Dr Mike Mulheron
Academic and research departmentsDepartment of Civil and Environmental Engineering.
Mike is a Reader in Construction Materials within the Department Civil and Environmental Engineering where he teaches a specialist MSc module on the Durability of Bridges and Structures. He previously worked as a Principal Engineer for Gifford and Partners where he was responsible for the Special Inspection of prestressed concrete bridge structures and the assessment and monitoring of concrete infrastructure. As a consequence he has practical experience of the assessment methods that are applied to concrete structures. His research has included covered the development of non-destructive methods for the assessment of reinforced concrete that were funded by both a Royal Society Brian Mercer award and subsequent EPSRC funding. This work has led to a prototype NMR device that is currently being used to assess moisture and moisture movements within the cover of concrete slabs during both their early-age curing and following environmental exposure. Over the past decade he has also received funding from industry to investigate the failure of structures subject to extreme environments. He has published more than 40 papers in the area of construction materials that mostly focus on durability issues and is currently supervising four EngD students supported by the SEES and MinMat EPSRC funded Doctoral training centres at the University of Surrey.
The strength and fatigue properties of cast iron samples taken from water distribution mains have been investigated. Specimens were sourced from three sections of pipe which had experienced varying amounts of corrosion in service, enabling the variable of pipe condition to be incorporated within the study. The strengths in four-point flexure of small specimens from the pipes examined were described using Weibull statistics; different characteristic strengths and Weibull moduli were obtained, according to the pipe condition. A further set of samples from each pipe were subjected to flexural fatigue at a range of stress levels (different stress levels were chosen for each pipe based on the short-term strength properties) and residual strength tests were carried out on the surviving samples from one stress level for each pipe. There is evidence of a fatigue effect for all sample sets. There were slight differences in the residual strength behaviour - the residual strength of the survivors was reduced in the samples from the section in best condition while the residual strength of the survivors from the other two pipe sections was relatively unaffected. These trends are discussed with reference to condition and fatigue stress level. The results suggest that mechanical fatigue may be a factor in the failure of water distribution pipes. The results may have implications for large diameter trunk mains as well as the small diameter water distribution pipes tested here. To assess the effect in more detail, consideration needs to be given to scaling effects in fatigue and the likely levels of any fatigue stress seen in service.
Cements, which are intrinsically brittle materials, can exhibit a degree of pseudo-ductility when reinforced with a sufficient volume fraction of a fibrous phase. This class of materials, called Engineered Cement Composites (ECC) has the potential to be used in future tunneling applications where a level of pseudo-ductility is required to avoid brittle failures. However uncertainties remain regarding mechanical performance. Previous work has focused on comparatively thin specimens; however for future civil engineering applications, it is imperative that the behavior in tension of thicker specimens is understood. In the present work, specimens containing cement powder and admixtures have been manufactured following two different processes and tested in tension. Multiple matrix cracking has been observed during tensile testing, leading to a “strain-hardening” behavior, confirming the possible suitability of ECC material when used as thick sections (greater than 50 mm) in tunneling applications.
The research work reported was carried out in 1987 as part of a four-year programme sponsored in part by the Institute of Demolition Engineers on the recycling of demolition debris. The physical and mechanical properties of crushed concrete and demolition debris from a variety of sources were examined to assess the suitability of these aggregates for use as granular sub-base materials. In particular, sieve analyses and compacted density tests were conducted, during the construction of a road in Portsmouth, to compare the use of crushed concrete and limestone as the upper part of the capping layer. The authors review recent research on the recycling of crushed aggregates, examining their physical and mechanical properties and gauging their suitability as sub-base materials for roads.
This study investigates sodium acetate [NAAC], a rather neglected bio-degradable de-icer, which may, however, present a viable solution towards sustainable and environment-friendly winter operations in certain situations. The results presented here are a selection of data obtained by SEM imaging and element mapping, together with X-Ray diffractometry in order to demonstrate the benign nature of NAAC solutions with regard to their interaction with cement pastes. The effect of the inclusion of microsilica in the cement paste in these tests is evaluated through the use of pure OPC and microsilica containing specimens. The results obtained suggest that sodium acetate is an effective de-icer that may deserve as much attention by researchers and the industry, in the same way as other well known alternative de-icers.
