The influence of controlled release fertilisers and the form of applied fertiliser nitrogen on nitrous oxide emissions from an andosol

A laboratory experiment was conducted to determine whether applying controlled release nitrogen fertilisers could reduce nitrous oxide emissions from an andosol maintained at different water contents, compared with applying standard nitrogen fertiliser. The effect of the form of N applied (NH₄-N or NO₃-N) was also investigated. Soil was collected from an arable field and sub-samples were treated with controlled release or standard fertiliser, applied at a rate of 200 g N g^–1 dry soil either as NH₄ ⁺ or NO₃ ^–. The soils were maintained at 40%, 55%, 70% or 85% water filled pore space (WFPS) and incubated at 25 °C for 50 days. Gas samples were collected and analysed every 3–4 days and soil samples were analysed on five occasions during the incubation. Emissions of N₂O were much greater from ammonium sulphate than from calcium nitrate fertiliser, indicating that nitrification was the main source of the N₂O. Emissions at 85% WFPS were greater than at the lower water contents in all treatments. The use of controlled release NH₄-N fertilisers reduced and delayed the maximum peak of emissions, but at 55% and 70% WFPS this did not always result in lower total emissions. Emissions from the controlled release NO₃-N fertiliser were very low, but only significantly lower than from standard NO₃-N fertiliser at water contents below 85% WFPS. The results demonstrate that choosing the appropriate form of fertiliser in relation to expected soil moisture could significantly reduce N₂O emissions. Applying the fertiliser in a controlled-release form could further reduce emissions by reducing the length of time that fertiliser nitrogen is present in the soil and available for nitrification or denitrification.     

Fertiliser influence on alkali release during straw pyrolysis

Comparative studies of alkali release from wheat and oat straws cultivated in the laboratory with chloride-rich and sulphate-rich fertilisers are reported. The release of alkali during pyrolysis in the temperature range 25-1060°C is measured using the sensitive surface ionisation technique. Straw cultivated with a chloride-rich fertiliser releases two to four times more alkali than straw fertilised with a sulphate-rich fertiliser, and the release takes place at lower temperatures. The temperatures for maximum alkali release are ∼800°C for straw cultivated with a chloride-rich fertiliser, and ∼870°C for straw supplied with a sulphate-rich fertiliser. The samples were also subject to simple water leaching, and alkali was observed to be easily removed by leaching irrespective of fertiliser. Application of chloride-free fertilisers is concluded to be a simple and efficient way to reduce the alkali release from the fuels, and the method can easily be combined with other methods in order to improve fuel quality.     

The long-term effects of manures and fertilisers on soil productivity and quality: a review

The results from 14 field trials comparing the long-term (20 to 120 years) effects of fertilisers and manures (farmyard manure, slurry, and green manure) on crop production and soil properties are reviewed. In total there were 24 paired comparisons of the effects of manure and fertiliser. Some of the trials also contained a control (no nutrient inputs) treatment. The input of nutrients as either fertilisers or manures had very large effects (150–1000%) on soil productivity as measured by crop yields. Manured soils had higher contents of organic matter and numbers of microfauna than fertilised soils, and were more enriched in P, K, Ca and Mg in topsoils and nitrate N, Ca and Mg in subsoils. Manured soils also had lower bulk density and higher porosity, hydraulic conductivity and aggregate stability, relative to fertilised soils. However, there was no significant difference (P < 0.05) between fertilisers and manures in their long-term effects on crop production. In the context of this set of international trials, the recent evidence from the Rothamsted classical long-term trials appears to be exceptional, due to the larger inputs of manures and larger accumulation of soil OM in these trials. It is suggested therefore that manures may only have a benefit on soil productivity, over and above their nutrient content, when large inputs are applied over many years. The evidence from these trials also shows that, because the ratio of nutrients in manures is different from the ratio of nutrients removed by common crops, excessive accumulation of some nutrients, and particularly P and N, can arise from the long-term use of manures, relative to the use of fertilisers. Under these conditions greater runoff of P, and leaching of N may result, and for soils with low P retention and/or in situations where organic P is leached, greater P leaching losses may occur. The use of manures, relative to fertilisers, may also contribute to poor water quality by increasing its chemical oxygen demand. It is concluded therefore that it cannot generally be assumed that the long-term use of manures will enhance soil quality – defined in terms of productivity and potential to adversely affect water quality – in the long term, relative to applying the same amounts of nutrients as fertiliser.     

