ZORN LAB LWD | Laboratory Light Weight Deflectometer

ZORN LAB LWD – Reliable Laboratory Modulus Targeting for LWD Field Testing

The ZORN LAB LWD is a precision tool designed to define target modulus values for unbound soils and soil-aggregate mixtures. These values serve as a reliable reference for in-situ testing with standard Lightweight Deflectometers (LWDs).

Based on the ASTM E3331-22 standard, the testing procedure involves measuring deflections on Proctor specimens at varying moisture levels in the lab. The recorded deflection data is then correlated with the moisture and density characteristics of the same specimen, enabling the determination of accurate modulus targets.

By combining laboratory-based compaction analysis with real-world LWD performance testing, this method enhances conventional quality assurance and quality control processes in geotechnical and construction projects.

Both the ASTM E3331-22 methodology and the LAB LWD device itself are backed by extensive research, including the TPF-5(285) Transportation Pooled Fund Project led by the Maryland Department of Transportation in 2017.

Precision Design for Reliable Lab-to-Field Correlation

The ZORN LAB LWD is a laboratory-adapted version of the proven ZORN Lightweight Deflectometer (LWD), developed in accordance with ASTM E2835. Engineered and manufactured in Germany by ZORN INSTRUMENTS, this compact device features a 150 mm diameter load plate and offers two plate variants to match common laboratory molds:

  • 152.4 mm (6-inch) Proctor mold

  • 150.0 mm metric equivalent

This tailored design allows seamless integration with standard laboratory compaction molds and ensures consistent, repeatable correlations between moisture-density data and the resulting stiffness or modulus values of granular materials.

With its 5 kg drop weight and adjustable drop heights, the LAB LWD can generate a variety of loads, enabling flexible stiffness evaluation for different soils and aggregates — ideal for fine-tuning construction materials before field deployment.

Lab–Field Consistency: Why Instrument Matching Matters

To ensure accurate, comparable results between lab and field testing, it’s essential to use the same type of LWD system throughout the process. According to ASTM E2835 and E2583, variations in:

  • instrument brand

  • buffer stiffness

  • deflection sensor positioning

…can lead to inconsistent results. That’s why ZORN recommends using the same LWD model in both lab and field applications. Our LAB LWD is specifically designed to meet this requirement.

Flexible Use Beyond the Lab – ZORN LAB LWD in the Field

While originally developed for testing compacted Proctor specimens in laboratory environments, the ZORN LAB LWD is also well suited for quick, on-site modulus evaluations.

In the field, it offers the same automated modulus calculation as the standard ZORN Lightweight Deflectometer (per ASTM E2835). However, due to its reduced plate diameter and lower impact force, the effective depth of influence is limited to approximately 200–300 mm.

ZORN LWD parameters

  • M =  17 kg (total mass)
  • l = 26,4" = 0,67 m (rod length)
  • m = 5 kg (falling weight)
  • h = 14,8" = 0,375 m (falling height)
  • k = 0,306 10 6 N/m (spring constant)
  • R = 3,0" = 75 mm (load plate radius)
  • F = 3,54 kN (max. impact force)
  • ơ = 200 kPa (max. ground pressure)

Good to Know: Expanded Application Potential

Recent research has shown that the ZORN LAB LWD can also be used in the lab to directly investigate the relationship between moisture content and bearing capacity in fine-grained soils. This makes the device particularly valuable in regions where construction materials often contain over 15% fines – a scenario commonly seen in many international projects.

Need help selecting the right configuration?
We are happy to advise you.

Contact Sales
Thorsten Hildebrand
Telefon: +49 3931 25273-262
eMail: sales(at)zorn-instruments.de

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