This paper addresses some practical questions regarding the influence of hydrophobic treatments on the movement of water in sandstone. The broad line gradient echo magnetic resonance imaging technique has been used for monitoring the depth of penetration of alkyl alkoxysilane treatment into untreated sandstone and subsequently to visualise the movement and spatial distribution profile of water in the untreated and silane treated sandstone matrix. The experimental results show that the effect of hyrdrophobic treatment depends on whether the stone is in short-term or prolonged contact with water. For short term exposure, the presence of a silane treatment prevents the movement of water into and out of the sandstone matrix. However, after continuous long-term contact with water the hydrophobic treatment is unable to prevent the ingress and internal redistribution of water. The ability of water to infiltrate treated regions of sandstone has significant practical implication for stone structures where deterioration may be due to outward movement of water from the interior to the surface of the stone matrix.
Abstract Building activities generate coarse (PM10 ≤ 10 μm), fine (PM2.5 ≤ 2.5 μm) and ultrafine particles (<100 nm) making it necessary to understand both the exposure levels of operatives on site and the dispersion of ultrafine particles into the surrounding environment. This study investigates the release of particulate matter, including ultrafine particles, during the mixing of fresh concrete (incorporating Portland cement with Ground Granulated Blastfurnace Slag, GGBS or Pulverised Fuel Ash, PFA) and the subsequent drilling and cutting of hardened concrete. Particles were measured in the 5–10,000 nm size range using a GRIMM particle spectrometer and a fast response differential mobility spectrometer (DMS50). The mass concentrations of PM2.5–10 fraction contributed ∼52–64% of total mass released. The ultrafine particles dominated the total particle number concentrations (PNCs); being 74, 82, 95 and 97% for mixing with GGBS, mixing with PFA, drilling and cutting, respectively. Peak values measured during the drilling and cutting activities were 4 and 14 times the background. Equivalent emission factors were calculated and the total respiratory deposition dose rates for PNCs for drilling and cutting were 32.97 ± 9.41 × 108 min−1 and 88.25 ± 58.82 × 108 min−1. These are a step towards establishing number and mass emission inventories for particle exposure during construction activities.
There are several methods of ensuring high performance and durability of concrete by the use of modem admixtures. Special superplasticising admixtures can be used to produce flowable mortars and concretes of low water-cement content and organic polymers may be incorporated with ordinary Portland cement to produce concrete mixes with improved fresh and hardened properties for special applications. Alternatively, durable concrete may be obtained by adding reactive cement replacement materials. As a consequence there is a need to provide comparative performance data for such materials to enable engineers make an informed decision in selecting materials most suited to specific situations.
Understanding of the emissions of coarse (PM10 ≤10 μm), fine (PM2.5 ≤2.5 μm) and ultrafine particles (UFP 90 % of the total particle number concentrations and
Grey cast iron water pipe networks have been installed around the world, often 100–180 years ago. Cohorts (which can be defined by age, size, casting technology and geographical location, to specify but a few groups) degrade at different rates due to environmental and in-service issues, which can lead to a significant loss in mechanical performance. Hence, the management of these assets can be extremely problematic in terms of identifying priorities. The current paper considers the causes of such degradation, the consequences for defining accurate and up-to-date condition assessment protocols and hence the type and urgency of rehabilitation strategies. It follows that understanding the integrity/life expectancy of water networks requires non-destructive evaluation (NDE) of large-diameter cast iron trunk mains, with particular reference to the kinds of defects that are likely to be present and the issues that make assessment difficult. From this, recommendations are outlined for asset managers required to specify NDE protocols, based on an understanding of the nature of the material and conditions in the field.
The fitness of ageing cast iron pipe is a problem for both clean water and wastewater networks. Whilst considerable effort has been put into understanding the condition of cast iron mains that carry potable water, wastewater systems have received less attention. Compared with clean water mains, wastewater trunk sewers typically have thinner walls, are often of lesser casting quality, and typically are exposed to a harsher and more complex internal and external environment. It has been established that corrosion is a leading cause of deterioration in cast iron mains. Research has shown that when predicting residual load capacity in clean water main, a loss-of-section approach is not applicable when dealing with corrosion pitting, which is more discrete and notch-like. This research examines the use of both loss-of-section and fracture mechanics models to provide a failure envelope for a ring from a pipe under combined vertical loading and internal pressure. Internal corrosion, defect size, and morphology of this corrosion have a significant effect on the residual strength of the pipe. The failure envelope predicted is rather different to that previously reported for clean water mains, which is not unexpected given the differences in component geometry and operational conditions.
