Study of red ceramic residues as pigments in matrices based on white Portland cement

ABSTRACT: The present study evaluated the use of red ceramic residues (RCR) as pigments in matrices based on White Portland cement. Five mortars were prepared for the present study: control mortar (M0), at 1:2,3 ratio (cement: sand) and water/cement ratio of 0.60, other four mortars were prepared containing RCR in 10% (M10), 20% (M20), 50% (M50), 100% (M100) of volume in replace to the sand. Colorimetric tests indicated a significant increase in the coloring, due to the increase of the RCR used. Tests of resistance to compression strength indicated a significant increase in the results as there was an increase in the substitution content of the sand by RCR. In the flexural tensile strength was no significant influence for contents of up to 50%. Therefore, the RCR showed potential as a pigmentation product and can contribute to the increase in compressive strength in Portland cement-based matrices.

CONCRETO PRODUZIDO COM AGREGADO GRAÚDO LATERÍTICO EM SANTARÉM, PARÁ

RESUMO: Avaliou-se a substituição da brita basáltica existente no concreto por material alternativo em abundância no município de Santarém-PA: a laterita. Foi avaliado o desempenho do concreto incorporado com agregado laterítico in natura em substituição parcial ao agregado graúdo de brita basáltica nos teores de 20% e 50%. Realizou-se a caracterização dos agregados graúdo e miúdo. De acordo com o método da ABCP, determinou-se o traço de referência em massa 1:1,71:3,03:0,53; confeccionou-se corpos-de-prova cilíndricos 10x20 cm utilizando 3 traços diferentes, de modo a substituir a brita basáltica pelo agregado laterítico, em 20% e 50%. Para cada traço foram quantificados a sua consistência, por meio do ensaio de abatimento do tronco de cone, resistência à compressão axial, resistência à tração por compressão diametral e módulo de elasticidade aos 28 dias. A substituição do agregado convencional de brita basáltica por agregado laterítico em seu estado natural promoveu diminuição da resistência a compressão simples, da resistência à tração por compressão diametral e do módulo de elasticidade com a inclusão do agregado laterítico na mistura. Destaca-se que acima de determinado teor de substituição o concreto torna-se inviável devido a necessidade de adicionar aditivo plastificante para manter a consistência desejada e que as duas misturas incorporadas com agregado laterítico se mostraram muito semelhantes após os 28 dias, no que tange a ganhos de resistência a compressão. ABSTRACT: This study is about the replacement of basaltic origin crushed stone by alternative material present in the municipality of Santarém, Pará State: the laterite. The aim were to evaluate the performance of concrete incorporated with natural lateritic aggregate, replacing the of crushed stone in 20% and 50%. The first stage was characterizing the coarse and fine aggregates that made up the studied concrete. According to ABCP dosing method it was determined the mass reference trait 1: 1.71: 3.03: 0.53; bodies of 10x20 cm were made for cylindrical test, using three different strokes so that the basaltic crushed stone gradually replaced by the lateritic aggregate in proportions of 20% and 50%. For each trait its consistency was quantified by means of the tapering test, axial compression strength, diametric compression tensile strength and the modulus of elasticity at 28 days. Was observed that the replacement of the conventional aggregate basalt crushed stone for aggregate of laterite in natural state promoted a decrease in the value of simple compressive strength, diametric tensile strength and modulus of elasticity with inclusion of a larger amount of lateritic aggregate in the mixture. It is noteworthy that above a certain substitution content, the concrete becomes not feasible due to the need for a large increase in the amount of plasticizer additive to the desired consistency is maintained and the two blends incorporated with lateritic showed very similar after 28 days in terms of gains in compressive strength.

Substitutions of Zr4+/V5+ for Y3+/Mo6+ in Y2Mo3O12 for Less Hygroscopicity and Low Thermal Expansion Properties

In this investigation, ZrxY2−xVxMo3−xO12 (0 ≤ x ≤ 1.4) is developed and the effects of the substitutions of Zr4+/V5+ for Y3+/Mo6+ in Y2Mo3O12 on the hygroscopicity and thermal expansion property are investigated. For the smaller substitution content (x ≤ 0.5), their crystal structures remain orthorhombic, while there is crystal water still in the lattice. The linear coefficients of thermal expansions (CTEs), for x = 0.1, 0.3, 0.5, and 0.7, are about −4.30 × 10−6, −0.97 × 10−6, 0.85 × 10−6, and 0.77 × 10−6 K−1, respectively, from 476 to 773 K, which means that the linear CTE could be changed linearly with the substitution content of Zr4+/V5+ for Y3+/Mo6+ in Y2Mo3O12. As long as the substitution content reaches x = 1.3/1.4, almost no hygroscopicity and low thermal expansion from room temperature are obtained and are discussed in relation to the crystal structure and microstructure.

