ABSTRACT
Obtained natural sands can present different particle size distributions (PSD), although they have the same mineralogical origin. These differences directly influence the physical and mechanical behavior of mortars and, therefore, the performance of mortar and ceramic renderings. Standardizing the particle size of sands based on pre-established requirements in normative standards (NBR 7214 or ASTM C778) is one way to minimize these effects. However, these standards do not consider the optimization of the granular skeleton through the analysis of bulk density and PSD, which may be insufficient to obtain satisfactory results. Therefore, this paper analyzes the effects of using different particle size ranges on the physical and mechanical behavior of cement and hydrated lime mortars. The properties of consistency index, bulk density, air content, capillary water absorption, water absorption by immersion, flexural strength, compressive strength, and dynamic modulus of elasticity were evaluated. For this purpose, standardized sands of the same mineralogical origin were made with different particle size ranges, being: (i) standardized sand constituted by 25% of coarse and fine fractions (S25-control), (ii) standardized sand constituted by 30% of coarse fraction and 20% of fine fraction (S30-20), and (iii) standardized sand composed by 40% of coarse fraction, and 10% of fine fraction (S40-10), respectively. The results indicated that variations in the particle size composition of the standardized sands are necessary to obtain mixtures with higher compactness and, therefore, mortars with better physical and mechanical performance. Thus, the dosage of the particle size fractions of standardized sand should consider the optimization of the granular skeleton, being the unit mass and the granulometric composition as important parameters to meet this premise.
ABSTRACT
In this work, the natural and modified carnauba powder from the addition of bentonite was evaluated for the adsorption of Cu(II) ions in synthetic solution. The results showed that the carnauba powder treated with bentonite (CPTB) showed a better percentage of removal of Cu(II) ions when compared to natural carnauba powder (NCP). The best results for both adsorbents were obtained with pH 5. The adsorption kinetics was governed by the pseudo-second-order model for both bioadsorbents studied. While the isothermal behavior was governed by the Langmuir model and showed that the adsorption capacity of the CPTB for Cu(II) was 21.98 mg·g-1. The interaction of the metal and CPTB was also investigated by means of thermodynamic parameters showing that the adsorption process is not spontaneous, although the values of ΔG° decrease with the increase in temperature from 20 to 40 °C and endothermic causing an increase in the degree of disorder at the solid/liquid interface. The results showed that the CPTB is a material with potential adsorbent for the removal of copper ions.
