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.

The goal of this study was to generate a method to examine seasonal variability by climatic classification and Pacific seasonal factors to identify extreme wet and dry events in northern Mexico for the period 1952–2013. Using the standardized precipitation and evapotranspiration index (SPEI) on scales of three months (SPEI-3) and 24 months (SPEI-24), the variability of extreme wet and dry events were measured. The SPEI-3 and SPEI-24 anomalies were divided by the standard deviation (standardized Z anomalies). A Pearson correlation for SPEI-3, SPEI-24, Pacific decadal oscillation (PDO) and the oceanic El Niño index (ONI) was applied. Wet extreme events were recorded in 1954, 1968, 1976–1977, 1981, 1984, 1986 and 2003, of which the greatest magnitude was recorded in 1984 for the Sinaloa-very dry region. Extreme dry events were recorded in 1952–1953, 1990, 1997, 2003 and 2011–2013. The Z anomalies of the wet extreme events observed coincide with +PDO phase anomalies. In this study, the El Niño southern oscillation (ENSO) has little influence on wet and dry extreme events in northern Mexico. The negative phase anomalies of sea surface temperature (−SST) in the equatorial and eastern Pacific are indicators of extreme wet events. This study shows for the first time the influence of the PDO and the ONI on seasonal variability of extreme wet and dry events by climatic classification through the SPEI index in northern Mexico.

Currently it is necessary to find alternatives towards a sustainable construction, in order to optimize the management of natural resources. Thus, using recycled fine aggregate (RFA) is a viable recycling option for the production of new cementitious materials. In addition, the use of polymeric microfibers would cause an increase in the properties of these materials. In this work, mortars were studied with 25% of RFA and an addition of polyacrylonitrile PAN microfibers of 0.05% in cement weight. The microfibers were obtained by the electrospinning method, which had an average diameter of 1.024 µm and were separated by means of a homogenizer to be added to the mortar. Cementing materials under study were evaluated for compressive strength, flexural strength, total porosity, effective porosity and capillary absorption, resistance to water penetration, sorptivity and carbonation. The results showed that using 25% of RFA causes decreases mechanical properties and durability, but adding PAN microfibers in 0.05% caused an increase of 2.9% and 30.8% of compressive strength and flexural strength respectively (with respect to the reference sample); a decrease in total porosity of 5.8% and effective porosity of 7.4%; and significant decreases in capillary absorption (approximately 23.3%), resistance to water penetration (25%) and carbonation (14.3% after 28 days of exposure). The results showed that the use of PAN microfibers in recycled mortars allowed it to increase the mechanical properties (because they increase the tensile strength), helped to fill pores or cavities and this causes them to be mortars with greater durability. Therefore, the use of PAN microfibers as a reinforcement in recycled cementitious materials would be a viable option to increase their applications.

The coastal city of Guasave, Sinaloa, located on the Mexican Pacific coast, is subject to extreme precipitation events, which have caused flooding with damage to the city’s infrastructure. The factors that influence flooding are vegetation, geology, degree of soil saturation, drainage characteristics of the watershed, and the shape of the topographic relief. Of the above factors, the topographic relief, which is the subject of the study, has been partially modified in some areas by infrastructure works (from 20.2 m to 17.6 m), and the population of the urban area has grown by 51.8% in 17 years (2004–2021); therefore, the objective is to evaluate the potential flood risk due to changes in this factor and the growth of the urban area. When using this method, the potential flood risk was determined considering four extreme events, 1982, 1990, 1998, and 2019. It was found that the potential risk increases for the whole city, being more intense in sector III, which, before the modification of the topographic relief, was the area with the lowest risk of flooding. In an extreme event such as Hurricane Paul in 1982, practically the entire city would be flooded.