Stratification of soil phosphorus,pH, and macro-cations under intensively cropped grass ley

The large amounts of nutrients applied to and removed from soil by intensive grass production may cause quick changes in the nutrient pools available to plants and exposed to leaching and runoff losses. Stratification of applied nutrients is especially important for phosphorus (P), which moves slowly in soil. To study the vertical distribution of extractable nutrients and soil pH in different types of ley soil, P fertilisers were incorporated or placed prior to sowing or broadcast annually at ten sites for 3 years. Then the soils were sampled in several layers 2.5 or 5 cm deep and analysed for pH and the concentrations of phosphorus, potassium (K), calcium (Ca), and magnesium (Mg) extractable with acid ammonium acetate. In mineral soils, broadcast P mainly remained within the uppermost 2.5 cm of soil, in which the concentrations of extractable P more than doubled during the study period. When commonly used NK and NPK fertilisers were applied, the uppermost 5 cm of soil was acidified by about 0.5 pH units and its Ca value decreased by about 25%. Broadcast K enriched a thin surface layer even if the K balance was negative. Estimation of the concentration of dissolved phosphate in runoff suggested that the high P losses that are possible at excessive levels of soil test P can be diminished by perennial grasses supplied with abundant water and other nutrients. Surface-applied P appeared to increase the losses, but even a shallow placement seemed to prevent them efficiently if all fertiliser granules become covered with soil.     

Effect of phosphate fertiliser type on the accumulation and plant availability of cadmium in grassland soils

Cadmium (Cd), a potentially toxic heavy metal for humans and animals, accumulates in the liver and kidneys of older animals grazing New Zealand and Australian pastoral soils. Phosphorus (P) fertiliser is the major input of Cd into these farming systems. A study was conducted to evaluate the effects, over 10 years, of annual application (30 kg P ha^–1 yr^–1) of four forms of P fertilisers having different solubilities and Cd contents [41, 32, 10 and 5 g Cd g^–1 for North Carolina phosphate rock (NCPR), single superphosphate (SSP), diammonium phosphate (DAP) made from low Cd phosphate rocks and Jordan phosphate rock (JPR) respectively] on soil and herbage Cd concentrations. Ten years of fertiliser application caused a marked increase in surface soil Cd concentrations. Total soil Cd was significantly higher in SSP and NCPR treatments compared to control (no P fertiliser), JPR and DAP treatments in the 0–30 and 30–75 mm soil depths. Plant-available Cd (0.01 M CaCl₂ extractable Cd) was higher in SSP treatments than in control and other fertiliser treatments. Chemical analysis of herbage samples showed that there was no significant difference in Cd concentration in pasture grasses between treatments in the second year of the trial but in the eighth and tenth year, plots fertilised with SSP and NCPR had significantly higher Cd in pasture grasses in most of the seasonal cuts compared to control, JPR and DAP. Cadmium recovery by both grasses and clover was less than 5% of Cd applied in fertiliser. Clover Cd concentration and yield were much lower than those for grass and therefore its contribution to pasture Cd uptake was very low (< 7%). A strong seasonal effect on grass Cd concentration, which is inversely related to pasture growth rate, was observed in all three sampling years — Cd concentration was highest during autumn and lowest in spring. Total Cd contents of the fertilisers and their rate of dissolution rather than soil pH [pH (H₂O) at 30–75 mm depth of 5.39, 5.20, 5.11 and 5.36 for NCPR, SSP, DAP and JPR treatments respectively]influenced soil and herbage Cd. These results showed that the use of P fertilisers with low Cd contents will reduce herbage Cd levels and has the potential of reducing Cd levels in grazing animals and their products.     

