Jan Wastiels

Low-temperature synthesized aluminosilicate glasses

The reaction below 100 °C of a dehydroxylated clay (metakaolinite: (Al2O3)(SiO2)2(H2O)0.05) suspended in an alkaline sodium silicate solution ((Na2O)(SiO2)1.4(H2O)x) leads to an amorphous glassy aluminosilicate, called in this work “low-temperature inorganic polymer glass” (LTIPG or IPG).The IPG material is amorphous according to X-ray diffraction (XRD). Its molecular structure is determined by solid state Al and Si magic angle spinning nuclear magnetic resonance (27Al and 29Si MAS NMR) spectroscopy. The polymer consists of SiO4 and AlO4 tetrahedra randomly distributed, with the restriction that no Al-O-Al bonds occur. The Al/Na ratio equals one, the overall cross-link density is almost four, and only few Si-OH groups are present.The reaction stoichiometry is deduced from differential scanning calorimetry (DSC) and 27Al and 29Si MAS NMR. The inorganic polymer glass is formed by the low-temperature reaction of silicate and metakaolinite in a one to one ratio, according to the following overall reaction equation (Na2O)(SiO2)1.4(H2O)x + (Al2O3)(SiO2)(H2O)0.05 aq.(< 100 °C) →(Na2O)(Al2O3)(SiO2)3.4(H2O)z with z about 0.4.Mechanical testing shows that the ultimate compressive strength of the inorganic polymer glass corresponds with the stoichiometric silicate/metakaolinite one to one mixing ratio.

Low-temperature synthesized aluminosilicate glasses. Part II Rheological transformations during low-temperature cure and high-temperature properties of a model compound

The reaction below 100 °C of a dehydroxylated clay (metakaolinite) suspended in an alkaline sodium silicate solution leads to an amorphous aluminosilicate, called in this work “low-temperature inorganic polymer glass” (LTIPG or IPG).Some Theological transformations during the isothermal hardening process are followed with dynamic mechanical analysis (DMA) and compared with differential scanning calorimetry (DSC) and modulated differential scanning calorimetry (MDSC). It can be concluded that the change in storage modulus (DMA) during the formation of the inorganic network can be characterized quantitatively with the evolution of the heat capacity (MDSC), and that the reaction rate is not decreased by the vitrification process. During the first heating after polymerization up to 1000 °C, the material shrinks due to the evaporation of residual water from the reaction mixture as illustrated by thermogravimetric analysis (TGA) and thermomechanical analysis (TMA). The low-temperature synthesized inorganic polymer glass is thermomechanically stable up to a temperature of at least 650 °C. In that temperature zone, the glass transition can be detected with TMA and DMA.

Recommendation of RILEM TC 232-TDT: test methods and design of textile reinforced concrete: Uniaxial tensile test: test method to determine the load bearing behavior of tensile specimens made of textile reinforced concrete

Textile reinforced concrete (TRC) is a high performance cementitious composite using straight and parallel aligned fibers of suitable materials, e.g. ARglass and carbon, as continuous reinforcement in form of textiles. Textile reinforced concrete is usually used for thin concrete elements or as strengthening layers for concrete structures. Textile reinforced concrete shows a multi linear stress-strain-behavior with three distinct stages (uncracked, multiple cracking, cracking completed). The crack formation in textile reinforced concrete is significantly finer than in customary reinforced concrete. Therefore, not only the tensile strength of the concrete but also the total tensile load bearing behavior of the composite material textile reinforced concrete is of importance. The uniaxial tensile test presented here is a test method to determine the load bearing behavior of tensile specimens made of TRC. Bond characteristics of textile reinforcement can not be derived from this tensile test since this information could only be derived indirectly from cracking patterns. However, in textile reinforced concrete cracking is mainly controlled by transverse fibers which are typically present in textile reinforcement. For bond properties reference is given to the RILEM recommendation TDT A.2 (pull-out).

Behaviour of concrete under multiaxial stresses — A review

Abstract The purpose of the present paper is to provide a survey of the behaviour of concrete, as determined by experimental research. After a description of the difficulties encountered in the experimental investigation of concrete, the experimentally determined behaviour under one, two and three dimensional stress systems is treated. An explanation of this behaviour is given, based on the internal structure of concrete.

Shell Elements of Textile Reinforced Concrete Using Fabric Formwork: A Case Study

Innovations in formwork solutions create new possibilities for architectural concrete constructions. Flexible fabric replaces the stiff traditional formwork elements, and takes away a limiting factor for creative designs. Combined with textile reinforcement, the production of a new range of curved and organic shapes becomes possible without the intensive labour for formwork installation. Besides a general introduction about the concepts of fabric formwork and textile reinforcement, this paper focuses on the production and structural evaluation of doubly curved shells. Creating a very interesting type of element from a structural point of view, the shape flexibility of both the fabric formwork and textile reinforcement make a perfect match to overcome practical production issues for thin shell elements. The application of shotcrete and the integration of non-metallic reinforcement allowed first of all the production of very thin concrete shell elements based on the design approach of the textile architecture. Comparing a shell structure with traditional reinforcement and one with textile reinforcement, a case study evaluates furthermore both the design and the structural performance of such a shell structure.

