# Experimental Study on the Flexural Behavior of Alkali Activated Fly Ash Mortar Beams
## 3 Test Results  
The comparison of the behavior of the beams is based on key aspects of the evolution of the beam with load, such as the cracking point, Pcr, the yielding of steel, Py, the maximum load, Pmax, the ultimate strength, Pult, among others. The stiffness in each zone of the P-d graph is also an important aspect for comparison. The P-d diagram will be the basis for this analysis (P corresponds to the total load applied at each instant, and d to the displacement in the mid-span of the beam). The load P is obtained from the sum of the loads registered in the four load cells responsible for measuring the value of the support reactions. The value of the displacement in the mid-span, d, is obtained by subtracting the value of the LVDTs at the supports from the value measured of the LVDT placed in the mid-span of the beam. The test results are presented in Figures 5-9. This type of beams generally presents three distinct phases in behavior, namely: State I, State II, and State III. State I, which corresponds to the Stiffness K\({}_{\rm L}\) extends from the origin to the point Pcr, corresponding to the beginning of cracking. The second state, Stiffness K\({}_{\rm HI}\), goes from Pcr to the point where the reinforcement yields Py. Finally, the third and last State is the \"plastic phase\" and starts at Py and extends past the maximum load Pmax, and ending at the last load point Pult (Pult is assumed to be the load 15% lower than the maximum load, according to NP EN1998-1 [31]). In beams where the failure occurs due to reinforcement failure, this point generally coincides with the last point of the graph. Figure 4: Beam under test. Figure 5: P-d experimental curves for beams Cem-2F6 and FA-2F6. Figure 8: P-d experimental curves for beams Cem-3F8 and FA-3F8. Figure 6: P-d experimental curves for beams Cem-3F6 and FA-3F6. Figure 7: P-d experimental curve for beam Cem-4F6. Figure 5 shows the P-d curves (load-deflection curves) for the insufficiently reinforced beams (\(\rho\) = 0.38%). The absence of State I in the fly ash beam curve is justified by the fact that these beams were cracked before the start of the test. This was provoked by the shrinkage due to the temperature of the curing time. This outcome was an assumed risk and could not be ruled out before casting. Since it did occur, this is an issue that needs to be further investigated. To cast these fly ash structures only under an optimized curing temperature of 60 to 70 degrees centigrade seems to be too restrictive to practical construction on site. Apart from this, it appears that there are no significant differences between both types of beams in terms of the stiffness of State II, nor in the values of Py and Pmax loads. In this case, the fly ash beam proved to be much more flexible and more ductile when compared to Cement (Cem) beam. Figure 6 shows the P-d curves of the lightly reinforced beams (\(\rho\) = 0.57%). In State II, both types of beams have similar behavior. In terms of ductility, the beams are equivalent, showing both a long level of ductility, despite the type of steel used for reinforcement (cold hardened steel). Figure 7 shows the P-d curve for beam CEM-4F6 (bellow normally reinforced: \(\rho\) = 0.75). Unfortunately, a rare malfunction of the data logger caused the loss of the recorded values of FA-4F6 beam. The relatively low value of the ductility of the beam stands out in this experimental curve. Figure 8 shows the P-d diagrams of the normally reinforced beams (\(\rho\) = 1.01%). Looking at the Py and Pmax points, it is clear that the ductility of the cement beams is much higher than that of the fly ash beam. Figure 9 shows the P-d curve of above normally reinforced beams (\(\rho\) = 1.34%). In this case, the ash beam revealed an absence of ductility. The cement beams also show a low level of ductility, which could be problematic for hyperstatic structures under seismic actions, for instance. The values of Py and Pmax are not very different when both beams are compared.