A novel lightweight cement composite incorporating micro-sized silica aerogel / Syed Nasir Shah

Syed Nasir , Shah (2022) A novel lightweight cement composite incorporating micro-sized silica aerogel / Syed Nasir Shah. PhD thesis, Universiti Malaya.

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Abstract

Lightweight cement composite (LCC) has gained more interest and is increasingly explored by researchers due to its many advantageous properties. Silica aerogel (SA), a synthetic ultralightweight material with a nano-porous structure and remarkable insulation properties, makes it a potential option to be incorporated in LCC. LCC incorporating SA (SA-LCC) would be an ideal insulating building material and could promote energy efficiency in buildings since the building sector consumes about 30-40% of global energy consumption. However, there are some challenges when it comes to incorporating SA into LCC. One of the difficulties is mixing SA with cement composite due to its ultra-lightweight and hydrophobic nature. Thus, this research aims to develop a chemical treatment for SA to ease its mixing and assess the influence of micro-sized SA on the properties of LCC. Therefore, a detailed study was conducted on both untreated and treated SA-LCC. The study was divided into 3 phases; where phase 1 focuses on developing chemical treatment for SA, characterizing untreated and treated SA, and evaluating the effect of different content of untreated/treated SA (20-80% of sand replacement) on the basic properties of LCC. The results of phase 1 revealed that the treated SA became temporarily hydrophilic and eased the mixing. In addition, the chemical treatment did not affect the pore structure, particle size distribution, chemical bonds, and crystallographic structure of SA. A significant reduction in the oven-dry density (up to 50%) and compressive strength (up to 80%) of SA-LCC was observed, while the porosity was increased (up to 260%). Phase 2 emphasizes the insulating properties, dimensional stability, durability performance, and microstructure characteristics of SA-LCC. Despite the increase in water absorption (140/290%) and decrease in water resistance (11/19%), the increase in porosity of LCC due to incorporation of untreated/treated SA improved the insulating properties. The noise reduction coefficient (NRC) improved up to 15%, whereas the thermal conductivity was improved up to 80%. Despite the beneficial insulating properties, the limitations of the SA-LCC include the higher shrinkage (10 times) and lower resistance to elevated temperatures, in addition to increased water absorption. Nevertheless, in overall, LCC with a low oven-dry density of about 1190 kg/m3 and adequate compressive strength (6.38 MPa) can be produced by incorporating treated SA, which has a low thermal conductivity (0.220 W/m.K) and good NRC (0.261). Therefore, in phase 3, in view of the observed limitations of the SA-LCC, a scaled lightweight sandwich wall panel (SWP) was introduced, which utilized calcium silicate board (CSB) as the skin. This is intended for wall application to suit the benefits of the SA-LCC. The practical application of treated SA-LCC as core for SWP shows that non-load bearing SWP can be produced with treated SA-LCC and 6 mm CSB as the skin with unit weight, compressive, and flexural strength of 1570 kg/m3, 2.4 MPa, and 4.7 MPa, respectively. The SWP also has good impact load resistance (70 J) and direct flame resistance. Furthermore, the SWP has satisfactory insulating properties with NRC and thermal conductivity of 0.259 and 0.561 W/m.K, respectively.

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