Recycled Glass Mortar Testing for Freeze-Thaw Damage

ISEF Category: Materials Science

Subcategory: Ceramic and Glasses  ·  Difficulty: Intermediate  ·  Setup: Home Setup  ·  Time: 1 to 2 Months

The Hook

Broken glass does not have to end up in a landfill. You can turn it into a building material test and ask whether it helps or hurts mortar. Your freezer becomes part of the experiment, and your data can tell a real materials story. This project connects recycling with durability, which is a problem builders care about.

What Is It?

Mortar is the paste that holds bricks or blocks together. It usually contains sand, cement, and water. In this project, you replace some sand with crushed recycled glass and ask how that change affects the finished material.

Think of sand like the filler in cookie dough. It helps the mixture hold shape and controls how water moves through it. Glass particles can behave differently because they are smoother, sharper, or more irregular than sand, depending on how you crush and sort them. That can change pore size, which is the size of the tiny gaps inside the hardened mortar.

Water-permeability means how easily water can pass through a material. Freeze-thaw cycling means freezing wet samples, then thawing them again. Water expands when it freezes, so repeated cycles can crack weak materials. Your project asks whether recycled glass makes mortar more open to water, more resistant, or more likely to fail over time.

Why This Is a Good Topic

This is a strong science fair topic because you can test a real materials question with simple tools and clear results. You can measure mass change, visible cracking, water movement, and strength trends without a university lab. The project connects recycling, construction, and durability, so your results matter beyond the classroom. You will also learn how to compare materials, control variables, and read data like a materials engineer.

Research Questions

• How does replacing sand with recycled glass affect water absorption in low-strength mortar?
• What is the effect of glass particle size on permeability in mortar?
• Does increasing the percentage of recycled glass change freeze-thaw damage after repeated cycles?
• To what extent does recycled glass alter visible cracking compared with plain sand mortar?
• Which glass-to-sand mix ratio gives the best balance of low permeability and freeze-thaw resistance?
• How does crushed clear glass compare with crushed colored glass in mortar durability?

Basic Materials

• Portland cement or mortar mix, low-strength type.
• Clean recycled glass containers or craft glass, sorted and washed.
• Play sand or masonry sand, dried and screened.
• Digital kitchen scale with 0.1 g accuracy.
• Mixing buckets or disposable mixing tubs.
• Measuring cups or graduated containers.
• Safety goggles.
• Work gloves.
• Dust mask.
• Small molds or plastic cups for sample casting.
• Plastic wrap or labeled sealable bags for curing and storage.
• Kitchen freezer with space for repeated cycling.
• Absorbent towels or paper towels.
• Ruler or calipers for sample dimensions.
• Waterproof labels and marker.

Advanced Materials

• Compression test device or access to a simple materials testing setup.
• Vacuum desiccator or sealable chamber for permeability preconditioning.
• Laboratory sieve set for particle size sorting.
• Balance with 0.01 g accuracy.
• Oven or drying cabinet for controlled drying.
• Vernier calipers or micrometer for sample geometry.
• Stereomicroscope or digital microscope for crack inspection.
• Image analysis setup for crack counting and surface mapping.
• Freeze-thaw chamber, if available.
• ASTM-style mold forms for standardized specimens.
• Porosity measurement tools, such as water uptake fixtures.
• Reference sand with known grading curve.

Software & Tools

• Google Sheets: Organizes mass, permeability, and freeze-thaw data, and helps you make graphs.
• ImageJ: Measures crack length, surface damage, and pore-related image features from photos.
• Python: Cleans repeated-measure data and compares mix groups with simple stats.
• R: Runs significance tests and plots group differences cleanly.
• PubMed: Helps you find review articles on recycled glass in mortar and freeze-thaw durability.

Experiment Steps

1. Define the mix variable you will change first, such as glass percentage or particle size.
2. Choose the outcome you will measure, such as water uptake, crack count, or mass loss after cycling.
3. Plan a control group with plain sand mortar so you have a baseline for comparison.
4. Design sample shapes, labels, and storage rules so every piece starts the same way.
5. Build a measurement plan that pairs visual inspection with a numeric test, so your results are not just subjective.
6. Set up a data table before you begin, so you can track each cycle and compare groups consistently.

Common Pitfalls

• Using mixed glass sizes without sorting them, which makes it hard to tell whether particle size or glass content caused the result.
• Letting samples dry unevenly before freeze-thaw cycling, which changes the amount of water inside each piece.
• Comparing cracked samples by eye only, which misses small damage and weakens your conclusions.
• Changing the water content between batches, which can shift permeability more than the recycled glass itself.
• Forgetting that fresh mortar needs a full control group, which makes it impossible to judge whether glass helped at all.

What Makes This Competitive

A stronger version of this project goes past a simple yes-or-no test. You can compare more than one glass size, track damage across repeated cycles, and combine mass, crack, and permeability data into one story. You can also test whether colored glass, clear glass, or a graded mix behaves differently. Careful controls and clean statistics will make your conclusion much stronger than a basic demonstration.

Project Variations

• Test crushed glass in plaster or grout instead of mortar to compare how different binders handle recycled aggregate.
• Compare clear bottle glass with mixed-color glass to see whether composition or color-linked processing changes durability.
• Replace freeze-thaw cycling with soak-dry cycling to see whether moisture stress alone changes permeability and cracking.

Learn More

• USGS Mineral Resources Program: Search for reports on recycled glass, aggregate, and construction materials research.
• NOAA Climate Data Online: Use freeze-thaw context by checking local temperature patterns and seasonal cycling.
• NASA Earth Observatory: Find background on materials reuse, waste streams, and environmental impacts.
• NIH PubMed: Search review articles on recycled glass in cementitious materials and durability testing.
• MIT OpenCourseWare: Look for introductory materials science and civil engineering lecture notes on porosity, transport, and mechanical behavior.