Fundaments On Design And Application Of High Ductile Cementitious Composite With Characteristic Of Low Shrinkage

PVA-ECC is a kind of high ductile fiber reinforced cementitious composites.Stress-crack opening relationship is the key to control the performance of PVA-ECC. Inorder to achieve strain-hardening and multiple cracking, stress-crack openingrelationship is studied.The PVA-ECC with low shrinkage characteristics can work withtraditional concrete, as well as increase the ductility and durability of structures. Thispaper is dedicated to the experimental and theoretical studies of ECC-concretecomposite beam with flexural performance.Two types of PVA fibers with different diameters and four kinds low-shrinkagecements are adopted. Comparison of compressive and tensile properties between twofiber-reinforced composites is studied. Experimental results show that the tensileperformance of the composites may greatly be influenced by the dimension of fibers. Asusing thicker fiber, the strain hardening and performances of multiple cracking can beobtained under tensile load. Whereas using thinner fiber leads to significant behaviorsof strain softening and single cracking. Some increase of tensile strength amongcomposites reinforced with thinner fibers is also observed, which is mainly due to theinfluence of fiber thickness upon its bridging capability. Ensuring that fibers pull out ofcement base instead of fracture is a fundamental requirement for optimizing its bridgingproperty.Using the above-mentioned four kinds of complexes and two kinds of fiber, we cansolve the stress-crack opening relationship with exiting methods. After adding polyvinylalcohol fibers, the stress-crack opening relationship of the composites changes to adouble peak mode. The second peak is greatly increased with increase of fiber content.The second peak stress larger than the cracking strength means strain-hardening andmultiple cracking performances can be expected under tension.Nowadays, the high price of PVA-ECC restrains its application in structures. Thecombination of ECC and ordinary concrete is a good way of reducing the cost. In thispaper, the practical effect of applying low-shrinkage PVA-ECC to composite beam wasstudied, and a corresponding model was established to predict flexural capacity of thebeam. Results shows that ECC could significantly improve the ductility of the beam.Observation was made that multiple fine cracking appeared in ECC layer, and whileascending to concrete layer, they transformed into one single cracking until failure. When the strength of ECC is relatively higher, beam capacity increased with thickerECC layer; Whereas when the strength of concrete layer is higher, influence of ECClayer thickness is not obvious. The corresponding model can be used to predict flexuralcapacity of the beam with different thickness of ECC layers.