By the Blocktec Editorial Team
A research team from Henan, China, load-tested six full-height autoclaved aerated concrete (AAC) self-insulation block walls under repeated side-to-side loading that imitates an earthquake. The results were published on 30 June 2020. Walls laid with 5 mm thin-layer mortar resisted cracking about 13% better and moved about 54% more before their first crack than walls laid with 10 mm insulation mortar.
How The Walls Were Built And Tested
The six specimens were each about 1.22 m long, 1.22 to 1.25 m high and 250 mm thick. They were built from blocks made by Henan Xing'an New Building Materials, each measuring 600 x 300 x 250 mm. The blocks had a dry density of 558 kg/m3, a compressive strength of 4.1 MPa, a thermal conductivity of 0.11 W/mK and water absorption of 63.5%. They fall under China class A5.0, B06.
The team compared three joint types, with two walls for each:
- 10 mm insulation mortar made with perlite and glass microspheres
- 5 mm thin-layer dry-mix mortar
- thin-layer bed joints, with the vertical joints filled with mineral wool board instead of mortar
The thin-layer mortar reached 17.1 MPa in compressive strength, against 8.7 MPa for the insulation mortar. In masonry tests, thin-layer walls gave 1.99 MPa compressive strength and 0.25 MPa joint shear strength. Insulation-mortar walls gave 1.84 MPa and 0.37 MPa.
Each wall carried a constant vertical load at the top, either 0.3 or 0.5 MPa. An actuator then pushed and pulled the wall sideways, first controlled by load, then in multiples of the displacement at which the wall first cracked. Testing continued until the wall's capacity dropped to 85% of its peak. Peak lateral loads across the specimens ranged from 57 to 98 kN.
What The Numbers Showed
All walls behaved elastically at first. Diagonal cracks appeared at roughly 60% of peak load, when the top of the wall had moved about 2 mm. After that, cracks crossed into X patterns and the walls slid along the bed joints.
The main comparisons:
- Thin-layer walls had about 13.1% higher cracking resistance than insulation-mortar walls.
- Thin-layer walls moved about 54.2% more at first crack.
- Their ultimate capacity was about 4.5% lower than insulation-mortar walls, a small trade-off.
- Energy dissipation, meaning how much shaking energy the wall absorbs, was 15.3% higher at cracking and 9.4% higher at peak load.
The walls with mineral wool in the vertical joints did worst. They reached only about 80.9% of the cracking load and 85.1% of the ultimate load of thin-layer walls. They deformed the least, showed more vertical cracks, lost stiffness faster and had the lowest capacity. Their energy dissipation was 10 to 12% below thin-layer walls. The researchers explained that unbonded vertical joints stop the wall from acting as one unit.
Raising the vertical compression from 0.3 to 0.5 MPa made the walls stiffer and stronger, but they absorbed less energy and the edge blocks crushed.
The heat transfer coefficients of all walls stayed between 0.508 and 0.541 W/m2K, so the joint type made little difference to insulation.
Background: Why Infill Walls Matter In Quakes
AAC self-insulation blocks are often used as infill walls inside steel and reinforced concrete frames. That means the wall has to work with the frame when the ground shakes. Earlier studies cited by the authors found that infill walls add shear demand on columns, that reinforcement or fiber mesh in the bed joints improves ductility, and that AAC walls can keep 40 to 50% of their vertical capacity after damage.
Design Recommendations And Code Checks
The authors recommend matching mortar strength to block strength and bonding the vertical joints with mortar rather than leaving them filled with soft board. They also checked how well design formulas predict wall shear capacity. China's JGJ/T17 AAC code and Eurocode 6 gave safe, conservative estimates for thin-layer walls. The US TMS 602 formula under-predicted capacity, and China's concrete block formula over-predicted it, which is the unsafe direction.
What This Means For Philippine Builders
This was a small laboratory study on six walls, in China, with one block type. It does not replace structural design or local code requirements, and your engineer should still decide how infill walls connect to the frame. But the direction is useful for anyone specifying AAC walls here.
First, joint thickness and bonding matter. Thin-bed adhesive joints, the walang palitada method Blocktec uses, performed better on crack resistance and energy absorption than thick insulating mortar joints in this test. Second, do not leave vertical joints unbonded. Mortar or adhesive in the head joints kept the wall acting as one piece. Third, ask your engineer which shear formulas they use. The study found some codes safe and others not for this wall type.
Blocktec imports AAC blocks, panels, lintel beams and thin-bed adhesive, and was the first AAC importer in the Philippines to receive the DTI-BPS Philippine Standard Certification Mark (License No. Q-6620). Our products comply with PNS ASTM C1691:2019 and ASTM C1693. Walls are laid with thin-bed adhesive and finished with skimcoat, with a 4-hour fire resistance rating. In Blocktec's own cost comparison, the wall system showed up to about 21% savings versus hollow blocks, depending on the project.
If you are planning infill walls, bring your plans to your structural engineer early and ask how the block grade, joint type and frame connection will be detailed.
Sources
- Materials (MDPI), via PubMed Central: On the Seismic Performance of Autoclaved Aerated Concrete Self-Insulation Block Walls (Jun 30, 2020)
Planning a build and want to see what a thin-bed AAC wall system could cost you? Send your wall area or blueprints to sales@blocktec.ph or visit blocktec.ph for a free estimate.