Variation in Polymerization Degree of C-A-S-H Gels and Its Role in Strength Development of Alkali-activated Slag Binders

To investigate the variation in the degree of polymerization calcium aluminium silicate hydrate(C-A-S-H)gel and its role in the evolution of the strength of waterglass slag binders,the compressive strength,hydration products,degree of hydration of the slag,and the degree of polymerization of C-A-S-H gels of binders were examined.The experimental results indicate that the pH of the pore solution increased with an increase in the Na_(2)O concentration.However,mortar with an optimum compressive strength value of 81.0 MPa at 28 d was obtained when water glass modulus was 1.5.The main hydration product is a C-A-S-H gel for which the quantity and the degree of polymerization depend strongly on the Na_(2)O concentration;for a given range,both increase with increasing Na_(2)O concentration,thus yielding an enhanced strength.A further increase in the Na_(2)O concentration continuously increases the quantity of C-A-S-H gels while drastically reducing the degree of polymerization.The positive effect of the former is counteracted by the adverse effect of the latter,ultimately,leading to a decreased strength.Furthermore,we reveal that the degree of polymerization for C-A-S-H gels may be affected by pH,through a series of complex chemical reactions.

A new O_2-microelectrode and its application

A new oxygen microelectrode was introduced. An internal guard cathode was added besides its normal cathode sensor. It has a low zero measuring current, high signal stability and its easy to construct. As it is small in size and high in stability, it may be used not only for routine environmental application, but for other scientific research work as well.

Monitoring atmospheric nitrous oxide background concentrations at Zhongshan Station,east Antarctica

At present,continuous observation data for atmospheric nitrous oxide（N_2O） concentrations are still lacking,especially in east Antarctica.In this paper,nitrous oxide background concentrations were measured at Zhongshan Station（69°22′25″S,76°22′14″E）,east Antarctica during the period of 2008–2012,and their interannual and seasonal characteristics were analyzed and discussed.The mean N_2O concentration was 321.9 n L/L with the range of 320.5–324.8 n L/L during the five years,and it has been increasing at a rate of 0.29% year-1.Atmospheric N_2O concentrations showed a strong seasonal fluctuation during these five years.The concentrations appeared to follow a downtrend from spring to autumn,and then increased in winter.Generally the highest concentrations occurred in spring.This trend was very similar to that observed at other global observation sites.The overall N_2O concentration at the selected global sites showed an increasing annual trend,and the mean N_2O concentration in the Northern Hemisphere was slightly higher than that in the Southern Hemisphere.Our result could be representative of atmospheric N_2O background levels at the global scale.This study provided valuable data for atmospheric N_2O concentrations in east Antarctica,which is important to study on the relationships between N2 O emissions and climate change.

N_(2)O emission and its influencing factors in subtropical streams, China

Background:Rivers and streams are one of the primary sources of nitrous oxide(N_(2)O)which is an important greenhouse gas with great global warming potential.Yet,over the past century,human activities have dramatically increased reactive nitrogen loadings into and consequently led to increased N_(2)O emission from the river ecosystems.Here,we carried out a study in two subtropical rivers,i.e.,Jinshui River and Qi River with slight and intense human disturbance in their respective catchments in China.The study intended to explore spatial variability and seasonality in N_(2)O emissions,and the relative importance of physicochemical variables,nitrification and denitrification potentials,and functional genes abundance influencing N_(2)O emissions.Results:N_(2)O concentration,N_(2)O saturation,and N_(2)O flux of Jinshui River peaked in high flow season.N_(2)O concentration,N_(2)O saturations,and N_(2)O flux in Qi River and downstream of Jinshui River were significantly higher than that in other areas in normal and low flow seasons.N_(2)O concentration was positively correlated with water temperature,water NO_(3)^(−),and DOC,negatively correlated with water NH4+and DOC/NO_(3)^(−)(the ratio of dissolved organic carbon to NO_(3)^(−)in water),and positively correlated with potential nitrification rate in high flow season,but not correlated with functional genes abundance.Both rivers had lower N_(2)O saturation and flux than many freshwater systems,and their EFr-5(N_(2)O emission factor for river)was lower than the recommended values of IPCC.Conclusions:While the two rivers were moderate sources of N_(2)O and N_(2)O emissions in river systems were normally elevated in the summer,areas with intense human disturbance had higher N_(2)O concentration,N_(2)O saturations,and N_(2)O flux than those with slight human disturbance.Physicochemical variables were good indicators of N_(2)O emissions in the river ecosystems.