Fly ash and blast furnace slag are the two major industrial solid by-products generated in most countries including India. Although their utilization rate has increased in the recent years, still huge quantities of these material remain unused and are stored or disposed of consuming large land area involving huge costs apart from causing environmental problems. Environmentally safe disposal of Fly ash is much more troublesome because of its ever increasing quantity and its nature compared to blast furnace slag. Bulk utilization of these materials which is essentially possible in civil engineering in general and more particular in geotechnical engineering can provide a relief to environmental problems apart from having economic benefit. One of the important aspects of these waste materials is that they improve physical and mechanical properties with time and can be enhanced to a significant level by activating with chemical additives like lime and cement. Class-C Fly ashes which have sufficient lime are well utilized but class-F Fly ashes account for a considerable portion that is disposed of due to their low chemical reactivity. Blast furnace slag in granulated form is used as a replacement for sand to conserve the fast declining natural source. The granulated blast furnace slag (GBS) is further ground to enhance its pozzolanic nature. If GBS is activated by chemical means rather than grinding, it can provide a good economical option and enhance its utilization potential as well. GGBS is latent hydraulic cement and is mostly utilized in cement and concrete industries. Most uses of these materials are due to their pozzolanic reactivity. Though Fly ash and GGBS are pozzolanic materials, there is a considerable difference in their chemical composition. For optimal pozzolanic reactivity, sufficient lime and silica should be available in desired proportions. Generally, Fly ash has higher silica (SiO2) content whereas GGBS is rich in lime (CaO) content. Combining these two industrial wastes in the right proportion may be more beneficial compared to using them individually. The main objective of the thesis has been to evaluate the suitability of the class-F Fly ash/GGBS mixtures with as high Fly ash contents for Geotechnical and Geo-environmental applications. For this purpose, sufficient amount of class-F Fly ash and GGBS were collected and their mixtures were tested in the laboratory for analyzing their mechanical behavior. The experimental program included the evaluation of mechanical properties such as compaction, strength, compressibility of the Fly ash/GGBS mixtures at different proportions with GGBS content varying from 10 to 40 percent. An external agent such as chemical additives like lime or cement is required to accelerate the hydration and pozzolanic reactions in both these materials. Hence, addition of varying percentages of lime is also considered. However, these studies are not extended to chemically activate GBS and only GGBS is used in the present study. Unconfined compressive strength tests have been carried out on various Fly ash/ GGBS mixtures at different proportions at different curing periods. The test results demonstrated rise in strength with increase in GGBS content and with 30 and 40 percent of GGBS addition, the mixture showed higher strength than either of the components i.e. Fly ash or GGBS after sufficient curing periods. Addition of small amount of lime increased the strength tremendously which indicated the occurrence of stronger cementitious reactions in the Fly ash/GGBS mixtures than in samples containing only Fly ash. Improvement of the strength of the Fly ash/GGBS mixtures was explained through micro-structural and mineralogical studies. The microstructure and mineralogical studies of the original and the stabilized samples were investigated by scanning electron microscopy (SEM) and X-Ray diffraction techniques respectively. These studies together showed the formation of cementitious compounds such as C-S-H, responsible for imparting strength to the pozzolanic materials, is better in the mixture containing 30 and 40 percent of GGBS content than in individual components. Resilient and permanent deformation behavior on an optimized mix sample of Fly ash and GGBS cured for 7 day curing period has been studied. The Resilient Modulus (Mr) is a measure of subgrade material stiffness and is actually an estimate of its modulus of elasticity (E). The permanent deformation behavior is also important in predicting the performance of the pavements particularly in thin pavements encountered mainly in rural and low volume roads. The higher resilient modulus values indicated its