Development and evaluation of an improved soil test for phosphorus, 3: field comparison of Olsen, Colwell and Resin soil P tests for New Zealand pasture soils

Soil tests suitable for estimating the phosphorus (P) status of soils fertilised with soluble or sparingly soluble P fertilisers (reactive phosphate rock) were evaluated using the New Zealand Ministry of Agriculture Technology (NZMAFTech) National Series forms of phosphate trials on permanent pastures located throughout NZ. This included a common core of treatments comparing Sechura phosphate rock (SPR) with triple superphosphate (TSP). At each site, a re-application of twice maintenance TSP was superimposed on one-half plots that previously had received six annual applications of increasing amounts of P (0, 0.5, 0.75, 1.0 and 2.0 times the maintenance rate) in the form of TSP or SPR. Before the re-application of TSP, soil samples (0–30 and 0–75 mm depths) were collected from each plot. All the trials were run for 1 year during which seven to ten harvests were taken. Pasture response was expressed as percent increase in yield obtained with re-application over the previous treatment.The 0.5 NaHCO₃ based (Olsen P) extractant with different combinations i.e. soil volume (Olsen (v)), soil weight (Olsen (w)), shaking time variations (Olsen (16 h)) and soil:solution ratio (Colwell), and Resin P soil tests were conducted on soils taken from the plots prior to re-application of TSP. The Olsen (v), Olsen (16 h) and Colwell P values increased with increasing rates of P applied in all soils with values for sparingly soluble P materials being less than where soluble P fertiliser had been previously applied. The Resin P values showed similar increases with P applied regardless of the solubility of previously applied fertiliser. When the yield increases caused by TSP application to all treatments (irrespective of fertiliser source) were regressed against soil test values, Resin P explained 76% of the variation in yield response, compared to 50% by Olsen (v), 42% by Olsen (w), 39% by Olsen (16 h) and 40% by Colwell P. Partitioning the data according to fertiliser source slightly improved the coefficient of determination for Resin P for both the soluble (R²=0.81) and sparingly soluble (R²= 0.80) P fertilisers. With 0.5 M NaHCO₃ (Olsen) extractants, R² values consistently indicated a poorer prediction for the SPR treatments. A Resin P model was able to account for more variance in yield response to re-applied TSP, than an Olsen P model because the Olsen model underestimated the yield response to re-applied TSP on the PR treatments. The Resin test is more suitable than the current Olsen test for assessing the plant available P status of soils previously fertilised with fertilisers of varying solubility.Dr. A.G. Sinclair died on 3 December 1996 whilst this paper was in preparation.     

Crop production,soil carbon and nutrient balances as affected by fertilisation in a Mollisol agroecosystem

A 19-year field experiment on a Mollisol agroecosystem was carried out to study the productivity of a wheat-maize-soybean rotation and the changes in soil carbon and nutrient status in response to different fertiliser applications in Northeast China. The experiment consisted of seven fertiliser treatments: (1) unfertilised control, (2) annual application of P and K fertilisers, (3) N and K fertilisers, (4) N and P fertilisers, (5) N, P and K fertilisers, (6) N, K and second level P fertilisers, and (7) N, P and second level K fertilisers. Without fertiliser, the Mollisols could support an average yield of 1.88 t ha⁻¹ for wheat, 3.89 t ha⁻¹ for maize and 2.12 t ha⁻¹ for soybean, compared to yields of 3.20, 9.30 and 2.45 t ha⁻¹ respectively for wheat, maize and soybean if the crop nutrient demands were met. At the potential yield level, the N, P and K removal by wheat are 79 kg N ha⁻¹, 15 kg P ha⁻¹, and 53 kg K ha⁻¹, by maize are 207 kg N ha⁻¹, 47 kg P ha⁻¹, and 180 kg K ha⁻¹, by soybean are 174 kg N ha⁻¹, 18 kg P ha⁻¹, and 55 kg K ha⁻¹. Crop yield, change in soil organic carbon (SOC), and the total and available nutrient status were used to evaluate the fertility of this soil over different time periods. This study showed that a fertiliser strategy that was able to maintain yields in the short term (19 years) would not maintain the long term fertility of these soils. Although organic carbon levels did not rise to the level of virgin soil in any treatment, a combination of N, P and K fertiliser that approximated crop export was required to stabilise SOC and prevent a decline in the total store of soil nutrients.     

