Effect of Fibre Additives in Concrete on Change of Thermophysical Properties

In recent years, we witnessed a rise in synthetic materials, mainly fibres, used for producing building materials. Fibres are, among other things, used to improve concrete poor energy absorption. Natural fibres reinforcement is found as the solution for low-cost building material mainly in developing countries. As processes in cement-based materials are moisture dependent, in this paper, we compare moisture dependence of thermophysical properties of cement-based materials with synthetic and some natural fibres. Thermal properties for samples with different types and amounts of fibres were measured by temperature response of each test specimen to heat flow impulses. This was done for increasing and decreasing relative humidity reached by artificial wetting in climatic chamber. The best results were achieved for the sample with 10% horse manure. Further on we would like to continue in testing and comparing mechanical properties of the samples as well.

Evaluation of the Moisture Dependence of Concrete Coefficient of Thermal Expansion and Its Impacts on Thermal Deformations and Stresses of Concrete Pavements

The coefficient of thermal expansion (CTE) is one of the material properties of concrete that has the largest impact on rigid pavement performance. Concrete CTE is typically measured in the laboratory, under saturated conditions, or estimated on the basis of the mix constituents, past experience, or both. Whichever method is used, the mechanistic-empirical design of concrete pavements traditionally assumes a constant value for this material property. This assumption has important consequences in relation to predicting thermal deformations and stresses since the CTE of concrete actually changes with the concrete’s internal moisture conditions. The experimental data presented in this study show that this assumption, together with the way CTE is measured in the laboratory, leads to systematic underestimates of thermal deformations and stresses in concrete pavements. The experimental data come from six concrete overlays of asphalt pavements that were instrumented with thermocouples, relative humidity sensors, and vibrating wire strain gauges to measure the expansion/contraction and bending of the slabs because of temperature and moisture-related actions. The apparent CTE of the overlay slabs reached values up to 65% larger than the CTE measured in the laboratory under saturated conditions. Using finite element method modeling, it was determined that thermal stresses were up to 70% larger than predicted using the saturated CTE.

Historical climate controls soil respiration responses to current soil moisture

Ecosystem carbon losses from soil microbial respiration are a key component of global carbon cycling, resulting in the transfer of 40–70 Pg carbon from soil to the atmosphere each year. Because these microbial processes can feed back to climate change, understanding respiration responses to environmental factors is necessary for improved projections. We focus on respiration responses to soil moisture, which remain unresolved in ecosystem models. A common assumption of large-scale models is that soil microorganisms respond to moisture in the same way, regardless of location or climate. Here, we show that soil respiration is constrained by historical climate. We find that historical rainfall controls both the moisture dependence and sensitivity of respiration. Moisture sensitivity, defined as the slope of respiration vs. moisture, increased fourfold across a 480-mm rainfall gradient, resulting in twofold greater carbon loss on average in historically wetter soils compared with historically drier soils. The respiration–moisture relationship was resistant to environmental change in field common gardens and field rainfall manipulations, supporting a persistent effect of historical climate on microbial respiration. Based on these results, predicting future carbon cycling with climate change will require an understanding of the spatial variation and temporal lags in microbial responses created by historical rainfall.

Impact of scaling to the resistive switching effect in organic polymer – based structures

The resistive switching effect has been studied in a set of organic polymer - based structures of a different composition and size scale from macro to micro. It is shown that scaling down reduces both the threshold switching voltage Vth and the respective effective electric field Eth. Furthermore, introduction of metal micro particles into a macro scale polymer matrix provides the same effect. Therefore the metal particle incorporation may be regarded as an alternative method of effective scaling, depending on an application. Switching speed of less than 15 ns, threshold voltage Vth ~ (2 – 25) V, 105 cycle endurance, no significant moisture dependence and high retention time 3.5 months for scaled down samples aswell as for metal doped macro samples have been demonstrated. These characteristics are suitable for constructing memory devices. The switching effect mechanisms are discussed.

Relationships between photosynthesis and formaldehyde as a probe of isoprene emission

Atmospheric oxidation of isoprene emission from land plants affects radiative forcing of global climate change. There is an urgent need to understand the factors that control isoprene emission variability on large spatiotemporal scales but such direct observations of isoprene emission do not exist. Two readily available global-scale long-term observation-based data sets hold information about surface isoprene activity: gross primary productivity (GPP) and tropospheric formaldehyde column variability (HCHOv). We analyze multi-year seasonal linear correlations between observed GPP and HCHOv. The observed GPP–HCHOv correlation patterns are used to evaluate a global Earth system model that embeds three alternative leaf-level isoprene emission algorithms. GPP and HCHOv are decoupled in the summertime in the southeast US (r=−0.03). In the Amazon, GPP and HCHOv are weakly correlated in March-April-May (MAM), correlated in June-July-August (JJA) and weakly anticorrelated in September-October-November (SON). Isoprene emission algorithms that include soil moisture dependence demonstrate greater skill in reproducing the observed interannual seasonal GPP–HCHOv correlations in the southeast US and the Amazon. In isoprene emission models that include soil moisture dependence, isoprene emission is correlated with photosynthesis and anticorrelated with HCHOv. In an isoprene emission model without soil moisture dependence, isoprene emission is anticorrelated with photosynthesis and correlated with HCHOv. Long-term monitoring of isoprene emission, soil moisture and meteorology is required in water-limited ecosystems to improve understanding of the factors controlling isoprene emission and its representation in global Earth system models.

