Early-age crack-free ultra-high-performance concrete under restrained ring test for large-scale production as an overlay

Abstract

While UHPC overlays are known for their strength and durability, their high autogenous shrinkage limits its widespread nationwide use, as it can result in delamination and early age cracking. To overcome these issues, incorporating pre-saturated lightweight sand (LWS) combined with expansive agents (EA), and shrinkage reducing admixtures (SRA) in UHPC mixes is recommended. To achieve an optimal balanced proportion among these mitigation measures, a sequence optimization process was conducted for a series of mixtures produced at a mixing volume of 127 ∼ 140 Liters. This process aimed to develop a crack-free UHPC mix at an early age under restrained conditions (AASHTO T334). The findings indicate that crack-free UHPC can be produced by incorporating LWS (50 % replacement of fine aggregate), SRA (2 % by weight), and EA (2 % by weight). The optimized mixture demonstrates autogenous shrinkage of less than 100 µɛ and bond strength of 3 MPa within 3 days. Furthermore, three mixing protocols (mono-batching, two-batching, three-batching methods) were devised based on the fine aggregates (river sand) moisture content. These protocols enable the production of homogenous UHPC at larger volumes while ensuring sufficient flowability and desirable hardened properties. The results indicate that the mono-batching method yields the highest performance and is suitable for river sand moisture content of 1.6 % (by weight) or higher. On the other hand, the two- and three-batching methods are more suitable for river sand moisture contents below 1.6 %.