LafargeHolcim (France)

Without change there is no innovation, creativity, or incentive for improvement, while our future economic growth relies on innovation and competitiveness. Fiber-reinforced concrete (FRC) clearly appears today as a promising mechanical and economical alternative to the conventional reinforcement steel mesh. However there is still a lack of a unified design philosophy adapted to this material. Model Code 2010 is one of the most widespread designing guidelines but established on the basis of steel FRC. Based on the Model Code guidelines, the current Eurocodes are also being revised and for the first time Eurocode 2 will be extended with a harmonized annex covering FRC with metallic fibers but not taking in consideration non-metallic fibers. Non-metallic fibers are taking some of the market share from steel FRC and this is due to their non-negligible performance and ductility in a concrete matrix, their resistance to alkali attack, and their relatively low cost. It therefore becomes essential to be able to rely on design guidelines adapted to these types of fibers because this absence significantly limits their use. In this study, the Model Code recommendations are adapted to the case of non-metallic fibers to provide engineers with simplified tools. A new adapted multi-linear stress-crack opening relationship was proposed, based on experimental studies and non-linear finite element modelling. The Model Code minimum ductility requirements for FRC use in structural applications have also been adapted to the case of non-metallic fibers following Hillerborg's concept of fracture energy and a new proposal of ductility classification was made.

The test campaign was carried out on cylindrical samples of bituminous mixtures with 40% RAP. This percentage of RAP is still considered to be the maximum in most study cases. The generalization of the TTSP is first proposed when considering small strain domain (for strain amplitudes below about 100 µm/m). We had measured the complex Young’s modulus (E*) and complex Poisson’s ratio (ν*) during cyclic loadings, performed with ENTPE’ experimental device. The analog model 2S2P1D (2 “Springs”, 2 “Parabolic elements”, 1 “Dashpot”), developed by ENTPE, was used to simulate the three-dimensional linear viscoelastic behavior of the tested material. The 3-directional (3D) thermo-mechanical behavior is then totally characterized with a master curve (plotted at a reference temperature) and a shift factor (aT), function of the temperature. The Time-Temperature Superposition Principle (TTSP) is then verified with a good approximation. Then, we had performed specific experiments (direct tensile test) on the same material to generalize the behavior in the nonlinear domain (ε ≈ %) of the TTSP considering the 1-directional (1D) and the 3-directional (3D) thermo-mechanical behavior. The time-temperature superposition principle (TTSP) was validate with the same shift factor (aT).

Carbonation of concrete is generally assumed to lead to reinforcing steel corrosion. This mindset has long dictated the research priorities surrounding the developments towards new, low-emission binders. Here, by reviewing documented practical experience and scientific literature, we show that this widely held view is too simplistic. In fact, there are many cases from engineering practice where carbonation of the cementitious matrix surrounding the steel did not lead to noticeable corrosion or to corrosion-related damage at the level of a structure. The influencing factors that can, however, lead to considerable corrosion damage are identified as the moisture state, the microstructure of the carbonated concrete, various species that may be present – even in minor amounts – in the concrete pore solution, and the cover depth. The circumstance that a reduced pH alone is not sufficient to lead to significant steel corrosion in concrete seriously challenges the established approach of assessing the durability performance based on carbonation testing and modeling. At the same time, this circumstance offers great opportunities for reducing the environmental impact of concrete structures with low-emission binders. To realize these opportunities, the focus in research and engineering should shift from studying carbonation to studying corrosion of steel in carbonated concrete.

Cet article constitue une etude preliminaire du comportement hygrothermique d’un bâtiment a colombage renove en beton de chanvre. Il est instrumente au niveau des ambiances (interieure et exterieure) ainsi qu’au sein de differentes parois. L’etude porte sur le mois d’aout 2019. La mesure de temperature exterieure est en accord avec le releve meteo France et montre un mois chaud, proche des records sur la periode 1980-2010. La confrontation de la temperature interieure a la temperature exterieure montre un bon niveau de confort thermique. L’etude du comportement au sein de la partie courante en beton de chanvre de la paroi sud souligne la contribution des parois au comportement thermique du bâtiment.

Pervious concrete use has increased since more than a decade thanks to its main feature of high water permeability. However the use of this material is still limited to light traffic areas, like car parks or walkways in urban areas. Recently LafargeHolcim Research Center has developed an innovative concept of concrete pavement structure using this type of material for heavy traffic highways. An ultra-thin innovative pervious concrete layer is laid directly (wet on wet) on top of an optimized concrete layer just after its placement. This innovative solution allows ensuring both structural performance and surface characteristics for road users in terms of safety, riding comfort and aesthetic. In order to evaluate the actual performance of this innovative pavement structure, an accelerated pavement test (APT) was carried out using the FABAC heavy traffic simulator of IFSTTAR in Nantes. A total of five million cycles of 6.5 tons half-axle load were applied. Structural performance and lifetime of the pavement were evaluated by comparison with a design process using the French-standard-design-software called Alize-LCPC. The evaluation of the bonding strength at the interface between the pervious wearing course and the structural concrete bottom layer showed good durability throughout the entire test, which could allow possible consideration of the surface layer in the whole pavement design process. Finally, dynamic friction tests conducted on the innovative wearing course during the APT allowed to evaluate and predict the evolution of its skid resistance throughout the pavement lifetime.

Civil engineering structures exposed to external sulphate are widely encountered in the world. Usual laboratory experiments used to characterize sulphate attack require long periods of time (e.g., for months). We have adapted a test already available in the literature: ground compacted materials placed in an oedometric cell are flushed with a sodium sulphate solution. The test was optimized by injecting a stoichiometric amount of sulphate in a single injection, whose duration and flow rate are controlled. We first analyzed the testing method in terms of permeability before and after compaction, of expansion behavior after sulphate injection, and of sulphate uptake during injection. Experimental results showed that the amount of sulphates retained in the sample is correlated to the duration of the injection. Reactive transport calculations simulating the injection/expansion periods highlighted the significance of mechanisms occurring at different time scales: flow of water, sorption of sulphate on C-S-H, and formation of secondary ettringite and diffusion of sulphate within the compact. Eventually, expansions of various cement pastes (namely, CEM I, CEM I + 20% limestone filler and CEM-III/C) correlate with results obtained on stress-free concrete samples made of those same paste. This testing strategy is promising to discriminate the sensitivity of various cements to sulphates with a laboratory experiment lasting on the order of a week.

This paper presents results of extensive experimental programme which took place in 2019. Two proprietary ultra-high performance fibre reinforced composite materials were tested for their blast (contact and close-in) resistance. In total, twenty-eight specimens were tested. Specimens were loaded with explosive charge of weight of 100 - 1000 g in various distances. All specimens were visually evaluated for the damage extend, failure mode and crack pattern. Results from the experiment were compared to the results available in literature for normal strength reinforced concrete. Results showed that both tested premixes performed better than ordinary mixtures in terms of blast resistance. Difference between tested materials and commonly used mixture are described as well. Finally, both materials were compared from the material properties point of view as well as by their blast resistance performance.

Porosity of archaeological pottery is a key parameter used to assess its ability to trap lipids during the use of the pot and to preserve them over time. Mercury intrusion porosimetry and gas chromatography were used to study the distribution of porosity and the preservation of lipids in different chrono‐cultural contexts. The data obtained show that the porosity pattern, related to the raw materials and the savoir‐faire of the potters, influences the amount of lipids accumulated in the pottery. A significant overall porosity together with a high level of small pores is generally favourable for the preservation of lipids, but variations related to the environmental context are observed.