Lightweight Concrete That Stops Projectiles Better Than Heavier Rivals

Concrete has long been the workhorse of protective engineering, shielding nuclear plants, military installations and other critical infrastructure from high-speed impacts. But conventional high-strength concrete carries a stubborn contradiction: the stronger it becomes, the denser and heavier it gets. A research team in China now reports that it has broken that trade-off, developing a lightweight concrete that reaches the C120 strength grade while weighing roughly 2,050 kilograms per cubic meter, about 400 kilograms per cubic meter lighter than typical C120 mixes, and then proving in live penetration tests that it stops projectiles better than both heavier conventional C120 concrete and ordinary C80 high-strength concrete.

The study, published in Case Studies in Construction Materials, tackles a bottleneck that has constrained protective design for years. Existing C120-grade high-strength concrete typically exhibits densities between 2,400 and 2,500 kilograms per cubic meter, which inflates the self-weight of protective structures, raises construction costs and limits use in weight-sensitive applications. Conventional C80 concrete is lighter, but its strength and anti-penetration performance fall short of the demands of high-end protective engineering. The researchers set out to achieve what they describe as a synergistic optimization of protective efficiency and structural economy: ultra-high compressive strength to withstand high-velocity projectile impact, combined with a substantially reduced density.

The key to the new material lies in its mix design, which was guided by particle close-packing theory. The team systematically analyzed how varying amounts of cement, silica fume and fly ash microspheres affect the packing density of particles in the cementitious system, then tuned the aggregate ratio, sand-binder ratio and fiber content to optimize apparent density, mechanical properties and workability. The resulting C120 lightweight high-performance concrete contains 682.5 kilograms of cement, 210 kilograms of fly ash and 157 kilograms of silica fume per cubic meter, achieving a 28-day compressive strength of 121.3 megapascals and a flexural strength of 17.2 megapascals at a density of just 2,050 kilograms per cubic meter.

Two ingredient choices stand out. First, all natural aggregates were replaced with ceramsite sand, a lightweight ceramic aggregate with particle sizes between 0.5 and 5 millimeters, a bulk density of 1,450 kilograms per cubic meter and a cylinder compressive strength of 8.5 megapascals. Its rough, porous surface forms a strong bond with the cementitious matrix, while its moderate particle strength preserves load-bearing capacity at a much lower density. Second, steel fibers were added at a volume fraction of about 2.0 percent. Each fiber is 13 millimeters long, 200 micrometers in diameter and has a tensile strength of 2,000 megapascals, providing the tensile reinforcement and impact toughness needed to restrain crack propagation during penetration. For comparison, the conventional C80 mix used haydite aggregate with natural sand and basalt fibers, reaching 82.6 megapascals of compressive strength at 2,450 kilograms per cubic meter.

To test the material under realistic ballistic conditions, the team cast cylindrical concrete targets measuring 900 millimeters in diameter and 600 millimeters thick, each enclosed in a 5-millimeter steel plate that provided lateral restraint while minimizing boundary effects. The dimensions were chosen so that the radial size exceeded 30 projectile diameters and the thickness exceeded 1.5 times the expected maximum penetration depth of 360 millimeters, ensuring that neither lateral boundaries nor the rear free surface would distort the results. After 28 days of standard curing at 20 degrees Celsius and at least 95 percent relative humidity, the targets were struck with pointed ogive-nose penetrators made of 35CrMnSiA steel, each 120 millimeters long, 24 millimeters in diameter and weighing 352 grams, launched from a 30-millimeter gun at approximately 700 meters per second at normal incidence.

The results were striking. Against the conventional C80 target, struck at 699 meters per second, the projectile penetrated 0.251 meters and opened a large frontal crater with a maximum diameter of 0.421 meters and a minimum of 0.348 meters, a nearly circular shape ratio of 1.21 characteristic of dispersed brittle failure. High-speed photography at 100,000 frames per second captured the concrete at the impact point being pulverized, radial cracks spreading outward and large chunks shearing away as the projectile head entered the material. The C80 matrix has low compactness and a weak transition zone between aggregate and paste, so stress waves rapidly induced interfacial cracking that extended irregularly, dissipating energy through large-scale crushing and spalling while severely damaging the specimen’s integrity.

