High strength lightweight concrete (HSLWC) is a type of high performance concrete that is characterized by its compressive strength, density and permeability. These properties are often optimized for specific structural requirements. It is suitable for construction of bridges, precast building elements and highway girders.

Typical LWAs include expanded clay, pumice and slate. Aerated lightweight concrete also is used. However, there are limitations. For example, the use of plastic reduces the density of the concrete, leading to lower strength.

The flexural strength of LWAC can be increased by adding fibers and nanomaterials. Furthermore, the flexural strength of the LWC can exceed normal weight concrete. Hence, it is suitable for projects requiring insulation.

The use of low volume steel fiber has been proven to improve the mechanical properties of the LWC. In addition, a high ratio of fly ash inclusion reduced the thermal conductivity. Nevertheless, the effect of this enhancement was not significant.

In order to investigate the impact of fly ash on the strength and workability of HSLWC, a series of experiments were conducted. Aggregates were used as the main aggregate and hollow microspheres from fly ash were added to replace sand. Resultantly, the maximum reduction in the workability of the concrete was 40 percent.

Various parameters were measured including density, permeability and design strength. Slump values with GO increased and decreased with increasing GO content. Moreover, slump values were significantly lower when HSLWC was used with GO.

The flexural strength of the LWAC was significantly higher than the cube compressive strength and splitting tensile strength. Among the six mixtures, the specimens with the lowest GO content had the highest flexural strength.