Effect of composition, solvent exchange liquid and drying method on the porous structure of phenol-formaldehyde gels

Organic gels have been synthesized by sol–gel polycondensation of phenol (P) and formaldehyde (F) catalyzed by sodium carbonate (C). The effect of synthesis parameters such as phenol/catalyst ratio (P/C), solvent exchange liquid and drying method, on the porous structure of the gels have been investigated. The total and mesopore volumes of the PF gels increased with increasing P/C ratio in the range of P/C B 8, after this both properties started to decrease with P/C ratio for P/C[8 and the gel with P/C = 8 showed the highest total and mesopore volumes of 1.281 and 1.279 cm3 g-1 respectively. The gels prepared by freeze drying possessed significantly higher porosities than the vacuum dried gels. The pore volume and average pore diameter of the freeze dried gels were significantly higher than those of the vacuum dried gels. T-butanol emerged as the preferred solvent for the removal of water from the PF hydrogel prior to drying, as significantly higher pore volumes and specific surface areas were obtained in the corresponding dried gels. The results showed that freeze drying with t-butanol and lower P/C ratios were favourable conditions for the synthesis of highly mesoporous phenol–formaldehyde gels.

Alternate wetting and drying irrigation for rice in Bangladesh: Is it sustainable and has plant breeding something to offer?

The crop management practice of alternate wetting and drying (AWD) is being promoted by IRRI and the national research and extension program in Bangladesh and other parts of the world as a water-saving irrigation practice that reduces the environmental impact of dry season rice production through decreased water usage, and potentially increases yield. Evidence is growing that AWD will dramatically reduce the concentration of arsenic in harvested rice grains conferring a third major advantage over permanently flooded dry season rice production. AWD may also increase the concentration of essential dietary micronutrients in the grain. However, three crucial aspects of AWD irrigation require further investigation. First, why is yield generally altered in AWD? Second, is AWD sustainable economically (viability of farmers' livelihoods) and environmentally (aquifer water table heights) over long-term use? Third, are current cultivars optimized for this irrigation system? This paper describes a multidisciplinary research project that could be conceived which would answer these questions by combining advanced soil biogeochemistry with crop physiology, genomics, and systems biology. The description attempts to show how the breakthroughs in next generation sequencing could be exploited to better utilize local collections of germplasm and identify the molecular mechanisms underlying biological adaptation to the environment within the context of soil chemistry and plant physiology.

Chloride ingress and carbonation in concrete exposed to cyclic wetting and drying

Carbonation and chloride ingress are the two main causes of corrosion in reinforced concrete structures. An investigation to monitor the ingress of chlorides and carbonation during a 9 month wetting and drying exposure regime to simulate conditions in which multiple mode transport mechanisms are active was conducted on a variety of binders. The penetration was evaluated using water and acid soluble chloride profiles, and phenolphthalein indicator. X-ray diffraction was also used to determine the presence of bound chlorides and carbonation. The results indicated that acid extraction of chlorides is quantitatively reliable and practical for assessing penetration. The effect of carbonation on binding capability was observed and the relative quantity of chlorides also showed a correlation with the amount of chlorides bound in the form of Friedel’s salt.

Evaporative Moisture Loss from Heterogeneous Stone: Material- Environment Interactions During Drying

The complexities of evaporation from structurally and mineralogically heterogeneous sandstone (Locharbriggs Sandstone) are investigated through a laboratory-based experiment in which a variety of environmental conditions are simulated. Data reported demonstrate the significance of material-environment interactions on the spatial and temporal variability of evaporative dynamics. Evaporation from porous stone is determined by the interplay between environmental, material and solution properties, which govern the rate and mode by which water is transmitted to, and subsequently removed from, an evaporating surface. Initially evaporation is marked by high rates of moisture loss controlled by external atmospheric conditions; then, when a critical level of surface moisture content is reached, hydraulic continuity between the stone surface and subsurface is disrupted and the drying front recedes
beneath the surface, evaporation rates decrease and are controlled by the ability of the material to transport water vapour to the surface. Pore size distribution and connectivity, as well as other material properties, control the timing of each stage of evaporation and the nature of the transition.

