David W. Law

Mechanical Properties of Corrosion-Damaged Reinforcement

Corrosion of embedded reinforcement is the most prevalent form of degradation of reinforced concrete structures, and may impair structural capacity through loss of bar section, loss of bond between reinforcement and concrete as a result of longitudinal cracking, or loss of concrete cross section. The effect of corrosion attack on mechanical properties of reinforcement is investigated through physical tests on bars with simulated and real corrosion damage and through a simple numerical model. Bars subjected to local or pitting attack may suffer a relatively modest loss of strength but a significant loss of ductility, and this is related principally to the variability of attack along the length of the bar. The numerical model supplements experimental work through a parametric study on the influence of steel characteristics. Finally, guidelines on assessment are suggested that are derived from results reported in the paper and from elsewhere in the published literature.

Influence of Surface Crack Width on Bond Strength of Reinforced Concrete

This paper reports the results of an experimental program to investigate the changes in the bond characteristics of deformed mild steel reinforcing due to chloride-induced corrosion. The principal parameters investigated are the cover depth, bar diameter, degree of corrosion, and the surface crack width. The results show a strong relationship between the average surface crack width and the average bond strength; the degree of corrosion does not demonstrate such a clear relationship. The bars with a 1 C/F (cover/diameter) show an initial increase in bond strength at the first visible crack; no similar initial increase is observed for the bars with 3 C/F. The bottom-cast bars display a higher bond strength with no corrosion, but a similar bond strength is observed for both top- and bottom-cast bars once cracking is observed.

The effect of using controlled permeability formwork on the durability of concrete containing OPC and PFA

Abstract This paper presents a study to assess the effect of using the controlled permeability formwork (CPF) on the durability of ordinary Portland cement (OPC) and pulverised fuel ash (PFA) based concretes cured for different times. An experimental program has been undertaken in which trial specimens have been tested at various ages following different curing periods and regimes. Various tests were conducted and assessed using a range of destructive and non-destructive techniques such as Schmidt hammer, water permeability, sorptivity absorption, ultrasonic pulse velocity, and chloride diffusion and resistivity. The durability and strength test results during the period from 28 to 90 days are presented to compare the effects of using CPF with those of traditional (plywood) formwork on OPC and PFA concrete mixes, as specified on actual construction projects in Australia. The results indicate that CPF gave improved performance compared to the traditional formwork for surface properties of concrete. However, the effects are minimal on the bulk properties of the concrete.

Correlations between mechanical properties of low calcium fly ash geopolymer concretes

This paper reports the correlation between existing standards for concrete and the major mechanical properties of geopolymer concrete produced from a range of low-calcium, Class F fly ashes. The data were collected at set points over a 1-year period and include four different sources of fly ash used in the manufacturing of geopolymer concrete. New relationships between mechanical properties and compressive strength were derived using statistical regression analysis. The applicability of current relationships of portland cement (PC) concrete as specified in Australian standards and American Concrete Institute codes for geopolymer concrete have been critically examined. The results indicated that the flexural strength of geopolymer concrete is higher than those predicted using current design equations for PC concrete with a similar compressive strength. However, the splitting tensile strength of geopolymer concrete is comparable to that predicted using the current design equation for PC concrete with similar compressive strength. It was also observed that the ACI 363 R equation significantly overestimates the splitting tensile strength of geopolymer concrete. Similarly, AS 3600 overvalues the elastic modulus of geopolymer concrete. Both of these overestimations may be critical when compressive strength is below 40 MPa.

Long-Term Mechanical Properties of Different Fly Ash Geopolymers

Geopolymer concrete is a sustainable construction material with the potential to act as a replacement for portland-cement (PC) concretes. A detailed investigation of the mechanical properties of four different fly ash geopolymer concretes was carried out up to 1 year of age. Compressive, flexural, and splitting tensile strengths, elastic modulus, and Poissons ratio of four geopolymer concretes at 1 year ranged between 28 and 88 MPa (4.06 and 12.76 ksi), 3.92 and 6.3 MPa (0.568 and 0.914 ksi), 1.86 and 4.72 MPa (0.27 and 0.684 ksi), 10.3 and 29 GPa (1493.5 and 4205 ksi), and 0.16 and 0.28, respectively. The results show an increase in performance observed between 90 and 365 days for all concretes depending on the fly ash properties. Tarong displayed the highest increase while Gladstone had the least, although Gladstone did display the best performance throughout. The nature of the gel matrix formed, in terms of uniformity and compactness, was observed to determine the mechanical properties. The nature of the interfacial transition zone formed between coarse aggregate and mortar and its density was observed to govern the tensile strength. An increase in porosity and microcracks was seen to negatively affect the compactness of the gel matrix, which in turn affected the elastic modulus.

