SEM image analysis in permeable recycled concretes with silica fume. A quantitative comparison of porosity and the ITZ

Recycled aggregates (RA) from construction and demolition can be used in permeable concretes (PC), improving the environment. PCs have a significant porous network, their cement paste and the interaction between the paste and the RA establishing their strength. Therefore, it is important to evaluate the porosity in the interfacial transition zones. The porosity of the cement paste, the aggregate and the interfacial transitional zones (ITZ) of a PC with recycled coarse aggregates (RCA) and silica fume (SF) is measured by means of image analysis–scanning electron microscope (IA)-(SEM) and by mapping the chemical elements with an SEM-EDS (energy dispersive spectrometer) detector microanalysis linked to the SEM and, as a contrast, the mercury intrusion porosimetry technique (MIP). In the IA process, a “mask” was created for the aggregate and another for the paste, which determined the porosity percentage (for the anhydrous material and the products of hydration). The results showed that using SF caused a reduction (32%) in the cement paste porosity in comparison with the PC with RA. The use of RA in the PC led to a significant increase (190%) in the porosity at different thicknesses of ITZ compared with the reference PC. Finally, the MIP study shows that the use of SF caused a decrease in the micropores, mesopores and macroporesPeer ReviewedPostprint (published version

Simulation and comparative analysis of waste in concrete slabs

Construction sector generates significant amounts of waste that affects the environment and obstructs a sustainable development. The horizontal structure (slabs and roofs) is one of the building elements, by its functional requirement (geometry and layout) and volume, who uses more raw material for its constitution (potential generators of waste) On the other hand, the choice of the system to use, is typically based on criteria such as the ease of construction, the economy availability or the technological feasibility; so, from a sustainable perspective, the generation of waste has not been considered or evaluated. This work compares and analyzes four different common elements used in slabs and the possible generation of waste produced for the construction and eventual demolition of them, in order to provide a new weighting criterion in the choice.Peer ReviewedPostprint (published version

Durability parameters of reinforced recycled aggregate concrete: Case study

Recycled concrete aggregate (RA) from pavement demolition was used to make concrete. Ten concrete mixtures with different replacement percentages of RA (coarse and fine) were made. The corrosion rate of steel and the electrical resistivity of concrete were determined on reinforced concrete specimens subjected to wetting-drying cycles (3.5% solution of NaCl). Corrosion rate was determined using the electrochemical technique of linear polarization resistance, while the electrical resistivity was measured by electrochemical impedance spectroscopy. The results show that the use of RA introduces more interfaces in concrete, which accelerates the steel corrosion process because the porosity increases and the electrical resistivity decreases. However, steel corrosion and the electrical resistivity in concrete are not significantly influenced by replacing a maximum 30% of coarse aggregate or 20% of fine aggregate with RA.Peer ReviewedPreprin

Simulation and comparative analysis of waste in concrete slabs

Construction sector generates significant amounts of waste that affects the environment and obsturcts a sustainable development. The horizontal structure (slabs and roofs) is one of the building elements, by its functional requirement (geometry and layout) and volume, who uses more raw material for its constitution (potential generators of waste) On the other hand, the choice of the system to use, is typically based on criteria such as the ease of construction, the economy availability or the tecnological feasibility; so, from a sustainable perspective, the generation of waste has not been considered or evaluated. This work compares and analyzes four different common elements used in slabs and the possible generation of waste produced for the construction and eventual demolition of them, in order to provide a new weighiting criterion in the choice.Peer ReviewedPostprint (published version

Influence of size reduction of fly ash particles by grinding on the chemical properties of geopolymers

Chemical properties of geopolymers were evaluated from the reduction of fly ash particle size by grinding. X-ray diffraction determined that at early curing ages new crystalline phases appear in the matrix of the geopolymer and they remain for 28 days, with increases in intensities up to 60%. In Fourier transform infrared spectroscopy, displacements were identified in the main band of the geopolymers at higher wavenumbers, attributed to the greater rigidity in the structures of the aluminosilicate gel due to the increase of the reaction products in the geopolymers obtained through fly ashsubjected to previous grinding, which is observable in the geopolymers matrix. Results indicate that the reduction of fly ash particle size by grinding has an influence on the chemical properties of geopolymers.Peer ReviewedPostprint (published version

