Matthieu Horgnies

Surfactant-induced growth of a calcium hydroxide coating at the concrete surface

In addition to its remarkable mechanical properties, high-performance concrete (HPC) also exhibits a very smooth surface with low porosity, which makes it particularly suitable for esthetic applications. Unfortunately, the constant environmental aggressions to which the urban buildings are exposed (organic or inorganic particles, algae, micro-organisms, staining from various sources) are a threat to their structural and esthetic durability. This article proposes an innovative method to protect HPC surfaces based on Ca(OH)2 growth at the fresh concrete/formwork interface. With the adequate surfactants used as demolding agents, it is possible to grow a continuous layer of Ca(OH)2 at the concrete surface which closes the porosity, reduces the water uptake, and gives the surface super-hydrophilic properties, facilitating self-cleaning mechanisms.

Composition of Concrete Surfaces after Demoulding and Coating: Comparative Study by XPS, FTIR and Raman Spectroscopies

Hardened concretes were studied by several spectroscopic techniques (FTIR, Raman and XPS) to determine the surface composition after demoulding and after coating. After demoulding, most of the paste was constituted of calcite but some areas were identified by µRaman as portlandite, ettringite, belite, alite and ferrite phases. The FTIR (in ATR mode) allowed detecting portlandite and C-S-H but it highlighted also organic residues from the demoulding oil. XPS allowed recording interesting atomic ratios to study the extreme surface and the presence of contamination. After post-treatments, the main organic units were determined by FTIR and XPS at the concrete’ surface. Raman was also interesting: no vibration modes of organic species were detected but mineral/hydrated phases were clearly characterized under a thick organic layer. Due to their own specificities, these complementary techniques allowed identifying the mineral/hydrated phases and organic residues/coating at the concrete surfaces.

Lightweight Structural Recycled Mortars Fabricated with Polyurethane and Surfactants

This paper reports on the properties of a new range of structural and lightweight mortars, including a low fraction of soluble nonionic surfactant, manufactured with different substitution rates of sand by polyurethane foam wastes. The characterization consists in substituting sand by polyurethane wastes and adding low fractions of nonionic surfactants with respect to the amount of cement. As characterized by the evolution of the mechanical strengths and porosity, the properties of the hardened mortars can vary significantly according to the chemical structure – hydrophilic–lipophilic balance value – of the nonionic surfactant. This new range of materials containing polymer wastes complies with the principle of sustainable development and contributes to a greener business model within the building sector.

Study Of The Microstructure And PoresDistribution Of Lightweight Mortar ContainingPolymer Waste Aggregates

The study of mortars containing polymer wastes is a key-topic to create new construction materials for a sustainable development. This work deals with the characterization of the microstructure of lightweight mortars containing polymer waste powder, which are recycled, such as aggregates. The observations of crosssections and fractured samples using Scanning Electron Microscopy (SEM) highlight that the particles of polymer are homogeneously dispersed into the mortar matrix. Numerous capillarity pores are detected into the hydrated cement paste. Calcium Silicate Hydrates covering the particles of polymer are also detected in environmental mode. The porosity is analyzed using two complementary techniques: (i) Mercury Intrusion Porosimetry (MIP) revealing the micro-pores sized from 170–200 μm up until 5–10 nm; and (ii) X-ray computerized axial tomography providing the macro-pores sized larger than 170 μm. The distribution of the total intruded volume is quantified by MIP according to the ratio sand/particles of polymer. The distortion of the pores distribution increases as a function of the content of polymer residues, excepted when the particles of polymer are replacing 25% of sand. In this specific case, the measurements by MIP and tomography show a homogeneous distribution of the larger pores, close to the one of the reference mortar.

Permeability and Porosity on Lightweight Mortars Fabricated with Polyamide Powder Wastes

This paper presents the results obtained in the production of lightweight mortars where different amounts of sand were replaced by polyamide powder wastes. The characterization of the materials obtained was carried out in fresh and hardened state, considering especially the vapor permeability and micro and macroporosity properties. It has been found that the progressive increase of polymer influences the behavior of the mortar, increasing the water vapour permeability as well as the total porosity of the material, which carried on a decrease in the density of the composites fabricated. These results suggest the employment of polyamide powder residue as sand could be useful with the aim of manufacture recycled lightweight masonry mortar.

Multi-technique investigation of calcium hydroxide crystals at the concrete surface

The durability and aesthetic qualities of high-performance concrete, which makes it particularly suitable for architectural applications, are constantly compromised by environmental aggressions. In this study, an innovative solution was developed to protect the concrete from these aggressions, which consists of growing a mineral coating on the concrete surface. The coating is composed of layered calcium hydroxide crystals, whose nucleation and growth are triggered byvarious non-ionic surfactants (the details of the process will not be presented). This paper describes the procedure used to investigate the structure of the formed crystals. Scanning Electron Microscopy and optical microtopography were used to determine the morphology of the crystals. Image analysis allowed the quantification of their amount, size and shape. The contribution and limits of each technique are discussed.

Characterization of the influence of the casting mould on the surface properties of concrete and on the adhesion of a protective coating

Protective coatings are deposited on concrete to improve aesthetics and to prevent ageing. However, their adhesion on concrete depends on several interlinked parameters. In this study, the surfaces of concrete are characterized according to the process of casting and post-treatment used (sandblasting) by using Scanning Electron Microscopy (SEM), Fourier Transformed-Infrared (FTIR) spectroscopy and profilometry. The surface properties are correlated to the adhesion force of a polyurea (PU) coating. The development of a specific peel test (a strengthened and porous membrane is introduced into the layer of liquid coating before its crosslinking) ensures a reproducible debonding of the coating/concrete system and allows measuring the fracture energy. Moreover, the interface after debonding is analyzed by FT-IR to highlight the presence of concrete/coating residues and to determine the locus of failure. Results underline that the nature of casting mould influences the concrete surface and modifies the adhesion of PU coating. The mould made of polyoxymethylene (POM) induces a micro-tearing of the extreme surface of concrete during demoulding. By increasing the roughness and the open porosity of the concrete surface, this tearing enhances the adhesion of the coating. On the contrary, the smooth concrete surface, induced by the use of a polyvinylchloride (PVC) mould, decreases the anchorage of the coating. Finally, the sandblasting of the surface, by increasing the roughness and the interface area, is an interesting treatment to promote the adhesion of PU coating, whatever the mould used for the casting.