Leaf functional traits differentiation in relation to covering materials of urban tree pits

Background Understanding the ecological strategies of urban trees to the urban environment is crucial to the selection and management of urban trees. However, it is still unclear whether urban tree pit cover will affect plant functional traits. Here, we study the response of urban trees to different tree pit covers, analyzed the effects of different cover types on soil properties and their trade-off strategies based on leaf functional traits. Results We found that there were obvious differences in the physical properties of the soil in different tree pit covers. Under the different tree pit cover types, soil bulk density and soil porosity reached the maximum under cement cover and turf cover, respectively. We found that tree pit cover significantly affected the leaf properties of urban trees. Leaf thickness, chlorophyll content index and stomatal density were mainly affected by soil bulk density and non-capillary porosity in a positive direction, and were affected by soil total porosity and capillary porosity in a negative direction. Leaf dry matter content and stomata area were mainly negatively affected by soil bulk density and non-capillary porosity, and positively affected by soil total porosity and capillary porosity. Covering materials of tree pits promoted the functional adjustment of plants and form the best combination of functions. Conclusion Under the influence of tree pit cover, plant have low specific leaf area, stomata density, high leaf thickness, chlorophyll content index, leaf dry matter content, leaf tissue density and stomata area, which belong to “quick investment-return” type in the leaf economics spectrum.

Accuracy in Cement Hydration Investigations: Combined X-ray Microtomography and Powder Diffraction Analyses

Cement hydration is a very complex set of processes. The evolution of the crystalline phases during hydration can be accurately followed by X-ray powder diffraction data evaluated by the Rietveld method. However, accurate measurements of some microstructural features, including porosity and amorphous content developments, are more challenging. Here, we combine laboratory X-ray powder diffraction and computed microtomography (μCT) to better understand the results of the μCT analyses. Two pastes with different water–cement ratios, 0.45 and 0.65, filled within capillaries of two sizes, ϕ = 0.5 and 1.0 mm, were analysed at 50 days of hydration. It was shown that within the spatial resolution of the measured μCTs, ~2 μm, the water capillary porosity was segmented within the hydrated component fraction. The unhydrated part could be accurately quantified within 2 vol% error. This work is a first step to accurately determining selected hydration features like the hydration degree of amorphous phases of supplementary cementitious materials within cement blends.

Durability Properties of Ultra-High Performance Lightweight Concrete (UHPLC) with Expanded Glass

It is important to ensure the durability and safety of structures. In the case of newly developed materials that are outside the current rules, it is important to investigate all aspects of structural safety. The material studied in the following is a structural lightweight concrete with an ultra-high-performance matrix and expanded glass as a lightweight aggregate. The material, with a compressive strength of 60–100 MPa and a bulk density of 1.5–1.9 kg/dm3, showed high capillary porosities of 12 vol% (ultra-high-performance concretes (UHPC) < 5 vol%). Since the capillary porosity basically enables transport processes into the concrete, the material had to be examined more closely from the aspect of durability. Freeze-thaw resistance (68 g/m2) and chemical attack with sulfate at pH 3.5 for 12 weeks (16 g/m2) showed no increase in concrete corrosion. Targeted carbonation (0.53 mm/year0.5) and chloride penetration resistance (6.0 × 10−13 to 12.6 × 10−13 m2/s) also showed good results against reinforcement corrosion. The results show that most of the measured capillary pores resulted from the lightweight aggregate and were not all present as a pore system. Thus, the durability was only slightly affected and the concrete can be compared to an UHPC. Only the abrasion resistance showed an increased value (22,000 mm3/5000 mm2), which, however, only matters if the material is used as a screed.

Development of High-Strength Foamed Concrete Compositions

Unlike traditional materials, the development of high-performance foamed concrete with a compressive strength of up to 20 MPa and a density of up to 1400 kg/m3 allows the use of foamed concrete as a constructive material with additional functions including good thermal insulation properties, sound insulation and capillary porosity needed to ensure hydrothermal conditions. Unlike autoclaved aerated concrete, foamed concrete can also be used in monolithic construction.The studies of high strength foamed concrete were performed by using mostly local mineral components and mixing technology by using planetary activator which provides a fundamentally new mixing mode that combines intensive mixing, foaming and activation of components. To realize the experimental part of the research, turbulence type foamed concrete mixer SPBU-LUKS was used.

