Tailor Made Concrete Structures – Walraven & Stoelhorst (eds)© 2008 Taylor & Francis Group, London, ISBN 978-0-415-47535-8

Low strength self compacting concrete for building application

Kosmas K. Sideris, Aggelos S. Georgiadis, Nikolaos S. Anagnostopoulos & Panagiota ManitaLaboratory of Building Materials, Democritus University of Thrace

ABSTRACT: Application of self compacting concrete for the construction of a new office building in thecity of Xanthi, Greece is described in this paper. The building was especially designed to have a bioclimaticbehaviour. Low strength (C25/30) and low fines self compacting concrete was designed for this application usinga new mix design and quality control method developed at the Laboratory of Building Materials of DemocritusUniversity of Thrace (DUTH).

1 INTRODUCTION

Self compacting concrete is the latest achievement inconcrete technology. It is widely used because of thematerial’s ability to spread into restricted sections andbe compacted by its own weight, without the use of anyexternal consolidation, improving this way the work-ing environment, reducing the manpower needed forcasting and significantly increasing the constructionspeed. The type of concrete produced in this paperenables the construction of high quality fair faced sur-faces inside and outside of the building, satisfying therequirements.

2 PROJECT PRESENTATION

The outcome of the first building application of SCCin Greece is expected to be a sustainable designedbuilding [Figure 1] which will succeed in minimizingthe environmental impact from construction activities,the environmental charges in the construction and theincrease of the construction’s lifetime. In addition theuse of SCC ensures superior quality with no blow-holes on the surface or inside the concrete mass, withno requirements for any plastering or other type ofcladding. In that way basic parameters of a bioclimaticbehaviour, like creation of a substantial thermal mass,shall be enhanced. Finally laboratory tests revealedthat the use of SCC will reduce the placing time by70% and the personnel needed by 50%, leading tovarious environmental and traffic benefits.

3 EXPERIMENTAL INVESTIGATION

3.1 Mixture composition

In order to produce a stable, robust and competitiveSCC of low strength class (C25/30) with low fines

Figure 1. 3D design of the building.

content, an innovative method for the production andquality control of SCC mixtures, was implemented(Georgiadis et al. 2006). Several mixtures were pro-duced and the characteristics measured were theirrobustness, viscosity, thixotropy and formwork pres-sure development. The water dosage was modified±10l t/m3 in the SCC mixtures, in order to measuretheir robustness.An NCC mixture of the same strengthclass was also produced and used as reference mixture(Table 1).

3.2 Experimental measurements

For each mixture (2 SCCs and the NCC), a columnin 1:2 scale with 25 cm edge and 1 m height was castin the laboratory. For each column the compressivestrength at the age of 7 and 28 days was measured afterdifferent curing in laboratory conditions (RH ≥ 95%,200C) and environmental conditions.The compressivestrength values are presented in Figure 2.

Furthermore for each mixture were measured thecasting rats, the pressure build-up while casting at

1057

Table 1. Mixture compositions and rheologicalcharacteristics.

Mixtures Compositions (Kg/m3)

Mix Design SCC1 SCC2 NCC

CEMII-A/M 42,5N 50,9 50,7 50CEMII-A/M 32,5N 305,1 303,9 300FILLER 101,4 50 –SAND 881,4 944,3 890COARSE 800 800 580AGGREGATES

WATER 192,9 188,9 195SUPERPL/ZER 5,7 5,81 3RETARDER 1,6 1,06 –V.M.A. – 1,06 –W/C 0,54 0,53 0,54W/P 0,42 0,46 –

Rheological characteristics

AIR CONTENT (%) 2,10% 2,20% 2,00%SLUMP FLOW D (cm) 72 71 19t50(sec) 2 3 –d at t30(mm) at rest 48 60 –d at t30(mm) mixed 52 61 –V FUNNEL 1 (sec) 9,28 16 –V FUNNEL 2 (sec) 14,12 25 –LBOX (h2/h1) 0,8 0,86 –

Figure 2. Compressive strength of SCCs and NCC (labora-tory curing).

different casting rates and the pressure developmentof the concrete from fresh to hardened state.

Finally, before the in situ casting, two L shapedwalls were cast at the concrete ready mix factory, inan attempt to measure the pressures in real state.

4 RESULTS AND DISCUSSION

As mentioned above, two different SCC mixture weredesigned in order to achieve different rheological fea-tures; this purpose was obtained by changing the type

Figure 3. Formwork pressures compared with the hydro-static pressure.

Figure 4. Laboratory Formwork, Pump, Pressure Sensorsand Specimens.

of the admixture and modifying the filler amount.Both concretes were robust, and had remarkable per-formance as far as compressive strength is concerned.Of course that is fully attributed the low w/c ratio andthe filler addition, factors that led to finer pores andlower total porosity.

Both SCCs developed formwork pressures rateslower than hydrostatic. As pointed out the mixtureswere designed to be thixotropic. As such they kepttheir flowing properties as long as kept in motion,but once left at rest, they build up a structure ableto withstand the concrete cast above without increas-ing the horizontal pressure against the form to the samedegree (Roussel).Taking into account parameters suchas casting rate, formwork geometry, reinforcement andthixotropy helped to succeed in quicker build up ofconcrete’s structure and eventually lower formworkpressures (Roussel, Billberg, Nunes 2006).

1058

Figure 5. Formwork and surface of L-shaped walls.

5 CONCLUSIONS

The application of self compacting concrete at thebuilding site is not yet easily accepted by contractors,Parameters such as quality control tests, transporting,casting rate and formwork pressure are usually trou-bling most engineers. The increased initial cost andthe higher compressive strength usually performed bySCC are also of great concern. Hopefully this paperproved that low strength low fines SCC designed forthis specific project was an exceptional material to beused in site, considering the structural, quality and costbenefits as compared with traditional concrete of thesame strength class.

ACKNOWLEDGMENTS

This paper is part of the PABETAMTH2 researchproject co-financed by National and CommunityFunds and by Private Funds (Concrete Industry). Thefinancial support provided is greatly acknowledged.

REFERENCES

Assaad, J., Khayat, K.H. & Mesbah, H. 2003. Assessment ofthixotropy and self-consolidating concrete. ACI MaterialsJournal: 100–111.

Billberg, P. Formwork pressure when using SCC – a doc-toral project.Proceedings of the 5th International RILEMSymposium: 491–496.

Georgiadis, A. Sideris, K. & Anagnostopoulos, N. 2006.Development of a new innovative method, for the pro-duction and quality control of self-compacting concretes.CONCRETE Journal 4 : 35–45.

Nunes, S. Figueiras, H. Oliveira,P.M., Coutinho, J.S. &Figueiras, J. 2006 A methodology to asses robustness ofSCC mixtures Cement and Concrete Research Journal 36:2115–2122.

Oesterheld, S. & Wallevik, O.Effect of stabilizers onthixotropy and reduction of formwork pressure. Pro-ceedings of the 5th International RILEM Symposium:497–502.

Roussel, N. A thixotropy model for fresh fluid concretes: the-ory and applications. Proceedings of the 5th InternationalRILEM Symposium: 267–272.

1059