📄 chemistry

Research and Statistical Analysis on the Impact Resistance of Supplementary Cementitious Material with Different Glass Fiber Content

This study investigates the dynamic impact resistance of glass fiber-reinforced cement mortar containing supplementary cementitious materials under varying water-binder ratios and fiber contents using Split Hopkinson Pressure Bar tests, revealing that a 1.5% fiber volume and 0.5 water-binder ratio optimize energy absorption and toughness while the material's failure behavior is effectively modeled by a two-parameter Weibull distribution.

Original authors: Wenlong Huo, Xiaonian Chen, Zhengxiong Bai, Xiuyu Wu

Published 2026-07-02

📖 5 min read🧠 Deep dive

CC BY 4.0

Original authors: Wenlong Huo, Xiaonian Chen, Zhengxiong Bai, Xiuyu Wu

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

The Big Picture: Building a "Bulletproof" Cement

Imagine you are building a wall. Usually, walls are great at holding up heavy books (static loads), but if someone throws a heavy rock at them or if there's an explosion nearby, the wall might shatter instantly.

This study is about making a special type of cement mortar (the "glue" and filler in construction) that is tougher and better at surviving sudden, violent hits. The researchers wanted to see if adding glass fibers (tiny, strong strands of glass) and some special "super-ingredients" (micro-silica and an expansion agent) could turn regular cement into a material that absorbs shocks like a sponge rather than shattering like a dry cookie.

The Ingredients: What Went Into the Mix?

The researchers created 216 small, cylindrical "test cakes" of cement. They tweaked the recipe in two main ways:

The Water Ratio (W/B): Think of this like the moisture in a cake batter. They tested three levels: a "dry" mix (0.3), a "medium" mix (0.4), and a "wet" mix (0.5).
The Glass Fiber (GF): This is the secret weapon. They added glass fibers in four amounts:
- 0%: No fibers (the control group).
- 0.5%, 1.0%, and 1.5%: Increasing amounts of tiny glass strands, like adding more and more steel rebar to a concrete bridge, but on a microscopic scale.

The Test: The "Air Cannon" Challenge

To see how tough these mixes were, they didn't just squeeze them; they hit them. They used a machine called a Split Hopkinson Pressure Bar (SHPB).

The Analogy: Imagine a high-speed air cannon shooting a projectile at your test cake. The researchers adjusted the air pressure (0.2, 0.3, and 0.4 MPa) to simulate different levels of impact, from a hard punch to a heavy blow.
The Goal: They wanted to see how fast the material could deform, how much energy it could soak up, and whether it would crack cleanly or turn into dust.

What They Found: The "Super-Cement" Secrets

1. The "Speed" Effect (Strain Rate)
When the material is hit slowly, it behaves one way. When hit fast (like an explosion), it behaves differently.

The Finding: The faster the hit, the stronger the material became, but it also broke into smaller, finer pieces. It's like how a piece of taffy stretches if you pull it slowly, but snaps if you yank it instantly. The material showed a "strain rate effect," meaning it got harder to break the faster you hit it, but the damage was more severe.

2. The "Wet" Mix Won
Surprisingly, the mix with the highest water ratio (0.5) performed the best at absorbing energy.

The Analogy: Think of a dry sponge vs. a damp sponge. The drier mix was too rigid and brittle. The wetter mix had more "give," allowing it to absorb the shockwave energy better without shattering immediately. It acted like a shock absorber in a car.

3. The Glass Fiber Magic
Adding glass fibers changed the game completely.

The Finding: When they added 1.5% glass fiber, the material became incredibly tough.
The Analogy: Imagine a highway. Without fibers, a crack is like a pothole that spreads instantly across the whole road. With fibers, the cracks are like potholes that hit a "speed bump" (the fibers). The fibers hold the material together, forcing the crack to take a longer, harder path to spread. This prevented the material from turning into dust and gave it high "ultimate toughness" (the ability to stretch and bend before breaking).

4. The Four Stages of Breaking
When they hit the samples, the stress-strain curve (a graph showing how the material reacted) had four distinct chapters:

Elastic Stage: The material stretches like a rubber band and wants to snap back.
Crack Expansion: Tiny invisible cracks start to form.
Plastic Deformation: The material starts to permanently deform (like bending a paperclip). The fibers helped this stage last longer, absorbing more energy.
Failure: The material finally gives way.

The Statistical "Crystal Ball"

The researchers didn't just look at the results; they used a mathematical tool called the Weibull distribution.

The Analogy: Think of this as a "failure prediction crystal ball." Because no two pieces of cement are exactly identical (some have tiny air bubbles, some are slightly denser), the strength varies. The Weibull test helped them predict the probability of a piece breaking at a certain strength.
The Result: The math worked perfectly. They found that the relationship between the air pressure used to hit the sample and the material's strength followed a smooth, curved line (a quadratic polynomial). This means they can now predict exactly how strong a mix will be just by knowing the recipe and the impact pressure.

