An Investigation of the Mechanical and Physical Characteristics of Cement Paste Incorporating Different Air Entraining Agents using X-ray Micro-Computed Tomography

Abstract

Improving the thermal insulation properties of cement-based materials is the key to reducing energy loss and consumption in buildings. Lightweight cement-based composites can be used efficiently for this purpose, as a structural material with load bearing ability or as a non-structural one for thermal insulation. In this research, lightweight cement pastes containing fly ash and cement were prepared and tested. In these mixes, three different techniques for producing air voids inside the cement paste were used through the incorporation of aluminum powder (AL), air entraining agent (AA), and hollow microspheres (AS). Several experiments were carried out in order to examine the structural and physical characteristics of the cement composites, including dry density, compressive strength, porosity and absorption. A Hot Disk device was used to evaluate the thermal conductivity of different cement composites. In addition, X-ray micro-computed tomography (micro-CT) was adopted to investigate the microstructure of the air-entrained cement pastes and the spatial distribution of the voids inside pastes without destroying the specimens. The experimental results obtained showed that AS specimens with admixture of hollow microspheres can improve the compressive strength of cement composites compared to other air entraining admixtures at the same density level. It was also confirmed that the incorporation of aluminum powder creates large voids, which have a negative effect on specimens’ strength and absorption.

Investigation and Preparation of the Plastering Mortar for Autoclaved Aerated Blocks Walls

“…The thermal conductivity of the material was evaluated through the dry density of the mortar [27]. The difference between the weight of the specimen under water-saturated and fully dried (dried at 105 • C to constant weight) conditions was used to calculate the water absorption of the hardened mortar.…”

“…The formation of the plaster layer of AABs from lightweight aggregates was considered to be the key to solving the "thermal bridges" effect [21,22]. Researchers have explored the potential of cork granules [23], perlite microspheres [24], expanded and vitrified small ball [25], air entraining agents [26,27], expanded vermiculite [28], phase change material [29], and expanded polystyrene beads [30]. Li et al [18] concluded that the heat transfer coefficient of plastering mortar is 0.48 W/(m•K), in which expanded perlite, vitrified microsphere, and 0.04% polypropylene fiber were added to prevent the shrinkage and cracking of the mortar.…”

Cement-Based Composites: Advancements in Development and Characterization

“…Abd Elrahman et al [8] performed a study towards the development of insulating light-weight cementitious composites in order to reduce the energy loss and consumption in buildings. Three different approaches towards incorporating air voids in cement pastes were proposed by introducing: aluminum powder, air-entraining agent, and hollow microspheres.…”

The performance of ultra-lightweight foamed concrete incorporating nanosilica

“…Chung et al [13] used micro-CT to evaluate the effect of pore size, distribution and shape on physical and mechanical properties of foamed concrete and they found that with increasing the density of concrete the solid content increase which keep the spherical shape of the pores and make them more isotropic. Abd Elrahman et al [14] compared three different approaches towards incorporating air voids in cement pastes by adding aluminum powder, air-entraining agent, and hollow microspheres and figured out the significant differences between the compressive strength of cement-based composites according to air-entraining admixtures. Zhihua et al [15] reported that cracking phenomenon of FC can be partially mitigated by the replacement of cement with 15-20 wt.-% of ultrafine blast furnace slag powder as well as the introduction of polypropylene fibers.…”