This paper provides a brief review of the adverse effects of rock salt on reinforced concrete bridge structures, the roadside natural environment, the life cycle of highway structures, and the attendant financial cost implications. It addresses the issue of whether the adoption of an alternative method of winter operations for highway bridges, combined with the use of alternate de-icing salts, could constitute a viable, cost-effective and sustainable solution. The University of Surrey and Anglia Polytechnic University in the UK are currently evaluating the effects of two biodegradable de-icers; Calcium Magnesium Acetate (CMA) and Sodium Acetate (NAAC), on the behaviour of reinforced concrete Highway bridge structures. Initial results obtained from this study are presented and discussed with respect to the optimum condition for their application on highway structures. Conclusions are drawn on the basis of the practical implication for the life cycle of corrosion-prone highway structures and the natural environment. The need for further investigation is identified.
In order to assess the remaining life of cast iron assets in the water sector, an understanding of their fracture and fatigue characteristics is necessary. The present work is concerned with the toughness and Paris crack growth behaviour of cast iron materials with a range of micro-structures, taken from trunk mains currently in service. When considered with other data from the literature, the results from the present study enable the range of fatigue crack growth behaviour likely to be seen in service to be quantified. The role of microstructure in fracture and fatigue behaviour is discussed. Calculations of fatigue life based on integration of the Paris law are then carried out and compared with previously published data for samples from cast iron distribution mains. The results from these investigations support the development of asset management tools for use in the water industry. (C) 2010 Elsevier B.V. All rights reserved.
Distribution networks are critical in providing continuous potable water supplies to households and businesses. Trunk mains are the major arteries of the distribution network and convey large volumes of water over long distances. Worldwide, much of this infrastructure is made of ageing cast iron and is deteriorating at different rates. Many of these mains are beginning to approach the end of their service lives (with some already exceeding their design life) and consequently out of large populations of pipes, some are failing, although some still have considerable residual life. Trunk main failures can have significant social, health and safety, environmental and economic impacts. It is therefore imperative to prevent the wide-scale failure of trunk mains through the implementation of proactive asset management strategies. Such approaches require accurate condition assessment data across the network in conjunction with deterioration modelling to predict how the assets' condition and performance changes over time. This work, being part of a wider collaborative project, has outlined a deterioration modelling framework on the basis of existing physical probabilistic failure models and research focussing on residual mechanical properties, corrosion and the NDT detection of flaws. The developed deterioration model can be used to characterise individual pipes (deterministic approach), as well as the cohort/network modelling of pipes (probabilistic approach). Deterioration is assumed to be predominantly based on corrosion. Previously this has been dealt with in a rather simplistic manner. The broader work has, on the one hand,shown that corrosion mechanisms are rather different than previously thought and, on the other, that their effect on a given pipe can be variable. A corrosion model capable of simulating the distribution of corrosion properties of the primary defects is to be incorporated within the proposed modelling framework and the development of important aspects of this model are discussed here. © 2014 WIT Press.
Waste is a complex societal problem: municipal solid waste (MSW) should be considered a resource, but the methods for capturing, treating, and utilising this resource are varied and often dependent on geopolitical factors. Previous research has, on the one hand explored the need for a more comprehensive waste composition specification in order to better manage municipal waste, and on the other focused on a problematic waste stream and the options available for dealing with it. The current work considers the use of multi-criteria decision making in order to assess the relative merits of different treatment options. A complex and problematic waste stream, wood, has been selected as a case study. For the purpose of the study, the work considers the options available to Surrey County Council in the UK. At the present time, for the conditions selected, energy from waste was considered to be the best option available for the treatment of wood with no discernible value for upcycling or reuse, but not contaminated with hazardous chemicals. When considering a different location with different circumstances, a different solution might be found.