Temperature for geopolymerization of fly ash. Mechanical behaviour

Alkali activation of fly ash (FA) is a chemical process which allows the transformation of the amorphous structure which makes up most of its particles, in compact cementitious skeletons geopolymers are called solid materials usually consist of a alkali hydroxide and solid precursor high content in silicon (Si) and aluminium. This paper presents the effect of temperature and the curing time in the alkali activation in FA pastes with 8M NaOH, geopolymers curing was carried out at room temperature, 60 °C and 80 °C at aged 7 14 and 21 days. Compression tests were conducted to obtain the strength of the geopolymer and analysis by X-ray diffraction to determine the new phases present resulting in higher compression resistance with higher temperature and curing time, a change was detected in the diffractogram because new phases present in the alkaline activation product.Peer ReviewedPostprint (published version

Analysis of the maturation process of geopolymer mortars

Mechanical and maturation of geopolymers mortars based on fly ash –FA¿ (FAM), properties are studied. The values of FAM in compressive strength were lower than conventional Portland cement mortars (PCM). For geopolymers were achieved in some cases compressive strengths up to 24.42 MPa, but in another study variables an abnormal behaviour was identified with loss of compressive strengths and elastic modulus (reaching only 14.51 MPa and 1.24 GPa). This behaviour can be attributed to a possible reaction between the aggregate and the alkaline medium, which appears to increase with +age of curing. Involvement implies that the reaction impedes or disrupts the geopolymerization process of FA, causing less compressive strength.Peer ReviewedPostprint (published version

Repercussion of mechanical behaviour in mortars with recycled aggregates by an overdose of PET additive

At present generation of domestic and industrial waste is a serious problem that must be controlled, so it is necessary to conduct further research of materials that minimize this problem by incorporating domestic and industrial waste in them; these materials must provide suitable properties, and perform the same function as the traditional material complies with virgin materials. This research focused on explaining the mechanical effects caused by overdose of unsaturated polyester resin made from post-consumer bottles made with polyethylene terephthalate (PET) (R-PET), cement-R- PET pastas and polymer modified mortars (PMM) with total or partial substitution of the recycled fine aggregate (AR) and additions of R-PET. The TGA and XRD results show that there is less development of the hydration products to a higher content of R-PET, causing reduction in the compressive strength of the PMM.Peer ReviewedPostprint (published version

Evaluation, comparison and differentiation of geopolymers by studying microstructural

Geopolymers are materials derived from an activation process materials with high content in silicon and aluminum, that in contact with an alkaline solution can acquire cementitious properties, and whose added value is to be environmentally friendly. This research have like objective to determine the efficiency of geopolymers using two different types of fly ash (FA) as a possible replacement of an alternative material to cement Portland (CP). The manufacturing process consisted of the FA activation using NaOH, the tests conducted included the chemical characterization of the FA through X-ray fluorescence (XRF) and X-ray Diffraction (XRD); as well as the determination of the compressive strength at various ages curing according to ASTM C10 and development of crystalline phases by XRD. The results showed that with increased age curing is achieved the development of resistance and the generation of crystalline phases, also acquiring compression strength above of 20 MPa at the age of 14 days cure.Peer ReviewedPostprint (published version

Carbonation rate and reinforcing steel corrosion of concretes with recycled concrete aggregates and supplementary cementing materials

Because of the significant environmental impact that the concrete production causes, and as sustainability contribution for this industry; presently some improvements are being implemented in its durability and its components are been replaced for alternative recyclable materials. Concrete carbonation is one of the main causes of reinforcement electrochemical corrosion. Coarse Recycled Concrete Aggregates (RCA) and Supplementary Cementing Materials (SCM) such as fly ash and silica fume were used to produce durable and environmentally friendly concrete and for the evaluation of its carbonation depth and carbonation-induced reinforcement corrosion when it is exposed to accelerated conditions. The depth of carbonation was observed by spraying a phenolphthalein solution on the fresh broken concrete surface. The corrosion rates of steel embedded in these concretes have been measured by the lineal polarization resistance technique. The results indicate that to use RCA and SCM increase the carbonation depth and corrosion current density.Postprint (published version