Structural Behaviour of Lightweight Concrete Block Masonry

Abstract

Lightweight concrete (LWC), an emerging masonry material, is produced by replacing natural sand with industrial waste, resulting in the conservation of natural resources and better waste management in addition to reducing production costs. LWC is accepted as an alternative to conventional masonry materials due to various advantages such as lower thermal conductivity, sound insulation properties besides its lighter weight, cost effectiveness and environmental friendliness. Consequently, considerable research effort has been made in this direction, as is apparent from the published literature. However, to build confidence for this masonry material among stakeholders, comprehensive research outputs are needed in all possible directions. The detailed literature review revealed that the strain rate sensitivity of different mechanical properties of LWC masonry and the effect of pre-compression on the shear bond behavior of LWC masonry are the two important aspects that have not received the attention of the research community. Therefore, the work presented in this thesis attempted to address the above two major research gaps through a systematic laboratory experimental program and numerical analysis through finite element modeling. This research work was carried out in three parts (a) evaluation of physical and mechanical properties of LWC masonry units with special attention to strain rate sensitivity, (b) evaluation of compressive strength properties of LWC masonry assemblies with special attention on strain-rate sensitivity and (c) evaluation of bond shear strength properties of LWC masonry assemblies with special attention to the effect of precompression in addition to strain rate sensitivity. The first part of the research is carried out with experimental investigations to determine the selected physical properties, such as density, moisture content, water absorption, initial absorption rate, and sorptivity of autoclave aerated concrete (AAC) and cellular lightweight concrete (CLC) masonry units. In addition, microstructure analyses (such as XRD and SEM) are also performed to understand material properties that affect strength properties in LWC. It also evaluates the mechanical parameters such as compressive strength, splitting tensile strength, and flexural strength of LWC units under varying strain rates. Along with that, the finite element model using Abaqus is proposed to predict the strength parameters of the LWC unit at different levels of strain rate. The proposed model seems to correctly capture both the maximum load and the crack patterns obtained from the laboratory experiments. An empirical relationship is established using the experimental results to find the strength properties of the LWC unit. Next, the present study evaluates the uniaxial compressive strength of the LWC masonry assembly through systematic laboratory tests under varying strain rate conditions followed by a numerical study. The results showed that the compressive strength of LWC masonry assemblage is considerably dependent on strain rate. It is found that the increase in the strength and elasticity parameter maintains a logarithmic relationship with the strain rates. The experimental procedure is always expensive and time-consuming, while numerical modeling can be an efficient way to study the behavior of any structure. Therefore, the numerical models are developed in this study using the finite element software (Abaqus). The proposed models can predict the strength of LWC masonry assemblage under different strain rates with significant accuracy but with less time and effort. The compressive strength of LWC masonry assemblages increases with the increase of strain rates. When the strain rate increases from 0.1 mm/min to 10 mm/min, the modulus of elasticity and uniaxial compressive strength increases by about 100% and 200% respectively, which is quite significant. In the last part of this study, both experimental and numerical strategies have been developed to study the shear response of LWC masonry assemblages under different levels of pre-compression considering low to high load rates. The peak shear strength observed during monotonic shear tests increased with increasing levels of precompression pressure and load rates. The experimental and numerical failure modes of the masonry triplets showed a reasonably good agreement. Particularly, failure modes were influenced by the pre-compression level, i.e., slipping occurred along with the brick-to-mortar interface for lower, while diagonal cracks developed in the mortar layers for higher compression levels. Therefore, the level of precompression was found to significantly affect the shear response and failure mode of the LWC masonry triplet.