Effect of Pseudomonas fluorescens on Buried Steel Pipeline Corrosion

Buried steel infrastructure can be a source of iron ions for bacterial species, leading to microbiologically influenced corrosion (MIC). Localized corrosion of pipelines due to MIC is one of the key failure mechanisms of buried steel pipelines. In order to better understand the mechanisms of localized corrosion in soil, semisolid agar has been developed as an analogue for soil. Here, Pseudomonas fluorescens has been introduced to the system to understand how bacteria interact with steel. Through electrochemical testing including open circuit potentials, potentiodynamic scans, anodic potential holds, and electrochemical impedance spectroscopy it has been shown that P. fluorescens increases the rate of corrosion. Time for oxide and biofilms to develop was shown to not impact on the rate of corrosion but did alter the consistency of biofilm present and the viability of P. fluorescens following electrochemical testing. The proposed mechanism for increased corrosion rates of carbon steel involves the interactions of pyoverdine with the steel, preventing the formation of a cohesive passive layer, after initial cell attachment, followed by the formation of a metal concentration gradient on the steel surface.

Probability distribution functions for cover used in 3-D model simulating concrete deterioration in port assets

In previous studies, a 1-D numerical predictive tool to simulate the salt induced corrosion of port assets in Australia has been developed into a 2-D and 3-D model based on current predictive probabilistic models. These studies use a probability distribution function based on the mean and standard deviation of the parameters for a structure incorporating surface chloride concentration, diffusion coefficient and cover. In this paper, this previous work is extended through an investigation of the distribution of actual cover by specified cover, element type and method of construction. Significant differences are found for the measured cover within structures, by method of construction, element type and specified cover. The data are not normally distributed and extreme values, usually low, are found in a number of locations. Elements cast insitu are less likely to meet the specified cover and the measured cover is more dispersed than those in elements which are precast. Individual probability distribution functions are available and are tested against the original function. Methods of combining results so that one distribution is available for a structure are formulated and evaluated. The ability to utilise the model for structures where no measurement have been taken is achieved by transposing results based on the specified cover.

Australian Seaport Infrastructure Resilience to Climate Change

A research project continuing at RMIT University is exploring the resilience of port structures in a changing climate. Research completed to date comprises of identifying types of port infrastructure vulnerable to climate change, establishing materials and exposure conditions, developing deterioration models based on current knowledge to simulate the effect of climate change on key port infrastructure and modeling the selected elements of infrastructure to derive outcomes which will aid in decision making in port infrastructure management. A considerable effort has been concentrated on identifying input climate data most appropriate for the models developed. The modeling approach is presented in this paper for quantitative projections of damage probability on port infrastructure taking into account the variability of material type, design considerations and environmental exposures with a changing climate. This paper provides a summary of the research undertaken in the development of material deterioration models and their responses to a changing climate load. Using climate information drawn from historical weather records and future climate projections, existing deterioration models were refined to include climate data into modeling runs in order to analyse changes to deterioration rates of different materials when impacted by a change in climate variables. Outputs from this modeling process will assist port authorities in making informed decisions on maintenance and capital budget planning allowing for impacts of climate change.

Probabilistic Modelling of the Deterioration of Reinforced Concrete Port Infrastructure

Port infrastructure is vulnerable to the corrosive marine environment leading to deterioration, loss of functionality, delays in shipping, major maintenance, remediation and, in the worst cases, loss of structural integrity and consequent replacement of the asset. Despite this, asset managers are unable to adequately plan for the prevention and minimisation of maintenance due to a lack of reliable predictive tools, that simulate the deterioration and a lack of a lifecycle model incorporating protection/maintenance options. This paper reports on a project to develop such a tool to facilitate the probabilistic modelling of the deterioration of reinforced concrete elements from construction through onset of corrosion to subsequent cracking and spalling. The Australian government funded project is in collaboration with several port authorities. The study has narrowed the key factors that have the most impact on the estimation of corrosion initiation and damage propagation allowing better definition of what data should be collected, how much and levels of accuracy required to ensure that predictive outputs obtained are as ‘robust’ as possible.

The site exposure of concrete cast using controlled permeability formwork

Abstract This paper presents a study to assess the effects of site exposure on the durability of concrete cast with ordinary Portland cement (OPC), pulverised fly ash (PFA) and ground granulated blast furnace slag (GGBS) using the controlled permeability formwork (CPF). An experimental program has been undertaken in which trial specimens have been placed on exposure sites at coastal locations in Australia. Various non-destructive tests were conducted such as Schmidt hammer, water permeability, air permeability, ultrasonic pulse velocity, steel potential mapping, linear polarisation resistance corrosion rate monitoring, chloride diffusion, accelerated chloride diffusion, and resistivity. The durability data are presented to compare the effects of using CPF with those of traditional (plywood) formwork for OPC, PFA and GGBS concrete mixes, as specified on actual construction projects in Australia. The results indicate that CPF gave improved performance compared to the traditional formwork for surface properties of concrete.