This paper reports the result of a study aimed at assessing the impact of Calcium-Magnesium Acetate (CMA) solutions on the corrosion of reinforcing steel embedded in concrete. It is part of a larger research to evaluate the efficacy of adopting alternative de-icing chemicals and methods in winter de-icing operations. This part of the study involves the use of half-cell potential and Linear Polarisation Resistance (LPR) techniques to compare the corrosion risk in small-scale reinforced concrete slabs subjected to a ponding regime with distilled water, salt water or CMA solutions over a period of one year. The influence of different de-icers on the corrosion behaviour of the reinforcement are compared. Further work concerning longer term effects is in progress to ascertain the significance of the observed changes on the mechanism of the interaction between CMA solutions and cement paste.
We present preliminary results of the first NMR T(1)-T(2) two-dimensional relaxation Correlation experiments performed using a one-sided NMR system in cement based materials. Two-dimensional correlation relaxometry has itself only recently been demonstrated in cement paste where it proved to be a particularly sensitive probe of pore-water dynamics providing direct information on exchange of water between the gel and capillary pore networks. Further to this we have observed differences in the structural development of a selection of cement pastes throughout the early stages of hydration and verified the theoretical frequency dependence of the ratio T(1)/ T(2). When coupled with instrumentation developments in one-sided NMR magnets the way is opened to detailed, spatially resolved studies of the development of hydration and porosity in the surface layers (top 50 mm) of cementitious materials. A new magnet, suitable for such applications, is discussed. (C) 2006 Elsevier Ltd. All rights reserved.
The issue of leakage within the water distribution system is one of importance not only at an economic level for the industry, but also as a result of an environmental agenda addressing issues of water sustainability. The present work is concerned with leakage from lead based assets, in particular distribution pipes. Very little is known about the failure mechanisms within lead based assets. The present paper presents the findings from a study in which lead samples from intact and failed pipes, sourced from the Thames Water area, have been examined. The failure mechanisms have been identified at the macroscopic level and the pipe microstructure has been characterised - aspects of the microstructure control particular properties of the pipe ( e. g. strength, creep and fatigue behaviour) and so may contribute to the potential failure modes. The present study is the first stage in a programme of work designed to develop a better understanding of the failure modes in lead assets, leading to the formulation of a more effective condition assessment model.
A new method of applying hydrophobic coatings to cement-based materials based on exposure to the treatment vapour is proposed. The method is demonstrated for the application of monomeric alkyl (isobutyl) alkoxy silane to cement paste and mortar samples manufactured and cured under a variety of conditions. The efficacy of the treatment is compared to conventional flood coating using magnetic resonance imaging (specifically SPRITE) to monitor the time dependent uptake of water into treated samples. It is concluded that the method as proposed is of significant benefit for some of the samples.
WX Weight of material to be managed by a particular option Abstract Waste is intricate to manage. With greater attention now being paid to the use of waste as a resource, there is an increasing need to develop sustainable and secure management options for the most complex material resource streams. In order to achieve this, it is necessary to look to those materials, which due to their complex structure have not traditionally been recycled, and so remain in the residual waste stream. This paper presents a methodology that has been developed to enable local authorities, or their equivalents, to assess the environmental and economic feasibility of collecting complex material streams separately, in order to improve their management of municipal solid waste. The methodology utilises available data from a number of sources, to determine the feasibility of options available. The methodology is applied to a case study in Surrey, England, in relation to the management of Absorbent Hygiene Products. Currently this waste is collected as part of the residual stream, and dealt with either through landfill or energy from waste. The result of applying the new methodology suggests that the optimum solution is the separate collection of Absorbent Hygiene Products and subsequent the sterilisation and recycling.
This paper presents an investigation into the behaviour of a number of pipe liner materials, with the specific aim of determining their ability to remain intact during failure of the cast iron host main. Three different liner systems have been evaluated along with an unlined control. One of the liners (epoxy resin lining) is a non-structural technique, whereas the other two (Subcoil and a new development) are semi-structural (or interactive) liners. Metallographic analysis and tensile tests were carried out on small samples cut from the cast iron host pipe in order to characterise the basic properties of the cast iron. Metallography revealed a microstructure typical of a grey cast iron, consisting of acicular graphite flakes with some rosettes; etching with 2% Nital acid etch revealed the presence of pearlite. Tensile tests on small samples cut from the pipes indicated significant non-linearity in the stress-strain response. Lined cast iron pipes were tested to failure in four-point bending. A circumferential notch was machined into the wall of some of the pipes, in order to simulate the reduction in host-pipe strength due to corrosion. In addition some tests were carried out under applied internal water pressure, to determine if this had any effect on liner behaviour. Both interactive liners survived host-pipe failure, whilst, as expected, the non-structural liner did not. A simple method was developed which enabled the bending moment curvature relationship in a bend test to be modelled from tensile data; this model gave satisfactory agreement with the experimental data.
