Recent research has shown that cellulose nanocrystals (CNCs) can be used at low dosage levels (approximately 0.2% by volume of cement) to increase the extent of hydration and to improve the flexural ...strength of cement pastes. However, the previous work was based on using a CNC made from a single source material and processing technique and was performed using only Type V cement. This work examines the influence of various raw material sources and processing techniques used to make the CNCs. In total, nine different CNCs were investigated with pastes made using Type I/II and Type V cements. Isothermal calorimetry (IC), thermogravimetric analysis (TGA) and ball-on-three-ball (B3B) flexural strength testing were used to quantify the performance of CNC-cement composites. IC and TGA results showed that CNCs increased the degree of hydration in all systems. IC results showed that the increase in total heat release was greater in the Type V than in the Type I/II cement paste systems. B3B flexural testing indicated an increase in flexural strength of up to 20% with both Type I/II and Type V systems. These results also showed that the performance of CNC-cement composites can be affected by the source and manufacturing process used to make the CNC.
•Concrete and GFRP from 18-year old dry-dock repair analyzed.•Concrete shows variability and clear degradation.•GFRP variability limited and degradation limited to surface.•GFRP can be a potential ...alternative to steel for marine structures.
Concrete and glass fiber reinforced polymer (GFRP) bar samples from an 18-year old repair project executed on an existing dry-dock were obtained by coring the dry dock in two regions. Several destructive and non-destructive tests were performed on both materials. Testing performed on the concrete showed substantial variability and clear evidence of damage occurring over the years. Further, there were significant differences in the concrete obtained from two different regions of the dock. The concrete was carbonated and chloride from seawater had penetrated significantly into its depth. The GFRP bars showed relatively lower variability in terms of test results. Electron microscopy and horizontal shear strength results suggest that the GFRP surface of the bars had suffered some damage, whereas the core had remained unaltered. These findings regarding limited damage to the GFRP, taken together with recent advances in GFRP production technology, support the notion that concrete reinforced with GFRP bars is an attractive alternative to conventional steel reinforced concrete for marine infrastructure applications.
The formation of calcium oxychloride in cold conditions due to a reaction between calcium chloride deicing salt and calcium hydroxide in the concrete causes substantial damage to pavement concretes. ...In this study, the role of supplementary cementitious materials (SCMs) in mitigating damage in cement pastes and mortars exposed to highly concentrated CaCl
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solutions and low temperatures is elucidated. Cementitious paste and mortar mixtures designed with different SCM replacement levels were prepared and immersed in 25% CaCl
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solutions and subject to low-temperature cycles (− 8–25 °C) for 360 days (180 cycles). Damage was reduced as the SCM replacement level and curing time were increased, as confirmed by bulk resistivity, visual observation, and light microscopy measurements. Substantial differences between paste and mortar behavior were observed with the mortars outperforming pastes.
The concrete industry faces an urgent need to identify new supplementary cementitious material (SCM) sources. One class of materials available in large volumes are basaltic materials, which are often ...stockpiled in landfills as a waste product from quarries and granule operations. Reactivity testing on some such materials has shown them to be inert. The thermal activation of basaltic fines, and their mixtures with fly ash and limestone was therefore evaluated in a furnace using different process variables. Physical and chemical characterization using X-ray diffraction, Fourier transform infrared spectroscopy, and electron microscopy was performed on the raw and thermally activated materials. The reactivity of the resulting materials was directly measured. Heating beyond 1300 °C and cooling results in complete amorphization for the tested materials and resulted in the highest reactivity. Thus, the activation of basaltic fines into SCMs is feasible, although optimization to reduce temperatures is needed.
In cold regions, calcium and magnesium chloride deicing salts damage concrete pavements due to the formation of certain deleterious chemical phases, including calcium oxychloride. While there is much ...research at a cement paste-scale, damage in concrete has been less studied. In this study, we evaluate concrete damage due to calcium and magnesium chloride and explain the roles of supplementary cementitious materials (SCM) replacement level, air entrainment, salt type, and exposure conditions in damage development. Various non-destructive test methods including bulk resistivity, mass change, and visual damage assessment were used to monitor the damage over time. Damage was reduced as the SCM replacement level and air content increased, regardless of exposure conditions. Bulk resistivity and visual assessment were promising indicators of damage. The product of 91-day bulk resistivity and the air content predicted concrete performance when exposed to concentrated deicing salts. Based on several criteria, mixtures with 20% fly ash replacement level or 35% slag mitigated damage significantly when the air content was greater than 5% by concrete volume. Damage mitigation mechanisms of SCM and air are discussed.
