Sep 12, 2017 - The properties of autoclaved aerated concrete (AAC) blocks are impacted by many factors including the mix design and production process ...
37th Cement and Concrete Science Conference 11-12 September 2017 University College London
The impact of mix design and materials on the microstructure of autoclaved aerated concrete blocks H. Beltagui, M. Sonebi, and S. Taylor School of Natural and Built Environment, Queen’s University Belfast, Belfast, BT7 1NN, UK H. Beltagui, and K. Maguire Quinn Building Products, Derrylin, Co. Fermanagh, BT92 9GP, UK
ABSTRACT The properties of autoclaved aerated concrete (AAC) blocks are impacted by many factors including the mix design and production process parameters, as well as the composition and properties of the various materials used. During the autoclaving process, silica typically provided by sand contributes to the formation of tobermorite, providing strength. However, these sands are becoming exhaustive, and their replacement with by-products available in greater quantities could be beneficial and provide economic savings. This study investigates the impact of the mix design and material properties on the resultant properties of AAC blocks. Using quantitative X-Ray diffraction (XRD) analysis and thermogravimetric analysis (TGA), a relationship was found to exist between the mix design, compressive strength, and the final hydration products formed. This is further enhanced by consideration of the microstructure and morphology of the final products through use of scanning electron microscopy (SEM). Despite two of the sands tested having similar chemical composition with high silica content consisting of crystalline quartz, they performed differently in terms of the strengths achieved. SEM revealed that the particle shape and surface characteristics of the materials played in a role in their contribution to strength development.
1. INTRODUCTION
insight and understanding on the differences achieved.
Autoclaved aerated concrete (AAC) is a light weight porous construction material, utilised for both for its load bearing capacity and thermal insulation capabilities. AAC is produced by mixing three main types of materials with water: (i) cement and/or lime, (ii) an air-entraining agent, and (iii) a source of silica. During the autoclaving process, the formation of tobermorite is promoted, providing the strength of AAC blocks. The properties of the final blocks are impacted by many factors including the mix design and production process parameters, as well as the composition and properties of the various materials used. A major player is the source of silica used. However, the silica sands currently used in the production of AAC are becoming exhaustive and, therefore, their replacement with byproducts available in greater quantities could be beneficial and provide economic savings: examples include pulverised fuel ash (PFA) and fines fraction currently not utilised form other sands. This study investigates the impact of the mix design and material properties on the resultant properties of AAC blocks, aiming to provide
2. MATERIALS AND METHODS 2.1 Materials The chemical composition of the raw materials used is shown in Table 1. Three different sources of silica are used, two sands and PFA; the two sands are very similar in composition with high silica content of ~ 92%, while the PFA had a lower silica content of ~ 52%. Table 1. Chemical composition of raw materials used for production of AAC blocks Oxide Cement Sand 1 Sand 2 PFA (%)
1
CaO
63.06
1.45
0.81
5.53
SiO2
19.83
92.67
91.96
51.77
Al2O3
4.8
2.08
3.23
21.54
Fe2O3
3.02
1.82
1.36
6.28 0.94
TiO2
0.31
0.37
MnO
0.08
0.03
MgO
0.20
0.36
2.06
P2O5
0.02
0.03
0.68
SO3
2.48
0.5
