Development of foam one-part geopolymers

Doctoral Thesis Civil Engineering, MaterialA produção de cimento Portland normal (CPN) o mais importante constituinte do betão requer uma elevada produção de energia com a consequente libertação para a atmosfera de dióxido de carbono e outros gases responsáveis por efeito de estufa (GEE). As preocupações ambientais relacionadas com as elevadas emissões de CO2 geradas durante a produção do CPN motivaram investigações para o desenvolvimento de novos materiais ligantes eco-eficientes. Os geopolímeros são ligantes alternativos ao CPN obtidos a partir de aluminosilicatos e activadores alcalinos. A geopolímerização é um processo quimico complexo que envolve a dissolução dos aluminosilicatos, o seu transporte, orientação e policondensação de produtos de reação. Contudo são reconhecidas algumas limitações aos geopolímeros correntes, bicomponentes (contendo soluções alcalinas e silicatos solúveis). A utilização de soluções alcalinas agressivas dificulta a aplicação dos geopolímeros. A utilização de silicato de sódio é responsável por uma elevada pegada carbónica dos geopolímeros. A durabilidade destes materiais é ainda tema controverso. Por exemplo os geopolímeros correntes (bicomponentes) estão associados à formação substancial de eflorescências pelo facto das soluções alcalinas e silicatos solúveis não reagirem totalmente durante o processo de geopolimerização. Este fenómeno é responsável por um aumento da permeabilidade dos geopolímeros e por uma redução da sua durabilidade. Consequentemente é necessário estudar novas e melhores misturas geopoliméricas. A descoberta dos geopolímeros monofásicos é considerada um importante acontecimento em termos de geopolímeros de baixas emissões de carbono aos quais basta juntar água, exactamente como sucede com o CPN. Contudo até ao presente momento estes novos ligantes tem estado associados a baixos valores de resistência à compressão. Alguns autores até referem uma perda de resistência ao longo do tempo em geopolímeros monofásicos à base de lamas vermelhas calcinadas e hidróxido de sódio. A presente tese pretende desenvolver novas misturas de geopolímeros monofásicos com um desempenho suficiente para poderem ser utilizadas pela indústria da construção. Na mesma foram estudadas as propriedades mecânicas e a durabilidade das novas misturas. Analisou-se a aplicabilidade de um modelo numérico para a previsão da resistência à compressão das novas misturas. Efetuou-se a caracterização dos produtos de reação através da análise da microestrutura e da espectroscopia de infravermelhos. Estudou-se a possibilidade da utilização dos geopolímeros monofásicos na produção de argamassas porosas leves com condutibilidade térmica melhorada. O seu desempenho foi comparado com o desempenho de argamassas porosas leves obtidas de geopolímeros correntes (bicomponentes) em termos de propriedades, custo e potencial de aquecimento global.The production of ordinary Portland cement (OPC) as the essential constituent of concrete requires considerable energy, releasing a significant amount of carbon dioxide and other greenhouse gases (GHGs) into atmosphere. Environmental concerns regarding the high CO2 emissions related to the production of OPC led to research efforts on the development of eco-efficient alternative binders. Geopolymers constitute promising inorganic binders alternative to OPC which are based on aluminosilicates by-products and alkali activators. The geopolymerization is a complex chemical process evolving dissolution of raw materials, transportation, orientation and polycondensation of the reaction products. However, there are still many drawbacks associated with traditional two part geopolymer mixes (containing alkaline species and soluble silicates). The caustic alkaline solutions make the handling and application of geopolymers difficult. The use of sodium silicate is responsible for a high carbon footprint of two part geopolymers. The durability of these binders is also subject of some controversy. For instance, current two part geopolymeric mixes can suffer from a high amount of efflorescence originated by the fact that alkaline or soluble silicates that are added during processing cannot be totally consumed during geopolymerisation. This phenomenon is responsible for an increase in geopolymer permeability and reduced durability. Therefore, the study of new and improved geopolymer mixes is needed. The discovery of one-part geopolymers is considered as a key event on the evolution of low carbon dioxide geopolymer technology in the “just add water” concept as it happens with OPC. However so far they were associated with very low compressive strength. Some authors even report a compressive strength decrease with time for one-part geopolymers based on calcined red mud and sodium hydroxide blends. The present thesis aimed to develop one part geopolymer mixtures with acceptable performance to be of some use for the construction industry. The mechanical properties and the durability performance of the new one-part geopolymer mixtures were studied. A numerical model to predict the compressive strength of one part-geopolymers was suggested. Hydration products results assessed with SEM/EDS and FTIR spectra were presented. The use of one part geopolymers for production of lightweight foam mortars with the improved thermal performance was studied. Comparisons to foam two part geopolymer mortars were made concerning properties, cost and global warming potential assessment