Two important parameters which control the fracture behaviour of glass fibres in cement composites, whether they contain one fibre type or are hybrids of two fibre types, are the perimeter of the glass strands in contact with hydrated cement and the way in which glass filaments fracture in multifilament strands. In scanning electron microscopy (SEM) observations, much improved images were obtained by detecting backscattered electrons rather than secondary electrons. This improvement gave good contrast between the fibre strands and the matrix, hence the perimeter of the glass strands could be determined using an image analyser. The progression of filament fracture within a strand was examined using two techniques, acid dissolution and light transmission through the filaments. These techniques showed that strands tend to fail progressively in hybrid composites containing glass and polypropylene fibres and that glass fracture continues to occur after the peak loan has been reached.
Single-sided magnets give hope that Nuclear Magnetic Resonance (NMR) might in future be used for in situ characterisation of hydration and water transport in the surface layers of concrete slabs. Towards that end, a portable NMR-MOUSE (MObile Universal Surface Explorer) has been used to follow the hydration of gypsum based plaster, a Portland cement paste and concrete mortar. The results compare favourably to those obtained using a standard laboratory bench-top spectrometer. Further, stray field imaging (STRAFI) based methods have been used with embedded NMR detector coils to study water transport across a mortar/topping interface. The measured signal amplitudes are found to correlate with varying sample conditions. (c) 2005 Elsevier Ltd. All rights reserved.
Two-dimensional nuclear magnetic resonance relaxation correlation studies of cement pastes have been performed on a unilateral magnet, the Surface GARField. Through these measurements, the hydration process can be observed by monitoring the evolution of porosity. Characteristic relaxation time distributions have been observed in different cement pastes: fresh white cement, prehydrated white cement and ordinary Portland cement. The observed T-1/T-2 ratio in these cements has been shown to agree with expectations based on high field values. (C)) 2007 Elsevier Inc. All rights reserved.
A new, portable NMR magnet with a tailored magnetic field profile and a complementary radio frequency sensor have been designed and constructed for the purpose of probing in situ the sub-surface porosity of cement based materials in the built environment. The magnet is a one sided device akin to a large NMR-MOUSE with the additional design specification of planes of constant field strength vertical bar B(0)vertical bar parallel to the surface. There is a strong gradient G in the field strength perpendicular to these planes. As with earlier GARField magnets, the ratio G/vertical bar B(0)vertical bar is a system constant although the method of achieving this condition is substantially different. The new magnet as constructed is able to detect signals 50 mm ((1)H NMR at 3.2 MHz) away from the surface of the magnet and can profile the surface layers of large samples to a depth of 35-40 mm by moving the magnet, and hence the resonant plane of the polarising field, relative to the sample surface. The matching radio frequency excitation/detector coil has been designed to complement the static magnetic field such that the polarising B(0) and sensing B(1) fields are, in principal, everywhere orthogonal. Preliminary spatially resolved measurements are presented of cement based materials, including two-dimensional T(1)-T(2) relaxation correlation spectra. (c) 2007 Published by Elsevier Inc.
As part of an on going programme to characterise the residual properties and understand the failure mechanisms of in-service grey cast iron water pipes, the fatigue crack propagation behaviour of grey cast iron samples has been studied. Specimens were sourced from three ex-service pipes. For each pipe the microstructure and composition were characterised and the fracture toughness was determined. The fatigue behaviour was investigated in terms of the crack growth rate (da/dN) as a function of the applied stress intensity factor range. Clear differences in the fatigue behaviour of the samples from different pipes were observed. The result from these investigations, which indicate that microstructural differences play a role in mechanical behaviour, will support the development of asset management tools for use in the water industry.
