Compressive Strength of Non Shrink Grout
Compressive strength is one of the most important performance properties of non shrink grout. It determines how much load the grout can safely carry once hardened and directly affects the stability, durability, and safety of structural elements such as machinery bases, columns, anchor bolts, and precast connections. Understanding the compressive strength of non shrink grout helps engineers and contractors select the correct product and grade for each application.
What Is Compressive Strength?
Compressive strength is the maximum load per unit area that a material can withstand under compression before failure. In simple terms, it indicates how strong the grout becomes after curing.
- Measured in MPa (megapascals)
- Determined through laboratory cube or cylinder tests
- Measured at specific curing ages such as 1, 3, 7, and 28 days
Higher compressive strength means the grout can support heavier loads without crushing or deformation.
Why Compressive Strength Matters in Non Shrink Grout
Non shrink grout is often used in critical load-bearing locations where failure is not acceptable.
- Ensures full and safe load transfer from structure to foundation
- Prevents settlement under static and dynamic loads
- Reduces vibration in machinery installations
- Improves long-term structural stability
If compressive strength is insufficient, the grout may crack, crush, or lose contact over time.
Typical Compressive Strength Ranges
Non shrink grout is available in different strength grades depending on formulation and application.
Low to Medium Strength Grout
- 20–30 MPa at 28 days
- Used for light equipment and non-critical applications
- Suitable for void filling and general construction works
Standard Structural Grade Grout
- 30–40 MPa at 28 days
- Used for column bases and anchor bolts
- Common in commercial construction
High Strength Non Shrink Grout
- 40–60 MPa or higher at 28 days
- Used for heavy machinery and industrial applications
- Designed for high static and dynamic loads
Strength Development Over Time
Non shrink grout gains strength progressively as it cures.
- 1 day: Early strength allows initial handling
- 3 days: Significant strength gain begins
- 7 days: Majority of design strength achieved
- 28 days: Full rated compressive strength reached
Some rapid-setting grouts are designed to achieve high early strength within 24 hours.
Factors Affecting Compressive Strength
Several site and material factors influence the final strength of non shrink grout.
Water Content
- Excess water reduces compressive strength
- Low water improves strength but reduces flow
- Correct mixing ratio is essential
Mixing Quality
- Insufficient mixing leads to uneven strength
- Over-mixing may trap air
- Mechanical mixing gives best results
Curing Conditions
- Proper curing improves strength development
- Rapid drying reduces final strength
- Moist curing is recommended
Temperature
- High temperatures accelerate setting but may reduce strength
- Low temperatures slow strength gain
- Extreme conditions should be avoided
Compressive Strength Testing Methods
Strength is verified through standard laboratory testing.
- Cubes or cylinders cast from fresh grout
- Tested according to relevant standards
- Samples cured under controlled conditions
- Load applied until failure
These tests confirm whether the grout meets project specifications.
Matching Strength to Application
Selecting grout strength should be based on load and performance needs.
- Light equipment: 20–30 MPa
- Columns and anchor bolts: 30–40 MPa
- Heavy machinery: 40 MPa and above
Over-specifying strength increases cost, while under-specifying risks failure.
Relationship Between Shrinkage and Strength
Non shrink grout balances strength with volume stability.
- Shrinkage compensation ensures full contact
- Full contact improves effective load transfer
- Better load transfer reduces stress concentration
This combination makes non shrink grout superior to ordinary cement grout.
Common Site Mistakes That Reduce Strength
Avoid these common errors to maintain rated compressive strength.
- Adding extra water for flow
- Poor curing practices
- Early loading before strength gain
- Using expired or improperly stored grout
Frequently Asked Questions (FAQ)
1. Is higher compressive strength always better?
No, strength should match application requirements to avoid unnecessary cost.
2. Can non shrink grout achieve concrete-level strength?
Yes, many non shrink grouts reach or exceed structural concrete strength.
3. Does flowable grout have lower strength?
Flowable grout may have slightly lower strength than stiff mixes but remains within design limits.
4. How soon can load be applied?
Only after the grout reaches the specified strength, often after 3–7 days.
5. Can strength vary between batches?
Yes, inconsistent mixing and water control can cause variation.
Raltro
Raltro is a construction materials knowledge platform focused on explaining performance characteristics of building products in real construction conditions. By detailing the compressive strength of non shrink grout, how it develops, and what affects it on site, Raltro helps engineers and contractors select the correct grout grade, apply it properly, and achieve reliable load-bearing performance in structural and industrial projects.