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American University in Cairo (2011)

Use of expanded polystyrene in developing solid and hollow block masonry units

Ali, Youmna Alaa Yahia

Titre : Use of expanded polystyrene in developing solid and hollow block masonry units

Auteur : Ali, Youmna Alaa Yahia

Université de soutenance : American University in Cairo

Grade : Master of Science in Construction Engineering 2011

Résumé
Light weight mortar of various densities are developed using Expanded polystyrene (EPS) to partially substitute sand. Lightweight mortars are used herein to develop three types of lightweight hollow blocks : 1-plain, 2- steel wire mesh reinforced (ferrocement) and 3- GFRP mesh reinforced (fibro-cement) as well as lightweight solid bricks. The objective of this research is to obtain lightweight masonry units of sufficient mechanical, long-term and thermal characteristics for low-rise building applications in arid environments. Different tests were conducted to assess the mechanical strength ; durability and thermal conductivity. Five mixtures were prepared ; four EPS mortar mixes with average density range 1748, 1498, 1258, 988 kg/m3, depending on the EPS content and a control mortar mix with average density 2118.4 kg/m3. The mechanical test program included the measurement of the compressive strength of cubes, cylinders, hollow blocks and solid bricks, in addition to the measurement of the static modulus of elasticity, the stress-strain curve, and splitting tensile strength of cylindrical specimens. The durability test program was conducted wholly on hollow blocks and involved 48-hour water absorption test as well as subjecting them to wet-dry cycles of saturated salt solution and of 5% concentration sulfuric acid solution. The thermal conductivity test was conducted with the hot wire method on solid bricks. A finite element numerical model was developed on the GAMBIT-FLUENT package to assess the equivalent thermal conductivity of the plain hollow blocks. The effect of the three mode of heat transfer, namely, conduction, convection and radiation was reported and the interaction between them was analyzed. The results showed that the addition of EPS aggregates to mortar reduced the density as well as the mechanical properties. For a density range between 2200 and 980 kg/m3, the compressive strength of the cubes ranged between 32.6 and 3.5 MPa, and the net compressive strength of the hollow blocks ranged between 9.5 and 2.4 MPa. For the same density range the modulus of elasticity and the split tensile ranged between 15.5 and 1.2 GPa, and 2.87 and 0.55 MPa respectively. The presence of EPS in the cement matrix tremendously improved the failure pattern of all the EPS mixes. On the other hand, the durability cycles proved that EPS hollow blocks were resilient to acid and salt exposure. The weight loss and compressive strength loss of the hollow blocks due to ettringite leach decreased significantly with the addition of EPS aggregates. The salt wet-dry cycles adversely affected the compressive strength plain, ferrocement and GFRP mesh reinforced hollow blocks. The plain hollow blocks suffered from efflorescence and salt crystallization that adversely affected the compressive strength. Moreover, the compressive strength of the GFRP mesh reinforced hollow blocks was the most affected and the ferrocement EPS hollow blocks were less affected. Furthermore, the thermal conductivity tests showed that the inclusion of EPS aggregates decreased the thermal conductivity of mortar remarkably. The average thermal conductivity of the control bricks was 1.8 W/m. K. and ranged between 1.53 and 0.16 W/m. K. for the EPS mortar bricks. However, the thermal conductivity obtained numerically for the hollow blocks considering all heat transfer modes was 1.43 W/m. K. for the control blocks and ranged between 1.27 and 0.25 W/m. K. for the densest and lightest EPS mortar hollow blocks respectively. The equivalent thermal conductivity determined from the thermal model suggested that lighter EPS hollow blocks of density range 1258 and 988 kg/m3 would be more thermally efficient if they were solid. This is because, thermal conductivity of the hollow blocks inflated when the radiation heat transfer mode was accounted for. Finally, the results show that EPS mortar hollow blocks and bricks are suitable for non-load bearing application of exterior walls within the limits presented by ASTM C 129 and the Egyptian Standards (EOS 2005/42 2005), maintain their integrity while resisting salts and acids and have superior thermal insulation

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Page publiée le 15 octobre 2012, mise à jour le 3 novembre 2017