Experimental investigation of cementitious composites exhibit strain hardening beam elements showing self-healing performances under bending loading

Within the scope of the thesis, cement-based composites, which are commonly a composite and exhibit strain hardening, were produced more economically with coarse aggregates and their performance was improved with the addition of nanomaterials. The performances in more economical productions were compared by using different material ratios in the mixtures. In this context, two different fly ash/portland cement (FA/PC = 0.20 and 0.70), two different aggregate/binder (A/B = 1.0 and 2.0), three different fiber types (nylon, polyvinyl alcohol, steel fiber) were used. Furthermore, two different nano materials (nano silica and nano alumina) were used to investigate the influence of nanomaterial type. In order to examine the size effect in mixtures, beam specimens of two different sizes were prepared. A total of 254 specimens were prepared for testing, including 128 structural beams (100×150×1000 mm), 84 small-scale beams (80×75×400 mm), and 42 compressive strength cube specimens (100×100×100 mm). The prepared beam specimens were subjected to 4-point bending test at different shear span/effective height (a/d) ratios at the end of 28 days. In order to examine the different dominant behaviors at the end of 28 days, 4 different a/d ratios (0.67, 1.11, 2.22, 2.96) for structural size beams and 3 different a/d ratios (0. 67, 1.11, 2.00) for small size beams were loaded and mechanical behaviors were obtained. In addition, both small and structural size beams produced were preloaded at the same a/d ratios at the end of 28 days and the first crack propagation was obtained. The crack widths formed were measured with the help of a hand microscope and cured in a saturated medium for 30 days. The mechanical performances of the beam specimens after 28 days and 28+30 days were examined. Self-healing occurred in specimens in both sizes. The self-healing performance of small size beams is better than structural size beams. As healing products, crack closure was observed in some of the specimens with the formation of C-S-H, while in some specimens due to the formation of CaCO3. The post-healing performance of the crack healing attained with the creation of C-S-H gel has also improved.