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Improving the knowledge of rheological and tribological characteristics of fresh concrete is important to contribute to the progress of construction sites and the final quality of the work. The objective of this study is to identify the effect of a superplasticizer based on polycarboxylic ether on the tribological behavior of fresh concrete at the concrete/formwork and concrete/oil/formwork interfaces. Friction tests on fresh concrete were carried out using a plan/plan tribometer. In order to study the behavior of the superplasticizer close to the formwork, three concretes with 30% of paste and different dosage of superplasticizer were formulated. The results show that the increase of the dosage of superplasticizer reduces the friction stress. The properties of the superplasticizer generate a deflocculating action of concrete grains and lead to a stabilisation of the soap-oil micellae present in the vicinity of the formwork. Thus, the efficiency of superplasticizer depends on the quantity of fines, on the quantity of soap formed and so, on the release agent formulation.

Abstract. Concrete surface quality is generally linked to the development conditions of concrete close to the formwork. This work aims to study the influence of the nature of release agent and the quantity of fine elements on the chemical interactions at the concrete/oil/formwork interface. Five concretes were prepared at 28, 30, 32, 34, and 36% of paste to study the influence of paste volume on the friction between formwork and fresh concrete. The friction tests were performed using an apparatus which can reproduce the same conditions of construction sites. In addition, a physicochemical investigation was achieved to identify the effect of fine elements on the ability to form the interstitial mediums at the interface. The formation of soap in the vicinity of the formwork surfaces was also studied as a function of the content and the nature of oils. The results showed that the friction between fresh concrete and formwork depends on the pore solution content present at the interface.

International audienceThis work aims to study the possibility to use asbestos-free fiber-cement waste in substitution of ordinary Portland cement for the production of mortars. The fiber-cement particles were incorporated in mortars in partial replacement of cement, with mass substitution rates of 5 and 20 %. Cement hydration rate, workability, total shrinkage, porosity accessible to water and mechanical performances of mortars made with ground fiber-cement were measured and compared with the properties of control paste and mortar (free of fiber-cement). The results showed that the presence of fiber-cement extended by 5–10 % the dormant period of the binder hydration, when compared to that of Portland cement, depending on the substitution rate considered. Furthermore, at 28 days, the replacement of cement with 5 and 20 % of fibercement caused a reduction of 14–35 % in compressive strength, when compared to the reference mortar performances. This decrease was greater than that observed on mortars containing limestone filler with the same substitution rate of cement. However, the strengths obtained were acceptable for structural applications