Search

The use of geopolymers has revolutionized research in the field of construction. Although their carbon footprint is often lower than that of traditional mortars with Portland cement, activators such as sodium silicate have a high environmental impact in the manufacturing of materials. Employing alternative alkali sources to produce geopolymers is necessary to obtain materials with a lower carbon footprint. The present research explores the use of rice husk ash (RHA) as an alternative source of silica to produce alkaline activators by four methods: reflux; high pressure and temperature reaction; thermal bath at 65 °C; and shaking at room temperature. To evaluate the efficiency of these methods, two types of experiments were performed: (a) analysing silica dissolved by the filtering/gravimetric method; and (b) manufacturing mortars to compare the effectiveness of the treatment in mechanical strength terms. The percentages of dissolved silica measured by the gravimetric method gave silica dissolution values of 70–80%. The mortars with the best mechanical strength results were the mixtures prepared with the thermal bath treatment at 65 °C. Mortar cured for 1 day (at 65 °C), prepared with this activator, yielded 45 MPa versus the mortar with commercial reagents (40.1 MPa). It was generally concluded that utilising original or milled RHA in preparing activators has minimal influence on either the percentage of dissolved silica or the mechanical strength development of the mortars with this alternative activator.

The granulometric distribution of the aggregates used in pervious concrete can significantly impact its mechanical and hydraulic properties by modifying granular skeleton and pore distribution. The unit weight increases when single-sized aggregates are combined, which results in improved mechanical properties. In this study, the maximum density methodology was applied to enhance pervious concrete’s mechanical strength by using three narrow-sized basaltic aggregates and their combination. The experimental results showed that the mechanical performance of the samples created with packed aggregates improved compressive strength by up to 81.2% and the energy support impact was higher than 225 J (50% higher than the reference sample) after curing for 28 days. Although the densification of packing aggregates increased, the greatest reduction in porosity was 24.3%. The lowest infiltration rate was 0.43 cm/s, a satisfactory value according to the literature. These findings suggest that the aggregates packing methodology is effective in producing optimized and sustainable pervious concretes.

[EN] Computer tools have been evolving at an incredible speed in education, especially at the university level. Twenty-five years ago, in university education, there were just beginning to be computer practices based mainly on tools such as Excel in experimental university careers. Today, thanks to the advance in technology, the radiography of universities are very different. Most students come to school daily with their laptops and tablets to college. They are part of the generations called "digital natives.¿ As higher education teachers, we cannot be oblivious to this reality, and we must rethink how to adapt teachings to the daily use of computer technologies. It also means being closer to the procedure these students will follow later when they are professionals in their field. This paper deals with the work done by the Construction Materials unit of the Civil Engineering School to adapt the dosage of concrete to the use of Excel, which was carried out with manual calculations using a calculator until this academic year. Expressly, the use of the Excel spreadsheet was limited to obtaining aggregate granulometric curves from the mixture of several of them so that they were as similar as possible to a series of theoretical curves through the use of equitable adjustments based on the use of a spreadsheet. The teacher's challenge in the classroom is twofold. On the one hand, he has the task of making the students understand the factors and limitations to be considered when carrying out concrete batching. On the other hand, it is to explain the use of a specific tool of the Microsoft "Excel" software to know how a least squares adjustment can be carried out. The present work explains in detail the challenges faced by the teachers, as well as the advantages and disadvantages of moving from a manual procedure (slower, more laborious, and with more room for thought) to a computerized process (more automatic and faster). The latter is how future civil engineers will carry out their work. The advantages of using this type of tool and the main problems detected in the students related to understanding the procedure they are carrying out will be indicated.

Made available in DSpace on 2022-04-28T19:53:00Z (GMT). No. of bitstreams: 0 Previous issue date: 2022-07-15 Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) This study evaluated the compressive strength performance and microstructure of binary blast furnace slag-sewage sludge ash (BFS-SSA) alkali-activated mortars, in which rice husk ash (RHA) was dissolved in NaOH solution to replace commercial sodium silicate. The dissolution of RHA, performed in a thermal bottle with NaOH solution, enhanced the compressive strength of the alkali-activated mortars based on BFS up to 4.5-fold. BFS-SSA based mortars (10–40% SSA), activated with NaOH/RHA-based sodium silicate suspensions, reached a compressive strength up to 30 MPa after 28 curing days at 20°C. The RHA dissolution enhanced the strength and sustainability of the BFS-SSA alkali-activated mortars. Universidade Estadual Paulista (UNESP) Faculdade de Engenharia de Ilha Solteira MAC – Grupo de Pesquisa em Materiais Alternativos de Construção, SP ICITECH – Instituto de Ciencia y Tecnología del Hormigón Universitat Politècnica de València (UPV) Universidade Estadual Paulista (UNESP) Faculdade de Engenharia de Ilha Solteira MAC – Grupo de Pesquisa em Materiais Alternativos de Construção, SP

[EN] This work studies the possibility of using geopolymer materials to enhance the mechanical and durability properties of hydrated lime¿pozzolan mixtures, which gave rise to the so-called ¿hybrid systems¿. Two different waste types were used as pozzolan in the lime¿pozzolan system: rice husk ash (RHA) and spent fluid catalytic cracking (FCC). The geopolymer fabricated with FCC was activated with commercial reagents (NaOH and Na2SiO3), and also with alternative sources of silica to obtain a lower carbon footprint in these mixtures. The alternative silica sources were RHA and residual diatomaceous earth (RDE) from the beer industry. The geopolymer mixture substituted the lime¿pozzolan mixture for 30% replacement in weight. The hybrid systems showed better mechanical strengths for the short and medium curing ages in relation to the lime¿pozzolan mixtures. Thermogravimetric analyses were performed to characterise the types of products formed in these mixtures. In the durability studies, hybrid systems better performed in freeze¿thaw cycles and obtained lower capillarity water absorption values., This research forms part of a project supported by MINECO and FEDER funds (ECOSOST RTI2018-097612-B-C21-AR).

