Efeito da utilização de biochar da casca de café sobre as propriedades do concreto

Abstract

Concrete is one of the most used materials in civil construction, due to its ease of production, the availability of raw materials and its good resistance and durability properties, in addition to the possible use for construction of the most varied forms. In its production it is possible to add additives to improve its properties and in this sense, research related to the application of biochar in this composite appears. The biochar has interesting properties, such as high porosity and good water adsorption. When combined with cement-based products, it can provide significant curing improvements for the composite. The coffee husk is an agro-industrial residue that can be converted into biochar, although it is still disposed of inappropriately, without a destination consistent with environmental preservation. However, the effect of biochar properties on curing concrete and its final properties is still poorly understood. In this sense, this study aimed to evaluate the effect of using the coffee husk biochar on the physical-mechanical, thermo-acoustic and durability properties of concrete. The biomass of the coffee husk was pyrolysed at a temperature of 450ºC to produce the biochar, which was used in mass / mass substitution of cement, in the percentages of 1, 3 and 5%. The biochar was characterized in terms of unit mass, granulometry, water absorption and microstructure. Firstly, the inhibition and slump test tests of the concretes were carried out and, later, the specimens were produced, the latter being evaluated for compression strength, resistance to compression by compression, water absorption, apparent porosity and apparent density, in the ages of 7 and 28 days. Still at 28 days, thermal conductivity, sound absorption and microstructure were evaluated. In order to analyze its durability, the concretes were subjected to the accelerated aging process and then, again characterized. The incorporation of coffee husk biochar to the composite provided a significant effect on the physical-mechanical and thermal properties of the concrete, in addition to promoting the inhibition of cement reactions, due to the gradual supply of water absorbed by the biochar. However, the acoustic performance of the concrete was not affected by the use of biochar. The porous structure of the biochar was degraded with the accelerated aging of the composite. The concrete with 1% biochar showed lower density and thermal conductivity than the control concrete, which also resisted the mechanical efforts dimensioned for the mix. Thus, the percentage of 1% biochar was considered the best for replacing cement in concrete.