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Although considerable research has been undertaken on alkali-activated binders for geopolymer concrete production, few of these studies have focused on clay based geopolymer concrete. This paper reports the results of an experimental investigation to optimize the mix design of geopolymer concrete prepared solely from clay material. Four Activator Modulus (AM); 1.0, 1.25, 1.5 and 1.75 for each of two Sodium Oxide (Na2O) dosages of 10% and 15% were selected for this investigation. A total of eight mix ratios comprising 72 specimens were tested. A comparison of physical behavior of clay based geopolymer mortar to that of fly ash based geopolymer mortar has been drawn throughout this paper. A Na2O dosage of 10% provided consistent strength for all AM tested, however the specimens prepared with Na2O dosage of 15% showed a reduction with time for all but the AM 1.0 specimens. Compressive strength of specimens prepared with AM of 1 for both of the Na2O dosage of 10% and 15% exhibited the superiority over other AM. The investigation showed potential for clay material to be an alternative to ordinary Portland cement (OPC).

Geopolymer concrete produced using 100% fly ash as the main binder is a sustainable construction material capable replacing Portland Cement (PC) concretes. At present PC production generates 5-7% of anthropogenic CO2 emissions world-wide, but it has been estimated that this can be reduced by 26-45% by replacing PC with geopolymer concrete. In order to be confident of the real world application of geopolymer concrete and the environmental benefits it can provide, in depth knowledge is required to ensure that the fly ash used will provide acceptable long term performance from the concrete produced. A series of geopolymer concrete specimens were prepared using four different fly ashes and tested for compressive strength, flexural strength, splitting tensile strength and elasticity modulus up to one year. Microstructural development between 28 and 365 days in different geopolymers were assessed using state of the art techniques. The 365-day compressive strength, flexural strength, splitting tensile strength and elasticity modulus of four fly ash geopolymer concretes were ranged 28-88MPa, 3.9-6.3MPa, 1.8-4.7MPa and 10-29GPa, respectively. Compressive strength variation is attributed to degree of reactivity of the fly ash, which is primarily governed by the quantity of finer particles in the reactive amorphous phase and sodium-aluminosilicate (N-A-S-H) gel formation. The CaO in fly ash also reacts with alkali to produce calcium-aluminosilicate (C-A-S-H) gel which provides additional strength to the concrete. The tensile strength of geopolymer concrete is governed by the gel-aggregate bond strength. Micro-cracks formed in the concrete due to high temperature curing can negatively affect the gel-aggregate bond strength. Moreover, larger crack widths lead to discontinuity and hence the formation of a less dense microstructure. This results in lower density and elasticity modulus for geopolymer concrete.

The environmental impact from the production of cement has prompted research into the development of concretes using 100% replacement materials activated by alkali solutions. This paper reports research into the durability of AAS concrete. The durability properties of AAS have been studied for a range of sodium oxide dosages and activator modulus. Properties investigated have included measurements of workability, compressive strength, water sorptivity, depth of carbonation and rapid chloride permeability. Microstructure studies have been conducted using scanning electron microscopy and energy dispersive X-ray spectroscopy. It was concluded that an activator modulus of between 1.0 and 1.25 was identified as providing the optimum performance for a sodium oxide dosage of 5% and that AAS concretes can exhibit comparable strength to concrete currently produced using Portland cement (PC) and blended cements. However, with regards to the durability properties such as water sorptivity, chloride and carbonation resistance; the AAS concretes exhibited lower durability properties than PC and blended concretes. This, in part, can be attributed to surface microcracking in the AAS concretes.

As a part of the collaborative studies between China, Australia and the UK, examing sulfate attack on concrete, this paper reports the experimental results obtained from the Chinese laboratory. Specimens were immersed in sodium and magnesium sulfate solutions with concentrations of 500mg/L, 5000mg/L and 50000mg/L. Investigations were conducted over approximately a one year period. Susceptibility to sulfate attack was assessed in terms of changes in the mass and length of specimens, the compressive strength of the concrete, as well as the diffusion depth of sulfate-ions into the concrete at fixed intervals. Several differences were observed between these results and those reported in studies from the UK laboratory.

This paper reports the results of a research project comparing the effect of surface crack width and degree of corrosion on the bond strength of confined and unconfined deformed 12 and 16 mm mild steel reinforcing bars. The corrosion was induced by chloride contamination of the concrete and an applied DC current. The principal parameters investigated were confinement of the reinforcement, the cover depth, bar diameter, degree of corrosion and the surface crack width. The results indicated that potential relationship between the crack width and the bond strength. The results also showed an increase in bond strength at the point where initial surface cracking was observed for bars with confining stirrups. No such increase was observed with unconfined specimens.