The Management of the conservation of Masjed-e Jame, Isfahan

Full version unavailable due to 3rd party copyright restrictionsMasjed-e Jame of Isfahan represents over one thousand year old tradition and history of mosque construction in Iran, demonstrating a variety of practical techniques, architectural styles and Iranian architectural decorations altogether in one building complex. The unique example of Iranian Islamic architecture was finally recognised as having international importance and therefore registered in 2012.The imperfections in Isfahan`s Masjed-e Jame nomination file may have delayed the registration process for its inclusion on the UNESCO World Heritage List (WHL) took a long time (4 years). Each nomination file is composed of nine sections. The aim of this thesis is to clarify the weak points of the registered nomination file of Masjed-e Jame as a World Heritage Site (WHS), based on UNESCO guideline and to propose improvements for increasing the quality of Masjed-e Jame conservation management plan by utilizing nomination files of some similar registered sites in the WHL. Additionally, to show how these suggestions improve the quality of nomination files of similar monuments under preparation. The research was conducted by selecting similar sites from the WHL. To select similar sites to the Masjed-e Jame, it was necessary to prepare a series of tables which consists of all the registered sites in UNESCO from around the world. All 981 registered monuments on WHL in 2013 were evaluated in three different phases and eliminated by different criteria at each phase to leave eight suitable case studies. The research continued by assessing the eight selected nomination files and categorizing each part of the file as either excellent, good, average, adequate and poor. This evaluation used the main sections of nomination files based on UNESCO guideline which are: 1. Identification of the properties; 2. Description; 3. Justification for inscription; 4. State of conservation and factors affecting the properties; 5. Protection and management of the property; 6. Monitoring; 7. Documentation; 8. Contact information of responsible authorities; 9. Signature on behalf of the state party. By clarifying the weak and strong points of each nomination file, the following recommendations were proposed to improve the quality of nomination file of Masjed-e Jame and also the application of the findings in to similar monument nomination files under preparation. These included: 1) Full details of the location of The management of the conservation of Masjed-e Jame, Isfahan D the site; 2) Providing list of the site`s owners; 3) The usage of maps beside the text and referring to the policies; 4) Appropriate scientific methods to solve or reduce problems with the building fabric, usage etc.; 5) Preparing lists of responsibilities related to the selected organizations; 6) The relationship to tourism; 7) The connections between universities and related organizations; 8) The concentration on the urgent priorities by separating projects into long and short term; 9) Documentation. Furthermore, a timetable by considering priority was proposed to improve the Masjed-e Jame conservation management plan

Flow performance of hybrid cement based mortars

This paper reports experimental results of 32 hybrid cement mixes regarding the joint effect of sodium hydroxide concentration, the use of a commercial superplasticizer and a biopolymer on the flow and compressive strength performance. The results show that the use of commercial admixtures led to a slightly increase in the flow of mortars with lower sodium hydroxide concentration. A mixture based on 80% fly ash, 10% calcium hydroxide and 10% waste glass showed the highest compressive strength. A compressive strength decrease was noticed concerning the use of the two admixtures that can due to the fact that those admixtures are not stable on high basic media. The authors would like to acknowledge the financial support of the Foundation for Science and Technology (FCT) in the frame of project IF/00706/2014-UM.2.15info:eu-repo/semantics/publishedVersio

Short-term compressive strength of fly ash and waste glass alkali-activated cement based binder (AACB) mortars with two biopolymers

The Roadmap to a Resource Efficient Europe aims that by 2020, waste will be managed as a resource. Thus materials that have the ability for the reuse of several types of wastes, such as alkali-activated cement-based binders (AACBs), will merit special attention. Some wastes like fly ash deserve special attention because they are generated in high amounts and have a very low reuse rate. This paper reports experimental results regarding the influence of the mix design of fly ash and waste glass AACB mortars containing two different biopolymers (carrageenan and xanthan) on their short-term mechanical performance. Microstructure and cost analysis are also included. The results show that a mixture of 80% fly ash, 10% waste glass, and 10% calcium hydroxide activated with an alkaline activator has the highest compressive strength. The results also show that the mortars with minor biopolymer carrageenan content are associated with a relevant increase in compressive strength and that the use of 0.1% of carrageenan leads to optimum compressive strength in most mixtures. The use of xanthan shows no beneficial effects on the compressive strength of AACB mortars. Several mixtures with xanthan even show a reduction in the compressive strength.The authors would like to acknowledge the financial support of the Foundation for Science and Technology (FCT) in the frame of project IF/00706/2014-UM.2.15.info:eu-repo/semantics/acceptedVersio

Shrinkage performance of fly ash alkali-activated cement based binder mortars

Some authors reported that Alkali-activated Cement Based Binder (AACB) mortars can have much higher drying shrinkage than Portland cement based composites. Its worth remember that shrinkage performance is a very important property for reinforced concrete composites just because a high shrinkage performance is associated to cracking tendency that leads to future durability problems. Usually shrinkage is assessed under unrestrained conditions. However, the use of a restrained ellipse ring test is especially interesting for materials that will be used in restrained conditions like repair mortars. This paper provides results on restrained and unrestrained shrinkage performance of fly ash AACB mortars. The restrained shrinkage was assessed with an elliptical ring that provides a faster and more reliable assessment of the cracking potential than circular rings. The results show that the mixtures with lower sodium silicate content are associated to a lower unrestrained shrinkage. Mixtures with lower sodium silicate content showed reduced average crack width under restrained conditions. The results also show that the reduction of sodium silicate content delays the appearance of cracks and is also associated to lower crack width. The use of AACB mortars in restrained conditions requires the use of a reduced sodium silicate content or else the use of fibres to prevent crack appearance.Foundation for Science and Technology (FCT): IF/00706/2014-UM.2.15info:eu-repo/semantics/acceptedVersio

