Influence of various auxiliary activators on CaO-activated cementless binder

Department of Urban and Environmental Engineering (Urban Infrastructure Engineering)Portland cement is the most commonly used construction material in the world, but it is being regarded as a major cause of global warming due to the carbon dioxide generation during the production process. Therefore, in this study, eco-friendly cementless binder was developed to replace Portland cement. The developed cementless binders are based on the ground granulated blast furnace slag (GGBFS) and fly ash, which are industrial byproduct, and CaO is used as the main activator. The CaO-activator has various advantages compared to the conventional alkali-activators (i.e., NaOH, KOH, and Na-silicate), but it has problems such as low early compressive strength and variation of physical properties depending on the source of raw materials. Therefore, in this study, various types of auxiliary activators were applied to CaO-activator and four different cementless binders were developed. To verify the mechanical properties and microstructural characteristics of the developed binders, X-ray fluorescence spectroscopy, X-ray diffraction, compressive strength, thermogravimetric, mercury intrusion porosimetry, isothermal calorimetry, pH meter, electrical resistivity measurement, and scanning electron microscopy with energy dispersive spectroscopy analysis were performed. To investigate the effect of CaCl2 on CaO-activated GGBFS/fly ash binder, various amounts of CaCl2 were incorporated. The samples with CaCl2 generated much higher compressive strength than the sample without CaCl2 at all curing period. In terms of compressive strength, substitution of 2wt% CaCl2 was considered to be the best mixture proportion. Interestingly, despite having no cement compound in this binder, CaCl2 had a very similar acceleration effect on the cementless binder. The reactions of binders generated significantly lower cumulative heats up to 72 h, although their initial heats up to 10 h were notably higher, compared to the cumulative and initial heats of Portland cement hydration. These high initial heats of binder might be advantageous in activating raw materials. XRD and TG/DTG results showed that the amorphous phase of the raw material was dissolved more by the addition of CaCl2, and which seemed to generate more quantity of reaction product, resulting in the denser cementitious matrix. The most distinct mineralogical changes due to CaCl2 addition were the formation of hydrocalumite and the removal of hydrotalcite and str??tlingite. From MIP results, the addition of CaCl2 induced pore-size refinement effect from the early stage of curing. In addition overall total porosity was reduced as more amount of CaCl2 substituted, resulting in higher early and final compressive strength. In the BSE images, the particle size of raw materials became smaller as CaCl2 was replaced, which seems to be due to the CaCl2 dissolving raw materials actively. As a result of EDS analysis, much higher Ca/Al and Na/Al ratios were measured as CaCl2 was added, which indicates that Ca and Na ions were produced more by dissolving the raw materials. As mentioned earlier, CaCl2 is used as an accelerator in Portland cement. However, the used of CaCl2 can cause the steel corrosion, ACI regulated the maximum dosage of CaCl2 varying with the structures. Therefore, in this study, the electrical resistivity of the binder was measured using four Wenner method to verify the possibility of steel corrosion. The higher electrical resistivity was measured as CaCl2 was added, which indicates that the possibility of corrosion of the steel bar is low even with the addition of CaCl2. The reason for this result seems to be that a denser matrix was generated as CaCl2 was added. When CaCl2 was applied to CaO-activated GGBFS/fly ash binder, satisfactory levels of mechanical properties were measured, but further experiment is required for commercialization due to concerns about steel corrosion. Therefore, other types of accelerator such as Ca(NO3)2 and NaNO3 was applied to CaO- activated GGBFS binder. In the compressive strength, the addition of each nitrate salt (Ca(NO3)2 and NaNO3) was clearly beneficial in developing strength during the early days of curing. The results showed that on day 3 of curing, the strengths were almost doubled for all samples, regardless of the cation type of the nitrate salts. However, a difference between the nitrate salts was seen on day 28 of curing, where the added Ca(NO3)2 was still effective in increasing the cementless binder???s strength compared to the control (without any nitrate salts), the added NaNO3 was not anymore. A pH meter measurement was conducted to verify the cation effect of each nitrate salts. In the presence of NaNO3, which generally increases the solubility of Ca(OH)2 in aqueous salt solutions, the higher pH of NaNO3 containing samples was obtained due to the increased amount of dissolving the Ca(OH)2. These higher pH seems to generate more reaction products and higher early strength measurements. In the samples with Ca(NO3)2, an additional supply Ca ion from Ca(NO3)2 resulted in a common ion effect, which