The Bottom Line

This study proves that by adding the right amount of glass fibers (specifically 1.5%) and adjusting the water content, you can create a cement mortar that acts like a high-tech armor. Instead of shattering when hit by a sudden impact, it absorbs the energy, delays the cracking, and holds together much better. This is a big deal for buildings that need to survive earthquakes, explosions, or other extreme impacts.

Technical Summary: Impact Resistance of Supplementary Cementitious Material with Different Glass Fiber Content

Problem Statement
Mortar is a critical material for bonding, filling, and repairing in construction; however, it is prone to shrinkage cracking, which compromises compressive strength and durability. While Supplementary Cementitious Materials (SCMs) like micro-silica (MS) and expansion agents (EA) are known to improve static mechanical properties and inhibit shrinkage, there is a relative scarcity of research regarding their performance under dynamic impact loads. Existing studies on fiber-reinforced mortar often rely on high cement content or anti-corrosion additives that may be environmentally unfavorable or induce initial damage. Consequently, there is a need to investigate the dynamic mechanical properties of mortar enhanced by SCMs and glass fibers (GF) to better understand their behavior under extreme loads such as explosions, impacts, and earthquakes.

Methodology
The study utilized a Split Hopkinson Pressure Bar (SHPB) device to conduct dynamic impact tests on 216 cylindrical specimens (ø75 mm × 37.5 mm). The specimens were composed of Ordinary Portland Cement (PC), micro-silica (10% by weight of PC), an expansion agent (8% by weight of PC), river sand, and glass fibers.

Variables: The study varied the Water-to-Binder (W/B) ratios (0.3, 0.4, 0.5) and Glass Fiber (GF) volume content (0%, 0.5%, 1.0%, 1.5%).
Testing Conditions: Dynamic impact tests were performed at three air gun pressures ( $P_g$ ): 0.2 MPa, 0.3 MPa, and 0.4 MPa, generating different strain rates.
Analysis: The researchers analyzed failure modes, stress-strain curves, and dynamic mechanical parameters (peak stress, ultimate strain, ultimate toughness). Furthermore, the experimental data were fitted using a two-parameter Weibull distribution to evaluate the statistical reliability of the impact resistance and to derive equations linking failure probability to impact pressure.

Key Results

Strain Rate Effect and Failure Modes: The specimens exhibited a clear strain rate effect. As the strain rate increased, the degree of specimen breakage intensified, transitioning from axial splitting tensile failure at low strain rates to granular crushing failure at high strain rates. The dynamic stress-strain curves were characterized by four distinct stages: elastic, crack expansion, plastic deformation, and failure. Notably, the plastic deformation stage strengthened with increasing strain rates.
Influence of W/B Ratio: Specimens with a W/B ratio of 0.5 demonstrated superior impact resistance and energy absorption capabilities compared to those with lower ratios (0.3 and 0.4). The higher porosity associated with the 0.5 ratio facilitated better pulse velocity reduction and energy absorption. The relationship between ultimate toughness and strain rate was found to be highly correlated and increased with the W/B ratio.
Influence of Glass Fiber Content: Increasing the GF content generally improved the dynamic compressive strength. Specifically, specimens with 1.5% GF content showed the highest dynamic compressive strength and ultimate toughness. The fibers altered the stress propagation path, reduced stress concentration, and inhibited crack formation. At 1.5% content, the fibers were evenly distributed, creating a synergistic effect that significantly enhanced resistance to impact damage.
Statistical Analysis (Weibull Distribution): The impact resistance data for all specimen groups were well-described by the two-parameter Weibull distribution, with high linear regression coefficients ( $R^2$ ). The study confirmed that the degree of linear correlation improved with higher GF content.
Predictive Modeling: The relationship between the dynamic compressive strength and the air gun pressure ( $P_g$ ) under different failure probabilities was found to follow a quadratic polynomial curve function.

Significance and Claims
The authors claim that these findings provide guiding significance for improving the impact resistance of mortar materials used in building filling and reinforcement. The study demonstrates that combining SCMs (MS and EA) with an optimal volume of glass fibers (specifically 1.5%) and a W/B ratio of 0.5 can effectively enhance the dynamic mechanical properties of mortar. The successful application of the two-parameter Weibull distribution allows for a reliable statistical description of the material's impact resistance, enabling the prediction of failure strength under specific impact pressures. The research highlights a pathway to developing environmentally friendly, high-performance mortar capable of withstanding extreme dynamic loads without relying on excessive cement or harmful additives.