Abstract: This paper presents the evaluation of lightweight concrete masonry blocks, incorporated with tire rubber and metakaolin, aiming reduce its bulk density and obtaining dimensional values of compressive strength and water absorption in according to the Brazilian standard (ABNT NBR 6136, 2016). Three mixtures of concrete were produced by the replacement of 9%, 18% and 27% (by volume) of the fine aggregate by tire rubber, and one mixture without rubber (reference). In all mixtures the procedure of replacing 10% (by weight) of cement to metakaolin was adopted. Family M-15x30 of concrete blocks were performed using an entirely manual process, with PVC molds and PET bottle devices to casting the hollow characteristic of blocks. The results indicated that the concretes produced with rubber and metakaolin provided bulk density values lower than 2000 kg/m³, thus featuring lightweight concrete characteristics. In the dimensional verification, all the blocks series produced reached of requirements of the current standard. Although only the R0, R1 and R2 series had structural function, however all mixtures achieved water absorption ratio lower than 13%. Therefore, the tire rubber as fine aggregate in concrete masonry blocks is thought to be a good alternative for reuse of this waste material.

Resumen: Este artículo evalúa bloques de mampostería de hormigón liviano, a los cuales se les ha incorporado caucho y metacaolín con el objeto de reducir su densidad aparente y obtener valores dimensionales de resistencia a la compresión y absorción de agua, en conformidad con la norma brasileña (ABNT NBR 6136, 2016). Se fabricaron tres mezclas de hormigón, reemplazando el 9%, 18% y 27% (en volumen) del agregado fino por caucho de neumáticos y además una mezcla sin caucho (referencia). En todas las mezclas, se adoptó el procedimiento de reemplazar el 10% (en peso) de cemento por metacaolín. Los bloques de hormigón del tipo M-15x30 se fabricaron manualmente, utilizando moldes de PVC y elementos de botellas PET para moldear huecos de los bloques. Los resultados indican que los hormigones fabricados con caucho y metacaolín arrojan valores de densidad aparente menores a 2000 kg/m3, presentando así características de hormigón liviano. En cuanto al análisis de las dimensiones, todas las series de bloques producidas cumplieron con los requisitos de la norma vigente. Si bien solo las series R0, R1 y R2 tienen función estructural, todas las mezclas obtuvieron tasas de absorción de agua inferiores al 13%. Por lo tanto, se considera que el caucho de neumáticos como agregado fino en los bloques de hormigón es una buena alternativa para reutilizar este material de desecho.

Abstract: Gypsum is the oldest synthetic construction material that is known, however it is a material about which there is little knowledge at the level of research, and in this work its study took place by making composites with the incorporation of rubber tires, aiming to obtain an alternative construction material. Thus, the objective was to investigate gypsum-based composites, with a mass incorporation of 5, 10, and 15% of two grades of vulcanized rubber residue from tire retreading processes. The granulometries are referred to as thin (sieve pass-through #0.60 mm) and thick (sieve pass-through #1.19 mm). The composites were investigated in terms of consistency (mini-slump), mass density, water absorption, surface hardness, flexural strength, compressive strength, scanning electron microscopy (SEM), and thermal behavior. The results revealed that rubber incorporation can be attractive in gypsum composites: in which the consistency decreased with the increase of the rubber content and the thick rubber granulometry favored the workability of the composites; the mass density was reduced, mainly with thin granulometry, as the rubber content in the composites increased; the water absorption showed that the high levels of rubber favor the penetration of water in the composites, regardless of the granulometry; the surface hardness showed reduced impact energy provided by the composite with 10% thin rubber; in both flexural strength and compression, the composite with 5% thin rubber showed a similar result to the control composite, while composites with 15% rubber suffered a gradual drop of up to 60 and 40%, respectively; with SEM it was observed that the thin rubber composites had smaller pores, in addition to more effective adhesion between the rubber particles; finally the rubber helps to reduce the thermal amplitudes during the day, mainly with the increase of the particle size and the rubber content.