seems to have a relatively low pH measured by lowering the solubility of Ca(OH)2. Although a lower pH was measured, higher compressive strength seem to be measured due to the supply of stable Ca ions. The type of reaction products analyzed with the XRD was very similar between the Ca(NO3)2 and NaNO3 group when the same weight of salts was used, although their compressive strength were significantly different. C-S-H and akermanite were identified in all samples. An Al2O3-Fe2O3-mono (AFm) phase was clearly identified in the samples containing any type of nitrate salts with more than 3wt%. This seemed to occur mainly when the quantity of salts was at 5wt%, causing the XRD peaks of this phase to increase significantly. AFm phase in our study was NO3 AFm or NO2 AFm or a mixture of NO3-and NO2 AFm phases. In the samples with Ca(NO3)2, weaker peaks of portlandite were identified and portlandite was not identified in the 3wt% Ca(NO3)2 and 5wt% Ca(NO3)2 samples. However, portlandite was clearly identified in the samples with NaNO3. The more amount of nitrate salts were substituted, the more total weight loss until 1,000C occurred. This weight loss indirectly suggests that more nitrates salts resulted in more GGBFS due to an increase of it dissolving. Overall TG results were consistent with XRD results. At 3 days of curing, the use of nitrate salts was clearly beneficial to produce C-S-H, regardless of the cation type in the salts. However, at 28 days of curing, the samples with NaNO3 clearly displayed a reduction of C-S-H when weight of the salt increased. The NO3-and/or NO2-AFm phase were significantly generated when nitrate salts replaced 3-5wt% of the total mixture. The pore size distribution was significantly dependent on the cation type of nitrate salts. The shape of the distribution curves of the samples with Ca(NO3)2 were roughly grouped in two curve shapes depending on the quantity of Ca(NO3)2, while those of the NaNO3 samples were not significantly changed by the dosage of NaNO3. In order to develop a cementless binder with satisfactory mechanical properties without concern about steel corrosion, calcium formate (Ca(HCOO2) was applied as an auxiliary activator to CaO-activated GGBFS binder and its effect was verified using various experiments. The addition of Ca(HCOO2), such as CaCl2, Ca(NO3)2, and NaNO3, acted as an accelerator and 1.3-2 times higher compressive strength was measured at 3 days of curing and 1.1-1.4 times higher compressive strength measured at 28 days of curing compared to samples without Ca(HCOO2). The extent of Ca(HCOO2)`s strength enhancement was comparable to that of samples with CaCl2. The highest compressive strength was achieved at 3wt% of Ca(HCOO2). As a result of MIP measurement, the pore-size refinement effect occurred as Ca(HCOO2) was replaced, and which seemed to be the main reason of increasing the compressive strength of the binder. Interestingly, in all other samples except samples with 3wt% Ca(HCOO2), a greater amount of total porosity was measured at 28 days compared to 3 days, suggesting the possibility of nanometer-sized pores. However, all samples with Ca(HCOO2) did not show any strength reduction during curing days, the influential degree of the pore formation on the strength seemed not to be significant in this study. The XRD patterns of samples can be divided into two groupssamples with 0-1wt% Ca(HCOO2) demonstrated relatively strong peaks of Ca(OH)2 without C2AH8, while samples with 3-5wt% CF showed strength C2AH8 peaks but no Ca(OH)2. This suggests that at least more than 3wt% of Ca(HCOO2) is necessary to significantly change the types of reaction products for the CaO-activated GGBFS system. C2AH8 is one of main reaction products of calcium alumina cement, and it is strength-contribution phase. As a greater quantity of Ca(HCOO2) was substituted, a greater amount of C2AH8 was produced, the presence of Ca(HCOO2) was likely the main cause of the C2AH8 generation. Thus, the formation of C2AH8 might have contributed to the enhanced strength. However, it is well known that C2AH8 is a metastable phase that can easily converted over time, and this conversion accompanies a significantly increase in porosity that results in strength reduction. In this study, the intensities of C2AH8 peaks also decreased at 28 days, compared to 3 days, and thus a portion of C2AH8 was removed. In the TG/DTG results, as the Ca(HCOO2) wt% and curing days increased, the more mass reduction was observed. This indicates that more reaction products were generated and more weight of GGBFS was dissolved because GGBFS was the only source of Si and Al in the formation of the reaction products (e.g., C-S-H, C2AH8). The second peaks of C2AH8 at ~200??C showed that more amount of Ca(HCOO2) replacement generated more amount of C2AH8. The DTG peaks of AH gel significantly grew in 1 and 5wt% contained samples from 3 days to 28 days, while those in 3wt% contained sample barely increased. The formation of AH gel generally increases porosity and reduces strength in calcium alumina cement, the trend of AH gel formation in the TG results also seems to be in agreement with the testing results of strength and porosity in this study.clos

