Abstract
Concretes have a high rate of propagation of cracks. In order to decrease the rate of crack propagation banana fibres have been reinforced in concrete. Banana fibres offer a relatively high surface area for bonding with concrete matrix. The proportion of fibres which have to be reinforced inside the concrete has been optimised to maximise compressive strength. Fibres have been coated with a softening agent to facilitate dispersion and reduce variability of test results.
Introduction
There has been research on various aspects of textile fibre reinforced concrete (RC). The load-bearing behaviour of textile RC and their simulation has been carried out by Hegger et al. [1]. In an article by Bruckner et al. [2], it was demonstrated that RC members can be strengthened with textile RC. Both the load carrying capacity and the shear loading capacity were found to be enhanced with an additional strengthening layer. Other than the ultimate load, the displacement of the strengthened RC members was found to be improved. In a work by Butler et al. [3], changes in the strength and toughness of textile RC with increasing age were determined by durability of the fibres matrix and the bond between the matrix and the fibres. Investigations were conducted on multi-filament yarns of AR glass, which were imbedded in matrices of varying alkalinity and hydration kinetics. The loading capacity of the fibre–matrix bonds was determined in direct tension tests on under-reinforced specimens after they had undergone accelerated ageing. The researchers also found the condition of the microstructure between fibre and matrix with the aid of both image analysis and analytical procedures. The group concluded that measured reductions in the toughness of the composite material could be attributed to diminishing protective effect of organic polymer sizing on the surface of the filaments as well as to the disadvantageous new formation of solid hydration phases (mainly Portlandite) in the fibre–matrix interface. In a study exploring the influence of bond properties in fibre RC by Hartig et al. [4], textile RC showed a complex mechanical behaviour, which according to the authors was a result of the heterogeneity of the cementitious matrix and the reinforcement yarn, as well as different bond conditions inside the yarn. A reduced two-dimensional model for simulating the uniaxial tensile behaviour of textile RC was presented. In the model, the longitudinal (loading) direction was discretised over the whole specimen length, while in the cross-sectional direction only the heterogeneity of the reinforcement was modelled by dividing the yarns into homogeneous segments arranged in a regular lattice scheme. The model also included limited tensile strength for matrix and the reinforcement.
Investigations into the use of natural fibre reinforcement in cement composite started when low-cost building material replacements for commercial asbestos reinforced cement composites were being looked for. Natural fibres, such as coconut husk [5–7], sisal [8], sugarcane [9], baggase [10], bamboo [11], and awkara, plantain and musamba [12], have been studied in detail and were found to impart favourable properties to composite mixtures.
Natural fibres are prospective reinforcing materials and their use so long has been more traditional than technical. They have long served many useful purposes but the application and developments of the material technology for the utilization of natural fibres as reinforcement in concrete happened in comparatively recent years.
In recent years there is an increasing trend towards using natural fibres as a reinforcing agent. This is because of few advantages of natural fibres, which are as follows:
Improved compressive and tensile strength. Better energy absorption characteristics and fatigue strength. Natural fibres do not rust, which is a major problem with steel RC.
There have been no works on the use of fibres from banana pseudostem as concrete reinforcement. This work explores the potential of banana pseudostem fibres as reinforcement in concrete.
Materials and methods
Banana pseudostem fibres were obtained from Krishi Vigyan Kendra, Pal, Jalgaon, Maharashtra, India. Banana fibres were extracted from the stems of banana plant. Longitudinal slices were prepared from stems and fed to fibre extracting machine. The fibre extracting machine, also known as a mechanical decorticator, consists of a pair of feed rollers and a beater. The slices were fed to the beater between the squeezing roller and the scrapper roller, following which the pulp got separated and fibres were extracted and air dried in shade. Details of the extraction process have been explained in a previous publication by the author [13]. One hundred fibres chosen at random, each of length 100 mm were cut and weighed. Mean value of the fibre denier was found to be 67 D. For fibre density, fibres were taken to have a circular cross section, which has been confirmed from the previous reference of the author [9]. The density of banana fibres was found to be 1.4 g cm−3, determined using a density gradient column prepared from xylene (0.865 g cm−3) and carbon tetrachloride (1.595 g cm−3).
