Fly Ash Fiber Research Articles

Experimental study on frost resistance of hybrid fiber fly ash concrete

Based on the orthogonal test, the optimized ratio of hybrid fiber fly ash concrete prepared with different volume admixtures of polypropylene fiber and polyacrylonitrile fiber, and different lengths, was obtained, and its frost resistance was evaluated in terms of mass change, dynamic elastic modulus, compressive strength, and splitting tensile strength before and after water and salt freezing. Then, the damage mechanism was discussed by combining the pore structure and SEM analysis. The results show that the tensile strength and relative dynamic elastic modulus of specimens after the water freezing cycle are better than those after the salt freezing cycle with the same number of freeze-thaw cycles, and the mass loss rate is less than that of the salt freezing cycle; the compressive strength and the splitting tensile strength of hybrid fiber fly ash concrete increased by 8.5% and 9.5%, and 46.8% and 12.1%, respectively, after 60 times of water freezing and salt freezing cycles compared with the benchmark fly ash concrete. As the number of freeze-thaw cycles increased, the pore air content and the frequency of large pores increased and the frequency of small pores decreased; in terms of the pore distribution of concrete, the distribution of pore structure was more reasonable for water freeze cycle relative to salt freeze cycle and for hybrid fiber fly ash concrete relative to the base fly ash concrete. Thus, it can be found that hybrid fibers incorporated into concrete can reduce the damage to the concrete interior by the freeze-thaw cycle and significantly improve the frost resistance of concrete.

Mechanical properties and pore structure of basalt–polypropylene fiber fly ash concrete exposed to high temperatures

The deterioration of concrete structures after fires has been widely concerned. The purpose of this paper is to study the influence of high temperature on the mechanical properties and pore structure of hybrid basalt–polypropylene fiber fly ash concrete. The mechanical properties and damage amount of hybrid basalt–polypropylene fiber concrete with different content of fly ash (FA0, FA10, FA20, and FA30) at different temperatures (20, 200, 400, 600, and 800 °C) were investigated. Additionally, the pore structure test was conducted, and the relationship between pore structure parameters and macromechanical properties was analyzed. The microstructure at different temperatures was observed by scanning electron microscopy (SEM) images. Finally, the main pore structure parameters affecting compressive strength, tensile strength, and damage amount were determined by using the gray correlation entropy method. From the results, after natural cooling at 200 °C, the compressive and tensile strength of concrete was slightly higher than that at room temperature, and it should be noticed that the FA10 concrete specimen showed better mechanical properties at different temperatures compared with other specimens. The increase in air content, spacing factor, and average chord length weakened the strength of concrete, while the increase in specific surface area had a positive impact on the compressive and tensile strength of concrete. The microstructure of FA10 at high temperature was better than that of FA0. The specific surface area was the main factor affecting the compressive and tensile strength, while the main factor affecting the damage amount was the spacing factor, followed by the average chord length.

Recycling and reinforcement potential for the fly ash and sisal fiber reinforced hybrid polypropylene composite

AbstractThe investigation explores mechanical, thermal and thermomechanical behavior of hybrid composites post‐recycling, and subsequent, 5 wt.% additional reinforcement to the recyclate of sisal (SSL) fiber fly ash (FA)/polypropylene (PP) hybrid composite. Impact of recycling and 5 wt.% of SSL fiber reinforcement of the recyclate on mechanical properties of hybrid composites made of 15–30 wt.% SSL and 5–15 wt.% FA were investigated. Noticeably, after recycling, a minimal loss of 2.39% only in tensile and 2.20% in flexural strength were recorded for the hybrid composites fabricated with 15 wt.% each of FA and SSL. The highest loss in tensile (10.32%) and flexural (4.22%) strength were reported for only 30 wt.% SSL fiber reinforced PP indicating that hybridization with FA has a benign effect on reducing property degradation. These lost properties were regained by reinforcing recycled composites with 5 wt.% of SSL fiber. Mechanical studies showed that the composite with 30 wt.% SSL fibers recycled and reinforced with additional 5 wt.% fibers showed a substantial improvement of ~10% and ~4% in the tensile and flexural strength while keeping the impact strength stable. FE‐SEM images confirmed a reduction (~67%) in aspect ratio of the SSL fiber due to reprocessing. DMA demonstrated a decrease of ~11% in storage modulus of the composites after first recycling. TGA confirmed an insignificant change in the degradation temperature of the recycled and re‐reinforced recycled composites versus fresh composites. The study paves the way for potential future recycling applications of waste natural fiber reinforced PP.

Study on mechanical properties and air-void structure characteristics of hybrid fiber fly ash concrete under sulfate attack

Sulfate attack is one of the common durability problems of concrete. The concrete structure in saline soil is particularly susceptible to sulfate attack. The aim of this paper was to investigate the effect of fly ash on the mechanical properties and pore structure of fiber reinforced concrete under sulfate attack. The sulfate resistance of different content of fly ash (0%, 10%, 20%) at different sulfate attack ages (0 d, 30 d, 60 d, 90 d, 120 d, 150 d) was presented. By analyzing the variation of mass loss rate, ultrasonic wave velocity, relative compressive strength and relative splitting tensile strength, the mechanical properties of concrete under sulfate attack were studied. In addition, the air-void structure test was carried out to explore the pore structure characteristics of concrete. The test results suggested that the contribution of fly ash could improve the sulfate resistance of concrete. At the same sulfate attack age, compared with other contents, the hybrid fiber fly ash concrete with 10% fly ash could strong against sulfate attack. At the later stage of sulfate attack, the corrosion resistance of concrete weakened, the mass loss rate, wave velocity, relative compressive strength and relative splitting tensile strength were reduced, while the pore structure parameters showed that fly ash could fill large pores for reducing corrosion damage. Adding 10% fly ash refined pores and enhanced the strength of concrete. The generation of pores is main factor for the deterioration of concrete structure. The fractal dimension well expressed the changes of pores in concrete. Based on fractal dimension and fly ash content, the damage model was established, which could predict the damage deterioration of hybrid fiber fly ash concrete under sulfate attack.

