# Pet Fiber Reinforced Wet-Mix Shotcrete with Walnut Shell as Replaced Aggregate
## 4 Conclusions  
The utilization of crushed walnut shell as lightweight coarse aggregate to attempt to produce lightweight wet-mix shotcrete was proposed and tested in this study. The mechanical, pumpability and shootability behaviors of wet-mix shotcrete with walnut shell were tested and discussed. In order to optimizing its properties, PET fiber was used as reinforcement element, and the behavior of PET fiber shotcrete was compared with conventional shotcrete. Based on the above experiments, the following conclusions were made:  
1. In this study, walnut shell was crushed with irregular shaped (polygonal or flaky) with 1-4 mm thickness. They were sieved into one size category, 5 mm to 10 mm. The surfaces of convex portion of crushed shell are relatively smooth, compared to rough surfaces of the concave side along the cracked edges. The specific gravity of walnut shell is obviously lower than that of the natural aggregate. Hence, walnut shell can be termed as lightweight aggregate as it has low specific gravity. 2. In the preliminary tests, compressive and splitting tensile strength of casting concrete with different dosage walnut shell were conducted. With increase of walnut shell, compressive and splitting tensile strength of concrete decreased. Compared with plain concrete (W0), the specimens W1, W2 and W3 with 25%, 50% and 75% replacement had the reduction of 28.7%, 41.9% and 63.6% in compression, as well as 28%, 47.93% and 68.8% in splitting tensile strength, respectively. Furthermore, a linear relationship between density and compressive strength was obtained with a good coefficient of determination, \(R^{2}\) of 0.9782. 3. In order to determine the pumpability of fresh concrete after adding walnut shell, pressure drop per meter was measured in tests. Slump and pressure drop declined slightly with increasing walnut shell replacement from 0% to 75%. Mixing aggregates with walnut shell were likely to cluster closely due to interlock characteristic of crushed walnut shell with angular and rough edges, which was beneficial for reducing separation and improving flowability of fresh concrete. Figure 19: Relation of rebound and build-up thickness. Additionally, appropriate dosage of walnut shell (W1 and W2) can improve the shootability of fresh concrete with low rebound rate and larger build-up thickness. 4. With mixing PET and PP fiber, splitting tensile strength of casting concrete (CSS) and shotcrete (SSS) had achieved about 40% improvement compared with blank specimens. However, adding fibers, PET or PP, caused the loss of the compressive strength of the samples. Wherein, the specimens (PP + PET) with two types of fiber had the interesting results of maximal value in terms of compression and splitting strength of casting concrete or shotcrete. Adding fibers reduced slump and flowability of fresh concrete. In addition, fibers improved the shootability in terms of reducing rebound rate and increasing build-up thickness. 5. A linear relationship between splitting and compressive strength of FC, FS, PC and total specimens was plotted with a coefficient of determination, \(R^{2}\), of 1, 0.96, 0.99, and 0.64, respectively. In addition, the relations of rebound, and density and build-up thickness were discussed. Wherein, the rebound rate increased with an increase in the density, except the outlier W3, and the build-up thickness presented an inverse correlation with rebound rate. The authors would like to acknowledge the team of wet-mix shotcrete in College of Mining and Safety Engineering for the financial and technical support. They also appreciated Wit Laboratory Mine Equipment Co., Ltd. for the preparation and execution of shotcrete tests.