Softener coating
To prevent the agglomeration of fibres, the fibres were coated with softener. A cationic softener with the constitution of dihydrogenated tallow dimethyl ammonium chloride (DHTDMAC) was used on the banana fibre to induce mutual repulsion and avoid agglomeration. As the cationic softener induced similar charge on the fibres, they resulted in mutual repulsion. Fibres were chopped into small pieces of length of around 20 mm using cutter and treated with the softener solution at 60℃ for 20 min with continuous stirring. The treated fibres were rinsed with water to remove excess softener followed by drying in an oven at 70℃.
Preparation of concrete blocks and testing
Preparation of mortar. The samples were manufactured at the Civil Engineering Department, IIT, Delhi. The concrete composition was according to standard method: British DOE system
According to the method concrete design was made using the following:
Mixing machine for mortar. Vibrator machine for settling of concrete. Sieve to purify sand. Cube moulds each of 15 cm length Gauging trowel having steel blade 100–150 mm in length with straight edge. Weighing balance of capacity 1000 kg with least count 0.01 kg. Ingredients of concrete.
Blocks (each of 15 × 15 × 15 = 3375 cm3) of non-reinforced material were made with the composition shown in Table 1.
Preparation of concrete
Each of the ingredients was weighed in required quantity and sand and gravel (stones) were added initially in the mixer. Cement and water were added simultaneously and the mixture was mixed for 3–5 min until a homogenous mixture was obtained. Moulds were filled with the mixture (concrete) and were settled through vibrating machine, and the process was continued until the cubes were completely filled. Excess amount of concrete was removed subsequently from the cubes’ top surface and the moulds were allowed to dry for 24 h in the atmosphere and concrete cubes kept in open water container for the curing process.
RC
A fibre volume fraction of 0.3% and 0.6% were used. The only difference in the process of formation of RC and non-RC is the addition of fibres. Banana fibres were added to the mixture slowly (Figure 1) in parts and continuous mixing was carried out to uniformly mix the fibre into the mixture. Thereafter, it was poured into the moulds and settled through vibrating machine and similar process described in non-reinforced case was carried out.
Fibre sprinkled in concrete mixture.
Testing of concrete
After 7 days and 14 days, three samples of each type were taken out for compressive strength testing. An AVER Birmingham, England®, compressive testing machine was used (Figure 2). The capacity of the system is 250 Ton. A digital controller allows that the tests can be carried out under displacement control or load control (closed loop system). The complete process, including starting and terminating the test and acquiring and saving data, was computer controlled. The axial displacement of the cylinders was measured between the load platens by two LVDTs, thus avoiding any deformation of the testing machine to be included in the measured displacement. The test for cube compressive strength of concrete was performed as according to Indian Standard IS516:1959 and British–European Standard BS-EN12390-3:2002. This procedure is similar to that recommended in ASTM C39 for cylinder compressive strength of concrete. The above standards recommend testing of three specimens to arrive at sample compressive strength value, as a standard practice in case of concrete testing.
Compressive testing of sample.
Results and discussion
Compressive stress of concrete blocks
Stress values of concrete blocks after 7 days curing for non-reinforced and reinforced cubes reinforced using fibres treated with and without softener.
CV: coefficient of variation.
Stress values of concrete blocks after 14 days curing for non-reinforced and reinforced cubes reinforced using fibres treated with and without softener.
CV: coefficient of variation.
Conclusion
Natural fibre RCs using banana fibres have been successfully manufactured and their performance in terms of compressive strength studied. It has been observed that increase in the compressive strength is restricted to a low volume fraction of 3% beyond which there is fall in compressive strength. The most important finding has been that the coating with a softener has been effective in decreasing the variability of the compressive values.
Footnotes
Declaration of Conflicting Interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The author(s) received no financial support for the research, authorship, and/or publication of this article.