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.

This paper describes experimental work to investigate the effect of reinforcement corrosion on the behaviour of concrete beams reinforced with plain round bars. Particular attention is paid to the bond between reinforcement and concrete. Four groups of beam specimens were tested, each designed to investigate specific aspects of structural performance including stiffness and deflection under service loads, ultimate flexural and shear strengths and deformation capacity at failure. Beams were conditioned to induce loss of cross-sectional reinforcement of up to 10% owing to corrosion, equivalent to 0·3 mm corrosion penetration, and longitudinal crack widths of 1·0 mm. Flexural stiffness of specimens detailed for a flexural mode of failure was not impaired by corrosion. Strength of beams with corroded bars equalled or exceeded that of companion non-corroded specimens in all cases, despite loss of bar section. It is concluded that an enhancement of anchorage capacity, believed to be associated principally with increased radial stresses on the bar–concrete interface in the vicinity of the end reactions, was able to offset loss of bar section.

This paper reports results of an experimental programme to measure changes in friction characteristics of the interface between reinforcement and concrete as a result of the formation of corrosion products on the surface of the steel. The aim of the study was to determine whether a weak corrosion layer contributes to reported reductions in residual bond capacity. Corrosion was carried out under accelerated conditions using three different conditioning regimes. Principal parameters included in the investigation are conditioning regime, the amount of corrosion, and the stiffness of the restraint to expansion of the corrosion products. Experimental results indicate that corrosion products do not impair friction characteristics of a bar/concrete interface when surface crack width does not exceed 1.0 mm.

This paper reports results of an experimental programme to measure changes in bond characteristics of plain round reinforcement as a result of corrosion. Principal parameters included in the investigation are the amount of corrosion, the presence of confining reinforcement in the form of links, cover thickness and the initial condition of the reinforcement. In the absence of confining links, bond strength of bars cast near the bottom of a pour is found to reduce with increasing corrosion. However, although top-cast bars were initially weaker, small amounts of corrosion were sufficient to raise bond strength to that of bottom-cast bars. With increasing corrosion, strength reduced in a similar manner to bottom-cast bars. Confining reinforcement had little influence on bond strength prior to the onset of corrosion, but plays an important role in maintaining strength once corrosion becomes established. Results from these tests suggest that surface crack width may provide a better parameter than section loss or corrosion penetration through which to assess residual bond strength. The reasons for this are explained, and empirical relationships for residual strength are derived.

This study investigates the durability of basalt fiber following immersion in a range of chemical solutions representative of the concrete medium. The tests were conducted over a 62-day period and the solutions were sodium hydroxide, sodium chloride, sodium sulfate and combinations of the three. Weight loss was observed in all alkali solutions, with the worst being the combination of sodium hydroxide with sodium sulfate. The impact of chloride was minimal in the alkaline environment and reduced the impact of the sulfate when both were present. Microstructure analysis using a Scanning Electron Microscope (SEM) found that the silica structure present in basalt fibers was degraded by the OH-from an alkaline medium. The study suggests the need for modification or treatment of basalt fibers before use as fiber reinforcement in concrete.

The measured weight loss data for a number of mild steel bars contained in Portland Cement concrete, together with predicted weight loss values monitored using potentiostatically controlled linear polarisation resistance (LPR) measurements are reported. Three sets of reinforced concrete specimens, each containing electrically isolated mild steel bars, were subjected to either • chloride-induced corrosion, • carbonation-induced corrosion • a control nitrogen rich environment with minimal corrosion. Each set of specimens was initially exposed to a 22-hour dry, 2-hour wet controlled environment for a duration of between 1026 and 1085 days. This was later changed to a 6-day dry, 1 day wet cycle for the carbonation exposure specimens after the initial set of gravimetric testing. The weight loss for each bar due to corrosion was recorded. Instantaneous LPR measurements were also taken on each bar at regular intervals throughout the exposure period. These resistance measurements were then integrated over the exposure period to estimate total weight loss. The results show that weight loss evaluated from experimental LPR measurements gives a significant over-estimate of the weight losses measured gravimetrically.

