27/07/2022

Is the deflectometer becoming obsolete?

Dynatest developed the first Falling Weight Deflectometer in 1980, more than 40 years ago, and the falling weight method has remained the same during this time. Does this mean that the measurement method is becoming extinct? On the contrary. There has never been a greater need for this non-destructive method than now.

The Falling weight deflectometer was first introduced by Dynatest in 1980, since then many manufactures have followed and the market is now characterized by several makes of different quality, but all use the same non-destructive test method.

The origin development of the Falling Weight Deflectometer was to estimate the pavement structural capacity and conditions on roads, highways, and runways. The deflection method can be used to evaluate new constructions but are also used to a large extent for existing roads as the pavement characterization is important for determining a cost-effective pavement management and allocation of funds and resources to maintain and rehabilitate the deteriorating highway infrastructure.

In recent years, additional applications have been added, both based on the lack of documentation of roads networks, but also based on sustainable measures and changes in the climate. Here, falling weights have already proven their usefulness as a very stable measuring method.

 

Lack of historic data

Due to the historic lack of material details of the road network, there are still many stretches of road where there is no insight into the construction of the road in the sublayers. The role of subgrade and foundation layers is to provide adequate performance, in terms of pavement support stiffness and durability, preserving upper layers from premature failure. Therefore, it is key to have a good knowledge of the roads material layers characteristics to estimate correctly the bearing capacity and plan the appropriate maintenance to provide the serviceability of the estimated load. With a falling weight, this information can be acquired and used to estimate the life and in case design the proper rehabilitation.

Use of renewable material

Our awareness of sustainability has further raised the need for measurements with deflectometers.  Healthy and innovative research is being carried out within the recycling of various materials in the asphalt and the base. Here, for example, there has been research into mixing rubber from tires with the asphalt, the use of glass or with a cold-recycle base. This is all to the benefit of our planet, but of course it should preferably not happen at the expense of road safety or with more costly repairs as a result. Therefore, the deflectometer has been moved closer to the development phase to ensure that these new sustainable mixtures can provide the necessary perform in term of elastic moduli and performance criteria.

Climate changes

Unfortunately, changes in the climate have already caused some issues for the road network around the globe. Higher temperatures put our roads under a lot of pressure. A road is strongest when it freezes, High temperatures makes the asphalt softer, thus the risk is high that heavy vehicles cause rutting due to the deformation, which will decrease the pavement evenness and consequently affects road quality that has consistent reflection in term of traffic safety also. In areas where extreme temperatures are experienced, it is recommended to test with a falling weight to evaluate the material properties estimating the long term performance based on the local condition.

Flooding is unfortunately also recognized as a threat to the bearing capacity of pavement structures around the world. The falling Weight deflectometer can support in the evaluation of the bearing capacity just after flooding and the deflection data can be used as parameter to evaluate embankment critical condition and in case support the decision to limit the infrastructure use. At the same time, deflection data can also estimate the reduction of the material stiffness and strength of the pavement materials to evaluate the road resilience.

The innovation is differentiated on software

Falling weights were developed over 40 years ago and the technology itself has survived even though several different types have been launched on the market both in terms of different weight sizes, mobility, and electronic vs hydraulic systems. However, what currently really differentiates the various brands is not the technology of the product itself, but the functions and user-friendliness of the software. Here, it is developed on the fly and several post analysis software have good and clever calculations integrated into their software, which make life easier for the user.

At the moment, layers elastic moduli estimation is the most appropriate way for pavement evaluation and performance prediction, and no discussion the FWD remains the best equipment to collect useful data….so in conclusion, long life to FWD.

What features would you wish were in your post analysis software?

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