Renovation techniques such as use of liners to extend the lifetime of pipe networks are well established in the water industry. As well as spanning gaps and bridging holes, interactive liners are capable of surviving circumferential (or ring) failure, as may be experienced by distribution mains under flexural loading; movement of the host main following failure leads to tensile and shear displacements of the liner near the fracture. Experiments were carried out on cast iron host pipes containing a simulated transverse fracture, with thin-walled (similar to 3 mm) medium density polyethylene liners having a variety of longitudinal gaps. The fracture plane was subjected to shear displacements up to similar to 50 mm and longitudinal separations up to similar to 20 mm. Pipes were held at a pressure of 10 bar for about 12 days to allow creep deformation to take place, while the ability of the liner to withstand the applied displacement and separation was determined. It was demonstrated that the liner material investigated could withstand lateral deflections of the order of 50 mm for considerable periods of time. The implications of this finding on current design guidelines need further consideration. However, if the outcomes are favourable, this could lead to increased use of interactive liners, with potential benefits to both the water industry and the customer.
Waste is a complex societal problem that brings together various stakeholders in order to manage it. However, a lack of sufficient information on the quantities and types of material in the waste stream can make sustainable waste management difficult. Since waste in one sector can be valuable as a resource in another, there is a need to understand the distribution of materials within the resource stream, especially those that go to landfill. Current work is seeking to address this; whilst much material is already recycled, this is not the only management option and there remain several problematic materials/components to be removed from residual waste. This paper, the first of two case studies, presents a more comprehensive waste composition specification in order to better manage municipal waste. In developing this approach, waste composition specifications currently in use have been reviewed and compared with the solid municipal (household) waste collected at community recycling centres and from the kerbside. Key primary and secondary descriptors for the better management of resources arising from municipal waste have been determined, and the impact of these changes on the information arising from composition analysis is discussed.
The in-service strength degradation, as a result of corrosion, of cast iron water distribution pipes has been investigated. The strengths of 1 m lengths of pipe extracted from the ground have been measured in either 3- or 4-point bending and the size of the controlling defect has been estimated by visual examination of the fracture surface. The application of Weibull statistics to the bend test data demonstrates that there is bimodal behaviour which suggests that there are two populations of flaws present. It is postulated that the larger flaw size population is associated with corrosion pits that form during the process of graphitisation, while the smaller flaw size population is associated with the inherent flaws within the (brittle) cast iron pipe material. A critical pit depth is identified at the transition between the two competing flaw populations, where there is a change in slope on the Weibull plot. It is shown also that the residual strength/pit depth data are described equally well by either of the two conventional analyses, i.e. loss of section and fracture mechanics. © 2002 Thames Water Utilities Ltd. Published by Elsevier Science Ltd. All rights reserved.
The development of equipment suitable for measuring tensile stress-strain curves on fresh concrete is described. With such weak materials, it is essential to eliminate friction effects and this is achieved by the use of air-bearing plates. The objective of the new equipment is to enable data to be obtained to define the rapidly changing tensile stress-strain performance in the first 6 h after water is added at the mixer. This information is important for understanding plastic shrinkage cracking. The equipment is also being used to investigate early-age internal cracking problems which have been observed with high-strength concrete and which are related to the internal tensile failure strain of the cement paste. Some typical tensile stress-strain curves obtained ruing the equipment are shown for two types of concrete.
The results of a magnetic resonance spin-spin relaxation analysis and broad-line magnetic resonance imaging (MRI) (gradient-echo and stray-held imaging) study of water and water transport in Portland cement pastes are presented. The effect of varying the cure conditions and the water to cement (w/c) ratio of the sample mix are discussed. The water sorptivity and the concentration dependence of the hydraulic diffusion coefficient are calculated for samples prepared with a 0.5 w/c ratio and, therefore, an open pore structure. In the case of 0.3 w/c ratio samples, little water transport is observed, and a closed pore structure is inferred. (C) 1998 Elsevier Science Inc.
