Irene Palomar

Assessment By Non-destructive Testing Of New Coating Mortars For Retrofitting The Architectural Heritage

Repairing or replacing the traditional coating lime-based mortars is a common measurement to retrofit building facades. The use of appropriate techniques and materials according to the originals is essential to ensure architectural values and to preserve the Architectural Heritage. Consequently, it is necessary to investigate the microstructure and properties of both traditional and today’s mortars by proper characterization. Non-destructive testing techniques (NDT) are always preferred because they can be tuned in the laboratory and also applied to evaluate on-site performance. In this paper, the assessment of lime-cement repair mortars’ microstructure and performance is carried out using NDT by ultrasonic pulses (US). Ten lime-cement mortars were designed using: hydrated lime; white cement; gap-graded siliceous aggregate (2–3 mm); three lightweight aggregates, expanded clay, perlite and vermiculite; two types of short fibres, cellulose and polypropylene. The samples were evaluated with compression and shear US waves (P- and S- respectively). Transmission times (UPV), compressive modulus (M), shear modulus (G), dynamic Young modulus (E), bulk modulus (K) and Poissons ratio (ν) were obtained. The raw US signals were also analysed by Hilbert transformation (HT) and Fast Fourier transformation (FFT). HT facilitated P- and S-wave transmission time measurements while FFT simplified the evaluation of US attenuation. Then, bulk density, open porosity, capillary absorption, thermal conductivity, acoustic absorption and compressive and flexural strength of samples were compared to the US parameters. NDT by ultrasonic pulses showed very good correlations with hardened properties and demonstrated to be a useful tool for predicting the physical and mechanical performance of lime-cement repair mortars.

Effect of Particle Size and Amount of Nanosilica and Microsilica on Early Age and Hardened Structure of Self Compacting Concrete

The paper presents an analysis of the experimental results of Self Compacting Concretes (SCC) with limestone filler and two types and up to three amounts of active silica-based additions, as microsilica and nanosilica, to evaluate the influence of the size particle and amount of silica-based additions. The experimental program combined early age monitoring of temperature, UPV, evaporation rate and free drying shrinkage, assessing early age drying cracking risk and evaluating hardened porosity, permeability and mechanical performance. At early ages, the pozzolanic effect was detected in the temperature profile after cement hydration is generalized, although the size effect of the additions facilitate hydrated products nucleation and accelerated solid microstructure development, bringing forward the interconnection among the solid particles. The smaller the particle size, the faster the UPV evolution and the earlier shrinkage began. Both effects together can increase the risk of early age cracking due to drying shrinkage.

Self-Compacting Concrete with Nanosilica and Carbon Nanofibers

This study aimed to assess the changes of behavior due to the addition of nanosilica and carbon nanofibers in SCC. The target was to identify variations at early ages and in the hardened state due to the addition of nano-size components. The setting process and early ages were monitored during the first 24 h, combining several experimental techniques as ultrasonic pulse velocity, temperature, capillary pressure, free shrinkage, cracking, and mass loss. In addition, the porous microstructure in the hardened state was evaluated measuring vapor permeability, mercury intrusion porosimetry and a mechanical characterization.

Early Age Drying Shrinkage Evaluation of Self-Compacting Concretes and Pastes with Mineral Additions

Early age (EA) drying shrinkage of cement based materials is a complex process because it comprises reaction evolution, microstructure development, stiffening and water evaporation due to environmental conditions. The occurrence of EA shrinkage can increase early age cracking risk which can compromise durability. Due to the larger amount of paste, moderate strength powder-type self-compacting concrete (SCC) is more prone to EA drying shrinkage than conventional concrete. To evaluate the effect of limestone filler, microsilica (MS), nanosilica (NS) and metakaolin (MK) on EA free drying shrinkage of cement pastes and SCC, an experimental program was carried out. Free shrinkage and mass loss were monitored on paste and SCC samples during 24 hours, subjected to surface desiccation to evaporate all the bled water during 6 hours, while temperature and Relative Humidity remained constant. It was observed that evaporation and free shrinkage were not related directly, although a physical relationship could be identified. Evaporation during EA shrinkage of pastes and SCC compositions showed similar values, while drying shrinkage depended on the presence of the aggregates. The effect of the paste components’ amount and type, the volumetric fraction of aggregates and the evaporation were assessed and some equations were proposed to estimate EA drying shrinkage of moderate strength powder-type self-compacting pastes and concretes.