Resumen: El yeso es el material de construcción sintético más antiguo que se conoce, sin embargo, es un material sobre el cual hay poco conocimiento a nivel de investigación, y en este trabajo su estudio se realizó haciendo compuestos con la incorporación de neumáticos de goma, con el objetivo de obtener un material de construcción alternativo. El objetivo era investigar los compuestos a base de yeso, con una incorporación en masa de, 5, 10 y 15%, de dos grados de residuos de caucho vulcanizado de los procesos de recauchutado de neumáticos. Las granulometrías se denominan delgadas (paso de tamiz # 0.60 mm) y gruesas (paso de tamiz # 1.19 mm). Los compuestos se investigaron en términos de consistencia (mini-asentamiento), densidad de masa, absorción de agua, dureza superficial, resistencia a la flexión, resistencia a la compresión, microscopía electrónica de barrido (SEM) y comportamiento térmico. Los resultados revelaron que la incorporación de caucho puede ser atractiva en los compuestos de yeso: donde la consistencia disminuyó con el aumento del contenido de caucho y la granulometría de caucho grueso favoreció la trabajabilidad de los compuestos; la densidad de masa se redujo, principalmente con granulometría delgada, a medida que aumentó el contenido de caucho en los compuestos; la absorción de agua mostró que los altos niveles de caucho favorecen la penetración de agua en los compuestos, independientemente de la granulometría; la dureza superficial mostró una energía de impacto reducida proporcionada por el compuesto con 10% de goma delgada; Tanto en la resistencia a la flexión como en la compresión, el compuesto con 5% de goma delgada mostró un resultado similar al compuesto de control, mientras que los compuestos con 15% de goma sufrieron una caída gradual de hasta 60 y 40%, respectivamente; con SEM se observó que los compuestos de caucho fino tenían poros más pequeños, además de una adhesión más efectiva entre las partículas de caucho; finalmente, el caucho ayuda a reducir las amplitudes térmicas durante el día, principalmente con el aumento del tamaño de partícula y el contenido de caucho.

Abstract: The aim of this paper is to evaluate, through bending tests, the structural behavior of reinforced concrete beams additionally reinforced by bamboo splints. The bamboo splints are prepared from the stems of the Bambusa vulgaris species. To examine the strength of adhesion between the bamboo splint and concrete, pull out tests are performed for the specimens. The results of the pullout tests of the test samples show the strengthening of the nodes leading to an increase of the normal tension and rupture of splint and not its slip. According to the results of the bending beams, the presence of bamboo splints increases their load capacity when compared with the reference beams. This is indicative of a reduction in the amount of steel required as the structural element. The insertion of the bamboo splints in the beams provides a better performance in terms of the deflection and also leads to a slight increase in the load capacity of the beams. It is worth mentioning that the beams additionally reinforced by bamboo splints exhibit the same pattern of cracking as for reference beams.

Resumen: El objetivo de este trabajo es evaluar, mediante ensayos de resistencia a la flexión, el comportamiento estructural de las vigas de hormigón con refuerzo adicional de tablillas de bambú. Las tablillas se prepararon con tallos de bambú de la especie Bambusa Vulgaris. Para determinar la resistencia a la adhesión entre las tablillas de bambú al hormigón, las probetas se sometieron a ensayos de flexión. Los resultados muestran un fortalecimiento de los nodos produciéndose un incremento tanto en la ruptura como en la tracción normal de las tablillas, pero en su deslizamiento. De acuerdo a los resultados de los ensayos a flexión de las vigas, la presencia de tablillas de bambú aumenta su capacidad de carga en comparación con las vigas de referencia. Lo anterior, implicaría una reducción de la cantidad de acero de refuerzo necesaria para el elemento estructural. La adición de tablillas de bambú al hormigón de las vigas mejora su comportamiento en términos de deflexión, produciendo además un leve incremento en la capacidad de carga de la viga. Cabe mencionar que las vigas con refuerzo adicional de tablillas de bambú mostraron el mismo patrón de agrietamiento que las vigas de referencia.

