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The compressive strength of exterior wall extruded polystyrene boards can vary significantly depending on environmental conditions (temperature, humidity, load type, climate cycles, etc.). The following are specific performance characteristics and data references for different scenarios:
1. Impact of Temperature Conditions
1. High-temperature environment (＞50°C)
Short-term high temperatures (≤70°C):
Polystyrene resin softens when heated, causing increased molecular chain movement and a temporary decrease in compressive strength.
Data example: A panel with a compressive strength of 300 kPa at room temperature (23°C) may decrease to 200–250 kPa (a decrease of approximately 17%–33%) at 70°C. After cooling to room temperature, the strength can partially recover (approximately 90%).
Long-term high temperature (＞70℃ and sustained for ＞1000 hours):
The resin undergoes thermal-oxidative ageing, molecular chains break, the closed-cell structure becomes brittle, and strength decreases irreversibly.
Data example: After one year in a 90℃ environment, compressive strength may decrease to 180–220 kPa (a decrease of 30–40%), and the board becomes brittle and prone to cracking.
2. Low-temperature environment (<-20°C)
Short-term low temperatures (≥-30°C):
Resin molecular chains contract tightly, temporarily increasing compressive strength but also increasing brittleness.
Data example: At -30°C, compressive strength may rise to 330–350 kPa (an increase of 10–17%), but impact resistance decreases by approximately 20% (prone to brittle fracture due to impact).
Ultra-low temperatures (<-50°C):
The material enters a glass transition state, becoming completely brittle, with a sharp drop in compressive strength and increased susceptibility to fracture, making it unsuitable for extremely cold regions.
II. Effects of Humidity and Water Environments
1. Long-term high humidity (environmental humidity >85%)
When the closed-cell rate of extruded polystyrene boards is ≥95%, water absorption is low (≤1.5%), and humidity has minimal impact on strength;
If the closed-cell rate is insufficient (e.g., <90%), water vapour penetrates the interconnected pores, causing internal softening and a gradual decrease in compressive strength.
Data example: A board with an 85% closed-cell rate stored in a high-humidity environment for one year may experience a strength reduction of 8%–12%.
2. Water immersion and freeze-thaw cycles
Long-term water immersion (soaking > 30 days):
Water gradually enters the closed cells, increasing self-weight and causing bubble walls to deform under pressure, resulting in strength reduction.
Data example: After 30 days of water immersion, compressive strength may decrease to 250–280 kPa (a reduction of 7%–17%).
Water inside the pores freezes and expands (volume increases by 9%), squeezing the bubble walls and causing them to rupture, leading to structural degradation.
Data example: After 50 freeze-thaw cycles, compressive strength may decrease to 210–240 kPa (a 20–30% decrease), and after 100 cycles, the decrease may reach 35–45%.
III. Influence of load type and duration
1. Short-term impact loads (e.g., construction foot traffic)
When the instantaneous load exceeds the design compressive strength value (e.g., temporary load of 500 kPa), local plastic deformation (crush pits) occurs, but if the load does not penetrate the panel, the overall strength is not significantly affected.
Characteristics: Deformation is concentrated at the load point, with strength retention in non-load areas exceeding 95%.
2. Long-term static loads (e.g., building self-weight)
Polystyrene exhibits ‘creep’ characteristics, where molecular chains slowly slip under sustained loads, leading to cumulative deformation and strength degradation.
Data example: After one year under a continuous load of 200 kPa, the measured compressive strength may decrease to 240–270 kPa (initial value 300 kPa, decrease of 10–20%); after five years, it may decrease to 210–240 kPa (decrease of 20–30%).
3. Cyclic loads (e.g., wind loads, seismic loads)
Periodic tensile and compressive forces cause fatigue damage to the bubble walls, resulting in micro-cracks and a gradual decrease in strength.
Data example: After 100,000 cycles of positive and negative wind pressure (±5 kPa), compressive strength may decrease by 15%-20%.
IV. Environmental Differences in Different Application Scenarios
Main environmental factors: diurnal temperature difference (ΔT = 15–25°C), wind load (±0.5–1.0 kPa), and ultraviolet radiation.
Strength change characteristics:
Temperature differences cause thermal expansion and contraction, potentially leading to stress concentration at the bonding interface between the panels and the substrate, indirectly reducing the effective compressive area;
Long-term UV exposure (>5 years) causes surface resin ageing, resulting in a 5%-8% decrease in compressive strength (requires a protective layer for isolation).
For floor extruded polystyrene boards, long-term creep must be prioritised. It is recommended to select products with a density ≥35 kg/m³ (compressive strength ≥350 kPa) to resist strength degradation over a 50-year service life;
For roof extruded polystyrene boards directly exposed to rain and snow, freeze-thaw cycles accelerate strength decline, so a waterproof layer must be used to reduce water ingress risks.
3. Severe cold regions (e.g., Northeast, Northwest)
While low temperatures enhance short-term strength, freeze-thaw cycles cause structural damage, and dry air accelerates surface cracking. Combined effects may result in a 25%-35% strength reduction within 5 years.
V. Technical Measures to Enhance Environmental Adaptability
Material Selection Optimisation
High-temperature environments: Select high-temperature-resistant modified polystyrene (e.g., with nano-fillers), which can increase the upper temperature limit to 90°C and improve strength retention by 15%;
Humid environments: Prioritise closed-cell extruded polystyrene boards with a closed-cell rate ≥98% and water absorption rate ≤0.5% to reduce water ingress risks.
Structural Protection Design
Add a breathable layer to exterior walls to reduce condensation accumulation;
Install reinforcing mesh above ground insulation layers to distribute loads and suppress creep deformation.
Construction Process Control
In extremely cold regions, ensure that insulation boards have aged for ≥120 days to reduce stress release in low-temperature environments;
Use an ‘inverted construction’ for roof insulation layers (waterproof layer below, extruded polystyrene board above) to prevent water ingress.