Influence of Calcium Sulfate Type on Evolution of Reaction Products and Strength in NaOH- and CaO-Activated Ground Granulated Blast-Furnace Slag

This study investigated the influences of CaSO4 type (i.e., anhydrite vs. gypsum) on strength development and reaction products in the activation of ground granulated blast-furnace slag (GGBFS) when different activators (i.e., CaO vs. NaOH) and sources of GGBFS were used. In the CaO-activation, the addition of calcium sulfates greatly enhanced 28-day strengths, regardless of the choice of CaSO4 or GGBFS source, through increasing the quantities of reaction products and reducing pore volume and size. However, in the NaOH-activation, the use of calcium sulfates showed the complex dependency of strength on the choice of CaSO4 type and GGBFS source, and it barely produced beneficial effects on the quantity of reaction products and reduction of pore volume and size. Thus, the results in this study indicate that the combination of CaO-activation and calcium sulfates is a more effective means of activating GGBFS to gain enhanced strength and significant quality control than the use of gypsum with NaOH-activation

Structural abnormalities in benign childhood epilepsy with centrotemporal spikes (BCECTS)

AbstractPurposeThe aim of this study was to investigate cortical thickness and gray matter volume abnormalities in benign childhood epilepsy with centrotemporal spikes (BCECTS). We additionally assessed the effects of comorbid attention-deficit/hyperactivity (ADHD) on these abnormalities.MethodsSurface and volumetric MR imaging data of children with newly diagnosed BCECTS (n=20, 14 males) and age-matched healthy controls (n=20) were analyzed using FreeSurfer (version 5.3.0, https://surfer.nmr.mgh.harvard.edu). An additional comparison was performed between BCECTS children with and without ADHD (each, n=8). A group comparison was carried out using an analysis of covariance with a value of significance set as p<0.01 or p<0.05.ResultsChildren with BCECTS had significantly thicker right superior frontal, superior temporal, middle temporal, and left pars triangularis cortices. Voxel-based morphometric analysis revealed significantly larger cortical gray matter volumes of the right precuneus, left orbitofrontal, pars orbitalis, precentral gyri, and bilateral putamen and the amygdala of children with BCECTS compared to healthy controls. BCECTS patients with ADHD had significantly thicker left caudal anterior and posterior cingulate gyri and a significantly larger left pars opercularis gyral volume compared to BCECTS patients without ADHD.ConclusionChildren with BCECTS have thicker or larger gray matters in the corticostriatal circuitry at the onset of epilepsy. Comorbid ADHD is also associated with structural aberrations. These findings suggest structural disruptions of the brain network are associated with specific developmental electro-clinical syndromes

Gypsum-Dependent Effect of NaCl on Strength Enhancement of CaO-Activated Slag Binders

This study explores the combined effect of NaCl and gypsum on the strength of the CaO-activated ground-granulated blast furnace slag (GGBFS) binder system. In the CaO-activated GGBFS system, the incorporation of NaCl without gypsum did not improve the strength of the system. However, with the presence of gypsum, the use of NaCl yielded significantly greater strength than the use of either gypsum or NaCl alone. The presence of NaCl largely increases the solubility of gypsum in a solution, leading to a higher concentration of sulfate ions, which is essential for generating more and faster formations of ettringite in a fresh mixture of paste. The significant strength enhancement of gypsum was likely due to the accelerated and increased formation of ettringite, accompanied by more efficient filling of pores in the system

