Tectosilicate-Reinforced AAC Composites

Pennsylvania State Univ University Park, University Park PA

Investigators

Abstract

9988534 Autoclaved aerated concrete (AAC) is a mature technology. The toughness of AAC can be improved by growing a reinforced phase in situ during the processing of the AAC. Minor changes in chemistry and processing and provide major changes in microstructure and the resulting physical and mechanical properties of AAC. For example, it has been found that partial replacement of CaO by NaOH and partial replacement of quartz by class F fly ash will lead to the formation of a second phase during the autoclaving process. Rather than forming relatively large hydrogenate crystals, which would happen if fly ash were substituted for quartz, the excess alumna in the fly ash can now combine with the sodium hydroxide to form network-structured materials such as crystalline feldspathoifds and zeolites (tectosilicates). Because these phases form during the autoclaving process, they will be in equilibrium with and randomly dispersed among the tobermorite crystals that normally form in AAC. Typically, the tectosilicates are 10-20 micrometers in size. The presence of second phases approximately the same size, as the tobermorite should increase toughness via crack blocking rather than crack bridging. Once this concept is experimentally verified and one is able to demonstrate that composite AAC has superior properties vis-a-vis concrete block, the prospect that AAC could become an integral part of the North American construction process will greatly improve. As North America develops more stringent energy and conservation requirements driven by a growing environmental conscience, AAC building materials could well become the building material of choice for the 21st Century.