In Japan, where about 75% of the land is mountainous, there is an inextricable relationship between the development of railway and road infrastructure and tunnel construction. The "NATM method" is a method widely used in the construction of tunnels. NATM is a method invented in Austria in the 1960s, and is applied in various conditions from hard rock to soft ground.Using the NATM method, bedrock is excavated using a tunneling machine and the exposed walls are sprayed with sprayed concrete to reinforce the tunnel walls to prevent collapse as the tunnel progresses. This sprayed concrete is called shotcrete whereby a special machine fitted with a nozzle at the end blasts fine granular concrete directly onto the tunnel wall.A set accelerator is mixed with the concrete to ensure it dries as quickly as possible, and while it works to strengthen the concrete, it also poses the problem of scattering fine dust into the air, which has been a problem for many years in mountain tunnel construction.
A time of trial and error
We hoped to harness our technologies to improve the working environment of essential workers engaged in the harsh job of tunnel construction. Believing that the technology behind VISCO TOP for controlling the viscoelasticity of concrete could be applied to solve this problem, the Kao Chemicals Business Division began work on the research and development of new thickeners.However, no matter how many times we conducted tests, results failed to meet our expectations and large amounts of dust were generated. Further, in the absence of a test spray machine, it was difficult to reproduce in-situ conditions, making it difficult to find an appropriate method of evaluation. It was a depressing time that yielded no real results.Then one day, as I was casually throwing a clump of concrete up against a wall, I released that how it scattered was very different depending on what materials were added. And I thought, "Maybe this is it? Maybe this is how I can test it!"
Reproducing in-situ conditions in a laboratory setting by changing how we think. Through a process of trial and error, we discovered a material that was both quick setting and achieved the desired level of viscoelasticity that also significantly reduced concrete spatter. This result was verified in a reproduction experiment using a spraying machine and the product made it through the process to commercialization.
Working without dust masks
One worker working on a site where VISCO TOP UT was first introduced was hesitant to follow a different procedure. However, once he started using it he realized there was really very little dust, experiencing the benefits first-hand, stating it was so good he could perform his work without wearing a dust mask. He was so impressed that at his next construction site, he proposed to the general contractor that they use VISCO TOP UT on this job as well. When I heard that it was to be used, I remember feeling so happy that I forgot the hardships we faced during the development process.
VISCO TOP UT was born through a process of trial and error and was a product of our desire to reduce pneumoconiosis caused by dust, which has been a long-standing problem in mountain tunnel construction. We will continue to make proposals for more innovative products to protect the lives of everyone involved in construction.