Long-term changes in phosphorus fractions in growers’ paddocks in the northern Victorian grain belt

Increases in P fertiliser use in Australian grain production systems over the past decades have not necessarily coincided with improved nutrient-use efficiency by crops because only a small proportion of applied P has been directly used by crops, leaving large amounts of the P in soil. Information on the transformation of applied P and the residual effectiveness of P fertiliser in growers’ paddocks under their crop rotations in a wide range of soil types may help to develop improved management practises for P fertilisers. The present study examined the size and changes of P pools in soils in the major regions used for grain production across northern Victoria. Soil samples were collected from 43 sites representing all the major soil types. In addition, samples were collected from adjacent ‘reference’ areas across fence-lines where remnant native vegetation was present to examine long-term changes in soil fertility as a result of cropping. Highly positive P balance in 27 growers’ paddocks indicates potentially high rates of P fertilization in excess of that exported/lost from these paddocks. The accumulated P was transformed into both labile and non-labile pools depending on the general chemical–physical properties of a particular soil. In particular, in soils with a sandy texture and low oxalate-extractable Al and Fe such as the sandy Calcarosols, the residual P fertilizer was preferentially transformed into labile and moderately labile pools. These P fractions can be available for subsequent crops. In contrast, a large proportion of P fertilizer applied to other soil types has been transformed into the non-labile P pools where crops have difficulty in accessing. It is suggested that P application rates should be reduced to avoid the loss of P through sorption/precipitation, leaching or run-off while still meet crop demand.     

The effect of soil P sorption properties and phosphorus fertiliser application strategy on ‘incidental’ phosphorus fertiliser characteristics: a laboratory study

The application of phosphorus (P) fertilisers to grazed pasture systems can increase the export of P in surface runoff. This increase can arise from interaction of recently applied fertiliser P with surface runoff (incidental effects) or the interaction between pseudo-equilibrated soil P and surface runoff (systematic effects). The former can represent a large proportion of annual exports. In this paper we investigate the effect of soil P buffering properties and fertiliser application strategy—split versus single applications—on incidental fertiliser effects, using laboratory studies. We used a weak electrolyte solution as a surrogate measure of runoff P and consequently defined ‘fertiliser half-life’ for six soils with widely differing P buffering properties. There was a significant (P < 0.01) exponential decay relationship between soil P buffering and fertiliser half life. For soils with low P buffering capacity, fertiliser half life was up to ~4 days, whereas for highly P buffered soils the half life was <0.5 day. There was also a highly significant (P < 0.01) effect of P buffering capacity on the magnitude of the incidental fertiliser effect, with the magnitude increasing as P buffering decreased. On one of our soils with buffering properties typical of soils used for dairying in SE Australia, we compared the effect on soluble P of a single application of 40 kg P ha⁻¹ with three applications of 13 kg P ha⁻¹. A simple comparative measure of the risk associated with the two fertiliser strategies—the area under the time by concentration curves—suggests that there is greater risk with a single application. Our results show that particular attention should be paid to timing of P fertiliser application on poorly buffered soils.     

