ZORN INSTRUMENTS offers dynamic variants of familiar laboratory tests for testing the mechanical load-bearing capacity of soils and mineral aggregate mixtures. Along with the dynamic ZORN CBR (laboratory), this range includes the modified plate load test using the ZORN LAB to determine the dynamic deformation modulus of classic Proctor samples. ZORN CBR and ZORN LAB are comparatively new material testing solutions for road construction. From both tests it is possible to determine performance characteristics that are of great value, particularly during the planning phase for road construction. The ZORN CBR and ZORN LAB are therefore used, e.g. during the conception and design of freeways in North America. In this way the subsequent usage of the Lightweight Deflectometer ZORN ZFG as an instrument for checking the quality in the implementation phase is made possible.
The determination of the density of mineral aggregate mixtures depending on the water content is one of the fundamental tests in the soil mechanics laboratory. With this test, the suitability of the material for use in road construction is determined depending on the portion of fines. In a comparison to the dry density of the material taken from the construction site, the Proctor density DPr responsible for the degree of compaction is determined. The determination of the density of mineral aggregate mixtures depending on the water content is one of the fundamental tests in the soil mechanics laboratory. With this test, the suitability of the material for use in road construction is determined depending on the portion of fines. In a comparison to the dry density of the material taken from the construction site, the Proctor density DPr responsible for the degree of compaction is determined.
"The dynamic CBR value is a complex strength characteristic that is dependent on the strength, the grain shape, the frost resistance and the grain roughness of the individual grain, the grain composition, the fines content, the water content and the compaction of the construction material mixture as well as the sensitivity to water of the portion of fines contained in the construction material mixture. It can be used to assess the sensitivity to frost or to estimate suitability for traffic and the compactability and load-bearing capacity of the construction material laid."
The calculation of the dynamic CBR value is based on a force/deformation curve. This value is approximated with the aid of a power function. The parameters for the power function are derived from the deformation values 2.5 mm and 5.0 mm. With the scaling of the ram pressure, the dynamic CBR value appears in percent (%), similar to the classic test. The dynamic CBR value is calculated based on an equation specified taking into account the maximum impact force (7,070 N) and the diameter of the load ram (50 mm) as well as the entry of the penetration depth s.
California Bearing Ratio (CBR) is a standard test for determining the load-bearing capacity of soils in earthworks and foundation engineering. In its classic implementation (static), a ram with a diameter of 50 mm penetrates a soil sample compacted according to Proctor with a constant velocity (1.27 mm/min). A ratio of the resulting force and the force for a standard soil with the same penetration depth is formed. The result is stated in percent (%). The classic implementation of CBR is labour-intensive, time-consuming and the result often unfortunately inaccurate. The ZORN CBR test setup utilises the familiar advantages of the dynamic plate load test: Speed, reproducibility and certainty in the implementation.
With this test, ZORN INSTRUMENTS is taking a further step forward in soil analysis. A Proctor soil sample is checked for load-bearing capacity using a modified falling weight deflectometer (ZORN LAB) and different ground pressures. If there are portions of fines, the typical load-bearing capacity losses as a function of the water content are apparent (Proctor curve).