Use of Coal Bottom Ash and CaO-CaCl2-Activated GGBFS Binder in the Manufacturing of Artificial Fine Aggregates through Cold-Bonded Pelletization

This study investigated the use of coal bottom ash (bottom ash) and CaO-CaCl2-activated ground granulated blast furnace slag (GGBFS) binder in the manufacturing of artificial fine aggregates using cold-bonded pelletization. Mixture samples were prepared with varying added contents of bottom ash of varying added contents of bottom ash relative to the weight of the cementless binder (= GGBFS + quicklime (CaO) + calcium chloride (CaCl2)). In the system, the added bottom ash was not simply an inert filler but was dissolved at an early stage. As the ionic concentrations of Ca and Si increased due to dissolved bottom ash, calcium silicate hydrate (C-S-H) formed both earlier and at higher levels, which increased the strength of the earlier stages. However, the added bottom ash did not affect the total quantities of main reaction products, C-S-H and hydrocalumite, in later phases (e.g., 28 days), but simply accelerated the binder reaction until it had occurred for 14 days. After considering both the mechanical strength and the pelletizing formability of all the mixtures, the proportion with 40 relative weight of bottom ash was selected for the manufacturing of pilot samples of aggregates. The produced fine aggregates had a water absorption rate of 9.83% and demonstrated a much smaller amount of heavy metal leaching than the raw bottom ash

The Draft Genome of an Octocoral, Dendronephthya gigantea

Coral reefs composed of stony corals are threatened by global marine environmental changes. However, soft coral communities of octocorallian species, appear more resilient. The genomes of several cnidarians species have been published, including from stony corals, sea anemones, and hydra. To fill the phylogenetic gap for octocoral species of cnidarians, we sequenced the octocoral, Dendronephthya gigantea, a nonsymbiotic soft coral, commonly known as the carnation coral. The D. gigantea genome size is similar to 276 Mb. A high-quality genome assembly was constructed from PacBio long reads (29.85 Gb with 108x coverage) and Illumina short paired-end reads (35.54 Gb with 128x coverage) resulting in the highest N50 value (1.4 Mb) reported thus far among cnidarian genomes. About 12% of the genome is repetitive elements and contained 28,879 predicted protein-coding genes. This gene set is composed of 94% complete BUSCO ortholog benchmark genes, which is the second highest value among the cnidarians, indicating high quality. Based on molecular phylogenetic analysis, octocoral and hexacoral divergence times were estimated at 544 MYA. There is a clear difference in Hox gene composition between these species: unlike hexacorals, the Antp superclass Evx gene was absent in D. gigantea. Here, we present the first genome assembly of a nonsymbiotic octocoral, D. gigantea to aid in the comparative genomic analysis of cnidarians, including stony and soft corals, both symbiotic and nonsymbiotic. The D. gigantea genome may also provide clues to mechanisms of differential coping between the soft and stony corals in response to scenarios of global warming

A Nationwide Survey of Lymphangioleiomyomatosis in Korea: Recent Increase in Newly Diagnosed Patients

In 2007, the Korean Interstitial Lung Disease Society had collected clinical data of patients who have diagnosed as Lymphangioleiomyomatosis (LAM) since 1990 through nationwide survey, which showed that LAM patients had increased sharply after 2004. The present study was performed to show the clinical features of Korean patients with LAM, and to establish the reason for the recent increase in the diagnosis. All 63 patients were women and the mean age at diagnosis was 36 yr. The most common presenting symptom was dyspnea and 8 patients had tuberous sclerosis complex. The survival rate at 5 yr after diagnosis was 84%. Compared with patients diagnosed after 2004 (n=34), the patients diagnosed before 2004 (n=29) complained with dyspnea more (P=0.016) and had lower FEV1% predicted (P=0.003), and DLco% predicted (P=0.042). The higher proportion of patients diagnosed after 2004 showed the normal chest radiography, and they were detected by routine chest CT screening (P=0.016). This study showed that clinical features of Korean patients with LAM were not different from those reported elsewhere. It is concluded that the reason for the increase of newly diagnosed patients is the result of increase in detection of the early stage LAM by the widespread use of chest CT screening

