Pet Fiber Reinforced Wet-Mix Shotcrete with Walnut Shell as Replaced Aggregate

Abstract

Abstract:In the rapidly developing modern society, many raw materials, such as crushed limestone and river sand, which are limited, are consumed by the concrete industry. Naturally, the usage of waste materials in concrete have become an interesting research area in recent years, which is used to reduce the negative influence of concrete on the environment. Hence, this paper presents the development of a sustainable lightweight wet-mix shotcrete by replacing natural coarse gravel with a kind of byproduct, nut shell (walnut). Fibers made from dumped polyethylene terephthalate (PET) bottles were mixed in the composite to improve the properties of the lightweight wet-mix shotcrete. The initial evaluation of the fresh concrete mixed with different volume fraction of walnut shell was carried out in terms of its performance capacities of mechanical properties (i.e., tensile and compressive strength), pumpability and shootability (i.e., slump, pressure drop per meter and rebound rate) and the results were compared with plain concrete. With increase of walnut shell, compressive and splitting tensile strength of casting concrete decreased, while slump and pressure drop reduced slightly. Additionally, appropriate dosage of walnut shell can improve the shootability of fresh concrete with low rebound rate and larger build-up thickness. In the second series tests, polypropylene (PP) fiber and multi-dimension fiber were also mixed in composite for comparative analysis. After mixing fibers, the splitting tensile strength had obtained marked improvement with slight reduction of compressive strength, along with acceptable fluctuation in terms of pumpability and shootability. Furthermore, relation of density and compressive strength, relation of rebound and density, build-up thickness and relation of compressive and splitting tensile strength were discussed. This study found wet-mix shotcrete incorporating PET fiber with walnut shell of about 35% coarse aggregate replacement could be used for roadway support as lightweight shotcrete per requirements of mine support.

Effects of PET Fibers on Pumpability, Shootability, and Mechanical Properties of Wet‐Mix Shotcrete

“…In order to ensure the consistency of experimental variables, PET fibers were cut from the same type bottle of Laoshan mineral water bottle. According to the previous experiments [11,13,17], Young's modulus was 3830 ± 47 MPa, the tensile strength was 108 MPa, and the calculated degree of crystallinity was 23 ± 1%.…”

“…Table 2 listed the mix proportion of wet-mix shotcrete. Note that the mixture proportions used in this study were based on practical experiments and literature studies [12,13,54,55].…”

“…ey have been proven to effectively reduce shrinkage and to enhance the ductility of concrete [13][14][15][16][17]. Recently, the environmental benefits of using these waste materials will encourage engineers to use them in engineering structures such as shotcrete support [18].…”

“…ere are two methods for producing the PET fiber. One way is to cut a PET bottle by hand or using a mechanical cutting device [11,13,19]; the other is to melt the PET bottle and then pull them into monofilaments by an extruder [15,[20][21][22][23]. e properties of PET fiber, such as physical, chemical, and mechanical features, affect the concrete reinforcement.…”

Influence of Polypropylene Fiber on Tensile Property of a Cement-Polymer Based Thin Spray-On Liner

“…According to Joong [19], tunneling shotcrete with 0.6-0.8% volume content of polyamide-fiber-reinforced shotcrete can yield significant improvement in the flexural ductility, toughness, and ultimate load capacity. Cheng [20] reported that fiber addition prevents the formation of plastic shrinkage cracks in underground shotcrete. Yin [21] reviewed that plastic fibers are synthetic fibers, which can be in the form of micro plastic fibers(with the diameter of 5 to 100 µm and length of 5-30 mm) or macro plastic fibers (which have a length of 30-60 mm and cross section of 0.6-1 mm 2 ).…”