It has recently been proposed that the pozzolanicity of supplementary cementitious materials can be determined by monitoring the heat released when supplementary cementitious materials are mixed with ...calcium hydroxide at high temperature and high pH. In this study, the heat release is measured using this procedure for a variety of different supplementary cementitious materials. In addition, thermogravimetric analysis is performed on the reacted material to determine the amount of calcium hydroxide consumed. The heat release and calcium hydroxide consumption can be used in conjunction to compare supplementary cementitious materials. Calcium hydroxide consumption can be used to determine the extent of reaction of supplementary cementitious materials in pastes where supplementary cementitious materials are used to replace a portion of cement.
Municipal solid waste incineration fly ash (MSWIFA) is a hazardous by-product of waste incineration. The objective of this research is to encapsulate the chloride in MSWIFA and to develop a ...utilizable construction material using MSWIFA, ground granulated blast-furnace slag (GGBFS), ladle furnace slag (LFS), and gypsum. A secondary objective of the work is to explain the hydration and encapsulation mechanisms in this material system using isothermal calorimetry (IC), X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and ion chromatography (IC). The predominant hydration products are ettringite, Friedel's salt, and C-S-H gel, with Friedel's salt and C-S-H dominating in systems high in LFS and ettringite and C-S-H gel dominating in systems low in LFS. The chloride encapsulation showed a strong correlation with the Friedel's salt amount; however, some encapsulation was also likely due to physical binding in the C-S-H gel. In a system with 30% MSWIFA (by mass), the optimal amount of LFS for strength and chloride encapsulation is 20%⁻40% (by mass).
The feasibility of using a muffle furnace and a balance to determine the calcium hydroxide (Ca(OH)
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) consumption of supplementary cementitious materials (SCMs) in model systems was investigated. ...SCMs were mixed with Ca(OH)
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in an alkaline solution and, after mixing, the paste was sealed inside a 50 °C oven for curing until testing. The chemically bound water and Ca(OH)
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consumption were determined using the furnace at two fixed temperatures and the results were compared with those from the thermogravimetric analysis. The protocol of the furnace test was optimized based on thermogravimetric analysis results. While further testing is needed, initial results demonstrated the validity of the method, and suggest that it is able to differentiate inert, latent hydraulic, and pozzolanic materials using reactivity thresholds for the chemically bound water and the Ca(OH)
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consumption. This new test could be used for rapid and low-cost screening of novel SCMs.
Modification of fineness, including by grinding or classification, is a commonly used beneficiation method for improving fly ash performance. In this study, five fly ashes, including off-spec and ...reclaimed ashes, were size fractionated by sieving into the following fractions: < 20 µm, < 45 µm, and > 45 µm. The original fly ash and the size fractions were characterized, and their reactivity was measured. For Class C fly ashes, the CaO contents decreased and SiO
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contents increased as the size fractions became coarser, with the > 45 µm size fractions having lower CaO contents that would allow them to be classified as Class F fly ashes. The > 45 µm size fractions had more angular or irregular particles (impurities and unburnt carbon), while the < 20 µm fractions had very limited amounts of such particles. There was a general reduction of reactivity from finer to coarser fractions as measured using a direct reactivity test. As expected, cement pastes made with finer fractions showed higher heat release and calcium hydroxide consumption. The magnitude of changes between the size fractions depended on the original fly ash composition and particle size distribution.
Two mine tailings are evaluated for their potential as supplementary cementitious materials. The mine tailings were milled using two different methods – ball milling for 30 minutes and disc milling ...for durations ranging from 1 to 15 minutes. The modified R3 test was carried out on the mine tailings to quantify their reactivity. The reactivity of the disc milled tailings is greater than those of the ball milled tailings. Strong correlations are obtained between milling duration, median particle size, amorphous content, dissolved aluminum and silicon, and reactivity of the mine tailings. The milling energy results in an increase in the fineness and the amorphous content, which do not appreciably increase beyond a disc milling duration of 8 minutes. The reactivity increases significantly beyond a certain threshold fineness and amorphous content. Cementitious pastes were prepared at 30% supplementary cementitious materials replacement level at a water-to-cementitious materials ratio of 0.40. No negative effects of the mine tailings were observed at early ages in cement pastes based on isothermal calorimetry and thermogravimetric analysis, demonstrating the potential for these materials to be used as supplementary cementitious materials.
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