The characterisation of different forms of water in low rank coals and some hydrothermally dried products

Equilibrium moisture contents were determined at 30 °C for a range of coals (raw and acid-washed) and hydrothermally dried (HTD) coals in desiccators at various relative humidities maintained by saturated salt solutions. The equilibrium moisture content at 15% relative humidity for a Loy Yang Low Ash coal was the same within the limits of error as that obtained from an isotherm generated by a microbalance (Intelligent Gravimetric Analyser).Total non-freezing water values for the coals and HTD products were measured using both ¹H NMR and differential scanning calorimetry (DSC). Higher values for the non-freezing water contents were obtained from DSC measurements, possibly because the calculation assumes that the enthalpy of the non-freezing water is constant and equivalent to that of the bulk water. This assumption is almost certainly erroneous and is not made in the calculation of non-freezing water from the ¹H NMR results. The values obtained by the ¹H NMR method corresponded to relative humidity values equal to about 92% for the raw coals and ≥96% for the HTD products.     

Phosphorus content in soil, uptake by plants and balance in three European long-term field experiments

The fate of phosphorus (P) derived from mineral fertilisers and organic manures, and the effective P balance, have been assessed in three long-term field experiments at Rothamsted (UK), Bad Lauchstaedt (Germany) and Skierniewice (Poland). This paper discusses the plant availability, uptake and overall utilisation of P over the last 30 years, based on soil test P availability indices and crop analyses determined by the standard methods used in each of the three countries. The data suggest that differences in soil type significantly influence the dynamics of P at the three locations, but most significantly between a loess Chernozem at Bad Lauchstaedt with a high organic matter content and the soils at the other two locations which have a low organic matter content. The application of P either as inorganic fertiliser or organic manure had a considerable influence on the availablity, uptake, leaching or fixing of P, but the crop recovery rate of P from mineral fertiliser did not exceed 35% with the smallest recovery (average 18%) occurring in the soil with the highest clay content at Rothamsted. At Bad Lauchstaedt and Rothamsted the most efficient utilisation of P (averages of 47% and 37%, respectively) was from soils treated with farmyard manure (FYM), with the greater quantity of P either leached or fixed (8 and 25 kg ha^-1 y^-1, respectively) occurring in soils treated with superphosphate. At Skierniewice, however, the reverse was true. Overall, the most efficient crop utilisation from mineral P (30% average) was from the loamy sand at Skierniewice. P balances for the three locations show that quantitatively, for the same P input, the amount of P either leached from or fixed in the plough layer of Broadbalk field, Rothamsted, was 2–3 times greater than at Skierniewice and 3–6 times greater than at Bad Lauchstaedt. The results suggest that differences in the soil physico-chemical properties, climate, the availability of other major nutrients, and the form in which P is applied, all influence the effectiveness of P fertilisation and P balance. The investigation highlights the importance of maintaining long-term field experiments and archived soil and crop samples on a world-wide basis for understanding nutrient cycling and fertility dynamics.     

Plant availability of inorganic and organic selenium fertiliser as influenced by soil organic matter content and pH

The objective of the present study was to investigate the influence of soil organic matter content and pH on plant availability of both inorganic and organic selenium (Se) fertilisers. Further, the risk of Se leaching after application of inorganic Se fertiliser was evaluated. A new interpretation of an older field study at different sites in Southern Norway showed that organic C was correlated with grain Se concentration in wheat, barley and oats, explaining up to 60% of the variation in Se concentration. Pot experiments with a peat soil, a loam soil and a peat/loam soil mixture were conducted for the present study at a range of pH values between pH 5 and 7. Below pH 6, Se uptake from added Se fertiliser was higher in the soil types with high organic matter content than in the loam. The opposite occurred at a soil pH above 6, where Se uptake was higher in the loam than in the peat soil. A simple leaching experiment after one growing season confirmed the findings of the pot experiments that Se availability in the loam soil with a relatively low organic matter content increased with increasing pH, whereas it decreased in the peat soil. Neither Se yeast, nor pure Se methionine, used as organic Se fertiliser, resulted in any significant uptake of Se when added at concentrations similar to the inorganic Se applications.     

