Deflection hardening of sustainable fiber–cement composites

Abstract

In the present study sisal fiber-cement composites reinforced with 4% and 6% of short fibers were developed and their physical-mechanical behavior was characterized. To ensure the composite sustainability and durability, the ordinary Portland cement matrix was modified by adding fly ash and metakaolin, and the natural aggregate was substituted by 10% and 20% of recycled concrete aggregate. Flat sheets were cast in a self-compacted cement matrix and bending tests were performed to determine the first crack, postpeak strength and toughness of the composites. Cyclic flexural tests were carried out to determine the stiffness variation of composite due to cracking formation and propagation. It can be seen that the reinforcement provided by short sisal fibers for recycled cement matrices guaranteed a composite with multiple cracking and an increase of strength after the first crack. Reduction of stiffness and increase the damping capacity of composite are verified with progressive cracking.

Short sisal fiber reinforced recycled concrete block for one-way precast concrete slabs

“…The fracture mode I parameters were obtained by performing inverse analysis (IA) according to the strategy described in Lima et al [22], considering the results registered in the four point bending tests described in Section 2.2, whose results are presented in Section 3.1 (Figure 8). In the simulations of the IA, and of the FRC block, the specimens were modeled with a 3D Reissner-Mindlin layered shell theory, while the material nonlinear behavior due to cracking was simulated with a multidirectional fixed smeared crack model (MDFSCM) available in the FEMIX computer program.…”

“…The binder of this material was composed of Portland cement and high content of both metakaolin and fly ash to guarantee the durability of the sisal fiber and also to ensure an adequate workability to the matrix for a proper fiber dispersion. Lima et al [21] used similar binder, but replaced part of natural aggregate by recycled concrete aggregate.…”

“…The produced self-compacting matrix allowed a more homogeneous material reinforced with 40 mm fiber length, having been registered a flexural hardening behavior with multiple cracking and small cracking space. Due to these characteristics, the application of this material for roof constructive element was numerically evaluated, having been demonstrated high potentialities for this type of application [22].…”

Uso de agregado miúdo reciclado em matrizes cimentícias para compósitos reforçados com fibras de sisal

“…A quantidade de adições minerais foi definida em estudo anterior [20], utilizando os mesmos materiais, em que se comprovou, através de análise termogravimétrica, o total consumo do hidróxido de cálcio formado pelo processo de hidratação do cimento. A presença da cinza volante visa garantir uma maior trabalhabilidade nos compósitos e melhor homogeneização das fibras.…”

“…Utilizando 10% de agregado reciclado, verifica-se um decréscimo de 37,5% e 43,2% na resistência à compressão, com a adição de 4% e 6% de fibras, respectivamente, enquanto que, para o uso de 20% de agregado reciclado essas reduções são de 42,8% e 49,0%, para os respectivos teores de fibra. Em comparação, com o uso de uma matriz convencional com traço, em massa, de 1:1:0,45 (cimento:areia:fator/água cimento), mas com adição de superplastificante, Lima et al [20] encontraram valores de redução de 30% e 50% na resistência à compressão com a introdução 4% e 6% de fibras de sisal de 25 mm. Verifica-se, portanto, que as características de autoadensabilidade da matriz utilizada, como uso de adições minerais, controle do tamanho do grão e aditivos, permitiu a produção de um compósito com maior comprimento de fibra e que conseguiu minimizar o efeito negativo sobre a resistência à compressão causado pela introdução de maiores teores de fibras, mesmo com a utilização de agregado reciclado.…”