[EN] In the last decade, herbaceous and agricultural biomass have been used as an alternative energy source. As consequence, large amounts of residual ashes containing potassium (potassium-rich ashes) have been generated. Olive biomass ash (OBA) and almond shell ash (ABA) have been successfully used as alkali source in the alkaline activation of ground granulated blast furnace slag (BFS). This study focuses on the production of new and alternative alkaline activators for BFS systems using nutshell ashes (NBA), mango seed-bark ashes (MBA) and hazelnut shell ashes (HBA). The chemical and mineralogical composition of these ashes were assessed and, the mechanical and microstructural properties of BFS pastes activated with NBA, MBA and HBA were evaluated. The results indicated that all assessed materials are potassium-rich ashes differing mainly on the amount of CaO and P2O5. The compressive strength of BFS pastes yielded about 26 MPa and, according to FESEM/EDS analysis, K2O (in the range 8.03¿24.33%) replaces chemical bounded Ca+2, forming C-(K)-A-S-H gel., We thank the Spanish Government MINECO and FEDER for funding the ECOSOST RTI-2018-097612-B-C21 Project.

Los cementos de activación alcalina (CAA) requieren de un componente alcalino para la activación del precursor. La fabricación del activador alcalino (AA) supone un consumo energético y de materias primas muy importante, de modo que la huella de carbono de los CAA está fundamentalmente influenciada por ese factor. Una alternativa es el uso de otras materias para la preparación del AA. En este trabajo se realiza un exhaustivo análisis de las diferentes alternativas: materias de base silícea para la preparación de silicatos alternativos y materias de base alcalina. Se comparan de forma relativa las huellas de carbono con respecto a cementos Portland comerciales, y se analiza el efecto que tiene la sustitución de reactivos comerciales por activadores alternativos.

The aim of this study was to use the electrical impedance spectroscopy technique (IS) to carry out a systematic study on the mechanism of metakaolin geopolymerization for up to 7 curing days. The study was developed on two batches of metakaolin (MK), and their reaction processes were compared. Interpretative fundamental elements were developed based on the effective electrical conductivity curves regarding the metakaolin geopolymerization. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) were previously carried out and used to interpret and validate the electrical behavior of the fresh and hardened MK-based geopolymer pastes. The results highlighted the sensibility of the impedance technique to the identification and description of the MK geopolymerization process, as well as the changes resulting from even slight variations in the metakaolin composition. Furthermore, this indicated that the geopolymerization process in highly alkaline solutions could be divided into seven stages, including the processes of dissolution, nucleation, precipitation and formation of the gel and, eventually, the retraction/microcracks constitution. Late dissolution processes could be observed during the more advanced stages and were attributed to particles not being fully hydrated.

Large amounts of waste are derived not only from construction processes, but also the demolition of existing buildings. Such waste occupies large volumes in landfills, which makes its final disposal difficult and expensive. Reusing this waste type is generally limited to being employed as filler material or recycled aggregate in concrete, which limits its valorisation. The present work proposes reusing construction and demolition waste to manufacture alkali-activated cement to improve its sustainability and recovery. Construction and demolition waste (C&DW) from a demolition waste collection plant in Valencia (Spain) was physically and chemically characterised. This residue contained large fractions of concrete, mortar, bricks, and other ceramic materials. X-ray fluorescence (XRF) analysis showed that its chemical composition was mainly CaO, SiO2 and Al2O3. X-ray diffraction (XRD) analysis revealed that it presented some crystalline products, and quartz (SiO2) and calcite (CaCO3) were the main components. Blends of C&DW and blast furnace slag (BFS) were alkali-activated with mixtures of sodium hydroxide and sodium silicate. The corresponding pastes were characterised by techniques such as thermogravimetry and scanning electron microscopy (SEM). The alkali-activated mortars were prepared, and the resulting mortars’ compressive strength was determined, which was as high as 58 MPa with the 50% C&DW-50% BFS mixture. This work concluded that it is possible to make new sustainable binders by the alkali activation of C&DW-BFS without using Portland cement.

Three-dimensional printed concrete (3DPC) is a relatively recent technology that may be very important in changing the traditional construction industry. The principal advantages of its use are more rapid construction, lower production costs, and less residues, among others. The choice of raw materials to obtain adequate behavior is more critical than for traditional concrete. In the present paper a mixture of cement, silica fume, superplasticizer, setting accelerator, filler materials, and aggregates was studied to obtain a 3DPC with high resistance at short curing times. When the optimal mixture was found, metallic fibers were introduced to enhance the mechanical properties. The fresh and hard properties of the concrete were analyzed, measuring the setting time, workability, and flexural and compressive strength. The results obtained demonstrated that the incorporation of fibers (2% in volume) enhanced the flexural and compressive strength by around 163 and 142%, respectively, compared with the mixture without fibers, at 9 h of curing. At 28 days of curing, the improvement was 79.2 and 34.7% for flexural and compressive strength, respectively.