Mechanical, structural and microstructural investigations of a novel concrete for special structural applications

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

Materials characterisation and concrete durability

In recent decades, microstructural materials characterisation techniques have been employed in the assessment of various types of newly-developed concretes such as geopolymer concrete, recycled and by-product concretes and fibre and nanofibre concretes. Characterisation techniques have also been used to understand durability issues resulting from exposure of concrete structures to harsh and corrosive environments such as maritime infrastructures and concrete members in acid sulphate soils. These corrosive environments can deteriorate and degrade concrete components and lead to the loss of integrity and diminished structural performance and serviceability. The use of microstructural analysis in assessing concrete performance, such as resistance to fire and flexural strength, can be of assistance to improve these properties of concrete. Some of these characterisation methods include scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray mapping (XRM), X-ray diffraction (XRD), simultaneous thermal analysis (STA), thermal mechanical analysis (TMA) and Fourier-transform infrared spectroscopy (FTIR). Although the mentioned methods are well-established techniques, there is a gap in the transfer of knowledge between the experts who can appropriately use these techniques and the structural/materials engineers who need to apply the results. Despite all the benefits these techniques possess, the complexity of the results given seems be an obstacle for engineers who need to interpret them and use them in practice. This paper discusses microstructural materials characterisation techniques with simple examples of their application in engineering practices for concrete structures, focusing on the background knowledge and proper sample preparation needed

A novel acid resistant green mortar for high corrosive environments

A new type of repair mortar (Aegis G) based on sustainable technology and industrial cementitious by-products with less than 10% OPC is developed. The new product consists of specified additives, accelerators and reinforcing agents, specially developed for this technology. The new acid resistant mortar showed high rate of hardening under normal conditions: >20MPa in 7 days, >40MPa in 28 days and >47MPa in 56 days for all batches tested during the last two years. Besides high tensile and flexural strength and modulus of rupture, the new product has excellent long term resistance to corrosive environments with very low permeability and minimal changes in the mechanical properties. The tested samples prepared from the product did not show any changes in their dimensions while 60MPa OPC cubes eroded and/or vanished completely when immersed in 5–20% sulphuric acid for 5–12 weeks .The new product has low shrinkage with outstanding adhesion properties to most construction surfaces. The failure occurred within the substrate concrete and not at the interface. The Aegis G is designed to provide long term resistance to most corrosive environments. The product is a versatile material that can be hand/trowel applied as well as spray applied and can be used for long term protection in a number of different aggressive environments which include: (1) re-lining of sewer trunk lines and manholes, (2) use as acid resistant grout for back fill of lining systems, (3) as acid resistant grout for use with impressed current cathodic protection, (4) lining channels of drinking water which require ion leaching resistant cement