Determination of the optimal replacement content of Portland cement by stone powder using particle packing methods and analysis of the influence of the excess water on the consistency of pastes

Cement is considered the basic component with the highest environmental impact in construction, in terms of CO2 emissions. As for the aggregates, the process of comminution of rocks, in addition to artificial sand, generates stone powder that ends up being stored outdoors, generating environmental damages. Thus, the replacement of cement by stone powder appears as an attractive alternative towards the sustainable concretes. In this context, the objective of this paper is to determine the maximum packing density in Portland cement, silica fume and stone dust pastes, to determine the optimal cement substitution content for the stone powder. In addition, it is intended to verify the influence of excess water on the consistency of the mixtures produced. The substitution was done in contents equal to 0%, 7%, 14% and 21% by volume and, for each content, the packing density was determined analytically by CPM model and combinations were reproduced experimentally. Excess water was checked by the mini Kantro cone test. The results showed that the higher cement substitution content of the stone powder obtained the higher packing density, experimental and analytical, and the higher workability, allowing economic and environmental advantages. Analyzing each material, the stone powder resulted in the highest packing density and silica fume is the lowest one. Therefore, finer particles resulted in lower packaging densities, due to the greater specific surface area, which demands more water. The agglomeration resulted in more empty gaps between the grains. In addition, mixtures flowability increased with the increase of the stone powder content. As the excess water is responsible for mixture lubrication, a higher packing density for a given volume of water improves the flowability.

Structure and Electrochemical Impedance of LiNi\(_{x}\)Mn\(_{2 - x}\)O\(_{4}\)

Ni-substitution spinel LiNixMn2−xO4 (x = 0, 0.1, 0.2) materials were synthesized by the sol--gel method. The structure and morphology of the samples were characterized by the X-ray diffraction (XRD) and the scanning electron microscopy. The ac conduction of the materials was investigated by electrochemical impedance spectroscopy (EIS) measurements. The refinement results showed that the substitution of Ni decreased the lattice constant and Mn--O distance, while increased Li--O bond length and 16c octahedral volume. The EIS results confirmed the decrease of conductivity with increasing Ni substitution content. Based on XRD and EIS results, the relationship between the crystal structure and electrochemical behavior of the materials was discussed and explained.

Measurement and Comparison of Pozzolanic Activity of Siliceous Materials Using Mechanical Tests

The classification of mineral additives used in cementitious materials is dependent on many factors such as morphology and composition, but it also depends on the kinetics of the reaction with calcium hydroxide, also known as its pozzolanicity. Several tests are used to evaluate the reactivity of siliceous material in the presence of calcium hydroxide, but some of these tests are not quantitative and there is no known correlation between the results of the various tests. Therefore, this study presents the results of compression and bending tests of samples containing different levels of substitution of cement by siliceous materials. Ground quartz, silica fume, and a silica-rich industrial waste at work were used. The results show that the mechanical tests are more affected by the substitution content than by the nature of the substitution.

Excess conductivity analysis for Y3−xNdxBa5−xCaxCu8O18−δ superconducting phase

Superconducting samples of type [Formula: see text] substituted by both [Formula: see text] and [Formula: see text] ions were prepared by a solid-state reaction technique. These substitutions affect the phase formation, lattice parameters, grains formations and superconducting transition temperature [Formula: see text]. The change in these parameters is mainly due to the partial substitution of [Formula: see text] by [Formula: see text] ions rather than the partial substitution of [Formula: see text] by [Formula: see text] ions. The analysis of the electrical resistivity [Formula: see text] versus temperature above [Formula: see text] was carried out using Aslamazov–Larkin (AL) and Lawrence–Doniach (LD) models. Different fluctuation regions starting from high temperature up to [Formula: see text] were estimated, and denoted by short-wave (sw), two-dimensional (2D), three-dimensional (3D) and critical (cr) fluctuations. A distinct crossover temperature [Formula: see text] from 2D to 3D, in the mean field region (MFR), is shifted to lower temperature by increasing substitutions content. The superconducting parameters such as zero temperature coherence length along the [Formula: see text]-axis [Formula: see text], inter-layer coupling strength [Formula: see text], Fermi velocity [Formula: see text] of the carriers and Fermi energy [Formula: see text] were calculated as a function of substitution content.

Effects of Fly Ash and Granular Blast-Furnace Slag on Development Rate of Strength of Concrete

Fly ash (FA) and granular blast-furnace slag (GBFS) are usual mineral admixtures to conventional concrete, and their contents substituted for Portland cement definitely affect development rate of strength of concrete. C30 and C60 concrete samples with FA and/or GBFS were prepared to study the influence of substitution content of the mineral admixtures on 3 d, 7 d and 28 d strength. The results reveal that the development rate of strength in period from 3 d to 7 d gets slow with increasing content of mineral admixtures except for concrete with only GBFS less than 20%. In the case of substituting FA as the only mineral admixture for part of cement, the development rate of strength of C30 concrete in period from 7 d to 28 d keeps roughly constant even that of C60 concrete increases. When substituting mineral admixtures in the presence of GBFS for cement within experimental range, the development rate of strength in period from 7 d to 28 d gets fast with increasing substitution content. The enhancing effect of combining FA and GBFS occurs in period from 7 d to 28 d for both C30 and C60 concretes (FA+GBFS≤40%), even occurs in period from 3 d to 7 d for C60 concrete. Based on 7 d strength and the development rate, 28 d strength of concrete can be predicted accurately.