A Review on Multi-Scale Toughening and Regulating Methods for Modern Concrete: From Toughening Theory to Practical Engineering Application

Abstract

Concrete is the most widely used and highest-volume basic material in the word today. Enhancing its toughness, including tensile strength and deformation resistance, can boost the structural load-bearing capacity, minimize cracking, and decrease the amount of concrete and steel required in engineering projects. These advancements are crucial for the safety, durability, energy efficiency, and emission reduction of structural engineering. This paper systematically summarized the brittle characteristics of concrete and the various structural factors influencing its performance at multiple scales, including molecular, nano-micro, and meso-macro levels. It outlines the principles and impacts of concrete toughening and crack prevention from both internal and external perspectives, and discusses recent advancements and engineering applications of toughened concrete. In situ polymerization and fiber reinforcement are currently practical and highly efficient methods for enhancing concrete toughness. These techniques can boost the matrix's flexural strength by 30% and double its fracture energy, achieving an ultimate tensile strength of up to 20 MPa and a tensile strain exceeding 0.6%. In the future, achieving breakthroughs in concrete toughening will probably rely heavily on the seamless integration and effective synergy of multi-scale toughening methods.

Fig. 1.

Multi-scale brittle characteristics of concrete [–22].

Fig. 2.

Ashby plot of the strength–toughness relationship for common materials [24].

Fig. 3.

Multi-scale toughening mechanism of natural nacre [40].

Fig. 4.

Toughening strategies at the atomic scale. (Top) Enhancement in initial fracture toughness: Ca/Si optimization [21], Al doping [45,46], polymer modification [43], and silicene modification [55]. (Bottom) Suppression of crack propagation: dislocation obstruction [56] and defect induction [57].

Fig. 5.

Toughening strategies at the nano- to microscale. (A) Morphological regulation [63]. (B) Orderly stacking [13,64,65]. (C) Interfacial optimization [50,53,66].

Fig. 6.

Scanning electron microscopy images of ITZ in concrete [78]. (A) 2,000×. (B) 8,000×. (C) 30,000×.

Fig. 7.

ITZ modification mechanism of nanomaterials [84].

Fig. 8.

(Left) Unsteady and steady-state crack propagation models. (Right) The relationship between fiber bridging stress and crack opening displacement [110].

Fig. 9.

Fiber distribution versus rheological performance [125].

Fig. 10.

Three optimized casting methods for UHPC. (A) Casting UHPC using an L-shape device [126]. (B) Casting UHPC using a 30° device [123]. (C) Extrusion of UHPC using a nozzle [127].

Fig. 11.

Effect of fiber reinforcement factor on UHPC fracture energy [132].

Fig. 12.

China UHPC application distribution in 2023.

Fig. 13.

The Fifth Nanjing Yangtze River Bridge.

Fig. 14.

Shanghai Grand Opera House (left) and Solar Ark 3.0 (right).