Christophe Baux

Behaviour of Fire-Proofing Materials Containing Gypsum, Modifications Induced by Incorporation of Inert Filler

The fire-proofing materials used to make fire breaks are usually calcium sulphate dihydrate or calcium silicate panels. During fire exposure, the gypsum panels are characterized by an isothermal stage on the unexposed side due to the latent heat consumption. This latent heat is induced by two endothermic phase changes during transformation of gypsum into hemihydrate and anhydrite. These phase changes cause thermal shrinkage that provokes panel cracking and the increased temperature on the unexposed side. To improve the thermomechanical properties of gypsum panels, a specific filler is added to the plaster before hydration. Thermomechanical analyses show that this filler reduces the shrinkage in gypsum during heating. Fire tests show that this decrease in thermal shrinkage reduces crack appearance. Unlike gypsum plaster without filler, the heat flow is reduced even after gypsum dehydration and the temperature of the unexposed side after the isothermal stage is stabilized. The inert filler decreases the latent heat and the thermal conductivity of the materials which also modifies the thermal behaviour of panels.

A new bidimensional material: Ln2(CO3)3.8 H2O (Ln=La, Ce): Synthesis and crystal structure

Abstract The slow diffusion through gel in a U-tube of trivalent lanthanide ions with TMA 3− , where TMA 3− stands for [C 6 H 3 (COO) 3 ] 3− , afforded single crystals suitable for crystalline resolution. The crystal structure has been solved for the Ce(III) compound and is reported here. The chemical formula is Ce 2 (CO 3 ) 3 .8 H 2 O and the space group of the crystalline structure is Pccn with: a =8.9421(7) A, b =9.5292(9) A, c =16.971(2) A and Z =4. The structure consists in planes in which the lanthanides ions are connected via bidendate carboxylato groups or μ 2 -oxo bridges. The isostructurality of the other compounds has been assumed on the basis of X-ray powder diagram and elementary cell determination.

New sulfur rich lanthanide based materials: synthesis and magnetic properties

A Gd(III) complex with tetrathiooxalate has been obtained by reacting trivalent lanthanide ion and tetraethylammonium tetrathiooxalate. Its synthesis and characterizations (EPR, ICP, FTIR, TGA) as well as its magnetic properties are reported here. The Gd(III)–Gd(III) magnetic interaction is weakly antiferromagnetic and the fit of the magnetic data leads to g =2.0 and J =−0.105 cm −1 . A new Y(III) sulfate has also been obtained as a by-product during unsuccessful attempts of crystallization of an Y(III) complex with tetrathiooxalate. Its crystal structure has been determined and is described here. The chemical formula is Y(SO 4 ) 2 .H 2 O.NH 2 (CH 3 ) 2 and it crystallizes in the space group P21/n with: a =8.5706(7) A, b =19.6491(17) A, c =5.6638(5) A, β =90.522(1) and Z =4.

Modélisation du comportement thermique haute température de matériaux minéraux

ABSTRACT High temperature thermal transfer in hydrated minerals (such as gypsum, cement…) is studied and modelled. Exposed to fire, the studied materials are subject to phases transitions correlated with a high dehydration latent heat. The development of an electric furnace allowing the realisation of unidirectional high thermal transfer. The results of these trials are collected and merge in a database of experimental results. Concurrently, a thermal transfer model is built. Thermal analyses such as DTA/TG are used to determine the degradation kinetics of hydrated minerals. The degradation kinetics is modelled with a classical solid state kinetic law based on the chemical reaction rate. This law is used to balance the dehydration latent heat introduced in the heat equation. The developed model is then based on an implicit scheme and uses the finite difference method. Modelled and experimental results are presented herein.

Les produits minéraux utilisés en protection incendie face aux nouvelles réglementations

ABSTRACT Two fireproofing materials are studied. These materials cannot be used above 1000—1100°C due to their loss of thermal and mechanical properties. Moreover, at such temperatures, their permeability towards hot (and/or) toxic gases increases dramatically. Results of severe thermal solicitations (based on new European standards) are presented herein. They confirm that the melting of at least one of the compounds completely modifies the thermal transfer conditions. Above a critical temperature, the melting front will diffuse through the material and will affect its permeability as well as its mechanical properties and thickness. Thus, development of new fireproofing materials (presenting a real high temperature resistance) imposes to master high temperature shrinkage. An optimized product is presented herein.

Fire Protection of Concretes: Formulation, Performances and Pathology

The efficiency of thin mineral passive fire protection layer applied on concrete is analyzed. The more suitable fireproofing material formulations are selected from results of laboratory scale fire test. Such tests consist in the direct exposure of protected concrete samples to the flame of a burner, at constant temperature (850°C). Various formulations of mineral fireproofing materials have been tested to identify the effects of binder type and the density. Formulation compromises are highlighted regarding requested fire performances. Selected formulations are used to protect real scale concrete slab exposed to standard fire (ISO 834). During the test, the concrete/fire protection layer interface temperature and the steel reinforcement temperature have been recorded. For small size slabs, fire proofing layer is completely efficient. The temperature increases are strongly delayed. For large size slabs, delamination of fire proofing layer appears, leading to rapid concrete degradation. To understand the mechanics of cracking and delamination of fire protection layer, laboratory scale tests are performed with two selected formulations varying the implementation methods (surface treatment of concrete, intervention on interface roughness, pre-cracking...). It appears that the occurrence of fire protection layer delamination can be avoided choosing the optimal implementation method without adjustment of the optimized formulations.

Mineral foams obtained with super sulfated cement

The purpose of this study is to evaluate the performances of Super Sulfated Cement (SSC) foams, focusing on structural, thermal and mechanical characteristics. The studied set of SSC foam samples is obtained with the same slurry. The chosen foaming method allows an interesting density variation: from 489 kg/m3 to 1793 kg/m3. Thanks to a CCD camera, the visual study of foam pore structure reveals two kinds of bubbles distribution and associated connectivity. This may partially explain the obtained thermal and mechanical behavior. Results show that SSC foams with low density (< 550 kg/m3) are usable as thermal insulator for non-loadbearing walls. Mean density SSC foams (550 kg/m3 < - < 640 kg/m3) can be used as slight-loadbearing and thermal insulating products in housing and SSC foams with high density (640 kg/m3 < - < 1200 kg/m3) as loadbearing products staying within lightweight class.

Mechanical Performances of Super Sulfated Cements

Tested super sulfated cements (SSC) are composed with various amounts of ground granulated blast furnace slag, gypsum or activated gypsum and Portland cement. Our initial results on the optimization of the composition and of the curing conditions of such cements are presented herein. Tests are conducted on the basis of standard mortar with two different gauging ratios according to old and new standards for SSC. Four types of curing are used. Mechanical performances are assessed at 2, 7, 28, 60 and 90 days on standard mortar samples (binder/sand mass ratio = 1/3). This study shows that, thanks to an optimization of the Portland cement content, it is completely possible to obtain super sulfated cement with a strength class 32.5N, and always in conformity with the new European standard. For a given SSC formulation, it is clearly demonstrated that the origin of the calcium sulfate addition that affects the development of sulfo-aluminous compounds in these mixtures constitutes a key point in the phenomena of setting and hardening. The use of heat-activated gypsum as a sulfate activator appears preferable.