Mechanical, Structural and Microstructural Investigations of a Novel Concrete for Special Structural Applications

摘要

Degradation of concrete members exposed to sulphuric acid environments is a key durability issue that affects the life cycle performance and maintenance costs of civil infrastructures. Groundwater, chemical waste, sulphur bearing compounds in backfill, acid rain in industrial zones and biogenic acid in sewage systems are the main sources of sulphuric acid affecting concrete structures.;In this research, as part of an ongoing research on development of novel concretes for special applications, an acid resistant mortar (ARM) with current applications in lining and repair purposes was converted to acid resistant concrete in the laboratory and investigated for structural applications in acidic environments. Mechanical properties of the initial acid resistant mortar material, this novel acid resistant concrete (ARC) and a type of conventional concrete (CC), as the control, have been studied in the laboratory subjected to an accelerated test, 7% (by volume) sulphuric acid. The studied mechanical properties included compressive strength, modulus of elasticity (MOE), modulus of rupture (MOR) and indirect tensile strength tests. Apart from acid resistance experiments, other important properties for a structural concrete such as drying shrinkage and concrete performance subjected to high rate strain loads and elevated temperatures were also evaluated for ARC and CC.;Structural performance of reinforced concrete (RC) flexural members made of this new concrete (ARC) and CC was assessed before and after different periods of continuous immersion in 7% sulphuric acid solution through static and cyclic loading under four-point bending tests to detect the effects of acid attack on structural performance of RC beams. Load- deflection behaviour, curvature- moment resistance at mid span, ultimate load capacity, ductility factor, stiffness degradation, dissipated energy and damping ratio were the main variables studied in these experiments. Application of ARC in beam-column joints, as another application for this concrete was also investigated due to possessing higher ductility than conventional concrete in mechanical properties tests aiming at reduction of transverse reinforcing bars in such members and the potential for seismic applications. Structural elements (i.e., beams and joints) were also modelled by using FE software ATENA to analyse the experimental results numerically.;Microstructural characterisation was also performed on ARC and CC samples before and after acid exposure using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray mapping (XRM) and X-ray diffraction (XRD) to gain a better understanding regarding the change of microstructure of materials after exposure to acid.;ARC showed superior performance than CC after exposure to acid in terms of loss of mechanical properties. Structural performance of ARC has been comparable to CC before exposure to acid and after a long period of exposure to acid it showed better performance than CC, particularly in terms of load bearing capacity. The application of ARC in beam-column joints allowed reducing transverse reinforcing bars in these joints (50% compared to CC). Microstructural characterisation also revealed significant facts regarding the deterioration mechanism in both types of concretes and their effect on mechanical properties.