Relationships between photosynthesis and formaldehyde as a probe of isoprene emission

Atmospheric oxidation of isoprene emission from land plants affects radiative forcing of global climate change. There is an urgent need to understand the factors that control isoprene emission variability on large spatiotemporal scales but such direct observations of isoprene emission do not exist. Two readily available global-scale long-term observations hold information about surface isoprene activity: gross primary productivity (GPP) and tropospheric formaldehyde column variability (HCHOv). We analyze multi-year seasonal linear correlations between observed GPP and HCHOv. The observed GPP-HCHOv correlation patterns are used to evaluate a global Earth system model that embeds three alternative leaf-level isoprene emission algorithms. GPP and HCHOv are decoupled in the summertime southeast US (r = −0.03). In the Amazon, GPP-HCHOv are weakly correlated in March-April-May (MAM), correlated in June-July-August (JJA) and weakly anti-correlated in September-October-November (SON). Isoprene emission algorithms that include soil moisture dependence demonstrate greater skill in reproducing the observed interannual seasonal GPP-HCHOv correlations in the southeast US and the Amazon. In isoprene emission models that include soil moisture dependence, isoprene emission is correlated with photosynthesis and anti-correlated with HCHOv. In an isoprene emission model without soil moisture dependence, isoprene emission is anti-correlated with photosynthesis and correlated with HCHOv. Long-term monitoring of isoprene emission, soil moisture and meteorology is required in water-limited ecosystems to improve understanding of the factors controlling isoprene emission and its representation in global Earth system models.

Impacts of soil moisture on de novo monoterpene emissions from European beech, Holm oak, Scots pine, and Norway spruce

Impacts of soil moisture on de novo monoterpene (MT) emissions from Holm oak, European beech, Scots pine, and Norway spruce were studied in laboratory experiments. The volumetric water content of the soil, Θ, was used as the reference quantity to parameterize the dependency of MT emissions on soil moisture and to characterize the severity of the drought. When Θ dropped from 0.4 m3 × m−3 to ~0.2 m3 × m−3 slight increases of de novo MT emissions were observed but with further progressing drought the emissions decreased to almost zero. In most cases the increases of MT emissions observed under conditions of mild drought were explainable by increases of leaf temperature due to lowered transpirational cooling. When Θ fell below certain thresholds, MT emissions decreased simultaneously with Θ and the relationship between Θ and MT emissions was approximately linear. The thresholds of Θ (0.044–0.19 m3 × m−3) were determined, as well as other parameters required to describe the soil moisture dependence of de novo MT emissions for application in the Model of Emissions of Gases and Aerosols from Nature, MEGAN. A factorial approach was found appropriate to describe the impacts of Θ, temperature, and light. Temperature and Θ influenced the emissions largely independently from each other, and, in a similar manner, light intensity and Θ acted independently on de novo MT emissions. The use of Θ as the reference quantity in a factorial approach was tenable in predicting constitutive de novo MT emissions when Θ changed on a time scale of days. Empirical parameterization with Θ as a reference was only unsuccessful when soil moisture changed rapidly

Impacts of soil moisture on de-novo monoterpene emissions from European beech, Holm oak, Scots pine, and Norway spruce

Impacts of soil moisture on de-novo monoterpene (MT) emissions from Holm oak, European beech, Scots pine, and Norway spruce were studied in laboratory experiments. The volumetric water content of the soil, Θ, was used as reference quantity to parameterize the dependency of MT emissions on soil moisture and to characterize the severity of the drought. When Θ dropped from 0.4 m3 m−3 to ~ 0.2 m3 m−3 slight increases of de-novo MT emissions were observed but with further progressing drought the emissions decreased to almost zero. The increases of MT emissions observed under conditions of mild drought were explainable by increases of leaf temperature due to lowered transpirational cooling. When Θ fell below certain thresholds, MT emissions decreased simultaneously with Θ and the relationship between Θ and MT emissions was approximately linear. The thresholds of Θ (0.044–0.19 m3 m−3) were determined as well other parameters required to describe the soil moisture dependence of de-novo MT emissions for application in the Model of Emissions of Gases and Aerosols from Nature, MEGAN. A factorial approach was found appropriate to describe the impacts of Θ, temperature, and light. Temperature and Θ influenced the emissions largely independent from each other, and, in a similar manner, light intensity and Θ acted independently on de-novo MT emissions. The use of Θ as reference quantity in a factorial approach was tenable in predicting constitutive de-novo MT emissions when Θ changed on a time scale of days. Only when soil moisture changed suddenly empirical parameterization with Θ as a reference was unsuccessful.

Transient Pulse Method for Measuring of Heat Conductivity of Autoclaved Aerated Concrete

The heat conductivity, specific heat and bulk density are the basic material parameters and thus indispensable. There are numbers of methods used for measurement of heat conductivity. However, the non-stationary (transient pulse method) measurements methods are preferred for description of heat conductivity moisture dependence. This article discusses on the establishment dependence of heat conductivity on water content for selected porous building materials by using non stationary measurement methods. Dependence of the thermal conductivity on the water content is necessary for coupled heat, air and moisture (HAM) simulation in building construction.