OH reactivity in urban and suburban regions in Seoul, South Korea – an East Asian megacity in a rapid transition

South Korea has recently achieved developed country status with the second largest megacity in the world, the Seoul Metropolitan Area (SMA). This study provides insights into future changes in air quality for rapidly emerging megacities in the East Asian region. We present total OH reactivity observations in the SMA conducted at an urban Seoul site (May-June, 2015) and a suburban forest site (Sep, 2015). The total OH reactivity in an urban site during the daytime was observed at similar levels (∼15 s(-1)) to those previously reported from other East Asian megacity studies. Trace gas observations indicate that OH reactivity is largely accounted for by NOX (∼50%) followed by volatile organic compounds (VOCs) (∼35%). Isoprene accounts for a substantial fraction of OH reactivity among the comprehensive VOC observational dataset (25-47%). In general, observed total OH reactivity can be accounted for by the observed trace gas dataset. However, observed total OH reactivity in the suburban forest area cannot be largely accounted for (∼70%) by the trace gas measurements. The importance of biogenic VOC (BVOCs) emissions and oxidations used to evaluate the impacts of East Asian megacity outflows for the regional air quality and climate contexts are highlighted in this study

Use of Bacteria to Activate Ground-Granulated Blast-Furnace Slag (GGBFS) as Cementless Binder

Ground-granulated blast-furnace slag (GGBFS) can be used as a cementless binder after activation. Recent approaches to activate GGBFS have focused on chemical methods that use NaOH, KOH, and CaO. This study introduces the use of bacteria to activate GGBFS as a biological approach. The presence of bacteria (volumetric ratio), curing temperature (23 &deg;C and 60 &deg;C), and number of curing days (3, 7, and 28 d) are investigated. The use of urea is considered owing to the possibility of calcium carbonate formation. The activated GGBFS is evaluated in the form of a cube (5 cm &times; 5 cm &times; 5 cm) for its strength, mineral identification, and pore size distribution. A brick (19 cm &times; 9 cm &times; 5.7 cm) is prefabricated to see the feasibility of commercializing bacteria-activated GGBFS based on water absorption and strength measurements. All results are compared with those of water-activated GGBFS. The results indicate that the use of urea inhibits the strength improvement of bacteria-activated GGBFS. Bacterial suspension enhances the GGBFS strength at a curing temperature of 60 &deg;C. Mineral identification tests show that the strength increase is primarily due to the formation of calcite. The compressive strength satisfies the commercial standard of concrete bricks; however, the water absorption rate must be resolved

Use of Bacteria to Activate Ground-Granulated Blast-Furnace Slag (GGBFS) as Cementless Binder

Ground-granulated blast-furnace slag (GGBFS) can be used as a cementless binder after activation. Recent approaches to activate GGBFS have focused on chemical methods that use NaOH, KOH, and CaO. This study introduces the use of bacteria to activate GGBFS as a biological approach. The presence of bacteria (volumetric ratio), curing temperature (23 °C and 60 °C), and number of curing days (3, 7, and 28 d) are investigated. The use of urea is considered owing to the possibility of calcium carbonate formation. The activated GGBFS is evaluated in the form of a cube (5 cm × 5 cm × 5 cm) for its strength, mineral identification, and pore size distribution. A brick (19 cm × 9 cm × 5.7 cm) is prefabricated to see the feasibility of commercializing bacteria-activated GGBFS based on water absorption and strength measurements. All results are compared with those of water-activated GGBFS. The results indicate that the use of urea inhibits the strength improvement of bacteria-activated GGBFS. Bacterial suspension enhances the GGBFS strength at a curing temperature of 60 °C. Mineral identification tests show that the strength increase is primarily due to the formation of calcite. The compressive strength satisfies the commercial standard of concrete bricks; however, the water absorption rate must be resolved