活性氧化铝基质新型复合吸附剂的制备和储热性能

研制了一种以活性氧化铝为基质、CaCl₂为吸湿盐的新型复合吸附剂,可用于以水为吸附质的热化学吸附储热系统,并对其内部结构、吸附性能和储热性能进行了研究。利用恒温恒湿箱确定出现溶液泄漏现象的最大含盐量,并对30℃和多种相对湿度工况下的动态和平衡吸附特性进行测量,研究了含盐量和相对湿度对吸附剂的吸附特性的影响,结果表明含盐量和相对湿度越大,复合吸附剂的吸水能力越强。利用全自动比表面积与孔隙度分析仪测量材料的比表面积和孔体积,利用同步热分析仪测试了复合吸附剂的储热密度,其中含盐量最高的复合吸附剂的储热密度最高,质量和体积储热密度分别达到0.51 kW·h/kg和610.2 kW·h/m³,具有良好的储热性能。     

Evaluation of partially acidulated phosphate fertilisers and reactive phosphate rock for hill pastures

The initial and residual effectiveness of two partially acidulated fertilisers, a single superphosphate (SSP): reactive phosphate rock (RPR) physical mix (SSP:RPR) and a partially acidulated phosphate rock (PAPR), and a RPR, North Carolina, were compared with SSP at two phosphate (P)-responsive sites in hill country. One site had received small annual inputs of SSP (125 kg ha^–1 y^–1) fertiliser for 10 years (LF) and the other site no SSP in the past 5 years (NF). The SSP, PAPR and RPR were applied at 3 rates (20, 40 and 60 kg P ha^–1) and SSP:RPR at one rate (40 kg P ha^–1) once only in the first year. Fertiliser treatments were applied with or without Grasslands Huia white clover (Trifolium repens L.) seed. Initial and residual pasture and legume responses were measured over two years.In the first year, pasture and legume response to applied P was much greater at the LF than NF site. A deterioration in legume content and vigour brought about by withholding fertiliser, rather than a difference in soil-fertiliser reactions, appears to be the main reason for the different response at the two sites in the first year. At the LF site the fully (SSP) and partially (SSP:RPR and PAPR) acidulated fertilisers were far more effective in stimulating legume growth than the RPR, while at the NF site no differences in pasture or legume production were found between fertilisers in the first year. Where fertiliser has been withheld for a number of years the use of SSP appears to be a wasteful and inefficient use of a processed fertiliser.Residual effects of RPR were greater than those of SSP, as shown by the greater yield of legume at both sites in the second year. The residual effectiveness of both the partially acidulated materials was much less than that of the RPR. Mixing and sowing white clover with the fertilisers had some beneficial effects on legume content at the NF site in both years and improved legume production at this site in the second year.     

Effect of humidity on the thermal conductivity of porous zirconia ceramics

This study focuses on the role of the water content on the effective thermal conductivity of porous ceramics placed in different conditions of relative humidity. Fully stabilized zirconia samples with variation in the capacity to take up water were prepared by varying the temperature of the thermal treatment. The pore volume fraction of the dried samples decreases from 56% down to 30%. Thermal conductivity measurements were made on samples placed in a chamber where the relative humidity was fixed between 3% and 99%. For all samples, the experimental values of the effective thermal conductivity increase significantly with the water content. Experimental results agree closely to analytical predictions based on the upper limit of the Hashin and Shtrikman expressions for calculating the thermal conductivity of the pores (constituted by air and water) and Landauer's effective medium expression for calculating the effective thermal conductivity of the material.     

Estimation of saturated air water content at elevated pressures using simple predictive tool

In a compressed air system, condensed water vapor can have corrosive effects on metals and wash out protective lubricants from tools, equipments and pneumatic devices. To protect against such undesirable effects in a compressed air system, it is necessary to be able to predict the water content of air in order to design and apply the appropriate type of drying to be used in the system. In this work, a simple predictive tool, which is easier than currently available models and involves a fewer number of parameters, requiring less complicated and shorter computations, is presented here for the prediction of water content of air as a function of temperature and relative humidity as well as for compressed saturated air as a function of pressure and temperature using an Arrhenius-type asymptotic exponential function. The proposed method predicts the amount of air water content for temperatures up to 45 °C, pressures up to 1400 kPa and relative humidities up to 100%. Estimations are found to be in excellent agreement with the reliable data in the literature with average absolute deviation being less than 1.4 and 2.2% for atmospheric air and saturated compressed air, respectively. The tool developed in this study can be of immense practical value for engineers and scientists to have a quick check on the water content of atmospheric air and saturated compressed air at various conditions without opting for any experimental measurements. In particular, engineers and scientists would find the approach to be user-friendly with transparent calculations involving no complex expressions.     

