as to their suitability for IC application. Special attention was paid to the material properties which affect water transport. Usage of different testing methods was necessary here and included: testing with ESEM, FT-IR, tea-bag test, sol fraction content examination and X-ray computed tomography (for SAP) as well as air content measurement and various methods for characterization of the porosity and other features of the microstructure. The observed delay in the start of pozzolanic reactions in case of fine-grained UHPC was rather surprising, but, under consideration of porosity, shed new light on permeability of young UHPC. The work at hand revealed numerous methods that can be used for studying the absorption capacity of polymers, but hardly representative for the behaviour of those polymers within concrete matrix. Because of its general availability and the relatively robust testing procedure, it was decided to focus on possibilities and limitations of using tea-bag test for evaluation of absorption capacity of SAP. New interpretation of tea-bag test results was deduced which enabled assessment of maximum absorption capacity of SAP from measurement of consistency of concrete before and after modification with IC. Influence of IC on hydration process was revealed by using two non-destructive methods, in particular ultrasonic measurement and concrete temperature record. It could be shown that the ionic polymer exhibits complex effects including retardation and acceleration of individual chemical processes. Additionally, X-ray computed tomography (CT) and instrumented ring tests were performed in order to understand scientific significance of the characteristic event appearing during shrinkage measurements, taken as time-zero (= starting point for evaluation of autogenous shrinkage data). Linkage of time-zero with certain phenomenon, e.g., changes of the SAP particles volume or specific value of yield stress, but not with final set, was suggested for the future investigations. By using two setups based on corrugated tube protocol it was possible to register and compare autogenous shrinkage of both UHPCs without and with modification by IC. The effectiveness of IC was shown to be dependent on the matrix in which IC was implemented. This was related to the observed changes in pore percolation that resulted from different absorption behaviour of SAP in the two UHPCs under investigation. Furthermore, the effect of fibres on effectiveness of IC was discussed. Description and discussion of mechanisms behind IC was supported by measurement of capillary pressure, total shrinkage tests with simultaneous mass loss measurement, free autogenous shrinkage tests and the CT measurement. Valuable source of information was furthermore the in-depth literature review. The most appealing finding of the work and the biggest paradox revealed was high efficiency of IC in mitigating autogenous shrinkage and simultaneously appearance of stage where very clear reverse in mode of polymer volume change was observed. This suggests partial reabsorption of water initially released. This puts interpretation of operative shrinkage mechanisms and ones standing behind IC effect in a new perspective. / Die innere Nachbehandlung (Internal Curing – IC) ist die derzeit aussichtsreichste Strategie, um das in zementgebundenen Baustoffen mit niedrigen Wasser/Zement-Werten ausgeprägt auftretende autogene Schwinden wirksam zu verringern und die damit einhergehende Rissbildung in jungem Beton zu vermeiden. Vor einer breiten baupraktischen Anwendung des IC sind noch viele offene Fragen zu beantworten. Die meisten dieser Fragen betreffen die derzeit interessanteste Klasse von wasserregulierenden Stoffen für das IC – die superabsorbierenden Polymere (SAP). Von entscheidender Bedeutung ist hier der noch weitgehend unerforschte Zusammenhang zwischen den Materialeigenschaften der SAP, dem Zeitpunkt der Wasserabgabe und der