Using Long-Term Outdoor Exposure Data to Benchmark Accelerated Durability Test Methods

Many performance-based durability test methods adopted in various national and international standards were developed decades ago based on short-term evaluations. Most durability tests use various methods to accelerate reactions in order to obtain results in a reasonably short period of time. Then pass/fail criteria are set for these tests in standard specifications. However, the acceleration techniques used maybe overly severe, and preclude the use of concrete materials and mix designs that perform perfectly well in the field. The inclusion of long-term field tests or outdoor exposure tests can be used to verify the appropriateness of both the test methods and the test limits. This provides more confidence that the results from the test methods are meaningful and that the adopted specification limits are appropriate. This approach has been used to verify or modify ASTM and CSA test methods for sulfate resistance, mitigation of alkali-silica reaction, de-icer salt scaling resistance, and for resistance to chloride ingress for marine and deicer exposures. However, in addition to the time and costs for such programs, another limiting factor can be that the materials and mix designs used in the long-term tests may no longer be representative of those currently in use. As another issue, the precision of all test methods needs to be evaluated by inter-laboratory test programs to provide confidence in the reproducibility of test results obtained. This contribution describes results from several long-term test programs and inter-laboratory studies focused on verifying specific standard test methods for durability

MAT-760: COMPARISON OF LABORATORY PERFORMANCE TESTS USED TO ASSESS ALKALI-SILICA REACTIVITY

Alkali-silica reaction of certain concrete aggregates can lead to premature deterioration and maintenance problems in concrete structures. The CSA A23.1-14A/ASTM C1293 concrete prism test (CPT) and the CSA A23.2-25A/ASTM C1260/ASTM C1567 accelerated mortar bar test (AMBT) are the two main procedures used in CSA and ASTM standards for examining the potential alkali-silica reactivity (ASR) of aggregates and also for assessing the effectiveness of supplementary cementing materials (SCMs) in suppressing ASR. The long testing duration of the CPT and the unreliability of the rapid AMBT have led to development and evaluation of a third method, the accelerated concrete prism test (ACPT). All three methods were performed using a range of different aggregates and SCM partial replacements of cement. Expansion data were compared with one another and with known field performance, where available. Results show good correlation between CPT and ACPT expansions and these tests appear to be good predictors of field performance. The AMBT, on the other hand, can be very misleading with certain aggregates

MAT-745: THE EFFECT OF GROUND GRANULATED BLAST FURNACE SLAG AND SILICA FUME ON THE DURABILITY OF HIGH PERFORMANCE CONCRETE IN BRIDGE DECKS

High-performance concrete typically has a low water to cementing materials ratio (w/cm), high binder content and may contain high levels of supplementary cementitious materials. The effects of ground granulated blast furnace slag (GGBFS) and silica fume (SF) on the durability of HPC were investigated. In this study, HPC mixtures at 0.33 w/cm were made with two sources of blended cements containing 8% SF mixed with 25 and 50% GGBFS replacements by mass of cement. The compressive strength, drying shrinkage, thermal deformation and transport properties were tested. The preliminary test results have shown that increased fineness of the blended cement enhances the transport and mechanical properties), but results in increased early age thermal deformation, drying shrinkage, leading to increased cracking potential

MAT-742: EFFECT OF SUPPLEMENTARY CEMENTITIOUS MATERIALS ON THE RESISTANCE OF MORTAR TO PHYSICAL SULFATE SALT ATTACK

Physical sulfate salt attack is one of the most rapid and severe deterioration mechanisms in concrete structures. One of the most common approaches to improve resistance of concrete to sulfate attack is to use supplementary cementitious materials. However, physical salt attack may still cause damage to concrete with supplementary cementitious materials. Moreover, according to some literature sources, some supplementary cementitious materials may even reduce resistance to physical salt attack. The current research investigates the effect of supplementary cementitious materials on the ability of mortars to resist physical sulfate salt attack and its relationship with pore structure and transport properties. Mortar specimens with 45 and 65% replacement of cement by ground-granulated blast-furnace slag and with 20 and 40% replacement of cement by fly ash were exposed to physical sulfate attack. The results show a good correlation between the pore microstructure and transport properties to the resistance to physical salt attack. Ground-granulated blast-furnace slag was found to improve the resistance to physical salt attack, while fly ash demonstrated a negative effect

MAT-739: INFLUENCE OF SLAG CHEMISTRY AND COMPOSITION ON THE HYDRATION AND MECHANICAL PROPERTIES OF SUPERSULFATED CEMENT

This research evaluates ways of improving early-age property of supersulfated cements. Mechanical performance of SSC was studied after optimizing the slag- calcium sulfate- alkali activator composition. This study was conducted using four slags of different chemical composition. The purpose was to find a correlation between slag composition and compressive strength and determine the influence of anhydrite content and alkali activator content on the hydration process of SSC. The results demonstrated that the compressive strength of mortars was strongly influenced by the Al2O3 content of the slag, which also influenced the optimum mix composition of the SSC mixtures. Mixtures containing slags with high Al2O3 required low amount of alkali activator in order to provide high strength values, while, increasing the activator content reduced the compressive strength. The heats of hydration of all the mixtures were also studied

Long-term mitigating effect of lithium nitrate on delayed ettringite formation and ASR in concrete – microscopic analysis

