Prediction on CO2 uptake of recycled aggregate concrete

Carbonation of concrete is a process which absorbs carbon dioxide (CO2). Recycled aggregate concrete(RAC) may own greater potential in CO2 uptake due to the faster carbonation rate than natural aggregate concrete (NAC).A quantitative model was employed to predict the CO2 uptake of RAC in this study. The carbonation of RAC and thespecific surface area of recycled coarse aggregates (RCAs) were tested to verify accuracy of the quantitative model. Basedon the verified model, results show that the CO2 uptake capacity increases with the increase of RCA replacementpercentage. The CO2 uptake amount of 1 m^3 C30 RAC within 50 years is 10.6, 13.8, 17.2, and 22.4 kg when the RCAreplacement percentage is 30%, 50%, 70%, and 100%, respectively. The CO2 uptake by RCAs is remarkable and reaches35.8%- 64.3% of the total CO2 uptake by RAC when the RCA storage time being 30 days. Considering the fact that theamount of old hardened cement paste in RCAs is limited, there is an upper limit for the CO2 uptake of RCAs.

Drought Tolerance and Recovery of the Sedge Carex planostachys (Cyperaceae) from Central Texas Woodlands

Carex planostachys Kunze (Cyperaceae, Cedar sedge) is an herbaceous species in a genus commonly inhabiting mesic or hydric habitats. Carex planostachys is found in arid and semi-arid Juniperus woodlands. Arid conditions impose survival challenges to plants in dry areas. Some plants have plasticity responses to soil water content and continued normal though reduced functions through droughts, but most herbaceous plants do not survive. Limited previous studies have suggested C. planostachys is tolerant of drought. Physiological responses of C. planostachys from Juniperus woodlands was examined is this study to determine how long plants could survive without water and if they are capable of recovery from very negative water potentials beyond what is considered the permanent wilting point for most herbaceous plants. Plants were placed in pots in partial shade in this experiment. Water loss from the soil with plants was an inverse 2nd order polynomial function with soil water decreasing from 32% to 8% by day 28 of the study. Leaf water potential was also an inverse 2nd order polynomial function but did not decline significantly until 14 days without watering. Leaf water potential was −10.0 MPa after 35 days without watering. Non-watered plants Anet, (photosynthetic rate) was significantly lower compared to the water treatment by day 21 as was stomatal conductance and transpiration. When non-watered plants were watered after 21, 28 or 35 days, full recovery of physiological responses occurred within 7 days. The length of time that C. planostachys was able to withstand drought was greater than the annual trends in lack of precipitation during springtime in this area. Carex planostachys can photosynthesize at water stress between −8 and −10 MPa. Carex planostachys drought and shade tolerance enables it to occupy an understory niche devoid of other herbaceous plants.

Effects of Photosynthetically Active Radiation and Air Temperature on CO_2 Uptake of Pterocarpus macrocarpus in the Open Field

Since trees and plants can absorb CO2, forests are widely regarded as a carbon sink that may control the amount of CO2 in the atmosphere. The CO2 uptake rate of plants is affected by the plant species and environmental conditions such as photosynthetically active radiation (PAR), temperature, water and nutrient contents. PAR is the most immediate environmental control on photosynthesis while air temperature affects both photorespiration and dark respiration. In the natural condition, PAR and temperature play an important role in net CO2 uptake. The effects of PAR and air temperature on the CO2 uptake of Pterocarpus macrocarpus grown in a natural habitat were studied in the present work. Due to many uncontrollable factors, a simple rectangular hyperbola could not represent the measured data. The data were divided into groups of 2oC intervals; CO2 uptake in each group may then be related to PAR by a rectangular hyperbola function. Using the obtained functions, the effect of PAR was removed from the original data. The PAR-independent CO2 uptake was then related to air temperature. Finally, the effects of PAR (I) and air temperature (Ta) on the CO2 uptake rate (A) were combined as: (-0.0575Ta2+2.6691Ta-23.264)I A= ——————————————— (-0.00766Ta2+0.40666Ta-3.99924) (-4.8794Ta2+227.13Ta-2456.9)+I