O trabalho aborda a aplicação da tecnologia do Concreto de Alta Resistência (CAR) para a produção de concretos com incorporação dos resíduos de Cinza de Casca de Arroz (CCA) através da substituição em massa de parte do material aglomerante, e borracha de pneus em substituição parcial do agregado miúdo em volume, avaliando suas influências sobre as propriedades de durabilidade e mecânicas. Para os concretos com CCA e borracha, foi possível verificar a redução da fragilidade através do aumento da capacidade de absorção de energia. Com relação à abrasão, os concretos contendo CCA e borracha apresentaram perda de massa inferior ao concreto sem resíduos, indicando que este material é atrativo para o uso em pavimentação. Contudo, espera-se que estes resíduos venham representar uma alternativa tecnológica e ecológica para a produção de concretos na construção civil

The paper discusses the application of High Strength Concrete (HSC) technology for concrete production with the incorporation of Rice Husk Ash (RHA) residues by replacing a bulk of the material caking and rubber tires with partial aggregate volume, assessing their influence on the mechanical properties and durability. For concrete with RHA and rubber, it was possible to reduce the brittleness by increasing the energy absorbing capacity. With respect to abrasion, the RHA and rubber concretes showed lower mass loss than the concrete without residues, indicating that this material is attractive to be used in paving. It is thus hoped that these residues may represent a technological and ecological alternative for the production of concrete in construction works.

Várias pesquisas realizadas com compostos a base de lítio tem mostrado resultados satisfatórios na redução da expansão associada à reação álcali-sílica (RAS), mas ainda existem muitas dúvidas sobre seus mecanismos de ação. A presente pesquisa avaliou os efeitos de uma adição química a base de nitrato de lítio (LiNO 3), utilizando várias dosagens, com o objetivo de entender seus mecanismos de ação sobre a expansão associada a RAS. O estudo dos efeitos do LiNO3 na RAS foi feito pelo método acelerado das barras de argamassa (ASTM C-1260), utilizando dois tipos de agregado reativo, levando o ensaio até 30 dias. Foram moldadas também barras de argamassa com uma adição mineral a base de cinza volante com o objetivo de comparar os efeitos de uma adição mineral com uma química na expansão devido a RAS. Os resultados do en- saio da ASTM C-1260 indicaram que as adições de lítio foram efetivas na redução da expansão, mas apresentaram valores de adição diferentes para o limite aceitável de 0.10% aos 14 dias para cada tipo de agregado. Foi observado também que as misturas contendo LiNO3 reduziram a expansão ao longo dos 30 dias, enquanto nas misturas contendo cinza volante a expansão continuou a aumentar ao longo do teste. O ensaio indicou que as dosagens de adição do lítio (Li2O/Na2Oeq) eficazes na redução da expansão foram muito elevado em relação aos encontrados na literatura, mostrando que segundo Folliard et al. (2003), o uso de cimento com elevado teor de álcalis (Na2Oeq= 0.9 ± 1.0%) e a modificação da ASTM C-1260, seria a melhor solução para obter valores de adição de lítio compatíveis com o de uso em campo.

Lithium-based additives have shown satisfactory results in the expansion reduction due to alkali-silica reaction (ASR), but many doubts remain about the mechanisms of ASR. The study herein assessed the effects of a lithium nitrate based (LiNO ) chemical addition, using several dosages, in order to understand its expansion mechanisms due to ASR. The study of the effects of LiNO3 on ASR was conducted by the accelerated mortar bar method (ASTM C-1260), using two kinds of reactivate aggregates, consequently, the test lasted up to 30 days. Mortar bars were also molded with a fly ash (FA) based mineral addition to compare the effects of a mineral addition with a chemical one on the expansion due to ASR. The results from the ASTM C-1260 test indicated that the LiNO3 addition was effective in the expansion reduction, but presented different addition values for the acceptable threshold of 0.10% at 14 days for each kind of aggregate. It was also observed that mixtures containing LiNO3 reduced the expansion up to 30 days, while for the mixtures containing fly ash the expansion continued to increase throughout the test. The test indicated that the dosages of lithium addition (Li2O/Na2Oeq), efficient in the expansion reduction for the acceptable threshold of 0.10% at 14 days, were very high when compared to those found in the literature. Folliard et al. (2003), states that the use of cement with a high alkali content (Na2Oeq= 0.9±1.0%) and the modification of the ASTM C-1260, would be the best solution to obtain lithium addition values compatible with field applications.