Building activities are recognised to produce coarse particulate matter but less is known about the release of airborne ultrafine particles (UFPs; those below 100 nm in diameter). For the first time, this study has investigated the release of particles in the 5-560 nm range from three simulated building activities: the crushing of concrete cubes, the demolition of old concrete slabs, and the recycling of concrete debris. A fast response differential mobility spectrometer (Cambustion DMS50) was used to measure particle number concentrations (PNC) and size distributions (PNDs) at a sampling frequency of 10 Hz in a confined laboratory room providing controlled environment and near-steady background PNCs. The sampling point was intentionally kept close to the test samples so that the release of new UFPs during these simulated processes can be quantified. Tri-modal particle size distributions were recorded for all cases, demonstrating different peak diameters in fresh nuclei (
The fluctuation of the bond stress as a function of the slip of deformed bar was determined experimentally, under displacement control, using 200 mm concrete cubes with centrally embedded 16 mm deformed bar designed to be in a confined condition. The observed global fluctuation in the bond stress, measured by linear variable differential transformers, was verified by independent measurement of the local strains along the length of the embedded bar using bonded electrical resistance (ER) strain gauges. In the pull-out tests, the failure mode was by shear. The ER strain gauges were installed inside grooves carefully machined in the steel bar to prevent direct friction from the concrete damaging the strain gauges. This approach also prevented damage to the wires and wire/gauge connection during the process of bar slip. The global fluctuation of the bond stress-slip behaviour was determined graphically and analysed using a number of statistical methods and independently verified from the local strain variation along the bar obtained from the strain gauge readings. Based on these observations, the fluctuation in bond stress with slip under displacement control has been shown to be mainly dependent on the transverse rib pattern of the bar.
The effective allocation of resources and prioritisation of maintenance actions for ageing infrastructure systems is an important issue. There are many uncertainties in the decisions making process which may be associated with the deterioration prediction or the effect of various actions on the performance of a system. Such uncertainties if not addressed can lead to incorrect decisions and wastage of resources. This paper examines the issue of effectiveness of preventative maintenance (PM) on reinforced concrete bridges deteriorating due to chloride induced corrosion from de-icing salts. The uncertainties associated with corrosion initiation prediction and the effectiveness of various preventative maintenance actions are incorporated in a stochastic methodology presented in this paper. The proposed methodology was developed as part of a wider study which integrates this model within a proactive preventative maintenance strategy optimisation framework for RC bridges. The development of the stochastic PM effectiveness model is presented and discussed here together with an illustrative example.
The use of preventative maintenance (PM) has been acknowledged as an effective way of reducing the whole life cost of maintaining bridges in good, safe and functional condition. However, there are many uncertainties associated with the need and effectiveness of PM. Such uncertainties if not addressed can lead to incorrect decisions and wastage of resources. In addition optimization procedures are necessary to produce strategies with minimum cost while maintaining the reliability of the bridge at an acceptable level. This paper examines the issue of effectiveness of different PM on reinforced concrete bridges deteriorating due to the corrosion of reinforcement from chloride ions. It investigates the applicability of an optimization methodology, using the principles of genetic algorithm (GA) to identify optimum PM strategies based on their effectiveness and cost. © 2006 Taylor & Francis Group.
Tests were developed to quantify parameters affecting the plastic shrinkage cracking of high-strength concrete of 28-day cube strength in excess of 70 MPa. The parameters measured were tensile stress-strain performance during the first 5 h after mixing and negative pore pressure development and free shrinkage during the first 24 h. Eight high-strength mixes were used containing a variety of supplementary cementing materials such as microsilica, pulverised fuel ash, granulated slag and metakaolin. Two types of superplasticers were included. Plastic shrinkage cracking was assessed using restrained ring tests in which measurements were taken using sealed samples and samples exposed to wind. The research has shown that there is no simple relationship between early age stress-strain curves, negative pore pressure, early age shrinkage and macrocracking in adverse conditions but two factors were always present when plastic cracking was observed, these being microsilica and wind.
In the study of hybrid fibre cement composites containing continuous polypropylene fibres and glass fibres, it is important to know the fracture behaviour of the glass fibre strand in order to minimise the discrepancies between experiment and theory. A new technique of light transmission through the glass fibres has been developed in order to obtain independent information about the failure of individual glass filaments within a strand. The technique gave quantitative results showing that in the hybrid composite, about 80% of the glass filaments were broken somewhere in the strands before the maximum stress in the composite was reached. This was in contrast to the composite reinforced with glass fibres alone where only about 30% of the filaments were fractured before the ultimate stress. The fractures of the glass filaments in the hybrid composite were more evenly distributed than in the singly reinforced composite which enabled greater strains to be achieved in the hybrid composite at the maximum stress. (C) 1998 Kluwer Academic Publishers.