Evaluation of the net CO_2 uptake in the Canada Basin in the summer of 2008

The third Chinese National Arctic Research Expedition （CHINARE） was conducted in the summer of 2008. During the survey, the surface seawater partial pressure of CO2 （pCO2） was measured, and sea water samples were collected for CO2 measurement in the Canada Basin. The distribution of pCO2 in the Canada Basin was determined, the influencing factors were addressed, and the air-sea CO2 flux in the Canada Basin was evaluated. The Canada Basin was divided into three regions： the ice-free zone （south of 77°N）, the partially ice-covered zone （77°-80°N）, and the heavily ice-covered zone （north of 80°N）. In the ice-free zone, pCO2 was high （320 to 368 patm, 1 patm=0.101 325 Pa）, primarily due to rapid equilibration with atmospheric CO2 over a short time. In the partially ice-covered zone, the surface pCOs was relatively low （250 to 270 patm） due to ice-edge blooms and icemelt water dilution. In the heavily ice-covered zone, the seawater pCO2 varied between 270 and 300 laatm due to biological COs removal, the transportation of low pCOs water northward, and heavy ice cover. The surface seawater pCO2 during the survey was undersaturated with respect to the atmosphere in the Canada Basin, and it was a net sink for atmospheric CO2. The summertime net CO2 uptake of the ice-free zone, the partially ice-covered zone and the heavily ice-covered zone was （4.14±1.08）, （1.79±0.19）, and （0.57±0.03） Tg/a （calculated by carbon, 1 Tg=10^12 g）, respectively. Overall, the net COs sink of the Canada Basin in the summer of 2008 was （6.5＋1.3） Tg/a, which accounted for 4%-10% of the Arctic Ocean COs sink.

Seasonal dynamics of gas regulation service in forest ecosystem

Using the 3-year observational data from ChinaFlux （Chinese Terrestrial Ecosystem Flux Research Network）, we studied the gas regulation flux dynamics and cumulative process of gas regulation value in Qianyanzhou middle subtropical plantation （QYF） and Changbai Mountain temperate mixed forest （CBF）. The gas regulation service was differentiated into vegetation gas regulation service and net ecosystem gas regulation service. Carbon tax approach, reforestation cost approach and industrial oxygen approach were employed to calculate gas regulation value. Results show that there was significant seasonal variation in vegetation gas regulation flux. Daily CO2 uptake fluxes averaged 82.00 kg·ha^-·d^-1 and 59.37 kg·ha^-·d^-1 and the corresponding 02 emission fluxes were 59.65 kg·ha^-·d^-1 and 43.19 kg·ha^-·d^-1 for QYF and CBF, respectively. The cumulative curves of vegetation gas regulation value always followed a sigmoid shape, and the annual gas regulation value produced by vegetation was RMB 14342.69 yuan·ha^-1 and RMB 10384.18 yuan·ha^-1 for both QYF and CBF, respectively. In terms of monthly net ecosystem gas regulation service, QYF appeared as a CO2 sink and O2 source for the whole year, while CBF appeared to be a CO2 sink and O2 source mainly in the period between May and September. The cumulative curves of net ecosystem gas regulation value presented a sigmoid （＂S＂） shape for QYF, while a unimodal type curve for CBF. The annual net ecosystem gas regulation value was 8470.52 yuan·ha^-1 and 5091.98yuan·ha^-1 for QYF and CBF, respectively. The economic value of both the vegetation gas regulation service and net ecosystem gas regulation service were mainly produced between May and October.

Strength Development and Products Evolution of β-C2S and γ-C2S Induced by Accelerated Carbonation Curing

Low calcium β-C2S and γ-C2S minerals with low hydration activity was activated by accelerated carbonation curing to be used as new binding materials.Synthetic β-C2S and γ-C2S were synthetized and compacted to prepare cube samples and then subjected to CO2 chamber for accelerated carbonation curing.The CO2 uptake,mechanical strength,and microstructure changes of β-C2S and γ-C2S were analyzed by TG,XRD,MAS-NMR,and MIP.The experimental results indicate the CO2 uptake of γ-C2S is much higher than that of β-C2S,but the compressive strength of γ-C2S samples is lower than that of β-C2S.Calcium carbonate and other carbonation products stack in the pore structure and the porosity is reduced from about 42% to 30.1% and 22.0% for β-C2S and γ-C2S samples after 2 h carbonation curing,respectively.The difference in compressive strength development is caused by the different properties of carbonation products.Except for calcium carbonate,there also exists obvious difference in properties of amorphous phases:γ-C2S formed silica gel in the whole carbonation progress;however,β-C2S can react to produce silica gel and C-S-H gel with high Van der Waals forces,and C-S-H gel will continue to react with CO2 to form calcium carbonate and silica gel in later carbonation reaction;In addition the microhardness of carbonated β-C2S was more higher than that of γ-C2S.