Elemental sulfur fertilizers and their use on crops and pastures

This paper reviews the use of elemental sulfur (S°) as a fertiliser and its efficacy in different pastoral and cropping situations. The effect of S° particle size on rate of oxidation is critical to the effectiveness of S° fertilisers. Emphasis is therefore centred on the issue of how particle size of S° affects the rate of oxidation in different environments and cropping systems, and the size of S° in different S° fertiliser products. Rate constants of S° oxidation offer the opportunity to generalise particle size relationships needed in S° fertilisers for different crops in different environments, or alternatively, to calculate the agronomic effectiveness of different S° fertilisers available on the market. Conversely they offer a technique to set specifications as to S° particle size requirements, which together with dispersion rate specifications provide the basis for the design of S° fertilisers for specified crops and environments.     

CORRELATIONS FOR THE EQUILIBRIUM MOISTURE CONTENT OF SOI.IDS

Water adsorption and desorption isotherms at various temperatures have been generated for a variety of particulate materials (ion exchange resin, silica gel, wheat and cellulose materials). Most of thc data were obraincd with the SPS Equilibrium Moisture Content rig, using a dynamic equilibration method. Equilibration over saturated salt solutions at 2°C (static method) was also used for some of the data. Seven semi-empitical correlations, available in the literature, and one developed by SPS have been used to relate the equilibrium moisture content of the material to the relative humidity and temperature of the air. These equations enable the equilibrium moisture content to be predicted under various conditions of relative humidity and temperature from a small number of tests. For each of the six materials tested at least one of the correlations gave a good fit. However, there was no correlation which predicted the equilibrium moisnrre content well for every one of the six materials.     

ESEM analysis of polymeric film in EVA-modified cement paste

Portland cement pastes modified by 20% weight (polymer/cement ratio) of poly(ethylene-co-vinyl acetate) (EVA) were prepared, cured, and immersed in water for 11 days. The effects of water saturation and drying on the EVA polymeric film formed in cement pastes were observed using environmental scanning electron microscopy (ESEM). This technique allowed the imaging of the EVA film even in saturated samples. The decrease of the relative humidity inside the ESEM chamber did not cause any visual modification of the polymeric film during its drying.     

Stress and strain state of concrete during freezing and thawing cycles

The objective of this work is to calculate the pressures, stresses, and strains induced into moist concrete during freezing and thawing. The applied theory is based on thermodynamics and the linear theory of elasticity. If no additional salts are dissolved in the pore water the inputs needed in the theory are relative humidity and temperature measured in the sample chamber and inside concrete and evaporable water amount in the pore structure. Theoretical results were compared with the test results made with two concretes cured under water or at 96% relative humidity. One of the concretes was air entrained and in the comparison concrete no air-entraining agents were used. In the test cylinders cured under water the largest tensional stresses in freezing occurred on the surface of the test cylinders both in the axial and tangential direction. The largest tensional stress was 2.2 MPa, both in air-entrained and in non air-entrained concretes. The largest tensional stresses in the warming phase took place at the end of the thawing period when the chamber temperature was around +5 °C. Then the maximum tension occurred in the middle of the concrete cylinder in the axial direction of the cylinder. This maximum tensional stress was over 2.5 MPa in the air-entrained concrete cured in the relative humidity of 96%. The thermodynamic pumping effect at the end of the thawing phase in every cycle can increase the pore water amount remarkably if free water or moisture is available on the surface of the structure or in the environment vapor. The thermodynamic pumping effect seems to be remarkably greater and more dangerous in air-entrained concretes.