# Pet Fiber Reinforced Wet-Mix Shotcrete with Walnut Shell as Replaced Aggregate
## 3 Experimental Analysis
### Results of the First Series of Tests
#### 3.2.3 Pumpability and Shootability  
As usual, slump test is the standard test for the workability of fresh concrete, which measures the consistency according to ACI 116R [61]. [PERSON] and [PERSON] [64] found the low slump (0-4 mm) showed a very low workability. However, it does not necessarily mean that low slump ensures less pumpability. To determine the pumpability of fresh concrete after adding crushed walnut shell, pressure drop per meter was measured in tests with pressure sensors. It can be seen in Figure 9a  
Figure 8: Relationship between density and compressive strength.  
Figure 7: Mechanical properties of casting concrete with crushed walnut shell.  
that slump declined slightly with increasing walnut shell replacement while the pressure drop also decreased from 0% to 75% (except point W3), which was expected because aggregates mixed with walnut shells are likely to cluster closely due to the thin walnut shells instead of some approximately spherical particles. Because thin shell with convex and concave portions is easily generating the framework of aggregates, also called aggregate interlock characteristic due to angular and rough edges of crushed shell [65], to resist the flow, then reduce the slump in Figure 10 (SW), and appropriate framework of aggregates can avoid separation at the same time improving flow of concrete with low pressure drop per meter in Figure 10 (FW) under the primeval condition of lubrication layer near inner pipe has been formed [66]. As shown in Figure 10, \(h_{2}>h_{1}\) means adding crushed walnut shell or fibers decreased the slump. \(l_{2}>l_{1}\) means the thickness of lubrication layer formed as pumping plain concrete (F0) was thinner than that of pumping mixtures with walnut shell (FW) or fibers (FF) because the situation that more coarse aggregates in Figure 10 (F0) is prone to dispersion near inner pipe wall effects the formation of lubrication layer while coarse aggregates in Figure 10 (FW) were likely to gather in the center of pipes with the interlock effect. However, too much walnut shell, causing too tight mixture and easily breaking lubrication layer in pipes, might produce huge resistance along with high pressure drop, which was the interpretation of outlier W3 in term of high pressure drop.  
Figure 9b indicates that rebound rate declined with increasing lightweight walnut shell from 0% to 50%, which is similar to the results in [60], and the build-up thickness changed in small range with fluctuating at 100 mm. Therein, W3 was an outlier with the largest rebound rate of about 20%. It also can be seen (Figure 11) in site that the rebound aggregates were very obvious during W3 test, and the  
Figure 10: The aggregate interlock or framework with crushed walnut shell or fibers in terms of slump or pipage tests. S: slump test; F: pipage test; \(h\): slump height; \(l\): thickness of lubrication layer; S0 and F0: plain concrete; SW and FW: concrete with walnut shell; SF and FF: concrete with fiber.  
Figure 9: Pumpability (**a**); and shootability (**b**) of fresh concrete with crushed walnut shell.  
divergent angle of spraying W3 (\(\alpha_{1}\)) is larger than that of W2 (\(\alpha_{2}\)) because more lightweight walnut shell mixed in W3 mixture was easily blew out from the spraying stream.  
According to the literature [54; 55; 67], more than 100 mm of slump and build-up thickness, lower than 0.04 MPa/m of pressure drop and 13% rebound rate, respectively, are more likely available in terms of pumpability and shootability. In order to guarantee the extent of lightweight concrete, another concrete mixture with 35% aggregate replacement of walnut shell was chosen but the splitting tensile strength should be enhanced. Hence, in the next series, fibers were mixed in concrete to reduce cracks and improve its splitting tensile strength.