Petr Hájek

New trends in sustainability assessment systems – based on top-down approach and stakeholders needs

Worldwide interest in future-proof buildings is growing, leading to increased demand for suitable methods and systems for assessing and communicating the sustainability of buildings. The number of stakeholders interested in sustainability assessment results as a basis for decision-making is growing. Ultimately, in order to bring about greater sustainability, stakeholders need to understand their potential impacts, but can only do so if this potential is clearly communicated to them through the system structure and through a language and in a format that suits their needs. Numerous systems exist, though these do not always meet the above requirements, do not always address all aspects of sustainability, may have certain methodological issues and may cause confusion through their sheer number. Therefore, there is a clear need for assessment systems to be developed further. This paper proposes that the issues raised can be tackled by a two-pronged approach: Firstly, by adhering to a top-down approach the str...

Influence of surface modification of wood with octadecyltrichlorosilane on its dimensional stability and resistance against Coniophora puteana and molds

A relatively new approach for wood protection against fungal decay is based on hydrophobization of wood and on lowering its moisture content. Water repellence of wood can be increased by polymerization of hydrophobic monomers in wood cell walls. It was found that Norway spruce wood after treatment with octadecyltrichlorosilane exhibited reduced water uptake by the wood cell walls, lowered water vapour sorption, and significantly increased dimensional stability of wood in terms of anti-swelling efficiency. Hydrophobicity and lower equilibrium moisture content were shown to cause increased resistance of the treated samples against brown-rot decay and molds.

Textile-reinforced concrete facade panels with rigid foam core prisms

Textile-reinforced concrete (TRC) is a material that is gaining new ground in the field of construction where it not only allows for the manufacture of reduced lightweight structures but also eliminates the problem of corrosion by using alkali-resistant textile reinforcement. The aim of this paper is to investigate the bending behaviour of a newly developed TRC facade panel that incorporates polystyrene foam prisms. Numerical simulations were employed in order to choose the geometry and repartition of prisms inside the facade panel. Experimental results revealed a reduced amount of concrete by 20% via the use of rigid foam prisms with a higher failure load by 16% but a lower elasticity limit by 49% in comparison with the regular facade panels.

SBToolCZ: Sustainability rating system in the Czech Republic

Several methods for complex assessment of building performance are available in Europe. The Czech Republic has followed the international group Green Building Challenge since 2005 and participated in the development of the international assessment framework SBTool. The Czech Technical University in Prague in cooperation with National Platform SBToolCZ and International Initiative for a Sustainable Built Environment (iiSBE) provides a localised national version of the tool called SBToolCZ for wide usage in building practice in the Czech Republic. This paper presents the Czech assessment methodology SBToolCZ, its structure, system of weights setting and form of final certificate. It also introduces one of the certified residential buildings – X-Loft in Prague – and describes the process of its certification and its main outcomes.

Thin Lightweight Panels Made of Textile Reinforced Concrete

Use of high performance concrete with reinforcement made of technical textile is increasing and new applications are being found. This paper presents new technology for the lightening of the panels made of textile reinforced concrete, which is being developed. The main focus of this research is to produce concrete elements suitable for use as facade panels with the least possible weight and environmental impact. Mechanical characteristics were measured on testing specimens with thickness of 18 mm with lightening representing 47% of their volume. Minimum thickness of concrete was 4 mm and therefore the reinforcement was covered by approximately 1.5 mm of concrete matrix. The strength of experimental test panels was measured in four-point bending stress test. Due to one-sided lightening and asymmetrical cross-section therefore, the tests were performed in both directions. For better interpretation of the results were the specimens of lightened panels tested alongside non-lightened specimens with the same thickness. Based on measured values, maximal dimensions of lightened facade panels were designed.

