Issue 43

S. Jing et alii, Frattura ed Integrità Strutturale, 43 (2018) 33-42; DOI: 10.3221/IGF-ESIS.43.02 38 In this paper, the uniaxial tensile experiment on an ECC thin plate specimen of the size 300mm×50mm×15mm was carried out. Steel sheets with a thickness of 1 mm were affixed to both ends of the specimen to prevent partial damage to the holding parts of the specimen, as shown in Figure 3. The experiment was carried out on a 1000kN microcomputer-controlled servo-hydraulic testing machine and the load was applied in the displacement control mode at a speed of 0.0025 mm/s. Meanwhile, the strain data were collected on both sides of the specimen with extensometers. The test apparatus is shown in Figure 4. Experimental phenomena and results The results showed that the failure process of all specimens could be divided into three stages: elastic stage, multiple crack development stage and failure stage. During the loading process, the first crack was found to have appeared in the weak section, and then there were many fine cracks that appeared immediately around it. All specimens exhibited quasi-strain hardening behaviour, and the ultimate tensile strain of ECC was much larger than that of ordinary concrete. The experimental results of the nine groups of different mixing ratios are shown in Figure 5. Figure 5 : Tensile Stress - strain Curve of 9 experimental groups. Orthogonal analysis It’s similar to the range calculation method of factor A in terms of compressive strength so it’s not repeated hereby. Calculation results are shown in Table 3. As can be seen in Table 3, the range decreasing order is: water-binder ratio, fly ash content, plasticizer content and sand-binder ratio, and the range of water-binder ratio is 1.051, which is far greater than the range of the other three factors. This indicates that the water-binder ratio has the greatest influence on the ultimate tensile strain of ECC, followed by fly ash content, plasticizer content and sand-binder ratio. The relationship curve diagram shows the change of each factor as an abscissa and the average ultimate tensile strain as an ordinate. Based on the results: 1) The water-binder ratio is the key factor that affects the ultimate tensile strain of high toughness cementitious composite, and the greater the water-binder ratio is, the higher the ultimate tensile strain is, meaning the better the toughness is. 2) The ultimate tensile strain increases with the increase of fly ash content. The chemical reaction of fly ash with cement hydrate can improve the properties of the interface between fibers and matrix; moreover, there are a large number of fly ash spherical particles attached at the surface of the fibers, reducing the adhesion between fiber and matrix and having a positive impact on the realization of the strain-hardening. 3) The experimental results show that the sand-binder ratio and plasticizer content have little effect on the ultimate tensile strain.