Carbonation Depth Model and Prediction of Hybrid Fiber Fly Ash Concrete

The concrete is weakly alkaline, the alkalinity of the concrete will be reduced after being carbonized, and the protective effect of the concrete on the steel bar will be weakened, even leading to corrosion of the steel bar. In this paper, fly ash is used to replace cement in the same amount, and basalt fiber and polypropylene fiber are added in a certain amount to make hybrid fiber fly ash concrete. Through rapid carbonation test, the influence of carbonation time and fly ash content on carbonation performance of hybrid fiber fly ash concrete is studied. The curve is fitted according to a single factor carbonation model with fly ash content as the main parameter, and the fitting curve and prediction formula are obtained. The results show that, in the same carbonization time, compared with the concrete without fly ash, the concrete with fly ash content of 5%, 10%, 20%, and 30% has average carbonization depth promotion rates of 6.4%, 14.9%, 59.8%, and 73.5%. When the fly ash content varies in the range of 10%∼20%, the carbonation resistance of hybrid fiber concrete changes most sensitively. At the same fly ash content, with the increase of carbonization time, the carbonization depth of concrete increases by 41.7%∼62.3%; Through the verification of the fitting curve and fitting formula obtained after fitting, it is concluded that the error of the prediction formula of carbonation depth of hybrid fiber fly ash concrete is within 9.1%, and the error of carbonation depth of 14 d and 28 d is within 4.3%. Replacing cement with fly ash has certain engineering significance and can achieve the purpose of recycling waste materials.

A Study on Elastic Deformation Behavior of Steel Fiber-Reinforced Concrete for Pavements

The present study discusses the experimental investigation of steel fiber-reinforced concrete slabs on ground under wheel load with the objective of understanding the stress behavior when subjected to central and edge wheel loading. The steel fiber-reinforced fly ash concrete slabs of 900 mm × 900 mm, 150 mm thickness were investigated in this study. Strain gauges and data acquisition system were used to measure the strains at the center and the edge of the slab under the action of the load. The load versus strain relationship under central and edge loading for reference concrete and steel fiber fly ash concrete showed a linear variation even up to the pressure of 2.5 MPa, which is much beyond the conventional tyre inflation pressure of 0.8 MPa. The load versus strain graphs clearly signify the higher modulus of elasticity of fly ash steel fiber-reinforced concrete. The stresses were calculated using IITRIGID software and ANSYS software and were found matching significantly. The value of modulus of elasticity of fly ash steel fiber-reinforced concrete (FS) using ANSYS model for experimental values of load and strains measured was approximated to 34,000 N/mm2 and was found to closely match with the experimentally obtained modulus of elasticity. No significant effect of Poisson’s ratio of concrete on load–strain characteristics was observed within the range 0.15–0.2 of concrete.

Compaction and strength characteristics of fly ash and fiber amended clayey soil

An experimental program was undertaken to investigate the effects of discrete polypropylene fibers and Class C fly ash on the stress–strain and shear strength behavior of clayey soil. Two types of fiber (fibrillated polypropylene fiber and multifilament polypropylene fiber) in two different lengths (6.0mm and 19.0mm) and two fiber dosages (i.e. 0.5% and 1.0% by dry weight of soil) were considered. At first, compaction characteristics of the untreated soil and seven different fly ash–soil mixtures (2.5%, 5.0%, 7.5%, 10.0%, 15.0%, 20.0%, and 30.0% by dry weight of soil) were evaluated at standard compaction energy. Considering compaction characteristics, unconfined compression tests of untreated soil and five different fly ash–soil mixtures (5.0%, 10.0%, 15.0%, 20.0%, and 30.0% by dry weight of soil) were carried out after 1-, 7-, 14-, 28- and 90-day curing periods. According to the obtained test results, untreated soil and two different fly ash–soil mixtures (i.e. 10.0, and 30.0% by dry weight of soil) were mixed with fibrillated polypropylene fiber and multifilament polypropylene fiber in two different lengths and in two different fiber dosages, separately. A total of 17 different fiber–fly ash–soil mixtures were composed, and their unconfined compression tests were carried out after 28-day curing period. According to unconfined compression test results, 6 different fiber–fly ash–soil mixtures were selected for UU triaxial tests at the end of 28-day curing period. The obtained test results indicated that the effect of fly ash content on the stress–strain behavior is superior to the effect of fibers. The post-peak strength behavior is strongly affected by fiber type, length and dosage. The magnitude of the effect increases as the fly ash content increases. Inclusion of fiber alone without fly ash decreases unconfined compressive strength (UCS) of the compacted fiber–clay mixtures. On the other hand, when combined with fly ash, fiber inclusion increases UCS depending on fiber type, length and dosage. Moreover, for both fiber types and fiber lengths, the higher the dosage of fiber, the higher the UCS is. The increase in UCS becomes as much as 218% for 30% fly ash content and 1.0% 19mm long fibrillated polypropylene fiber.