Nanocoating on alkali-resistant glass fibers by octadecyltrichlorosilane to improve the mechanical strength of fibers and fibers/epoxy composites

Surface defects cause the measured tensile strength of alkali glass fibers to be significantly lower than their theoretical values. Coatings can be used to “heal” surface flaws and to modify surface properties. In the present work, the nanocoating on alkali-resistant glass (ARG) fiber rovings was carried out by self-assembled monolayers (SAMs) of octadecyltrichlorosilane (OTS). The ARG roving was dipped into OTS nanosol, which deposited the organic–inorganic SAMs of OTS on the ARG surface. The assessment of changes in the fiber surfaces was characterized by scanning electron microscopy (SEM) and fluorescence microscopy, while the chemical changes were characterized by X-ray photoelectron spectroscopy (XPS). Furthermore, the influence of nanocoating on the tensile properties of ARG and OTS-treated ARG with and without an epoxy matrix was also studied. The SEM analysis revealed the formation of nanoscale layers on the ARG surfaces and the XPS confirmed the deposition of organic–inorganic monolayers. The tensile strength of ARG rovings with and without the epoxy matrix was improved significantly. The OTS treatment almost created a superhydrophobic nanocoating on ARG, which was confirmed by the sessile drop water contact angle, and the water absorption by the ARG/epoxy composites reduced.

Coating of wood by means of electrospun nanofibers based on PVA/SiO2 and its hydrophobization with octadecyltrichlorosilane (OTS)

Abstract Poly(vinyl) alcohol (PVA)/nanosilica (SiO2) based electrospun nanofibers has been deposited on wood substrate by means of the roll electrospinning process. The nanofibrous coating was hydrophobized by self-assembled monolayers of octadecyltrichlorosilane (OTS) via a sol-gel dipping process. The PVA/SiO2 nanofiber coating and OTS hydrophobized coating were characterized by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and energy dispersive X-ray analysis (EDXA). All methods confirmed the formation of OTS monolayers on hybrid coatings. The adhesive strength and resistance to scratch of nanofibers coating was also evaluated.

Cohesion of Composite Reinforcement Produced from Rovings with High Performance Concrete

The reinforcement of concrete with composite technical textile creates a tensile load-bearing capacity. It allows the elimination of steel reinforcement and minimisation of concrete cover. Based on this, the concrete cover is designed with respect to the cohesion of reinforcement with concrete. By using of textile reinforcement very thin structures could be created. The aim of this paper was to determine the interaction conditions of carbon and basalt composite reinforcement in a matrix of epoxy resin with high performance concrete (HPC). The tensile strength of used composite reinforcement and the other mechanical parameters of HPC were determined by experimental tests. Experiments copied the production method of technical textiles. These two combinations of materials present the influence on the design of the structures with textile reinforcements.

Symmetrically separated sequences in the unit sphere of a Banach space

Abstract We prove the symmetric version of Kottmans theorem, that is to say, we demonstrate that the unit sphere of an infinite-dimensional Banach space contains an infinite subset A with the property that ‖ x ± y ‖ > 1 for distinct elements x , y ∈ A , thereby answering a question of J.M.F. Castillo. In the case where X contains an infinite-dimensional separable dual space or an unconditional basic sequence, the set A may be chosen in a way that ‖ x ± y ‖ ⩾ 1 + e for some e > 0 and distinct x , y ∈ A . Under additional structural properties of X, such as non-trivial cotype, we obtain quantitative estimates for the said e. Certain renorming results are also presented.

The Effect of Surface Treatments of Textile Reinforcement on Mechanical Parameters of HPC Facade Elements

Development of extremely thin concrete structures and demand for extremely thin elements are the reason of using composite non-traditional materials as reinforcement. Steel reinforcement is not very chemically resistant and it limits the thickness because of the required concrete cover as protection. This is the reason why textile reinforced concrete (TRC) going to be very famous and modern material. TRC in combination with fine grain high performance concrete (HPC) allows a significant saving of concrete. Due to its non-corrosive properties of composite technical textiles it is possible to design very subtle structures and elements. TRC and HPC in general are developed at the Faculty of Civil Engineering and the Klokner Institute, CTU in Prague. This present paper investigates the cohesion influence of textile reinforcement on four point bending test. All small experimental panels were reinforced with the same 3D technical textile from AR-glass roving with different type of cover layer. Different conditions of interaction between technical textiles and HPC were ensured by modified surface using silica sand and silica flour.