suitability for use as subgrade or sub-base materials in pavement construction. Permanent axial strain was found to increase with the number of load cycles and accumulation of plastic strain in the sample reduced with the increase in confining pressure. Consolidation tests were carried on Fly ash/GGBS mixtures using conventional oedometer to assess their volume stability. However, such materials develop increased strength with time and conventional rate of 24 hour as duration of load increment which requires considerable time to complete the test is not suitable to assess their volume change behavior in initial stages. An attempt was thus made to reduce the duration of load increment so as to reflect the true compressibility characteristics of the material as close as possible. By comparing the compressibility behavior of Fly ash and GGBS between conventional 24 hour and 30 minutes duration of load increment, it was found that 30 minutes was sufficient to assess the compressibility characteristics due to the higher rate of consolidation. The results indicated the compressibility of the Fly ash/GGBS mixtures slightly decreases initially but increase with increase in GGBS content. Addition of lime did not have any significant effect on the compressibility characteristics since the pozzolanic reaction, which is a time dependent process and as such could not influence due to very low duration of loading. Results were also represented in terms of constrained modulus which is a most commonly used parameter for the determination of settlement under one dimensional compression tests. It was found that tangent constrained modulus showed higher values only at higher amounts of GGBS. It was also concluded that settlement analysis can also be done by taking into account the constrained modulus. The low values of compression and recompression indices suggested that settlements on the embankments and fills (and the structures built upon these) will be immediate and minimal when these mixtures are used. In addition to geotechnical applications of Fly ash/GGBS mixture, their use for the removal of heavy metals for contaminated soils was also explored. Batch equilibrium tests at different pH and time intervals were conducted with Fly ash and Fly ash/GGBS mixture at a proportion of 70:30 by weight as adsorbents to adsorb lead ions. It was found that though uptake of lead by Fly ash itself was high, it increased further in the presence of GGBS. Also, the removal of lead ions increased with increase in pH of the solution but decreases at very high pH. The retention of lead ions by sorbents at higher pH was due to its precipitation as hydroxide. Results of the adsorption kinetics showed that the reaction involving removal of lead by both the adsorbents follow second-order kinetics. One of the major problems which geotechnical engineers often face is construction of foundations on expansive soils. Though stabilization of expansive soils with lime or cement is well established, the use of by-product materials such as Fly ash and blast furnace slag to achieve economy and reduce the disposal problem needs to be explored. To stabilize the soil, binder comprising of Fly ash and GGBS in the ratio of 70:30 was used. Different percentages of binder with respect to the soil were incorporated to the expansive soil and changes in the physical and engineering properties of the soil were examined. Small addition of lime was also considered to enhance the pozzolanic reactions by increasing the pH. It was found that liquid limit, plasticity index, swell potential and swell pressure of the expansive soil decreased considerably while the strength increased with the addition of binder. The effect was more pronounced with the addition of lime. Swell potential and swell pressure reduced significantly in the presence of lime. Based on the results, it can be concluded that the expansive soils can be successfully stabilized with the Fly ash-GGBS based binder with small addition of lime. This is also more advantageous in terms of lime requirement which is typically high when Fly ash, class-F in particular, is used alone to stabilize expansive soils. Based on the studies carried out in the present work, it is established that combination of Fly ash and GGBS can be advantageous as compared to using them separately for various geotechnical applications such as for construction of embankments/fills, stabilization of expansive soils etc. with very small amount of lime. Further, these mixtures have better potential for geo-environmental applications such as decontamination of soil. However, it is still a challenge to activate GBS without grinding.

