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-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

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

TOI-836 : a super-Earth and mini-Neptune transiting a nearby K-dwarf

Funding: TGW, ACC, and KH acknowledge support from STFC consolidated grant numbers ST/R000824/1 and ST/V000861/1, and UKSA grant ST/R003203/1.We present the discovery of two exoplanets transiting TOI-836 (TIC 440887364) using data from TESS Sector 11 and Sector 38. TOI-836 is a bright (T = 8.5 mag), high proper motion (∼200 mas yr−1), low metallicity ([Fe/H]≈−0.28) K-dwarf with a mass of 0.68 ± 0.05 M⊙ and a radius of 0.67 ± 0.01 R⊙. We obtain photometric follow-up observations with a variety of facilities, and we use these data-sets to determine that the inner planet, TOI-836 b, is a 1.70 ± 0.07 R⊕ super-Earth in a 3.82 day orbit, placing it directly within the so-called ‘radius valley’. The outer planet, TOI-836 c, is a 2.59 ± 0.09 R⊕ mini-Neptune in an 8.60 day orbit. Radial velocity measurements reveal that TOI-836 b has a mass of 4.5 ± 0.9 M⊕, while TOI-836 c has a mass of 9.6 ± 2.6 M⊕. Photometric observations show Transit Timing Variations (TTVs) on the order of 20 minutes for TOI-836 c, although there are no detectable TTVs for TOI-836 b. The TTVs of planet TOI-836 c may be caused by an undetected exterior planet.Publisher PDFPeer reviewe

TOI-836: A super-Earth and mini-Neptune transiting a nearby K-dwarf

We present the discovery of two exoplanets transiting TOI-836 (TIC 440887364) using data from TESS Sector 11 and Sector 38. TOI-836 is a bright ($T = 8.5$ mag), high proper motion ($\sim\,200$ mas yr$^{-1}$), low metallicity ([Fe/H]$\approx\,-0.28$) K-dwarf with a mass of $0.68\pm0.05$ M$_{\odot}$ and a radius of $0.67\pm0.01$ R$_{\odot}$. We obtain photometric follow-up observations with a variety of facilities, and we use these data-sets to determine that the inner planet, TOI-836 b, is a $1.70\pm0.07$ R$_{\oplus}$ super-Earth in a 3.82 day orbit, placing it directly within the so-called 'radius valley'. The outer planet, TOI-836 c, is a $2.59\pm0.09$ R$_{\oplus}$ mini-Neptune in an 8.60 day orbit. Radial velocity measurements reveal that TOI-836 b has a mass of $4.5\pm0.9$ M$_{\oplus}$ , while TOI-836 c has a mass of $9.6\pm2.6$ M$_{\oplus}$. Photometric observations show Transit Timing Variations (TTVs) on the order of 20 minutes for TOI-836 c, although there are no detectable TTVs for TOI-836 b. The TTVs of planet TOI-836 c may be caused by an undetected exterior planet

TOI-836: A super-Earth and mini-Neptune transiting a nearby K-dwarf

peer reviewe

Assessing the Impact of Curing on Chloride Penetration Resistance of the Concrete Cover Using Sorptivity Profiling

The chloride penetration resistance of the near-surface concrete cover depth is greatly influenced by the type and extent of curing provided. Very short or ineffective curing regimes result in less cement hydration and a more porous surface due to early evaporation of capillary water. The resultant depth-dependent capillary pore structure results in a depth-dependent resistance to ingress of aggressive fluids, such as chloride solutions. Without reliable performance test methods for pre-qualification and quality assurance, minimum requirements for curing in specifications for concrete structures exposed to chlorides are typically prescriptive. In this paper, a series of modified rate of absorption tests is used to describe and quantify the effect of curing on the chloride penetration resistance of two concretes subjected to four different curing regimes, including accelerated moist curing. The proposed test method can be used to optimize curing for durability performance and allow credit for use of accelerated curing.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Workability retention and compressive strength of self-compacting concrete incorporating pumice powder and silica fume

This paper presents the results of an experimental study carried out to investigate the performance of self-compacting concrete (SCC) mixes, which produced using blended binders containing pumice powder in various proportions. As a volcanic material, pumice possesses pozzolanic properties and can effectively be added to the concrete mixture. The influence of pumice powder on the self-compactibility properties such as slump flow, V-funnel flow, U-box and J-ring flow and compressive strength was investigated. Also, in order to clearly understand the effect of pumice powder on the workability retention of concrete, the slumps were measured with elapsed time. The comparison has been made between SCC with pumice powder to other mixtures with fly ash and slag through tests on fresh and hardened concrete. In all of the mixtures the portland cement was partially replaced from 10% to 50% by pumice, fly ash and slag. The incorporation of more than 30% of pozzolanic materials in the binary blended portland cement mixtures results in a significant decline in the fresh and hardened test results. In addition, to improve the properties of SCC containing pumice, the ternary blended cement replacement with pumice and silica fume (SF) was developed. The results revealed that incorporation of SF substantially enhanced the properties of the mixtures