Auswirkung auf das autogene Schwinden. In der vorliegenden Arbeit werden verschiedene Einflussfaktoren auf die Wirksamkeit von SAP zur Verringerung des autogenen Schwindens untersucht. Für die Experimente wurde ein feinkörniger und ein grobkörniger ultra-hochfester Beton (UHPC) sowie ein schon detailliert charakterisiertes SAP genutzt. Das experimentelle Programm wurde auf folgende Untersuchungsziele ausgerichtet: Absorptionsvermögen der SAP, Zeitfenster der Wassermigration aus dem Frischbeton in das SAP sowie vom SAP in den erhärtenden Beton, autogenes Schwindmaß sowie effektiver Beginn des autogenen Schwindens. Ziel der Arbeiten ist die Beschreibung der Mechanismen, die IC zugrundliegen – und dies zu verschiedenen Betonaltern und unter Berücksichtigung der an den untersuchten UHPC beobachteten Unterschiede. Bei der Charakterisierung der Hauptkomponenten des betrachteten Systems – UHPC und SAP – wurde auf die Materialeigenschaften fokussiert, die den Wassertransport beeinflussen. Dazu wurden u. a. folgende Untersuchungsmethoden angewendet: ESEM, FT-IR, Teebeuteltest, Sol-Fraction Test, Röntgentomographie (für SAP) sowie verschiedene Verfahren zur Charakterisierung der Poren im Beton. Im feinkörnigen UHPC wurde überraschenderweise ein verzögerter Beginn der puzzolanischen Reaktion festgestellt, der bei Berücksichtigung der vorliegenden Porosität zu einer Neubewertung der Permeabilität von UHPC in jungem Alter führte. In der vorliegenden Arbeit werden verschiedene Methoden zur Beschreibung des Wasserabsorptionsvermögens von SAP benannt, deren Aussagekraft bei Anwendung dieser Polymere im Beton aber sehr eingeschränkt ist. Aufgrund seiner einfachen Verfügbarkeit und Robustheit wurde daher der Teebeutetest zur Bestimmung der Wasserabsorption des SAP genutzt. Die Wasserabsorption der SAP im Beton wurde durch Gegenüberstellung von Konsistenzmessungen am Beton vor und nach Zugabe von SAP und Ergebnissen der Teebeuteltest abgeschätzt. Der Einfluss des IC auf die Hydratation wurde zerstörungsfrei mit Ultraschall- und Betontemperaturmessungen erfasst. Auf dieser Grundlage konnten Hypothesen zu den komplexen Wechselwirkungen zwischen ionischem Polymer und der Beschleunigung oder Verzögerung einzelner chemischer Prozesse formuliert werden. Mit Hilfe von instrumentierten Ringversuchen und X-ray Computertomographie wurden die Auswirkungen des IC mit SAP auf das autogene Schwinden, den Aufbau von Zwangsspannungen bei behindertem Schwinden und Time-Zero diskutiert. Dabei konnte ein Zusammenhang zwischen Time-Zero und verschiedenen Phänomenen, wie z. B. Volumenänderung des SAP oder der Fließgrenze des erhärtenden Betons, nicht aber zum Ende des Erstarrens aufgezeigt werden. Das autogene Schwinden beider untersuchter UHPC (jeweils mit und ohne IC) wurde mit Hilfe von Corrugated Tube-Versuchen gemessen. Es konnte gezeigt werden, dass wie Wirksamkeit des IC von der Betonzusammensetzung sowie der in den UHPC infolge Wechselwirkungen mit den SAP verschieden ausgebildeten Porenstruktur der Matrix abhängt. Weiterhin konnte ein Einfluss von Faserzugaben auf die Wirksamkeit des IC gezeigt werden. Die Beschreibung und Diskussion der Mechanismen des IC wurde durch Messungen des Kapillardrucks, des Gesamtschwindens, des freien autogenen Schwindens, des Masseverlustes und Computertomographie unterstützt. Eine wichtige Erkenntnisquelle war zudem die umfangreich gesichtete und diskutierte Literatur. Das interessanteste und zugleich paradoxe Ergebnis der Untersuchungen ist die Tatsache, dass die bei Einsatz von SAP beobachtete Verringerung des autogenen Schwindens eindeutig mit einer zeitgleichen Umkehr der Volumenänderung der SAP einhergeht: die bis dahin dominierende Wasserabgabe geht in eine erneute Wasseraufnahme über. Dies stellt die Interpretation der Triebkräfte des Schwindens und die dem IC zugrundliegenden Mechanismen in einen neuen Zusammenhang.

<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>