The lightweight C120 target, struck even faster at 726 meters per second, performed dramatically better. Penetration depth was only 0.158 meters, and the frontal crater shrank to a maximum diameter of 0.263 meters and a minimum of 0.157 meters, a shape ratio of 1.68 indicating localized, concentrated compressive failure rather than widespread destruction. The steel fibers raised tensile strength and impact toughness, increasing the energy absorbed during penetration, while the tightly bound lightweight aggregate interface suppressed crack initiation and radial expansion. Impact energy was dissipated through plastic compression within a small contact zone, leaving the overall structure intact. Notably, recovered projectiles showed more extensive surface abrasion on those that had penetrated the C120 target than on those that hit the C80, evidence that the lighter material actually imposed greater axial and sidewall frictional resistance.

A cross-literature comparison reinforced the finding. The team benchmarked its results against a published test of C120 ultra-high performance concrete with a density of 2,450 kilograms per cubic meter and a cube compressive strength of 117.9 megapascals, impacted at 728 meters per second by a smaller 15-millimeter, 101.8-gram projectile. Because both projectiles remained essentially rigid, the impact energies and penetration resistances could be compared quantitatively. The new lightweight concrete faced roughly 3.44 times the impact kinetic energy and a 34.3 percent higher sectional energy density, yet its penetration depth was 10.7 percent shallower. Its average penetration resistance reached 1.30 gigapascals, about 51.2 percent higher than the 0.86 gigapascals of the denser UHPC, and the strength-normalized resistance index rose from 7.3 to 10.7, all while the target density was 16.3 percent lower.

The data also revealed an unexpected mathematical pattern. The researchers defined a penetration depth-density coupling coefficient K, the ratio of penetration reduction to density reduction, and found K equals 2.54: every 1 percent decrease in density corresponded to a roughly 2.54 percent decrease in penetration depth. This superlinear inverse coupling suggests the material offsets the loss of inertial resistance from being lighter through mix optimization and improved interface performance, shifting anti-penetration behavior from density-dominated inertia toward domination by intrinsic material properties. Marginal-efficiency analysis told a similar story: moving from C80 to the new C120 raised compressive strength by 50 percent, but basic anti-penetration efficiency, the reciprocal of penetration depth, rose 58.86 percent, and density-normalized intrinsic efficiency rose 85.96 percent, gains that far exceed what strength increase alone would predict and that break the conventional trend of diminishing returns in traditional high-strength concrete.

Finally, the team built a finite element model using the K&C concrete constitutive model with a quarter-symmetry mesh of hexahedral elements, and validated it against the experiments. The simulations reproduced the full penetration process, including radial cracks from constrained lateral expansion, circumferential cracks from unloading tensile waves after the projectile’s compressive effect vanished, the funnel-shaped spallation crater, and the steady-state cylindrical tunnel phase, with projectile deceleration curves and instantaneous penetration depths matching the measured data closely. The authors note that their tests covered a single projectile size at roughly 700 meters per second under normal incidence, so velocity dependence, scale effects and oblique or repeated impacts remain for future study. Even so, the validated model and the material itself point toward practical use as external protective layers for nuclear power plants, substations and oil storage facilities, where a shield that is both lighter and harder to penetrate could reshape how critical infrastructure is defended.

Subject of Research: Anti-penetration performance of a new lightweight high-performance C120 concrete

Article Title: Research on the anti-penetration performance of a new type of lightweight high-performance concrete

Article References: Liu, J., Zhang, C., Wang, G., Cao, S., Li, L., Dang, A., & Liu, X. (2026). Research on the anti-penetration performance of a new type of lightweight high-performance concrete. Case Studies in Construction Materials, 25, Article e06592. https://doi.org/10.1016/j.cscm.2026.e06592

Image Credits: AI Generated

DOI: 10.1016/j.cscm.2026.e06592

Keywords: lightweight concrete, high-performance concrete, anti-penetration, projectile impact, protective engineering, ceramsite aggregate, steel fibers, finite element simulation, penetration depth, compressive strength, critical infrastructure, materials science