Béton | EPFL Graph Search

thumb|Aspect hétérogène de la surface d'un béton de ciment, appelé communément béton, et constitué de ciment, d'eau et de granulats fins (sable) et grossiers (graviers). Le béton est un assemblage de matériaux de nature généralement minérale. Il met en présence des matières inertes, appelées granulats ou agrégats (graviers, gravillons, sables), et un liant (ciment, bitume, argile), c'est-à-dire une matière susceptible d'en agglomérer d'autres ainsi que des adjuvants qui modifient les propriétés physiques et chimiques du mélange. Mêlé à de l'eau, on obtient une pâte, à l'homogénéité variable, qui peut, selon le matériau, être moulée en atelier (pierre artificielle), ou coulée sur chantier. Le béton fait alors « prise », c'est-à-dire qu'il se solidifie.

Lorsque l'argile est employée, on parle traditionnellement de « pisé », de « torchis » ou, plus récemment, de « béton de terre », probablement le plus ancien de tous les bétons.
Lorsque le ciment est employé comme liant, on obtient u

Quantification of effects of fly ash type on concrete early-age cracking

The mechanisms that contribute to early-age cracking are complex. Determining the relative importance of each mechanism as well as the combined cracking potential for a given concrete material is essential for the concrete industry to construct structures with a long service life. A method for quantifying the cracking risk of a concrete mixture is presented. The method involves testing for the concrete heat of hydration, setting time free thermal and autogenous movement, restrained stress, and mechanical property development. The concrete uniaxial stress under restrained conditions is measured using a rigid cracking frame. This test setup was used to quantify the effects of using fly ash on the concrete cracking risk using four different fly ashes with varying calcium oxide contents. All fly ashes reduced the cracking risk because of the decrease in the heat of hydration of the cementitious materials and, to a lesser extent, the increased early-age creep.

American Concrete Institute2008

Hydration, microstructural development and dimensional stability of cementitious materials made of portland cement clinker and fluoroanhydrite

Carolina Prieto Gomez

The production of Portland cement accounts for 5 to 8% of the global anthropogenic CO2 emissions. In the past years, the cement industry has attempted to reduce this contribution by the use of mineral additions on the cement or in the concrete mix. The typical additions in cement are materials with pozzolanic properties such as fly ash, silica fume, etc. Other attempts have been done using materials obtained as byproducts from other industrial processes. This is the case of the chemical gypsums i.e. calcium sulfates. Calcium sulfate can be obtained in the production of several acids such as boric (borogypsum), hydrofluoric (fluorgypsum or fluoroanhydrite), phosphoric (phosphogypsum), etc. or in desulfurization process in coal burning power plants. In this work, the reaction mechanisms of a binder made of 60% fluoroanhydrite and 40% Portland cement clinker have been studied. This binder is currently being produced in Mexico in the preparation of aerated concrete mixes intended to be used in low-cost housing. This work aims to gain insight on the mechanisms of reaction of the binder made of fluoroanhydrite- Portland cement clinker on the one hand and the dimensional stability aspects related with this binder and its application in the construction industry on the other. Model mixes prepared with different proportions of materials were also studied to understand the effect of the fluoroanhydrite on the properties of the binder. The hydration kinetics of the binder was studied by means of isothermal calorimetry and chemical shrinkage. The microstructural development was studied by a combination of techniques such as SEM, XRD, mercury intrusion and others. The dimensional stability of the binder was approached mainly by length change tests carried under different conditions. As this product is a calcium- sulfate based binder the results under high relative humidity conditions were highlighted. The reaction kinetics of the binder were found to be affected by the impurities present in the fluoroanhydrite; hydrofluoric acid traces particularly retard the hydration of both fluoroanhydrite and the clinker. Other aspects such as aging and the ethanolamine-based grinding agent used on the production of the binder were found responsible of the delayed reaction of the binder compared to Portland cement clinker. The hydration of the binder in water immersion is not very different from that observed under medium relative humidity; however, the dimensional stability of the binder is importantly affected by this parameter. The composition of the binder was found to play an important role.

EPFL2010

Simplified concrete resistivity and rapid chloride permeability test method

A simplified method of measuring concrete resistivity, as an index of permeability, has been developed that is similar to ASTM C1202 or the rapid chloride permeability test (RCPT). It is significantly faster and easier to perform, however In this test, cylinders 100 x 200 mm (4 x 8 in.) were cured in 100% relative humidity and tested using the same solutions, test cells, and rubber gaskets as specified in ASTM C1202. To eliminate the problem of the temperature rise of the sample during the test, only one current reading was taken (after 5 minutes) that could be used to calculate the concrete resistivity. Testing was conducted on various different concrete mixtures after 91 days of moist curing using both the new quicker method and the standard ASTM 0202 method. An empirical correlation between the new method and the standard method demonstrates the validity and promise of the new method.

2008

Hydration, microstructural development and dimensional stability of cementitious materials made of portland cement clinker and fluoroanhydrite

Carolina Prieto Gomez

EPFL2010