The applicability of Weibull statistics to the condition assessment of cast iron water distribution pipes has been considered. The effect of Weibull modulus, characteristic strength, sample size and mode of loading (tension or flexure) on the strength of cast iron water distribution pipes is investigated. The strength distribution of cast iron samples cut from sections of five different water distribution pipes recovered from the ground have been characterized. Strengths have been measured in flexure, at two different temperatures (ambient and 0 degrees C), and in tension at ambient temperature using two different sample sizes. It is shown that characteristic strength values in flexure decrease with increasing size of graphite flake and that there is no significant difference between the results at the two temperatures investigated. For samples of the same volume tested in tension and flexure, the reduced strength measured in tension is consistent with Weibull predictions. However, the strength of large samples tested in tension was not significantly different from the small samples, perhaps because the samples were of the same thickness and conventional Weibull scaling is not applicable. Finally, using a method which treats a large pipe as an assembly of small samples, the strength distributions from the small samples tested in tension are used to make a prediction of the strengths of 1 m span sections of pipe loaded in three-point bending, which were reported in previous work. The predicted pipe strengths are close to the lower end of the measured pipe strength distribution. Overall, this work suggests that Weibull analysis is a useful tool to examine the strength distribution of removed from cast iron water pipes and so has the potential to contribute in the assessment of asset condition.
This paper describes the details of a laboratory investigation aimed at ascertaining the effect of penetrating surface treatments on the micro-porosity and water transport properties of three building stones used in the construction of historic buildings and monuments within Europe. The pore-structure and morphology of treated and untreated stone specimens were assessed using a combination of helium autopycnometry, mercury intrusion porosimetry and scanning electron microscopy techniques. Water repellence and transport properties were evaluated using the Karsten tube and magnetic resonance imaging techniques respectively. It was found that surface penetrating treatments have a pore-refining effect on the stone matrix, the extent of internal alteration being dependent on the initial pore-structure. A treatment efficiency index has been established for evaluating the performance of treated surfaces.
In recent years there has been considerable interest in the development of additives and admixtures which reduce or eliminate the ingress of chloride ions into reinforced concrete. One method of increasing the tolerance of RC structures to the presence of chloride ions is the application of corrosion inhibitors. These materials interfere with one or more stages of the corrosion process reducing the overall rate of corrosion. This paper presents the results of a study of two corrosion inhibitors, an admired anodic inhibitor (calcium nitrite) and a commercially available surface applied 'penetrating' inhibitor (a modified amino alcohol). Tests on three concrete mixes were used to investigate the influence of the admixed inhibitor on the workability, set characteristics and 28-day strength of fresh and hardened concrete. The corrosion behaviour of steel bars embedded in equivalent concrete mixes were also examined and the ability of both corrosion inhibitors to suppress corrosion was investigated as a function of time, depth of cover and concrete duality. It is concluded that over the time scale of these experiments both corrosion inhibitors were successful in reducing the rate of reinforcement corrosion.
Plastic shrinkage cracking in concrete usually occurs during the first 5 hours after placing and therefore the mechanics of fibre reinforcement were studied during this period. Two types of polypropylene fibres were mixed at 0.1% by volume. The development of bond strengths and the stresses which the fibres could sustain across cracks were measured by uniaxial tensile tests during the first 5 hours after mixing. Fibre stresses up to 130 MPa at 5 hours were achieved which were equivalent to a composite post-crack strength of 65 kPa. Restrained ring tests were used to assess the amount of cracking which occurred during the first 24 hours in a different high strength mix and, although the results were very variable, the fibres were found to reduce the crack area by between 40% and 85% compared with plain concrete, depending on fibre type.
It is shown that broad line gradient echo magnetic resonance imaging is an ideal tool with which to study the ingress of hydrophobic polymer surface treatments into porous building materials, specifically in this case sandstone. It is further shown that the method can be used to quantitatively visualize the movement of water into and through the treated material, both from the surface and bulk, as a function of time. The influence of treatment cure time, cure temperature and substrate hydration on the subsequent water transport have been investigated. For the first time direct evidence of water pumping through a treated surface is presented.