A slab filler, and method for implementing fillers in a two-way concrete slab for building structures, are disclosed. The filler comprises an upper keeper tray and a lower keeper tray, and a volumetric filling element. The upper keeper tray is attached to a top of the volumetric filling element and the lower keeper tray is attached to a bottom of the volumetric filling element. The filler comprises a plurality of indicators positioned on all corners of the keeper tray to indicate an amount or level of a concrete fed on the filler. The filler further comprises grooves at an end of the spacer, configured to securely hold one or more belts. Spacers and belts are configured to receive one or more rebar. Further, the volumetric filling element is a high-density material, where the filler is incorporated without upper keeper tray and lower keeper tray.