3.1.3 Mix designThe aim was to prod

3.1.3 Mix design
The aim was to produce a number of reference concretes for use by the partners in the later
tasks of the project in assessing and developing test methods. A control mix considered to be
a “good” SCC by the partners was the initial target and, subsequently, three series of mixes
with variations of each of the principal properties, i.e. filling ability, passing ability and
segregation resistance were developed.
Importance was attached to the following:
• the concretes should be easy to produce and reproduce
• the concretes should have a long open time to allow partners to carry out several tests on
the same batch of concrete with the properties changing as little as possible
The focus was solely on the fresh properties and no attention was given to the properties in
the hardening or hardened state such as heat development, durability, strength, shrinkage etc.
Control mix
Despite the different practices in different countries, the initial consensus of the partners was
that the properties of the control mix should be in the ranges:
• slump flow: 650 – 700 mm
• L-box: 0.8 – 0.85
• T50: 2 - 4 secs
• no visible segregation during handling or testing
After extensive testing, including comparison of results obtained in the laboratories of UCL
and DBT, the mix shown as mix C in Table 2 was close to meeting all the criteria and was
adopted. The combined grading of the aggregate was close to the mean for all partners’
typical mixes, and the coarse aggregate content was 50% of the dry-rodded bulk density. The
paste content (41% by volume) was higher than that of much SCC used in practice, but the
aim was not to produce an efficient SCC in commercial terms, but one suitable for a control