Early volume changes of high performance self-compacting CEMENTITIOUS SYSTEMS containing pozzolanic POWDERS

Syed Ali Rizwan1 and Thomas A Bier1

(1) Institute for Ceramics, Glass and Building Materials Technology, Agricolastr. 17, T U Freiberg, 09599, Germany.

Abstract This study is an ongoing investigation by the authors on high performance (HP) self compacting cementitious systems (SCCS) and addresses early volume changes of cementitious systems using inert and pozzolanic powders. The systems investigated contained lime stone powder (LSP-relatively inert) and pozzolanic materials like fly-ash (FA), rice-husk ashes (RHAs both amorphous and crystalline) and as produced powder type silica fume (SF). Two sand types were used. One had 0-2 mm size fraction (S1) while the other had 80% 0-2 mm and 20% 2-4 mm size fractions (S2). Such systems were generally studied for linear early shrinkage in two exposure conditions in the laboratory wherein constant temperature and humidity conditions were maintained. The results on HP SCMs (self-compacting mortars) indicate that incorporating powdered superplasticizer (SP) reduced the shrinkage. Covering a formulation also did the same. At higher water-cement ratios shrinkage got reduced due to dilution effect. Regarding HP SCM systems using LSP, the early uncovered shrinkage remains almost the same for all the cements used in both exposure conditions. FA systems showed expansion in covered condition with all cements. The shrinkage of such systems got reduced when 20% RHA was incorporated into FA. However, 20% addition of RHAP (crystalline) gave a higher expansion in covered conditions with all cements compared with 100% FA system The effect of sand type demonstrated that coarser sand S2 showed slightly lesser shrinkage with a higher maximum pore size. The study showed that suitable ternary binders when used in an appropriate way could reduce early shrinkage of HP SCCS.

Keywords: High performance. Self-compacting, early shrinkage, secondary raw materials,MIP.

1.INTRODUCTION Structural and construction engineers are only interested in the total magnitude of early shrinkage and certainly not in the contributions of various parallel operating mechanisms towards the total shrinkage of a cementitious system. This is perhaps the reason why most codes prescribe the total permissible shrinkage values only. HP SCCS are being increasingly used in the construction industry. These systems use very high amounts of fillers usually selected from lime stone powder (LSP), fly-ash (FA), silica fume(SF) and rice-husk ash (RHA) or their combinations to replace part of the cement and to improve such properties like reduction in water demand/early shrinkage, high flow, easy placements, high strength and durability. Usually such systems use low w/c ratio and high flow levels obtained by using superplasticizer (SP).Volume change of the cementitious systems in early ages has been undertaken by several investigators using linear or volume measurements with each technique having its own plus and minus points [1-4] and no standard method for the determination of drying shrinkage measurement of concrete exists [5]. Moreover no or very little work has been done regarding the total early shrinkage determination of SCCS especially those containing pozzolanic powders. In general shrinkage has been attributed to the paste component or to cement content necessitating the systematic early volume change measurements starting with cement pastes and then moving on to mortars or concretes. Combination of pozzolanic additions with fly-ash (FA) in concrete are generally not recommended in Germany although their use in Scandinavian countries has been successful [6].These aspects were therefore the basis of this investigation. The data on flow, strength, microstructure, and on the other details of the systems reported herein can be seen elsewhere [7-9].

2.EXPERIMENTAL

2.1Materials For HP self-compacting paste (SCP) systems, secondary raw materials (SRMs) included SF, RHA and RHAP. XRD analysis showed that RHA was amorphous (imported from USA) while RHAP was crystalline (imported from Pakistan). SF was local German as produced powder type. In paste systems all these pozzolanic powders were 10% of cement mass. Table 1 gives the properties of powders used. LSP had 92.3% CaCO3 content by mass.Table 1: Physical and chemical composition of cements and mineral admixtures.

Oxides

CEM I 42.5R

CEM II/A-LL 32.5R-CEM III/B 32.5N- NW/HS/NA

LSPLafargeSFRHARHAPFA

SiO218.9218.7431.017.079590.0+87.9651.44

Na2O1.481.250.860.470.100.140.781.23

MgO1.721.387.501.130.40.370.902.51

Al2O35.094.788.862.530.2