The use of recycled materials as binders to stabilize soft clay in laboratory

Construction on the site with soft clay is difficult in many ways. The challenges are
the low undrained shear strength and high compressibility of soft clay. Mass
stabilization, as one of the ground improvement method, is able to improve
properties of soft clay.

During mass stabilization process, the adding of suitable binders improves strength
and load bearing capacity of soft clay. Mass stabilization is an economical and
environmentally friendly ground improvement method when binders based on
recycled materials are used. Binder is the main matter, which defines the
environmental and economical effects of mass stabilization.

The objective of this thesis was to find out the most suitable type of binder or binder
mixture and the right proportion of ingredients for soft clay in Depot of Vuosaari,
Helsinki. This study dealt with tests of several kinds of binder in laboratory
condition for further in-situ mass stabilization. Gypsum from VTT Oy, ashes
mixture from Ecolan Oy and fly ash from HELEN Oy were the main researched
materials in this study. Cement and lime-cement mixture were also used as the
reference materials. Unconfined compression tests were the main tests carried out
to evaluate and measure the undrained shear strength of stabilized clay. Samples
were tested at the age of 28 days and 3 months. In addition, in the aim of getting
more comprehension of binders, bending test and compression test were performed
on pure binders. In this study, all the binders took a certain degree of increase to the
strength of soft clay. Ashes mixture from Ecolan mixed with cement performed as
the best combination with a highest undrained shear strength (over 600 kPa).