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The incorporation of supplementary fine materials into mortars and concretes is a common strategy employed to enhance both their rheological and mechanical properties. While organic molecule-based admixtures are primarily utilized to regulate the setting time in pre-mixed concretes and mortars, their effects become more intricate in the presence of fine materials. This study delves into the interplay between flowability and setting times of cement pastes with 50 wt% of fines (basalt filler, fly ash and quartz filler) in place of cement and three organic admixtures at 0.5 % and 1.0 % (wt% of cement). The results unveil compelling insights: the incorporation of retarding additives proves notably advantageous, markedly decreasing viscosity and prolonging the initial stage of paste formation by as much as 305 h. Nevertheless, the efficacy of these additives diminishes significantly in the presence of fine particles, especially when utilizing basalt filler. This prompts an in-depth exploration into the intricate interactions transpiring between the fine materials and the setting retardants. The implications of these interactions underscore their pivotal role in refining the application of retarding additives in scenarios involving fine materials.

The alumina industry produces the red mud (RM) as one of its by-products. The red mud waste has pozzolanic potential, mainly when calcined at 600oC. In this paper, the microstructure of cement pastes constituted by 15% of dry and calcined red mud at 600, 700, 800 and 900oC were investigated by scanning electron microscopy analysis. To assess the evolution of the heat of hydration of pastes produced with until 15% of red mud in replacing the cement was used a semi-adiabatic calorimeter. Water absorption by capillarity and wetting angle tests were realized on mortars constituted by 5 and 10% of red mud in replacement of cement. The images of the microstructures of the pastes produced with red mud showed the formation of the hydration products calcium silicate hydrate, fase AFm (monosulfate) and ettringite. The pastes produced with 5, 10 and 15% red mud showed higher heat of hydration than the reference pastes (only cement). The mortars produced with 5% of dry and calcined red mud at 600, 700, 800 and 900oC showed lower sorptivity than the reference mortar. The results shown that the replacement of the cement by red mud waste influence in the hygrothermal and microstructural properties of cementitious composites.

A fine fraction of recycled aggregates from the processing of construction and demolition waste (CDW), have a very effective potential use in mortar as a partial fine aggregate replacement for natural sand, an also contribute to the development of sustainable materials, specifically to produce coating mortar. This paper presents the results of a study using recycled aggregate in mortar as a replacement for natural sand, analyzing the effects of pre-wetting and the performance in mortar composition with a fine sand (1.2/ 0.15 mm). In this study was investigated the behavior of recycled aggregate dry and wet previously until to saturated surface dry condition (reaching this value by capillary absorption test of the granulometric prepared curve). Five different compositions have been defined, varying the quantity of fine and determined the physical properties of recycled aggregate. Then the mortars were prepared and evaluated in the fresh state: specific gravity, water retention and workability, and in the hardened state: hygrothermal and mechanical properties. The results showed that the wetting of the aggregate affects the properties of the mortar, as well the addition of fines. There is an advantage when is realized wetting of the recycled aggregate CDW. The addition of fine in mortars must be controlled, and the fine aggregates improved the almost properties and in excess can reduce the hygrothermals properties.

The building materials are evaluated for their mechanical behavior, durability and most recently, about the risk of environmental contamination. Some heavy metals can be found in the waste added in cementitious matrices. The techniques of introducing the wastes in cementitious matrices allow the stabilization and solidification of the contaminants. However, this immobilization should be monitored and the effectiveness of this method is investigated by carrying out leaching tests, among other procedures. The objective of this study was to analyze the influence of heavy metals in the hydration process of cementitious matrices by way of tank tests carried out on mortar, previously contaminated with the heavy metals Zn2+, Cr3+ and Pb2+ at a concentrations of 20, 40, 80 and 160 ppm and to propose the use of electrical impedance spectroscopy (EIS) coupled to represents the leaching mechanisms. In the electric test was used an alternating current, varying the frequency of 200 kHz to 2 MHz. For assess the leaching behavior were performed the tank test (NEN 7375). The results showed that the heavy metals how the zinc and lead, can retard the setting time of the mortars and this was observed in the impedance spectrums throughout cure time of mortars. During the tank test the electrical impedance of the contaminated mortars were lower than the reference mortar and the output of portlandite caused an increase in the electrical impedance values. The electrical test is a not destructive technique, faster than the leaching tests and in the future, it can be performed to aid environmental testing.

On a global scale, thermoelectric energy remains the main source of the energy industry. This process results in a large amount of coal waste. Among them, the bottom ash still has no suitable application in civil construction and usually is discarded in sedimentation basins. The objective of this investigation is to evaluate the valorization of bottom ash in alkali activation pastes. Rheological, mechanical, microstructure, and durability properties were assessed for application to external structures. Bottom ash and metakaolin were used as aluminosilicate and as an alkaline solution a mixture of sodium silicate and NaOH was made. A room temperature cure was adopted for all the samples. The findings show that the alkali activation of bottom ash (BA) was not satisfactory to achieve minimum strength and durability. BA samples require supplementation to improve its mechanical and durability properties. At 28 days of reaction, the formation of superficial cracks was observed, which contributed to the deterioration in the durability tests. However, metakaolin and bottom ash (MKBA) mixtures resulted in the best performance. It was observed an increase of reaction degree and compressive strength (47.9 MPa at 28 days), greater development of thermal conductivity, and reduced deterioration through wetting and drying cycles, marine environments, and sulfate attack.