Assessment of Electrical Resistivity and Oxygen Diffusion Coefficient of Cementitious Materials from Microstructure Features

A newly proposed modified non-contact electrical resistivity measurement was used to test the resistivity of concrete and cement mortar. The oxygen diffusion coefficients of concrete and mortar were determined by a gas diffusion measurement, and the capillary porosity of concrete and cement mortar was measured by mercury intrusion porosimetry (MIP) measurement. The obtained electrical resistivity and capillary porosity results were verified with other researchers’ data, the measured electrical resistivity results can be estimated by a simple equation from the capillary porosity results. The obtained oxygen diffusion coefficient results were quantitatively correlated with capillary porosity and electrical resistivity measurement results. The proposed equations can be practically used to assess the electrical resistivity and oxygen diffusion coefficient.

Regulation Of The Resistance Of Cement Concrete With Polymer Additive And Activated Liquid Medium

The article presents the results of studies of cement concrete with a polymer reagent and an activated (magnetically treated) liquid medium. A decrease in the total and capillary porosity of the cement stone and an increase in microporosity up to 18% indicate an increase in the resistance of concrete in aggressive environments.

Effects of Water-to-Cement Ratio on Pore Structure Evolution and Strength Development of Cement Slurry Based on HYMOSTRUC3D and Micro-CT

Changing the water-to-cement ratio is one of the major ways to develop cement slurry with different densities, which in turn will greatly affect the pore structure and mechanical properties of cement slurry. In the current study, the cement hydration model HYMOSTRUC3D was used to investigate the effects of water-to-cement (w/c) ratio (0.40, 0.44, 0.50) on the pore structure evolution and strength development of cement slurry. The microstructure of the cement stone was characterized via scanning electron microscope (SEM) and micro-computed tomography (micro-CT), and the mechanical strength of the cement stone was tested and analyzed via a mechanical tester. The simulated compressive strength and capillary porosity are in good agreement with the measured data, where the relative error between the simulated results and measured results are within 0.6~10.7% and 13.04~25.31%, respectively. The capillary porosity is proved as the main factor affecting the compressive strength of cement stone with different w/c ratios. Herein, the mathematical relationship between the measured capillary porosity and compressive strength could be well fitted via the mathematical prediction models of the Balshin function (R2 = 0.95), Ryshkewitch function (R2 = 0.94), Schiller function (R2 = 0.96), and the linear regression function (R2 = 0.95). Moreover, the linear regression function (y = −2.38x + 82.76) can be used to characterize and predict the quantitative relationship between the compressive strength and capillary porosity of cement stone. The findings in this study will provide a reference value in the fields of oil and gas cementing and building concrete.

Modifying Mechanical Strength and Capillary Porosity of Portland Cement-Based Mortar Using a Biosurfactant from Pseudomonas fluorescens

We characterized the effects of a biosurfactant derived from Pseudomonas fluorescens on slump loss, mechanical strength, capillary porosity, and bacterial colonization inside Portland cement-based mortar samples. Standard tests were used to evaluate the utility of this biosurfactant as an admixture. The addition of 1.5% biosurfactant increased the plasticity and improved the workability of fresh samples. Although compressive and flexural strengths of mortars with biosurfactant were lower than those of mortars without biosurfactant after a short curing period (28 days), the addition of biosurfactant increased the compressive strength of mortar after a long curing period (180 days), with 1% biosurfactant having the highest value. After 180 days, mortar with biosurfactant had significantly lower capillary absorption coefficient A values (P<0.05) than mortar without biosurfactant. Furthermore, the addition of biosurfactant reduced the relative abundance of the mortar-deteriorating bacterial genus Pseudomonas (phylum Proteobacteria).

Zeolite-Containing Terra-Silicea as a Component of Composite Binders

The work is devoted to the study of the zeolite terra silicea (ZTS) for the subsequent development of composite binders based on its properties. Zeolite-containing rock - Terra silicea has high adsorption properties, due to the crystal-chemical features of the structure of its minerals and the predominance of capillary porosity in the rock. The rock-forming zeolite-containing Terra silicea mineral (clinoptilolite), due to the crystal chemical characteristics of its structure, is expected to act as a “battery” of the mortar part of the hydrating system, ensuring the solution intake in the later stages of hardening and, thereby, creating conditions for monolithic structure during the operational period.