Stay-in-Place Formwork of TRC Designed as Shear Reinforcement for Concrete Beams

In order to reduce on-site building time, the construction industry shows an increasing interest in stay-in-place formwork with a reinforcement function after concrete hardening, such as CFRP formwork confinement for columns. The current combined systems however do not answer the demand of the building industry for a material system that is both lightweight and fire safe. High performance textile reinforced cement (TRC) composites can address this need. They can be particularly interesting for the shear reinforcement of concrete beams. This paper describes a preliminary analysis and feasibility study on structural stay-in-place formwork made of TRC. Comparative bending experiments demonstrate that a fully steel reinforced beam and an equivalent beam with shear reinforcement in TRC formwork show similar yielding behaviour, indicating that the TRC shear reinforcement system actually works. Moreover, the cracking moment of the concrete was more or less doubled, resulting in a much lower deflection in serviceability limit state than calculated. Digital image correlation measurements show that the latter is due to the crack bridging capacity of the external TRC shear reinforcement.

Modular pedestrian bridge with concrete deck and IPC truss girder

Abstract The paper reports on the design, by means of analytical and numerical tools, the experimental verification of structural elements and the joining procedure of a 13 m span pedestrian bridge, which is composed of a concrete deck and three truss girders made of Inorganic Phosphate Cement (IPC) sandwich panels. The IPC is a cementitious matrix which does allow reinforcement with glass fibres. The bridge project wants to examine the feasibility of building structures with IPC, in view of the advantages of this material: low manufacturing cost, non-inflammable behaviour, chemical resistance and an environmentally friendly composition. The IPC sandwich panels that compose the truss girders, are connected by steel elements, which allow a rapid assembly by pin joints. The design is accompanied by experimental tests on bridge components. These tests reveal that the metal connections are the weak point of the bridge. This is due to assembly problems related to the manufacturing accuracy of both IPC sandwich panels and steel connection elements, and due to the uncertainties as to the connections of the steel inserts to the IPC skins of the sandwich panels. The design shows that in spite of the low stiffness of the glass fibre reinforced IPC, the use of IPC still leads to realistic dimensions of the bridge structure, and to the confirmation that sufficient strength can be obtained for structural applications. The main novelty of the project appears in the bridge concept, which is an act of composite thinking. The project applies classical methodologies for calculations, validation and prototype realization, but shows that a workable structure can be obtained by the synergetic combination of materials, with in this case the IPC as main component.

Analysis and verification of the performance of sandwich panels with textile reinforced concrete faces

Textile-reinforced concrete (TRC) is a composite material that recently gained renewed interest. Due to an improved durability, the usage of this composite in lightweight constructions becomes possible. In this article, the behavior of sandwich panels with TRC faces is studied. In the first part, several models are used in a finite element analysis and their advantages and disadvantages are discussed. In the second part, the calculated nonlinear behavior of the panels is compared to experimental observations.

Numerical analysis and experimental validation for static loads of a composite bridge structure

Abstract The development of a new structure is performed in many different phases. The first phase is the conceptual design, which is necessary to give a preliminary shape to the structure. Afterwards the structural analysis phase follows which is the most important part of the development of a new structure. Analytical methods in complex structures are very demanding and sometimes even impossible to be applied. For this reason the numerical methods are entering the stage and give solutions concerning the structural integrity of the structure that is being examined. In the present work the numerical analysis of an IPC pedestrian bridge and the corresponding experimental results are presented. The aim of this work is to provide the scheme of a numerical modeling procedure that will be applied in the future for the dimensioning of similar structures. In addition different types of elements were investigated as well as different sizes of mesh in order to conclude to a model that gives an exact solution taking into account the computational cost. The model is validated by using real test data extracted from the experimental analysis performed on a real prototype under static loading.

Modelling of an IPC-concrete modular pedestrian bridge

This paper shows the usefulness of FEM in the design process of a modular bridge composed of a concrete deck and three truss girders made of inorganic phosphate cement (IPC) sandwich panels. The analytical calculation of the truss, which is based on simplified hypotheses concerning the structural behaviour and the constitutive behaviour of the IPC, is validated by FEM. The design of the connections is done by FEM in order to control the distribution of the stresses in the panels and in the connection elements. The result of the design is satisfactory and is the basis for the future realisation of a prototype bridge.