Geopolymers are a relatively new class of materials that have many broad applications, including use as substitute for ordinary Portland cement (OPC), use in soil stabilisation, fire resistant panels, refractory cements, and inorganic adhesives. Geopolymers are an alternative binder to Portland cement in the manufacture of mortars and concrete, as its three-dimensional alumino silicate network develops excellent strength properties. Use of geopolymers in place of ordinary Portland cement is also favoured owing to the possible energy and carbon dioxide savings. Geopolymer is typically synthesized by alkali activation of pozzolanas at moderate temperatures (< 1000C). The focus of the thesis is synthesis and characterization of geopolymers as construction materials. In this context, the role of compositional factors, such as, pozzolana type (fly ash, kaolinite, metakaolinite, ground granulated blast furnace slag, red soil), alkali (sodium hydroxide is used in this study) activator concentration, Si/Al (Si= silicon, Al = aluminium) ratio of the pozzolana and environmental factors, namely, curing period and temperature are examined. Besides synthesizing geopolymers that could be an alternate to concrete as construction material, sand-sized aggregates were synthesized using geopolymer reactions. This was done as river sand is becoming scarcer commodity for use as construction material. Several compositional and environmental factors were varied in geopolymer synthesis in order to identify the optimum synthesis conditions that yield geopolymers with maximum compressive strength. Besides varying external (compositional and environmental) factors, the role of internal microstructure in influencing the compressive strength of the geopolymer was examined. Micro-structure examinations were made using X-ray diffraction (XRD), scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) studies. The studies on compositional and environmental factors in geopolymer synthesis brought out several interesting results. The results firstly brought out that amongst the pozzolanas studied, ASTM class F fly ash is most suited for maximum compressive strength mobilization upon geopolymer reactions. Moderate temperature (75-1000C) was adequate to mobilize large compressive strengths. Room temperature curing needed more than 7 days before the pozzolana-NaOH paste began to develop strength. Curing period of 56 days was needed for the geopolymer to develop significant strength (19.6MPa). A similar range of compressive strength could be developed by the pozzolana-NaOH paste upon curing for 3 days at 1000C. Likewise curing the pozzolana-NaOH paste at temperatures > 1000C led to reduction in compressive strength from shrinkage and breakage of bonds. A caustic soda (NaOH) concentration of 10 M was adequate to develop maximum compressive strength of the geopolymer. Caustic soda concentrations in excess of 10 M did not result in further improvement of strength. The Si/Al ratio also contributes to strength mobilization. The Si/Al ratio of the geopolymer was enhanced by mixing commercially obtained silica gel with the pozzolana. Maximum strength mobilization was observed at Si/Al ratio = 2.45 corresponding to 6.5 % silica gel addition to the pozzolana (on dry mass basis). Comparing compressive strengths of geopolymers with varying silica gel contents, geopolymer specimens with least water content and largest dry density did not exhibit maximum compressive strength indicating that the physico-chemical (bond strength, micro-structure) played a pivotal role than physical parameters (dry density, water content) in dictating the strength of the geopolymer. MIP results showed that bulk of the porosity in fly ash geopolymer specimens is contributed by macro pores and air voids. Geopolymerization leads to bulk consumption of cenospheres in fly ash and forms polymerized matrix with network of large pores. After geopolymerization, all the main characteristic peaks of Al–Si minerals observed in fly ash persisted, suggesting that no new major crystalline phases were formed. Presence of small amount of inorganic contaminants in fly ash can drastically reduce the strength of the fly ash geopolymer. For example, 5-20 % presence of red soil reduces the strength of fly ash geopolymer by 16 to 59 %. Presence of unreacted clay coupled with less porous structure is responsible for the reduction in compressive strength of fly ash geopolymer subjected to red soil addition. MIP studies with geopolymers also revealed that there is good bearing between compressive strengths and maximum intruded volume (from MIP test) of geopolymers. For example, fly ash geopolymer specimen exhibits highest total intruded volume (0.3908 cc/g) and largest compressive strength of 29.5 MPa, while red soil geopolymer specimen exhibit least intruded volume (0.0416 cc/g) and lowest compressive strength (5.4 MPa). Further, analysis showed that specimens with larger airvoids+macropores volume had larger compressive strength, suggesting that geopolymers with more porous microstructure develop larger compressive strength. All geopolymer specimens exhibited tri-modal nature of pores i.e. macro-pore mode (entrance pore radius: 25-5000 nm), mesopore mode (entrance pore radius: 1.25 to 25 nm) and air void mode (entrance pore radius >5000 nm). The micro pores (entrance pore radius < 1.25 nm) do not contribute to porosity of the geopolymer specimens. Sand particles prepared from geopolymer reactions (FAPS or fly ash geopolymer sand) predominated in medium sized (2mm to 0.425 mm) sand particles. Their particle size distribution characteristics (uniformity coefficient and coefficient of curvature) classified them as poorly graded sand (SP). Dissolution, followed by polymerization reactions led to dense packing of the Si–O–Al–O– units that imparted specific gravity of 2.59 to FAPS particles which is comparable to that of river sand (2.61). Dissolution in strongly alkaline medium imparted strongly alkaline pH (12.5) to the FAPS particles. The river sand is characterized by much lower pH (7.9). Despite being characterized by rounded grains, the FAPS particles mobilized relatively high friction angle of (35.5o) than river sand (∅ = 28.9o). The river sand-mortar (RS-M) and fly ash geopolymer sand-mortar (FAPS-M) specimens developed similar 28-day compressive strengths, 11.6 to 12.2 MPa. Despite its higher water content, FAPS-mortar specimens developed similar compressive strength and initial tangent modulus (ITM) as river sand-mortar specimens. The FAPS-M specimen is more porous (larger intruded volume) with presence of larger fraction of coarser pores. Total porosity is majorly contributed by macro-pores (67.92%) in FAPS-M specimen in comparison to RS-M specimen (macro-pores = 33.1%). Mortar specimens prepared from FAPS and river sand exhibit similar pH of 12.36 and 12.4 respectively. FAPS-mortar specimens have lower TDS (1545 mg/L) than river sand-mortar specimens (TDS = 1889 mg/L). The RS-M and FAPS-M specimens exhibit leachable sodium levels of 0.001 g Na/g RS-M and 0.007 g Na/g-FAPS-M respectively in the water leach tests. The larger leachable sodium of FAPS-M specimen is attributed to residual sodium hydroxide persisting in the FAPS even after washing. The ultra-accelerated mortar bar test (UAMBT) shows that the percentage expansion of FAPS-M and RS-M specimens are comparable and range between 0.07 to 0.08 %.

Aujourd'hui, les problèmes environnementaux sont plus graves que jamais. Des mesures urgentes devraient être prises dans tous les domaines de l'activité humaine, y compris la construction. L'un des principaux contributeurs à l'impact négatif de cette industrie sur l'environnement est la fabrication du ciment Portland ordinaire (OPC) nécessaire à la production de béton et d’autres matériaux cimentaire. Malgré son importance, il présente un inconvénient important: sa production est accompagnée par de grandes quantités de gaz à effet de serre. Ils représentent 5 à 8% des émissions mondiales totales de CO2. Des matériaux cimentaires plus écologiques sont maintenant nécessaires.Des réductions significatives de l’impact sur l’environnement ne peuvent être obtenues que par l’utilisation de liants de nouvelle génération dont la fabrication ne nécessite pas beaucoup de processus et de traitements supplémentaires. L'une d'elles consiste à utiliser des déchets industriels comme liants (différentes laitiers, cendres volantes, cendres de biomasse, etc.). De cette manière, il y a non seulement une réduction de l'impact de processus tels que l'extraction minière ou la calcination, mais également le recyclage des déchets (un principe de l'économie circulaire).Une possibilité consiste à utiliser du laitier de haut fourneau (GGBS) comme base pour ce ciment de nouvelle génération. En raison de sa réactivité relativement faible avec l'eau, des suppléments (également appelés activateurs) doivent être utilisés pour favoriser le processus d'hydratation. Le carbonate de sodium (Na2CO3) est l’un des activateurs les plus prometteurs et en même temps les moins étudiés. Un tel ciment alkali-activé présente des propriétés mécaniques et de durabilité élevées, ainsi qu'une empreinte CO2 très faible. Parmi les principaux problèmes qui entravent son utilisation à l'échelle industrielle, on peut mentionner une évolution de la résistance lente à jeune âge et de rhéologie médiocre.L'objectif de la présente thèse est de développer une nouvelle conception du liant à base de laitier activé par Na2CO3, qui répondrait à toutes les exigences modernes du secteur de la construction, en particulier les propriétés rhéologiques et le développement de la résistance à jeune âge. Ce liant doit toujours répondre à au moins trois critères principaux: faible impact