Self-compacting concrete for improved construction technology

Richard McCarthy


Akademisk avhandling som med tillstånd av Kungliga Tekniska högskolan i Stockholm framläggs till offentlig granskning för avläggande av teknologie licentiatexamen fredagen den 4 december 2015 kl. 10.15 i Sal B1, Brinellvägen 23, Kungliga Tekniska högskolan, Stockholm. Avhandlingen försvaras på svenska.

Diskussionsledare: Prof. Terje Kanstad, NTNU, Trondheim, Norge
Huvudhandledare: Prof. Johan Silfwerbrand, KTH, Stockholm
Handledare: Prof. em. Håkan Sundquist, KTH, Stockholm



Self-compacting concrete (SCC) offers a variety of benefits. Most of them are well known in the whole concrete sector today. The most important advantages are increased degree of mechanisation and productivity, easiness of placing, improved quality of the finished structure (the inside as well as the outside), improved working environment, lower construction costs and possibilities to save labour. Sweden was in fact among the first countries in Europe to use SCC already over 10 to 15 years ago. However, during the following years the use of SCC didn´t increase as a result of the benefits. Today, the share of SCC in on-site casting is quite low. The market share of cast-in-place SCC is still only about 10 %. The share in the precast concrete industry is substantially higher. There are some possible explanations for this difference. Some examples are greater need for knowledge and experience, unsatisfactory robustness and varying material properties at site. Other significant issues are uncertainty around formwork pressure and a current lack of updated standards and codes regarding formwork design. Finally, and maybe the most important factor, is the short term focus in cost assessments.

The methods used in this thesis are a comparison of international design methods for vertical formwork through benchmarking (Paper I), investigation of the existing production technique with SCC through site visits and telephone interviews with Swedish contractors (Paper II) and measurements of formwork pressure as well as fresh concrete properties in field studies (Paper III and IV).

Current versions of codes for design of formwork for concrete are only covering conventional concrete (Paper I). However, the comparison between international codes showed both similarities and differences. The interviews showed that a majority of the contractors are in favour of the SCC technique, but SCC must be considered as a method instead of a material in order to encourage them to consider the wider effects and benefits of SCC (Paper II). Two results from the field studies (Paper III and IV) are significant. Firstly, the relationship between pressure sensor values and strain in the steel frames has shown very good correlation, regardless of form element and level. Secondly, the torsional moment development with time has been used as input to the calculation of formwork pressure with two international methods. The correlation between calculated and measured formwork pressure was fairly good.

One of the main objectives of this thesis was to find possibilities to increase the use of SCC. In order to achieve the objectives, the benefits of SCC must be highlighted more clearly. Anyone working with SCC must be well educated, quality controls must be improved at all levels, more user-friendly test methods must be developed and improved robustness is crucial. Current versions of codes for design of formwork for concrete must be adapted to SCC. A more long term focus during cost assessments is needed. SCC is slightly more expensive than conventional concrete, but one tends to forget the benefits that shortened construction time and the possibility of fewer workers can give in the end.