Development of high performance lightweight concrete using ultra high performance cementitious composite and different lightweight aggregates

To reduce the dead load of concrete structures, this study developed a high performance lightweight aggregate concrete (HPLAC) by combining the use of ultra high performance cementitious composite (UHPC) and different types of aluminosilicate lightweight aggregates (LWAs). The physicochemical properties of two types of LWAs (i.e. expanded clay and expanded shale) influencing the HPLAC were elaborated and compared. The composition distribution and micromechanical properties in the interfacial regions of paste and LWAs were revealed by elemental mapping and nanoindentation. The results showed that the incorporation of the clay LWAs or shale LWAs in the HPLAC led to similar density and thermal conductivity values, while the use of the shale LWAs induced a lower water absorption and higher strength of HPLAC as compared to the clay LWAs due to the fine pore structure and higher pozzolanic activity of the former. The internal curing effect provided by the pre-wetted shale LWAs was more efficient in enhancing the hydration of binder, and the Al dissolution from the shale LWAs further densified the interfacial bonding to form a dense rim surrounding LWAs, resulting in improved micromechanical properties at the interface. The X-ray CT results indicated that the adoption of UHPC was beneficial to preventing segregation of the LWAs and steel fibers in the HPLAC. By virtue of the physical-chemical interactions of LWAs, the synergetic use of UHPC and pre-wetted shale LWAs was able to produce an HPLAC with high structural efficiency, good thermal insulation, low autogenous shrinkage and permeability.