These experimental data highlight the complexity of evaporation, demonstrating that different regions of the same stone can exhibit varying moisture dynamics during drying and that the rate and nature of evaporative loss differs under different environmental conditions. The results identify the importance of material-environment interactions during drying and that stone micro-environmental conditions cannot be inferred from ambient data alone.
These data have significance for understanding the spatial distribution of stone surface weathering-related morphologies in both the natural and built environments where mineralogical and/or structural heterogeneity creates differences in moisture flux and hence variable drying rates. Such differences may provide a clearer explanation for the initiation and subsequent development of complex weathering responses where areas of significant deterioration can be found alongside areas that exhibit little or no evidence surface breakdown.

A commentary on climate change, stone decay dynamics and the ‘greening’ of natural stone buildings: new perspectives on ‘deep wetting’

Environmental controls on stone decay processes are rapidly changing as a result of changing climate. UKCP09 projections for the 2020s (2010–2039) indicate that over much of the UK seasonality of precipitation will increase. Summer dryness and winter wetness are both set to increase, the latter linked to projected precipitation increases in autumn and spring months. If so, this could increase the time that stone structures remain wet and possibly the depth of moisture penetration, and it appears that building stone in Northern Ireland has already responded through an increased incidence of algal ‘greening’.This paper highlights the need for understanding the effects of climate change through a series of studies of largely sandstone structures. Current and projected climatic trends are therefore considered to have aesthetic, physical and chemical implications that are not currently built into our models of sandstone decay, especially with respect to the role played by deep-seated wetness on sandstone deterioration and decay progression and the feedbacks associated with, for example surface algal growth. In particular,it is proposed that algal biofilms will aid moisture retention and further facilitate moisture and dissolved salt penetration to depth. Thus, whilst the outer surface of stone may continue to experience frequent wetting and drying associated with individual precipitation events, the latter is less likely to be complete, and the interiors of building blocks may only experience wetting/drying in response to seasonal cycling. A possible consequence of deeper salt penetration could be a delay in the onset of surface deterioration,but more rapid and effective retreat once it commences as decay mechanisms ‘tap into a reservoir of deep salt’.

Exposure of mortars to cyclic chloride ingress and carbonation

The presence of chloride ions is one of the primary factors causing the degradation of reinforced concrete structures. An investigation to monitor ingress of chlorides during a 24-week wetting and drying exposure regime to simulate conditions in which multiple-mode transport mechanisms are active was conducted on a variety of binders. Penetration was evaluated using free and total chloride profiles. Acid extraction of chlorides is quantitatively reliable and practical for assessing penetration. X-ray diffraction was used to determine the presence of bound chlorides and carbonation. The ability of the cement blends to resist chloride penetration was, from best to worst, ground granulated blast-furnace slag, microsilica, pulverised-fuel ash, Portland cement. The effect of carbonation on binding capability was observed and the relative quantity of chlorides also showed a correlation with the amount of chlorides bound in the form of Friedel’s salt.

Electrical Based Sensors and Remote Monitoring System for Assessing the Corrosion Related Activity in Concrete at Hangzhou Bay Bridge

Concrete structures in marine environments are subjected to cyclic wetting and drying, corrosion of reinforcement due to chloride ingress and biological deterioration. In order to assess the quality of concrete and predict the corrosion activity of reinforcing steel in concrete in this environment, it is essential to monitor the concrete continuously right from the construction phase to the end of service life of the structure. In this paper a novel combination of sensor techniques which are integrated in a sensor probe is used to monitor the quality of cover concrete and corrosion of the reinforcement. The integrated sensor probe was embedded in different concrete samples exposed to an aggressive marine environment at the Hangzhou Bay Bridge in China. The sensor probes were connected to a monitoring station, which enabled the access and control of the data remotely from Belfast, UK. The initial data obtained from the monitoring station reflected the early age properties of the concretes and distinct variations in these properties were observed with different concrete types.