The linear polarisation resistance (LPR) method can be used to measure the active rate of corrosion of steel reinforcement in concrete structures. However a single measurement may be sensitive to the ambient environmental conditions and thus may not be representative of the mean annual rate of corrosion. The LPR measurement may be dependent upon the temperature at the time of sampling and on any wetting/drying effects resulting from rainfall and wind or sunshine. Recent studies have examined the behaviour of a series of reinforced concrete specimens subject to chloride contamination or carbonation induced corrosion in a controlled laboratory environment. LPR measurements taken at frequent intervals have been related to a wet/dry cycle imposed upon the specimens to promote corrosion activity. In addition, similar studies have been carried out, of an in situ reinforced concrete specimen exposed to the ambient weather conditions. The study is only partly completed, but interim results show the variability of LPR measurements and the influences the environment may exert on single spot measurements.

This paper reports the results of galvanostatic pulse transient response experiments to determine the corrosion parameters associated with actively corroding reinforcing steel in concrete. Galvanostatic pulse measurements have been conducted on a number of short 100 mm sections of steel reinforcing bar embedded in chloride contaminated concrete. The duration of the applied galvanostatic pulse was 90 s and the lateral distance of the point of measurement from the bar varied from zero to 400 mm. All of the bars monitored were conditioned so that they were actively corroding at different rates. Analysis of the galvanostatic pulse transient response has enabled the separate components that make up the measured transients to be isolated and evaluated. These components display a range of resistivities and capacitances, dependent on the corrosion condition of the reinforcing steel, which may be attributed to the corrosion process, to effects within the concrete cover, or to film effects on the surface o...

Use of a sensor controlled guard ring has been developed in recent years to enhance the accuracy of linear polarisation corrosion rate measurements on reinforced concrete structures. The sensors are used to monitor potential differences measured on the concrete surface above the reinforcing steel. These data are then used to confine the corrosion measurement to a known area of reinforcing steel. The role of the sensors is paramount in maintaining adequate confinement of the perturbation applied to the reinforcing steel. Experiments were conducted on reinforced concrete specimens containing both active and passive zones of reinforcing steel. Polarisation resistance measurements were taken using both a potentiostatically controlled guard ring device developed at the University of Liverpool and a galvanostatically controlled commercial device. Both devices indicated that the orientation of the sensor electrodes can affect the polarisation resistance determined when taking measurements on passive stee...

The use of a sensor controlled guard ring has been developed in recent years to enhance the accuracy of linear polarisation corrosion rate measurements on reinforced concrete structures. The established method of measurement uses a galvanostatically controlled guard ring device. In the method reported in this article the reinforcing steel is polarised potentiostatically by an inner auxiliary electrode and the real time plot of the current response is displayed on a laptop computer which controls the guard ring device. The area of steel polarised is confined by a current applied from an outer guard ring electrode which is controlled by two sensor electrodes positioned between the inner auxiliary and outer guard ring electrode. The potential between the two sensor electrodes is continually monitored, and the current output from the guard ring electrode varied to maintain a constant potential difference between the two sensor electrodes. The method has been validated on an electrical test circuit simulating active and passive reinforcement corrosion. Further testing has been conducted on a reinforced concrete specimen and the results compared with those of commercially available galvanostatically controlled equipment and those of standard unconfined linear polarisation resistance measurements.

Results of galvanostatic pulse transient response experiments were reported to determine the corrosion parameters associated with passive and actively corroding reinforcing steel in concrete. Galvanostatic pulse measurements were conducted on a number of short sections of steel-reinforcing bar embedded in concrete. The duration of the applied galvanostatic pulse varied from 45 s to 600 s. The bars displayed a range of corrosion rates, from passive steel to highly active corrosion. Analysis of the galvanostatic pulse transient enabled separate components, which made up the measured transient, to be isolated. These components displayed a range of resistances and associated capacitances, dependent upon the corrosion state of the reinforcing steel, which may be attributed to the corrosion process or other effects within the bulk concrete. The corrosion rate was calculated from the summation of the separate resistive components and compared with the corrosion rate determined from linear polarization resistance (LPR) measurements on the same specimens. Results from the galvanostatic pulse transient analysis showed that significant errors in evaluating corrosion rates using the LPR method may be incurred if the usual 30-s equilibrium period was used for measuring actively corroding steel bars.