Performance of waste based alkaline mortars submitted to accelerated carbon dioxide curing

Carbon dioxide sequestration is crucial for targets limiting global warming could be achieved. This paper discloses results of an investigation concerning the performance of fly ash/waste glass alkaline-based mortars with two additives and recycled aggregates exposed to accelerated carbon dioxide curing. Mechanical properties as well as water absorption, drying shrinkage and carbon sequestration potential were studied on it. The results show that the mixtures with calcium hydroxide and sodium hydroxide concentration of 8M leads to the highest compressive strength (10 MPa) which is high enough for the production of masonry blocks. Significant correlations between the flexural strength and the compressive strength were noticed. The mixtures show a low water absorption by immersion (9%) as well as by capillary (1.4 kg/m2.H0.5). The results of the modulus of elasticity show that increasing the sodium hydroxide molarity increased the stiffness of the mixtures. The results of drying shrinkage are in line with the results of the capillary water absorption and of the elastic modulus. A maximum CO2 sequestration (164 kgCO2eq/m3) is noticed for the mixture with a sodium concentration of 8 M based on the additive calcium hydroxide.The authors would like to acknowledge the financial support of the Foundation for Science and Technology (FCT) in the frame of project IF/00706/2014-UM.2.15.info:eu-repo/semantics/publishedVersio

Carbon dioxide sequestration of fly ash alkaline-based mortars containing recycled aggregates and reinforced by hemp fibres

Carbon dioxide sequestration is crucial so targets for limiting global warming can be achieved. This paper discloses results of an investigation concerning the performance of fly ash/waste glass alkaline-based mortars with recycled aggregates reinforced by hemp fibres exposed to accelerated carbon dioxide curing. Compressive strength, carbon footprint and cost were studied on it. The results show that hemp fibres lead to a reduction on mechanical properties but not as high as reported by others. A high correlation was found between compressive and flexural strength The results also show that accelerated curing provides a high carbon sequestration. Furthermore, the use of at least 8% hemp fibres leads to carbon negative emissions -19,7 kgCO2eq/m3 for fly ash/waste glass alkaline-based mortars with recycled aggregates based composites.The authors would like to acknowledge the financial support of the Foundation for Science and Technology (FCT) in the frame of project IF/00706/2014-UM.2.15.info:eu-repo/semantics/publishedVersio

Experimental and numerical investigations on the flexural performance of geopolymers reinforced with short hybrid polymeric fibres

Geopolymers have much higher drying shrinkage than Portland cement based composites Shrinkage performance is an important property for reinforced concrete composites just because a high shrinkage performance is associated to cracking tendency that leads to future durability problems. This paper provides results experimental and numerical investigations of fly ash based geopolymeric mortars reinforced with short hybrid polymeric fibres (SHPF). The results show that SHPF improved the flexural performance, while reducing the compressive strength and flexural stiffness of geopolymeric mortars. The addition of 0.8% SHPF increased about two times the fracture energy and about 50% the tensile strength. The adopted constitutive model well-captured the flexural performance of the tested beams.Foundation for Science and Technologyinfo:eu-repo/semantics/publishedVersio

Durability of alkali-activated binders: a clear advantage over Portland cement or an unproven issue?

The alkali activation of alumino-silicate materials is a complex chemical process evolving dissolution of raw materials, transportation or orientation and polycondensation of the reaction products. Publications on the field of alkali-activated binders, state that this new material is likely to have high potential to become an alternative to Portland cement. While some authors state that the durability of these materials constitutes the most important advantage over Portland cement others argue that it’s an unproven issue. This paper presents a review of the literature about the durability of alkali-activated binders. The subjects of this paper are resistance to acid attack, alkali–silica reaction, corrosion of steel reinforcement, resistance to high temperatures and to fire, resistance to freeze–thaw. Special attention is given to the case of efflorescences, an aspect that was received very little concern although it is a very important one

Eco-concrete: one-part geopolymer mixes

The geopolymerization of alumino-silicate materials is a complex chemical process evolving dissolution of raw materiais, transportation or orientation and polycondensation of the reaction products. Publications on the field of geopolymeric binders, state that this new material is likely to have high potential to become an altemative to Portland cement composites, Classical two part geopolymers could be made more eco-efficient with a lower carbon dioxide footprint if the use of sodium silicate is avoided. Besides current geopolymeric mixes can suffer from efflorescence originated by the fact that alkaline and/or soluble silicates that are added during processing cannot be totally consumed during geopolymerisation. Therefore new geopolymer mixes are needed. This paper presents experimental results on a novel kind of mixes termed one-part geopolymers. Compressive strength results and efflorescences observations show that the new mixes already analyzed are promissing