In the past decades, incorporating crumb rubber into concrete has attracted attention in the field of building materials due to the properties improvement it brought. In this study, crumb rubber of two particle sizes (40CR and 80CR, which have a sieve size of 400 μm and 220μm, respectively) is incorporated into engineering cementitious composite (ECC) material to replace silica sand. Furthermore, three different replacement percentages (0, 15%, 25% by volume) for each crumb rubber size are conducted in this study. The influence of crumb rubber on the ECC is revealed via density, compressive strength, flexural performance, drying shrinkage, restrained shrinkage and environment footprint. The experimental results show that the incorporation of crumb rubber into ECC increases bending deformation capacity, decrease density and compressive strength. While the free drying shrinkage of ECC increases with the addition of crumb rubber, lesser crack number, crack width and cracking tendency were found in the restrained ring test when compared to ECC without crumb rubber. In terms of crumb rubber size, ECC with smaller crumb rubber appear to have lower density and higher bending defamation capacity and shrinkage than those with larger crumb rubber. In addition, incorporating crumb rubber into ECC reduces CO2 emission, thus improve the greenness of ECC to a certain degree.
Glass fiber reinforced polymer (GFRP) has been proposed to replace steel as a reinforcing bar (rebar) material due to its high specific tensile strength and non-corrosive material property. Various GFRP rebars and design guidelines were de-veloped in the past. However, the usage of the rebars has not been widespread in the construction industry due to vari-ous restrictions (e.g., lack of standardized shape, lack of confidence in long-term performance of GFRP reinforced con-crete (RC) members, and lack of price competitiveness over conventional steel rebar). In this study, the applicability of GFRP rebars in real concrete structures is evaluated by focusing on the fatigue performance of GFRP RC members. A fatigue test was conducted on concrete decks reinforced with the GFRP rebar. Eight full-scale decks were constructed and tested in the laboratory. The test parameters were rebar type, reinforcement ratio in the bottom transverse direction, and cyclic load magnitude. It was observed that a GFRP reinforced concrete deck on restrained girders behaves simi-larly to a steel reinforced concrete deck, except for deflection behavior. Also, the study results showed that the GFRP RC deck was strongly affected by the magnitude of the applied cyclic load. Also, the test result showed that a load of 58% less than or equal to the maximum static load carrying capacity should be applied to the deck to safely carry a load of two million cycles. The GFRP RC deck on restrained girders showed reasonably good fatigue resistant capacity.
Shear fatigue of reinforced concrete members without transverse reinforcement has been observed to be potentially governing for the strength of some structural members subjected to large live loads of repetitive nature (as traffic, wind or wave actions). Although extensive experimental programmes have been performed in the past and a rational ap-proach to the problem can be performed on the basis of Fracture Mechanics, most design codes still ground shear fa-tigue design on empirical equations fitted on the basis of existing data. These empirical formulas show inconsistency amongst them and some neglect potentially relevant parameters as the ratio of maximum and minimum fatigue load levels. In this paper, a consistent design approach is presented, by using the principles of Fracture Mechanics applied to quasi-brittle materials in combination with the Critical Shear Crack Theory. This approach leads to a simple, yet sound and rational, design equation incorporating the different influences of fatigue actions (minimum and maximum load levels) and shear strength (size and strain effects, material and geometrical properties). The accuracy of the design expression is checked against available test data in terms of Wöhler (S-N) and Goodman diagrams, showing consistent agreement to experimental evidence. In addition, the estimate of the number of cycles until failure is shown to be significantly more accurate and with lower scatter than current empirical shear fatigue formulations of Eurocode 2 or fib-Model Code 2010.
Calcium silicate hydrate (C-S-H) is a dominant hydration product of cementitious materials. Therefore, its chemical composition and physical properties affect the performance of concrete. The purpose of this study is to investigate the chemical composition (CaO/SiO2 molar ratio (Ca/Si ratio), and H2O/SiO2 molar ratio (H2O/Si ratio)) and physical prop-erties, such as density and specific surface area, of C-S-H. These factors are measured using synthesized C-S-H samples and C-S-H generated from various cementitious materials. Experimental results show that the H2O/Si ratio of C-S-H is proportional to the Ca/Si ratio independent of the mix proportion, curing temperature and type of binder. The density and specific surface area of C-S-H are affected by its Ca/Si ratio. A linear relationship is observed between the Ca/Si ratio and density of C-S-H independent of the mix proportion, curing temperature and type of binder. An inversely proportional relationship is found between the Ca/Si ratio and specific surface area of C-S-H.