When concrete structures—such as pier supports—are placed in water, they can have a detrimental effect on the surrounding environment by causing the pH to rise. This rise in pH can harm and kill animal and plant life. The concentration of hydroxyl ions leached from concrete can be affected by a number of factors, including cement type, shape of structure, ratio of surface area and volume, and the flow of the water. This paper presents the results of a research project that investigated three mixtures: 100% ordinary portland cement (OPC), 30% pulverized fly ash (PVA), and 65% ground-granulated blast-furnace slag (GGBS). Tests were conducted in both stagnant and flowing water using a range of specimen geometries and sizes. The results showed that the mixture, volume/surface area, and geometry of the specimen can affect both the rate of leaching and the cumulative number of moles of hydroxyl ions leached.

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.

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.

The kinetics of the gas phase isomerisation of cyclobutene initiated by direct single photon excitation of C–H stretching overtones have been studied and the observed behavior has been interpreted using a treatment which combines RRKM theory and models accounting for weak intermolecular energy transfer. Results obtained from the excitation of five different overtone states spanning an energy range of 5070 cm−1 have allowed us to examine the form of the dependence on energy of the energy transfer step sizes 〈ΔE〉 deduced from numerical solutions of the collisional master equation using an exponential‐down model, for the collider gases cyclobutene, SF6, CHF3, CH4, CO2, H2, CO, N2, Ar, and He. Our calculations indicate very small energy transfer step sizes, particularly for the most inefficient collider molecules. We discuss the factors which might contribute to the determination of low values for 〈ΔE〉 and the sensitivity of the master equation calculations to details of the RRKM model. Our results, when expr...

In part I of this study [Baggott, Clase, and Mills, Spectrochim. Acta Part A 42, 319 (1986)] we presented FTIR spectra of gas phase cyclobutene and modeled the v=1–3 stretching states of both olefinic and methylenic C–H bonds in terms of a local mode model. In this paper we present some improvements to our original model and make use of recently derived ‘‘x,K relations’’ to find the equivalent normal mode descriptions. The use of both the local mode and normal mode approaches to modeling the vibrational structure is described in some detail. We present evidence for Fermi resonance interactions between the methylenic C–H stretch overtones and ring C–C stretch vibrations, revealed in laser photoacoustic spectra in the v=4–6 region. An approximate model vibrational Hamiltonian is proposed to explain the observed structure and is used to calculate the dynamics of the C–H stretch local mode decay resulting from interaction with lower frequency ring modes. The implications of our experimental and theoretical studies for mode‐selective photochemistry are discussed briefly.

The distribution of products resulting from the isomerization of gas phase 1‐methylcyclopropene (1) induced by C–H stretch overtone excitation has been studied in a search for mode specific effects. Quantum yields for the disappearance of 1 have been determined as a function of the total pressure of a mixture of 1 and methylenecyclopropane and of the added bath gases SF6 and Ar using a combination of intracavity dye laser photolysis and end product analysis by gas chromatography. These data, together with the ratios of the yields of the major isomerization products, are adequately reproduced by RRKM theory and a weak collisional energy transfer model: no evidence for mode specificity is obtained. The experimental data demonstrate the importance of inefficient collisional energy transfer but allow some conclusions to be drawn concerning the applicability of RRKM theory which are not strongly dependent upon the details of the energy transfer model.

This paper presents the effect of silica fume and nano silica, used individually and in combination with the set accelerator and/or hydrated lime, on the properties of class F high volume ultra fine fly ash (HV-UFFA) cement composites, replacing 80 % of cement (OPC). Compressive strength test along with thermogravimetric analysis, X-ray diffraction and scanning electron microscopy were undertaken to study the effect of various elements on the physico-chemical behaviour of the blended composites. The results show that silica fume when used in combination with the set accelerator and hydrated lime in HV-UFFA cement mortar, improves its 7 and 28 day strength by 273 and 413 %, respectively, compared to the binary blended cement fly ash mortar. On the contrary, when nano silica is used in combination with set accelerator and hydrated lime in HV-UFFA cement mortar, the disjoining pressure in conjunction with the self-desiccation effect induces high early age micro cracking, resulting in hindering the development of compressive strength. However, when nano silica is used without the additives, it improves the 7 and 28 day strengths of HV-UFFA cement mortar by 918 and 567 %, respectively and the compressive strengths are comparable to that of OPC.

The first known case of metastatic Burkitt lymphoma to the penis is presented. The penis is a rare site of metastatic neoplasm in spite of its rich blood supply. Less than 200 cases have been reported in the last one hundred years. Local control was achieved with radiation therapy.