environnemental, faibles risques de danger dans les applications sur le terrain et être économiquement compétitif à l'échelle industrielle.Dans le présent travail, l’influence de différents paramètres tels que le rapport eau/liant, la concentration de Na2CO3, la finesse du laitier et les conditions de durcissement sur les propriétés du mélange à jeune âge et à long terme a été étudiée. Sur la base des résultats du processus d’hydratation, les additifs à base de phosphonate qui permettent de contrôler efficacement la rhéologie de tels liants ont été testé avec succès. Ils permettent non seulement de contrôler le temps de prise, mais fournissent également un effet plastifiant.En ce qui concerne l’amélioration des propriétés de résistance au jeune âge, différentes méthodes ont été utilisées. L’utilisation d’un traitement thermique ou d’une augmentation de la finesse du GGBS s’est avérée efficace. L’exploration des causes d’une longue période d’induction a montré que l’accélération pouvait également être obtenue par l’ajout d’une source de calcium à cinétique de dissolution contrôlée. En conséquence, le liant est devenu plus réactif et plus robuste à certains facteurs (concentration d’activateur, rapport eau/liant, conditions de durcissement, etc.). Pour compenser l'empreinte carbone supplémentaire de la source de calcium ajoutée, le liant a été dilué avec succès par le calcaire sans aucune dégradation des propriétés à un certain pourcentage de dilution. / Today, environmental problems are more acute than ever. Urgent measures should be taken in all spheres of human activity including construction and civil engineering. One of the major contributors of negative environmental impacts from this industry is the manufacturing of ordinary Portland cement (OPC) required for concrete and other cementitious materials production. Although its importance to economical development, it has a significant drawback - its production is accompanied by the emission of large quantities of greenhouse gases. They account for 5-8% of total world CO2 emissions. More environmentally friendly cementitious materials are now required.Significant reductions of the environmental impact can be achieved only through the use of new-generation binders whose manufacture does not require a lot of additional processes and treatments. One route is through the use of industrial wastes as binders (different slags, fly ash, biomass bottom ash, etc.). In this way there is not only a reduction in the impact of processes such as mining or calcination, but also the recycling of waste materials (circular economy principle).One possibility is to use ground granulated blast furnace slag (GGBS) as the basis for such a new generation cement. Due to its rather low reactivity with water, additional supplements (also called activators) should be used to promote the hydration process. One of the most promising, and at the same time least studied, activators is sodium carbonate (Na2CO3). Such alkali-activated cements present high mechanical and durability properties, as well as a very low CO2 footprint. Among the main problems hindering its industrial scale adoption are their poor rheology and too slow strength gain within the first days of hardening.The objective of the present thesis is to develop a new binder based on Na2CO3 activated GGBS that would meet all the modern requirements of the construction industry, in particular regarding the rheological properties and early age strength development. In addition this binder should always respond to at least three main criteria: low environmental impact, low health and safety concerns in field applications, and be economically competitive at industrial scale.In the present work, the influence of different parameters like water/binder ratio, Na2CO3 concentration, slag fineness and curing conditions on both early age and long term properties of the mixture were studied. Based on the results of the hydration process analysis, phosphonate based additives that allow for the effective control of the rheology of such binders were successfully tested. They not only allow control over the setting time, but also provide a plasticizing effect.Regarding the improvement of early age strength properties, various methods have been used. The use of heat treatment or an increase of GGBS fineness turned out to be efficient. Exploring the causes of the long induction period has shown that acceleration can also be achieved by the addition of a calcium source with controlled dissolution kinetics. As a result, the binder became more reactive and robust against certain factors (activator concentration, Water/Binder ratio, curing conditions, etc.). To compensate for the additional carbon footprint from the added calcium source, the binder was successfully diluted by limestone without any degradation of the properties below some dilution percentages.