Abstract: This paper presents long-term results and microscopic analyses for a six-year experimental study on the effectiveness of lithium nitrate in mitigating delayed ettringite formation (DEF) with or without alkali-silica reaction (ASR). In the previous publication [1], interesting findings were found showing that lithium nitrate is effective in controlling DEF or ASR-DEF mechanisms in concretes. In the present study, microstructural features associated with microcracking and ettringite infilling showed relatively reduced intensity of internal distress and damage when lithium nitrate was admixed in DEF expansive concrete. Microanalysis done using plots of Al/Ca and S/Ca shows that, the use of lithium nitrate leads to formation of non-expansive ettringite similar to normal early-age ettringite formed in moist-cured concretes. These observations give some insights into the mechanism responsible for mitigation of DEF by lithium nitrate

MAT-759: PARTICLE SIZE ANALYSIS AS A MEANS TO BETTER UNDERSTAND THE INFLUENCE OF FLY ASH VARIABILITY IN CONCRETE

Fly ash is generated from thermal power stations as an industrial by-product of coal combustion materials. Its particles are generally glassy, spherical in shape, and typically range in size from 0.5-300 µm. Coal fly ash is widely used as a partial cementitious material in concrete, which not only offers economic and environmental benefits but also improves concrete performance. However, variability of the physical description and chemical composition of fly ash has been considered to be a major barrier to its increased use in cement and concrete. In this study the variability and properties of fly ash are characterized with an emphasis on particle size analysis as a means for fly ash producers to better understand material properties in relation to the process of production, classification, and potential modes of utilization. Fly ash samples were collected from different coal-fired power plants from certain Indian and Canadian sources. The particle size analysis results using Laser Diffraction Technique showed a wide variation between the particle size distributions of the studied sources. However, no correlation between the varied size distributions and chemical compositions of fly ash samples was found. Laboratory experiments on the selected fly ash samples are being undertaken to correlate fly ash characteristics and their effects on the performance of concrete mixtures with cementitious replacement level up to 50%

Complete genome sequence of Salmonella enterica serovar Typhimurium U288

Salmonella enterica serovar Typhimurium U288 has firmly established itself within the United Kingdom pig production industry. The prevalence of this highly pathogenic multidrug-resistant serovar at such a critical point in the food chain is therefore of great concern. To enhance our understanding of this microorganism, whole-genome and plasmid sequencing was performed

Salmonella Typhimurium-specific bacteriophage ΦSH19 and the origins of species specificity in the Vi01-like phage family

<p>Abstract</p> <p>Background</p> <p>Whole genome sequencing of bacteriophages suitable for biocontrol of pathogens in food products is a pre-requisite to any phage-based intervention procedure. Trials involving the biosanitization of <it>Salmonella </it>Typhimurium in the pig production environment identified one such candidate, ΦSH19.</p> <p>Results</p> <p>This phage was sequenced and analysis of its 157,785 bp circular dsDNA genome revealed a number of interesting features. ΦSH19 constitutes another member of the recently-proposed <it>Myoviridae </it>Vi01-like family of phages, containing <it>S</it>. Typhi-specific Vi01 and <it>Shigella</it>-specific SboM-AG3. At the nucleotide level ΦSH19 is highly similar to phage Vi01 (80-98% pairwise identity over the length of the genome), with the major differences lying in the region associated with host-range determination. Analyses of the proteins encoded within this region by ΦSH19 revealed a cluster of three putative tail spikes. Of the three tail spikes, two have protein domains associated with the pectate lyase family of proteins (Tsp2) and P22 tail spike family (Tsp3) with the prospect that these enable <it>Salmonella </it>O antigen degradation. Tail spike proteins of Vi01 and SboM-AG3 are predicted to contain conserved right-handed parallel β-helical structures but the internal protein domains are varied allowing different host specificities.</p> <p>Conclusions</p> <p>The addition or exchange of tail spike protein modules is a major contributor to host range determination in the Vi01-like phage family.</p

Spectroscopic Transit Search: a self-calibrating method for detecting planets around bright stars

We search for transiting exoplanets around the star $\beta$ Pictoris using high resolution spectroscopy and Doppler imaging that removes the need for standard star observations. These data were obtained on the VLT with UVES during the course of an observing campaign throughout 2017 that monitored the Hill sphere transit of the exoplanet $\beta$ Pictoris b. We utilize line profile tomography as a method for the discovery of transiting exoplanets. By measuring the exoplanet distortion of the stellar line profile, we remove the need for reference star measurements. We demonstrate the method with white noise simulations, and then look at the case of $\beta$ Pictoris, which is a $\delta$ Scuti pulsator. We describe a method to remove the stellar pulsations and perform a search for any transiting exoplanets in the resultant data set. We inject fake planet transits with varying orbital periods and planet radii into the spectra and determine the recovery fraction. In the photon noise limited case we can recover planets down to a Neptune radius with an $\sim$80% success rate, using an 8 m telescope with a $R\sim 100,000$ spectrograph and 20 minutes of observations per night. The pulsations of $\beta$ Pictoris limit our sensitivity to Jupiter-sized planets, but a pulsation removal algorithm improves this limit to Saturn-sized planets. We present two planet candidates, but argue that their signals are most likely caused by other phenomena. We have demonstrated a method for searching for transiting exoplanets that (i) does not require ancillary calibration observations, (ii) can work on any star whose rotational broadening can be resolved with a high spectral dispersion spectrograph and (iii) provides the lowest limits so far on the radii of transiting Jupiter-sized exoplanets around $\beta$ Pictoris with orbital periods from 15 days to 200 days with >50% coverage.Comment: Accepted for publication in A&A, 8 pages, 8 figures. The Github repository can be found at https://github.com/lennartvansluijs/Spectroscopic-Transit-Searc