In the early research work Nr. 22/88 (VSS-Report Nr. 349) the Heidelberger cement (Germany) and several Swiss portland cements have been investigated in the laboratory and in the field. The results showed that by careful choice of cement types, cracks due to shrinkage could be significantly reduced. The present research aims to develop recommendations pertaining to the kinds of cement that are suitable for application in soil cement.
Further investigations of the influence of various domestic and foreign types of cement to the formation of cracks in cement stabilized layers, in order to recommend suitable types of cement for the production of cement stabilization.
The work was carried out in three stages:
In the first stage hydraulic binders from Germany and abroad were studied in the laboratory. Mortar samples with standard sand in accordance with SIA were produced 215 001 and the degree of shrinkage and the modulus of elasticity measured. From this, the shrinkage stresses were calculated. The cement content of the mortar samples was about 450 kg / m. In these experiments in the laboratory, the influence of the cement on the shrinkage behavior was clearly recognisable.
In the second stage of the selected types of cement and the soil material from Filderen near Zurich stabilization samples (stability samples) were prepared and their shrinkage behavior investigated analog stage 1. The stability samples showed a cement content of 100 kg / m. The measurements have shown that the influence of the cement on the shrinkage behavior of the stability samples due to the comparatively low cement content was far lower than in the mortar samples. This result was surprising.
In the third and final stage six experimental fields were created at a new track in Filderen. The 30 cm thick stabilizer layer (supplied two from Germany and four from the Swiss cement industry) with six selected cements and the existing soil Alike built-layered. The surface of the stabilizer layer was observed for two weeks, followed by the shrinkage cracks measuring. It has been shown that all six test fields had more or less shrinkage cracks with crack intervals of 5 to 15 m.
The trial field with the cement Protego 3L HS had the least cracks (two transverse cracks, crack spacing is about 10 m). After the crack shot on the stabilizer surface an 8 cm thick bituminous HMT was built (end of June 1999). The test track was then released to the construction-site. After almost a year, the test track was twice checked by the local construction management: For the first time on 28 May 2000 and the second time on 14 June 2000. For both checks no cracks on the HMT were found. Apparently the incorporation of water content and the fines for the shrinkage of cement stabilization play a big role. By contrast, the influence of the type of cement because of the small salary (about 100 kg / m) is small or insignificant.
The measurement of the shrinkage of stability samples with eight different types of cement showed only minor differences (Table 4.7, maximum 1.13 ‰, minimum value: 0.91 ‰ and mean: 1:02 ‰, aged 14 days deviations from the mean ± 11%.).