Gravity-Filled Preplaced Aggregate Concrete: Experimental Study on the Feasibility of Production and Strength Assessment

Abstract

Preplaced aggregate concrete (PAC), known as two-stage concrete, offers a promising alternative to conventional concrete production. The PAC process consists of two steps: placing aggregates in a mold and injecting grout, which can be done through pumping or gravity. Reviewed studies highlight the importance of mortar fluidity for quality PAC, noting that pumping is often essential for complete filling of voids in aggregate skeleton with 20 mm maximum size coarse aggregate (MSA). However, limited studies have explored the use of gravity-based pouring of mortar with this aggregate size. This study strategically investigates the feasibility of PAC production through a nonvibratory gravity filling method, varying the size and gradation of aggregates and vibration efforts while keeping the sand-to-cement and water-to-cement ratios constant at 1 and 0.4, respectively. The finalized mixes are assessed for compressive and flexural strength. Systematic evaluation of the mortar characteristics showed that PAC can be produced through nonvibratory effort of gravity pouring in a loose state of coarse aggregate size in the range of 16–20 mm. However, based on the strength, vibratory assistance produces PAC with compressive strength and flexural strength being 5% higher than that of the reference concrete (RC). Although the compressive strength of PAC produced through a nonvibratory approach could only reach 34 MPa, the nonvibratory method yielded approximately 30% and 20% lower compressive and flexural strengths, respectively, compared with the reference concrete. Regarding material consumption, the vibratory method saved cement and sand by 6% and 38%, respectively, whereas non-vibratory-assisted PAC consumed more cement, with savings in sand up to 35%. PAC produced with compacted state of aggregates had challenges pertaining to producibility, with two out of three cube specimens and all the beam specimens being honeycombed. The study also highlights the significance of aggregate specific gravity in PAC density.