Preparation and properties of lightweight, high-strength, and low-shrinkage ECC materials for new steel bridge deck composite pavement

To address the challenges of conventional cement concrete pavement materials for orthotropic steel-concrete composite bridge decks, including high self-weight, low tensile deformation capacity, high brittleness, and susceptibility to cracking, all of which adversely affect their service life, a novel lightweight, high-strength, high-toughness, and low-shrinkage Engineered Cementitious Composite (ECC) material has been developed. This advancement was achieved through three strategies: 1) the incorporation of calcium carbonate whiskers for microstructural enhancement, 2) hybrid reinforcement using organic fibers and steel fibers for toughening, and 3) the synergistic application of expansion agents paired with internal curing aggregates for shrinkage reduction. The mechanisms underlying the performance enhancement of this ECC material were investigated through low-field nuclear magnetic resonance and scanning electron microscopy. Furthermore, a new composite pavement structural system for steel bridge decks based on the developed ECC was proposed. The results indicate that, Compared to PE fibers, steel fibers have a lesser impact on the workability of ECC materials but significantly improve their strength, toughness, and crack propagation control. A hybrid mix of 1 vol% PE fibers and 0.5 vol% SF provides optimal performance. Substituting fly ash cenospheres (FAC) with ceramic sand as fine aggregate increases the apparent density and compressive strength of the ECC material. The synergistic combination of 5% expansion agent and ceramic sand reduces 56-day drying shrinkage to 465 με.,which reduced by 45% vs. control group greatly enhancing its volume stability. The addition of micron-sized calcium carbonate whiskers optimizes the pore structure of the ECC matrix, increases the roughness and frictional strength at the fiber-matrix interface, thereby improving the mechanical properties and durability. The developed ECC material achieves the following comprehensive properties: slump flow >520 mm, slump >250 mm, apparent density <1950 kg/m³, 28-day compressive strength >75.0 MPa, 28-day axial tensile strength >3.5 MPa, 28-day tensile strain >5.5%, 28-day bending strength >12.0 MPa, toughness index I 20 >25.0, and 56-day shrinkage <500 με.